Effect Of Insecticides On Thermal Biology Characteristics Of Diamondback Moth, Plutella Xylostella (Linn.)

In this thesis, the interrelationship between the body temperature of the larvae of diamondback moth, Plutella xylostella (Linn.) , and the environmental temperature was investigated, the supercooling point as well as the freezing point of each life stage of diamondback moth was measured, the thermoregulation ability of diamondback moth larvae either from a higher temperature environment to a lower one or from a lower one to a higher one was observed and the effect of 4 insecticides including abamectin, chlorpyrifos, fipronil and cypermethrin on body temperature, thermoregulation ability, supercooling point and freezing point of 3rd instar larvae of diamondback moth was studied. The main results were as follows:1. The physiological thermoregulation ability of diamondback moth larvae was weak for their bogy temperature was always near to the environmental temperature. But when environmental temperature was set at 16℃or 20℃,their body temperature was a little higher than environmental temperature. On the contrarary, while the environmental temperature was set at 30℃or 35℃, the body temperature was a little lower. Because of the poor thermoregulation ability, the body temperature of the diamondback moth larvae could become same as the environmental temperature within a comparatively short time either when they were removed from a higher temperature environment to a lower one or vice versa. The effect of insecticides on thermoregulation ability of the tested insects was also found to be weak.2. Just like what was found in the endothermal animals, insecticide exposure could firstly decrease and then increase the body temperature of the tested insects, which could be most easily to see when the environmental temperature was set at 25℃or 30℃. Take chlorpyrifos at 25℃as the example, 12h after treatment, the body temperature of all the treated insects was lower than that of control except those from the treatment of chlorpyrifos at the concentration of 800mg/L. Among them, the body temperature of control insects was 25.19℃, and that of the insects from the concentration of 200mg/L treatment was 24.45℃, which was significantly lower (P<0.05). Then the body temperature of the insects from the chlorpyrifos treatments increased and higher than control 48h after treatments. At this time, the body temperature of control insects was 24.74℃and that from the treatment at 100mg/L was 25.28℃. Also, the difference was significant (P<0.05).3. The supercooling point of egg, first to 4th instar larvae, pupae and adult of diamondback moth was -17.94℃,-7.91℃,-8.57℃,-16.21℃,-13.53℃,-17.07℃and -15.91℃, respectively and the freezing point was -17.73℃,-6.79℃,-6.70℃,-14.73℃,-3.63℃,-16.40℃and -14.95℃, respectively. Effect of insecticide treatment on supercooling point or freezing point of the tested insects could be seen, but that varied with the insecticide type, concentration and the duration after treatment. For example, 24h after fipronil treatment, the supercooling point of the insects from the treatment of 1.0 mg/L was -4.15℃and it was significantly higher than that of control, which was -6.46℃(P<0.05). The effect of insecticides on freezing point was similar with that on supercooling point.