EU food safety watchdog EFSA has comprehensively discredited a study into the effects of neonicotinoid pesticides on bee colonies, produced by the UK government to support its stance on the neonicotinoid issue.

The study played a central role in Defra's appeals to the departments of other member states to delay a decision on tightening pesticide regulations, which in the event was taken by the European Commission last month. Defra ministers had urged their European counterparts not to commit to restrictions on the deeply controversial pesticides until the study was published.

Background to the study

In January, an EFSA review of evidence on three commonly used neonicotinoid pesticides, launched by the Commission in response to studies published in the journal Science, found that the pesticides pose a risk to bee health. EFSA urged European decision-makers to introduce a partial ban on preparations containing the three neonicotinoids evaluated (thiamethoxam, clothianidin and imidacloprid), including banning their use on crops attractive to bees.

Manufacturers of the chemicals still insist that, when used correctly, their products do not threaten bee health; they maintain that habitat loss and disease present the greatest threat to bees, populations of which are declining around the world.

Siding with industry, the UK government rejected calls to restrict use of neonicotinoids in January. The government said that it would not support such a ban until a definite link between use of the chemicals and impacts on bees had been demonstrated in field testing; opponents were heavily critical of this stance, arguing that it flew in the face of the precautionary principal, which forms the basis of risk assessment policy and is legally binding in the EU.

Even so, Defra commissioned agency Food and Environment Research Agency (FERA) to conduct a field experiment examining the effects of neonicotinoid exposure on be colonies. The study's findings were inconclusive, though the authors suggested no ill-effects were observed.

EFSA evaluation reveals 'weaknesses' in FERA study

Delivering its evaluation of the FERA investigation on Tuesday (4th June), EFSA announced that it had "identified several weaknesses in [the] study" and declared that, "Given these weaknesses, the Authority considers that the study does not affect the conclusions reached by EFSA regarding risks for bees related to the use of the neonicotinoid pesticides."

EFSA criticised the scope of the FERA study (which only examined one crop – oilseed rape – and two of the three named neonicotinoids). The study also failed to investigate two important routes of pesticide exposure to bees (through dust and guttation).

In a damning evaluation of FERA's study, EFSA experts highlighted "a number of deficiencies" in the report, including:

• Inconsistencies and contradictory statements regarding the objectives of the study.
• Absence of suitable control bee colonies – FERA's control bees were found to have been exposed to thiamethoxam, a neonicotinoid that was not being tested in the experiment.
• The use of bumblebees in tests, when previous research had focused on honeybees, an entirely different species of insect.
• Environmental conditions were varied across the three the test sites, which reduced the sensitivity of the study in detecting effects on colonies.
• Finally, EFSA raised concerns about the conclusions the authors made based on their results.

The FERA study, which has not been peer-reviewed, is no longer accessible on the Defra website.