Scientists have another theory about what could be killing off the bees: dementia caused by aluminum poisoning.
A scientific study found high amounts of aluminium contamination in bees at levels that would cause brain damage in humans. Bees rely on their tiny brains to navigate to flowers to collect pollen and nectar to eat.
Researchers from the universities of Keele and Sussex studied the levels of aluminium in pupae – the bag-like form bumblebee larvae take before they emerge as fully grown adults.
The scientists found that the pupae contained levels of between 13 and 200 ppm (parts per million). To put it in context, just 3ppm would be considered as potentially pathological in human brain tissue, reports the Daily Mail.
Previous research has found when bees forage for nectar they do not actively avoid nectar which contains aluminium.
Researchers at University of Sussex collected pupae from colonies of naturally foraging bumblebees and sent them to Keele University where their aluminium content was determined.
Pesticide residues have been seen as one of the most significant causes of a decline in bee numbers.
But the researchers, whose work is published in the journal Public Library of Science One, suggest the possibility that this aluminium is also contributing to the decline.
The Bumblebee Conservation Trust says Bumblebees are mainly under threat because of changes to the countryside in the UK.
'Changes in agricultural techniques have meant that there are far fewer wildflowers in the landscape than there used to be, meaning that many of our bumblebee species are struggling to survive.'