RELATIONSHIPS BETWEEN PARASITOID HOST-RANGE AND HOST-DEFENSE - A COMPARATIVE-STUDY OF EGG ENCAPSULATION IN 2 RELATED PARASITOID SPECIES

Parasitoid host range may proceed from traits affecting host suitabili ty, traits affecting parasitoid foraging behaviour, or both. We tested the hypothesis that encapsulation can be used as a reliable indicator of parasitoid host range in two closely related larval endoparasitoid s of Lepidoptera. Cotesia glomerata (L.) (Hymenoptera: Braconidae) is gregarious and a generalist on several species of Pieridae, whereas C. rubecula (Marshall) is solitary and specific to Pieris rapae (L.). We determined the effects of host species (Pieris brassicae (L.), P. nap i (L.) and P. rapae) (Lepidoptera: Pieridae) and host developmental st age (early first, second and third instar) on encapsulation of parasit oid eggs. Host species and parasitoid species, as well as the resultin g interaction between these two factors had significant effects on enc apsulation of Cotesia eggs. Encapsulation in Pieris hosts was much low er for C. glomerata (<34%, except for second and third instar of P. ra pae) than for C. rubecula (>32%), even when the latter was parasitizin g P. rapae. Encapsulation increased with the age of the larvae, althou gh the only significant difference was for C. glomerata. Overall, P. r apae showed a stronger encapsulation reaction than P. brassicae and P. napi. Encapsulation levels of C. glomerata corresponded well to patte rns of female host species and host age preference for oviposition and parasitoid larval performance. In contrast, percentages of encapsulat ion of C. rubecula were not consistent with host preference and host s uitability. We argue that encapsulation alone is unlikely to provide a sufficient explanation for C. glomerata and C. rubecula host range.