Does a herbicide affect honeybee behavior?

FARINA WALTER M.

Ribeirao Preto

Congreso; XI Encontro sobre abelhas; 2015

USP-FAPESP

Glyphosate (GLY) is a broad spectrum herbicide used for weed control. During the evaluation stages for product approval, only lethal effect studies on invertebrates were reported. Sub-lethal damage of GLY to non-target organisms such as insect pollinators has not been evaluated. Honeybee Apis mellifera is the main pollinator in agricultural environments and a well-known model for behavioral research. Moreover, honeybees are also accurate biosensors to determine environmental pollutants and their appetitive behavioral response is a suitable tool to test sub-lethal effects of agrochemicals. With this in mind, we studied the effects of GLY traces on honeybees exposed chronically or acutely to this herbicide. We focused on sensitivity to reward, olfactory conditioning of the proboscis extension response (PER) and foraging related behaviors. Results show that mortality, food uptake and locomotive activity did not differ between treated groups. However, reduced sensitivity to sucrose and learning performance were found for the groups chronically exposed to concentrations of 2.5 and 5.0 mg/L of GLY (values within the range of recommended doses). When olfactory PER conditioning was performed with sucrose reward that contained the same GLY concentrations (i.e. acute exposure), elemental associative learning and short-term memory retention decreased significantly for the treated group. We also performed an experiment in which honeybee homeward trajectories were tracked using harmonic radar technology. Forager honeybees were trained to an artificial feeder, and then captured, fed with sugar solution containing GLY concentrations of 2.5, 5 and 10 mg/L, and then released from a novel site. We found that honeybees that had been fed with solution containing 10 mg/L GLY spent more time performing homeward flights and performed more indirect homing flights. Altogether, these results show that GLY at concentrations used in this study produced sub-lethal effects in honeybees, reducing chemosensory perception and learning abilities. Moreover, since honeybees did not interrupt their foraging activity in GLY-contaminated food sources, successful foragers can become a source of a constant inflow of nectar with GLY traces into the hive, which in turn could have long-term negative consequences on colony survival.Keywords: Apis mellifera, glyphosate, sub-lethal effects, associative learning, sensitivity to reward, navigation.