Sustainable parasitic mite control for honeybees
Honey bees are threatened by the varroa mite, an obligate external parasite. The number of beekeepers has diminished substantially as the management of honey bees for pollination, honey, and other hive products has become extremely difficult due to varroa. Beekeepers currently depend on two miticides–fluvalinate and coumaphos–for varroa control. Dependence on these chemicals is not sustainable because of the development of mite resistance, hive wax contamination (a continuous low-level source of exposure during all honey bee life stages), and hive product contamination. This project is designed to help beekeepers reduce their use of miticides, resulting in lower residue levels in hive products. Production costs will be reduced due to lower colony mortality. The number of healthy colonies for honey production and pollination will increase.
Two changes in beekeeper behavior are targeted in this project. Even though the varroa mite was introduced to the United States more than 18 years ago, beekeepers have been reluctant to monitor for this pest due to the large time commitment already needed to manage honey bee colonies. We are working to modify beekeeper behavior by showing them time-efficient methods of monitoring for varroa destructor. A part of the strategy has been to demonstrate fast monitoring methods, the importance of the information for ensuring colony survival, and how the information can be used to reduce the amount of time expended on colonies that are too weak to survive. Additionally, we have been using the information collected by beekeepers to determine if more efficient methods of monitoring and treatment exist.
The second behavioral change we are targeting is the increased use of Integrated Pest Management (IPM) tactics to control varroa. Beekeepers have relied almost exclusively on chemical controls since the introduction of varroa, and our goal is to increase to at least two the number of IPM tactics used. Beekeepers are also being encouraged to watch how other diseases and pests respond to the tactics implemented as we (Dewey Caron) has observed that screened bottom boards will decrease mite levels but will increase wax moth populations if the screens are not open to the ground.
Since 2004 we have been recruiting beekeepers from West Virginia, Pennsylvania, Maryland, New Jersey, and Delaware to monitor the levels of varroa mites in their colonies.
Approximately 100 beekeepers were recruited each year and most monitored for at least part of the summer. Our goal has been to convince beekeepers to monitor as frequently as possible (2X per month or more but at least once a month) but this has been very difficult to achieve. Fortunately, an alternative has presented itself. Early in this project we found that monitoring for mites as early in the season as possible may be a useful tactic to reduce mite numbers. We have been encouraging beekeepers to monitor for mites in early April to determine if colonies with elevated mite levels exist (more than 1 mite in a powdered sugar shake or more than 10 mites per day on a 3-day sticky board). Treatment of these colonies help to reduce mite levels in all colonies in an apiary and reduce the need for later treatments.
We are evaluating the reasons that some beekeepers lack interest in monitoring for varroa. It is possible that the cost of not monitoring is underestimated while the cost of monitoring is overestimated. It may be necessary to quantify this relationship before we see a large increase in the number of beekeepers who monitor for varroa.
Another method we have been using to motivate beekeepers has been to encourage them to submit their monitoring data to Penn State as part of a research project. During 2004 and 2005 we used the data to predict colony collapse prior to the event. Beekeepers were quite impressed with these results and we plan to continue this data collection in 2006.
We have had mixed success with the completion of beekeepers conducted experiments using IPM tactics to control varroa. Each year a large number of beekeepers begin experiments but only a small number complete the data collection process. Reasons for the lack of completion vary from colony collapse to family emergencies. Beekeepers have not reported lack of completion due to lack of interest. During 2005 we improved the quality of the data from a half dozen beekeeper lead experiments by increasing our participation in the data collection. While these data will lead to a publication of the results, the time commitment needed to obtain these data far exceeded the time it would take to conduct our own experiment. Thus we are only able to work intensely with a small number of beekeepers each year.
Two beekeeper behaviors are targeted for change: 1) monitoring: 500-1000 beekeepers will monitor varroa levels and 2) implementation of IPM tactics: 100 beekeepers will implement at least two IPM tactics. Approximately 200 beekeepers each year will be recruited to begin monitoring. Some will be successful at monitoring all season while others will not. We will encourage those who were successful to continue participating in subsequent years while those who stopped partway through the season will be asked to make another attempt to tract the mites in their colonies.
Of the approximately 5000 hobbyists and 700 sideliners in MAAREC, 300 beekeepers are expected to participate in planning workshops. Ten beekeepers from the 300 participants will evaluate IPM tactics. Workshops will be held at the beekeeper’s apiary to demonstrate IPM tactics and monitoring, with approximately 50 beekeepers attend each. During the second year 40-80 beekeepers will implement multiple IPM tactics.
Beekeepers are expected reduce their use of miticides in their honey bee colonies. The result will be lower residue levels, by at least 50%, reduced production cost of production due to decreases in the annual colony mortality from 40-60%, and increases in the supply healthy bees for honey production and pollinating field crops and wild plants.
Verification of reaching our targets will be obtained through annual beekeeper surveys. Additionally, we will obtain the annual statistics of the beekeeping industry from each MAAREC state to verify changes in management practices.
Two beekeeper behaviors have been targeted: 1) monitoring of colonies for varroa mites, done by few beekeepers currently, will increase and 2) adoption of at least two Integrated Pest Management (IPM) tactics to control varroa. We continue to recruit beekeepers to monitor their colonies. Of the beekeepers who monitored colonies for varroa, a majority have continued with this effort. We are beginning to see beekeepers, the innovators, talk to other beekeepers about the need to monitor for varroa. We are continuing to recruit beekeepers into the monitoring project. As we did last year, announcements for recruiting more beekeepers have been sent to state and local beekeeping associations for insertion into newsletters. A regional announcement is on the MAAREC web site. More beekeepers will be recruited during the next 4 months at various state and county beekeeper meetings, through newsletter announcements and direct contact by apiary inspectors and study personnel.
The number of beekeepers participating in experiments in 2005 exceeded the number of participants in 2004. We are recruiting more beekeepers to perform experiments.
We are exceeding the target of 100 beekeepers implementing at least two IPM tactics. The beekeepers monitoring for varroa have reported that they have implemented at least one IPM tactic and most have implement two or more. Those beekeepers who have implemented only one IPM tactic are considering additional methods to reduce varroa population growth. We have begun to encourage beekeepers to evaluate the impact IPM tactics implemented to reduce varroa population growth on other pests and diseases of the honey bee. We are stressing the need to integrate their management of diseases and pests.
We are continuing to obtain information from beekeepers concerning their management practices and needs. State apiary inspection data for 2005 are being collated by the various state agencies for our use. We anticipate submitting a publication with these results in the near future.
Impacts and Contributions/Outcomes
We continue to test our ability to predict mite levels using early spring data. A spatial concentration of colonies with high levels of mites has been observed and we are using apiary and colony level humidity, temperature, wind and other weather data to predict trends in mite population growth. Based upon our early spring mite collections, we are testing spring mite thresholds in our colonies. Beekeepers participating in the mite monitoring project have been asked to monitor as early in the season as possible – April or early May. Among interested beekeepers, we are testing spring thresholds. If there are colonies acting as ‘seed’ colonies, we predict that targeted spring miticide treatments may be sufficient.
Last year (2005) beekeepers tested for ‘soft’ miticides. One test was a modification of the application method of formic acid. Most beekeepers in the United States are unwilling to treat their colonies during the honey flow because honey supers need to be removed for the duration of the treatment. We tested a 24-hour ‘flash’ formic acid treatment. The first test used a single 24-hour treatment and the second test used two 24-hour treatments. Formic acid concentrations used were higher than the levels used in the labeled product. Unlike the labeled product we did not observe any adverse colony impacts, e.g., absconding, dead of bees or the queen. This result is likely due to the very short exposure time (24 hours versus several weeks). Both treatment regimes (one or two 24-hours treatments) were effective at reducing mite numbers in colonies. The two 24-hour treatments reduced mite numbers equal to that observed with coumaphos or fluvalinate. Because we have become interested in the impact of varroa control treatments on other pests and diseases of the honey bee, we obtained samples of bees for viral analysis. Surprisingly, the ‘flash’ formic acid treatment caused viral levels to increase at least one order of magnitude. A successful varroa control tactic resulted in lethal virus levels. We will be modifying our formic acid treatment this spring to see if it is possible to control varroa without increasing viral levels.
Other soft chemical controls were evaluated including Sucrocide, other organic acids such as oxalic acid, and essential oils. Thus far, we have shown variable results, compared to published research, when these tools are used by beekeepers. While Sucrocide® has been shown to effectively reduce mite numbers, when the participating beekeepers used this tactic Sucrocide did not reduce mite numbers in colonies. Based upon the responses to questions, beekeepers modified the application method even though they were asked to follow the printed instructions. Modifying application methods seems to be common among beekeepers and this behavior needs to be taken into account when designing control tactics. The tactic needs to be efficacious even if the application method is modified or it needs to be extremely difficult to modify.
This project has produced benefits to sideline and hobbyist beekeepers and those who rely on honey bees for pollination and bee products. Beekeepers are reducing their application of miticides without prior knowledge of the level of mites in the colony. The unnecessary use of miticides results in adverse impacts on honey bees, increased costs from pesticide unnecessary use and potential contamination of hive products. Additionally, this project is reducing the use of miticides in honey bee colonies through the implementation of IPM tactics. The beekeeper toolbox is being expanded by increasing beekeeper knowledge of how to effectively monitor for varroa and implement non-pesticide options for varroa control. The reduction in pesticide use results in the lowering production costs and pesticide residues in bee products and the rising of the supply healthy bees for honey production and pollinating field crops and wild plants.
University of Delaware
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