Repellency of insecticides and the effect of thiacloprid on bumble bee colony development in red clover (Trifolium pratense L.) seed crops

Abstract

The study intended to compare repellency of three insecticides on bumble bees and honey bees in Norwegian red clover (Trifolium pratense L.) seed crops, and to examine effects of thiacloprid on bumble bee colony development in the field. The repellency study was carried out in a large-scale field trial in SE Norway in 2013. On average for observations during the first week after spraying, 17 and 40 % less honey bees (P=0.03) and 26 and 20 % less bumble bees (P=0.36) were observed on plots sprayed with the pyrethroids lambda-cyhalothrin and alpha-cypermethrin, respectively, than on unsprayed control plots. No pollinator repellency was found on plots sprayed with the neonicotinoid thiacloprid. Compared with unsprayed control the seed yield increases were 22 % on plots sprayed with thiacloprid vs. 12-13 % on plots sprayed with pyrethroids (p=0.10). Follow-up studies in 2014-2016 focused on the effect of thiacloprid on bumble bee colony development in commercially reared nests of Bombus terrestris placed into red clover seed crops at the start of flowering. Unsprayed control crops were compared with crops sprayed either at the bud stage or when 18-44 % of flower heads were in full bloom. Chemical analyses of adult bumble bees showed that thiacloprid was taken up in bees when crops were sprayed during flowering, but not detected when crops were sprayed at the bud stage. The bumble bees in late-sprayed crops also developed weaker colonies than in unsprayed crops. Dead bees with a high internal concentration of thiacloprid were found in one crop sprayed during night at 35% flowering. This shows that thiacloprid is not bee-safe if sprayed after anthesis and that spraying has to be conducted at the bud stage to reduce its contamination of nectar and pollen.

Impacts of Neonicotinoids on the Bumble Bees Bombus terrestris and Bombus impatiens Examined through the Lens of an Adverse Outcome Pathway Framework

“…This finding suggests that bumble bees are unable to detect neonicotinoids in their food source, and do not interpret them as sweet. This information helps explain why several studies have determined that bumble bees do not avoid neonicotinoids when present in a food source (Gels et al 2002;Larson et al 2013;Havstad et al 2019). When these findings are taken together, there is evidence that bumble bees may face some of the same cellular-level impacts as a result of neonicotinoid exposure as honey bees.…”

“…This finding suggests that bumble bees are unable to detect neonicotinoids in their food source, and do not interpret them as sweet. This information helps explain why several studies have determined that bumble bees do not avoid neonicotinoids when present in a food source (Gels et al 2002; Larson et al 2013; Havstad et al 2019).…”

“…One study documented effects on thiacloprid which found effects on whole nest measures (reduced weight) and the presence of reproductives (drones and queens) (Ellis et al 2017). One additional study found that bumble bee colonies placed on thiacloprid-sprayed clover had reduced nest weights (Havstad et al 2019).…”

Sublethal effects of neonicotinoids in bees: a review

“…Dead bees with a high internal concentration of thiacloprid were found in an overnight spray culture with 35% flowering. This shows that thiacloprid is not safe for bees if sprayed after anthesis and that spraying should be performed in the budding phase to reduce nectar and pollen contamination (Havstada et al, 2019). Despite the small number of articles published regarding thiacloprid toxicity in bees, it can be observed that this insecticide alters several characteristics of bees.…”

Acetylcholine and Its Receptors in Honeybees: Involvement in Development and Impairments by Neonicotinoids

“…Therefore, bees need to be protected from exposure to neonicotinoids. Many studies investigated survival after insecticide treatment targeting the cholinergic system [35][36][37][38][39][40][41][42], and numerous studies have examined their effect on brood development by registering colony constitutions of honeybees (e.g., [43][44][45]) or bumblebees (e.g., [46][47][48]). Furthermore, sub-lethal neonicotinoid effects on adult honeybees comprise disturbances of navigation and orientation [49][50][51], walking behavior [52], learning and memory [53,54], foraging behavior [55], and nurse-larva-interactions [56].…”