LIFE-CYCLE OF THE DAMSELFLY CALOPTERYX ATRATA IN RELATION TO PESTICIDE CONTAMINATION

The life cycle of the damselfly Calopteryx atrata was investigated in relation to pesticide contamination occurring in its aquatic habitat. Calopteryx atrata emerged from the River Onogawa around May and stayed as immature adults in forests away from the stream. From late June to mid-August, mature adults were engaged in reproduction at the stream. On the other hand pesticide contamination occurred from April to Augu st with its peak in May and June, following transplantation of young r ice plants. Mature nymphs of C. atrata experienced pesticide contamina tion, but may have tolerated it. Hatched nymphs had high susceptibilit y to two of the commonly used insecticides, fenitrothion (mortality oc curred at > 4.0 mu g l(-1) in 24 h and at > 2.0 mu g l(-1) in 48 h) an d fenthion (> 2.0 mu g l(-1) in 24 h and > 1.0 mu g l(-1) in 48 h). Ha tching was estimated to occur mainly in August, when pesticide contami nation was not as high as the susceptibility level. However, the level of pesticide contamination in August is variable due to its origin fr om aerial spraying, so hatched nymphs may experience a hazardous amoun t of pesticides depending on the year or place. The population of C. a trata does not escape the risk of pesticide contamination completely a nd may be affected by it.