Spraying in Almond Orchards May Kill Pollinator Bees

An almond orchard in full bloom. Scientists say spraying fungicides during bloom – when honey bees are pollinating the future crop – is killing the bees, which are farmers’ sole means of pollination.

(CN) – Without honey bees, almond farmers would have no crop. But scientists have discovered that fungicides commonly used in almond orchards are putting their main pollinators in extreme danger.

In a new study published in the Journal of Economic Entomology, researchers from the U.S. Department of Agriculture and Texas A&M University analyze the threat the fungicide iprodione poses to honey bees.

Whether used alone or in combination with other common fungicides, iprodione leads to a significant reduction in the 10-day survival rate of forager honey bees when they are exposed at standard field usage levels, according to the team’s findings.

“Given that these fungicides may be applied when honey bees are present in almond orchards, our findings suggest that bees may face significant danger from chemical applications even when responsibly applied,” said co-author Juliana Rangel of Texas A&M.

The researchers tested the effects of fungicides on honey bees through a wind-tunnel experiment, in which groups of bees were exposed to various dosage levels and combinations of the chemicals. The fungicides were sprayed and carried through the wind tunnels at speeds that simulated aerial crop dusting, after which the bees were taken to separate habitats and monitored daily over a 10-day period.

Different combinations of fungicides – which included boscalid, pyraclostrobin and azoxytrobin – along with iprodione on its own, were tested in trials that were repeated three times in September, October and November 2015.

The results show a significant increase in the mortality rate of honey bees exposed to the fungicides. In two of the three trials, 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 the honey bees were exposed to a combination of fungicides.

While the exact reasons why fungicides negatively affect honey bees are largely unknown, the team notes previous research has shown that some of these chemicals have a heightened potential to persist in residual amounts in beeswax in hives.

California’s almond industry produces roughly 80 percent of almonds consumed worldwide, according to the Almond Board of California, and growers rely almost exclusively 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,” said Adrian Fisher II, lead author of the study and a doctoral student in Rangel’s lab at Texas A&M.

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