Interaction between Varroa destructor and imidacloprid reduces flight capacity of honeybees

Interaction between Varroa destructor and imidacloprid reduces flight capacity of honeybees

Honey bees exposed to high levels of the parasitic mite Varroa destructor fly shorter distances, with a larger effect when also exposed to the neonicotinoid insecticide imidacloprid.

Current high losses of honeybees seriously threaten pollination of crops. Several factors may cause these losses, such as parasite and disease loads, and exposure to neonicotinoid insecticides, although the relative contribution of these factors is still unknown.
Exposure to the parasitic mite Varroa destructor, and related diseases, is generally seen as one of the important stressors in honeybee colonies. The role of insecticides in causing high colony losses remains highly debated. Recent studies show it is unlikely that field-realistic, sub-lethal doses of neonicotinoid insecticides are the sole cause of colony declines. The question remains to what extent insecticide exposure negatively influences foraging behaviour in combination with other stressors such as V. destructor.

Researchers from Wageningen University and Research Centre tested both the relative and interaction effects of a neonicotinoid insecticide and high V. destructor loads on flight capacity. They used a chronic, sub-lethal dose of the neonicotinoid insecticide imidacloprid to simulate field-realistic insecticide colony exposure. Flight capacity of forager honeybees was assessed in flight mills. The study tested the hypothesis that bees from colonies exposed to imidacloprid or V. destructor will have a lower flight capacity and that this effect will be stronger when honeybees are exposed to both stressors.

The researchers show for the first time that flight distances and flight times reduce for forager bees that were raised in colonies exposed to both high levels of V. destructor mites and a field-realistic, chronic sub-lethal dose of imidacloprid. This effect was more pronounced for the stressor V. destructor. The interaction between the two stressors suggests the possible effect of one stressor on the vulnerability of bees for other stressors: bees weakened by one stressor, here high loads of V. destructor, may be vulnerable to the negative effects of an insecticide. The distance covered is a vital proxy for the flight capacity of honeybees as it integrates speed with endurance.

Increasing our understanding of the relative and interactive effects of V. destructor and neonicotinoid insecticides on flight capacity and the accompanied food-collecting capacity is vital to explain colony collapse and reduced pollination services of honeybees. Reduced flight capacity decreases the food-collecting ability of honeybees and may hamper the use of precocious foraging as a coping mechanism during colony (nutritional) stress. Ineffective coping mechanisms may lead to destructive cascading effects and subsequent colony collapse.

Interaction between Varroa destructor and imidacloprid reduces flight capacity of honeybees. Lisa J. Blanken, Frank van Langevelde and Coby van Dooremalen. Proceedings of the Royal Society B, 282: 20151738. (early online).

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Honeybees with the parasitic mite Varroa destructor (B. Cornelissen, WUR)