Some Aspects of the Biology of Sesamia Nonagrioides Botanephaga and Chilo Aleniellus in Southern Ghana.

Abstract

Studies were conducted on some aspects of the biology of Chilo aleniellus (Strand) and Sesamia nonagrioid.es botanephaga Tams and Bowden in Southern Ghana. The life cycle of S. n. botanephaga revealed 8 developmental stages; the egg, 5 larval instars, a prepupa and a pupa. Female S. n. botanephaga was found to lay 330 } 17.7 eggs within a period of 5 days. She required three surfaces to lay her eggs, which were mainly deposited, on the inner side of the leaf sheath fitting tightly on to the maize stem. The mated females laid more eggs per female (33 0 } 17.7 eggs) than the virgin female (2 68 } 9.2 eggs). The incubation period of the eggs of S. n. botanephaga was found to be 5.23 } o.o3 (5-7) days in the laboratory. The mean larval duration was 29 days and the prepupal period lasted for 2.00 } 0.01(1 - 3) days. The first instar larvae dispersed in 1-3 days after hatching. The third, fourth, fifth, and sixth instar larvae fed actively producing large quantities of frass. Pupae frequently occurred close to the exit hole (less than 6 cm). The pupal period varied from 6 to 10 days. The life cycle of S. n. botanephaga was completed in 38.2 } 0.28 (29 - 50) days. Adults of S. n. botanephaga lived for four to ten days. The adults reared in the aboratory showed a sex ratio of 2:3(male: female) which was significantly different from the expected ratio (1:1) (male: female). Female C. aleniellus laid no egg in the laboratory when paired or single. No mating was observed in the adults of C. aleniellus. The larva of C. aleniellus went into diapause in the minor cropping season in December 1998 and came out of diapause in the beginning of the major cropping season in April 1999. Adults from the field collected larvae showed a sex ratio of 1:1(male: female) with no significant difference between the number of males and females.