Insects 2021, 12, 536. https://doi.org/10.3390/insects12060536 www.mdpi.com/journal/insects
Using Citizen Science to Scout Honey Bee Colonies that
Naturally Survive Varroa destructor Infestations
Arrigo Moro 1,*, Alexis Beaurepaire 1, Raffaele Dall’Olio 2, Steve Rogenstein 3, Tjeerd Blacquière 4, Bjørn Dahle 5,6,
Joachim R. de Miranda 7, Vincent Dietemann 8,9, Barbara Locke 7, Rosa María Licón Luna 10, Yves Le Conte 11 and
Peter Neumann 1
1 Institute of Bee Health, Vetsuisse Faculty, University of Bern, 3003 Bern, Switzerland;
email@example.com (A.B.); firstname.lastname@example.org (P.N.)
2 BeeSources, 40132 Bologna, Italy; email@example.com
3 The Ambeessadors, 10439 Berlin, Germany; firstname.lastname@example.org
4 Wageningen Plant Research, Wageningen University & Research, 6708 PB 1 Wageningen & Blacqbee, 141
RK 18 Aalsmeer, The Netherlands; email@example.com
5 Norwegian Beekeepers Association, NO-2040 Kløfta, Norway; firstname.lastname@example.org
6 Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sci-
ences, 1433 Ås, Norway
7 Department of Ecology, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden;
email@example.com (J.R.d.M.); firstname.lastname@example.org (B.L.)
8 Swiss Bee Research Center, Agroscope, 3003 Bern, Switzerland; email@example.com
9 Department of Ecology and Evolution, Biophore, UNIL-Sorge, University of Lausanne, 1015 Lausanne,
10 Wild Bees Project, 01170 Crozet, France; firstname.lastname@example.org
11 UR 406 Abeilles et Environnement, INRAE, 84914 Avignon, France; email@example.com
* Correspondence: firstname.lastname@example.org
Simple Summary: Citizen Science is a valuable resource that can substantially contribute to the
conservation of biodiversity. However, its use in honey bee research has remained minimal. The
Survivors Task Force of the COLOSS association created and promoted an online surveying tool
with the aim of identifying potential cases of Western honey bee, Apis mellifera, populations that are
surviving infestations with ectoparasitic mites Varroa destructor without control measures by bee-
keepers. The reports suggest that there could be twice as many naturally surviving colonies world-
wide than are currently known. The survey also shows that citizens can be readily engaged through
social media, personal networks, and promotional campaigns to gather valuable and previously
inaccessible data. These reports of surviving honey bee colonies will now be validated through the
new initiative Honey Bee Watch, a global and multi-year Citizen Science project founded to connect
citizens, beekeepers, and scientists. This will enable to increase scientific knowledge, mitigate honey
bee colony losses, and develop education and conservation campaigns.
Abstract: Citizen Science contributes significantly to the conservation of biodiversity, but its appli-
cation to honey bee research has remained minimal. Even though certain European honey bee (Apis
mellifera) populations are known to naturally survive Varroa destructor infestations, it is unclear how
widespread or common such populations are. Such colonies are highly valuable for investigating
the mechanisms enabling colony survival, as well as for tracking the conservation status of free-
living honey bees. Here, we use targeted Citizen Science to identify potentially new cases of man-
aged or free-living A. mellifera populations that survive V. destructor without mite control strategies.
In 2018, a survey containing 20 questions was developed, translated into 13 languages, and pro-
moted at beekeeping conferences and online. After three years, 305 reports were collected from 28
countries: 241 from managed colonies and 64 from free-living colonies. The collected data suggest
that there could be twice as many naturally surviving colonies worldwide than are currently known.
Further, online and personal promotion seem to be key for successful recruitment of participants.
Although the survivor status of these colonies still needs to be confirmed, the volume of reports and
responses already illustrate how effectively Citizen Science can contribute to bee research by
Moro, A.; Beaurepaire, A.;
Dall’Olio, R.; Rogenstein, S.;
Blacquière, T.; Dahle, B.;
de Miranda, J.R.; Dietemann, V.;
Locke, B.; Licón Luna, R.M.; et al.
Using Citizen Sci
ence to Scout
Honey Bee Colonies
Insects 2021, 12, 536.
Cristina Castracani and
Received: 21 May 2021
6 June 2021
9 June 2021
MDPI stays neu-
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This article is an open access article
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tribution (CC BY) license (http:
Insects 2021, 12, 536 2 of 12
massively increasing generated data, broadening opportunities for comparative research, and fos-
tering collaboration between scientists, beekeepers, and citizens. The success of this survey spurred
the development of a more advanced Citizen Science platform, Honey Bee Watch, that will enable
a more accurate reporting, confirmation, and monitoring of surviving colonies, and strengthen the
ties between science, stakeholders, and citizens to foster the protection of both free-living and man-
aged honey bees.
Keywords: citizen science; COLOSS; honey bee; honey bee watch; monitoring; natural selection;
Citizen Science is an effective tool for engaging the general public in research pro-
jects. It is most commonly used in media-friendly subjects such as ecology and conserva-
tion [1–4]. By definition, this discipline relies on the active involvement of the public in
the provision of data and the co-creation of scientific knowledge [5,6]. For scientists, this
offers many opportunities, such as real-time access to large-scale data and direct contact
with both citizens and practitioners . Citizen Science simultaneously offers citizens the
opportunity to partake in research questions that interest them, while also providing the
possibility of advancing their education , with multiple benefits to all actors involved
[9,10]. As such, the use of Citizen Science for facing the multiple challenges affecting
global biodiversity has been widely increasing, even in bee research . However, de-
spite the need to mitigate the current global health crisis affecting Western honey bees, A.
mellifera [12,13], Citizen Science almost exclusively focused on the quantification of winter
losses of managed colonies  and has not yet been capitalized for finding possible so-
lutions to this problem.
Severe losses of managed colonies of Western honey bees have in fact been thor-
oughly monitored in the last decades  and the ectoparasitic mite Varroa destructor has
been widely recognized as one of the major drivers of these losses. Generally, infestations
with this parasite lead to the death of a colony within two years unless appropriate control
measures are taken . Beekeepers worldwide therefore rely on mite control measures
(primarily regular acaricide treatments), in order to keep their stocks alive . However,
these acaricides vary in efficacy, are prone to resistance development by the mites and
contaminate hive products and can thus only be used outside the foraging season . As
it stands, chemical treatments therefore do not represent a long-term solution to V. destruc-
tor . Non-chemical alternative treatments have also been developed , but are cur-
rently not widely used and represent an increased work load for the beekeepers. The dis-
covery of naturally V. destructor-surviving populations [19,20] led to the realization that
the Western honey bee possesses certain traits enabling their survival without the need
for mite control , similar to what is observed in the original host Apis cerana . This
encouraged scientists and beekeepers to search for or establish A. mellifera populations
capable of surviving V. destructor infestation without mite control  in order to identify
traits that are most amenable to natural or artificial selection [19,21,23]. Unfortunately,
identifying or establishing such populations takes much time and effort, leading to a re-
search that focuses on only a few populations . However, considering a more diverse
group of V. destructor-surviving A. mellifera populations that undoubtedly exist  would
provide increased opportunities to investigate known survival mechanisms and discover
novel ones. Moreover, a diversity of naturally surviving populations could represent an
important asset for the re-establishment of A. mellifera in the wild.
European A. mellifera populations have been considered almost extinct in the wild as
a consequence of the spread of V. destructor . However, recent evidence suggests that
free-living honey bee colonies can survive in the wild in a self-sustainable manner [26–
30]. Despite these few occurrences, there remains a large gap of knowledge on the current
Insects 2021, 12, 536 3 of 12
abundance, distribution, and diversity of free-living A. mellifera populations. As their
identification is most efficiently achieved with large-scale coordinated efforts, it appears
high time to mobilize Citizen Scientists for a large-scale survey on this topic.
Beekeepers represent the major stakeholders upon which honey bee health ulti-
mately depends [31,32]. Their participation in bee health research is therefore both desir-
able and mutually beneficial. Furthermore, the recent development of online surveying
platforms makes it much easier to involve stakeholders such as beekeepers as well as the
general public in participatory research . As the level of contribution among users of
such platforms is often uneven , the use of multiple communication channels, including
social media and newsletters, can foster wider and more representative engagement by
citizens . Here, we present the outcome of an online survey organized by the members
of “Survivors”, a Task Force within the COLOSS (Prevention of honey bee COlony
LOSSes; www.coloss.org, accessed on 7 June 2021) association, aimed at both beekeepers
and the general public, for mapping and identifying new cases of A. mellifera colonies that,
either in the wild or in managed apiaries, survive V. destructor infestation without the need
for mite control.
2. Materials and Methods
In March 2018, during a COLOSS Survivors Task Force workshop in Bern, Switzer-
land, an online survey was created (Figure 1) and later translated into 13 languages: Chi-
nese, Dutch, English, French, German, Italian, Norwegian, Russian, Serbian, Slovenian,
Spanish, Swedish, and Ukrainian. The survey was developed using the Google® Form
platform, activated and made accessible from the Survivors Task Force webpage
(https://coloss.org/taskforces/survivors/, accessed on 7 June 2021). The survey was simul-
taneously disseminated through local national beekeeping networks of the COLOSS Sur-
vivors Task Force members through a variety of channels. The initiative was further pro-
moted during a beekeeping conference in the Netherlands in 2018, followed by a passive
online campaign using social networks.
The survey started with an introductory question asking the responder for possible
cases of surviving A. mellifera populations (Figure 1). As the survey aimed at identifying
surviving honey bee populations, rather than individual colonies, a stipulation was in-
cluded to only submit reports of a minimum of five surviving colonies from managed
beekeeping operations. This requirement was not imposed for free-living survivors,
which inevitably are well-dispersed individual colonies, wherever they are found (Figure
1). Depending on the answer to the introductory question, the user was directed to one of
three sections (Figure 1). The first section concerned managed surviving colonies and con-
tained seven questions. These questions aimed at collecting data regarding the general
location of each case (i.e., region and city name), the number of years these colonies was
known to survive without mite control, the number of colonies in the surviving group at
the date of the report, and finally the proportion of colonies that needed to be replaced
annually to maintain the population size, as a measure of the population’s ability to sur-
vive V. destructor unaided. The second section concerned possible cases of free-living sur-
vivors and contained a single question about the general location of the colony, together
with an open-text field to provide other relevant information. The third section combined
questions from Sections 1 and 2, for users reporting cases of both managed and free-living
surviving colonies. At the end of the survey, the user was given the possibility to submit
a personal contact, for future case validation and collaborative research (Figure 1). The
respondent’s personal data were treated confidentially, in compliance with the General
Data Protection Regulations (GDPR) of the European Union .
Insects 2021, 12, 536 4 of 12
Figure 1. Flow diagram of the online survey on honey bee, Apis mellifera, colonies surviving infesta-
tions with Varroa destructor without acaricidal treatments. The first question directed respondents
to one of three sections, depending on whether they intended to report cases of managed A. mellifera
colonies surviving without conventional treatment against V. destructor (left), free-living surviving
A. mellifera colonies (middle), or both (right).
In January 2021, the reports were compiled and screened to remove duplicate reports
and cases already known to science. The compiled data set was analyzed statistically with
respect to a range of factors relevant to the aims of the project, using R software . For
potentially stable surviving populations of managed survivors, the reports were ranked
in three classes: “gold”, “silver”, and “bronze”, according to the reported survival time,
the number of colonies in the group, and the annual proportion of colony replacement.
For all classes, the minimum requirement for inclusion was an annual replacement rate of
less than 50%. Cases reporting more than 30 colonies surviving for more than 10 years
were considered as the “gold” standard. Next, groups surviving more than 10 years but
Insects 2021, 12, 536 5 of 12
involving fewer than 30 colonies, were considered silver class. Last, groups of more than
30 colonies surviving for a period between five and ten years, were considered as bronze
class. All reports falling outside these criteria were included into a fourth class.
Additional voluntary information added to reports on free-living colonies were ana-
In total, 305 reports were collected from 28 countries (Figure 2; Table 1), comprising
64 reports on free-living colonies and 241 on managed colonies. The majority of users pro-
vided a contact for future case confirmation (N = 216, 86%). Most of the reports were from
the United Kingdom (N = 86, 28%), The Netherlands (N = 77, 25%), and the USA (N = 68,
Figure 2. Global reach of the COLOSS Survivors Task Force online survey on possible cases of honey
bee, Apis mellifera, colonies that, in an apiary or free-living, are surviving Varroa destructor mite in-
festations in the absence of chemical treatments. Regions indicated by respondents are highlighted
with different colors, depending on the type of surviving colonies (managed, only free-living, or
both). The majority of reports were submitted from UK, The Netherlands, and USA.
Overall, only a few reports were submitted on possible cases of free-living colonies
(N = 64, 20%, Table 1). Respondents consistently provided the general locations in which
these colonies were located (Table 1), and a large proportion also provided voluntary ad-
ditional information on each case (N = 48, 75%). From this information, a count of the
reports that mentioned the type of nests in which the free-living colonies resided (N = 35,
72%) or whether the respondent monitored these nests (N = 20, 41%) could be extracted
purposefully (Table 2).
Insects 2021, 12, 536 6 of 12
Table 1. Number of reports, divided per category, collected by the COLOSS Survivors Task Force survey on putative cases
of untreated A. mellifera colonies surviving V. destructor infestation. The country in which these colonies were reported to
occur is specified.
Category of Answer
Number of Answers
Managed survivors 241
Bangladesh (1), Belgium (12), Canada
(3), Colombia (1), Egypt (2), Finland
(2), France (1), Germany (1), India (3),
Iran (1), Ireland (1), Israel (1), Italy (16),
Kenya (1), Lithuania (3), Netherlands
(62), Poland (1), Portugal (4), Romania
(1), Saudi Arabia (1), Serbia (1), Spain
(1), Switzerland (3), Thailand (1), Tur-
key (1), UK (63), USA (53)
Free-living survivors 64
Austria (1), Belgium (1), France (1), Ire-
land (2), Italy (1), Kenya (1), Nether-
lands (15), Portugal (2), Serbia (1),
Spain (1), UK (23), USA (15)
Table 2. Counts and proportions of users who did or did not submit case-specific information on
free-living colonies to the COLOSS Survivors Task Force survey. In total, 64 reports on free-living
colonies were submitted. The counts and proportions of instances in which the type of nests was
mentioned are also given, together with those in which the user reported to be voluntarily monitor-
ing the colonies.
Types of Response
Number of Answers
No reported information
Described nest type
When reporting about managed surviving colonies (Total N = 241), almost all re-
spondents (N = 224, 93%) indicated the number of colonies composing the group. Among
these, 195 (87%) described groups of five to 30 colonies, 44 (22%) of which untreated and
surviving for less than three years, 70 (36%) for a period between three and five years, 51
(26%) for a period between five and 10 years, and 30 (15%) for more than 10 years (Figure
3). Few respondents described managed groups consisting of more than 30 colonies (N =
29), of which 6 (20%) were untreated and surviving for less than five years, 11 (37%) for a
period between five and 10 years, and 12 (41%) for more than 10 years (Figure 3).
Insects 2021, 12, 536 7 of 12
Figure 3. Time span over which the reported managed honey bee, Apis mellifera, colonies were not
subjected to treatments against Varroa destructor. The number of answers from the COLOSS survey
is shown (dark gray = surviving populations with >30 colonies, N = 29; light gray = groups between
five and 30 colonies, N = 195).
Respondents reporting of managed surviving colonies also indicated the proportion
of colonies that needed to be replaced annually in order to maintain the stock (Figure 4).
Among these, the majority (N = 160, 80%) reported replacing less than one-quarter of the
colonies per year (Figure 4), while the remaining respondents reported replacing between
one-quarter and one-half of the colonies in their stock (N = 32, 16%, Figure 4) per year.
Another eight (4%) reports indicated an annual replacement rate of more than one-half.
Because these high rates suggest that these colonies did not develop a stable relationship
with V. destructor, these eight reports were not considered as potential survivors and were
Interestingly, 44 reports (18%) collected on managed, untreated groups could be clas-
sified as potentially stable populations of survivors as nine gold, 25 silver, and 10 bronze
cases were found (Figure 5).
Figure 4. Annual colony replacement rate in groups of managed honey bee, Apis mellifera, colonies
not treated against parasitic mites Varroa destructor. The number of answers from the COLOSS Sur-
vivors Task Force survey is shown (dark gray = groups with >30 colonies, N = 26; light gray = groups
between five and 30 colonies, N = 174).
<3 years 3 to 5 years 5 to 10 years >10 years
Reported time without conventional treatments
Number of answers
Reported rate of annual colony replacement
Number of answers
Insects 2021, 12, 536 8 of 12
Figure 5. Counts of reports on potentially self-sustaining managed A. mellifera populations surviv-
ing Varroa destructor based on group composition, proportion of annual colony replacement, and
untreated period as collected by the COLOSS Survivors Task Force survey. The reports are divided
by classes (gold, silver, and bronze) and regions. Dark gray = cases for which a replacement rate
between 25 and 50% was reported; light gray = cases for which a replacement rate lower than 25%
was reported. Gold class (N = 9) was defined by managed groups of colonies composed of more
than 30 colonies with an annual replacement rate below 50% and untreated for more than 10 years.
Silver class (N = 25) were managed groups of colonies composed of a number between five and 30
colonies with an annual replacement rate below 50% and untreated for more than 10 years. Bronze
class (N = 10) were managed groups of colonies composed of more than 30 colonies with an annual
replacement rate below 50% and untreated for a period between five and 10 years. Only cases pre-
viously unknown to scientific literature have been included.
By providing access to previously unreported cases of untreated A. mellifera colonies
potentially surviving V. destructor infestations without treatments, this survey will help
improve our understanding of the mechanisms underlying survival of colonies. The out-
put of this survey further illustrates the potential of Citizen Science to provide valuable
and large-scale data for solving the major health problems that Western honey bees are
currently facing worldwide.
Despite a low investment in online and personal communications to promote the
survey, its outreach was substantial. Notably, it engaged responders from continents not
included in previous COLOSS surveys . Interestingly, the majority of reports were
collected from three countries: United Kingdom, the Netherlands, and the USA (Table 1).
This pattern seems to largely stem from the way by which the survey was promoted. Most
answers were submitted after the authors personally promoted the survey during a con-
ference held in the Netherlands in 2018, at which attendees were mostly local or from the
UK and USA. Following this event, a modest social media campaign was launched to fur-
ther promote the survey within the conference attendee’s networks. Moreover, in the
same period, the link to the survey was also spread to Dutch beekeepers through an online
newsletter. As has been the case for other citizen science initiatives , the recruitment of
participants through personal engagement and the use of online and social media plat-
forms appeared to have been crucial for the successful dissemination of this initiative.
The survey of the COLOSS Survivors Task Force lists among the few scientific initi-
atives aimed at mapping free-living and surviving A. mellifera colonies on an international
scale . In the northern hemisphere, free-living colonies are considered to be very rare
[25,37] and are notoriously difficult to spot in the field . As a consequence, few reports
Insects 2021, 12, 536 9 of 12
(i.e., 20% of the total answers, Table 1) were collected on such cases in comparison to man-
aged colonies. The data collected on free-living colonies provided only an indication of
their locations (Table 1). A comparative analysis of the data derived from these cases was
not possible given that the majority of information collected consisted of anecdotal re-
ports. Most likely, this was due to the lack of precise instructions given to users when
submitting information on such colonies (Figure 1). Yet, more than one-third of the re-
sponses collected suggested that responders were voluntarily monitoring the free-living
colonies known to them (Table 2). This considerable level of public engagement is prom-
ising and suggests that there are good perspectives for successfully implementing a more
advanced version of this Citizen Science tool capable of obtaining more detailed data on
free-living honey bee colonies. This is the goal of a follow-up initiative developed by a
core team of members within the COLOSS Survivors Task Force. The team launched
Honey Bee Watch (www.honeybeewatch.com, accessed on 7 June 2021), which aims at
pursuing this study in greater depth, over a much longer timeframe, and with a much
wider scope that includes all Apis species so to provide more data over their distribution
and conservation status [38,39].
The potential cases of survivors managed by beekeepers collected in the survey may
substantially contribute to the number of previously known cases of untreated popula-
tions of Western honey bees surviving V. destructor infestation. Current scientific literature
indicates that approximately 20 untreated and surviving populations are managed by bee-
keepers/breeders or are part of scientific projects [20,40–51]. The answers collected from
this survey reported twice as many cases, the majority of which in regions with no previ-
ously reported cases (Figure 5). The data also suggest that some of these honey bee colo-
nies may have reached a stable equilibrium with V. destructor, as the majority of respond-
ents reported an annual colony replacement rate <25% (Figure 5). This indicates adapta-
tions of both the honey bee host to the selection pressure imposed by the parasite [23,43]
and the local mites to its host . Yet, despite the promising data obtained, these poten-
tial novel cases need to be confirmed via thorough investigation and long-term monitor-
ing before they can be considered as surviving mite infestations. With each respondent’s
approval, and after funding has been secured, phenotypic and molecular tests will be per-
formed by the Honey Bee Watch study on gold, silver, and bronze cases. Inspired by the
level of citizens’ engagement that the present initiative generated, Honey Bee Watch will
initiate a more strategically focused communication campaign to continue collecting data
on untreated and free-living honey bee colonies.
Given the relevant contributions that Citizen Science initiatives have demonstrated
in multiple conservation and ecological studies , using this tool to investigate the extent
of A. mellifera populations surviving V. destructor without treatments appears both mean-
ingful and fruitful. Through the COLOSS Survivors Task Force survey, beekeepers, and
citizens, incentivized by social media and promotional campaigns, were motivated to sub-
mit data on and monitor untreated and free-living colonies. In the process, they have be-
come a valuable reporting resource on potentially self-sustainable and V. destructor sur-
viving A. mellifera populations. As the initiative reported here has ended, the results gath-
ered are calling for case validation and the development of a more advanced citizen sci-
ence platform. To fulfil such aims, COLOSS Survivors Task Force members initiated
Honey Bee Watch (www.honeybeewatch.com, accessed on 7 June 2021), aimed at expand-
ing data collection on untreated, surviving, and free-living honey bee colonies. Overall,
this initiative, together with the results obtained from the scientific validation of the cases
presented here, may ultimately demonstrate how bridging the gap between scientists,
practitioners, and citizens can help discover solutions to promote large-scale conservation
Insects 2021, 12, 536 10 of 12
Author Contributions: Conceptualization, A.M., P.N., A.B., R.D., S.R., T.B., B.D., J.R.d.M., V.D., B.L.,
R.M.L.L., and Y.L.C.; methodology, A.M., P.N., A.B., R.D., S.R., T.B., B.D., J.R.d.M., V.D., B.L.,
R.M.L.L., and Y.L.C.; software, A.M.; formal analysis, A.M.; data curation, A.M.; writing—original
draft preparation, A.M.; writing—review and editing, A.M., P.N., A.B., R.D., S.R., T.B., B.D.,
J.R.d.M., V.D., B.L., R.M.L.L., and Y.L.C.; funding acquisition, P.N. All authors have read and agreed
to the published version of the manuscript.
Funding: This research was funded by the UniBe international 2021 program of the University of
Bern (A.M., P.N.) and by the Vinetum Foundation (P.N.) Financial support was provided to
COLOSS by the Ricola Foundation Nature & Culture and Véto-pharma.
Institutional Review Board Statement: Not applicable.
Data Availability Statement: Data used in the submitted manuscript can be available after reason-
able request to the corresponding author. Personal data of survey respondents will not be provided
as it would violate privacy laws.
Acknowledgments: The authors thank all the responders that submitted reports to the survey and
contributed to its dissemination. We also thank Melissa Oddie and Robin F.A. Moritz from the
COLOSS Survivors Task Force for the fruitful discussions and their input in composing the first
draft of the survey and Jonathan Powell of the National Beekeeping Trust for disseminating and
promoting our initiative.
Conflicts of Interest: The authors declare no conflicts of interest.
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