Honey bees at risk from almond-crop fungicides

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Honey bees could be at risk from almond-crop fungicides and use of these fungicides could indirectly affect the productivity of almonds orchards, a new study has shown.

One of the most commonly used fungicide – iprodione – either used alone or in combination with other common fungicides causes a significant reduction in the 10-day survival rate of forager honey bees (Apis mellifera) even if they are exposed at rates common to usage in the field. The findings are startling considering that use of fungicides is a common thing in almond orchards and one of the primary ways for growers to defend their crops from infection.

Texas A&M University scientists and colleagues tested the effects of fungicides on honey bees via a wind-tunnel experiment exposing several groups of honey bees to various dosage levels and combinations of fungicides including iprodine on its own and in combination with boscalid, pyraclostrobin, and azoxytrobin. The bees were then taken to separate habitats and monitored daily over a 10-day period. Findings have been published in Journal of Economic Entomology.

Results indicated a significant increase in mortality rate among honey bees exposed to the fungicides compared to a control group. Bees exposed to the recommended concentration of iprodione died at two to three times the rate of the unexposed bees after 10 days. The effect was even more pronounced when iprodione was combined with the other fungicides. Scientists aren’t still able to point out the exact reasons for fungicides’ negative effect on honey bees.

The almond industry in California alone produces about 80 percent of almonds consumed worldwide, according to the Almond Board of California, and growers rely almost entirely on managed honey bees for pollination.

“Our results may help to encourage discussions on altering spraying regimes or perhaps finding different ways to apply chemicals in such a manner that takes the biology and behavior of pollinators into account,” says Adrian Fisher II, lead author on the study and a doctoral student at Texas A&M.