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

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