Suitability of cowpea sprouts to optimize rearing of biocontrol agents Phanerotoma syleptae and Liragathis javana

Abstract

Abstract The legume pod borer Maruca vitrata is a key insect pest of cowpea, Vigna unguiculata Walp. The present study was designed to optimize the efficiency of mass rearing two of its biological control agents, the larval parasitoid Liragathis javana and ovo-larval parasitoid Phanerotoma syleptae, by comparing their performance on M. vitrata hosts reared on sprouting grains of 10 different varieties of cowpea as feeding substrate. Thus, 25 M. vitrata larvae of 24 hours old, 25 M. vitrata eggs of 24 hours parasitized by P. syleptae and 25 larvae of 48 hours parasitized by L. javana were reared on sprouts of 10 cowpea varieties in laboratory at a relative humidity of 70–80% and a temperature ranging from 25 to 26°C till pupae stage. Fecundity of M. vitrata and the two parasitoids were assessed per variety. Experiments were replicated 3 times. Results revealed significant difference between varieties for the development of unparasitzed larvae of M. vitrata and L. javana or P. syleptae-parasitized larvae. The cumulative daily fecundity shows different patterns: higher in IT 84D-449 for M. vitrata and L. javana but higher in Kpodji for P. sylepatae. Mortality of parasitized (by L. javana and P. syleptae) larvae and unparasitized (M. vitrata larvae) was lower in Kpodji variety. No significant differences were observed between male and female proportions (sex-ratio), regardless of insect species and cowpea variety except the varieties Tawa and Vitoco in L. javana. Data were discussed with regard to the optimization of mass rearing of the three insect species for the biological control against M. vitrata using L. javana and P. syleptae.