Veronica Yurchak, Vegetable Specialist, UMD; vjohnso4@umd.edu
The goal of this series is to increase awareness and knowledge of beneficial insects in cropping systems and to help differentiate them from pests of concern. This week’s feature beneficial is the feather-legged fly, Trichopoda pennipes (Figure 1). Overwintering as a larva inside the body of the overwintering bug, this relatively small fly will emerge soon and begin laying eggs on the body surface of some of our more troublesome true bug vegetable pests, including stink bugs and squash bugs (Figure 2). In time, these eggs will hatch, and the emerging larvae will bore into the insect and develop inside, feeding on the internal tissues of their host. During the final larval development stage, the parasitoid will tunnel its way out of the insect and pupate in the soil below. After about two weeks, a new generation of adults will emerge to further parasitize more true bug insects. Each female fly can lay several hundred eggs, and there are likely between two and three generations per year in Maryland.
Figure 1. Adult feather-legged fly feeding on goldenrod.
Figure 2. Image shows the whitish egg of a feather-legged fly on the back of a southern green stink bug.
Feather legged flies are relatively small, about the size of a house fly, and can be seen hovering above squash plants and other vegetables in search of prey. Adults can also be found feeding on the nectar of nearby flowers. These flies have a bright orange abdomen, large eyes characteristic of many flies, and a fringe of short black hairs on their hind legs. They locate prey by detecting the aggregation pheromones (signal chemicals) produced by many true bugs, usually for the purposes of mating or defense. Some studies have determined that parasitism of squash bugs can be as high as 80%, however, parasitized host insects can continue to feed and lay eggs for days while the parasitoid is developing inside. Thus, this parasitoid alone is typically not enough to prevent economic crop damage when pest pressure is high. However, agricultural habitats with abundant flowers for adult feeding can support a diverse community of natural enemies that together can maintain lower pest densities and delay the need for additional pest control measures.