Plant trichomes indirectly enhance tritrophic interactions involving a generalist predator, the red imported fire ant

Abstract

Morphological defense traits of plants such as trichomes potentially compromise biological control in agroecosystems because they may hinder predation by natural enemies. To investigate whether plant trichomes hinder red imported Wre ants, Solenopsis invicta Buren (Hymenoptera: Formicidae), as biological control agents in soybean, Weld and greenhouse experiments were conducted in which we manipulated Wre ant density in plots of three soybean isolines varying in trichome density. Resulting treatment eVects on the abundance of herbivores, other natural enemies, plant herbivory, and yield were assessed. Trichomes did not inhibit Wre ants from foraging on plants in the Weld or in the greenhouse, and Wre ant predation of herbivores in the Weld was actually greater on pubescent plants relative to glabrous plants. Consequently, Wre ants more strongly reduced plant damage by herbivores on pubescent plants. This eVect, however, did not translate into greater yield from pubescent plants at high Wre ant densities. Intraguild predation by Wre ants, in contrast, was weak, inconsistent, and did not vary with trichome density. Rather than hindering Wre ant predation, therefore, soybean trichomes instead increased Wre ant predation of herbivores resulting in enhanced tritrophic eVects of Wre ants on pubescent plants. This eVect was likely the result of a functional response by Wre ants to the greater abundance of caterpillar prey on pubescent plants. Given the ubiquity of lepidopteran herbivores and the functional response to prey shown by many generalist arthropod predators, a positive indirect eVect of trichomes on predation by natural enemies might be more far more common than is currently appreciated.