Intraguild predation of parasitoids by Solenopsis invicta: a nondisruptive interaction
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The outcome of intraguild predation among natural enemies can have significant ramifications for herbivore suppression and biological control. Manipulating habitat complexity may alter the strength of intraguild predation, since changes in habitat complexity are often associated with concomitant changes in natural enemy abundance. Using a combination of greenhouse and field experiments, we determined if asymmetric intraguild predation by a pervasive generalist predator, the red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), disrupts important parasitoids in a collard, Brassica oleracea L. (Brassicaceae), agroecosystem. The effect of habitat complexity on this interaction was assessed by conducting field experiments in a simple, collard monocrop and a more complex, collard-white clover intercrop. Neither the density of adult parasitoids nor the percentage parasitism of caterpillars was affected when S. invicta abundance was manipulated. Solenopsis invicta reduced the survival of the diamondback moth larvae, Plutella xylostella (L.) (Lepidoptera: Plutellidae) by 26% and 42% in greenhouse and field experiments, respectively, but there was no preference of S. invicta for parasitized or unparasitized caterpillars. An increase in habitat complexity significantly affected the abundance of both S. invicta and parasitoids, but had no overall effect on their interaction. The results of this study suggest that although S. invicta is an intraguild predator of parasitoids because it preys upon parasitized caterpillars, the action of S. invicta may not compromise overall biological control. This study's findings are important, because they suggest that the presence and conservation of multiple natural enemies may result in sustained pest suppression in agroecosystems, even complex systems containing many species of natural enemies including strong intraguild predators such as S. invicta.
