Around the world, species of many important pollinators are suffering unprecedented declines. Bee populations have been hit especially hard; in the United States and Europe the decline of a number of bee species is causing major concern.

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Recently, a number of studies have linked the phenomenon with the use of certain agricultural pesticides. Earlier this year, two studies published in the journal Science showed common agricultural pesticides interfere with bees’ ability to navigate and reduce the amount of queen bees produced in a colony, suggesting their use may have an part to play in colony collapse disorder, wherein worker bees abruptly disappear from a hive or colony. Although the agchem industry has claimed that loss of habitat and disease are principally responsible for the bee declines, national governments, including those of France and Italy, have reacted by introducing strict controls on the pesticides concerned and launching their own investigations.

The release of the first brace of Science studies in May coincided with an announcement from researchers at Reading University, who suggested bees, the most significant insect pollinators, are worth more to the UK and wider EU than had previously been assumed. The revelation led environmental organisation Friends of the Earth to call for a government investigation into the findings and a temporary suspension of neonicotinoid pesticides implicated in bee decline. As yet, the government has declined to be drawn into the debate.

On Sunday (21st October) researchers from Royal Holloway University in London, also published a study which showed exposure to a combination of pesticides is more harmful to bees than exposure to either chemical on its own. This scenario is thought to be relatively common, which led the scientists to conclude current risk assessments for agricultural chemicals are inadequate.

This year EU risk assessments have come under fire from German researchers for their failure to protect certain animals, including bats, and from the EU’s own health and safety watchdog, which suggested testing is flawed and current methods are not rigorous enough.  

Royal Holloway study

Dr Nigel Raine, of Royal Holloway University said, "We are looking at the effects of multiple pesticides, not just neonicotinoids, but also pyrethroids, which is the sort of situation that bees are faced with in the field, they visit multiple crop species which may have different pesticides applied to them."

Over four weeks, bees were housed in colonies in a laboratory in London and exposed to low levels of pesticides, intended to mimic levels of exposure in the countryside; they were allowed access to the outdoors and their foraging was monitored by scientists. Bees were monitored through radio tagging.

Bees exposed to chemicals were only half as successful as a control group and the number of bees found dead or failing to return after leaving the hive was twice as high. Dr Raine added, "What we found is that this chronic exposure to low levels of pesticide is affecting the behaviour of individual bees and therefore the performance of colonies."

The researchers found that bees exposed to both neonicotinoids and pyrethroids performed worst. Bees exposed to neonicotinoids sent out more foragers, but these performed poorly, gathering less pollen. This is in line with the worrying findings made by other studies earlier in the year.

The Holloway team said that their study exposed an integral flaw in pesticide risk assessment, as many more than the two studied varieties of chemical are used in the field and current testing focuses on lethal doses of a single chemical, rather than the cumulative effects of many or the potential for pesticides to adversely affect bees without killing them outright, potentially leaving them open to infection and other threats.

The team summarised their report that, "Chronic exposure of bumblebees to neonicotinoid and pyrethroid [pesticides] at concentrations that could approximate field-level exposure impairs natural foraging behaviour and increases worker mortality" and suggested their research showed "that combinatorial exposure to pesticides increases the propensity of colonies to fail." They have called for further research to be conducted into the phenomenon.

It is estimated that bees pollinate a third of the world’s agricultural crops. The insects are thought to be responsible for 80 per cent of insect pollination around the world.

In response to the growing weight of evidence accumulating in Europe, a coalition of scientists have set up the STEP (Status and Trends of European Pollinators) initiative and pressure has been mounting from both the European Parliament and Commission to investigate and address the potential problems.

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