Scientific Documents

Bee Mortality and Bee Surveillance in Europe

Question number: EFSA-Q-2009-00801
Adopted: 3 December 2009

Report (4298 KB)


The Agence Francaise de Sécurité Sanitaire des Aliments (AFSSA) set up a consortium of seven European bee disease research institutes in order to answer the European Food Safety Authority (EFSA) call CFP/EFSA/AMU/2008/02 to assess existing surveillance systems, and to collate and analyse existing data and publications related to honey bee colony mortality across Europe. This consortium gathered partners representing the following countries: France, Germany, Italy, Slovenia, Sweden, Switzerland and the United Kingdom. The project was divided into three work packages: (i) a description and critical analysis of surveillance programmes that measured colony loss, (ii) the collection and analysis of the epidemiological datasets on colony losses, (iii) a critical review and selection of relevant literature on the possible causes and risk factors of colony losses.

Description and critical analysis of surveillance programmes
A standardized surveillance network assessment tool (SNAT) was developed to analyse the European colony loss surveillance programmes. Twenty-seven European Ecconomic Area (EEA) countries were selected to be part of the study. Twenty-five SNATs from 24 countries were completed, received and processed. Some Member States completed several SNATs, two countries had no surveillance system in place (Ireland and Portugal) and one country provided no answer (Romania). The SNAT analysis allowed the countries to be classified into four categories: those with (i) a very good level of compliance with the standards of a good operating system (1 system), (ii) an upper intermediate level of compliance (4 systems), (iii) a lower intermediate level of compliance (12 systems) or (iv) a low level of compliance (8 systems).

Eighty percent of the surveillance systems were found to comply with less than 50% of the 40 items covered by the questionnaire. This generally low level of compliance reflects a broad margin for improvement in most of the European surveillance systems considered within the project. Concerning surveillance procedures and protocols, of the 18 systems stating that they have in place active surveillance procedures, only 6 can be considered as valid active systems able to produce representative figures of the true colony loss situation for the countries in question.

It was found that colony loss surveillance systems in Europe are characterised by a variety of the approaches and operational methodologies. Nevertheless, the majority do share common aspects, in particular the weakness of the systems implemented, and the lack of representative data produced.

The project advocates the improvement of the surveillance systems and has produced a set of 20 recommendations, designed to enhance honey bee surveillance systems at the European level.

Collection and analysis of the epidemiological datasets on colony losses

Data from surveillance networks were collected and standardised in order to allow analysis at the European level. The only indicator that appeared to be commonly used was the “global colony loss rate” during the over-wintering period. Therefore, not all aspects of colony losses (such as summer losses) could be addressed through this study. Temporal and geographical analyses showed an important variability in colony losses. However, such trends are difficult to interpret considering the wide variation in the quality of the systems that produce these data.

Nevertheless, the project noted (i) a baseline colony loss rate around 10% each year at the European level and (ii) a higher rate of colony loss in some countries during the years 2003 and 2008.

This analysis clearly highlights an absence of shared epidemiological indicators, collected following common surveillance procedures and based on comparable populations. Trend analysis and mapping suggests some periods of higher colony loss rates, but these findings should not be over interpreted. They serve to illustrate the fact that existing data collection systems are not robust enough for between-country comparisons across Europe, or the analysis of trends at the European level.
Harmonisation of surveillance procedures at a European level should lead to the establishment of a consistent and robust set of epidemiological indicators, calculated following the same rules and protocols in all countries, and produced by comparable active surveillance procedures applied across comparable populations. This recommendation is essential, as this will not only allow accurate comparisons to be drawn between the status of different European countries, and thus facilitate the objective assessment of fluctuating colony losses within Europe. An appropriate tool to monitor colony losses at a European level is important since it will provide National and European decision makers, and also the beekeeping industry, with accurate figures about colony mortality which, in turn could focus control and research activities.

Critical review and selection of relevant literature

The literature review work package provided the opportunity to develop a specific methodology for literature search and analysis. The “priority 1” references selected and reviewed validated the objectivity of the literature search which is expressed through the range and diversity of topics included (none of the topics appeared to be over-represented).

The results of this work regarding risk and causative factors involved in colony losses have to be taken as a “snap shot” of the scientific community’s opinion as they are today; these are “time sensitive”, and evolving due to the amount of ongoing research which is likely to lead to new findings and a better understanding of the factors involved in the coming months or years.

There is a consensus amongst the scientific community that the causes of colony losses in Europe and in the United States are likely to be multifactorial (in the two aspects of this term: combination of factors at one place and different factors involved according to place and period considered). Factors implicated include beekeeping and husbandry practices (feeding, migratory beekeeping, treatments and so forth), environmental factors (climate, biodiversity, etc.), chemical factors (pesticides) or biological agents (Varroa, Nosema, etc.) which together create stress, weaken bees’ defense systems allowing pests and pathogens to kill the colony (e.g. one or several parasites, viruses, etc.).

High concentrations of pesticides have rarely been identified in relation to colony losses (CCD in USA and winter colony losses in Europe) although acute events of pesticide toxicity are well described during the production season (and clearly differentiated from CCD and winter colony losses). However, the questions of possible synergistic effects of various pesticides and the effect of chronic exposure to sublethal doses of pesticides remains, and requires further investigation. Biological agents such as parasites, viruses or bacteria, alone or in combination, have clearly been identified as important factors in colony losses. Nevertheless, there is still a lack of knowledge about the exact mechanisms and/or interactions involved, this must also be addressed. Even though the multifactorial origin of colony losses is well acknowledged, the respective role of each factor as a risk or causative agent is unknown, and no hierarchy of relative threat posed by each one has been established. These matters require further investigation using appropriate epidemiological studies (case control and longitudinal studies).

There are many inconsistencies in the ways in which “colony losses” are defined. Up to 17 different definitions for CCD exist in the literature. This means that reports may not always be referring to the same phenomenon, and this creates confusion when trying to explain the origin of what has been identified in the field. The described pathology is varied, with authors using the same descriptions for different sets of circumstances. A specific study should be undertaken to clearly categorise and quantify the various expressions of colony losses in the field. This study should be closely linked to the strengthening of surveillance systems.

Published: 15 December 2009