EFFECTS OF EXPERIENCE ON PARASITOID MOVEMENT IN ODOR PLUMES

Insects commonly improve the effectiveness with which they locate biot ic resources through learning, but the mechanism by which experience e xerts its effects has rarely been studied in detail. The effect of ovi position experience on upwind movement of the eucoilid parasitoid, Lep topilina heterotoma (Thomson) (Hym.: Eucoilidae), in odour plumes of h ost microhabitats, was quantified with the use of a Kramer-type locomo tion compensator. A 2 h exposure to host Drosophila melanogaster larva e in either fermenting apple-yeast or decaying mushroom substrate (kno wn to affect their preference for these odours in glasshouse and field choice experiments) had a number of effects on movement in plumes of each substrate. Females experienced with a particular substrate walked faster and straighter, made narrower turns and spent more time in upw ind movement (i.e. toward the source) in a plume of odour from that su bstrate than in odour from an alternative substrate. Inexperienced fem ales, by contrast, generally showed little or no significant differenc e in responses to alternative odours. In addition to affecting the mea n values of movement parameters, experience also affected variability around those means. When walking speed or path straightness in an odou r plume was increased by experience, variability among individuals was correspondingly decreased. The consequences of odour learning for mic rohabitat choice is discussed briefly.