The Effects of Pesticides on Bees

21 October 2012
Posted by Ginny Smith.

A paper published in Nature this week suggests that common pesticides may be having a bigger effect on bees than was previously thought. Currently, pesticides are tested on bees, but only for 96 hours, and only ever one pesticide at a time. Richard Gill, from Royal Holloway University and his colleagues argue that this is not enough, as effects may be caused by the combination of pesticides the bees are exposed to, and may take longer to take effect than the current tests allow for.

Honeybee (Apis mellifera) landing on a milk thistle flower (Silybum marianum).The team exposed bumblebee colonies to pesticides for 4 weeks, at levels similar to those found in the field.  The pesticides were put in feeders of sugar syrup or on filter paper in the path of the bee's foraging, but the bee could choose how much contact to make with these. Individual bees were followed by tagging them with micro-chips, and the colony as a whole was also evaluated. The team found that one of the pesticides tested reduced the number of adult bees emerging from pupae, as well as reducing the number that returned after foraging, while the other caused more worker bees to die in the nest. Colonies exposed to both pesticides showed additive effects, and these colonies were the most likely to fail.

Bees are a vital part of our eco-system; they account for 80% of insect pollination, and their numbers are currently in decline. It is important to work out why so we can try to increase these numbers again and sustain both crops and wild plants. This study looked at bumblebees, which live in smaller colonies than the more commonly studied honey bees, so are more susceptible to a fall in worker numbers.

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