FIELD EVIDENCE THAT HOST SELECTION BY CONOPID PARASITOIDS IS RELATED TO HOST BODY-SIZE

The body size of the host insect In which a parasitoid develops can ha ve important effects on its development and life history. Large and sm all host body size have both been suggested to be advantageous to para sitoids, depending on the life-history of the species concerned. We te st field data on the bumblebee Bombus terrestris and its conopid paras itoids for evidence of differences in size between parasitised and unp arasitised worker bees. Bees acting as hosts for conopid parasitoids a re on average larger-bodied than unparasitised bees. This result holds for bees collected in two different years, and whether bees are colle cted while foraging or from the nest. The results we present demonstra te differential parasitism of hosts of different body sizes, but do no t necessarily indicate active host choice by conopids. However, they a re in agreement with independent evidence that conopids develop more s uccessfully in large- than in small-bodied hosts.