University of Ghana http://ugspace.ug.edu.gh B O O K N U M B E R 1 ± S Q 3 ........... Th n & t s . t M a ACCESSION NO Sffi™ U S p University of Ghana http://ugspace.ug.edu.gh BIOLOGY OF COWPEA FLOWER THRIPS AND HOST PLANT RESISTANCE BY A B V U L A I B a B A S A L 1 F U B . Sc . (HONS) , D i p . Ed. (CAPE COAST) A THESIS SUBMITTED TO THE UNIVERSITY OF GHANA IN PAPTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN ZOOLOGY DEPARTMENT OF ZOOLOGY UNIVERSITY OF GHANA LEGON, GHANA OCTOBER 1982 University of Ghana http://ugspace.ug.edu.gh 1. ABSTRACT Biology of cowpea flower thrips Megalurothrips sjostedti, was studied under field conditions. Population studies showed that the trend of thrips populations was closely tied with the flowering cycle of the cowpea crop. Peak thrips populations coincided with peak flowering of the crop. The seasonal abundance of thrips was mainly governed by weather factors. Thrips were found to oviposit mainly in the calyx of the cowpea flower. Evaluation of different sampling methods for thrips on cowpea indicated that water traps were most consistent. An artificial infestation method was developed for evaluating resistance of cowpeas to flower thrips in the screenhouse. Comparative yield studies without protection against flower thrips revealed a superior performance of cowpea cultivar TVx 3236 over other cultivars. The first phase of a negative field screening of cowpea germplasm showed that further sources of resistance to flower thrips were apparent in some accessions. University of Ghana http://ugspace.ug.edu.gh 11. ACKNOWLEDGEMENTS I am i n d e b t e d t o many p e o p l e i n c o n n e c t i o n w i t h t h i s work. I f I have i n a d v e r t e n t l y o m i t t e d some p e o p l e wh er e I s h o u l d have n o t , I hope i t w i l l be exc use d as o v e r s i g h t o r i g n o r a n c e . I n p a r t i c u l a r I have t o e x p r e s s my s i n c e r e g r a t i t u d e t o t h e f o l l o w i n g : P r o f . R. Kumar, my i n t e r n a l s u p e r v i s o r a t th e U n i v e r s i t y o f Ghana whose i n t e r e s t and a d v i c e we re most i n v a l u a b l e , Dr s. S . R . S i n g h , my I I T A s u p e r v i s o r and L . E . N . J a c k a i who t o g e t h e r have t i r e d l e s s l y s o u g h t my w e l f a r e and p r o g r e s s , P r o f . E . V . Doku o f t h e Crop S c i e n c e D e p a r t m e n t , U n i v e r s i t y o f Ghana f o r n o m i n a t i n g me f o r an I I T A - s p o n s o r e d r e s e a r c h , Dr. W.H. Reeves who made e v e r y t h i n g p o s s i b l e by a r r a n g i n g f o r a N e t h e r l a n d s gov er nment s c h o l a r s h i p f o r me, and l a s t l y , Mrs . V. O. Ojo f o r th e e x c e l l e n t t y p i n g . A. B. S a l i f u O c t o b e r 1 9 8 2. University of Ghana http://ugspace.ug.edu.gh i n , DEDICATION Thi s work i s d e d i c a t e d t o my p a r e n t s f o r t h e i r p a t i e n c e and u n d e r s t a n d i n g . University of Ghana http://ugspace.ug.edu.gh 1 v. CERTIFICATION We c e r t i f y t h a t t h i s work was c a r r i e d o u t by M r . A. B. S a M f u i n t h e D ep a r t me n t o f Z o o l o g y , U n i v e r s i t y o f Gh ana , Legon and a t t h e I n t e r n a t i o n a l I n s t i t u t e o f T r o p i c a l A g r i c u l t u r e , I b a d a n , N i g e r i a . S u p e r v i sors R. Kumar, Ph. D. ( R a j . ) , b . R . S i n g h , B . b e . ( A g r f c . ) Ph. D. ( Q 1 d . ) , F . R . E . S . ( I n d i a ) , M . S c . , P h . D . ' K a n s a s ) ( L o n a . ) , F . E . S . I . P r o f e s s o r o f Z oo l o g y . University of Ghana http://ugspace.ug.edu.gh v. TABLE OF CONTENTS PAGE ABSTRACT........................ ................................ ................................................................ ................. 1 ACKNOWLEDGEMENTS. „ . . . . . . . . . ..................................................... • • • 11 DEDICATION.................................................................................................................................. 11 1 CERTIFICATION BY SUPERVISOR..................................................................................... i v LIST OF FIGURES................................................................................................................. x i L I ST OF PLAI ES....................................................................................................................... x i i L I ST OF TABLES.................................................................................................. . . . . x i i i CHAPTER 1: INTRODUCTION. . . . ................................................................ 1 1 . 1 : i m p o r t a nc e o f cowpe a................................................ . . 1 1 . 2 : P r o d u c t i o n a r e a s ; c u l t i v a t i o n p r a c t i c e s . . . I 1 . 3 : Food v a l u e and u t i l i z a t i o n o f c o wpe as ................... 2 1 . 4 : R el e va n ce o f t h e s t u d y ........................................................ 4 1 . 5 : O b j e c t i v e s o f t h e s t u d y ........................................................ 5 CHAPTER 2: REVIEW OF LITERATURE.................................................................. 6 2.1 : O r i g i n o f cowpe a............................................................................... 6 2 . 2 : The cowpea p e s t c o m p l e x ................................... .............. 7 2 . 3 : Cowpea d i s e a s e s .................................................. ................. 1 4 University of Ghana http://ugspace.ug.edu.gh v i . PAGE 2 . 4 Y i e l d l o s s e s i n cowpea................ .................................... .......1 6 2 . 5 P e s t s t a t u s and d i s t r i b u t i o n o f t h r i p s , M e g a l u r o t h r i p s s j o s t e d t i ................................................ .......1 ° 2 . 6 B i o l o g y o f t h r i p s . , ........................................................ .........2 0 2 . 6 . 1 G ene ra l b i o l o g y . . . . .......................................................20 2 . 6 . 2 B i o l o g y o f M. s j o s t e d t i ........................................ .. . • 20 2 . 7 Samp l i ng o f t h r i p s ................... . . . . . . . . . 21 2 . 7 . 1 G ene ra l s a m p l i n g . . =. . . ........................................... .......21 2 . 7 . 2 Sa mp l in g o f M. s j S s t e d t i ................................................ .......22 2 . 8 Host p l a n t r e s i s t a n c e ........................ . . . . „ . . . 2 2 2 . 9 Host p l a n t r e s i s t a n c e i n c owpea.....................................24 2 . 9 . 1 L e a f h o p p e r r e s i s t a n c e ........................................................ ...... 2 5 2 . 9 . 2 A p hi d r e s i s t a n c e . . .................................... ....................... .......25 2 . 9 . 3 R e s i s t a n c e t o l e p i d o p t e r a n p e s t s . . ................... ...... 25 2 . 9 . 4 R e s i s t a n c e t o pod s u c k i n g b u g s .................................... 26 2 . 9 . 5 R e s i s t a n c e t o f l o w e r t h r i p s ........................................ ...... 2 ^ CHAPTER 3: STUDIES ON THE BIOLOGY OF FLOWER THRIPS ON COWPEA.......................................... ........................................ ... ................28 3.1 M a t e r i a l s and me t ho ds ........................................................ ......28 3 . 1 . 1 T h r i p s p o p u l a t i o n s t u d i e s ........................................... ........28 3 . 1 . 2 C o un t in g o f t h r i p s ................................................ .. . . „ 29 University of Ghana http://ugspace.ug.edu.gh v i i . PAGE 3 . 1 . 3 I d e n t i f i c a t i o n o f s p e c i e s . . . . . . . . 31 3 . 1 . 3 . 1 P er mane nt m o u n t i n g ................................................ ................. 31 3.1.4 Oviposit!on sites., .. .. .. .. .. .. . 32 3 . 1 . 5 S ea sonal v a r i a b i l i t y i n t h r i p s p o p u l a t i o n . 34 3 . 1 . 6 E f f e c t o f r a i n f a l l on t h r i p s p o p u l a t i o n s . . 34 3 . 2 R e s u l t s ................... * . 0 < , .............................* .« • • 35 3 . 2 . 1 P o p u l a t i o n s t u d i e s . , . . . . * . . . .= . . . 35 3 . 2 . 2 I d e n t i f i c a t i o n o f s p e c i e s ........................................ ....... 35 3 . 2 . 3 O v i p o s i t i o n s i t e s .................................................................... 38 3 . 2 04 S ea sonal abundance o f t h r i p s . . ................ ....... 42 3 . 3 D i s c u s s i o n . . . . „ . . . . . . . . . . . . . 42 3 . 3 . 1 P o p u l a t i o n s t u d i e s . . „ ........................................ ...............42 3 . 3 . 2 O v i p o s i t i o n s i t e s . . .< . „ ........................ .. . . . 44 3 . 3 . 3 Sea sonal v a r i a b i l i t y i n t h r i p s p o p u l a t i o n s . 45 CHAPTER 4 : EVALUATION OF DIFFERENT SAMPLING METHODS FOR COWPEA FLOWER THRI PS........................................... ....... 48 4 .1 M a t e r i a l s and m e t ho ds ................................................... ....... 48 4 . 1 . 1 Use o f w a t e r t r a p s ..................................................................49 4 . 1 . 2 Use o f s t i c k y t r a p s ........................................................ .......5 2 4 . 1 . 3 Use o f sweep n e t . . . .............................................................52 4 . 1 . 4 Use o f a l c o h o l ( 3 0 % ) ................................................ ..........5 5 4 . 1 . 5 D i r e c t counts o f t h r i p s t h r o u g h j a r r i n g pi a n t s . . .........................................................................................55 University of Ghana http://ugspace.ug.edu.gh v i i i . PAGE 4 . 1 , 6 S amp l i ng e f f i c i e n c y ........................ .. . . . . . 56 4 . 2 R e s u l t s . . . . „ . . . «. < ................................ • • • 57 4 . 2 . 1 Crop g r o w t h , p h e n o l o g y and s a m p l i n g e f f i c i e n c y . . . . . ........................ - .................................. ...........57 4 . 3 D i s c u s s i o n .................... . . . . . . . . . . . . 59 CHAPTER 5: DEVELOPMENT OF A SCREENHOUSE SCREENING TECHNIQUE FOR EVALUATING RESISTANCE TO FLOWER THRIPS BY COWPEAS.. . . . . . . . . . . 64 5 .1 M a t e r i a l s and m e t h o d s ................................................... ...........64 5 . 1 . 1 Scr ee nhous e s c r e e n i n g . , ........................................... .......... 64 5 . 1 . 2 F i e l d e v a l u a t i o n o f t h r i p s damage s e v e r i t y . 6 8 5 . 2 R e s u l t s . . ........................ .. ................................................... ........69 5 . 2 . 1 Scr ee nhous e e x p e r i m e n t s , . . . . . .................................69 5 . 2 . 2 F i e l d e v a l u a t i o n o f t h r i p s damage s e v e r i t y . 69 5 . 3 D i s c u s s i o n ...........................................................................................73 5 . 3 . 1 Scr eenhouse e x p e r i m e n t s ................................................... .....73 5 . 3 . 2 F i e l d e v a l u a t i o n o f damage s e v e r i t y . ................ .....74 CHAPTER 6 : COMPARATIVE YIELD OF DIFFERENT COWPEA C UL T I ­ VARS WITHOUT PROTECTION AGAINST FLOWER THRI PS.......................... .......................................................................77 University of Ghana http://ugspace.ug.edu.gh i x . PAGE 6 . 1 M a t e r i a l s and m e t h o d s . . . . . . . . . .................................. 77 6 . 1 . 1 Second season 1981 t r i a l ................... ....................... .................77 6 . 1 . 2 E a r l y f i r s t season 1982 t r i a l . . . 0 . . . . . . 78 6 . 2 R e s u l t s ........................................... .. . 0 0 0 .0 . 79 6 . 2 . 1 Second season 1981 t r i a l . . . . ........................... ................. 79 6 . 2 . 2 F i r s t season 1982 t r i a l . . . . . . . . . . ... . . 79 6 . 3 D i s c u s s i o n . . . . . „ . . . . . ......................... . . . . . 82 6 . 3 . 1 Second season 1981 t r i a l . . . . . . . . . . . . . 32 6 . 3 . 2 F i r s t season 1982 t r i a l .................. .................. .. . . 83 CHAPTER 7: GERMPLASM SCREENING FOR RESISTANCE TO FLOWER T H R I P S . . . . . . . . . . . „ . . . . . . . . . . . . 85 7.1 M a t e r i a l s and m e t h o d s . . „ . . . . . . . . . . . . . 85 7 . 2 R e s u l t s and c omment s . . . * . . . . . . „ . . . . 85 CHAPTER 8 : SUMMARY.................................................................... _ oo _ 89 REFERENCES. 92 University of Ghana http://ugspace.ug.edu.gh X . PAGE APPENDIX: RAW DATA SUWARY AND ANALYSIS. 1. Key t o t h e s p e c i e s o f t h r i p s i n f e s t i n g legumes i n N i g e r i a , o . . ...................- . . . . • • • ° • = • • • • 2 . C h i - s q u a r e t e s t f o r d i s t r i b u t i o n o f eggs o f M. s j o s t e d t i i n t h e cowpea f l o w e r . , . . . . . . . . 108 3. Mean m o n t h l y r a i n f a l l and t e m p e r a t u r e f o r 1 9 8 1 / 8 2 ( I I T A ) . . . . . . . . . . . . . . - o. 109 4 . Mean number o f t h r i p s p e r raceme a t 7 DAI and a n a l y s i s o f v a r i a n c e - 1 s t s c r e e n i n g ......................... 1 1 0 5. Number o f t h r i p s p e r f l o w e r a t 10 DAI and a n a l y s i s o f v a r i a n c e - 1 s t s c r e e n i n g . . . . . . . H I 6 . Number o f t h r i p s p e r raceme a t 7 DAI and a n a l y ­ s i s o f v a r i a n c e - 2 nd s c r e e n i n g . . . . ................ .. . H 2 7. Number o f t h r i p s p e r f l o w e r a t 10 DAI and a n a l y ­ s i s o f v a r i a n c e - 2 nd s c r e e n i n g ........................................... H 3 8 . Y i e l d o f 4 cowpea c u l t i v a r s - 2nd season 1981 and a n a l y s i s o f v a r i a n c e . . ........................ .. . . . . _ 1 1 4 9" Y i e l d o f 4 cowpea c u l t i v a r s - 1 s t season 1 9 8 2 , and a n a l y s i s o f v a r i a n c e . . ................................... 115 University of Ghana http://ugspace.ug.edu.gh x i . L I S T OF FIGURES FIGURE PAGE 2 . 1 The o c c u r r e n c e o f s e l e c t e d p e s t s o f copweas i n A f r i c a shown a c c o r d i n g t o t h e d e v e l o p m e n t o f t h e crop . » « . « . » . o • • . o « . . • . . o . CO « . . . . c . 2 . 2 E s t i m a t e d y i e l d l o s s e s and s t a t u s o f s i l e c t e d cowpea p e s t s i n A f r i c a . . 0 . 0 . . . . . 0 . . . . . . . . 3.1 P o p u l a t i o n t r e n d o f M. s j o s t e d t i on TVx 3 2 3 6 . . . . 3C 3 . 2 P o p u l a t i o n t r e n d o f M. s j o s t e d t i on V I T A - 7 . . . . . 36 3 . 3 P o p u l a t i o n t r e n d o f M. s j o s t e d t i on TVu 1 5 0 9 . . . . 37 3 . 4 P o p u l a t i o n t r e n d o f M. s j o s t e d t i on I f e B r o w n . . . 37 3 . 5 Seasonal abundance o f M. s j o s t e d t i a t I I T A ( 1 9 8 1 - 8 2 ) . . . . . . . . . . . . . . . . . . . . . . 0 . . 39 4 . 1 L i n e o f t r a v e r s e a l o n g wh ic h sweep n e t c o l l e c t i o n s were m a d e . . .......................................................................................... . . 53 4 . 2 Frequency d i s t r i b u t i o n o f o t h e r a r t h r o p o d s c au gh t by w a t e r t r a p s . . . . . . . . . . . . . . . . . . . . . . . . 60 5 .1 R e gr e ss io n o f t h r i p s i n j u r y on number o f t h r i p s Pe r f l o w e r . . . ........................................ ......................................... . . . ^5 7.1 Frequency d i s t r i b u t i o n o f 3687 cowpea germpl asm a c c e s si o ns o v e r a 5 - p o i n t s c a l e f o r r e s i s t a n c e to f l o w e r t h r i p s . . ........................................................ 87 University of Ghana http://ugspace.ug.edu.gh xi i . L I S T OF PLATES PAGE P ro c e d u r e o f t a k i n g samples i n a l c o h o l . . . . . . . 20 An egg o f M. s j o s t e d t i l o d g e d i n t h e p e t a l o f a cowpea f l o w e r ........................................ „ .. .......................................... 33 M e g a ! u r o t h r i p s s j o s t e d t i ( T r y b o m . ) . . . . . . , 40 F r a n k l i n i e l l a s c h u l t z e i ( T r y b o m . ) . . . . . . . . . . 40 S e r i c o t h r i p s o c c i p i t a l i s Hood......................, ..................... 41 U n i d e n t i f i e d s p e c i e s X........................ , , , , , . . . . . . 41 Wa t e r t r a p mount ed i n t h e f i e l d , ................................ . . . 50 A s t i c k y t r a p mounted i n t h e f i e l d . . ................... ..... 51 A j a r r i ng b o a r d ............................................................................. 54 J a r r i n g boa rd i n u s e ........................................................ .. . . 54 Caged p o t t e d p l a n t s i n t h e s c r e e n h o u s e . , , . . . . . 66 A p o r t i o n o f t h e f i e l d on c o m p a r a t i v e y i e l d t r i a l ( 1 s t season , 1 9 8 2 ) .................................................. ..... ....................... 83 University of Ghana http://ugspace.ug.edu.gh x i i i . L I S T OF TABLES TABLE PAGE 3.1 Mean number o f eggs o f M. s j o s t e d t i i n v a r i o u s p a r t s o f t h e cowpea p l a n t ..................................................... 38 4.1 R e l a t i v e e f f i c i e n c y o f 5 s a m p l i n g methods f o r cowpea f l o w e r t h r i p s ................................................................ 58 5 . 1 Key f o r v i s u a l e v a l u a t i o n o f t h r i p s damage s e v e r i t y on c owpea............................................. ................... 57. 5 . 2 Mean number o f t h r i p s and v i s u a l r a t i n g i n d i c e s f o r t h r i p s damage f o l l o w i n g i n f e s t a t i o n o f caged p o t t e d cowpea c u l t i v a r s w i t h 30 a d u l t M. s j o s t e d t i - 1 s t s c r e e n i n g ........................ t . 70 5 . 3 Mean number o f t h r i p s and v i s u a l r a t i n g i n d i c e s f o r t h r i p s damage f o l l o w i n g i n f e s t a t i o n o f caged p o t t e d cowpea c u l t i v a r s w i t h 30 a d u l t M. s j o s t e d t i - 2nd s c r e e n i n g ................................................ 71 5 . 4 S e v e r i t y i n d e x and mean number o f t h r i p s p e r f l o w e r o f 4 cowpea c u l t i v a r s ................................................. 72 C o m p a r at i v e y i e l d p e r f o r m a n c e o f 4 cowpea c u l t i v a r s , I I T A 2nd s e a s o n , 1 9 8 1 ......................... . . . 80 University of Ghana http://ugspace.ug.edu.gh x i v. TABLE PAGE 6 . 2 C o m p a r a t i v e y i e l d p e r f o r m a n c e o f 4 cowpea c u l t i v a r s . I I T A 1 s t season 1 9 8 2 ...................... 81 University of Ghana http://ugspace.ug.edu.gh 1 . CHAPTER ONE 1. INTRODUCTION 1.1 I m p o r t a n c e o f cowpea. The cowpea, V i g n a u n g u i c u l a t a (L.) Walp. , i s one o f t h e f o o d legumes wh ic h a r e i m p o r t a n t s ou rc es o f n u t r i e n t and p r o v i d e s u pp l e m e n ­ t a r y p r o t e i n s t o d i e t s based on c e r e a l g r a i n s a n d / o r s t a r c h y foods ( A y kr o y d and D o u g h t y , 1 9 6 4 ) . The amino a c i d p r o f i l e o f cowpea c o m p l e ­ ments t h a t o f c e r e a l g r a i n s and as a consequence c e r e a l and cowpea combined p r o v i d e p r o t e i n o f a h i g h e r b i o l o g i c a l v a l u e t han e i t h e r a l o n e (Dema, 1 9 6 3 ) . 1 . 2 P r o d u c t i o n a r e a s ; c u l t i v a t i o n p r a c t i c e s Cowpeas t h r i v e w e l l i n s e m i - a r i d and humid t r o p i c a l r e g i o n s t h a t a r e l o c a t e d w i t h i n l a t i t u d e s 0° and 30° N o r t h o r Sout h o f th e e q u a t o r , w i t h an annual r a i n f a l l o f 250-1000mm ( S i n h a , 1 9 7 7 ) . A l t h o u g h cowpeas a r e grown t h r o u g h o u t t h e l o w l a n d t r o p i c s most o f t h e t o t a l w o r l d p r o d u c t i o n comes f r om West A f r i c a and th e N o r t h e a s t e r n r e g i o n s o f B r a z i l , wh ic h each produces a round 1 . 0 t ons o f cowpea seed a n n u a l l y ( S u m m e r f i e l d e t a ] _ . , 1 9 7 4 ) . I t i s e s t i m a t e d t n a t cowpea p r o d u c t i o n ( i n m i l l i o n s o f h e c t a r e s ) i s o v e r 4 . 8 i n West A f r i c a , a b o ut 1 . 0 i n E a s t A f r i c a , 0 . 8 5 i n I n d i a , 0 . 6 s c a t t e r e d o v e r S o u t h e a s t e r n A s i a , c l o s e to 1 . 5 i n B r a z i l and L a t i n Amer ic a and a b o u t 0 . 2 i n th e U n i t e d S t a t e s o f Amer ic a ( S i n gh and van Emden, 1 9 7 9 ) . N i g e r i a i s University of Ghana http://ugspace.ug.edu.gh 2 . a l e a d i n g p r o d u c e r o f cowpeas. Between 1 9 7 1 - 1 9 7 5 o u t o f a mean annual w o r l d c u l t i v a t e d a r e a o f 4 , 4 8 9 , 8 0 0 h e c t a r e s N i g e r i a a l o n e c u l t i v a t e d 81. 1% o f t h e t o t a l a r e a , and pro duce d 75.0% o f t h e mean annual w o r l d p r o d u c t i o n o f 1 , 1 2 9 , 4 0 0 m e t r i c tons f o r t h e same p e r i o d . In A f r i c a n t r a d i t i o n a l c u l t i v a t i o n systems cowpeas a r e o f t e n c u l t i v a t e d bot h as a m i xe d c r o p and i n m o n o c u l t u r e . I n N o r t h e r n N i g e r i a where t h e b u l k o f N i g e r i a cowpeas a r e p r o d u c e d , s ma l l s c a l e f a rm e r s i n t e r c r o p cowpeas w i t h such crops as s orghum, m i l l e t , c o t t o n and g r o undnut s ( B o o k e r , 1 9 6 4 ; R a h e j a , 1 9 7 8 ) . I n T a n z a n i a f a r m e r s u s u a l l y i n t e r c r o p cowpeas w i t h m ai z e and m i l l e t (Kayumbo, 1 9 7 5 ) . Cowpeas have been shown t o i n c r e a s e y i e l d o f m i l l e t when i n t e r ­ p l a n t e d a t low d e n s i t i e s o f 5 , 9 8 0 and 1 1 , 9 6 0 p l a n t s p e r h e c t a r e i n Kano, N i g e r i a ( S t e e l e , 1 9 7 2 ) . I n S o u t h w e s t e r n N i g e r i a most o f t h e crop i s grown as l a t e season c rop by l o c a l f a r m e r s who grow d a y l e n g t h s e n s i t i v e i n d e t e r m i n a t e c u l t i v a r s d u r i n g t h e months o f J u l y to S epte mber and h a r v e s t i n N ovember -December . However, e a r l y season d a y l e n g t h n e u t r a l d e t e r m i n a t e c u l t i v a r s a r e somet imes grown by p l a n t i n g i n A p r i l o r e a r l y May and h a r v e s t i n g l a t e J u l y o r Augus t ( N a n j u , 1 9 7 8 ) . 1 . 3 Food v a l u e and u t i l i z a t i o n o f cowpeas The n u t r i t i v e v a l u e o f cowpea seed compares f a v o u r a b l y w i t h t h a t o f o t h e r p l a n t and a nimal d e r i v e d food s o u r c e s . The p r o t e i n University of Ghana http://ugspace.ug.edu.gh 3. c o n t e n t o f cowpea seed i s h i g h , u s u a l l y r a n g i n g f r om 19 t o 26%. The p r o t e i n i s h i g h i n t h e amino a c i d l y s i n e , b u t , l i k e o t h e r legume seed p r o t e i n s , i s d e f i c i e n t i n t h e s u l p h u r - c o n t a i n i n g amino a c i d s c y s t i n e and m e t h i o n i n e . The n u t r i t i v e v a l u e o f cowpea s e e d can be i n c r e a s e d by c o ok in g t o l e s s e n t h e a c t i v i t y o f such h e a t l a b i l e a n t i n u t r i t i o n a l f a c t o r s as h a e m a g g l u t i n i n s and t r y p s i n i n h i b i t o r s . P r o x i m a t e a n a l y s i s o f t h e cowpea seed shows t h a t i t c o n t a i n s 23. 4% o f p r o t e i n 1.3% o f f a t and 56. 8% c a r b o h y d r a t e s ( P u r s e g l o v e , 1 9 6 8 ) . I t c o n t a i n s a b o u t 342 c a l o r i e s p e r 100 g and a l l e s s e n t i a l amino a c i d s i n s u f f i c i e n t amounts f o r growth ( Oy enuga , 1 9 6 8 ) . P r o t e i n s p r o v i d e d m a i n l y by t h e c o t y l e d o n s ranges i n c o n c e n t r a t i o n s f rom a b o ut 17 to 40% ( B r e s s a n i and E l i a s , 1 9 8 0 ) . The v e g e t a b l e p r o p o r t i o n c o n t a i n s 3 . 3 1 g o f p r o t e i n p e r 1 0 0 g w h i l e t h e l y s i n e , m e t h i o n i n e and t r y p t o p h a n c o n t e n t a r e 198 mg, 20 mg and 33 mg p e r 100 mg r e s p e c t i v e l y ( F A 0 , 1 9 7 0 ) . V i t a m i n c o n t e n t s i n c l u d e V i t a m i n A ( 2 0 0 - 3 0 0 I U ) , V i t a m i n C ( 40 I U ) , V i t a m i n D ( 2 6 - 7 8 u g / 1 0 0 g ) and V i t a m i n E ( 3 . 0 7 - 5 . 0 7 mg/ 1 OOg) ( E s t e r and M u n s e l l , 1 9 37 ; Oyenuga and Ogunmodede, 1 9 6 8 ) . A p a r t f rom t h e i r use i n soups cowpeas a r e used i n a v a r i e t y o f c u l i n a r y p r e p a r a t i o n s . In many p a r t s o f ^Jest A f r i c a some o f t h e d i f f e r e n t ' b e a n ' foods i n c l u d e r o a s t e d corn and cowpea; cowpea stew and f r i e d p i a n t a i n , 1moin m o i n ' a n d s e v e r a l o t h e r s ( D o v l o e t a 1 . , 1 9 7 5 ) . Cowpea l e a v e s and pods may be used as v e g e t a b l e i n some c o u n t r i e s such as I n d i a , C hi na and Uganda. I t may a l s o be used f o r l i v e s t o c k f e e d , g r e e n manure and s o i l e r o s i o n c o n t r o l . In University of Ghana http://ugspace.ug.edu.gh 4. s u b s i s t e n c e a g r i c u l t u r e on s m a l l fa rms the n i t r o g e n - f i x i n g a b i l i t y o f cowpea i s i m p o r t a n t . 1 . 4 R e l e v an c e o f t h e s t u d y N o t w i t h s t a n d i n g t h e i m p o r t a n c e o f cowpea as a s o u rc e o f p r o t e i n f o r th e d e v e l o p i n g n a t i o n s o f th e w o r l d , y i e l d s a r e s t i l l be low e x p e c t a t i o n i n such a r e a s . I n s e c t p e s t s and d i s e a s e s a r e a m a j o r c o n s t r a i n t t o i n c r e a s e d p r o d u c t i o n o f cowpeas; ( s e e c h a p t e r 2 f o r l i t e r a t u r e r e v i e w ) . T h i s i s a p t l y d e m o n s t r a t e d by s p e c t a c u l a r i n c r e a s e s i n y i e l d f o l l o w i n g i n s e c t i c i d e a p p l i c a t i o n ( B o o k e r , 1 9 6 4 , 1 9 6 5 ; T a y l o r , 196 8; K o e h l e r and M e h t a , 1 9 7 2 ; Kayumbo, 1 9 7 5 ) . Of pa ra mo u nt i m p o r t a n c e among th e numerous cowpea p e s t s i s t h e cowpea f l o w e r t h r i p s M e g a ! u r o t h r i p s s j o s t e d t i ( T r y b o m . ) ( T h y s a n o p t e r a , T h r i p i d a e ) . Th i s t i n y b l a c k i n s e c t i n f e s t s cowpea f l o w e r buds and open f l o w e r s . Sev er e i n f e s t a t i o n s can l e a d t o t o t a l y i e l d l o s s ( S i n g h and A l l e n , 1 9 8 0 ) . A l t h o u g h t h e p e s t s t a t u s o f M_. s j o s t e d t i had l on g been e s t a b l i s h e d n o t much work has been done on i t , e s p e c i a l l y i n t h e a r e a o f h o s t p l a n t r e s i s t a n c e . E f f e c t i v e h o s t p l a n t r e s i s t a n c e i n v e s t i g a t i o n s r e q u i r e s a t h or ough knowl edge o f t h e b i o l o g y o f t h e p e s t v i s - a - v i s th e h o s t p l a n t . T h e r e f o r e t h e o b j e c t i v e s o f t h e p r e s e n t s t u d y we re e x t e n d e d t o i n c l u d e b i o l o g y s t u d i e s . University of Ghana http://ugspace.ug.edu.gh 5. 1 . 5 O b j e c t i v e s o f th e s t u d y The o b j e c t i v e s o f t h e p r e s e n t s t u d y we re d e f i n e d t o i n c l u d e t h e f o l l o w i n g : 1. S t u d i e s on b i o l o g y o f f l o w e r t h r i p s M e g a ! u r o t h r i p s s j o s t e d t i ( Trybom. ) . 2 . E v a l u a t i o n o f d i f f e r e n t s a m p l i n g methods f o r f l o w e r t h r i p s on cowpea. 3. D ev el opme nt o f a s c r e e n h ou s e s c r e e n i n g t e c h n i q u e f o r e v a l u a t i n g r e s i s t a n c e t o f l o w e r t h r i p s . 4. C o m p a r a t i v e y i e l d o f cowpea c u l t i v a r s w i t h o u t p r o t e c t i o n a g a i n s t t h r i p s . 5 . Cowpea germplasm s c r e e n i n g f o r r e s i s t a n c e t o f l o w e r t h r i p s . University of Ghana http://ugspace.ug.edu.gh 6 . CHAPTER TWO 2. REVIEW OF LITERATURE 2 .1 O r i g i n o f cowpea The cowpea, V i g n a u n g u i c u l a t a (L.) Walp., has been c u l t i v a t e d s i n c e N e o l i t h i c t i m e s . One o f t h e e a r l i e s t works w i t h t h e o r i g i n o f c r o p s p e c i e s was w r i t t e n by de C a n d o l l e i n 1 88 6. He s t r e s s e d t h e i m p o r t a n c e o f t h e p r e s e n c e o f w i l d forms o f t h e c rop p l a n t a t t h e o r i g i n . V a v i l o v ( 1 9 5 1 ) c o n s i d e r e d t h a t th e a r e a o f maximum d i v e r s i t y o f a c rop p l a n t i s a l s o l i k e l y t o be t h e c e n t r e o f d o m e s t i c a t i o n o f the s p e c i e s . The c e n t r e o f o r i g i n o f cowpea i s a m a t t e r o f c o n t r o v e r s y . N e v e r t h e l e s s th e d i s t r i b u t i o n o f t h e w i l d cowpeas, wh i ch a r e f o u n d o n l y i n A f r i c a i s one o f t h e s t r o n g e s t l i n e s o f e v i d e n c e f a v o u r i n g A f r i c a as th e o r i g i n o f t h e c r o p . T h i s o b s e r v a t i o n was t h e main c r i t e r i o n used by P i p e r ( 1 9 1 3 ) , D a l z i e l ( 1 9 3 7 ) , V a v i l o v ( 1 9 5 1 ) , B u r k i l l ( 1 9 5 1 ) , S au e r ( 1 9 5 2 ) , C obl ey ( 1 9 5 6 ) , S t a n t o n ( 1 9 6 6 ) , V e r d c o u r t ( 1 9 7 0 ) , S t e e l e ( 1 9 7 2 ) , Westphal ( 1 9 7 4 ) , H a r l a n ( 1 9 7 5 ) and Rawal ( 1 9 7 5 ) , a l l o f whom c o n cl ud e d t h a t cowpeas were d o m e s t i c a t e d i n A f r i c a , W i t h i n A f r i c a some a u t h o r s f a v o u r e d E t h i o p i a as t h e r e g i o n o f o r i g i n ( e . g . V a v i l o v , 1 95 1; S t e e l e , 1 9 7 2 ) b u t o t h e r s s u g g e s t e d West A f r i c a ( e . g . P i p e r , 1 9 1 3 ; R ac hi e and R o b e r t s , 1 9 7 4 ; R a w a l , 1 9 7 5 ) . University of Ghana http://ugspace.ug.edu.gh 7 . 2 . 2 The cowpea p e s t complex Many i n s e c t p e s t s a t t a c k a l l p a r t s o f cowpea p l a n t s a t e v e r y s t a g e o f gro wt h as w e l l as seeds i n s t o r a g e . V a r i o u s w o r k e r s have a t t e m p t e d t o c l a s s i f y t h e p e s t complex on cowpea so as t o show t h e i r r e l a t i v e i m p o r t a n c e on th e c r o p . Booke r ( 1 9 6 3 ) d i v i d e d cowpea p e s t s i n t o m a j o r and m i n o r p e s t s o f p r e f l o w e r i n g , f l o w e r i n g and p o s t - f l o w e r i n g ph ase s. Under t h i s c l a s s i f i c a t i o n t h e f o l i a g e b e e t l e O ot he ca m u t a b i 1 i s ( S a l b . ) i s r e g a r d e d as a p r e - f l o w e r i n g p e s t , t h e l egume pod b o r e r Maruca t e s t u l a l i s ( G e y e r ) , a f l o w e r i n g p e s t and t h e pod s u c k i n g bug Anopl ocnemi s c u r v i p e s F . a s a p o s t - f l o w e r i n g p e s t . T a y l o r ( 1 9 6 4 ) f u r t h e r expanded B o o k e r ' s ( 1 9 6 3 ) c l a s s i f i c a t i o n and p u t t h e p e s t complex i n t o f o u r m a j o r g r o u p s , ( a ) The r o o t - f e e d i n g s p e c i e s . ( b ) The l e a f and s t e m - f e e d i n g s p e c i e s , ( c ) The f l o w e r - f e e d i n g s p e c i e s . ( d ) The pod and s e e d - i n f e s t i n g s p e c i e s . In a r e c e n t r e v i e w S i ngh ( 1 9 8 0 ) gave a c o m p r e h e n s i v e o v e r v i e w o f th e cowpea compl ex . The t i m e o f i n f e s t a t i o n r e l a t i v e t o crop p he nol ogy was t a ke n i n t o a c c o u n t ( F i g . 2 . 1 ) . T h r e e main groups a r e i d e n t i f i a b l e under t h i s c l a s s i f i c a t i o n : a) Those p e s t s wh ic h a r e common t h r o u g h o u t t h e v e g e t a t i v e g ro wt h. b) Those wh ic h i n f e s t a t t h e a p p e a r a n c e o f f l o w e r s and c) Pests wh ic h a r e p r e v a l e n t t h r o u g h o u t t h e r e p r o d u c t i v e p e r i o d . Pe st s i n the f i r s t c a t e g o r y i n c l u d e l e a f h o p p e r s , a p h i d s and b e e t l e s . wh ic h University of Ghana http://ugspace.ug.edu.gh 0c "> £ s“= c0n0 ■a — CoJ o CD o i ^ xo: cn (/> c a c -8 y o vir Q_ < _ £ £ Ocn 0D0 a) Q5 . -Oo o • • I c: o £ . 5 a q o° ®£. o£ a®, cfc • 3 2 QJ O 5 t s 3 E u S. c=5j a>: — (n > a«, ■ 'O O QJ O a P _0 O5 o a -J O .J _ l Q. o □ — cn \ cnb on S ' % <0̂D ' f c . - O * $ \ \ " °O o a{= 0c0n cn ^ Ccn z- a>>N Co^ X. ~Qo) c_n CD 00

VO r^. LD aC\j * cv cnj cn oc CNJ O V OCNJ (XI — O5J un CO cn CO coo cn CNJ ir> * ^ rCNJ OJ ro QJ C L o O V O O 1 • C\J on »— co LO m cn + 1 + 1 + 1 + 1 + 1 cn CO c n j 00 00 o r^cn cn r— VO r - CSJ cn CNJ cn o un co o m 1 C O ro QJ Q CO EL i l cn on o o o + 1 + 1 + 1 + 1 + 1 + 1 | x CO co O CNJ o cn QJ CO VO vo cn r * s . o _ CO Z3 • co E■ • » o •— o Ln o> < \ J CNJ CO CNJ cn cn CO r-- on o ,— o O + 1 C+ 1 + 1 + 1 + 1 + 1 a T VO co oo cc •— c n c o cn CNJ -Q CD lo E 1— ra O3J University of Ghana http://ugspace.ug.edu.gh 59. T a b l e 4 . 1 shows t h e r e l a t i v e e f f i c i e n c y o f t h e f i v e m e t h o d s t h a t w e r e i n v e s t i g a t e d . A c c o r d i n g t o S o u t h w o o d ( 1 9 6 6 ) an RV o f a b o u t 25 i s p r o b a b l y s u f f i c i e n t f o r m o s t p e s t ma na ge men t p u r p o s e s . Thus i n t h i s s t u d y an RV o f 25 was c o n s i d e r e d as a b a s i c c r i t e r i o n o f a c c e p t a b l e v a r i a b i l i t y . 4 . 3 Pi s c u s s i o n From t h e r e s u l t s m o s t t e c h n i q u e s w e r e w i t h i n t h e r e a l m o f s u f f i c i e n c y f o r t h e v a r i a b i l i t y c r i t e r i o n . H ow e v e r m o re c o n f i d e n c e can be p l a c e d i n t h e w a t e r t r a p t h a n i n t h e o t h e r m e t h o d s . The w a t e r t r a p was m o s t c o n s i s t e n t , w i t h a mean RV o f 1 4 . 8 . I t a l s o s a m p l e d a f a i r p r o p o r t i o n o f t h e p o p u l a t i o n s , t h u s i t a c t u a l l y g a v e a t r u e p i c t u r e o f t h e i n f e s t a t i o n l e v e l . The m e t h o d may be a c c e p t a b l e f o r f u r t h e r p o p u l a t i o n s t u d i e s . T h r i p s c a u g h t i n w a t e r t r a p s w e r e e a s i l y c o l l e c t e d i n a r e a d i l y i d e n t i f i a b l e c o n d i t i o n . The r e l a t i v e e f f i c i e n c y o f w h i t e w a t e r t r a p s w e r e i n v e s t i g a t e d by L e w i s ( 1 9 5 9 ) . He s t a t e d t h a t c a t c h e s w e r e l e s s c o n s i s t e n t a t h i g h e r l e v e l s and w e n t f u r t h e r t o s u g g e s t t h a t t h e y be u s e d a t v e g e t a t i o n l e v e l w h e r e t h e w i n d s p e e d i s l o w and w h e r e t h e i r a n g u l a r o u t l i n e w i l l c a u s e l e a s t t u r b u ­ l e n c e i n t h e a i r f l o w i n g p a s t t h e m . F i g u r e 4 . 2 shows t h e p r o p o r t i o n o f o t h e r i n s e c t s and a r a c h n i d s c a u g h t by t h e w a t e r t r a p . T h e r e was a h i g h p r e p o n d e r a n c e o f d i p t e r a , f o l l o w e d b y h y m e n o p t e r a . The e f f i c -je n c ^ o f w a t e r t r a p s i s known t o d e p en d on t h e a c t i v i t y o f i n s e c t s ( L e w i s 1 9 5 9 ) . I t i s t h e r e f o r e n o t u n e x p e c t e d t h a t more d i p t e r a and University of Ghana http://ugspace.ug.edu.gh Frequency of occurrence (%) University of Ghana http://ugspace.ug.edu.gh 61. h y m e n o p t e r a w e r e c a u g h t - t h e t wo g r o u p s a r e a c t i v e f l i e r s . The p r o p o r t i o n s o f h e m i p t e r a n and l e p i d o p t e r a n i n s e c t s w e r e r a t h e r l o w . D u r i n g t h e e x p e r i m e n t a l p e r i o d t h e m a j o r p o d - s u c k i n g h e m i p t e r a n p e s t s w e r e s c a r c e . I n a d d i t i o n t h e s a m p l i n g r e g i m e e nded a t a p o i n t ( 5 5 DAP) when p o p u l a t i o n s o f t h e s e i n s e c t s had j u s t b eg an t o r i s e . W a t e r t r a p s w e r e m a i n l y m o u n t e d d u r i n g d a y l i g h t . M o s t l e p i d o p t e r a a r e n o c t u r n a l a nd h en ce t h e l o w p r o p o r t i o n s e n c o u n t e d w e r e p a r t i a l l y j u s t i f i e d . M o s t c o l e o p t e r a c a u g h t w e r e c h r y s o m e l i d s p l u s a f e w b r u c h i d s . T h e r e was a s ud de n o u t b r e a k o f Z o n o c e r u s v a r i e q a t u s a t some p o i n t d u r i n g t h e e x p e r i m e n t a l p e r i o d . T h i s i n s e c t a c c o u n t e d f o r t h e o r t h o p t e r a n s r e c o r d e d i n t h e e x p e r i m e n t . I t a p p e a r s t h a t t h e w a t e r t r a p h o l d s p r o m i s e as a t o o l f o r f a u n a l s u r v e y s i n cowpea e n t o m o l o g y . H o w e v e r , as f a r as t h r i p s a r e c o n c e r n e d , one p e r t i n e n t o b s e r v a t i o n c a n n o t be o v e r l o o k e d . The l a r v a e o f t h r i p s a r e m o s t l y c o n f i n e d t o t h e i n t e r i o r o f f l o w e r buds and open f l o w e r s . T h e r e f o r e t h e w a t e r t r a p t e n d t o u n d e r e s t i m a t e t o t a l p o p u l a t i o n by o m i t t i n g t h e i m m a t u r e s . T h i s can a f f e c t t h e e f f i c i e n c y o f t r a p p i n g . One o t h e r m e t h o d t h a t h e l d p r o m i s e was t h e use o f s t i c k y t r a p s . RVs o b t a i n e d f r o m t h i s m e t h od w e r e i d e n t i c a T t o t h o s e o b t a i n e d by use o f w a t e r t r a p s . S t i c k y t r a p s have been e v a l u a t e d f o r s a m p l i n g t h r i p s ( L e w i s , 1 9 5 9 ) . C o u n t s w e r e r e a s o n a b l y c o n s i s t e n t , b u t w er e l a b o r i o u s t o s o r t . Compared t o w a t e r t r a p s a t h i g h e r l e v e l s t h e y showed g r e a t e r p r e c i s i o n . T a y l o r ( 1 9 6 2 ) showed t h a t i f t h e w i n d University of Ghana http://ugspace.ug.edu.gh 6 d. s pe ed was known t h e c a t c h e s o f s m a l l i n s e c t s on c y l i n d r i c a l s t i c k y t r a p s c o u l d be c o n v e r t e d t o a m e a s u r e o f a e r i a l d e n s i t y . Bas ed on t h i s o b s e r v a t i o n s t i c k y t r a p s w o u l d be c h o s e n i n p r e f e r e n c e t o w a t e r t r a p s b e c a u s e t h e r e l a t i o n s h i p b e t w e e n w i n d s p e e d and t h e c a t c h o f t h e w a t e r t r a p i s l i k e l y t o p r o v e l e s s s i m p l e t h a n t h a t f o r t h e s t i c k y t r a p . From t h e r e s u l t s o f T a b l e 4 . 1 h o w e v e r , one o b v i o u s a d v a n t a g e o f t h e w a t e r t r a p o v e r t h e s t i c k y t r a p s t a n d s o u t . When t h r i p s p o p u ­ l a t i o n s a r e s p a r s e , t h e w a t e r t r a p s t i l l makes c a t c h e s when t h e s t i c k y t r a p b a r e l y does s o . L i k e w a t e r t r a p s s t i c k y t r a p s may a l s o o m i t t h e i m a t u r e s o f t h r i p s . The sweep n e t i s p e r h a p s t h e m o s t w i d e l y use d e q u i p m e n t f o r s a m p l i n g i n s e c t s f r o m v e g e t a t i o n . I t s a d v a n t a g e s i n c l u d e s i m p l i c i t y and s pe ed ( S o u t h w o o d , 1 9 6 6 ) . H o w e v e r i n t h i s e x p e r i m e n t t h e s e a d v a n t a g e s w e r e o u t w e i g h e d by l a r g e d e p a r t u r e s f r o m t h e v a r i a b i l i t y c r i t e r i o n s e t f o r s a m p l i n g e f f i c i e n c y . The m e t h o d i s t h u s u n r e l i a b l e . L a r g e v a r i a t i o n s b e t w e e n sweep n e t s a m p l e s w e r e n o t e d by G r ay and T r e l o a r ( 1 9 3 3 ) who s w e p t A n a p h o t h r i p s o b s c u r u s f r o m a l f a l f a , t a k i n g 25 sweeps p e r s a m p l e . The mean c o e f f i c i e n t o f v a r i a t i o n f o r 40 s a m p l e s was + ? 4 . 9 % ; 50 sweeps d e c r e a s e d t h e v a l u e t o + 4 7 . 8 % , 100 t o *36.9% and 200 t o + 2 4 . I t . Thus t o a t t a i n a c c e p t a b l e v a r i a b i l i t y as d e f i n e d i n t h i s e x p e r i m e n t w i l l mean t a k i n g more t h a n 200 sweeps t o t h e s a m p l e . I n p r a c t i c a l p e s t management t e r m s t h i s seems u n r e a l i s t i c . From t h i s e x p e r i m e n t an i n f e r e n c e may be t h a t s w e e p i n g p r o v i d e s a much l e s s p r e c i s e e s t i m a t e f o r a s i m i l a r a mo un t o f e f f o r t when c o mp ar e d t o t h e o t h e r me th od s u n d e r t h e t e s t . University of Ghana http://ugspace.ug.edu.gh 63. S a m p l i n g t h r i p s by p i c k i n g rac eme s a n d / o r f l o w e r s i n a l c o h o l was n o t a g oo d p r o c e d u r e on b a s i s o f t h e v a r i a b i l i t y c r i t e r i o n . H o w e v e r , u n l i k e t h e o t h e r m e t h o d s t h i s p r o c e d u r e s a m p l e s b o t h a d u l t s a nd i m m a t u r e s t a g e s , s i m u l a t a n e o u s l y . C o n s i d e r i n g t h e f a c t t h a t b o t h a d u l t s and i m m a t u r e s do t h e damage t o c o w p e a s , t h e d i s a d v a n t a g e s o f t h e a l c o h o l p r o c e d u r e o f a l a r g e r v a r i a b i l i t y and d i s r u p t i o n o f n o r m a l g r o w t h , may be o u t w e i g h e d by i t s a b i l i t y t o c a t c h b o t h f o r m s o f t h e i n s e c t . University of Ghana http://ugspace.ug.edu.gh 6 4 . CHAPTER FIVE 5. DEVELOPMENT OF A SCREENHOUSE SCREENING TECHNIQUE FOR EVALUATING RESISTANCE TO FLOWER THRIPS BY COWPEAS. The I n t e r n a t i o n a l I n s t i t u t e o f T r o p i c a l A g r i c u l t u r e m a i n t a i n s a cowpea g e r m p l a s m c o l l e c t i o n o f o v e r 1200CL I n o r d e r t o s c r e e n a l a r g e c o l l e c t i o n as t h i s , r e l i a b l e and r a p i d f i e l d s c r e e n i n g t e c h n i q u e s a r e r e q u i r e d , H o w e v e r f i e l d t e c h n i q u e s w h i c h r e l y on n a t u r a l i n f e s t a t i o n a r e o f t e n b e s e t w i t h some d e f i c i e n c i e s ( G u t h r i e , 1 9 8 0 ; O r t e g a e t a l . 1 9 8 0 ) . T h e r e f o r e m a t e r i a l s e l e c t e d f r o m t h e f i e l d u n d e r n a t u r a l i n f e s t a t i o n w i l l h a ve t o go t h r o u g h an u l t i m a t e s c r e e n u s i n g a r t i f i c i a l i n f e s t a t i o n m e t h o d s . The p u r p o s e o f t h i s s t u d y was t o d e v e l o p a s c r e e n h o u s e s c r e e n i n g t e c h n i q u e t h a t c o u l d be u t i l i z e d i n e v a l u a t i n g r e s i s t a n c e o f cowpeas t o f l o w e r t h r i p s , M e g a l u r o t h r i p s s . j o s t e d t i . I n a d d i t i o n an a t t e m p t was made t o d e t e r m i n e p o s s i b l e c o r r e l a t i o n b e t w e e n t h r i p s i n f e s t a t i o n and damage s e v e r i t y . 5 . ] M a t e r i a l s and m e t h o d s 5 . 1 , 1 S c r e e n h o u s e s c r e e n i n g S c r e e n i n g me t h o d s w er e d e v e l o p e d a t one l e v e l o n l y : S i n g l e c ag ed p o t t e d p l a n t s . F i v e cowpea c u l t i v a r s wer e u s e d i n t h e t e s t and t h e s e wer e TVu 1 5 0 9 , TVx 3 2 3 6 , I f e Brown (TVu 3 6 2 9 ) , V I T A - 6 and TVu 76. University of Ghana http://ugspace.ug.edu.gh 65.. TVu 1509 and TVu 76 w er e i n c l u d e d as r e s i s t a n t and s u s c e p t i b l e c h e c k s . The e x p e r i m e n t was l a i d o u t i n a c o m p l e t e l y r a n d o m i s e d d e s i g n . Each o f t h e f i v e c u l t i v a r s was sown s e p a r a t e l y i n t e n 1 7 . 8 cm d i a m e t e r p l a s t i c p o t s i n t h e o p e n . Ten d a y s a f t e r p l a n t i n g (DAP) p l a n t s w e r e t h i n n e d t o one p l a n t p e r p o t . A t 13 DAP p l a n t s w e r e s p r a y e d a g a i n s t a p h i d s w i t h d i m e t h o a t e 40 EC a t t h e r a t e o f 50 g . a . i . / h a . When p l a n t s showed s i g n s o f f l o w e r bud i n i t i a t i o n , t h e y w e r e t r a n s f e r r e d i n t o a s c r e e n h o u s e . I n t h e s c r e e n h o u s e p l a n t s w e r e e ac h c a g e d w i t h f i n e n y l o n mesh bags s u p p o r t e d by t h i n a l u m i n i u m r o d s t h a t had been p u s h e d i n t o t h e s o i l i n t h e p o t s . Bags w e r e f u r t h e r s e c u r e d t o t h e r i m o f p o t s w i t h r u b b e r b a nd s ( P l a t e 5 . 1 ) . When p e d u n c l e s had e l o n g a t e d t o a b o u t 2 c m , e a c h p l a n t was i n f e s t e d w i t h a t o t a l o f 30 a d u l t M. s j o s t e d t i c o l l e c t e d f r o m a f i e l d n u r s e r y . A t s e v e n day s a f t e r i n f e s t a t i o n ( D A I ) e a c h r e p l i c a t e o f e ac h c u l t i v a r was v i s u a l l y r a t e d f o r t h r i p s damage. T h i s c o n s i s t e d o f s t i p u l e b r o w n i n g , b u d b r o w n i n g and a b s c i s s i o n , f l o w e r a b s c i s s i o n and d i s t o r t i o n . R a t i n g was b a se d on a s c a l e o f 1 - 5 , r e p r e s e n t i n g s l i g h t t o h e a v y damage. The r a t i n g c h a r t i s s u m m a r i s e d i n T a b l e 5 . 1 . A damage s e v e r i t y i n d e x f o r e a c h c u l t i v a r was o b t a i n e d by f i n d i n g t h e sum o f a l l i n d i c e s f o r t h e t e n r e p l i c a t i o n s and d i v i d i n g by t h e n um b e r o f r e p l i c a t i o n . A f t e r r a t i n g s a m p l e s o f t wo r a ceme s p e r p l a n t f r o m each c u l t i v a r w er e t a k e n i n v i a l s o f a l c o h o l . Back i n t h e l a b o r a t o r y rac eme s w e r e d i s s e c t e d and t h r i p s c o u n t e d . R a t i n g was r e p e a t e d a t 10 DAI and samp les o f t wo f l o w e r s p e r p l a n t f r o m e ac h c u l t i v a r t a k e n s i m i l a r l y . University of Ghana http://ugspace.ug.edu.gh University of Ghana http://ugspace.ug.edu.gh 67. T a b l e 5 . 1 : Key f o r v i s u a l e v a l u a t i o n o f t h r i p s damage s e v e r i t y on c o w p e a . PLANT PART AND DAMAGE CHARACTERISTICS SEVERITY INDEX STIPULES BUDS FLOWERS A l l s t i p u l e s w i t h QX a b s c i s s i o n . No N or m a l f o r m and c o l o r . 1 n o r m a l c o l o r , i . e . b r o w n i n g . Racemes No a b s c i s s i o n . m o s t l y GREEN. wi t h f u l l y s e t h e a l t h y b u d s . 20% o f a l l s t i p u l e s S I i g h t a b s c i s s i o n N or ma l f o r m a nd c o l o r . 2 b r o w n e d and d r y . (10% - 4 0%) . V e r y V e r y s l i g h t a b s c i s s i o n . f e w b r o w n e d o 50% o f a l 1 s t i p u l e s 40-60% a b s c i s s i o n . Some a b s c i s s i o n . 3 b r o w n e d and d r y . R e m a i n i n g buds Number o b v i o u s l y r e d u c e d , m o s t l y b r o w n e d . w i t h some s l i g h t l y m a l ­ f o r m e d . 80% o f a l l s t i p u l e s 50-80% a b s c i s s i o n . O n l y f e w f o r m e d . 4 b r o w n e d and d r y . R e m a i n i n g buds G r e a t e r p r o p o r t i o n b r o w n e d and d r y . m a l f o r m e d and d i s c o l o r e d . A l l s t i p u l e s 100% a b s c i s s i o n . N o n e - t o - v e r y f e w 5 b r o w n e d and d r y . P l a n t s m o s t l y w i t h f o r m e d . M a l f o r m e d and b a r e p e d u n c l e s o n l y . d i s c o ! o r e d . University of Ghana http://ugspace.ug.edu.gh 68. Bot h a d u l t s and l a r v a e w er e r e c o r d e d d u r i n g c o u n t i n g . The e x p e r i m e n t was r e p e a t e d u s i n g t h e same c u l t i v a r s . 5 . 1 . 2 F i e l d e v a l u a t i o n o f t h r i p s damage s e v e r i t y A f i e l d t r i a l was r u n c o n c u r r e n t l y w i t h t h e s c r e e n h o u s e e x p e r i m e n t s t o m e a s u r e t h r i p s damage s e v e r i t y u n d e r f i e l d c o n d i t i o n s . F o u r cowpea c u l t i v a r s w e r e use d i n t h e t r i a l ; TVu 1 5 0 9 , TVx 3 2 3 6 , I f e Brown (TVu 3 6 2 9 ) and V I T A - 6 . They w er e p l a n t e d i n p l o t s 4 r o w s , 5 m l o n g and 0 . 7 5 m a p a r t . D i s t a n c e b e t w e e n p l a n t s was 0 . 2 0 m and 1 . 2 5 m b e t w e e n a d j a c e n t p l o t s . Each c u l t i v a r was r e p l i c a t e d f o u r t i m e s i n a c o m p l e t e l y r a n d o m i s e d d e s i g n . R e l a t i v e s u s c e p t i b i l i t y o f t h e f o u r cowpea c u l t i v a r s was a s s e s s e d by m a k i n g a s u b j e c t i v e v i s u a l r a t i n g o f t h r i p s f e e d i n g i n j u r y s e v e r i t y . A s c a l e o f 1 - 5 r e p r e s e n t i n g s l i g h t t o h e a v y damage was use d t o r a t e 15 c o n s e c u t i v e p l a n t s i n 1 row o f e ac h c u l t i v a r i n e a ch r e p l i c a t e o f t h e t e s t . R a t i n g was b a s e d on damage t o s t i p u l e s , f l o w e r bud s and f l o w e r s . The r a t i n g c h a r t i s s u m m a r i s e d i n T a b l e 5 . 1 . R a t i n g was done a t 48 and 52 DAP r e s p e c t i v e l y . A t 52 DAP a l s o 20 f l o w e r s p e r r e p l i c a t e o f eac h c u l t i v a r w e r e s a m p l e d t o d e t e r m i n e t h r i p s p o p u l a t i o n s . A damage i n d e x f o r e ac h c u l t i v a r was c a l c u l a t e d by m u l t i p l y i n g t h e number o f p l a n t s f a l l i n g i n t o e a c h r a t i n g c l a s s by t h e c l a s s n u mD e r , t h e n a d d i n g t h e p r o d u c t f o r eac h c l a s s and d i v i d i n g t h e sum by t h e n u mb er o f p l a n t s r a t e d . The r a t i n g s f o r t h e f o u r r e p l i c a t i o n s a t e a c h DAP w e r e University of Ghana http://ugspace.ug.edu.gh 69 , a v e r a g e d t o o b t a i n a mean i n d e x s e v e r i t y r a t i n g f o r t h e e n t i r e t e s t . The r e s u l t s o f t h e f i e l d t e s t a r e s u m m a r i s e d i n T a b l e 5 . 4 . 5 . 2 Resul t s 5 . 2 . 1 S c r e e n h o u s e e x p e r i m e n t s The r e s u l t s o f t h e t wo e x p e r i m e n t s on s c r e e n i n g t e c h n i q u e a r e s u n m a r i s e d i n T a b l e s 5 . 2 and 5 . 3 . I n t h e f i r s t e x p e r i m e n t ( T a b l e 5 . 2 ) t h e r e was no s i g n i f i c a n t d i f f e r e n c e i n t h r i p s f o u n d i n r a ceme s b e t w e e n TVu 1 5 0 9 , TVx 3 2 3 6 , V I T A - 6 and I f e Brown a t 7 D AI . I n t e r m s o f t h r i p s p e r f l o w e r TVx 3236 c om p a r e d f a v o u r a b l y w i t h TVu 1 5 0 9. I f e Brown and V I T A - 6 w e r e n o t d i f f e r e n t a l s o . TVu 76 was s i g n i f i c a n t l y d i f f e r e n t f r o m a l l o t h e r c u l t i v a r S o TVu 76 was a l s o s i g n i f i c a n t l y r a t e d f o r t h r i p s damage, when c om p a r e d t o t h e o t h e r c u l t i v a r s o f t h e t e s t . T h e r e w e r e no d i f f e r e n c e s i n damage s e v e r i t y b e t w e e n TVu 1509 and TVx 3236 on t h e one hand and I f e Brown and V I T A - 6 on t h e o t h e r . The same t r e n d o f o b s e r v a t i o n s w e r e o b t a i n e d i n t h e s e c o n d e x p e r i m e n t . 5 . 2 . 2 F i e l d e v a l u a t i o n o f t h r i p s damage s e v e r i t y T a b l e 5 . 4 i n d i c a t e s t h e mean n um b er o f t h r i p s p e r f l o w e r and t h e mean v i s u a l r a t i n g i n d i c e s f o r t h e f o u r c u l t i v a r s . I f e Brown and V I T A - 6 w e r e s i g n i f i c a n t l y r a t e d f o r t h r i p s damage c ompar ed w i t h TVu 1509 and TVx 3 236. Damage i n d e x was 2 . 5 f o r I f e Brown and V I TA - 6 . The i n d i c e s w er e 1 . 0 and 1 . 2 f o r TVu 1509 and TVx 3236 r e s p e c t i v e l y . University of Ghana http://ugspace.ug.edu.gh 70. Table 5 .2 : 1st screen ing: Mean number o f th r ip s and v is u a l r a t in g indices f o r th r ip s damage fo l lo w in g in fe s t a t io n o f caged potted cowpea c u l t iv a r s w ith 30 a d u l t M. s j f t s t e d t i . *Mean Number o f th r ip s Cul t i v a r Damage index Per raceme (7 DAI) Per f lo w er (10 DAI) TVu T5T79 3 .4 b 6 .7 c 1 .8 c TVx 3236-01G 1 .5 b 8 .4 c 2 .0 c I f e Brown 5.1 b 31.5 b 2 .9 b VITA-6 6 .9 b 26 .2 b 3 .0 b TVu 76 1 9 .8 a 6 1 .5 a 3 .9 a LSD IP 5% 8 .6 6 .4 0 .9 S.E. 2 .9 4 .6 0 .3 CV 88.7 37.9 14.3 *Means followed by the same l e t t e r are not s ig n i f i c a n t a t 5 % (Duncan's M u lt ip le Range T e s t ) . University of Ghana http://ugspace.ug.edu.gh 71. T a b l e 5 . 3 : 2nd s c r e e n i n g . Mean n umb er o f t h r i p s and v i s u a l r a t i n g i n d i c e s f o r t h r i p s damage f o l l o w i n g i n f e s t a t i o n o f cagd p o t t e d cowpea c u l t i v a r s w i t h 30 a d u l t M. s j o s t e d t l . *Mean n um b e r o f t h r i p s Damage Cu 1 1 i v a r i n d e x P e r raceme ( 7 DAI ) P e r f l o w e r ( 1 0 D A I ) TVu 1509 2 . 9 a 3 . 6 a 1.2 a TVx 3 2 3 6 - 0 1 G 2 . 5 a 10.6 a 1 . 9 a I f e Brown 4 .1 a 2 9 . 5 b 3 . 2 b V I T A - 6 3 . 7 a 2 8 . 5 b 3 .1 b TVu 76 8 . 5 b 3 1 . 4 b 4.1 b LSD @ 5% 3 . 6 7 . 3 1.1 S . E . 1.2 2 . 5 0 . 4 CV 6 3 . 0 2 6 . 8 1 8 . 3 ♦Means f o l l o w e d by t h e same l e t t e r a r e n o t s i g n i f i c a n t a t 5% ( D u n c a n ' s M u l t i p l e Range T e s t ) . University of Ghana http://ugspace.ug.edu.gh Table 5.4: Severity index and mean number of th rips per flower of 4 cowpea cu ltiva rs . C u ltiva r Severity index Mean number of th rip s/ f l ower TVu 1509 1.0 16.8 TVx 3236 1.2 18.2 Ife Brown 2.5 30.5 VITA-6 2.5 44.2 0.6 5.6 University of Ghana http://ugspace.ug.edu.gh 73. On the number of th rips per flower the same s ig n if ic an t trend was observed. 5.3 Discussion 5.3.1 Screenhouse experiments In both experiments TVu 1509 and TVx 3236 performed bette r in a ll measurements. The rate of development of th rips appeared retarded on TVu 1509 and TVx 3236 as compared to the other cu ltiva rs . This probably points to the presence of some a n tib io tic factors in these two cu ltiva rs . RCesingh (1980) id en tif ied the mechanism of resistance of TVu 1509 to th rips as antib ios is. I t is l ik e ly that the same compound is present in both TVu 1509 and TVx 3236, bearing in mind that TVx 3236 has TVu 1509 as one of its parents (IITA, 1980). This speculation needs fu rth e r evaluation however. Compared to TVu 76, Ife Brown and VITA-6 are less more susceptible to M. s jo s te d ti. In both experiments however, there were large varia tions between samples taken at 7 DAI. Coefficients of va ria tion (CV) were w ith in acceptable range (Southwood, 1966) at 10 DAI, in both experiments. Probably consistent samples are possible at 10 DAI and the rea fte r in th is type of screening technique. Two of the most important a ttrib u tes of any screening methodology are precision and repea tab ility (Jackai, 1982). Precision is determined by low sample v a r ia b il ity (Southwood, 1966). Most importantly, precision and repea tab ility are best assessed by the response of the res is tan t and susceptible checks to insect damage. In the method outlined here, University of Ghana http://ugspace.ug.edu.gh 74. these checks, (TVu 1509 and TVu 76) were h igh ly polarised in both measurements of th rips populations and degree of damage caused by th rips. The s ta t is t ic a l analysis showed that th e ir differences were h igh ly s ign ifican t. I t would appear that th is a r t i f ic ia l in fes ta tion method expounded here could be a useful tool of separating h igh ly susceptible from po ten tia lly useful cu ltiva rs . In addition i t could be used to elim inate escapes carried over from f ie ld screening methods. Further­ more th is method, lik e most a r t i f ic ia l in fes ta tion methods could provide information on the mechanism of resistance which are not obtainable from f ie ld methods (Kogan, 1979). 5.3.2 Fie ld evaluation of damage seve rity In the f ie ld t r ia l both TVu 1509 and TVx 3236 were comparatively superior to Ife Brown and VITA-6 as regards th rips in festa tion and degree of damage. Resistance to insects has been various ly expressed in terms of plant damage, insect counts, pupal weights and oviposition preference (Painter, 1951). Based on the f i r s t two parameters i t appears that TVu 1509 and TVx 3236 show some leve ls of resistance to flower th rips. The resistance of TVu 1509 to flower th rips has long been id en tif ied and characterised as an tib ios is (Singh ,1977b; Roesingh, 1980). TVx 3236 is a progeny of a cross between TVu 1509 and Ife Brown as stated in section 5.3.1. Thus i t may be expressing the gene for resistance against th rips from its res is tan t progenitor TVu 1509. University of Ghana http://ugspace.ug.edu.gh 75. 10 2 0 3 0 4 0 5 0 Mean number of thrips per flower Fig. 51 Regression of thrips injury severity on number of thrips per flower (I IT A ,se co n d seaso n , 1981) University of Ghana http://ugspace.ug.edu.gh 76. In an attempt to measure the influence of number of th rips on the damage severity of the four c u ltiva rs , the corre la tion coeffic ien t andlinear regression of seve rity index on number of th rips per flower were computed. A non-significant (P < .05) pos itive corre la tion (+ 0.89) was obtained (Figure 5.1 ). Each un it increase in the number of th rips per flower was associated with an increase of 0.06 in damage seve rity (Y 0.233 + 0.057 X). The computed r^ value (0.81) indicated that about 80% of the difference in damage seve rity could be a ttribu ted to the number of th rips in fes ting flowers. However th is observation is not accurate because of non-significance of the corre la tion coeffic ient. I t only provides a p relim inary ins igh t as to the re la tionsh ip between levels of in festa tion and plant su scep tib ility . The observation probably suggests that i t is impractical to use a part of the plant to asses the re la tionsh ip between whole plant s u sc e p tib ility and th rips in fes ta tion pressure. Analysis using to ta l number of th rips per plant may provide a more re lia b le measure of association. University of Ghana http://ugspace.ug.edu.gh 77. CHAPTER SIX 6. COMPARATIVE YIELD OF DIFFERENT COWPEA CULTIVARS WITHOUT PROTECTION AGAINST FLOWER THRIPS, MESALUROTHRIPS SJOSTEDTI T r ia ls were conducted during the second season of 1981 and ea rly f i r s t season of 1982, to compare the y ie ld of d iffe ren t cowpea cu ltiva rs which were not protected against flower th rips. The aim of the study was to assess the u t i l i t y of leve ls of th rips resistance shown by some cowpea cu ltiva rs . 6.1 Materials and methods 6.1.1 Second season 1981 t r ia l Four cowpea c u lt iva rs , TVx 3236-01G, TVu 1509, Ife Brown (TVu 3629) and VITA 6 were used in the t r ia l . Planting was done on a f la t contour and plants were thinned down to one plant per stand at ten days a fte r planting (DAP). Plots consisted of 4 rows 5 m long, and spacing was 0.75 m between rows and 0.20 m between plants in a row. A ll plots were replicated four times in a randomised block design. Manual weeding was done once at 45 DAP but no f e r t i l i z e r was applied. At 53 DAP, Endosulfan (Thiodan EC) was applied at a rate of 250 g a.i./ha to check Maruca and pod-sucking bugs in festa tion w ithout affecting th rips. Raceme and flower samples were taken at 42 and 48 University of Ghana http://ugspace.ug.edu.gh /8. DAP to determine th rips numbers as described in section 3.1.1 of Chapter three. A ll p lots were harvested between 75-80 DAP. Pods were fu rth e r dried in drying chambers and la te r machine-threshed to obtain seed weight. 6.1.2 Early f i r s t season 1982 t r ia l Cowpea c u lt iva rs , TVx 3236, VITA-5, VITA-6 and VITA-7 were used in the t r ia l . P lot size was 5 rows 5 m long and spacing was 0.75 m between rows and 0.20 m between plants in a row. A ll plots were replicated four times in a randomised block design. Two weeks p r io r to the planting of the experimental materia l, a susceptible c u lt iv a r, TVx 7-5H was planted along the border rows to serve as a spreader. Plants were thinned down to one plant per h i l l at 10 DAP. There was one manual weeding at 40 DAP and no f e r t i l i z e r was applied. Spreader rows were la te r pulled out when the experimental material was 35 days old. Endosulfan (Thiodan EC) was again applied at 55 DAP to check Maruca and pod-sucking bugs without affecting th rips. Samples of racemes at 38 DAP and of flowers at 48 DAP were taken to estimate th rips in festa tion. Around 61 DAP there was a sudden rise in populations of pod-sucking bugs made up of Acanthomia tomentosi col 1 i s , R ip to rtus dentipes, Nezara v ir id u la and Anoplocnemis curvipes. Another spray of Endosulfan was then applied at 65 0AP to check th is in festa tion. University of Ghana http://ugspace.ug.edu.gh 79. A ll plots were harvested between 79-82 DAP. Pods were machine- threshed to obtain seed weight. 6.2 Resul ts 6.2.1 Second season 1981 t r ia l Results of the second season (1981) t r ia l are tabulated in Table 6.1. The resu lts indicated that there was no s ig n if ic a n t difference in y ie ld between TVu 1509 and TVx 3236. The two c u lt iva rs also showed no differences in the number of th rip s found in racemes and flowers. S im ila rly there was no s ig n if ic an t d iffe rence in the y ie ld of Ife Brown and VITA-6 . Except fo r the number of th rip s in flowers these two c u lt iva rs also showed no s ig n if ic an t difference in th rips per raceme, 6.2.2 F irs t season 1982 t r ia l The resu lts of the f i r s t season 1982 t r ia l are summarised in Table 6.2. There was no s ig n if ic an t difference in number of th rips in racemes at 38 DAP, between TVx 3236, VITA-5 and VITA-6. Probably th is observation suggests that the three c u ltiva rs experienced the same in i t ia l in festa tion leve ls. However a ll three were s ig n if ic a n tly d iffe ren t from VITA-7 in terms of th rips numbers at 38 DAP. There were no s ign if ican t differences in number of th rips found in flowers between TVx 3236 and VITA-5 on the one hand and VITA-6 and VITA-7 on the other. University of Ghana http://ugspace.ug.edu.gh 80. Table 6.1: Comparative y ie ld performance of 4 cowpea c u lt iva rs . IITA 2nd season 1981 (*DQP: 30/9/81). ** Mean number of th rips Cul t iv a r Yie l d kg/ha Per Raceme (42 DAP) Per flower (48 DAP) TVu 1509 0.7 b 21.0 a 701 b TVx 3236 0.8 b 20.8 a 676 b Ife Brown Oo 9 ab 26.0 a 195 a VITA-6 1.2 a 48.7 b 213 a L.S.D at 5% 0.4 11.2 56.3 S.E. 0.1 3,5 17.6 CV 27.0 23,9 7.8 *00P Date of planting. **Means followed by the same le t te r are not s ig n if ic an t at 5% (DMRT). University of Ghana http://ugspace.ug.edu.gh 81. Table 6.2: Comparative y ie ld performance of 4 cowpea cu ltiva rs. IITA 1st season 1982 (DOP: 24/3/82). ♦Mean number of thrips Cultivar Yield kg/ha Per raceme (38 DAP) Per flower (48 DAP) TVx 3236 0.3 b 6.8 a 988.4 b VITA-5 0.8 ab 16.5 a 546.4 a VITA-6 1.1 ab 54.9 b 477.5 a VITA-7 1.4 a 73.9 b 616.7 a L.S.D. @ 5% 0.7 14.2 231.5 S.E. 0.2 4.4 72.4 CV 54.9 23.4 22.0 *Means followed by the same le tte r are not s ign ificant at 5% (DMRT). University of Ghana http://ugspace.ug.edu.gh 82. A very high s ig n if ican t difference in y ie ld was obtained between TVx 3236 and each of the three c u ltiva rs which themselves were not s ig n if ic a n tly d iffe ren t from each other. 60 3 Pi scussion 6o3.1. Second season 1981 t r ia l The overa ll resu lts during the second season (1981) indicated that TVu 1509 and TVx 3236 were superior in terms of th rips in fes ta tion and y ie ld when compared w ith Ife Brown and VITA-60 The fact that TVu 1509 and TVx 3236 had consistently less number of th rips may indicate the presence of some resistance factor. TVu 1509 was found to re s is t th rips in fes ta tion (IITA , 1976, 1977, 1978). In t r ia ls conducted at I IT A i t consistently outyielded contemporary cu ltiva rs . I t suffered less damage to flower buds and flowers and less y ie ld loss due to thrips (IITA , 1977). Thus the resu lts obtained in th is study conform w ith e a r l ie r findings. The mechanism of resistance of TVu 1509 to flower th rips was id en tif ied as antib ios is (Roesingh,1980). TVu 1509 was subsequently crossed with Ife Brown, and a single selection id en tif ied as TVx 3236 was shown to combine resistance to flower th rips with good y ie ld potential and seed qua lity (IITA , 1980). I t is thought that TVx 3236 has an an tib io tic e ffect, as th is report and e a r lie r investigations (IITA, 1980) have shown that th is c u lt iv a r reduces thrips populations,. University of G hana http://ugspace.ug.edu.gh University of Ghana http://ugspace.ug.edu.gh 84. 6°3„2. F irs t season 1982 t r ia ls The resu lts during th is period showed that VITA-7 was most susceptible of a ll the cu ltiva rs of the t r ia ls . As compared to Table 6.1 however, there was a large v a r ia b i l i t y w ith in samples taken at 38 DAP than was the case w ith samples taken at 42 DAP. Apparently consistent samples of th rips from racemes are obtainable around 42 DAP. Again the t r ia l fu rthe r revealed the superior performance of TVx 3236. The reasons fo r th is have already been expounded. Apart from work carried out at IITA, various m ultilocationa l t r ia ls have confirmed th is th rips resistance and higher y ie ld s of TVx 3236. I t is ye t another source from which other res is tan t genotypes could be sought through breeding. University of Ghana http://ugspace.ug.edu.gh 85. CHAPTER SEVEN 7. GERMPLASM SCREENING FOR RESISTANCE TO FLOWER THRIPS Megalurothrips sjCstedti is a major pest of cowpeas in trop ica l Africa. Severe infestations can lead to to ta l y ie ld losses (Singh and A llen, 1980). The use of insecticides has been the princ ipa l method of protecting cowpeas against th rips and other insect pests. Studies conducted at IITA indicate tha t the use of th rips res is tan t cu ltiva rs in integrated control schemes can increase y ie lds with minimum cost. This t r ia l was therefore conducted as an addition to the on-going search fo r sources of resistance to th rips. 7.1 Materials and methods A to ta l of 3700 en tries , representing a part of the over 12000 World Cowpea Germplasm maintained at IITA were screened in the f ie ld fo r resistance to flower th rips. The t r ia l was conducted during the f i r s t season of 1982. Screening was done on f la t experimental contours that were bordered by pigeon peas. Pigeon peas maintain a continuous popu­ la tion of thrips and thus serve as a spreader. Also f ifte en days before the planting of the experimental materia l, susceptible cu lt iva rs (a mixture of VITA-7 and TVx 7-5H) were planted on 3 border rows that University of Ghana http://ugspace.ug.edu.gh 8 6 . run down the length of each contour. This was to ensure that adequate th rips populations were present. A ll accessions were planted in 3 m, single rows. When the experimental cu ltiva rs were f if te en days old, the th rips susceptible border rows were uprooted; th is concentrated th rips populations across the experimental contours. Between 45 - 55 days a fte r planting (DAP), the te s t c u lt iva rs were rated v is u a lly on a 5-point scale fo r apparent f ie ld resistance to th rips damage. Rating was done by three independent persons and involved an independent and subjective assessment of th rips damage seve rity . Damage assessment was based mostly on flower and pod setting. A f in a l ra ting fo r each accession was obtained by averaging the scores of the three persons. A ll accessions that were rated above 3 were pulled out. Those which were rated as apparently res is tan t ( i.e . scores 1-3) were given an insectic ide treatment to protect pods against pod-sucking bugs and Maruca damage. 7,2 Results and comments The resu lts of the screening exercise are summarised in Figure 7.1, Out of 3700 accessions, 11 did not germinate. 37 en tries (represen­ ting 2.2% of the to ta l entry) scored 2. 485 (13.2,); 771 (20.9") and 2311 (62.7%) were rated in categories 3, 4 and 5 respec tive ly . In a l l, 604 accessions (making 16.4" of the to ta l accession rated) indicated some potentia l leve ls of f ie ld resistance to flower th rips. These were scheduled to go in replicated f ie ld t r ia ls to fu rth e r assess these potentials. University of Ghana http://ugspace.ug.edu.gh 87. 60 C 50 icn 2 i/ i f i v Q o c 3C Q 5 a o 20 10 2 3 4 Degree of resistance Figure 7 I Frequency distribution o f 3 6 8 7 cow pea germ plasm accession s over a 5 - point scale fo r re s is ta n ce to flower thrips University of Ghana http://ugspace.ug.edu.gh 88. Several factors were bound to m ilita te against the r e l ia b i l i t y of th is negative screening t r ia l. However some observations were made in order to ascertain to a reasonable extent, that the t r ia l was measuring resistance to flower th rips. I t was necessary to check whether insects other than th rip s or diseases caused depression in flower and pod setting. Levels of flower pests, espec ia lly Maruca were very low in a ll four experimental contours. Very few flower samples were found to have been damaged by Maruca and other 1epidopterous larvae. In addition there was a large population of hy lid frogs that fed on both adult and larvae of Maruca. Meloid beetles which also damage flowers were s ig n if ic a n tly absent. Disease incidence was ra ther low in a ll accessions. University of Ghana http://ugspace.ug.edu.gh 89. CHAPTER EIGHT 8. SUMMARY The biology of cowpea flower th rips M.s jos ted ti was studied arte the response of cowpea cu ltiva rs to th rips in fes ta tion evaluated. Three th rips species, apart from M_. s jo s te d ti. were found to occur on the cowpea crop. However, M. s josted ti was found to account fo r more than 90% of the cowpea th rips pests. Using sta in ing techniques, M. s josted ti was found to ovipos it mainly in young flower buds and calyx tube of open flowers. The population build up of th rips was found to be tied closely w ith the development of f lo ra l buds and flowers. As the cowpea crop matured and f lo ra l structures became less abundant the th rips popula­ tion f e l l. On a ll cu ltiva rs tested, th rips populations became s ig n if ic a n t around 37 days a fte r planting (DAP). The seasonal abundance of M. s josted ti was found to be determined la rge ly by weather factors. Heavy ra in fa ll tended to mechanically dislodge thrips from plants. Higher temperatures probably retarded development of thrips. University of Ghana http://ugspace.ug.edu.gh 90. 7. Two population peaks of M. sjOstedti were apparent during the year; one in May and the other in November. 8. The November peak was the highest. I t has therefore been suggested that f ie ld screening techniques that re ly on natural in fes ta tion should be undertaken during th is period. 9. On evaluating 5 d iffe ren t sampling methods fo r th rip s on cowpea, the use of water traps was found to be most adequate in terms of v a r ia b i l i t y between samples. I t has been suggested that the p o s s ib ility of u t i l iz in g the method in fu ture be fu rth e r pursued. 10. CylindrincaI s tic ky traps were also found to be promising as regards estimation of th rip s populations. 11. Using an a r t i f ic ia l in fes ta tion method, a screenhouse screening technique was developed to evaluate resistance of cowpeas to flower th rip s . I t was found tha t the technique was e ff ic ie n t at separating high suscep tib ilit ie s from po ten tia lly useful materials. 12. In an attempt to measure the influence of number of th rip s on the damage seve rity of cowpea c u lt iva rs , a nonsignificant positive corre la tion was obtained. The computed r^ value indicated that about 80% of the difference in damage seve rity could be a ttrib u ted University of Ghana http://ugspace.ug.edu.gh 91 . to the number ot th rips in festing flowers. I t has been suggested that future corre la tion studies should involve whole plant samples. 13 The cowpea c u lt iv a r TVx 3236 was found to be moderately res is tan t to M. s jo s ted ti. On comparing y ie lds without protection against flower th rips TVx 3236 was most superior. The mechanism of resistance of TVx 3236 however, remains to be worked out. 14. Large varia tions in th rips numbers were often noted in samples of racemes taken between 37 - 40 DAP. I t was apparent that consistent samples invo lv ing racemes were obtainable only a fte r 40 DAP. 15. Results of the f i r s t phase of a negative t ie ld screening t r ia l for cowpea germplasm material indicated that other sources ot resistance to flower th rip s were apparent in some accessions, i t has been suggested that fu rthe r evaluation should be made in rep licated t r ia l s . University of Ghana http://ugspace.ug.edu.gh 92. REFERENCES Allen, D.J. and van Damme, P. (1981). On the th rips transmission of Cowpea Yellow Mosaic Virus. Trop. Ag ric r 58(2), 181 - 184. Andrewartha, H.G., and Birch, L.C. (1954)„ The d is tr ib u t io n and abundance of animals. 782 pp. Un ive rs ity of Chicago Press, Chicago. Ansari, A. (1978). A progress report on Studies on the Bionomics of Aphis craccivora Koch, on cowpea. IITA, N igeria. (Unpublished). Appert, J„ (1964). Pests of cowpea, Vigna unguiculata (L J Walp. L1 Agronomic Tropicale E x tra it du IRAT No. 10, 788 - 799. Aykroyd, W„R. and Doughty, J. (1964). Legumes in human n u tr it io n . Rome FAQ N u trit iona l Studies No. 19. 138 pp. Rome. Beck, S.D. (1965). Resistance of plants to insects. Ann; Rev. Entomol. ]_0, 207 - 232. Booker, R.H. (1963). Notes on the pest complex of cowpea in Northern Nigeria and possible method of contro l. Proc. 1st Nigerian Grain Legume Conference, Inst, hyric . Res., Ahmadu Bello Univ. Samaru, Mimeo. ___________________ U9fa4), Pests of cowpea and th e ir control in Northern Nigeria. Bull, ent. Res. 55, 663 - 672. ___________________ (1965). L is t of insect species found in association with cowpea at Samaru. Inst, of Agric. Res., Samaru, Za ria . Misc„ paper No. 9. University of Ghana http://ugspace.ug.edu.gh 93. Bressani, R. and E lias, L.G. (1980). N u trit iona l value of Legumes for human and animals. IN Summerfield, R.J. and R.H„ Bunting, eds. Advances in Legume Science, pp. 1 35-155. K.ew, Botanic Gardens. Bullock, J.A„ (1965)„ The assessment of populations of Thrips nigro- pilosus Uzel on pyrethrum. Ann, appl. B io l. 55̂ , I - 12c B u rk in , I.H. (1951). Habits of man and the o rig ins of cu ltiva ted plants of the Old World. Proc. Linn. Soc. (Lond.). 164, 12 - 42. de Candolle, A. (1886). O rig in of cu ltiva ted plants. 2nd ed ition, reprinted 1959. Hafner Publishing Co», New York. Carlson, E.C, (1964). Effect of flower th rips on onion seed plants and a study of th e ir control. J. econ. fcnt. 57, 735 - 741. Caswell, H_R. (l978)„ In s titu te of Ag ricu ltu ra l Research, Samaru, N igeria, unpublished report. Caveness, F. (1973). Nematode attack on cowpeas in N igeria. Proc. 1st IITA Grain Legume Improvement Workshop. In te r. Inst. Trop. Agric. Ibadan, p. 302. Chant, S,R. (1959). Viruses of cowpea, Vigria unguiculata (L.) Walp., in Nigeria. Ann, appl. B io l. 47, 565 - 572. Cobley, L.S. (1956). An introduction to the botany of trop ica l crops. Longmans Green and Co., London University of Ghana http://ugspace.ug.edu.gh 94. Da lz ie l, J.M. (Iy37). Ihe useful plants of trop ica l West Africa London, Crown Agents fo r the Colonies. Davidson, J. (1944). On the re la tionsh ip between temperature and rate of development of insects at constant temperature. J. Anim. Ecol. 13, 26 - 38. Davidson, J„ and Andrewartha, H.G. (1948). Annual trends in a natural population of Thrips imaginis, (Thysanoptera). J. Anim. Ecol. 17, 193 - 199. Dema, I S: (1963). Factors affecting legume d is trib u tio n and consumption in N igeria. Proc. 1st Nigeria Grain Legume Conference, I.A.R., Samaru, Zaria, N igeria. Dovlo, F.E., Williams, C.E. and Zoaka, L. (1975). Cowpeas: home preparations and use in West A frica. Ottawa, IDRC - 055e. 96pp. Ebong, U.U. (1965). 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Nigeria Agric. J . 5, 29 - 37. __________________ (1969). On the population dynamics and f l ig h t a c t iv ity of Taeniothrips s josted ti (Trybom.) .(Thysanoptera:Thri pidae) on cowpea, Bull. Ent, Soc. N ige ria . 2, 60 - 71. _________________ (1974). On the population dynamics of Taeniothrips s jostedti (Trybom.) (Thysanoptera:Thripidae) on cowpea and an alternate host, Centrosema pubescens Benth., in N igeria. Rev. Zool. A fr ic . 88, 689 - 702. University of Ghana http://ugspace.ug.edu.gh 105. Taylor, T.A. (1978). Maruca te s tu la lis (Geyer): An important pest of tropical grain legumes. Ij i Pests of Grain Legumes: Ecology and Control, eds. S.R. Singh, H.F. van Emden and T, A jibo la Taylor. 454 pp. Academic Press, London and New York. Usua, E.J. (1975). A progress report on the Bionomics of Maruca tes tu­ la l is (Geyer). IITA, Ibadan, Nigeria (unpublished). van Halteren, P. (1971). Insect pests of cowpeas, Vigna unguiculata (L.) Walp. in the Accra Plains, Ghana. Ghana J. Agric. Sci 4, 121 - 123. Vavilov, N.I. (1951). The o rig in , va ria tion , immunity and breeding of cu ltiva ted plants. 105 pp. Ronald Press Co., London. Verdcourt, B. (1970) Studies in the Leguminosae - Papilionidae to r the "Flora of trop ica l East A frica". IV. Kew, Royal Botanical Garden, Bull 24, 507 - 56y. Westphal, E. (1974). Pulses in Ethiopia; th e ir taxonomy and A g ricu ltu ra l significance. Centre fo r Ag ricu ltu ra l Publish ing, Wageningen. Williams, R.J. (1y75;. Diseases of cowpea, (Vigna unguiculata (L.) Walp.) in Nigeria. PANS, 21, 253 - 267 University of Ghana http://ugspace.ug.edu.gh 106. APPENDIX 1 KEY TO THE SPECIES OF THRIPS INFESTING LEGUMES IN NIGERIA (A fte r Okwakpam and Youdeowei, 1980) 1. Apex of abdomen conical, forewings not constricted, w ith at least one longitudinal ve in......................... 2 Apex of abdomen tubular, forewings constricted at middle w ithout venation...........................................Haplothrips gowdeyi 2. In te r-oce lla r setae large and prominent; forewings with poste rio r vein. Abdomen without brown and white bands......................... .................. ............... 3 In te r-oce lla r setae not prominent; forewings w ithout poste rio r vein; Abdomen w ith brown and white bands................................................. „........ Sericothrips o cc ip ita lis 3. Anterio r angular setae ha lf as long as Targe posterio r angulars, hind margins of pronotum with 8 setae between the inner pa ir of the poste rio r angulars; an te rio r vein of fore-wings with a gap University of Ghana http://ugspace.ug.edu.gh 107. and 2 d is ta l setae; abdominal segment VIII with in terrupted comb; body co lour pale to b lack ish brown.....................................................................................................Megalurothrips s jS s t e d t i A n te r io r angular setae as long as large p o s te r io r angulars , hind margin o f pronotum with 10 setae between the inner p a i r o f p o s te r io r angulars; a n te r io r vein o f fore-wing without gap; abdominal segment VIII without comb; body co lour brown ye llo w , head and prothorax much pa le r than rest o f body....................................... . . .......... .......................................... F r a n k l in ie l l a s c h u ltz e i University of Ghana http://ugspace.ug.edu.gh 103. APPENDIX 2 Chi-Square tes t fo r d i s t r i b u t i o n of eg g s of M e g a l urothr ips s j o s t e d t i in two parts of the cowpea f lower. Repl ication Flower Totals part 1 2 3 4 5 Calyx 25(24.8)* 21(20.9) 23(21.7) 29(28.6) 15(17.0) 113 Co ro 11 a 7(7.2) 6(6.1) 5(6.3) 8(8.4) 7(5.0) 33 32 27 28 37 22 *N umbers in brackets are the expected values. x2 £ (0 - E)2 0.082 E d.f = 4 and x2 (tab) = 18.47, P < .001 University of Ghana http://ugspace.ug.edu.gh 109. APPENDIX 3 Mean monthly ra in fa ll and temperature fo r 1981/1982 (IITA). Ra infa ll (mm) Temperature September 250.0 25.6 October 145.6 26.7 November o.O 27.3 December o.O 28.0 January 1.6 27.2 February 44.6 28.4 March 92.7 28.4 AP f il 87.9 28.1 May 102.5 26.8 June 168.4 25.9 Ju1y 137.5 24.3 August 78.2 24.2 University of Ghana http://ugspace.ug.edu.gh no . APPENDIX 4 Number o f th r ip s per raceme at 7 D A I- ls t screenhouse screen ing. C u lt iv a r I II III IV V Mean TVu 76 11.6 45.0 16.8 10.3 15.3 19.8 TVx 3236 2.0 1.2 1.2 1.2 1.8 1.5 Ife Brown 5.1 3.0 5.7 5.8 5.8 5.1 VITA-6 9.0 6.8 5.8 8.0 5.0 6.9 TVu 1509 2.9 2.0 5.3 3.9 2.7 3.4 A nalys is o f variance (ANOVA) Source of DF SS MS F v a r ia t io n Treatment 4 1053.57 263.39 6.23 Erro r 20 845.14 42.26 Total 24 1898.71 79.11 University of Ghana http://ugspace.ug.edu.gh 1 1 1 . APPENDIX 5 Number of th rips per flower at 10 DAI. 1st screenhouse screening. C u ltiva r I I I I I I IV V Mean TVu 76 55o0 95.0 69.0 45.5 43.0 61.5 TVu 1509 5.0 8.0 5.0 6.8 8.5 6.7 VITA-6 32.0 20.0 34.0 25,0 20.0 26.2 Ife Brown 31.0 28.0 38.3 30.0 30.0 31.5 TVx 3236 8.0 7.5 8.4 10.3 8.0 8.4 Analysis of variance (AN0VA) Source of DF SS MS F va ri ation Treatment 4 9844.31 2461.08 23. 77 Error 20 2070.48 • 103.52 Total 24 11914.78 University of Ghana http://ugspace.ug.edu.gh 1 12 . APPENDIX 6 Number of th rips per raceme at 7 DAI. 2nd screenhouse screening. Cu1t i var I I I I I I IV V Mean TVu 1509 2.1 2.0 4.4 4.2 1.6 2.9 TVu 76 8.4 4.3 7.4 5.4 16.8 8.5 Ife Brown 2.7 8.0 5.0 2.6 2.0 4.1 TVx 3236 2o2 1.9 1.5 4.0 2.1 2.3 VITA-6 3.0 5.0 6.0 2.1 2.2 3.7 Analysis of variance (ANOVA) Source of DF SS MS F varia tion Treatment 4 118.43 29.61 4.08 Error 20 145.06 7.25 Total 24 263.49 10.98 University of Ghana http://ugspace.ug.edu.gh 113. APPENDIX 7 Number of thrips per flower at 10 DAI. 2nd screenhouse screemni Culti var I I I l l IV V Mean TVu 1509 2. 3 3.4 2.0 8.0 2.2 3.6 VITA-6 25. 0 39.0 23.0 29.8 26.0 28.6 Ife Brown 31. 0 28.0 38.3 20.0 30.0 29.5 TVx 3236 13. 6 8.0 8.3 10.3 13.0 10.6 TVu 76 32. 0 30,0 34.0 41.0 20.0 31.4 Analysis of variance (AN0VA) Source of DF varia tion SS MS F Treatment 4 3236.51 809.13 26.24 Error 20 616.80 30.84 Total 24 3853.31 160.55 University of Ghana http://ugspace.ug.edu.gh 114. APPENDIX 8 Yield of 4 cowpea cu ltiva rs . 2nd season, 1981. Culti var I I I I I I IV Mean TVu 1509 676 690 706 732 701 TVx 3236 682 617 650 755 676 Ife Brown 190 189 223 178 195 VITA-6 240 198 220 194 213 Analysis of variance (ANOVA) Source of DF SS MS P varia tion B1 ock 3 3490,5 1163.5 0. 93 Treatment 3 940859.0 313619.67 252, 69 Error 9 11173.5 1241.1 Total 15 955523 University of Ghana http://ugspace.ug.edu.gh APPENDIX 9 Yield of 4 cowpea cul tiva rs . 1st season , 1982 Cu lti var I I I I I I IV Mean TVx 3236 999.0 1141.0 1152.0 661.6 988.4 VITA-5 573.6 558.8 583.4 469.6 546.4 VITA-6 799.5 486.8 323.2 300.5 477.5 VITA-7 619.8 591.6 709.5 545.9 616.7 Analysis of variance (AN0VA) Source of varia tion DF SS MS F Block 3 149406.95 49802. 32 2.37 Treatment 3 623653.99 207884. 66 9.91 Error 9 188888.28 20987. 59 Total 15 961949.22 PLATE 4.1: A water trap mounted in the f ie ld