EFFECTS OF BELOWGROUND PREDATOR WEED INTERACTIONS ON DAMAGE TO PEANUT BY SOUTHERN CORN-ROOTWORM (COLEOPTERA, CHRYSOMELIDAE)

The below-ground effects of weeds (Amaranthus retroflexus L., Chenopodium album L., Ambrosia artemisiifolia L., Digitaria sanguinalis L., Setaria viridis L., Panicum dichotomiflorum Michx.) and increased soil moisture on damage to peanut pods by southern corn rootworm, Diabrotica undecimpunctata howardi Barber, was investigated in a 2-yr field and greenhouse study. Field experiments demonstrated that weedy areas had less pod damage overall and higher predator numbers than nonweedy areas. However, increased soil moisture, which increased southern corn rootworm oviposition and egg and larval survival, confounded the results. Greenhouse studies showed that three broadleaf species and three grass species were not as good food sources as peanuts for southern corn rootworm larvae. Although the presence of weeds growing with peanuts did not lower larval survival, weeds did significantly (P ≤ 0.05) slow larval developmental rate. In greenhouse studies, damage to peanut pods was approximately 66% in peanut-only (control) treatments, 55% in peanut + weed treatments, 32%in peanut predator treatments, and 9%in peanut + weed + predator treatments. The interaction of predators and weeds in lowering the amount of damage caused by southern corn rootworm was significant (P ≤ 0.05). Field and greenhouse experiments demonstrated that at least two factors were operating to reduce pest damage in this belowground, multispecies plant association. Predators and the structural complexity of the weed-crop root association may be working synergistically to reduce southern corn rootworm damage to peanuts. © 1990 Entomological Society of America.