Mixtures of entomopathogenic nematodes provided successful suppression of Bactrocera tau by stimulated dispersal, aggregation, and invasion

Bactrocera tau Walker, a well-known pest in various agricultural regions, poses a significant threat to Trichosanthes kirilowii Maxim (TK), commonly known as “Gualou” (Chinese Snake Gourd/Chinese Cucumber), a traditional Chinese medicinal plant. This study aimed to explore a novel management strategy that employs mixtures of entomopathogenic nematode (EPN) species with high virulence to soil-dwelling larvae and pupae of B. tau and their behavioral mechanisms. Laboratory bioassays identified Steinernema carpocapsae (Sc) and Heterorhabditis indica (Hi), that were highly virulent to B. tau larvae, achieving up to 100 % mortality at 25 infective juveniles (IJs) /larva. However, pupal mortality was significantly lower across all tested EPN species, with S. feltiae showing the highest efficacy at 1600 IJs/pupa, resulting in a 60.00 ± 4.52 % mortality rate. Pan experiments, simulating field conditions, indicated a synergistic interaction in Sc + Sf mixtures, which caused the highest corrected mortality of 79.50 ± 1.27 % against B. tau. Field trials demonstrated that EPN mixtures of Sc + Sf when applied twice, resulted in a 58.71 % reduction in adult fly populations and protected 76.82 % of TK fruits from decay compared to the insecticide emamectin benzoate. Behavior bioassays revealed EPN mixtures of Sc + Sf and Hi + Sf exhibited higher dispersal, aggregation, and invasion rates than single EPN species, with Sc + Sf outperforming Hi + Sf. This study highlights the potential of using EPN mixtures to target both larval and pupal stages of B. tau, providing a sustainable and effective pest management strategy. The enhanced behavioral mechanisms observed between mixed EPN species could further improve the application and efficacy of EPN-based biocontrol in agricultural systems.