Impact of four insecticides on Japanese beetle (Coleoptera: Scarabaeidae) egg predators and white grubs in turfgrass.

Field experiments were conducted to measure the effects of four commonly used turfgrass insecticides (isofenphos, diazinon, imidacloprid, halofenozide) on white grubs (Coleoptera: Scarabaeidae) and ant predators of white grub eggs. Ant populations were measured over time with canned tuna, whereas predation by the ants was measured with artificially placed Japanese beetle, Popillia japonica Newman, eggs. The effectiveness of each insecticide at controlling Japanese beetle grubs, when applied at different times during the growing season, also was measured. Isofenphos and diazinon significantly reduced both ant numbers and white grub egg predation, whereas imidacloprid and one halofenozide treatment did not significantly impact either measurement. A second halofenozide treatment significantly reduced white grub egg predation. Isofenphos and diazinon were ineffective at controlling Japanese beetle grubs when applied in June but were highly efficacious when applied in August. Evidence of enhanced biodegradation was found in plots that received both June and August applications of diazinon. Both June and August applications of imidacloprid and halofenozide provided good control of white grubs.