Neonics

During the last decade, some European beekeepers have reported heavy losses of honey bee colonies located near crops treated with the neonicotinoid imidacloprid (Rortais et al., 2005). Although Bonmatin et al. (2005) and Chauzat et al. (2006) found low ppb levels of the imidacloprid in a high percentage of pollen samples collected from maize, sunflower and canola, when pesticide residues from all matrices were pooled together, analysis did not show a significant relationship between the presence of pesticide residues and the abundance of brood and adults, and no statistical relationship was found between colony mortality and pesticide residues (Chauzat et al., 2009).

GMOs

Numerous studies have been conducted to determine the impact of GE crops on honey bees. Canadian scientists found no evidence that Bt sweet corn affected honey bee mortality (Bailey et al., 2005). Studies conducted in France found that feeding Cry1ab protein in syrup did not affect honey bee colonies (Ramirez-Romero et al., 2005).  There is no evidence that the switch to Bt crops has injured honey bee colonies in the USA. To the contrary, it has benefited beekeeping by reducing the frequency of pesticide applications on crops protected by Bt, especially corn and cotton.  

Natural pesticides

Natural product based varroacides have come into widespread use as synthetic pesticides have dwindled in effectiveness. Thymol and menthol, monoterpenoid constituents of plant-derived essential oils, are used for control of Varroa and tracheal mites, respectively. Thymol is the chief constituents in the fumigants Apilife Var_ (tablets) and Apiguard_ (gel), both of which are registered under Section 3. Essential oil-based varroacides were exempted from extensive testing for EPA registration because they are common food additives and “generally recognized as safe” for human consumption (Quarles, 1996).

However, monoterpenoids such as thymol and menthol may not necessarily be safe for honey bees, since these compounds play a role in plants as broad spectrum pesticides (Isman, 2006). Indeed, thymol and menthol were found to be among the most toxic of all terpenoids tested when applied to honey bees as a fumigant. Despite being naturally derived, these compounds may harm honey bees: thymol treatment can induce brood removal (Marchetti and Barbattini, 1984; Floris et al., 2004) and may result in increased queen mortality (Whittington et al., 2000).

SOURCE:
Pesticides and honey bee toxicity – USA
Reed M. Johnson, Marion D. Ellis, Christopher A. Mullin, Maryann Frazier
Apidologie 41 (2010) 312–331
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