Evaluation of Resistance to the Organophosphate Chlorpyrifos Through LC₅₀ and Life History Trait Analysis in Two Siblings: Drosophila Melanogaster and Drosophila Simulans

Abstract

Introduction: Insecticide resistance and its management has become a major challenge in agriculture and medical health field. Chlorpyrifos (CP) known for its neurotoxic property to the target species, however, due to its extensive application it becomes the second most detected insecticide in food and water causing potential health risks to the non- targets.

Objectives: In the present study, resistance to chlorpyrifos was evaluated through lethal dose and various traits analysis in two non- target species i.e., Drosophila melanogaster and Drosophila simulans.

Methods: The LC₅₀ was calculated initially after exposing the flies to six different concentrations of CP. Based on the mortality rate, two sub lethal concentrations of CP (0.3ppm and 0.5ppm) were used further to study the effects on fecundity, developmental stage duration and pupation height in F₁ and after a consistent exposure for 10 generations(F₁₀). The LC₅₀ was calculated for F₁₀ and compared with the F₀ generation. In all experiments, the results control/F₀, F₁ and F₁₀ flies were compared to evaluate its adverse effect and resistance developed by the flies.

Results: The fecundity rate and pupation height were significantly reduced (~50-75%) on CP-exposure in F₁. The delayed development is observed in F₁ CP treated, i.e., egg to larva emergence, larval, pupation and pupation to adult duration, however, the larval stage was found to be most significantly affected. Similarly, the recovery rate of all stages was faster than the larval duration in F₁₀ generation. The higher resistance factor (RF) ratio (F₁₀ to F₀) observed in D. melanogaster CP-exposed flies evidenced its ability to develop faster resistance than D. simulans.

 Conclusions: The findings will help to understand how important is to monitor insecticide-resistance for its management and regulation with a view to prevent health risk of other non-targets including human.