In the PNW Winter Loss Survey this past April, 250 Oregon and Washington backyard beekeepers provided information on monitoring bee colonies for mites, including 12 SOBA members. Thirty-seven percent (37%) said they did not monitor for mites . Twenty seven (27%) sampled pre-treatment and 30% sampled both before and following treatment. Thirty-seven percent used sticky boards, 20% visual inspection of adults and 21% visual inspection of drones, while 17% used sugar shake and 5% used alcohol washing as their sample method. Many who used the sticky board mite drop also visually inspected for mites. Most of the monitoring was done in July, August and September.
As we progress with our BeeInformed survey and monitoring activity, we find that the best way to really tell what is happening relative to mite numbers is sampling colony mites via adult bees. Sticky boards can be a backup to adult monitoring but with debris and difficulty in counting, sticky boards simply do not provide a close enough estimate of total colony mite numbers to provide a good assessment.
Likewise, visually inspecting adults or closely examining drone brood is not accurate enough to help tell us what is happening in the hive. Most of the (phoretic) mites on the adult bees are on the underside of the abdomen, wedged between segments of the adult abdomen and simply not visible unless individual bees are picked up and examined very closely. In August and September, most colonies are simply not rearing enough drone brood to use that method to assess mite numbers.
So how do we use adult bees to determine mite pressure on our colony? The most accurate and fastest, easiest method of sampling adults is to collect a 300 adult bee sample and “wash” the mites from their bodies. Collect adults directly into a wide-mouth jar by drawing the jar downward over the bees clinging to a brood frame or shake 2-3 brood frames into a honey bucket, dishpan or other convenient collecting device and scoop out a ½ cup of adult bees. The ½ cup sample should be put into a jar to which the solid lid is replaced with a screen mesh lid. Next, add rubbing alcohol (caution flammable so do away from the hive and especially a smoker) or a low sudsing soap such as automobile window washer fluid or finely powdered sugar (confectioners’ sugar is OK) to the jar (enough liquid to cover the bees or 2 tablespoons of sugar). The jar with bees and fluid or sugar should then be shaken vigorously. Shake and roll at least one minute.
When using powdered sugar, put the jar in the sun for another minute or more and then re-shake. Pour out the liquid through a coffee filter or shake out the sugar like you would a salt shaker into a white collecting container (pan, dish or picnic plate). Mites removed from the adult workers will be obvious in the liquid filter or in the sugar shaken out (you can mist the sugar with water to dissolve it to more easily reveal the mites). To check your accuracy, add more alcohol/soap/sugar and repeat a 2nd time. The number of mites per 100 bees will quite accurately tell you the size of the mite populaiton present in the colony. To get the number of mites per 100 bees, divide the total mite number by the size of the sample (count the number of dead bees of your sample when using alcohol/soap) or use the convention that ½ cup = 300 bees — so divide the number of mites by 3.
(c) Kathy Keatley Garvey
It is good to have a June sample, a July sample and then immediately after supers are removed, or early August if you are not harvesting, take a sample of each colony. If you have more than 10 colonies, take a sample from every 3rd colony. If you find your mite number no higher than 3-5% (i.e. no more than 3-5 bees/100 adult bees in your sample), it indicates you have relatively little risk that mites will significantly impact your colony overwintering. However sample again in September and October as the mite numbers on adult bodies increase dramatically as brood rearing slows in the fall. This is the time when we need healthy, relatively mite-free bees to rear the fat fall bees colonies need to overwinter.
If mite numbers are higher, (the higher the number the greater the risk that mites might negatively impact overwintering success), you should consider a mite control (chemical or mite reduction technique or begin to prepare for the possibility of winter colony loss). OR-WA backyarder loss rate last winter was 29%, for the 12 SOBA members returning a survey it was 27 %. Using the wash/shake method post-treatment also is the best way to determine if what you have been doing, or elect to do in August/September, really is effective in reducing mite numbers to the 3-5% level.
See pnwhoneybeesurvey.com/survey-results/2015-survey-reports/ for details on losses and what SOBA beekeepers are doing that might be helping to keep loss levels at the lowest levels.