Impact of Exposure to Traditional Neurotoxic Insecticides on the Performance of Entomopathogenic Nematode Heterorhabditis sp. (Rhabditida: Heterorhabditidae) Against Galleria mellonella (Lepidoptera;Pyralidae)

Abstract

The integration of chemical insecticides with the biocontrol agent, entomopathogenic nematodes (EPNs) belonging to the Heterorhabditidae family, necessitates an understanding of the potential adverse effects of these insecticides on the biocontrol agent. Therefore, the primary objective of this research was to investigate the impact of two organophosphates (profenofos and chlorpyrifos), a carbamate (methomyl), and two pyrethroids (lambda-cyhalothrin and deltamethrin) on the viability and virulence of three strains of EPNs: Heterorhabditis sp. NEM 08, Heterorhabditis sp. NEM 15, and Heterorhabditis bacteriophora HP88. This investigation involved assessing their action on viability and infectivity toward the last instar larvae of Galleria mellonella upon exposure to recommended field rates for varying durations: 6 hours, 24 hours, and 48 hours. The results concerning EPN viability revealed that profenofos caused the most significant reduction in EPN viability, ranging from 44.9% to 65.9% after 48 hours of exposure. Additionally, the EPN strains exhibited varying levels of tolerance. Profenofos also had the highest adverse impact on infectivity, resulting in reductions ranging from 65.9% to 82.2% after 48 hours of exposure. Chlorpyrifos followed, which causing reductions in infectivity ranging from 25% to 55.6% after 48 hours of exposure. In contrast, Lambda-cyhalothrin had the least adverse effect on EPN viability and infectivity. Furthermore, it was observed that prolonged exposure time intensified the adverse effects on EPN viability and infectivity. These findings provide valuable insights for the integrated use of these neurotoxic insecticides with EPNs in insect control programs, helping in the selection of the most tolerant EPN strains for this purpose.