Sublethal effects of larval insecticide exposure on adult mayfly body-size

A.C. Alexander¹, J.M. Culp², K. Liber³, D.J. Baird², and A.J. Cessna⁴.¹Canadian Rivers Institute, Department of Biology @ the University of New Brunswick, ²National Water Research Institute, Environment Canada, 10 Bailey Drive, Fredericton, NB, CAN, ³Toxicology Center @ the University of Saskatchewan (Saskatoon), 44 Campus Drive, Saskatoon, SK, CAN, ⁴Agr and Agri Food Canada, Res Ctr, Lethbridge, AB, CAN

Soluble agricultural insecticides can impair the development and growth of larval mayflies, and have broad impacts on the success of benthic invertebrate populations. Employing field-deployed mesocosms, we examined the effects of 24-h pulse and 20-d press (continual) exposures of the common agricultural insecticide, imidacloprid, on mayfly body-size metrics. Benthic invertebrate communities with the mayfly genera, Baetis sp. (Family Baetidae) and Epeorus sp. (Family Heptageniidae), were exposed to sublethal concentrations (0, 0.5, 1, 5, 10 ppb) of imidacloprid to examine this insecticide’s effects on larval development and adult body size. MANOVA analyses indicated that exposure to imidacloprid significantly reduced head length of Baetis males (F(5,96)=3.05; p<0.05) and thorax length of Epeorus males (F(5,44)=2.61; p<0.05). Females of neither genus were significantly impacted with respect to body-size metrics as a result of the pulse or press exposures. Larval Epeorus also exhibited reduced development (wingpad length to width ratio) in 1 ppb press exposures (F(3,178)=7.21; p<0.01), but were not affected by a 10-fold increase in concentration (10 ppb) of imidacloprid delivered in a 24-h pulse. Because fecundity is positively related to invertebrate development and body size, sublethal doses of this widely applied agricultural insecticide have the potential to reduce reproductive success of mayfly populations.