FORAGING FOR SOLITARILY AND GREGARIOUSLY FEEDING CATERPILLARS - A COMPARISON OF 2 RELATED PARASITOID SPECIES (HYMENOPTERA, BRACONIDAE)

In the present study we apply a comparative approach, in combination w ith experimentation, to study behavior of two parasitoid species that attack caterpillar hosts with different feeding strategies (gregarious or solitary). In a semifield setup, consisting of clean cabbage plant s and plants infested with one of two host species, the foraging behav ior of the specialist Cotesia rubecula, an obligate parasitoid of soli tarily feeding Pieris rapae larvae, was compared to that of the genera list Cotesia glomerata, a polyphagous parasitoid of several Pieridae s pecies (mainly the gregariously feeding Pieris brassicae). Cotesia glo merata displayed equal propensity to search for and parasitize larvae of both host species. Although C. glomerata exhibited a relatively pla stic foraging behavior in that it searched differently under different host distribution conditions, its behavior seems more adapted to sear ch for gregariously feeding hosts. Females exhibited a clear ''area-re stricted'' search pattern and were more successful in finding the greg ariously feeding caterpillars. Cotesia rubecula showed a higher propen sity to search for P. rapae than for P. brassicae, i.e., females left the foraging setup significantly earlier when their natural host P. ra pae was not present. C. rubecula showed a more fixed foraging behavior , which seems adapted to foraging for solitarily feeding host larvae. In a setup with only P. rapae larvae, the foraging strategies of the t wo parasitoid species were quite similar. In a choice situation C. glo merata did not show a preference for one of the host species, while Co tesia rubecula showed a clear preference for its natural host species. The latter was shown by several behavioral parameters such as the num ber of first landings, allocation of search time, and percentage paras itization.