Effect of the anthranilic diamide insecticide, chlorantraniliprole, on Heterorhabditis bacteriophora (Rhabditida: Heterorhabditidae) efficacy against white grubs (Coleoptera: Scarabaeidae)

Combinations of the anthranilic diamide, chlorantraniliprole, and the entomopathogenic nematode Heterorhabditis bacteriophora were tested for control of third-instar white grubs in turfgrass. In greenhouse experiments, the combinations had a synergistic or additive effect on the oriental beetle, Anomala (=Exomala) orientalis mortality, whether chlorantraniliprole was applied 1 week before H. bacteriophora or simultaneously. Combinations caused mortality to occur more rapidly than for the single agents. H. bacteriophora-chlorantraniliprole combinations had a synergistic effect on mortality of Japanese beetle, Popillia japonica, and northern masked chafer, Cyclocephala borealis, larvae in greenhouse experiments. Synergistic and additive effects on larval mortality were also observed in field experiments with A. orientalis and P. japonica. Across all experiments, synergistic interactions (based on a χ2 test) were observed in 64% of the combinations. Significant control (based on ANOVA) was observed in 12% of the chlorantraniliprole alone treatments and 29% of the H. bacteriophora alone treatments, but significant control occurred in 76% of the combination treatments. H. bacteriophora progeny production per dead larva recovered in greenhouse experiments did not differ between H. bacteriophora alone and the combination treatments. Nematode densities were higher at 28 days after treatment in soil from the combination treatments due to the higher number of larvae succumbing to nematode infection. H. bacteriophora and chlorantraniliprole were compatible in tank mixes. Agitation in solution with up to 900 ppm chlorantraniliprole did not affect survival, infectivity, and reproduction of H. bacteriophora. H. bacteriophora-chlorantraniliprole combinations offer a safe and highly IPM compatible alternative for remedial white grub control.