MOVEMENT OF AN INSECT PARASITOID IN SIMPLE AND DIVERSE PLANT ASSEMBLAGES

1. It has been proposed that herbivore populations are lower in divers e than in simple plant habitats because of greater abundance and/or hi gher efficiency of natural enemies in mixed plant stands. However, hig her enemy colonization is expected in mono-rather than multispecific v egetation if the response of specialist natural enemies to habitat div ersification is similar to that of monophagous herbivores. 2. We used release-recapture experiments to determine how the presence of maize ( non-host plant) influences the movement of the parasitoid Pediobius fo veolatus in the absence of hosts. We then assessed how vegetation dive rsity affects wasp reproduction (parasitism) and subsequent density in the presence of its hosts, Mexican bean beetle larvae. 3. Fewer femal e wasps immigrated into and more emigrated out of a bean-tall maize in tercrop than bean monocultures. Bean plant density and the presence of maize per se did not significantly affect parasitoid immigration. Ins tead, maize height was the primary factor contributing to lower female immigration into the bean-tall maize plots. However, tall maize plant s did not impede the wasps' within-habitat movement. 4. When wasps wer e released outside the plots, higher parasitism was recorded in monocu ltures, irrespective of host density. In contrast, when wasps were rel eased within the plots, significantly higher parasitism rates were fou nd in the bean-tall maize habitat. 5. Results suggest that female wasp s accumulate in the bean-tall maize habitat in response to resources o ther than hosts and, ultimately, wasp density may be determined primar ily by differential emigration rather than by immigration rates.