The effects of chlorpyrifos on cholinesterase activity and foraging behavior in the dragonfly, Anax junius (Odonata)

We examined head capsule cholinesterase (ChE) and foraging behavior in nymp hs of the dragonfly, Anax junius, exposed for 24 h to 0.2, 0.6 and 1.0 mu g l(-1) of the organophosphorus (OP) insecticide, chlorpyrifos [O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate]. The invertebrate community is an important component of the structure and function of wetland ecosyst ems, yet the potential effects of insecticides on wetland ecosystems are la rgely unknown. Our objectives were to determine if exposure to environmenta lly realistic concentrations of chlorpyrifos affected foraging behavior and ChE activity in head capsules of dragonfly nymphs. Nymphs were exposed to different concentrations of chlorpyrifos and different prey densities in a factorial design. ChE activities and foraging behaviors of treated nymphs w ere not statistically different (p greater than or equal to 0.05) from cont rol groups. Prey density effects exerted a greater effect on dragonfly fora ging than toxicant exposures. Nymphs offered higher prey densities exhibite d more foraging behaviors but also missed their prey more often. High varia bility in ChE activities within the control group and across treated groups precluded determination of relationships between ChE and foraging behavior s. It appears that A. junius is relatively tolerant of chlorpyrifos, althou gh the concentrations we tested have been shown in other work to adversely affect the prey base; therefore the introduction of this insecticide may ha ve indirect adverse affects on top invertebrate predators such as Odonata.