Sex Ratios, Development, and Parasitization Behavior of the Parasitoids Cotesia rubecula and Cotesia glomera/a (Hymenoptera: Braconidae)

Abstract

Cotesia rubecula and Cotesia glomerata are braconid parasitoids. Females of both of these wasps oviposit in first or second instar Pieris rapae larvae, and the wasp larvae develop and feed on the host internally. C. rubecula is solitary and females oviposit one to two eggs in a host. C. glomerata is gregarious, with females ovipositing 16-52 eggs. Roughly seven to ten days after oviposition, late instar Cotesia larvae emerge from the host caterpillar, spin cocoons and continue development, emerging as adults five to ten days later. Most Hymenoptera have a haplodiploid genetic system. Unfertilized eggs develop as haploid males and fertilized eggs develop as diploid females. Gregarious species such as C. glomerata typically have a high frequency of inbreeding. Matings between genetically similar individuals may occur, resulting in production of diploid males. These males are either unable to develop properly or are sterile. In species with a single gene locus for sex determination successive inbreeding would produce many diploid males. The use of multiple loci for sex determination may have evolved in species which habitually inbreed, circumventing this diploid male problem. Due to mortality among Cotesia wasps and high frequency of all-male broods, insufficient data were collected to draw conclusions about sex determination in these parasitoids. C. rubecula and C. glomerata were found to have similar timeframes for development from oviposition to adulthood, but differed in the amount of time spent as larvae and pupae. At the field site, 26.1 % of P. rapae collected had been parasitized by C. rubecula, 29.1 % died in the laboratory and may have been parasitized, while 44.9% of P. rapae larvae pupated normally.