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Do glyphosate-based herbicides affect honeybees or other beneficial insects?

Category: Environment and Wildlife

Studies show that glyphosate is relatively non-toxic to honeybees. There aren’t many studies conducted using realistic exposure levels in-forest scenarios; however, studies done in the agricultural sector show no significant effects on bees. Honey produced by hives in or near treatment areas has been shown to contain small amounts glyphosate, though in concentrations too low to raise health concerns. Minimal or no effects are typically observed in studies on other “beneficial” insects or spiders.

Adequate laboratory data exist to demonstrate that glyphosate is essentially non-toxic to bees and other beneficial insects. Of the few higher tier studies examining potential effects of glyphosate-based herbicides on honeybees, one showed no significant effects on brood survival, development or mean pupal weight resulting from worst-case exposure scenarios, while two studies demonstrated deleterious effects on learning behaviour and carotenoid antioxidant levels in honeybees. In a study conducted under an agro-forestry scenario, glyphosate residues were observed in pollen and honey collected from hives placed at various distances from treated sites. Maximal levels occurred in pollen from a hive situated within the treated area. Toxicological risks associated with glyphosate in this study were reportedly negligible. Given that commercial apiaries or personal bee-keeping operations are quite unlikely to be located in opeartional forest environments, the potential effects of glyphosate-based herbicides in forestry on honeybees per se is generally not of concern. Of greater ecological interest is the potential effects of treatments on wild bees which might utilize disturbed forest cutover sites as foraging areas. Unfortunately, the differences in area treated, probability, frequency and magnitude of potential exposures as well as potential differences in foraging habits of wild bee species or other pollinators versus those of honeybees, severely limit the utility of agricultural scenarios in terms of estimating risks to these organisms. This is considered an area where further ecotoxicological research may be warranted, although it is likely that results would parallel those of several existing field studies which demonstrate that typically the only significant effect on other beneficial insects in forestry is temporary decline in abundance on treated sites related to changes in vegetative habitat.

Tier 1 laboratory toxicity testing demonstrates that glyphosate is not acutely toxic to bees and other beneficial insects (Giesy et al. 2000; Hassan et al. 1988; PMRA 2015). As cited by Durkin (2003) Palmer and co-workers have investigated the toxicity of glyphosate to bees (Palmer and Beavers 1997c; Palmer and Krueger, 2001a; Palmer and Krueger, 2001b). Based on these data, the U.S. EPA (1993) classified glyphosate as practically non-toxic to bees. Boily et al (2013) conducted studies on various pesticides, including glyphosate, on bees and found that chronic exposure to low-level glyphosate concentrations had no significant effect on bee mortality, weight or protein content, but did result in a significant depression in acetylcholine esterase activity. Ferguson (1988) showed that colonies supplied directly with sucrose solution containing 5% of a formulated glyphosate product had no effect on bee colonies. Burgett and Fisher (1990) conducted a field study in which Honeybee hives and the surrounding blooming vegetation were over sprayed with a formulated glyphosate product at 6.8 Kg a.e./ha and reported no acute or chronic effects for adult honeybees or for brood production. Laberge et al. (2007) reported on a field study conducted in an agro-forestry environment in which hives were placed within or at various distances from treated sites. Detectable residues of glyphosate were observed in approximately 50% of the pollen samples and 3 of 9 honey samples, with maximal residues of 8.2 mg/Kg in pollen sampled 3 days post-treatment from a hive situated directly within the treated area. Based on toxicological risk assessment, the authors concluded that risks associated with glyphosate were negligible. Similarly, Thompson et al. (2014) recently examined the effect of realistic worst-case exposure levels of glyphosate-based herbicide based on residues observed in pollen and nectar following applications at 2.88 Kg a.e./ha. In the exposure study, the maximum residues found in pollen taken from traps in an enclosed greenhouse where bees were allowed to forage on treated plants ranged from 87.2 to 629 mg a.e./Kg, were much higher than maximal residues found in nectar (2.78 -31.3 mg a.e./Kg) with both types of residues declining rapidly with time post-spray. Based on these data, the authors conducted a subsequent effects study in which colonies were exposed directly to three different levels of glyphosate in sucrose solution with the maximum test level being 301 mg a.e./L. The authors reported no significant effects on brood survival, development or mean pupal weight resulting from such exposures. Herbert et al. (2014) conducted studies at levels considered relevant to agricultural use scenarios and observed impaired learning and responsiveness to nectar as a reward, but no effect on foraging-related behavior. These workers postulated that trace glyphosate residues could be transferred to Honeybee broods with potential long-term consequences. Helmer et al. (2014) documented reduced carotenoid antioxidant levels in Honeybees exposed for 10 days to realistic levels glyphosate in sugar solution, but no effect on lipid peroxidation. Overall, results from a number of lab and simulated field studies generally suggest no significant risks of acute or chronic effects of glyphosate on adult Honeybees or brood production. The two studies conducted under agricultural scenarios which suggest potential effects on learning or antioxidant levels may be suggestive of aspects that should be included in potential future higher tier field studies examining glyphosate–based herbicide effects on wild bee species or other pollinators under typical forest use scenarios.

Preston and Trofymow (1989) examined potential effects on arthropod populations in a British Columbia red alder site and observed the only effect to be a temporary reduction in mites on one of the treatment sites at 20 days post-treatment, with no differences at 180 days. Whitehouse and Brown (1993) found no changes in the population of predatory insects following treatment of a clearcut area in Maine at a rate of 1.7 Kg a.e./ha. Brust (1990) reported no significant acute or chronic effects on carabid beetle longevity or on their food consumption and showed no toxic or repellent effects in field studies. However, owing to changes in plant communities large carabids tended to leave glyphosate treated agricultural fields for a period of ~ 28 days. In contrast, Duchesne et al. (1999) reported no change in abundance and that species richness and diversity of carabids increased following glyphosate and other vegetation management treatments in a boreal mixed-wood ecosystem study. Haughton et al (2001) examined the effect of glyphosate on non-target spiders under both laboratory and field conditions and found no significant direct effects and only short-term indirect effects associated with vegetative habitat change. Young et al. (2001) also reported on potential toxic effects of glyphosate on spiders reporting no significant acute effects at exposure rates up to an equivalent of 2.16 Kg/ha, noting that results supported limited data suggesting general lack of effect on non-target arthropods. Santillo (1989) reported an 89% reduction in herbivorous insects captured on herbicide treated clearcuts as compared to controls 1 year post treatment. Evidence of recovery (only 25% difference) was observed in year 3 for herbivorous insects, a 29% difference between treated and untreated sites through 3 years for invertebrates captured by pitfall traps, and no trend in predatory insect numbers. Gagne et al. (1999) observed reductions in arthropod numbers in sites where conifers were released via glyphosate herbicide treatment or via brush saw treatments, as well as in naturally regenerating boreal forest cutovers and attributed the observed differences to natural fluctuations. In this study, the relative abundance of foliar arthropods did not differ between treated and untreated sites two-years post-spray. Overall results suggest no or minimal direct effects on beneficial insects other than transient reductions in herbivorous species which occur in conjunction with changes in preferred habitat.

In April 2015, the PMRA released their latest review of glyphosate and declared that the weight of evidence indicates that glyphosate does not present unacceptable risk to human health. The full PMRA glyphosate review can be found here or please visit here for a summary version of the full PMRA review.



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Burgett, M. and Fisher, G. 1990. A review of the Belizean honey bee industry: Final report prepared at the request of The Belize Honey Producers Federation. Department of Entomology, Oregon State University, Corvallis, Oregon. (as referenced in Monsanto 2014; Backgrounder – glyphosate and Bee Safety).

Laberge L, Legris J, Couture G. Glyphosate residues in pollen and honey after applications in an agro-forest environment. Draft Report Ministere des Ressources naturelles du Quebec, Direction de lenvironement forestier Quebec. 1997.

Helmer SH, Kerbaol A, Aras P, Jumarie C, Boily M. Effects of realistic doses of atrazine, metolachlor, and glyphosate on lipid peroxidation and diet-derived antioxidants in caged honey bees (Apis mellifera). Environmental Science and Pollution Research. 2014.

Young DH, Spiewak SL, Slawecki RA. The effect of the herbicide glyphosate on non-target spiders: Part I. Direct effects on Lepthyphantes tenuis under laboratory conditions. Pest Management Science. 2001; 57(11):1033-6.