Rapid adaptation of Chironomus yoshimatsui to acetylcholinesterase inhibitors (pyraclofos and pirimicarb) in a multi-generation study.

We evaluated the real effects of pollutants through a multi-generation study. We tested whether short-term exposure (48 h) of successive (first and second) generations of Chironomus yoshimatsui neonates (<24-h-old) to two acetylcholinesterase inhibitor insecticides, pyraclofos, and pirimicarb, would change insecticide sensitivity and life-cycle parameters over four generations. Additionally, we tested whether acetylcholinesterase (AChE) activity levels would be associated with this sensitivity change. Sensitivities (48 h EC50 value, using immobility as the endpoint) in chironomids (<24-h-old) and insect life-cycle parameters (the number of larvae per egg mass and adult size) were investigated. Parental chironomids produced larvae that were less sensitive than those in the control group following the two 48 h pirimicarb exposure events, whereas exposure to pyraclofos did not affect sensitivity. The AChE activity in larvae with low sensitivity to pirimicarb was significantly higher than that in the control. Thus, increased AChE activity might be associated with low sensitivity. The life-cycle parameters in chironomids recovered from the effects of pyraclofos and pirimicarb suggested they could adapt to the insecticides by changing biomass allocation. Our study suggested potential chemical risks of insecticide stress and how aquatic organisms adapt to it.