June 5 (UPI) -- For the first time, honeybee researchers have identified a "synergistic time-lag interaction" between parasitic Varroa mites and neonicotinoid insecticides. The two stressors, the latest research showed, combined to reduce the survival of honeybees during the winter.
Several studies have firmly established the negative impacts of neonicotinoids on bee health, and Varroa mites are now ubiquitous among honeybee colonies. But studies looking at the effects of the two stressors in combination have produced inconclusive results.
For the new study, scientists exposed parasite-free honeybee colonies to two neonicotinoid insecticides, thiamethoxam and clothianidin, through pollen paste feeding. The mass and longevity of worker bees were unaffected.
However, when scientists exposed colonies infested with the ectoparasitic mite Varroa destructor, they measured a negative synergistic impact on bee health. However, the negative effect was only measured 16 weeks after neonicotinoid exposure.
In temperate regions, bees must survive the winter for colonies to persist. The synergistic time-lag effects of mite infestations and neonicotinoids exposure could explain the prevalence of wintertime colony collapse.
Scientists published the results of their study this week in the journal Scientific Reports.
"Future mitigation efforts should concentrate on developing sustainable agro-ecosystem management schemes that incorporate reduced use of neonicotinoids and sustainable solutions for V. destructor mites," researchers wrote.