Effects of sublethal phosphine exposure on respiration rate and dispersal propensity of adult females of Tribolium castaneum

An understanding of how sublethal exposure to phosphine affects an organism’s respiration is important for predicting its effects on activities depending on a reliable energy source including movement. After treatment with the appropriate sublethal doses of phosphine (LC₁₀), both resistant and susceptible Tribolium castaneum beetles suffered reductions in respiration rates, flight initiation rates and successful location (by walking) of aggregation pheromone lures. The susceptible beetles showed a significantly greater reduction in their respiration rate (53.5%) after exposure to sublethal doses of phosphine compared to the resistant beetles (37.5%), although the respiration rate was still higher in susceptible beetles than in resistant ones. Simultaneously, much larger decreases in the activities associated with both walking and flight were observed in the susceptible beetles, after exposure to sublethal doses of phosphine, compared to the decreases recorded in resistant beetles. The relatively greater reduction in the locomotory responses of susceptible beetles showed that these insects may withstand exposure to phosphine by remaining relatively still and reducing their respiration rate. They would thus minimize their exposure to phosphine, but perhaps only incidentally because the lack of movement may be the result of impairment. By contrast, phosphine-resistant beetles, when exposed to phosphine fumigation, continue to move and may even remove themselves from areas of phosphine exposure. An understanding of how the survivors of sublethal exposures behave is important for predicting the spread and local build-up of phosphine resistance genes and thus improving the control and resistance management of stored grain pests.