The Effects of Carbaryl Exposure of the Penultimate Larval Instars of Xathocnemis Zealandica on Emergence and Fluctuating Asymmetry

Abstract

The occurrence of pesticide residues in freshwater systems has become a concern 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. Therefore it is important to investigate the effects of exposing selected instars of potential bioindicator species. In a laboratory experiment damselfly 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 concentration which did not affect emergence success (10 ppb) were analyzed for their level of fluctuating asymmetry (FA), deviation from bilateral symmetry, and compared with those from controls. The level of FA in cell patterns in wings was increased whereas the level of FA for wing length did not show any differences.