This study analyzed honey bee colony health in relation to pesticide exposure by monitoring 60 commercial honey bee colonies over one year (2014-2015) across three beekeeping operations. The researchers developed a new method to assess colony health by tracking the fractional change in bee population on each pallet between June 1st (peak population) and October 1st (pre-winter assessment).
Key findings include:
- Negative Correlations: Imidacloprid and cyprodinil were individually negatively correlated with colony health. Groups of chemicals showing negative correlations with colony health include neonicotinoids, neonicotinoids combined with methoxyfenozide, neonicotinoids with organophosphates, neonicotinoids with diflubenzuron, and various fungicide groups.
- Positive Correlations: Tau-fluvalinate and dinotefuran (at very low concentrations) showed a positive correlation, likely due to their effects on Varroa mite control.
- Pesticide Presence: Pesticide residues were largely absent before almond pollination but were widely detected after colonies pollinated almonds, with the mix of pesticides being similar across operations.
- Reproductive Failures: 42 of 60 colonies exhibited symptoms of reproductive failures, and these colonies had a lower survival rate (64%) compared to those without reproductive failures (82%).
- Study Limitations: The study had a limited number of beekeepers (three), which prevented robust statistical significance testing. Variability in Varroa management also precluded analysis of its impact.
The study concludes that increasing amounts of certain pesticide groups are systematically associated with greater declines in honey bee populations, indicating that adverse health effects observed in lab settings also occur in the field under commercial management practices.
