Movement of an insect parasitoid in simple and diverse plant assemblages

Abstract. 1. It has been proposed that herbivore populations are lower in diverse than in simple plant habitats because of greater abundance and/or higher efficiency of natural enemies in mixed plant stands. However, higher enemy colonization is expected in monorather than multispecific vegetation if the response of specialist natural enemies to habitat diversification 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 foveolatus in the absence of hosts. We then assessed how vegetation diversity affects wasp reproduction (parasitism) and subsequent density in the presence of its hosts, Mexican bean beetle larvae.
3. Fewer female wasps immigrated into and more emigrated out of a bean-tall maize intercrop than bean monocultures. Bean plant density and the presence of maize per se did not significantly affect parasitoid immigration. Instead, maize height was the primary factor contributing to lower female immigration into the bean-tall maize plots. However, tall maize plants did not impede the wasps' within-habitat movement.
4. When wasps were released outside the plots, higher parasitism was recorded in monocultures, irrespective of host density. In contrast, when wasps were released within the plots, significantly higher parasitism rates were found in the bean-tall maize habitat.
5. Results suggest that female wasps accumulate in the bean-tall maize habitat in response to resources other than hosts and, ultimately, wasp density may be determined primarily by differential emigration rather than by immigration rates.