Pesticide Sprays and Olfactory Disruption in Honey Bee Communication

For a considerable period, the detrimental impact of pesticide sprays on honey bees has been recognized. In a recent study, researchers have unraveled the consequences of such sprays on the sense of smell in bees, potentially disrupting their social signals.

Honeybees inhabit dynamic communities and engage in constant communication using chemical signals that serve as social cues. For instance, nurse bees, responsible for tending to larvae that develop into queens and worker bees, consistently monitor the larvae in darkness using pheromones.

Larvae emit brood pheromones signaling their need for food, and worker bees produce alarm pheromones to warn others of potential dangers. If these chemical cues are weakened or not properly perceived, the colony may struggle to thrive.

Since 2007, honey bees have faced significant challenges, with one of the stressors being insecticides that impact their health. The use of these insecticides, often in combination with other chemicals, can unexpectedly heighten toxicity levels for bees.

For many years, it was assumed that fungicides do not have an adverse impact on insects because they are designed for fungal targets. Surprisingly, in addition to insecticides, fungicides also have an adverse effect on bees, and combining the two can disrupt colony function.”

May Berenbaum, Professor, Entomology, Carl R. Woese Institute for Genomic Biology

For over 10 years, concerns have arisen from almond orchards, the destination for two-thirds of U.S. honey bee colonies annually during the flowering season, pointing to pesticide spray mixtures. The issue primarily revolves around the utilization of allegedly inert substances known as adjuvants, designed to enhance the adhesion of insecticides to plants.

Due to the historical perception of adjuvants as biologically harmless, they have not undergone the same rigorous safety testing as other insecticidal agents.

Recently, researchers have shown that adjuvants alone or when used in combination with fungicides and insecticides are toxic to bees.”

May Berenbaum, Professor, Entomology, Carl R. Woese Institute for Genomic Biology

The combinations pose a particular risk to nurse bees.

The health of the queens is paramount. If healthy queens are not produced, the colony can suffer.”

May Berenbaum, Professor, Entomology, Carl R. Woese Institute for Genomic Biology

In investigating the impact of combinations on nurse bees, the researchers conducted tests on the olfactory system of honey bees using the adjuvant Dyne-Amic, the fungicide Tilt, and the insecticide Altacor.

Bees were divided into four groups of ten, and for a week, they were exposed to either untreated commercial pollen or pollen treated with Dyne-Amic, Tilt, and Altacor, or all three combined.

Afterward, the bees were anesthetized on ice, and one antenna was meticulously removed from each bee. The researchers then exposed the antennae to chemical mimics of brood and alarm pheromones, recording the antennal response through electroantennography.

Through this method, Ling-Hsiu Liao, a Research Scientist, and Wen-Yen Wu, a Graduate Student in the Berenbaum lab, discovered that when nurse bees consumed pollen contaminated with the three chemicals, their antennal responses to certain brood and alarm pheromones were altered. This finding suggests that commonly-used pesticides may disrupt honey bee communication.

The manner in which these chemicals interact and impact the bees remains unclear.

Liao stated, “There are many possible explanations for how consuming these chemicals can affect the sensory responses of bees. The antenna detects and triggers the response to olfactory signals. In this study, we did not look at what other changes are triggered, particularly changes in behavior.”

Apart from elucidating the molecular pathways affected, the researchers are keen on examining various combinations of frequently employed pesticides and exploring how bees in different populations respond. Their goal is for this research to prompt beekeepers to reconsider their approaches to managing and safeguarding their colonies.