Pesticide exposure predicts honey bee deaths

Madeline Pfeifer
Science & Tech Correspondent

Pesticide exposome predictive of honey bee deaths

Honey bee colonies have been diminishing at alarming rates in the U. S. This is of particular concern, considering that bees provide irreplaceable pollinating services, and are valued at over $200 billion worldwide. The impact of agricultural pesticides on colony deaths has been previously studied.

Up until this study, performed by a team at The University of Maryland, research was directed primarily toward understanding the effects of individual pesticides. This study, though, aimed to evaluate the effects of multiple pesticides that accumulate within bee colonies over a given period of time.

This investigation integrated a concept that is utilized in human cancer research, the exposome. The exposome of an organism encompasses all environmental exposures within that individual’s lifetime. Pesticide levels were monitored to determine the pesticide exposome of each bee colony. Each colony was evaluated as a superorganism, since it functions as a cohesive unit.

The researchers tracked 91 honeybee colonies for an agricultural season, between March and January. The bees traveled up the east coast to pollinate crops, and the colonies were assessed at each location. Bees, beebread and wax were collected at each inspection site and analyzed.

The total number of pesticides, the total number of relevant pesticides, and a Hazard Quotient (HQ) were calculated. An HQ estimates the total hazard posed to the colony due to the toxicity of the pesticides present.
Ninety-three different pesticides compounds were identified in the collected samples. The team found that the total number of pesticide products found in wax was higher in colonies that had perished than in those that had survived.

The researchers also discovered that increased HQ scores correlated with increased rates of queen replacement. The queen bees play an imperative role in the colony’s survival, so the researchers deemed it crucial to track the deaths of the queens.
Possibly the most notable finding of this study involved fungicides. The team found elevated levels of fungicides in individual hives. These increased levels were associated with colony deaths, despite the previously established notion that fungicides are relatively safe for bees.

Unexpectedly, the team did not note any significant contribution from neonicotinoid pesticides. The widespread usage of neonicotinoids has been largely critiqued due their apparent linkage to bee mortality. The lack of neonicotinoid presence may be because the team did not analyze the appropriate matrix, like the nectar. Still, the team suggests that the number of separate pesticides that bees are exposed to, not the dose, is predictive of colony death. This refutes the primary idea of toxicology, that the dose makes the poison.
Developing a plan that minimizes the amount of pesticide products that honey bees are exposed to, while still benefiting farmers, is a complicated work in progress. By outlining which environments are particularly threatening for honey bees, the findings of this study can provide helpful insights for farmers so that this concerning problem may be resolved.

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