Browsing by Author "Overholt, W.A."

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Cross mating studies among five fruit fly parasitoid populations: Potential biological control implications for tephritid pests
(BioControl, 2008-10) Billah, M.K.; Kimani-Njogu, S.W.; Wharton, R.A.; Overholt, W.A.; Wilson, D.D.; Cobblah, M.A.
The reproductive compatibility between four different species/populations of the tephritid parasitoid Psyttalia (Walker) species from Kenya and individuals of the morphologically identical Psyttalia concolor (Szépligeti) (Hymenoptera: Braconidae) from a laboratory culture in Italy used in augmentative biological control of olive fly, Bactrocera oleae (Gmelin) (Diptera: Tephritidae) was assessed through cross mating tests using single-pair and group mating methods. Reciprocal crosses among the species resulted in the production of viable offsprings up to the second generation. In spite of the successful production of viable offspring in the laboratory, Psyttalia species are known to have specific host fruit and/or host fly preferences and populations/species may be isolated in one way or the other. However, it is not known whether these populations/species interbreed in the field. We discuss the ability of these parasitoids to interbreed and the potential effects of that on their use as biological control agents, especially in environments where other closely related species are present or in situations where multiple parasitoid introductions are intended. © 2007 International Organization for Biological Control (IOBC).
Cross mating studies of Psyttalia species (Hymenoptera: Braconidae): Potential implications for biological control of tephritid pests
(BioControl 53 (5): 709-724, 2008) Billah, M.K.; Kimani-Njogu, S.W.; Overholt, W.A.; Wharton, R. A.; Wilson, D.D.; Cobblah, M.A.
The reproductive compatibility between four different species/populations of the tephritid parasitoid Psyttalia (Walker) species from Kenya and individuals of the morphologically identical Psyttalia concolor (Szépligeti) (Hymenoptera: Braconidae) from a laboratory culture in Italy used in augmentative biological control of olive fly, Bactrocera oleae (Gmelin) (Diptera: Tephritidae) was assessed through cross mating tests using single-pair and group mating methods. Reciprocal crosses among the species resulted in the production of viable offsprings up to the second generation. In spite of the successful production of viable offspring in the laboratory, Psyttalia species are known to have specific host fruit and/or host fly preferences and populations/species may be isolated in one way or the other. However, it is not known whether these populations/species interbreed in the field. We discuss the ability of these parasitoids to interbreed and the potential effects of that on their use as biological control agents, especially in environments where other closely related species are present or in situations where multiple parasitoid introductions are intended.
The effect of host larvae on three Psyttalia species (Hymenoptera: Braconidae), parasitoids of fruit-infesting flies (Diptera: Tephritidae)
(International Journal of Tropical Insect Science, 2005-09) Billah, M.K.; Kimani-Njogu, S.; Overholt, W.A.; Wharton, R.A.; Wilson, D.D.; Cobblah, M.A.
Three species of fruit fly parasitoids, Psyttalia concolor (Szépligeti), Psyttalia cosyrae (Wilkinson) and Psyttalia lounsburyi (Silvestri) (Hymenoptera: Braconidae) were reared on different host larvae to determine the effects of host species, size and colour on parasitoid development. Ovipositor, ovipositor sheath and hind tibia lengths were found to be different for progenies from preferred and non-preferred host larvae. Ratios of ovipositor-tibia and ovipositor sheath-tibia showed no difference when P. concolor was reared on a bigger host (Ceratitis cosyra (Walker) (Diptera: Tephritidae), whereas rearing P. cosyrae on a smaller host (C. capitata (Wiedemann) showed significant differences. Comparison of the linear measurements, ratios and number of flagellomeres of parasitoids reared on preferred hosts, separated the species into their natural groupings. When reared on a different-coloured host, P. lounsburyi lost its dark markings but other characters remained unchanged. Morphometric analysis also indicated differences between parasitoids reared on preferred host larvae and those reared on non-preferred host larvae. Rearing parasitoids on larvae other than their preferred hosts resulted in colour and size changes, and thus, these characters alone were not reliable for the identification of parasitoids. This is especially important in post-release sampling surveys to ascertain establishment of the parasitoids in new environments where they may adapt to new host species. © ICIPE 2005.
Parasitization of Selected African Stemborers By Cotesia Flavipes Cameron and Cotesia Sesamiae (Cameron) (Hymenoptera:Braconidae) with Emphasis on Host Selection and Host Suitability.
(University of Ghana, 1995-01) Ngi-Song, A.; Overholt, W.A.; Lwande, W.; Njagi, P.G.N.; Ayertey, J.N.; University of Ghana, College of Basic and Applied Sciences, School of Agriculture, Department of Crop Science
Chilo partellus (Swinhoe) is a major pest of maize and sorghum in East Africa and indigenous natural enemies have been unable to maintain the pest population at a level acceptable to farmers. In Kenya, a classical biological control programme was initiated in an attempt to increase natural suppression of Chilo partellus and other stemborers. To do this, a natural enemy of Chilo partellus, Cotesia flavipes Cameron (Hymenoptera: Braconidae), has been introduced into Kenya from Pakistan since 1991. This work investigated the host and host habitat location, the acceptability and suitability of Chilo partellus and indigenous stemborer hosts for the development of Cotesia flavipes and a local natural enemy, Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae), as well as the semiochemicals involved in host finding. The host selection process of the larval parasitoids Cotesia flavipes and Cotesia sesamiae was studied in the laboratory. Female parasitoids were attracted to odours from uninfested maize, sorghum and napier grass in a Y-tube olfactometer. In a dual choice test, the three plant species infested with Chilo partellus, Chilo orichalcocillellus Strand, Busseola fusca (Fuller) or Sesamia calamistis Hampson larvae were more attractive than uninfested plants. Cotesia flavipes and Cotesia sesamiae did not show preference for any of the stemborer species under study in dual choice tests. Odours from frass, produced by the four stemborer species fed on maize, sorghum, and napier grass were attractive to both parasitoid species. Cotesia flavipes was more attracted tofrass produced by Chilo species than frass produced by B. fusca in dual choice tests. No preference was observed in other combinations. Cotesia sesamiae was equally attracted to all types of frass. Attractive volatiles from infested plants were collected using activated charcoal traps and were subjected to gas chromatography –electroantennography (GC-EAD) and gas chromatography-mass spectrometry (GC-MS). Twelve GC-EAD active peaks were observed. Three of the peaks were identified as anisole, (E)-β- farnesene, and (Z)-3-hexenyl acetate. Other chemicals identified from maize infested with Chilo partellus included myrcene, 2-heptanone, 4, 8 -dimethyl-1, 3, 7- nonatriene, (Z)-2-hexenal, (Z)-3-hexen-l-ol, cyclosativen, cedrene and a-copaene. GC comparison of infested and uninfested maize seedlings showed a quantitative and qualitative difference in the volatile composition. Anisole, (E)-β- farnesene and 4, 8-dimethyl-l, 3, 7-nonatriene were absent in the volatile collection of uninfested maize. The chemical composition of the headspace of artificially damaged maize seedlings treated with larval regurgitant was similar to that of infested maize seedlings. Behavioural bioassays showed that Cotesia flavipes was attracted to volatile extracts of infested and uninfested maize and that they were attracted to synthetic anisole, (E)-β-farnesene, (Z)-3-hexenyl acetate. Chilo partellus, Chilo orichalcocillellus, B. fusca and S. calamistis, were exposed tofemale of Cotesia flavipes and Cotesia sesamiae to assess their acceptability for oviposition and suitability for the development of the parasitoids. There were no differences in the acceptability of the four hosts exposed to Cotesia flavipes. In contrast, Cotesia sesamiae preferred S. calamistis larvae (92%), followed by the two Chilo species. Busseola fusca larvae were least attacked (48.8%) by Cotesia sesamiae. The suitability of the four hosts also varied with the parasitoid species. In B. fusca both parasitoid species did not develop and egg encapsulation was observed. Chilo partellus, Chilo orichalcocilielius and S. calamistis were suitable hosts for the development of Cotesia flavipes. However, a higher mortality of immature parasitoids was observed in S. calamistis as compared to Chilo partellus. No differences were found in the mean number of progeny per female, or the sex ratio. The most suitable host for Cotesia sesamiae was S. calamistis, followed by the two Chilo species, which were equally suitable. When third, fourth, fifth and sixth instars of Chilo partellus were exposed to Cotesia flavipes females, third instars were less suitable than fourth, fifthor sixth instars as measured by immature parasitoid mortality. Total haemocyte counts increased in the blood counts in parasitized larvae two to six days after parasitization, suggesting an active immune interaction between the suitable host, Chilo partellus, and the invading parasitoids.