Efficacy of combined applications of insecticides and entomopathogenic fungi for masked chafer grub, Cyclocephala spp. (Coleoptera: Scarabaeidae), control in turfgrass

The combined application of insecticide and entomopathogen could be a better management option for pestiferous insects if the combined treatments are more efficacious than the sum of single treatments.  In Virginia, laboratory experiments were carried out to determine the efficacy and interactions of combined applications of two insecticides, imidacloprid and chlorantraniliprole, and two species of entomopathogenic fungi, Metarhizium anisopliae and Beauveria bassiana, against masked chafer grubs, Cyclocephala spp. (Coleoptera: Scarabaeidae), which are one of the important pests of turfgrass in Virginia.  Mature third instar grubs are difficult to control using currently available insecticides or entomopathogenic fungi labeled for white grub control in turf when applied alone. Experiments were conducted on both non-overwintered and overwintered third instar masked chafer grubs. Treatments included two rates of the insecticides (one quarter and one half of the recommended rate), the full recommended rates of both fungi species, and each combination of insecticide plus fungi.  Mortality was determined four weeks after treatment. Results showed that, for non-overwintered grubs, the combined application of one half the recommended rate of chlorantraniliprole plus the full recommended rate of the fungus B. bassiana caused the highest (55%) grub mortality four weeks after treatment. However, the single and combined applications did not vary significantly. The efficacy and interactions of combined applications of insecticides and entomopathogenic fungi are discussed.