α-Terpineol affects social immunity, increasing the pathogenicity of entomopathogenic nematodes to subterranean termites (Isoptera)

Abstract

Biocontrol of subterranean termites is largely impeded by their social immune responses. Studies on biocontrol agents combined with natural insecticides and their possible effects on the immune defense mechanisms of termites are limited. In this study, we investigated the effects of a combined biocontrol strategy using a plant-derived insect ATPase inhibitor, α-terpineol, with the entomopathogenic nematodes (EPNs) Steinernema carpocapsae against the subterranean termite Coptotermes formosanus Shiraki. Survival assays showed that even a low lethal concentration of α-terpineol significantly increased the EPNs-induced virulence in C. formosanus. α-terpineol treatment majorly inhibited the activity of Na+- K+- ATPase, which disturbed the EPNs-induced enhancement of locomotor activity and grooming behavior in termites treated with the combined strategy. Furthermore, the combination treatment had a synergistic inhibitory effect on innate immune responses in C. formosanus, which were measured as changes in the expression of immune-related genes and activities of immune system enzymes. In conclusion, α-terpineol can weaken the immune defense of termites against EPNs at low lethal concentrations, and is a suitable non-synthetic insecticide to prove the biocontrol efficiency of EPNs on C. formosanus. This study provides a theoretical basis and technical reference for a novel biocontrol strategy that promises to overcome the problems of host immune defense in termites.