Pesticide Mixtures Disrupt Honey Bee Communication and Colony Function

Honey bees are essential pollinators that contribute to the production of many crops and plants. However, they are also facing multiple threats, such as habitat loss, parasites, diseases, and pesticides.

Among these, pesticides are particularly concerning, as they can impair the bees' ability to communicate with each other using chemical signals.

The Role of Smell in Honey Bee Society

(Photo : PHILIP FONG/AFP via Getty Images)

Honey bees live in complex and dynamic communities, where they constantly exchange information using chemicals that serve as social cues.

These chemicals, called pheromones, can convey various messages, such as the need for food, the presence of danger, or the quality of a potential mate.

For example, nurse bees, which are responsible for taking care of the larvae that will become queens or workers, use pheromones to monitor the larvae's development and nutritional needs.

The larvae emit brood pheromones to indicate that they are hungry and need to be fed. Similarly, worker bees produce alarm pheromones to warn their nestmates of an intruder or a predator.

To perceive these pheromones, honey bees rely on their sense of smell, which is mediated by their antennae.

The antennae contain sensory cells that can detect different odors and send electrical signals to the brain. The brain then processes these signals and triggers appropriate behavioral responses.

For instance, when a bee smells the alarm pheromone, it becomes more alert and aggressive, ready to defend the colony.

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The Impact of Pesticides and Adjuvants on Honey Bee Smell

Pesticides are chemicals that are used to control pests, such as insects, fungi, or weeds, that can harm crops or plants.

However, pesticides can also have unintended effects on non-target organisms, such as honey bees.

In particular, pesticides can interfere with the bees' sense of smell, which can disrupt their social signals and affect their colony function.

One of the ways that pesticides can affect the bees' smell is by directly damaging their antennae or their sensory cells.

This can reduce the bees' ability to detect or discriminate between different odors, or alter their sensitivity to certain smells.

For example, a study by researchers at the University of Illinois at Urbana-Champaign found that exposure to a commonly-used insecticide, called Altacor, reduced the bees' response to brood pheromones, which could impair their nursing behavior.

Another way that pesticides can affect the bees' smell is by interacting with other chemicals that are used in combination with them.

These chemicals, called adjuvants, are added to the pesticide formulations to enhance their effectiveness or application. Adjuvants can increase the "stickiness" of the pesticide, so that it stays longer on the plants.

However, adjuvants can also have adverse effects on bees, either alone or in combination with pesticides or fungicides. The same study by the Illinois researchers found that exposure to a commonly-used adjuvant, called Dyne-Amic, reduced the bees' response to alarm pheromones, which could affect their defensive behavior.

The researchers also found that exposure to a mixture of Dyne-Amic, Altacor, and a fungicide, called Tilt, had a synergistic effect, meaning that the combination was more harmful than the sum of its parts.

The mixture reduced the bees' response to both brood and alarm pheromones, as well as to floral odors, which could affect their foraging behavior.

The researchers concluded that these commonly-used pesticides and adjuvants can interfere with honey bee communication by affecting their sense of smell.

They suggested that more studies are needed to understand how these chemicals interact and influence the bees, and to develop safer alternatives that can protect both the crops and the pollinators .

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