The Varroa mite, Varroa destructor, has become an increasingly common pest in honey beehives since it was first detected in Californian beehives in 1987 and soon spread throughout the state, causing up to 50 percent hive loss by 1992 (Kraus and Page 1995). Now established in Nevada, the Varroa mite, combined with other honey bee pests and stresses, is creating more challenges than ever for beekeepers in the Silver State. Considering an Integrated Pest Management approach to maintain healthy bee colonies is necessary, but unfamiliar to many small-scale beekeepers. Pest management requires regular monitoring and management of the bee colony for diseases, queen strength and food availability. It is necessary for all beekeepers to use best management practices for the health of all honey bees in the area.
Varroa Mite Life Cycle
Understanding the life cycle of the Varroa mite is a major tool in monitoring for the mites and planning effective treatment. Varroa mites reproduce in capped cells which makes them difficult to treat. Only when the mites reach maturity and leave the honeycomb cells are they vulnerable to treatment. A complete summary of the Varroa mite life cycle can be found at Varroa Mite Reproductive Biology
Starting an IPM Treatment Program for Your Bees
Monitoring Varroa Mite Populations
The level of damage that is caused by Varroa mites will be very different based on hive condition, environmental conditions, other diseases and bee behavior (Brown et al. 2013). A treatment threshold is the number of mites relative to the number of bees or size of hive which makes it necessary to apply a treatment. Treatment thresholds have not been scientifically determined for Nevada. As such, treatment threshold recommendations in this publication are based on scientific treatment threshold limits determined in other places in North America. These limits are intended to be used as a guide until treatment thresholds can be determined for Nevada. In a normal, healthy hive with no other diseases and without any environmental stress, a threshold of 3,000-4,000 mites in the colony is used as the treatment threshold (Brown et al. 2013). If bees have other stress factors, the threshold should be lowered to 1,000 mites in the colony (Brown et al. 2013). Monitoring should take place every 3 or 4 weeks while the bees are actively brooding, as that is when Varroa mites are increasing inside the colony.
Risks to bees also vary with treatment type and should also be considered when deciding to apply a treatment. Mechanical treatments can be applied frequently with very few side effects and little decrease in productivity. Chemical treatments need to be applied according to the label directions and improper application can result in damage to the hive or resistance to the chemical by the mites. Some chemicals should not be applied during honey flow. All these factors should be considered along with the mite count prior to treatment. Monitoring should also occur after the treatment to ensure that the treatment was successful and the varroa mite population has been reduced. Most monitoring should be repeated 48 after the treatment.
Adult bees can be collected directly from the brood chamber by brushing bees off the brood comb with a bee brush into a container. Bees from the brood chamber have the highest number of mites per bee compared to adult bees from elsewhere in the hive. Collect approximately 200 bees to have an accurate count of mites (Branco et al. 2006).
Adult bees can also be collected as foraging bees return to the hive. This method requires less disturbance of the hive than collecting from the brood chamber, but there will be fewer mites on foraging adult bees than adult bees collected from the brood chamber.
Adult bees then need to “rinsed” to get the mites off of them for an accurate count. Using one-fourth cup rubbing alcohol or powdered sugar, shake the bees around in a sealed jar until they are well coated (OMAFRA 2015, Madedo and Ellis 2002). Rubbing alcohol will kill the bees. The mites will then be in the liquid or powdered sugar. If powdered sugar was used, count the bees before opening the jar near the hive to release them. Compare the number of bees versus the number of mites to the levels given in the treatment threshold (OMAFRA 2015).
Mite numbers can be determined by monitoring capped brood. A count of 200 brood, 50 from four different brooding areas, was shown to be very effective at estimating the mite population size (Branco et al. 2006). Mites prefer to reproduce in drone comb (Wilkinson and Smith 2002), so collect evenly from both drone and worker brood or use a monitoring protocol for only drone brood (Brown et al. 2013, Charriere et al. 2003). To monitor for mites in comb, use an uncapping tool and uncap a section of comb. Count the number of brood and the number of mites, making sure to look inside the comb chambers and on the brood for the mites (Brown et al. 2013).
From a Sticky Board
Monitor with a sticky board by placing a sticky card or plastic sheet treated with oil, petroleum jelly or other sticky substance under a screened-bottom board (OMAFRA 2015, Calderon and Lin 2003). Screened bottom boards can be made or purchased and must have a mesh bottom that allows the mites to fall through but fine enough to prevent honey bees from contacting the sticky surface. Openings of 3 square millimeters have been used effectively (Branco et al. 2006, Calderon and Lin 2003). Leave the sticky board in place for 24 hours, and then count the number of mites that naturally fall from the bees during this period (Calderon and Lin 2003, Sammataro et al. 2002). Monitoring with a sticky board is most effective during active brooding cycles, when mites are emerging with new adults (Ostiguy and Sammataro 2000). Monitoring during dormant brooding cycles, when a colony is queenless, or weak colonies with few bees will have misleadingly low estimations (Branco et al. 2006).
To estimate the total mites in a hive from either direct observations of 200 bees or brood, or the numbers of mites counted in a 24 hour period, multiply the number counted by 20-40 when brood is present and 250-500 when brood is not present (Martin 1998, Strange and Sheppard 2001). Treatment thresholds specific to Nevada have not been developed. These recommendations are estimates, and the condition of the hive and environmental factors should also influence the decision to treat for varroa mites.
Powdered Sugar Method
The powdered sugar method is very effective at reducing phoretic mite load on adult bees between 29 percent to more than 70% (Aliano and Ellis 2005, Ellis et al. 2009). The powdered sugar prevents Varroa mites from being able to grip onto the bees (Ramirez 1994). The powdered sugar method is most effective if used prior to establishment of brood or during periods when brood recruitment is low, especially during the winter time (Fakhimzadeh 2001). This method can be very effective on packaged bees, swarms and nucs to remove phoretic mites prior to establishing a new hive. Continued use throughout the spring and summer when the bees are rearing brood has had mixed scientific results. While powdered sugar did reduce mite loads on adult bees, it cannot suppress the mite level enough to be used as a sole treatment (Oliver 2007). This treatment should be combined with consistent monitoring and other treatment methods when the mite load is too high.
Dust bees thoroughly to ensure that they are covered with a fine dust. Dry powder is most effective (Macedo et al. 2002). While there are many ways to accomplish covering the bees in a fine dust, use a method that is simple and easy, as this technique is most effective when frequently used. Techniques used effectively include: trapping bees in a mesh cage, powdering them in the cage and returning them to the hive (Aliano and Ellis 2005), using a hardware cloth screen the size of the hive, and using a cup and bee brush to apply over the top of a hive box and a machine that blows the powder throughout the hive. In a standard hive box, a 1 –pound bag finely sieved throughout the hive should be effective as long as the bees are not tightly clustered. Combine with the screened bottom board technique below to ensure that mites that fall off from the powder sugar treatment are effectively removed from the hive.
Screened-bottom boards are bottom boards made of mesh too fine for the bees to get through, but open enough for varroa mites to fall through. See above. Hardware cloth with a 3 square millimeter opening is typically used (Brown et al. 2013). Mites can only live a short time without a bee host, but it has not been scientifically determined how far the hive should be off the ground to prevent the mites from reentering the hive. Elevating the hive also protects against small vertebrate predators such as skunks and raccoons, as their more delicate bellies will be exposed to disturbed bees. Opened screened-bottom boards also aid in ventilating the hive. During cold weather, the screen may need to be covered. Combining the screened bottom with the sticky board monitoring method, where the mites are trapped and cannot re-infest the hive, may be more effective than using the screen bottom only.
Drone Brood Trapping
Mites are naturally attracted to the brood locations of drone brood. To encourage drone brood production, a special foundation with a larger cell size is placed in the brood box. When 50 percent of the larval cells have been capped, check the brood for mites at least every nine days during peak brood rearing periods (Brown et al. 2013). If mites are present, replace the filled drone comb with another empty drone comb. Freeze the comb with the mites for 48 hours to kill the mites. (This will also kill the drone brood.) Continue to switch these two drone combs throughout the brooding season as 50 percent of the brood cells in the frame are capped and mites are detected (Brown et al. 2013). The bees will clean out the dead brood when you put the frozen drone comb back into the hive; however, you can assist them by using a brood comb to scrape out some of the dead brood before replacing it in the hive. If the weather is cool, defrost the comb before placing it back into the hive to prevent the frozen comb from excessively cooling the hive.
Purchasing of Varroa Resistant Bee Stock
Several lines of bees have been developed that resist Varroa mite infestation, including several Russian honeybee species that have a greater natural resistance to the pest (Stanimirovic et al. 2005). There are also lines of bees that have been selected to be more “hygienic”, which clean the hive of infested or infected brood or have grooming behaviors that remove a higher number of mites. Purchasing a resistant or hygienic queen and re-queening an existing colony or purchasing packages or nucs of resistant or hygienic bees for new hives will
provide a resistant colony. These strains of bees have not been scientifically evaluated in Nevada climates, so other unknown characteristics may affect the ability of the bees to thrive in Nevada. You may have to change other hive maintenance techniques to meet the needs of this different strain.
Pesticides Available for Use in Nevada
Pesticides are a necessary tool when other control methods are not effective at keeping the mite population under control or when a mite population is already well established in a hive. However, the mites can develop resistance to any chemical treatment if chemicals with different active ingredients are not rotated or if chemicals are applied when the mite population is not high enough to cause significant hive damage. Always read and follow all label instructions on any chemical used for mite control. Information provided here is for reference only, and label instructions should be followed over any information provided in this fact sheet. This is important for preventing the development of resistance, preventing negative impacts on your bees and for your safety. If you do not have the instructions for a pesticide, contact the department of agriculture, the pesticide manufacturer, or the University of Nevada Cooperative Extension office. Varroa mites have developed resistance to many chemicals that were once effective. Monitor before and after treatment to determine the effectiveness of a chemical. Resistance to a chemical can be reported to the Nevada Department of Agriculture. Chemical registrations change frequently. Visit the Nevada Department of Agriculture’s website to determine if a particular pesticide is currently registered for use in Nevada.
Many pesticides are packaged in sizes that are more than a small scale beekeeper can utilize at one time. Make sure to read the label for storage to ensure that you can use the product at a later time. If the product cannot be stored for a long enough period of time, consider purchasing and treating with other local small scale beekeepers. This will ensure that the product applied is at the proper strength to reduce the chance of chemical resistance.
API LIFE VAR
EPA Registration Number: 73291-1
NV Product Number: N3098-2
Apilife VAR is a chemical hive strip applicator treatment with the active ingredient Amitraz. Honey supers should be removed prior to treatment and should not be replaced until 14 days after the chemical strips are removed from the hive. These chemical strips are used for 42 days and must be removed by 56 days after placement on the hive. The strips must be placed where active bees will contact the strips and disperse the chemical throughout the hive. You do not need a pesticide applicators permit to purchase the chemical and the chemical is readily available online or through bee supply retailers.
EPA (Environmental Protection Agency)
Registration Number: 79671-1
NV Product Number: N3133-1
Apiguard is a thymol based treatment for varroa mite in the form of a slow-release gel available in pre-filled trays or a tub that allows you to apply the dose to a tray. The trays are left in place for two weeks, then a second treatment is applied and can be left for two to four weeks. Apiguard cannot be used during honey flow, as it can contaminate honey. Application must occur when temperatures are above 59 degrees Fahrenheit and the colony is active.
Thymol is distributed throughout the hive by the bees during regular hive processes, so access to the trays is important. Make sure that there is sufficient space between the lid of the hive and the tray to allow bees to easily access the chemical in the tray. Bees may distribute the gel quickly during warmer temperatures, but do not apply the second treatment until two weeks has passed. The housecleaning bees will carry the thymol throughout the hive during the two period, even after the gel is gone. Gel remaining at the end of the treatment should be left in the hive, either on a piece of wax foundation or smeared across the tops of the frames to ensure that the full dose is distributed throughout the hive.
Apiguard is labeled for fall or spring use. Spring use may cause an undesired pause in egg-laying. Take this into consideration when choosing a spring treatment. Mesh floors should be closed during treatment, as the thymol vapors are heavier than air. Temperatures above 100 degrees Fahrenheit will cause excessive volatilization of the thymol and can be lethal to bees. Use of thymol in forms not designed for beehives can result in bee death or in sub-standard treatment which will not kill the varroa mite and increase resistance of varroa mite to thymol treatment.
MITE-AWAY QUICK STRIPS
EPA Registration Number: 75710-2
NV Product Number: N3103-2
Mite-away quick strips contain the active ingredient formic acid. This chemical requires special chemical personal protective equipment including the proper NIOSH approved organic vapor respirator and acid resistant gloves. This equipment should be worn anytime you are visiting the hive yard during the 7 day treatment period or while working with the chemical strips. The chemical is sensitive to temperature and will volatize at a different rate based on temperature. The strips should only be used when the ambient temperature is going to be between 50 and 92 degrees Fahrenheit for the entire treatment period. If the ambient temperature is higher than 92 degrees Fahrenheit, the chemical will volatilize too quickly and result in a concentration of the chemical that can cause adverse side effects, such as excessive brood mortality or abandonment of the hive by your bees. If the ambient temperature is below 50 degrees Fahrenheit, the chemical may not reach the proper concentration to control the mites or may not spread properly throughout the hive. Mite-away was tested to be effective in fall control of Varroa mites in fall treatments in North Eastern USA (Calderone 2010), resistance has been documented. Always follow up after a treatment with monitoring to be sure the product has been effective.
ZOECON APISTAN ANTI-VARROA MITE STRIP
EPA Registration Number: 2724-406 NV
Product Number: N2277A-535
Apistan can be purchased in 3 different formulations, each with a different percentage of the active ingredient fluvalinate on the strip. Each formulation is used for different purpose: whole hive treatment, package bee treatment or queen bee treatment. Be sure to follow the directions based on the dosage strength on your strip. Whole hive strips can are left in the hive for 42 days. The other formulations for package bees and queens are only in contact with the bees for a few days. The strips must not be used when honey is being produced, so you should not have supers on your hive(s) when using this product. There is some resistance of mites to this product and you should monitor mite levels during treatment to ensure that the treatment is effective.
EPA Registration Number: 87243-1
NV Product Number:
Apivar is another treated strip treatment product with the active ingredient Amitraz. Amitraz causes the mites to become paralyzed and they can no longer feed. The
chemical disperses through the hive when the bees come in contact with the strip, so it is important for bees to move across the strips. Strips should be placed in active parts of the hive to ensure distribution throughout the hive. Check to ensure that the strips are still in the most active parts of the hive during treatment and move them if necessary. The active ingredient does not need to volatilize to be effective, making this product less sensitive to temperature variations.
Strips may be left in hives for up to 56 days. Strips should be disposed of following label directions and local land field requirements. Apivar cannot be used when honey supers are present and must be removed two weeks prior to applying honey supers. To help prevent resistance development, do not leave strips in the hive over winter, remove by 56 days.
Temperature does not directly affect the active ingredient. Cool temperatures do reduce bee movement and may limit the distribution of Apivar. Strips should not be stored for more than two weeks, so plan to utilize this product in the amount that comes in each vacuum sealed package.
CHECKMITE+ BEEHIVE PEST CONTROL STRIP
EPA Registration Number: 11556-138- 61671
NV Product Number: N1641-4
Checkmite+ is also a strip treatment product, but it uses the active ingredient coumaphos. You should use proper protective equipment when applying Checkmite+. It is an organophosphate powder which acts as a nerve poison. The powder may blow during strong winds. Use chemical resistant gloves. Do not use gloves which can absorb the material, such
as standard bee gloves, or latex gloves. Plan to have a bag that can be tightly closed for placing any materials that have come into contact with the powder and to contain any residue from the package. Do not get the powder on your clothing. Follow proper chemical safety for removal and disposal of the gloves after use and be sure to follow proper washing of hands and anything else that may have chemical on it before doing anything else. Comply with all laws regarding chemical disposal. The strips remain in the hive 42 days and you must wait 14 days before replacing your supers, as the honey collected during that time will be contaminated with the chemical. This chemical can interfere with queen rearing, mating and drone rearing. Consider these effects when applying the chemical. Varroa mites are increasingly resistant to this chemical (Mussen 2010), so monitoring for effectiveness is important.
HOPGUARD I and HOPGUARD II
EPA Registration Number: section 18 exempt
NV Product Number: section 18 exempt
HopGuard is another strip treatment product with a hops extract as the active ingredient in this strip. The primary concern for protecting the applicator is to wear protective clothing to prevent contact of body, skin, eyes or mouth with the chemical as it can cause irritation. HopGuard II strips have a more liquid chemical in the strips and can drip on gloves and clothing. Plan to use chemical resistant gloves and protective equipment for your clothing and to have a disposal bag available. Monitor before and after application to ensure control.
Varroa mite management is necessary for any beekeeper and has many variables that should be considered when planning the best approach for managing this damaging pest. Rotate chemicals, so that you avoid chemical resistance. Use multiple strategies to reduce varroa mites and keep your bees healthy. Monitor your hives frequently and intervene when increased mite levels are detected. Using all of these approaches will help you to successfully manage varroa mites in your hives.
Acknowledgments: This project was supported by Agriculture and Food Research Initiative Competitive Grant no. 1138157 from the USDA National Institute of Food and Agriculture.
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