The challenges of predicting pesticide exposure of honey bees at landscape level

Abstract

To evaluate the risks of pesticides for pollinators, we must not only evaluate their toxicity but also understand how pollinators are exposed to these xenobiotics in the field. We focused on this last point and modeled honey bee exposure to pesticides at the landscape level. Pollen pellet samples (n = 60) from 40 Belgian apiaries were collected from late July to October 2011 and underwent palynological and pesticide residue analyses. Areas of various crops around each apiary were measured at 4 spatial scales. The most frequently detected pesticides were the fungicides boscalid (n = 19, 31.7%) and pyrimethanil (n = 10, 16.7%) and the insecticide dimethoate (n = 10, 16.7%). We were able to predict exposure probability for boscalid and dimethoate by using broad indicators of cropping intensity, but it remained difficult to identify the precise source of contamination (e.g. specific crops in which the use of the pesticide is authorized). For pyrimethanil, we were not able to build any convincing landscape model that could explain the contamination. Our results, combined with the late sampling period, strongly suggest that pesticides applied to crops unattractive to pollinators, and therefore considered of no risk for them, may be sources of exposure through weeds, drift to neighboring plants, or succeeding crops.Pollinators like bees cover very large areas every day, visiting numerous plants for nectar, pollen, or gum collection and water sources. So doing, they also unintentionally collect airborne particles or substances diluted in the air. This has lead to using honey bees, a species often used as a model, and beekeeping products as biological indicators for environmental monitoring [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] . Monitoring of exposure to various environmental contaminants has already been carried out; these contaminants include heavy metals 2,5,14,15,17 , pesticides 3, 4, 11-13 , polycyclic aromatic hydrocarbons 6, 7, 9, 10, 18 and radioactivity 16 . Unfortunately, it is often not possible to identify the specific sources of contamination.The exposure of honey bees to pesticides has been linked to increased probability of colony disorders and losses [19][20][21] , alone or in combination with other stress-creating factors like poor nutrition or pathogen and parasite loads [22][23][24] . For this reason, it is crucial to understand the possible exposure pathways of honey bees to pesticides once they are released in the environment. Pesticide risk assessment is not just about the evaluation of the toxicity of the products. Ideally, we should also be able to accurately estimate how living organisms will be exposed to these products in the environment.Efforts to model the exposure of bees to pesticides have been carried out recently for risk assessment purposes. Some models aim to estimate direct contact exposure for spray applications 25 , while others have focused on contact exposure through dust 26 or on estimating pesticide intake [27][28][29] . Several routes of exposure are t...

Why are monarch butterflies declining in the West? Understanding the importance of multiple correlated drivers

“…For example, both insect behavior (Stoner ) and chemical persistence and movement (Simon‐Delso et al. ) contribute to pesticide exposure risk. Even if the data existed (and they do not, at least not for our 1981–2016 study period), a simple overlay of pesticide use with habitat use would not determine exposure per se.…”

Risk of potential pesticide use to honeybee and bumblebee survival and distribution: A country‐wide analysis for The Netherlands

“…We assumed that bees only forage on parcels containing bee attracting crops (Appendix ). However, a recent study found a risk of exposure to pesticides through weeds present in crops unattractive to bees (Simon‐Delso, San Martin, Bruneau, Delcourt, & Hautier, ), suggesting that these exposure routes should be incorporated in future studies. Furthermore, all flowering crops were assumed equal (e.g., same size, nutritional value), crop attractiveness was assumed to be binary (either attractive or non‐attractive for bees), the varying routes of exposure ignored (the median lethal dosages by contact were used to calculate the hazard quotients), the toxicity of active ingredient combinations was assumed to be additive and the food intake rate of honeybees and bumblebees were assumed to be equal.…”

Effects of chronic dietary thiamethoxam and prothioconazole exposure on Apis mellifera worker adults and brood

“…THI is commonly found in association with fungicides, especially in pollen, including the systemic fungicide prothioconazole (PRO) . Mean PRO residues in bee pollen were reported at 182.9 μg kg –1 .…”

“…7,13 THI is commonly found in association with fungicides, especially in pollen, 5,6 including the systemic fungicide prothioconazole (PRO). 14 Mean PRO residues in bee pollen were reported at 182.9 μg kg -1 . 15 Fungicide residues within the hive have been correlated to colony dysfunction.…”