Mass Rearing Optimization of Cotesia vestalis (Hymenoptera: Braconidae) Based on the Host and Parasitoid Densities

The present study aimed to explore some simple ways to optimize the mass rearing of Cotesia vestalis (Haliday) (Hymenoptera: Braconidae), one of the most important biocontrol agents of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae). The effects of host and parasitoid initial densities on the quantity and quality of produced wasps were investigated. In particular, a factorial experiment was established using three different host densities (20, 50, and 100 P. xylostella larvae per cage) in presence of C. vestalis at three different densities (2, 5, and 7 females, with a 24-h exposure) in well-ventilated cages. There was a significant effect of wasp's initial density on the percentage parasitism (measured based on the cocoon and emerged adult wasps); comparatively the greatest percentage parasitism was obtained with five wasps per cage. Initial host density had no significant effects on the percentage parasitism, sex ratio, and larval period, but it influenced the survival rate (measured based on the cocoon and adult emerged) and pupal period of produced wasps, and also percentage host mortality. The density of 20 host larvae was the best in this regard. These findings were discussed in the contexts of optimum mass rearing, life history, and potential of C. vestalis as a biological control agent.