Bee health: impact of co-exposure by colonies to pesticides and infectious agents

The results of the expert assessment indicate that a large number of infectious and parasitic agents affect bee colonies, as well as numerous xenobiotic residues (insecticides, fungicides and acaricides) found in bee-keeping matrices, and a wide range of stress factors to which bees may be exposed both concomitantly and successively. The expert assessment highlights the multi-factorial nature of the causes of bee colony mortality, and emphasises the role of co-exposure to pesticides and infectious agents in determining their collapse.

In this context, the Agency recommends taking action on all of these factors, through the assimilation of good bee-keeping practices and compliance with them, as well as through a general reduction of bee exposure to pesticides. The Agency also emphasises the importance of eventually setting up a unified and well-structured national-level observation network, in order to produce updates on the health status of colonies through the establishment of reference hives. In the frame of discussions to be organised at EU-level, the Agency also recommends devising and integrating additional tests into the procedure for assessing insecticide toxicity, in order to measure the effects of co-exposure to fungicides and acaricides.

Throughout the world, a large number of pollinator species contribute to the survival and evolution of over 80% of all plant species. About 20 000 bee species are part of this group of pollinators, and 850 of them are found in France, including the honey bee, Apis mellifera.

For many years now, a phenomenon resulting in the weakening and mortality of bee colonies has been seen in numerous countries and is responsible for reduced honey production. This bee colony weakening, collapse and mortality, which has been observed in most countries where intensive farming is practised (Europe, the Americas), has been the subject of numerous studies which attempt to understand the mechanism or mechanisms involved.

A better understanding of exposure with concomitant and successive stress factors

In this context, the Agency issued an internal request in 2012 on the issue of co-exposure by bees to stress factors and the interactions between these factors.

In the opinion and report is has published today, the Agency proposes a definition of "normal" bee colony health, as well as health indicators that can be used by bee-keepers, bee health technicians, veterinary practitioners and researchers. This definition is an essential prerequisite to properly evaluating the health of a colony.

Bees are exposed to numerous stress factors which can interact with each other. These include factors of an infectious, chemical, physical, nutritional, bee-keeping, and weather-based nature, among others. A large number of infectious and parasitic agents can affect bee colonies and numerous xenobiotics (mainly insecticides, fungicides and acaricides) have been found in bee-keeping matrices.

Hives are co-exposed to many combinations of factors. In all likelihood, the presence of infectious agents in colonies, and bees' exposure to various types of pesticides with diverse modes of action, cause them to switch from a "normal" state of health to one in which pathologies are expressed that may lead to their collapse through a lowering of the bees' immune defences or of their detoxification mechanisms.

ANSES's recommendations

Although in certain cases bee mortality is caused by just one factor, the Agency's work highlights the often multifactorial nature of the causes of colony mortality and emphasises the significance of co-exposure of bees to pesticides and infectious agents in particular.
These phenomena are even more severe when bees are exposed to several compounds. Certain interactions have already been demonstrated in the scientific literature, and the Agency recommends pursuing research to study other potential interactions.

In general, ANSES notes that despite the acuteness of bee colony weakening phenomena and their now established nature, the deployment of numerous studies supported by various operators over the last several year has not provided a solid diagnosis of colony health on the national level, nor of their co-exposure to infectious and chemical hazards.

Because of this, and while it is not possible to have an effect in the short term on stress factors such as the climate, ANSES emphasises the need to take action on all the factors identified as contributing to colony weakening.

To do this, and to avoid additional stress factors – zootechnical and nutritional factors in particular –, the Agency emphasises the importance of maintaining biodiversity as well as compliance with good bee-keeping practices in order to maintain healthy bees and colonies. It also recommends reducing the use of inputs in agricultural practices in order to lower the overall exposure of bees to plant protection products.

In the framework of discussions to be organised on the European level, the Agency recommends that prior to market authorisation of plant protection products (insecticides in particular), the procedure for assessing the toxicity of these products should incorporate tests for measuring the effects of chronic chemical co-exposure along with certain other compounds, including:

• an anti-Varroa acaricide;
• a fungicide known to inhibit the detoxification mechanisms of bees;
• an insecticide with the same mode of action as the product to be tested and known to be present in bee-keeping matrices, if the plant protection product to test is an insecticide.

Actual implementation of this proposal is subject to a modification of EU regulations, following development of the necessary tests and procedures.

Last, the Agency recommends using quantitative methods in the qualification of hive status with regard to infectious agents, as well as the creation of reference hives, grouped into a network in order to provide the most complete coverage of France possible, and enabling regional guidelines to be established for the various players involved.

This recommendation should enable harmonised guidelines to eventually be drafted in addition to the creation of a well-organised observation network to produce updates on the health status of colonies, their co-exposure to infectious and chemical agents, and their evolution, under the responsibility of a national coordination unit.