The neonicotinoid clothianidin impairs memory processing in honey bees.

Neonicotinoids act as agonists on the nicotinic Acetylcholine receptor (nAChR) in insect brains, an essential molecular component of central brain structures involved in learning and memory formation. Sublethal doses might, therefore, impair neural processes necessary for adaptive experience dependent behaviour and thus reduce the fitness of pollinating insects on the individual and community level. First, the question was addressed whether clothianidin has an aversive taste for honey bees and concluded with both a laboratory and a semi-field experiment that bees are unable to distinguish between control and contaminated sucrose solutions. In the laboratory, proboscis extension response conditioning was performed with forager bees exposed to different concentrations of clothianidin (0.1, 0.3 and 0.8 ng/bee) before learning, after learning during memory consolidation, and just before memory retention. These tests at different timings allowed uncovering an impairment of the consolidation and retrieval of memory due to the exposure to clothianidin. It was concluded that an acute exposure to clothianidin has an adverse effect on memory processing in honey bees.

Honey Bees' Behavior Is Impaired by Chronic Exposure to the Neonicotinoid Thiacloprid in the Field.

The decline of pollinators worldwide is of growing concern and has been related to the use of plant-protecting chemicals. Most studies have focused on three neonicotinoid insecticides (clothianidin, imidacloprid, and thiamethoxam) currently subject to a moratorium in the EU. Here, we focus on thiacloprid, a widely used cyano-substituted neonicotinoid thought to be less toxic to honey bees and of which use has increased in the last years. Honey bees (Apis mellifera carnica) were exposed chronically to thiacloprid in the field for several weeks at a sublethal concentration. Foraging behavior, homing success, navigation performance, and social communication were impaired, and thiacloprid residue levels increased both in the foragers and the nest mates over time. The effects observed in the field were not due to a repellent taste of the substance. For the first time, we present the necessary data for the risk evaluation of thiacloprid taken up chronically by honey bees in field conditions.