VIII SIMPOSIO INTERNAZIONALE ICPBR

HAZARDS OF PESTICIDES TO BEES

Bologna, 4-6 Settembre 2002

Metodologie dei test e studi sugli effetti dei pesticidi sulle api

Sub-lethal effects in honeybees: their significance and use in pesticide risk assessment

Helen M. Thompson and Tricia Brobyn

National Bee Unit, Central Science Laboratory, Sand Hutton, York, UK and Pesticides safety Directorate, Mallard House, Kings Pool, 3 Peasholme Green, York, UK. E-mail: h.thompson@csl.gov.uk

There is increasing concern, particularly amongst bee-keepers, that sub-lethal effects may have significant impacts on honeybee colonies. Current assessment of risk to honeybees is based on mortality in laboratory studies and, for more toxic compounds, mortality in semi-field or field studies. The design of studies is the subject of both OECD and EPPO guidelines with emphasis on the mortality of adult bees and confirmation of bees foraging in the crop. There is no guidance on what sub-lethal effects should be recorded and what significance they might have in risk assessment.

A wide variety of sub-lethal effects have been reported in bees following exposure to pesticides, many occurring at doses well below estimated exposure levels following field application at recommended rates. Such effects include developmental and morphogenic effects in larvae and adults, reduced egg laying, failure to re-queen, reduced longevity, reduced foraging, changes in communication of food sources and homing behaviour, alterations in nest-mate recognition resulting in exclusion of returned foragers from the hive and repellency. The effects are dependent on the dose and route of exposure.

To be able to take sub-lethal effects into account in risk assessment the correlation between laboratory observations and effects in semi-field and field studies and longer term consequences of these changes e.g. effects of reduced lifespan on over-wintering survival need to be more fully understood.

Greater attention should be paid to sublethal effects in the laboratory. This is particularly important for compounds which may not otherwise undergo higher tier testing, due to their low acute toxicity or low application rates, but may result in effects at the colony level. Semi-field and field studies should routinely include observations of behaviour and activity levels at the hive entrance, full colony assessments both at the termination of the trial and delayed effects as well as the behaviour of foraging bees as all of these impact on colony development and survival. The longer term consequences of sub-lethal changes in colonies e.g. over-wintering survival, should also be assessed.