Encounters With Parasitized Hosts: To Leave or Not To Leave a Patch

Abstract

Several factors determine the amount of foraging time which the parasitoid Leptopilina heterotoma will spend on a patch with hosts, like the composition of the host medium, the age and size of the host patch, the number of searching conspecifics, and the number and quality of host larvae. How encounters with already parasitized hosts influence foraging time is the topic of this paper. When parasitized hosts are stung early during a visit to a patch, an increase in foraging time is the result compared with visit times on patches without hosts. Frequent contacts with parasitized hosts, however, lead to a decrease of foraging time. When a host patch is being exploited by L. heterotoma the ratio of parasitized hosts to unparasitized hosts increases. In such a situation, with a low density of unparasitized and a high density of parasitized hosts, visit times were shorter than on patches with only a low density of unparasitized hosts. The difference in searching time could not be attributed to the parasitoid measuring an increase in interval time between contacts with unparasitized hosts in the situation where a combination of parasitized and unparasitized hosts was offered: interval times were the same whether parasitized hosts were present or absent. The shorter visit times on patches with a combination of parasitized and unparasitized hosts could neither be attributed to a difference in the structure of the patch nor to differences in kairomone composition. It is the contacts with parasitized hosts which causes a shortening of the searching time on patches where a large proportion of the hosts is parasitized.