Several studies suggest that red imported fire ants (Solenopsis invicta) are important biological control agents in a variety of crop and orchard systems. These studies however, also suggest that fire ants can be serious intraguild predators and potentially disrupt biological control. Fire ants are known to decrease ladybeetle and green lacewing numbers, and interfere with parasitic wasps. Increasing habitat complexity with mixed cropping systems may reduce intraguild predation and allow other beneficial organisms to coexist with fire ants. This study compared the effects of fire ants on herbivore and natural enemy populations in a complex, collard intercrop and a simple, collard monocrop. We focused our study on the Diamondback moth (DBM), Plutella xylostella, the most economically important pest of collards. Parasitism of DBM larvae was high and did not differ among cropping systems. Fire ants were intraguild predators of DBM parasitoids because they attacked DBM larvae, but fire ants preferentially attacked unparasitized larvae in field experiments. Herbivore populations were lower in the intercrop due to greater predation by fire ants and other natural enemies. Overall, fire ants were negatively correlated with other natural enemies in the monocrop and positively correlated in the intercrop, suggesting that habitat complexity mediates the intensity of intraguild predation by fire ants.
Species 1: Hymenoptera Formicidae Solenopsis invicta (red imported fire ant, fire ant)
Species 2: Lepidoptera Plutellidae Plutella xylostella (Diamondback moth)
Keywords: intraguild predation, biological control
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