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Effects of carbaryl exposure on the last larval instar of Xanthocnemis zealandica – fluctuating asymmetry and adult emergence
Author(s) -
Hardersen Sönke
Publication year - 2000
Publication title -
entomologia experimentalis et applicata
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.765
H-Index - 83
eISSN - 1570-7458
pISSN - 0013-8703
DOI - 10.1046/j.1570-7458.2000.00700.x
Subject(s) - fluctuating asymmetry , biology , damselfly , instar , carbaryl , odonata , larva , toxicology , zoology , pesticide , ecotoxicology , ecology
Fluctuating asymmetry (FA), a measure of developmental stability, has been suggested as a monitoring tool for environmental pollution. Aquatic pollution events are often transitional and the level of FA in populations exposed to such incidents has not yet been investigated. Research into the morphological effects of transitional pollution also provides a tool to elucidate the timing and duration of any ‘window of opportunity’ for the determination of FA in the developing organism. The present study was undertaken to investigate if exposure of the last instar of the damselfly Xanthocnemis zealandica (McLachlan) (Zygoptera: Coenagrionidae) to different levels of insecticidal stress resulted in different levels of FA in the wings of the adult insects and if adult emergence was altered by different concentrations of pesticide. Three concentrations of carbaryl (40 ppb, 2 ppb and 0.1 ppb) and a control were used. The emergence success of the damselflies was not affected by any treatment, but the insecticide had a stimulatory effect on the developing larvae. Exposure of the last instar of X. zealandica to carbaryl at 40 ppb had no consistent effect on FA in metric traits and increased FA in meristic traits compared with the control. Segregation of the emerged adults into two groups revealed more details about the ‘window of opportunity’ in the meristic traits. Larvae which had already completed more than half of their development when the experiment started did not show significant differences in the level of FA. In contrast, damselflies which were exposed for more than half of the final instar showed a clear difference in their levels of FA. The greater difference in the latter group was mainly caused by a decrease of FA in the controls rather than by an increase in the treatment. These data suggest that the ‘window of opportunity’ for the determination of the level of FA of the meristic traits in damselfly wings closes approximately halfway through the final larval instar.