Synergistic Effect of Commercial Pesticides and Entomopathogenic Fungi on Coptotermes heimi (Wasmann) (Blattodea: Rhinotermitidae)

Abstract

The subterranean termite, Coptotermes heimi (Wasmann) (Blattodea: Rhinotermitidae), is recognized as a building infesting lower termite species in Pakistan, India, and Bangladesh. The irrational and extensive use of insecticides against C. heimi in urban environments has resulted in insecticide resistance and environmental contamination. This study was performed to control C. heimi using naturally occurring endogenous strains of entomopathogenic fungi Fusarium falciforme, Aspergillus terreus, Penicillium citrinum, and Fusarium solani in combination with sublethal concentrations of commercial insecticides fipronil, chlorpyrifos, and imidacloprid in a no-choice feeding assay for 12 days. The termite percent mortality rate for the combination of imidacloprid (25 ppm) with F. solani (1×109 conidia/ml) was 83%, higher than the combined percent mortality caused by these two variables in individual treatment at a continuous exposure of 12 days. Similarly, another combination of fipronil and F. falciforme showed an enhanced percent mortality (91%) compared to the individual percent mortality of these two variables in separate treatments. These results showed that sublethal concentrations of insecticides suppress the immune response and reduce the repellency of infected termites. Entomopathogenic fungi with a combination of sublethal concentrations can be used against insect pests and may reduce the insect resistance of targeted pests. Further detailed studies are necessary for developing and implanting this approach in successful field trials.