Performance of honeybee colonies located in neonicotinoid‐treated and untreated cornfields in Quebec

Abstract

Twenty‐two honeybee (Apis mellifera) colonies were placed in four different cornfield areas in order to study the potential in situ effects of seed‐coated systemic neonicotinoid pesticides used in cornfields (Zea mays spp) on honeybee health. Two apiaries were located in two independent neonicotinoid‐treated cornfield areas and two others in two independent untreated cornfield areas used as controls. These experimental hives were extensively monitored for their performance and health traits over a period of one year. Trapped pollen was collected and microscopically identified to define the visited flowers and the amount of corn pollen collected by bees. Liquid chromatography–mass spectrometry was performed to detect pesticide residues in honeybee foragers and trapped pollen. Honeybee colonies located in neonicotinoid‐treated cornfields expressed significantly higher varroa mite loads than those in untreated cornfields. However, brood production and colony weight were less disturbed by the treatment factor. Sublethal doses of neonicotinoids were detected in the trapped corn pollen and none in bee foragers. Overall, our results show that forager bees collected 20% of corn pollen containing variable concentrations of neonicotinoids. Colonies located in treated cornfields expressed higher varroa loads and long‐term mortality than those in untreated cornfields. On the other hand, no significant differences were observed regarding the brood production and colony weight.

Honey Bee Survival and Pathogen Prevalence: From the Perspective of Landscape and Exposure to Pesticides

“…Colonies located in AG areas, with potentially higher risk of exposure to pesticides, exhibited significantly higher (F = 41.9, n = 301, p < 0.001) varroa infestation than those of the NAG areas ( Figure 2 ). These data are in agreement with previously published studies testing the effects of exposure to pesticides on varroa loads [ 31 , 32 ]. However, contradictory results were recently obtained while studying the effect of clothianidin-dressed oilseed rape on honey bees, showing no difference in varroa infestation in hives of insecticide treated and untreated fields [ 45 ].…”

“…It however remains challenging while conducted honey bee in situ studies to judge or evaluate each factor individually, as most factors affecting colony health act in complex synergistic manners with variable level implications [ 2 , 27 , 28 , 29 , 30 , 31 ]. Many studies have shown synergetic effects of exposure to pesticides and honey bee pathogens [ 28 , 32 ], in particular varroa mite infestation levels [ 32 ]. Others described positive correlations among pests and pathogens such as varroa, viruses and nosema [ 2 , 33 , 34 ], which clearly reduces the probability of identifying the first factor that triggered the colony decline.…”

The Environmental Risks of neonicotinoid pesticides: a review of the evidence post-2013

“…Because only one study has explicitly measured neonicotinoid concentrations in wildflower pollen it is difficult to judge whether wildflower pollen consistently contains higher or lower concentrations of neonicotinoids than crop pollen. However, when looking at honeybee pollen diets in neonicotinoid-treated agricultural areas outside of the main flowering period of attractive crops, or where flowering crops are unattractive to a specific bee species, neonicotinoid concentrations are generally low, in the region of 0.04-0.40 ng/g from pollen diets comprised of 95.3-100% wildflower pollen (Cutler and Scott-Dupree 2014;Botías et al 2015;Long and Krupke 2016;Alburaki et al 2016). Whilst the highest levels of acute exposure come from pollen diets containing a proportion of crop pollen, because honeybees collect pollen over the whole season, total exposure to neonicotinoids may primarily be determined by concentrations in wildflowers.…”

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

“…Honey bees may also contact insecticides applied to crops both before and during crop bloom. Outside of colonies, honey bees are becoming increasingly exposed to imidacloprid, a systemic, neurotoxic insecticide commonly applied aerially or as soil drenches and seed treatments in agronomic and horticultural crop fields 16,17 . Neonicotinoids at sub-lethal doses were shown to impair the olfactory memory of honey bees and their learning capacity 18,19 .…”