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

Masked chafer grubs, Cyclocephala spp. (Coleoptera: Scarabaeidae), are one of the important pests of turfgrass in Virginia. Insecticides provide effective control of grubs, however, most of the insecticides available are only effective against early instars.  Entomopathogenic fungi are labeled for white grub control in turf but are not very effective when applied alone. This study was conducted to determine the efficacy and interactions of combined applications of an insecticide (chlorantraniliprole) and two species of entomopathogenic fungi, Metarhizium anisopliae and Beauveria bassiana, against third instar masked chafer. Treatments included two rates of the insecticide (one quarter and one half of the recommended rate), the full recommended rates of the both fungi species, and each combination of insecticide plus fungi. Mortality was determined four weeks after treatment. The result of this study showed that the combined application of one half the recommended rate of the insecticide 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 efficacies and interactions of combined applications of the insecticide and entomopathogenic fungi are discussed.