Insects and Insecticides

Written evidence submitted by Dr Nigel Raine


1. Defra state they will keep regulation of neonicotinoids under review in light of new evidence on effects of these pesticides to bees as it emerges.

2. Defra’s commitment to update the risk assessment for bees and pesticides by the end of 2012 is highly desirable. This revised risk assessment should include:

i. sublethal effects of pesticide exposure.

ii. exposure to multiple pesticides.

iii. chronic exposure (as well as acute tests).

iv. larval exposure.

v. bumblebees and solitary bees (as well as honeybees).

3. A new study (Gill et al. 2012) provides evidence that field-level exposures of pyrethroid and neonicotinoid pesticides change the behaviour and survival of an important insect pollinator – the bumblebee (Bombus terrestris). All detrimental effects were most severe when colonies were exposed to both pesticides. This suggests the combined effects of pesticides could be more harmful to bees than exposure to single chemicals, something not assessed under the current risk assessment framework.


1. There is widespread interest in the possible impacts exposure to pesticides could be having on bees from a range of stakeholders, including farmers, beekeepers, the public, researchers, pesticide companies, policy makers, etc. Publication of the document ‘Neonicotinoid insecticides and bees: the state of the science and the regulatory response’ in September shows Defra are reacting to new scientific findings as relevant studies are published. They have also committed to continue this watching brief stating that: "As our knowledge develops, we (Defra) will continue to consider the need for further research and for any changes to the regulation of neonicotinoids."

2. At any point in time Defra will be making a decision on the regulatory status of any pesticide with partial evidence (i.e. the body of research and related information available at that time). It is for the committee to judge whether the evidence reviewed by Defra fully supports the conclusions drawn in the September report (pb13818). The proposed course of action "to update the process for assessing the risks of pesticides to bees in the light of developments in the science - including the latest research" seems a reasonable response given the speed with which the evidence base is growing and the importance of neonicotinoids to agriculture. It would be unfortunate if a putative neonicotinoid ban resulted in an increased usage of other pesticide classes which might have worse consequences for bees. However, the speed with which the risk assessment for bees and pesticides is updated is completed should be closely monitored. At present this document states the aim to complete this task by the end of 2012 – it would be highly desirable to see a firmer commitment to completion of this process by a specific date in print.

3. Looking forward a common criticism of the studies reviewed in this report is the lack of field-realism. A recently published study by Gill et al. (2012), investigated whether exposure to two of the most commonly used pesticides on flowering crops in the UK, at field-level concentrations, detrimentally affects bee behaviour and colony survival. This study, unlike any other, directly investigated whether sublethal effects on multiple individuals might be amplified to affect overall colony success. Understanding this is crucial given that the most important insect pollinators, honeybees and bumblebees, are eusocial so colony function relies on the efficient collective behaviours of numerous individuals. Specifically, we studied the effects that exposure to sublethal doses of the pyrethroid lambda-cyhalothrin (LC) and the neonicotinoid Imidacloprid (IMD) had on bumblebee (Bombus terrestris) colonies over a 4-week (chronic) exposure period.

4. Gill et al. (2012) found that whilst IMD had only subtle effects on individual worker foraging behaviour this culminated in a significant reduction in overall colony performance and survival potential. Moreover, simultaneous exposure of colonies to both IMD and LC caused a significant increase in overall worker losses in comparison to independent exposure of each pesticide, and higher levels of colony failure (collapse). These findings are of particular concern given that the methods of exposure used are typical of those bees encounter in the environment in the UK.

5. Previous empirical studies on the effects of pesticides have focused primarily on honeybees which, due to their large colony, size present a challenge when studying colony effects. Consequently, the vast majority of studies to date have investigated single pesticide effects on specific behavioural traits of individuals under relatively artificial scenarios (reviewed in Cresswell 2011). Moreover, many of these studies have looked at an acute period of exposure (i.e. a comparatively high dose over a short period) rather than a more realistic chronic response (low level exposure over a longer time period). Honeybees are important pollinators, but there are also a wide variety of other bee species and other insect pollinators that play a major role in pollinating crops and wild plants. However we know much less about the possible effects of pesticides on insect pollinators other than honeybees.

6. One of the few studies to date on pesticide effects on bumblebees (Whitehorn et al. 2012) recently reported that colony queen production can be affected by IMD exposure (although it was unclear from this work what mechanism underpinned this observed effect). The study by Gill et al. (2012) is highly novel because it reports that chronic exposure to field-realistic levels of two pesticides both produce detrimental effects on individual bee behaviour with knock-on consequences for colony growth, success and survivorship. These results indicate there is a significant need to determine the effects of combined exposure to multiple pesticides during the risk assessment process for use of these chemicals (i.e. the situation bees typically face when foraging in the UK).

7. The Gill et al. (2012) study adds much needed information about the effects pesticides can have on bumblebees.

8. As an active researcher investigating pesticide effects on bees, I am very keen to support and work with the policy/decision making community to make the best decisions with robust evidence bases to allow our farmers to continue to provide food at the same time as allowing our bees to thrive (and continue to provide their vital role as pollinators of crops and wild plants).


Cresswell, J. E. (2011). A meta-analysis of experiments testing the effects of a neonicotinoid insecticide (imidacloprid) on honey bees. Ecotoxicology 20: 149-157.

Gill, R. J., O. Ramos-Rodriguez and N. E. Raine (2012). Combined pesticide exposure severely affects individual- and colony-level traits in bees. Nature 491: 105-108. doi:10.1038/nature11585

Whitehorn, P. R., S. O'Connor, F. L. Wackers and D. Goulson (2012). Neonicotinoid pesticide reduces bumble bee colony growth and queen production. Science 336: 351-352.

2 November 2012

Prepared 19th November 2012