S. Hardersen et Sd. Wratten, The effects of carbaryl exposure of the penultimate larval instars of Xathocnemis zealandica on emergence and fluctuating asymmetry, ECOTOXICOL, 7(5), 1998, pp. 297-304
The occurrence of pesticide residues in freshwater systems has become a con
cern in recent decades. In order to establish biomonitoring programs it is
vital to investigate the response of organisms to varying concentrations of
pesticides. Levels of pollutants fluctuate in freshwater systems and thus
only some instars of aquatic insects may be exposed to pollution stress. Th
erefore it is important to investigate the effects of exposing selected ins
tars of potential bioindicator species. In a laboratory experiment damselfl
y larvae of the penultimate instar were exposed to three concentrations of
carbaryl (100 ppb, 10 ppb, 1 ppb) plus controls until the adult damselflies
emerged. Carbaryl at 100 ppb reduced emergence by more than 90%. The lower
carbaryl concentrations did not affect emergence success but increased the
developmental speed slightly The adult damselflies from the highest concen
tration which did not affect emergence success (10 ppb) were analyzed for t
heir level of fluctuating asymmetry (FA), deviation from bilateral symmetry
, and compared with those from controls. The level of FA in cell patterns i
n wings was increased whereas the level of FA for wing length did not show
any differences.