Effects of Volatiles from Maruca vitrata Larvae and Caterpillar-Infested Flowers of Their Host Plant Vigna unguiculata on the Foraging Behavior of the Parasitoid Apanteles taragamae

The parasitoid wasp Apanteles taragamae is a promising candidate for the biological control of the legume pod borer Maruca vitrata, which recently has been introduced into Benin. The effects of volatiles from cowpea and peabush flowers and Maruca vitrata larvae on host selection behavior of the parasitoid Apanteles taragamae were investigated under laboratory conditions by using a Y-tube olfactometer. Naïve and oviposition-experienced female wasps were given a choice between several odor sources that included (1) uninfested, (2) Maruca vitrata-infested, and (3) mechanically damaged cowpea flowers, as well as (4) stem portions of peabush plants carrying leaves and flowers, (5) healthy M. vitrata larvae, and moribund (6), and live (7) virus-infected M. vitrata larvae. Responses of naïve and oviposition-experienced female wasps did not differ for any of the odor source combinations. Wasps were significantly attracted to floral volatiles produced by cowpea flowers that had been infested with M. vitrata larvae and from which the larvae had been removed. Apanteles taragamae females also were attracted to Maruca vitrata-infested flowers after removal of both the larvae and their feces. Female wasps discriminated between volatiles from previously infested flowers and mechanically damaged flowers. Uninfested cowpea flowers attracted only oviposition-experienced wasps that had received a rewarding experience (i.e. the parasitization of two M. vitrata larvae feeding on cowpea flowers) before the olfactometer test. Wasps also were attracted to uninfested leaves and flowers of peabush. Moreover, they were also attracted to healthy and live virus-infected M. vitrata larvae, but not when the latter were moribund. Our data show that, similarly to what has been extensively been reported for foliar volatiles, flowers of plants also emit parasitoid-attracting volatiles in response to being infested with an herbivore

Short Communication - Effects of Calyx Fluid from a Population of Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) on the Immune Response of Its Host Busseola fusca Fuller (Lepidoptera: Noctuidae)

Busseola fusca Fuller is one of the major lepidopteran stemborers of maize and sorghum in Africa. Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) is an indigenous, gregarious larval endoparasitoid that attacks mid- to late-instar stemborer larvae, which is reported to be one of the most important larval parasitoids of B. fusca in many countries in sub-Saharan Africa. Previous work has shown that two biotypes of C. sesamiae occur in Kenya which express differential abilities to develop in B. fusca. A biotype from western Kenya successfully develops in B. fusca, while a biotype from the eastern coastal area does not. We treated fourth-instars of B. fusca with calyx fluid from C. sesamiae from western Kenya (Kitale) before offering them to C. sesamiae from the Coast (Mombasa) for oviposition, and found that the eggs were not encapsulated. This suggests that factors in the calyx fluid of C. sesamiae from the western Kenya biotype were responsible for suppressing the immune system of B. fusca. We speculate that polydnaviruses in the calyx fluid were involved in disarming the host immune system, and that the polydnaviruses in the two biotypes are genetically different. RÉSUMÉ En Afrique, le lépidoptère Busseola fusca est l'un des foreurs les plus importants sur le maïs et le sorgho. Cotesia sesamiae (Cameron) (Hyménoptère: Braconidae) est un parasitoïde larvaire grégaire et interne qui attaque les larves des foreurs à partir du troisième stade. Il est considéré comme le parasitoïde indigène le plus important de B. fusca dans plusieurs pays d'Afrique sub-saharienne. Des études antérieures ont montré qu'il existe au Kenya deux biotypes de C. sesamiae ayant différentes capacités de développement dans B. fusca. Le biotype originaire de l'Ouest du Kenya se développe avec succès dans B. fusca, tandis que le biotype originaire de l'Est, sur la côte du Kenya, n'arrive pas á se développer dans B. fusca. Nous avons traité les larves du quatrième stade de B. fusca avec le fluide du calyx de C. sesamiae originaire de l'Ouest du Kenya (Kitale) et les avons offertes à C. sesamiae de la côte (Mombasa) pour ponte, nous avons observé que les oeufs pondus n'étaient pas encapsulés. Ce qui suggère que des facteurs dans le fluide du calyx de C. sesamiae de l'Ouest du Kenya étaient responsables de la suppression du système immunitaire de B. fusca. Nous pensons que des virus presents dans le fluide du calyx sont impliqués dans la suppression du système immunitaire de l'hôte et que les virus des deux biotypes sont probablement différents génétiquement