OVERWINTERING MICROHABITAT SELECTION BY AN ENDOPARASITOID (HYMENOPTERA, APHIDIIDAE) - INDUCED PHOTOTACTIC AND THIGMOKINETIC RESPONSES IN DYING HOSTS

Aphidius nigripes Ashmead, an endoparasitoid of the potato aphid, Macrosiphum euphorbiae (Thomas), not only has the ability to modify host behavior, but does so differently depending on its physiological state. A previous study indicated that just prior to death, parasitized aphids that contain diapausing parasitoid larvae leave the host plant to mummify in concealed sites, while those containing nondiapausing parasitoids generally remain on the plant. This study explored the proximal factors involved in the selection of an overwintering microhabitat by a host containing a diapausing A. nigripes larva. Parasitized aphids showed negative phototaxis, thigmokinesis, and chose a dark rather than a light-colored substrate when seeking a site to mummify. However, their behavior was not influenced by either gravity or the presence of another mummy. The combined effects of these behavioral patterns would result in dormant parasitoids overwintering in sheltered sites, thereby reducing the negative effects of adverse climatic conditions and the actions of natural enemies. The utilization of these proximal cues may also enhance parasitoid, survival by reducing aphid wandering time prior to mummification. © 1990 Plenum Publishing Corporation.