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

Abstract

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 fve larval instars of M. vitrata and their infuence 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 ofspring production. In a choice situation, female parasitoids preferred to oviposit in the frst three larval instars. The development of immature stages of the parasitoid was observed inside three-day-old hosts, whereby the frst two larval instars of T. javanus completed their development as endoparasites and the third larval instar as ectoparasite. The development time was faster when frst 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.