Study on susceptibility differences of Tetranychus cinnabarinus (Boisduval) males and females to acaricides.

The carmine spider mite, Tetranychus cinnabarinus (Boisduval), is an important agricultural arthropod pest. This study investigated acaricide susceptibility differences between sexes to determine the biochemical mechanisms potentially involved in these differences. The susceptibility of females and males to seven acaricides (pyridaben, cyflumetofen, abamectin, chlorpyrifos, propargite, profenofos and fenpropathrin) was compared with laboratory bioassays. Males were more susceptible than females for each acaricide. Differences in the lethal concentration 50 % (LC) values between the sexes were observed to range from 2.04-fold to 6.05-fold. The surface area was markedly greater for females than males (by 1.87-fold) and the weight was significantly greater for females compared to males (by 4.67-fold). The specific surface area of male was 2.61-fold higher than that of female. There were no differences in the cuticle structure, whereas the thickness of females was 1.63-fold than that of males. The penetration rate of males was statistically significantly higher than that of females, both in pyridaben and cyflumetofen. Synergism experiments and biochemical assays suggested the involvement of the three detoxification enzyme systems in the sexual susceptibility of T. cinnabarinus. The activities of cytochrome P450 monooxygenases (P450s) (p < 0.01), glutathione-S-transferase (GSTs) (p < 0.05) and carboxylesterase (CarEs) (p < 0.05) in females were significantly higher than that in males. The results reveal that the individual size (specific surface area), cuticle thickness, and detoxification enzyme activity were involved in the sexual susceptibility to acaricides of T. cinnabarinus.