Synergistic Effects of Indigenous Entomopathogenic <i>Fusarium</i> spp. with Low-Dose Termiticides for Sustainable <i>Coptotermes heimi</i> Control

Subterranean termites such as Coptotermes heimi are major structural pests in South Asia, causing severe economic damage to cellulose-based materials and wooden infrastructure. Conventional chemical termiticides, although effective, raise concerns regarding environmental persistence, non-target effects, and the development of resistance. This study evaluated the synergistic potential of two indigenous entomopathogenic fungi (Fusarium solani and F. falciforme) in combination with sublethal concentrations of three commercial insecticides—fipronil, imidacloprid, and chlorpyrifos against C. heimi under laboratory conditions. Compatibility assays confirmed that the tested concentrations of the insecticide did not significantly inhibit fungal germination, growth, and sporulation. Virulence bioassays revealed that F. solani combined with imidacloprid produced 83.33 ± 2.72% mortality, while F. falciforme with fipronil achieved the highest recorded mortality of 91.11% by day 12, both exceeding the effects of individual treatments. Other combinations yielded additive effects, with mortality increasing steadily over time. These results demonstrate that compatible fungus–insecticide pairings can enhance termite control while reducing chemical inputs, supporting their integration into sustainable pest management strategies.