Phthorimaea operculella; FOOD-PLANTS; Potato; Plant role in location by hymenopteran parasite, chemical cues; CHEMICAL-SIGNALS; Kairomones, role in location by hymenopteran parasites; HYMENOPTERAN-PARASITES; Orgilus lepidus; Location in food plant by parasite, sources of cues Orgilus lepidus; CHEMORECEPTION-; Plant odour role in lepidopteran host location; CHEMICAL-SIGNALS; Lepidopteran host kairomones, role in host location; LEPIDOPTERAN-HOSTS; Phthorimaea operculella; Host location in food plant, sources of cues. The responses of the parasitic wasp Orgilus lepidus to potato plants infested by its host Phthorimaea operculella were investigated. Wasps flew to both undamaged and mechanically damaged potatoes when they were presented alone in a flight tunnel, indicating that the odour of potato alone is attractive to them. When given a choice, females flew preferentially to either mechanically damaged plants or to plants infested by P. operculella rather than to intact plants. Thus, when O. lepidus is searching for hosts, it first flies toward the odour of plants, especially those that are damaged. There was no difference in the behaviour of wasps on either undamaged or mechanically damaged potato levels, but they spent considerably more time probing with their ovipositor on leaves infested by their host. Wasps responded similarly to leaves infested with hosts and leaves from which hosts were removed, indicating that plant damage caused by their host or host products are the primary cues used to discriminate different kinds of damage. none