A High Soldier Proportion Encouraged the Greater Antifungal Immunity in a Subterranean Termite

Involvement of a catalase gene in lignin catalysis and immune defense against pathogenic fungus in Coptotermes formosanus: a potential new target for termite control

BACKGROUND

Detoxifying enzymes are likely involved in lignin feeding and immune defense mechanisms within termites, rendering them potential targets for biological control. However, investigations into the dual functionality of termite detoxification enzymes in vivo have not been documented.

RESULTS

In this study, the complete cDNA of the catalase gene (Cfcat) derived from Coptotermes formosanus Shiraki was amplified. CFCAT comprises an open reading frame spanning 1527 bp, encoding a 508-amino acid sequence. The highest expression was observed in the epidermal tissues (including the fat body and hemolymph) followed by the foregut/salivary gland. Furthermore, we confirmed the catalase activity of the recombinant Cfcat protein. Using RNA interference (RNAi) technology, the importance of Cfcat in the lignin-feeding of C. formosanus was demonstrated, and the role of Cfcat in innate immunity was investigated. Survival assays showed that Cfcat RNAi significantly increased the susceptibility of C. formosanus to Metarhizium anisopliae. Irrespective of the infection status, Cfcat inhibition had a significant impact on multiple factors of humoral and intestinal immunity in C. formosanus. Notably, Cfcat RNAi exhibited a more pronounced immunosuppressive effect on humoral immunity than on intestinal immunity.

CONCLUSION

Cfcat plays an important role in the regulation of innate immunity and lignin feeding in C. formosanus. Cfcat RNAi can weaken the immune response of termites against M. anisopliae, which may aid the biocontrol efficiency of M. anisopliae against C. formosanus. This study provides a theoretical basis and technical reference for the development of a novel biocontrol strategy targeting detoxifying enzymes of termites. © 2024 Society of Chemical Industry.

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

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.