Ecological relevance and sensitivity depending on the exposure time for two biomarkers

Biomarkers are widely used to assess pesticide stress, but their ecological relevance and exposure time dependent sensitivity is still heavily debated. We studied both aspects in larvae of the damselfly Coenagrion puella, comparing the impact of low doses of atrazine, carbaryl, and endosulfan on two key biomarkers (acetylcholinesterase [AChE] activity and fluctuating asymmetry [FA]) and their relationship with life history traits (mortality, development time, growth rate, and body size). Larvae exposed to the pesticides had, in general, longer development times. Size, growth rate, and mortality were not affected by any of the pesticides. In the long-term exposure, AChE activity was diminished by atrazine treatments and stimulated by carbaryl treatments, and was not affected in the endosulfan treatments. FA decreased with increasing endosulfan concentrations and showed no reaction to atrazine or carbaryl. Overall, short-term exposure tended to overestimate the results of long-term exposure decreasing growth rates and enhancing inhibition of AChE activity in atrazine and carbaryl treatments. In line with its ecological relevance, relationship between biomarkers and life history traits showed that AChE inhibition was positively correlated with mortality, while FA was traded off with size. These results show that caution should be exerted when using these biomarkers to assess pesticide pollution in field situations.