Abstract
Volatile compounds are important cues for honey bees (Apis mellifera L.), which they need for their ecology, behaviour and social communication. While in the external environment bees locate food sources by floral scents, inside the hive, the queen mandibular pheromone (QMP) is a key regulator of the colony life and the alarm pheromone, 2-heptanone, mediates the response against intruders and parasites. The widely reported alterations of various behaviours in and outside the hive due to exposure to pesticides could therefore be caused or enhanced by a disturbance of odour perception. In the present study, an influence of neonicotinoid pesticides at field concentrations on the bees’ ability to perceive volatiles is tested at the very periphery of the olfactory system. The antennal responses to apple (Malus domestica L.) flower volatiles were investigated by electroantennography (EAG) and by GC-coupled electroantennographic detection (GC-EAD). The main bioactive molecules benzyl-alcohol, linalool, benzyl acetate, and six other common flower volatiles were presented at different concentrations to the antennae of 108 bees collected in autumn and in the following spring. Bees were sampled from colonies subjected to two different treatments by Imidacloprid or Thiacloprid, both at sublethal concentrations, and from a control group. We investigated short-term and long-term effects of the treatments. The results show: 1) several specific neonicotinoid-induced changes in antennal responses to flower VOCs with effects varying between short- and long-terms although no general trend emerged; 2) season-related differences in VOCs’ perception; 3) short-term symptoms of increased signal degeneration in response to the positive control in the antennae of bees exposed to Thiacloprid and Imidacloprid; 4) a short-term enhanced response to the QMP and to a high concentration of the alarm pheromone in the Thiacloprid-treated bees, which might underlay previously reported enhanced aggression. Together this suggests that volatile-specific alteration of neonicotinoid-exposed bees may contribute to explain various observed behavioural changes.