Assessment of Chronic Sublethal Effects of Imidacloprid on Honey Bee Colony Health

Abstract

Here we present results of a three-year study to determine the fate of imidacloprid residues in hive matrices and to assess chronic sublethal effects on whole honey bee colonies fed supplemental pollen diet containing imidacloprid at 5, 20 and 100 μg/kg over multiple brood cycles. Various endpoints of colony performance and foraging behavior were measured during and after exposure, including winter survival. Imidacloprid residues became diluted or non-detectable within colonies due to the processing of beebread and honey and the rapid metabolism of the chemical. Imidacloprid exposure doses up to 100 μg/kg had no significant effects on foraging activity or other colony performance indicators during and shortly after exposure. Diseases and pest species did not affect colony health but infestations of Varroa mites were significantly higher in exposed colonies. Honey stores indicated that exposed colonies may have avoided the contaminated food. Imidacloprid dose effects was delayed later in the summer, when colonies exposed to 20 and 100 μg/kg experienced higher rates of queen failure and broodless periods, which led to weaker colonies going into the winter. Pooled over two years, winter survival of colonies averaged 85.7, 72.4, 61.2 and 59.2% in the control, 5, 20 and 100 μg/kg treatment groups, respectively. Analysis of colony survival data showed a significant dose effect, and all contrast tests comparing survival between control and treatment groups were significant, except for colonies exposed to 5 μg/kg. Given the weight of evidence, chronic exposure to imidacloprid at the higher range of field doses (20 to 100 μg/kg) in pollen of certain treated crops could cause negative impacts on honey bee colony health and reduced overwintering success, but the most likely encountered high range of field doses relevant for seed-treated crops (5 μg/kg) had negligible effects on colony health and are unlikely a sole cause of colony declines.

Weight of evidence evaluation of a network of adverse outcome pathways linking activation of the nicotinic acetylcholine receptor in honey bees to colony death

“…Although numerous studies report effects of neonicotinoids on foraging behavior in bees, some contradictory evidence following exposure to the neonicotinoids also has been reported (Dively et al, 2015;Franklin et al, 2004;Pilling et al, 2013). Some of these studies examined the effects on foraging after exposure to seed-treated crops; however, Dively et al (2015) fed 10 replicate colonies 0, 2, 20, or 100 μg/kg imidacloprid over a 12-week period, reporting no adverse effects on foraging activity as measured by the number of foragers returning to the hive or the number of animals loaded with pollen pellets.…”

“…Some of these studies examined the effects on foraging after exposure to seed-treated crops; however, Dively et al (2015) fed 10 replicate colonies 0, 2, 20, or 100 μg/kg imidacloprid over a 12-week period, reporting no adverse effects on foraging activity as measured by the number of foragers returning to the hive or the number of animals loaded with pollen pellets. Nevertheless, this study noted a 12% decrease in foraging activity compared to control during late August and early September, observations collected after the pesticide exposure period (Dively et al, 2015).…”

Enfraquecimento e perda de colônias de abelhas no Brasil: há casos de CCD?

“…Vários estudos têm mostrado que uma ampla gama de agrotóxicos pode ser encontrada nas colônias e que estes compostos podem interagir com agentes patogênicos (Pettis et al 2013). Efeitos de inseticidas sobre as rainhas foram documentados, mas o efeito em toda a colônia muitas vezes não é observado de forma significativa (Sandrock et al, 2014;Dively et al, 2015). Outros estudos de campo foram realizados, mas os resultados ainda são controversos (Pilling et al, 2013;Cutler et al, 2014;Rundlöf et al, 2015).…”

“…Em estudos de campo, realizados com tiametoxam por Pilling et al (2013) e com clotianidina por Cutler et al (2014), ambos no tratamento de sementes e com as doses recomendadas, nenhum efeito adverso foi observado sobre as abelhas campeiras. No entanto, Dively et al (2015) encontraram alterações significativas na taxa de sobrevivência das abelhas expostas às doses de 20 e 100 µg kg -1 de imidacloprido, em comparação ao grupo-controle, durante três anos. Porém, a dose de 5 µg kg -1 -dose residual encontrada nas matrizes vegetais, como pólen e néctar em girassol (Schmuck et al, 2001), e em coletas em diferentes culturas (Bonmatin et al, 2003) -, não causou alterações de comportamento de forrageamento e da taxa de sobrevivência.…”

Bee studies stir up pesticide debate

“…In March, Goulson reanalysed 3 data from a 2013 study by the UK Food and Environment Research Agency (see go.nature.com/w9jlti), which had concluded that neonicotinoid pesticides do not harm bees: Goulson found that they do. In the same month, work from the United States found 4 that the probable harm from exposure to imidacloprid in seed-treated crops was "negligible" in honeybees, and last year a study 5 done in Canada reached a similar conclusion for clothianidin on oilseed rape.…”