LAUSR

The parasitoid species Cotesia vestalis (Haliday) (Hymenoptera: Braconidae) is an important parasitoid, mass multiplied and used against the diamondback moth Plutella xylostella (Linneaus) (Lepidoptera: Plutellidae) worldwide. The present study was carried out to investigate the effect of host larval instars on parasitism and fitness to determine the most suitable host age for mass multiplication and augmentative releases of the parasitoid. Host age had a significant impact on the fitness of the parasitoid. Although C. vestalis was able to parasitize all stages of P. xylostella, it preferred the 2nd instar larvae. The biological and population growth parameters such as survival, fecundity, intrinsic rate of increase, finite rate of increase, mean generation length and weekly multiplication rate were higher when parasitism was on the 2nd instar larvae than the others. Therefore, the 2nd instar larvae are recommended for the mass production of high-quality individuals of the parasitoid.