Honey bees love oilseed rape flowers, but don’t get on well with the pesticides commonly used to protect the crop (Image: Nigel Cattlin/Visuals Unlimited/Getty)

If they eat the wrong thing, bees cannot find their way home. Two new studies confirm that a group of widely used pesticides subtly affect the insects’ behaviour, and may be partly to blame for their falling populations.

Neonicotinoid pesticides are used around the world to protect major crops like oilseed rape (canola). But studies have suggested that they are harmful to bees – they make them more susceptible to gut parasites, for example.

In field tests of 75 colonies of buff-tailed bumblebees (Bombus terrestris), David Goulson at the University of Stirling, UK, and colleagues found that food treated with realistic levels of one neonicotinoid, called imidacloprid, dramatically slows their spring population growth.


Dosed colonies also produced 85 per cent fewer queens than control colonies – a major problem as only the new queens survive the winter to found new colonies the following year.

Navigation failure

A second study offers a possible explanation. Mickaël Henry of the National Institute for Agricultural Research in Avignon, France, and colleagues fed low levels of another neonicotinoid, thiamethoxam, to colonies of European honey bees Apis mellifera.

Dosed bees were less likely to return to their hives after foraging, suggesting that the pesticide impaired their ability to navigate.

The findings will add weight to calls for neonicotinoids to be banned, or more strictly regulated. Germany, France and Slovenia already have strict limits on their use, and US beekeepers recently petitioned the Environmental Protection Agency to ban another neonicotinoid, clothianidin.

Goulson says the most important thing is to improve the testing of new insecticides. The tests are typically done in the lab and focus on whether the insecticide kills desirable insects like bees, but cannot detect subtle effects on navigation – effects that can be critical in the wild.

Journal references: Goulson et al: Science, DOI: 10.1126/science.1215025; Henry et al: Science, DOI: 10.1126/science.1215039