PIERIDAE-; AGGREGATING-BEHAVIOUR; Hymenopteran parasitoid foraging behaviour, relationship; HYMENOPTERAN-PARASITES; Cotesia glomerata & C. rubecula; Parasitoid foraging behaviour, solitarily vs gregariously feeding hosts Cotesia glomerata; Cotesia rubecula; FORAGING-; Searching for solitary vs gregarious lepidopteran hosts; LEPIDOPTERAN-HOSTS; Pieridae; Foraging for solitarily vs gregariously feeding hosts, comparative study In the present study we apply a comparative approach, in combination with 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 plants and plants infested with one of two host species, the foraging behavior of the specialist Cotesia rubecula, an obligate parasitoid of solitarily feeding Pieris rapae larvae, was compared to that of the generalist Cotesia glomerata, a polyphagous parasitoid of several Pieridae species (mainly the gregariously feeding Pieris brassicae). Cotesia glomerata displayed equal propensity to search for and parasitize larvae of both host species. Although C. glomerata exhibited a relatively plastic foraging behavior in that it searched differently under different host distribution conditions, its behavior seems more adapted to search for gregariously feeding hosts. Females exhibited a clear "area-restricted" search pattern and were more successful in finding the gregariously feeding caterpillars. Cotesia rubecula showed a higher propensity to search for P. rapae than for P. brassicae, i. e., females left the foraging setup significantly earlier when their natural host P. rapae 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 two parasitoid species were quite similar. In a choice situation C. glomerata did not show a preference for one of the host species, while Cotesia rubecula showed a clear preference for its natural host species. The latter was shown by several behavioral parameters such as the number of first landings, allocation of search time, and percentage parasitization. none