Bumble bees are important pollinators whose populations have declined over recent years, raising widespread concern. One conspicuous threat to bumble bees is their unintended exposure to trace residues of systemic neonicotinoid pesticides, such as imidacloprid, which are ingested when bees forage on the nectar and pollen of treated crops. However, the demographic consequences for bumble bees of exposure to dietary neonicotinoids have yet to be fully established. To determine whether environmentally realistic levels of imidacloprid are capable of making a demographic impact on bumble bees, we exposed queenless microcolonies of worker bumble bees, Bombus terrestris, to a range of dosages of dietary imidacloprid between zero and 125 μg L(-1) and examined the effects on ovary development and fecundity. Microcolonies showed a dose-dependent decline in fecundity, with environmentally realistic dosages in the range of 1 μg L(-1) capable of reducing brood production by one third. In contrast, ovary development was unimpaired by dietary imidacloprid except at the highest dosage. Imidacloprid reduced feeding on both syrup and pollen but, after controlling statistically for dosage, microcolonies that consumed more syrup and pollen produced more brood. We therefore speculate that the detrimental effects of imidacloprid on fecundity emerge principally from nutrient limitation imposed by the failure of individuals to feed. Our findings raise concern about the impact of neonicotinoids on wild bumble bee populations. However, we recognize that to fully evaluate impacts on wild colonies it will be necessary to establish the effect of dietary neonicotinoids on the fecundity of bumble bee queens.

In the original publication of the article, the conversion of imidacloprid concentrations from lg L -1 into parts per billion (ppb) has been miscalculated in certain sections of the text. The authors would like to correct this error and provide the corrected conversions in the altered text below (correct ppb values given in italics).• …exposure to imidacloprid at an environmentally realistic level of 1 lg L -1 (=0.8 ppb)… • …oocytes were smaller in bees from microcolonies exposed to imidacloprid at 125 lg L -1 (98 ppb)… • …syrup dosed with imidacloprid at 1 ppb (1.28 lg L -1 )…• …the strongly detrimental effects of imidacloprid on fecundity at dosages of 39 ppb (50 lg L -1 )… • Except at relatively high dosages (i.e. above 98 ppb)… • …the detrimental effects of imidacloprid on bumble bee fecundity at dosages below 98 ppb… • …dietary imidacloprid at levels up to approximately 39 ppb… • …bumble bee workers feeding on syrup at the highest dosage, 98 ppb… • …microcolonies feeding on syrups at dosages of 16 ppb (20 lg L -1 )… • …microcolonies exposed to an intermediate dosage of imidacloprid, 39 ppb… • …imidacloprid at 39 ppb may have disrupted social interactions.The online version of the original article can be found under