Effects of temperature stress and pesticide exposure on fluctuating asymmetry and mortality of Copera annulata (Selys) (Odonata: Zygoptera) larvae

Although there have been some investigations into the effects of insecticide on the level of fluctuating asymmetry (FA) of adult damselflies, the cooperative effects of environmental factors on FA of larval damselflies were known little. This paper explored effects of exposure to temperature and pesticide on larval development of the damselfly Copera annulata (Selys). A conventional life history trait (mortality) and developmental instability (estimated by calculating fluctuating asymmetry of bilaterally symmetrical structures) were used to measure stresses in this paper. The results showed that temperature and different concentrations of pesticide produced significant effects only on developmental stability of some characters. The FA values of three traits decreased at lower concentrations, then increased slowly with increased insecticide doses. The FA values of four traits decreased slowly with increased temperatures. However, the interaction between different concentrations of insecticide and temperature was complicated and only produced significant effects on five traits. Insecticide treatment did not significantly affect mortality of the larvae of damselfly. However, mortality was significantly positively associated with temperature. There were significantly negative associations between mortality and the FA values of three traits. These results may be caused by higher mortality and short rearing time although we did not find the significant effects of concentrations on mortality. Therefore, we speculate FA may be induced if larval damselflies were treated during longer term and FA has potential as a more specific bioindicator of stresses if we guarantee enough longer rearing time without higher mortality under stressful environment.