Sublethal Effects of Imidacloprid on Honey Bee Colony Growth and Activity at Three Sites in the U.S.

Abstract

Imidacloprid is a neonicotinoid pesticide heavily used by the agricultural industry and shown to have negative impacts on honey bees above certain concentrations. We evaluated the effects of different imidacloprid concentrations in sugar syrup using cage and field studies, and across different environments. Honey bee colonies fed sublethal concentrations of imidicloprid (0, 5, 20 and 100 ppb) over 6 weeks in field trials at a desert site (Arizona), a site near intensive agriculture (Arkansas) and a site with little nearby agriculture but abundant natural forage (Mississippi) were monitored with respect to colony metrics, such as adult bee and brood population sizes, as well as pesticide residues. Hive weight and internal hive temperature were monitored continuously over two trials in Arizona. Colonies fed 100 ppb imidacloprid in Arizona had significantly lower adult bee populations, brood surface areas and average frame weights, and reduced temperature control, compared to colonies in one or more of the other treatment groups, and consumption rates of those colonies were lower compared to other colonies in Arizona and Arkansas, although no differences in capped brood or average frame weight were observed among treatments in Arkansas. At the Mississippi site, also rich in alternative forage, colonies fed 5 ppb imidacloprid had less capped brood than control colonies, but contamination of control colonies was detected. In contrast, significantly higher daily hive weight variability among colonies fed 5 ppb imidacloprid in Arizona suggested greater foraging activity during a nectar flow post treatment, than any other treatment group. Imidacloprid concentrations in stored honey corresponded well with the respective syrup concentrations fed to the colonies and remained stable within the hive for at least 7 months after the end of treatment.

Single and interactive effects of Varroa destructor, Nosema spp., and imidacloprid on honey bee colonies (Apis mellifera)

“…6), which is approximately 1% of the acute oral LD50 (=3.7 ng/bee). Similar for Meikle et al (2016), whose lowest exposure of 20 lg/L imidacloprid in sugar water (0.76 ng per bee per day as calculated by Blacqui ere and van der Steen [2017]) did not result in less bees in the colonies after six weeks of exposure. The exposure period was similar.…”

Effects of coumaphos and imidacloprid on honey bee (Hymenoptera: Apidae) lifespan and antioxidant gene regulations in laboratory experiments

“…Our bioassays identified sublethal effects of imidacloprid at concentrations as low as 5 ppb and 20 ppb on worker bees. Interestingly, honey bees exposed to 5 ppb imidacloprid within the hive exhibited greater foraging activity, while higher doses (20 and 100 ppb) did not 34 . Sublethal effects of imidacloprid that we observed profoundly affect bee health, both positively, by tempering the harmful effects of coumaphos, and negatively, by impairing food consumption by individual worker bees.…”

“…Imidacloprid, a common crop insecticide found in many hive products, by itself, is highly toxic to honey bees if applied incorrectly, and has an acute oral LD 50 ranging from 4 × 10 −3 to 5 × 10 −3  μg per bee 23 . Moreover, imidacloprid above 20 μg/kg (20 ppb) can cause sublethal physiological and behavioral abnormalities in workers and queens 32–34 . Earlier studies, confirm that bulk feeding sublethal concentrations of 100 ppb imidacloprid to honey bees has no overt negative effects on colony development.…”

Chronic toxicity of clothianidin, imidacloprid, chlorpyrifos, and dimethoate to Apis mellifera L. larvae reared in vitro

“…A tremendous amount of work has been conducted to evaluate the toxicity of imidacloprid to bees, especially regarding possible sublethal effects . However, there is still some uncertainty regarding its effect on honey bee health due to inconsistent results or tests including test concentrations higher than those honey bees reasonably can encounter in the field.…”