Does an Autoparasitoid Disrupt Host Suppression Provided by a Primary Parasitoid?

Theory predicts that intraguild consumers such as predators or parasitoids may displace more specialized heterospecific competitors and thereby actually increase the population densities of a shared host or prey. We tested this idea with a native primary parasitoid, Eretmocerus eremicus, and an exotic autoparasitoid Encarsia sophia, both attacking the sweetpotato whitefly Bemisia tabaci. Autoparasitoids are intraguild consumers that attack and kill both the immature stages of hemipteran hosts, such as whiteflies, and heterospecific and conspecific parasitoids. In population cages on cotton plants in the field in 1997 and 1998, we introduced whiteflies and then parasitoids in a replacement design with constant total numbers of parasitoids, as follows: (1) control (whiteflies only), (2) E. eremicus only, (3) E. sophia only, and (4) both E. eremicus and E. sophia. Destructive samples of plants were taken 2, 4, and 6 wk after wasp releases, and immature whitefly and wasp stages were censused. In 1997, there were no significant differences in whitefly densities among treatments. In 1998, the control treatment densities were significantly greater than parasitoid treatments, but there was no difference among the parasitoid treatments, indicating equivalent suppression of whitefly populations by the two parasitoid species. In both years, similar patterns in parasitoid dynamics were observed. Densities of E. eremicus were significantly higher in the absence of E. sophia. In contrast, E. sophia densities were unaffected by the presence of E. eremicus. The results suggest that interference by the autoparasitoid reduced primary parasitoid density, but with no concommitant disruption of host suppression. The results support theoretical predictions that no disruption should occur when both parasitoids are equally efficient and suggest that an autoparasitoid may be as efficient as a primary parasitoid in suppressing host densities.