Use of odors for in-flight orientation to the host and for host recognition by the parasitoid Brachymeria intermedia (Hymenoptera: Chalcididae)
Brachymeria intermedia is a primary parasitoid of pupae of the gypsy moth, Lymantria dispar (Lepidoptera: Lymantriidae). Previous studies established how females determine the acceptability of potential hosts through contact with their cuticular kairomones. This work investigates how olfactory cues initially may lead females to their hosts.
Inexperienced females were less likely to walk toward the host than females with oviposition experience; however, a single antennal contact with the host was sufficient to increase the probability of walking to the host suggesting that females learned the odor of their host on the first encounter (Chapter 1). Olfactory conditioning was then demonstrated using a novel odor (Chapter 2). Through a single oviposition experience on their natural host in presence of vanilla odor, wasps were induced to drum and drill in a vanilla-scented paper roll. Although some wasps were conditioned when exposure to odor coincided with pre-oviposition drumming on the host, conditioning was most successful when odor exposure coincided with oviposition. Evidently, conditioning occurred through the formation of an association between the odor and the 'aroused' state underlying host acceptance. Results support the hypothesis that conditioning occurs through a stimulus-arousal association rather than, as is generally assumed, through a stimulus-stimulus association.
Wasps were also conditioned to fly toward a source of vanilla odor in a wind tunnel (Chapter 3). Then, upon approaching vanilla-scented paper rolls hung on a vertical cylinder, conditioned wasps landed on them readily, whereas few wasps landed on real pupae. However, more wasps reached pupae or pupal cases than white scented paper rolls. Thus, visual and olfactory cues appeared to mediate the foraging behavior of wasps in conflicting ways. Conditioned wasps flying upwind, along a plume of vanilla odor flew shallow zigzag tracks (Chapter 4). Contrary to male moths flying to sex pheromone, wasps flew similar zigzag tracks along ribbon and turbulent plumes of vanilla odor. When the plume was removed while wasps were flying upwind, wasps either maintained an upwind course, or drifted sideways, flying alternately upwind and downwind before turning around and flying downwind. No wasp casted upon plume loss, as is typical of male moths.
Anatomy & physiology;
0433: Anatomy & physiology