IMPACT OF GENERALIST PREDATORS ON A BIOLOGICAL CONTROL AGENT,CHRYSOPERLA CARNEA: DIRECT OBSERVATIONS

Abstract

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.

A brown-world cascade in the dung decomposer food web of an alpine meadow: effects of predator interactions and warming

“…This suggests intraguild predation, although we cannot exclude the possibility that the attack happened after the death of the small predators due to starvation. These findings are consistent with those of previous studies arguing that antagonistic interactions between predator species are more likely to happen when interspecific interference and/or intraguild predation are involved (Oksanen et al 1981, Rosenheim et al 1999, Finke and Denno 2004, Barton and Schmitz 2009.…”

Biotic interactions, ecological knowledge and agriculture

“…Numerous studies demonstrate increased abundance and diversity of natural enemy populations in hedgerows, for example, but few have identified the extent to which pests or natural enemies migrate from the hedgerows into adjacent fields, and even fewer have attempted to quantify the impacts on biological control (Letourneau 1998). Biological control may not be enhanced by hedgerows if the availability of pollen and nectar is so high within the hedgerows so that natural enemies do not disperse into adjacent agricultural fields to feed on crop pests (Bugg et al 1987); or if the hedgerow attracts new pests, non-pest prey that natural enemies prefer over the crop pest; or top predators that prey on the natural enemies of interest (Pollard 1971;Bugg & Pickett 1998;Rosenheim et al 1999;Nicholls et al 2001). Natural enemy dispersal ranges, which can vary from a few metres to over a kilometre for some parasitoid species (Corbett 1998), will determine the effectiveness of various habitat patterns at enhancing biological control.…”

Effects of mass releases of Trichogramma brassicae on predatory insects in maize

“…Both parasitoids and predators have been cited as a source of high mortality in C. carnea (Bay et al, 1993;Rosenheim et al, 1999). Alrouechdi et al (1981) studied the effect of parasitoids on chrysopid populations in olive plantations and found that the highest mortality rates were caused by larval and pupal parasitoids.…”