General and species-specific impacts of a neonicotinoid insecticide on the ovary development and feeding of wild bumblebee queens

Abstract

Bumblebees are essential pollinators of crops and wild plants, but are in decline across the globe. Neonicotinoid pesticides have been implicated as a potential driver of these declines, but most of our evidence base comes from studies of a single species. There is an urgent need to understand whether such results can be generalized across a range of species. Here, we present results of a laboratory experiment testing the impacts of field-relevant doses (1.87-5.32 ppb) of the neonicotinoid thiamethoxam on spring-caught wild queens of four bumblebee species: Bombus terrestris, B. lucorum, B. pratorum and B. pascuorum. Two weeks of exposure to the higher concentration of thiamethoxam caused a reduction in feeding in two out of four species, suggesting species-specific anti-feedant, repellency or toxicity effects. The higher level of thiamethoxam exposure resulted in a reduction in the average length of terminal oocytes in queens of all four species. In addition to providing the first evidence for general effects of neonicotinoids on ovary development in multiple species of wild bumblebee queens, the discovery of species-specific effects on feeding has significant implications for current practices and policy for pesticide risk assessment and use.

Keywords: bumble bee queens; insect pollinator; insecticide toxicity; neonicotinoid insecticide; parasites; sublethal effects.

Figure 1.

The average daily amount of syrup consumed by four species of bumblebee queen, treated with one of three thiamethoxam exposure scenarios (control, no pesticide; low, 1.87 ppb; high, 5.32 ppb). Bars show mean (±s.e.) consumption (grams) per unit volume of bee (cubic millimetres). An asterisk indicates a significant interaction (p < 0.05) between species and the high-dose treatment (electronic supplementary material, table S3).

Figure 2.

The average daily amount of thiamethoxam consumed by queens of four species of bumblebee. Values calculated from actual residue levels. Boxplots show the median (central line), interquartile range (box), range which lies within 1.5 times the interquartile range from the box (whiskers) and outliers (dots).

Figure 3.

The relative oocyte length (Z-score for mean oocyte length) of four species of bumblebee queen after exposure to one of three thiamethoxam exposure scenarios (control, no pesticide; low, 1.87 ppb; high, 5.32 ppb). Boxplots show the median (central line), interquartile range (box), range which lies within 1.5 time of the interquartile range from the box (whiskers) and outliers (dots).