Does carbaryl increase fluctuating asymmetry in damselflies under field conditions? A mesocosm experiment with Xanthocnemis zealandica (Odonata : Zygoptera)

1. Previous laboratory experiments have shown that the insecticide carbaryl reduces emergence success and increases fluctuating asymmetry in cell patt erns of damselfly wings. These effects were validated using mesocosms. Twen ty artificial ponds, each containing Xanthocnemis zealandica, were exposed to three replicated (n = 5) concentrations of carbaryl contamination plus c ontrols. Emergence success, level of fluctuating asymmetry in meristic and metric traits of the wings, and average size of the damselflies were measur ed. 2. The degradation of carbaryl was relatively constant for the first 5 week s but later increased considerably, probably because of enhanced biodegrada tion, 3. Carbaryl at 100 p.p.b. (nominal concentration) reduced emergence success 10 days after application, whereas carbaryl at 10 p.p.b, and 1 p.p.b, had no effect. 4. To investigate how the level of fluctuating asymmetry and size were affe cted by carbaryl, damselflies from ponds with the highest concentration whe re emergence success was not affected (10 p.p.b.) were analysed over four t ime periods. Fluctuating asymmetry of the wings increased during the season but was not affected by carbaryl at 10 p.p.b. 5. Size, measured as average length of the front wings, was affected by dat e of emergence but not by exposure to carbaryl at 10 p.p.b. 6. Three main reasons for the absence of increased levels of fluctuating as ymmetry as a result of carbaryl exposure are suggested.