An Insight in the Reproductive Biology of Therophilus javanus (Hymenoptera, Braconidae, and Agathidinae), a Potential Biological Control Agent against the Legume Pod Borer (Lepidoptera, Crambidae)

Abstract

Therophilus javanus is a koinobiont, solitary larval endoparasitoid currently being considered as a biological control agent against the pod borer Maruca vitrata, a devastating cowpea pest causing 20-80% crop losses in West Africa. We investigated ovary morphology and anatomy, oogenesis, potential fecundity, and egg load in T. javanus, as well as the effect of factors such as age of the female and parasitoid/host size at oviposition on egg load. The number of ovarioles was found to be variable and significantly influenced by the age/size of the M. vitrata caterpillar when parasitized. Egg load also was strongly influenced by both the instar of M. vitrata caterpillar at the moment of parasitism and wasp age. The practical implications of these findings for improving mass rearing of the parasitoid toward successful biological control of M. vitrata are discussed.

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

“…On the other hand, some endoparasitoids can ensure the development of their progeny through maternal factors such as the venom fluid injected in the host at the time of parasitism 26 . Previous work has highlighted the presence of a venom gland attached to the reproductive tract of T. javanus females 4 and hypothesized that the venom fluid might be secreted in the host during parasitism 27 . Although the venom function has not been elucidated in more detail to date, we speculate it could regulate metabolic processes in parasitized M. vitrata caterpillars in order to affect its development and hence ensure complete development of the parasitoid larva 28 .…”

“…It was shown that parasitizing early host stages can reduce the development time in koinobionts parasitoids 16 ; however, adult fitness of the offspring may be affected, in terms of short life expectancy, small size eggs, and reduced oviposition period 30 . Moreover, it has already been assessed that the development in early M. vitrata larval instars reduced the offspring potential fecundity in T. javanus 4 . Our observations further show that the sex-ratio of the offspring population was male-biased when stemming from three-day-old hosts, while the parasitoid produced more females when the oviposition occurred in four-day-old M. vitrata hosts.…”

“…In the case of a parasitoid, this knowledge is a prerequisite prior to its introduction in a novel environment as a biological control agent 3 . Already, the biological potential of this newly introduced natural enemy has been investigated with regard to reproductive biology 4 and the ability of this natural enemy to localize a plant-feeding M. vitrata caterpillar 5 . However, life traits estimation could provide additional and critical information on quantitative and ecological function of natural enemies 6 , and population growth can be estimated by assessing fertility life table parameters 7 .…”

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

“…Insect colonies were reared at the laboratories of the International Institute of Tropical Agriculture Benin (IITA-Benin) near Cotonou, Benin (12:12 L:D photoperiod; 26 °C ± 1.1 °C average temperature; 76% ± 7% relative humidity), with the methodology described in detail by Aboubakar Souna et al (2017) , and briefly summarized below.…”

“…Parallel studies investigating the reproductive potential of T. javanus have evidenced its considerable fecundity and suitability for mass rearing ( Aboubakar Souna et al, 2017 ). However, long-term reduction of M. vitrata populations depends mainly on how efficiently foraging T. javanus females will be able to detect and parasitize M. vitrata caterpillars throughout the cropping season and particularly during the offseason on alternative host plants.…”