Dr Dara Stanley of New Holloway, University of London has been looking at the effects of neonicotinoid pesticides on ‘efficiency’ of bumblebee pollination of apples. Several studies have already implicated these pesticides in the decline of foraging behaviour of bees / bumblebees. As some 30% of agricultural crops depend on pollination by bees and bumblebees, hover flies and other arthropods (with an estimated global value in excess of $350 billion / year) then the effects of these pesticides needs to be evaluated, so that informed debate on the banning or restriction of their use can take place.
Dr Stanley and associates exposed some bumblebees to ‘low’ levels of neonicotinoids (such as might be found in wild flowers), others were exposed to no pesticide. It was found that those exposed to neonicotinoids collected less pollen from apple flowers and that their visits to the flowers were less frequent - when compared to those bumblebees exposed to no neonicotinoids.
The flowers that had been visited by the ‘exposed’ bumblebees developed apples that were later harvested; these were found to contain fewer seeds (some 36% less) than those fruits formed from flowers pollinated by the ‘normal’ bumblebees. Thus, the process of pollination (pollen transfer from anthers to stigmas) was less effective when the bumblebees were exposed to neonicotinoids.
These results are important as they indicate that the neonicotinoids can significantly affect the bumblebees’ ability to pollinate important crops - and presumably other plants.
There has also been a report on the effect of the neonicotinoids on butterflies. As neonicotinoids can remain in the environment, they can be absorbed by wild flowers - for example, those around the edges of fields. These plants provide food for caterpillars (munching on the leaves) and nectar for the adult butterflies. Now several species that live on farmland have shown population declines that may be associated with the rising use of the ‘nerve agent’ pesticides - for example, small tortoiseshells, small skippers and wall butterflies.
Neonicotinoids were banned for use on flowering crops by the EU for three years in 2013, but the UK government partially lifted the ban last year for use on oilseed rape in some areas.