Evidence that honey bee associative learning is impaired by glyphosate traces.

HERBERT L; FARINA WM

Buenos Aires

Congreso; 42º Congreso Internacional de Apicultura Apimondia 2011; 2011

Apimondia

Evidence that honey bee associative learning is impaired by glyphosate traces Herbert, L.T.; Arenas, A.; Farina, W.M. Grupo de Estudio de Insectos Sociales, Departamento de Biodiversidad y Biología Experimental, IFIBYNE, CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Buenos Aires, Argentina. Tel: (+5411) 4576 3445. walter@bg.fcen.uba.ar   Glyphosate is a broad spectrum herbicide used for weed control. During the evaluation stages for product approval, only studies of lethal effects on invertebrates were reported. However, the possibility that glyphosate causes sub-lethal damage to insects that forage in agricultural ecosystems cannot be discounted. Honey bees are the main pollinators in agricultural settings and can be taken as sensitive indicators of changes within these ecosystems. Due to the intensive use of glyphosate over the last decades, the potential effects on the principal insect pollinator for cultivated areas need to be considered. The honey bee is a well known experimental model for studying learning and memory processes under carefully controlled experimental conditions. Hence, we approached this issue by studying the putative effects of this agrochemical on the behavior of worker bees reared in the laboratory from emergence to two weeks of age. Laboratory reared bees were exposed to different concentrations of glyphosate (0mg, 2.5mg and 5mg per liter of the offered food; i.e. 50%w/w sucrose solution) during their whole lifespan. The olfactory conditioning of proboscis extension, a procedure in which harnessed bees learn to associate an odor with sugar reward, was performed on bees of 15 days of age. Acquisition curves, memory retention, mortality, solution intake and locomotor activity (LA) were recorded for individuals exposed to the three treatments. Mortality, food uptake and LA did not differ between treated groups, although a tendency towards higher mortality was observed in the bees exposed to the solution contaminated with glyphosate. Olfactory learning was however, impaired by glyphosate traces, showing a significantly lower acquisition for bees exposed to 2.5 and 5mg/L concentrations. In contrast, memory retention at short and long term did not differ between treatments. These results imply that even though glyphosate at concentrations found in nature as a result of standard spraying does not necessarily have a large impact on mortality; it could impair the associative learning between a floral odor and its nectar, which in turn would have negative consequences on foraging for resources by honey bees.