Progeny fitness determines the performance of the parasitoid Therophilus javanus, a prospective biocontrol agent against the legume pod borer.

Therophilus javanus (Bhat & Gupta) is an exotic larval endoparasitoid newly imported from Asia into Africa as a classical biological control agent against the pod borer Maruca vitrata (Fabricius). The parasitoid preference for the five larval instars of M. vitrata and their influence on progeny sex ratio were assessed together with the impact of larval host age at the time of oviposition on development time, mother longevity and offspring production. In a choice situation, female parasitoids preferred to oviposit in the first three larval instars. The development of immature stages of the parasitoid was observed inside three-day-old hosts, whereby the first two larval instars of T. javanus completed their development as endoparasites and the third larval instar as ectoparasite. The development time was faster when first larval instars (two- and three-day-old) of the host caterpillars were parasitized compared to second larval instar (four-day-old). The highest proportion of daughters (0.51) was observed when females were provided with four-day-old hosts. The lowest intrinsic rate of increase (r) (0.21 ± 0.01), the lowest rate of increase (λ) (1.23 ± 0.01), and the lowest net reproductive rate (Ro) (35.93 ± 6.51) were recorded on four-day-old hosts. These results are discussed in the light of optimizing mass rearing and release strategies.

Volatiles from Maruca vitrata (Lepidoptera, Crambidae) host plants influence olfactory responses of the parasitoid Therophilus javanus (Hymenoptera, Braconidae, Agathidinae).

Plants damaged by herbivores are known to release odors attracting parasitoids. However, there is currently no information how leguminous plants damaged by the pod borer Maruca vitrata attract the exotic larval parasitoid Therophilus javanus, which was imported into Benin from the putative area of origin of the pod borer in tropical Asia for assessing its potential as a biological control agent. In this study, we used Y-tube olfactometer bioassays to investigate T. javanus response towards odors emitted by four M. vitrata-damaged host plants: cowpea Vigna unguiculata, the most important cultivated host, and the naturally occurring legumes Lonchocarpus sericeus, Sesbania rostrata and Tephrosia platycarpa. Olfactory attraction of T. javanus was influenced by the species of plant damaged by the pod borer. Moreover, odors released from M. vitrata-infested host plant organs (flowers and pods) were discriminated over non-infested organs in cowpea and T. platycarpa, respectively. These results are discussed in the context of the possible impact of M. vitrata host plants on T. javanus foraging activity and subsequent establishment in natural environments following experimental releases.