Some pesticides can interact to increase their toxicity to honey bees

Farmers are often faced with managing numerous pests. Economic losses caused by these pests may demand simultaneous use of several pesticides to maintain agricultural productivity. In some cases, pesticides with low toxicity can enhance an organism’s susceptibility to more toxic pesticides; this effect is known as potentiation. An example of potentiation involves certain fungicides — compounds used to kill fungi — enhancing the toxicity of insecticides — compounds used to kill insects. Given that both fungicides and insecticides can be used when crops are blooming, pollinating insects not targeted by farmers may be exposed to combinations of these pesticides and may be susceptible to potentiation effects.

In our study, we tested the toxicity of several fungicides and insecticides to honey bees, an important pollinator of many crops. Honey bees were exposed in the laboratory to a single fungicide or insecticide or a fungicide and insecticide in combination. A drop of pesticide solution was applied to individual bees and the lethal effects were recorded over 2 days.

Although no field-relevant test concentrations of individual pesticides caused significant mortality, two combinations of fungicide and insecticide resulted in potentiation: the fungicide propiconazole potentiated the toxicity of the insecticide acetamiprid, and exposure to the fungicide flusilazole potentiated the toxicity of the insecticide spinetoram. Identifying pesticides that pose limited risk to honey bees, both alone and in combination, may help farmers conserve pollination services, while simultaneously controlling pests and diseases.

Read the full paper — Honey bee survival is affected by interactions between field-relevant rates of fungicides and insecticides used in apple and blueberry production by Paul Manning, Krilen Ramanaidu and G. Christopher Cutler on the FACETS website.