Indoxacarb and thermoregulatory behaviour of Colorado potato beetle, Leptinotarsa decemlineata (Say)

摘要

The effect of indoxacarb, an oxadiazine insecticide, applied at manufacturers' recommended concentration, 170 mg L~(-1) H_2O, and at a double concentration, 340 mg L~(-1) H_2O, on insect thermoregulatory behaviour, the metabolic rate at various temperatures (10, 15, 20, 25, 30 and 35 °C) and muscle resting potential was studied. Different developmental stages of Colorado potato beetle, Leptinotarsa decemlineata Say, have been used in experiments. Colorado beetle showed the highest susceptibility toindoxacarb at temperatures below 17 °C and over 31 °C. The toxicity of indoxacarb was highest for the youngest developmental stages of the insect and when the insecticide was applied during the night. A clear positive correlation between the ambient temperature and metabolic rate both in control and in intoxicated (10 to 30 °C) insects has been found. Indoxacarb exerts a significant stimulating effect on the beetles metabolic rate, especially at the initial stage of experiments. Insect thermal preferences were tested in a temperature gradient system up to 3 days. Temperatures selected in thermal gradient by intoxicated beetles were approximately the same as those at which insects were least susceptible to treatment, 20-21 °C on average, and they were higher by up to 2.5 °C as compared with control insects. Indoxacarb exerted only a minor effect on muscle resting potential in the beetle.