Interspecific Competition Between Cotesia vestalis (Halliday) and Diadegma semiclausum (Hellen), Parasitoids of Plutella xylostella (L.)

Abstract

Interspecific competition among parasitoids plays an important role in the population dynamics of parasitoids and their host insects and can affect the outcome of the biological control programme. The aim of the present study was to examine the intrinsic competition between Cotesia vestalis and Diadegma semiclausum, the two most common parasitoids of Plutella xylostella, to determine whether they can be used together compatibly against the pest. Both the parasitoid species were able to multiparasitize the host larvae already parasitized by the other species; however, most of the parasitoids emerged belonged to the species having priority for parasitism. The survival of the host larvae was low (52 ± 3.7%) when the host larvae were first parasitized by D. semiclausum and then followed after 24 h by C. vestalis, as compared to other combinations or individual parasitism, where these values varied from 76 to 80%. When second-instar larvae of the host were offered to females of both the parasitoids simultaneously in the same arena, C. vestalis proved to be a better competitor than D. Semiclausum as the proportion of the progeny developed was 63.2% for C. vestalis and 36.8% for D. semiclausum. Although C. vestalis and D. semiclausum were able to multiparasitize the host larvae, the level of multiparasitism was only 9.5 and 10.1%, indicating that both can be used together for the suppression of P. xylostella in the field.