Possible causes of pollinator declines
There are a number of pressures on pollinator populations, but there is a lack of information about their relative importance or to what extent they have led to the declines we are now seeing. Possible causes include the following:
- The loss of basic habitat requirements in our landscapes such as floral resources other than flowering crops that provide food to pollinators. Flowering crops are usually in bloom for only a fraction of a pollinator's life cycle, so in order to survive and reproduce effectively they need alternative sources of nectar and pollen throughout their active season. The loss of other basic needs such as nesting sites and materials may also contribute to the problem.
- The simplification of the landscape with the promotion of monocultural crops, larger fields and less traditional features such as hedgerows, set-aside land and wildflower rich grassland. This results in less of the food and nesting resources occuring in landscapes and the isolation of resource-rich semi-natural habitats..
- The intensive use of agro-chemicals including pesticides that may have a direct affect on insect pollinators, and herbicides that remove important floral resources.
- Pests and diseases affecting domesticated pollinators such as honey bees and which may spread to wild populations.
- Over-reliance on domesticated honey bees for pollination which may compete with wild pollinators for scarce resources.
Research into these pressures has typically focussed on a single cause, but in reality they may interact with each other. For example, a lack of floral resources occuring in the countryside due to intensive farming may lead to nutritional stress in insect pollinators which in turn can make them more vulnerable to attack from pests and diseases or to the effects of pesticides. There is therefore a need for research to identify the underlying causes of pollinator declines and the interactions between them, and this is one of the broad aims of the work funded by the UK Insect Pollinator Intiative.
For further information see:
Goulson, D. et al. 2008. Decline and conservation of bumble bees. Annual Review of Entomology 53: 191-208
Potts, S.G. et al. 2010. Declines of managed honeybees and beekeepers in Europe? Journal of Apicultural. Research 49: 15–22