Impact of Generalist Predators on a Biological Control Agent,chrysoperla Carnea: Direct Observations

Generalist predators in terrestrial arthropod communities have traditionally been viewed as predators whose dynamics are less tightly coupled to any particular prey species, but whose ecological roles are in other respects analogous to those of specialist predators. Biological-control theory for predator–prey interactions has been based upon a model of communities composed of three discrete trophic levels—plants, herbivores, and predators—in which biological control agents are top consumers and in which different species of predators interact only through competition for shared prey. Experiments employing single-plant field enclosures have suggested, however, that some generalist predators in the cotton agroecosystem function as higher-order predators, releasing populations of an herbivore, the cotton aphid Aphis gossypii, from control by another predator, the lacewing Chrysoperla carnea. Here we demonstrate through focal observations of neonate C. carnea foraging freely in the field that the high levels of mortality observed experimentally are not an artifact of cage confinement. Five generalist predators in the order Hemiptera were observed preying on neonate C. carnea. Neither cannibalism nor predation by heterospecific chrysopids was observed. The only other potential source of lacewing mortality observed was dislodgment from the plant, which occurred primarily on trichome-rich plant structures. A model of terrestrial arthropod communities incorporating higher-order predators may provide valuable insights into the regulation of herbivore populations and suggest useful avenues for biological-control research.