Using molecular techniques to assess the effects of biodiversity on predation in agroecosystems
There remains some debate over whether increasing predator diversity promotes or detracts from biological control of a focal pest within agroecosystems. Practices that conserve generalist predators within agroecosystems often inherently increase the diversity of predators within a habitat. Although increased predator abundance and diversity likely inflicts greater mortality on a focal pests, this also likely increases intraguild interactions that could weaken potentially important trophic linkages within the pest-based food webs. The corn rootworm, Diabrotica virgifera virgifera, has recently been targeted in a conservation biological control program that involves implementing winter cover crops to aggregate predators within the corn agroecosystem (relative to leaving the soil bare during the fallow period). Predator abundance and diversity increased substantially in the cover-cropped system. We examined how predator diversity and conservation efforts affected the strength of trophic interactions between the target pest and its natural enemies using qPCR-based gut analysis of the predator community.
Increasing predator diversity and abundance led to a stronger trophic linkage to rootworm prey. This was particularly true for predators that were most affected by the rootworm's hemolymph defense. Based on our data, biocontrol within cropland is favored by biodiversity, and this is in large part because the predator community needs to be saturated in order to consume pests that are of low quality as prey. Agronomically feasible ways of increasing predator diversity can reduce the damage that this pest inflicts on the crop.