Evaluation of chronic toxicity of four neonicotinoids to Adalia bipunctata L. (Coleoptera; Coccinellidae) using a demographic apporach

Acute mortality estimates are the most widely used measures of toxicity and often they are used as endpoint in ecological risk assessment. Such methods do not provide enough information about the actual effects that may occur in pesticide-exposed populations over longer time periods than a few days. In this study we utilize demographic and population modelling for estimation of pesticide effects on a beneficial species. Bioassays were carried out in the laboratory to assess the demographic responses of the coccinellid Adalia bipunctata, exposed as larvae or adults, to four neonicotinoids, including imidacloprid, thiacloprid, thiamethoxam, and acetamiprid at sublethal dose. Demographic parameters were calculated by means of life tables. Life table data were also used to generate an ageclassified projection model (Leslie matrices). The elasticity of population growth rate to change in each of the individual vital traits was calculated. Finally the Delay in Population Growth Index, a measure of population recovery, was calculated to compare the time required to a control population and pesticide-exposed populations to reach a predetermined number of individuals. Exposure of larval stage to imidacloprid, thiamethoxam, and acetamiprid, and adult stage to imidacloprid and thiamethoxam, significantly reduced all the demographic parameters in comparison with control, with the sole exception of mean generation time, and results in a pronounced slower increase in the coccinellid population. For all the insecticide tested, the perturbation analysis showed that survival, in particular of larval and imaginal stages, had the greatest effect on population growth. Neonicotinoids caused significant population delays with a more pronounced effect when the coccinellid were exposed as adult.