Impact of generalist predators on a biological control agent, Chrysoperla carnea: Direct observations

Generalist predators in terrestrial arthropod communities have traditionall y been viewed as predators whose dynamics are less tightly coupled to any p articular prey species, but whose ecological roles are in other respects an alogous to those of specialist predators. Biological-control theory for pre dator-prey interactions has been based upon a model of communities composed of three discrete trophic levels-plants, herbivores, and predators-in whic h biological control agents are top consumers and in which different specie s of predators interact only through competition for shared prey. Experimen ts employing single-plant held enclosures have suggested, however, that som e generalist predators in the cotton agroecosystem function as higher-order predators, releasing populations of an herbivore, the cotton aphid Aphis g ossypii, from control by another predator, the lacewing Chrysoperla carnea. Here we demonstrate through focal observations of neonate C. carnea foragi ng freely in the field that the high levels of mortality observed experimen tally are not an artifact of cage confinement. Five,generalist predators in the order Hemiptera were observed preying on neonate C, carnea. Neither ca nnibalism 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 m odel of terrestrial arthropod communities incorporating higher-order predat ors may provide valuable insights into the regulation of herbivore populati ons and suggest useful avenues for biological-control research.