none Helicoverpa (Heliothis) zea; HYMENOPTERAN-PARASITES; Microplitis croceipes; Parasite searching behaviour Microplitis croceipes; BREEDING-SITE; Searching time, marking & spatial memory role; EXPERIENCE-; Visual cues, effect on breeding site selection; MEMORY-; Chemical & visual cues, breeding site selection relations; SCENT-MARKING; Breeding site discrimination relations; LEPIDOPTERAN-HOSTS; Helicoverpa (Heliothis) zea; Searching for host, memory of chemical & visual cues. The ability of free-ranging parasitoids to discriminate between previously visited and unvisited sites containing host kairomone (caterpillar frass) but not hosts was tested. Females of Microplitis croceipes, a host specialist and plant generalist larval parasitoid of Helicoverpa (Heliothis) zea, were allowed to fly freely in a simulated plant patch in a flight chamber. Wasps spent less time searching frass sites previously searched by themselves or by conspecifics than unsearched frass sites. In addition to chemical marking, spatial memory of visual cues was implicated as a mechanism for discriminating against self-visited, host-free sites.