Importance of Adult Food Sources to Host Searching of the Larval Parasitoid Microplitis croceipes

We conducted field experiments to determine the effects of food availability and parasitoid hunger on the searching behavior of Microplitis croceipes (Cresson) (Braconidae; Hymenoptera) in small corn and soybean plots. In both corn and soybean plots where food was not available, females which were well-fed prior to release parasitized more hosts than unfed females. Well-fed females spent more time hovering and less time searching undamaged leaves than did unfed females. Because hovering time is an indicator of active host searching, the better parasitization rate by well-fed females can be explained by the greater proportion of time spent in active host searching. These results suggest that the lack or shortage of food sources in the field reduces the parasitoid′s effectiveness. We also found that in a corn plot without food, unfed females more often superparasitized hosts than did well-fed females. However, when food (honey) was provided in a plot, most unfed females found and fed on honey soon after release. After feeding, they quickly began a hovering search, primarily around damaged plants, apparently in search of host larvae. More time was spent hovering by unfed females than by well-fed females in a corn plot with food. In the case of a soybean plot with food, unfed females parasitized more hosts than did well-fed females. These behaviors suggest that feeding experience of females in the field may facilitate their host searching around plants with food. On the basis of these findings, we suggest that it is possible to manipulate the parasitoids′ hunger state as a tool for parasitoid release programs.