Honeybees do not spend most of their time feeding on crop plants such as corn and soybean even when they live in agricultural regions, a new study has shown.

The insects still get most of their pollen from trees, flowering weeds and gardens, which could explain why pesticide exposure of bees is more widespread and varied than previously thought.

In a new study published in the journal Nature Communications on May 31, Purdue University researchers Christian Krupke and Elizabeth Long tracked the pollen sources and pesticide levels of Indiana honeybees over a period of 16 weeks.

Samples taken from the hives revealed that the bees foraged from 30 plant families. The researchers also found that the pollen samples contained residues of pesticides from nine chemical classes, which include neonicotinoids, a new type of insecticide commonly used as corn and soybean seed treatment.

Studies have found evidence that the use of neonicotinoids is behind the widespread decline of honeybee populations. The European Union and other countries have already banned some neonicotinoids following results of studies that link the use of these chemicals to colony collapse disorder (CCD), which has been plaguing bees since 2006.

The insecticide pyrethroids, which are often used by households to control mosquitoes and other pests, however, were found to have the highest concentration in samples of bee pollen.

Because pyrethroids are often used near homes and gardens with flowering plants where the insects are likely to go to, bees tend to be exposed to these chemicals more frequently.

The researchers observed a distinct increase in pyrethroids levels in August and September, when the chemicals are typically sprayed to get rid of mosquitoes, hornets and other pests.

"Pesticides used in agricultural production, although important, were not the contaminants that posed the highest risks in honey bee-collected pollen," the researchers wrote in their study.

"Rather the pyrethroids phenothrin and prallethrin, used mainly as dusts or sprays to manage mosquitoes, fleas and ticks, stood out as posing exceptionally high risks to honey bees throughout the sampling period and across all sites."

The researchers noted that while crop pollen was found to be a minor part of the samples they collected, the bees in the study were exposed to a wider range of chemicals than expected, suggesting that agricultural chemicals are just part of the problem and that homeowners are important contributors regardless that the bees live near crop fields.

"If you care about bees as a homeowner, only use insecticides when you really need to because bees will come into contact with them," Long said.

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