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Bumblebees can be exposed to pesticides or plant protection products directly during the spraying or on utilizing polluted pollen, nectar or other plant secretions. The greatest danger is the spraying of flowering plants particularly with insecticides (for instance pyrethroids) – this should certainly be avoided.  Herbicides also reduce the food resources of bumblebees. 

 

Before pesticides are marketed a risk evaluation for bees is carried out – the creatures to be protected are however generally honeybees. The results are often also transferred to wild bees, i a bumblebees. There are however important differences in the behaviour pattern of the latter. Because the bumblebee colony is only annual, in spring only the young female bumblebees are active. They are just about to create a colony. Thus coming in contact with pesticides at this time can be fatal for the whole future colony. In addition the bumblebee colonies are smaller and so more influenced by the loss of individuals. Unlike honeybees, trophallaxis – sharing eaten and partly digested food with other colony members – is not practiced among bumblebees. Simply put: the toxics in the food brought into the hive by honeybees are diluted, but not among bumblebees. It is often recommended to close the hives for some time to protect honeybees and to spray in early mornings or late in evening. The nests of bumblebees however cannot be closed and they go out collecting even in early morning and late evening.     

 

Pesticides may affect bees, among them also bumblebees, lethally or they may not kill directly but affect behaviour, physiology and vitality. Researchers have found that plant protection preparations influence the division of labour, development and life length, foraging behaviour, discernment of smells, social behaviour, orientation and learning capacities, reproduction, resistance to pathogens etc of bees negatively.

 

As a recommendation it should be stated that chemical pesticides must not be used routinely and simply as prophylaxis; the need of them must previously be ascertained in the field. Plant and biological control methods should rather be preferred and as a first step overall use of different preventive tactics should be employed – rotation of crops, favouring natural enemies of pests and suitable soil cultivation methods.