Tag Archives: mite control

Mite Monitoring – it does make a difference

by Dewey M. Caron

Varroa mites continue to change the beekeeping landscape. In the ‘good ‘ol days’ it was far easier to start a bee colony and keep them alive than today. After introduction of the varroa mites into the U.S. (1987), there was an unprecedented rapid approval of tau-fluvalinate pesticide by EPA for in-hive mite control. And the resulting miticide Apistan® worked very well in killing mites.

Unlike the tracheal mite, varroa mite did seem to be controllable at first. Beekeepers changed from a chemophobic attitude about pesticides (chemicals around bees were to be avoided – ‘feared’) to chemophilic (chemicals were tolerated/useful – ‘liked’). But all too soon we began to understand the ‘unintended consequences’ to the hive environment and our honey bees when we began putting a pesticide inside a bee colony. We seriously contaminated our beeswax with the miticide and mites developed resistance to this chemical within several years meaning it became ineffective.

The subsequent generation of pesticides (Coumaphos – an organo-phosphate compound, developed to kill enemy soldiers in war-time) and Hivestan (fenpyroximate pyrazole) were even more detrimental in the bee environment and mites even more rapidly acquired resistance. Current sole synthetic miticide Apivar (amitraz), although generally not as harmful to bees or their environment, is showing signs of mites developing resistance to it as well.

A mite management concept has begun to creep into our language – IPM, Integrated Pest Management. IPM fits with the concept that it is not practical (impossible) to kill every last mite in our colonies (nor possible to keep them out) but rather we should seek to manage the mite population at a level that is minimally damaging. As we manage the honey bee population for gain, we need to incorporate and integrate mite management – an integrated control program.

The question beekeepers need ask is NOT does my colony(ies) have mites? but rather HOW MANY mites does my bee colony(ies) have? To determine how many means varroa mite monitoring, a crucial first step of an IPM management program. When we determine HOW MANY we become better informed bee colony stewards. HOW MANY helps us know the risk of doing nothing and helps us target seasonally appropriate control(s) to slow mite population growth with goal of keeping mite populations at less damaging, more tolerable levels.

One early (alternative) non-chemical mite control treatment was use of Screen Bottom Boards. With widespread adoption of screen bottom boards in place of solid boards, a whole industry developed incorporating mite monitoring sticky boards beneath the bottom screen (one example shown at right). There were attempts in Georgia, Washington State, and by myself in the Mid-Atlantic States, to determine how best to count fallen mites with a sticky board and how to interpret the numbers – a threshold was developed.

This threshold number has been modified as we have learned that mites vector and enhance viruses. Initially 50 mites per days was a threshold. The number has been lowered, initially to one per hour (24/day) and now one per every 2 hours the mite board is in use (12/day). If boards collect more mites the risk to the colony increases with higher mite fall.

Currently 79% of beekeepers responding to the PNW winter colony loss survey indicate they use a screen bottom board as a mite control technique. (see Screen Bottom Boards – a 4 year perspective  Report posted to www.pnwhoneybeesurvey.com). However after 4 years of survey data for Oregon and Washington small-scale beekeepers, a clear picture emerges that screen bottoms aren’t very useful in reducing mites:

The four year average – 41.3% winter loss level of those using SBB  vs 43.4% loss level for those not using SBB – represents a mere 5% gain (i.e. improved winter colony survival) with screen bottom boards.

A constant discussion has been should the colony bottom be left exposed during winter or should the screen be closed as a winterizing management? Closure was often achieved by using a mite monitoring board with the screen bottom. Four years of survey data tallying the always and sometimes left open response compared with the closed in winter response reveals:

10 percentage point difference in favor of closing the SBB over the winter period (i.e. less winter loss if the board is closed in the fall.)

How Best to monitor Mites

Beekeepers generally have available 5 methods to assess the mite population in their colonies. Sticky boards were initially considered a good tool to do whole colony mite number assessment. However there are problems in use of this tool. Foremost with sticky boards, when used to asses mite colony population, was and remains how to quickly and accurately count the mites on the boards. Mites are tiny, sticky boards collect lots of debris and ants and other scavengers may remove fallen mites.

Natural mite fall (i.e. mite drop not enhanced with use of a control), can vary a great deal for a variety of reasons. Size of colony makes for variation, time of season, degree of auto-grooming behavior by bees and also how the boards are inserted and how long they are left inside adds to more variation. Efforts to reduce counting by sampling only a portion of the drop proved impractical as a large portion of a sticky board still needs to be counted to obtain an accurate assessment.

Sticky bottom boards are useful in providing a quick ‘snapshot’ as to whether there are few or many mites in a colony. It can help validate the effectiveness of a control that was used if utilized post-treatment. They are not adequate to provide a precise estimate of mite population without accurate, time-consuming counting and multiple, repeated sampling.

BOTTOM LINE: Screen Bottom Boards are not an effective mite monitoring method

More problematic as monitoring tool is using a visual method of counting number of mites. This is used for colony worker adults or number of mites within drone brood cells. The phoretic mites, (i.e. those on the adults), are highly mobile and some of the mites are deeply embedded between body segments to enable them to feed on adult hemolymph and fat body. Their deep reddish color and compact flattened body means they blend into the adult color patterns.

The counting of reproductive mites within drone cells has proved to be highly variable. The reproductive female mites are easier to see on the white drone pupae (compared to adult bodies) and sampling of drone pupae within capped cells with use of a cappings scratcher is easy. However numbers are not easily correlated to the actual population level within the colony.  One serious drawback with this method is during the fall months, when mite population assessment is most critical, there are often no or few capped drone brood cells available to assess.

BOTTOM LINE: Visual mite monitoring methods are not effective enough

Thus today we believe counting of the mites on the adults by washing the adults to remove their mites (the feeding mites as well as those ‘riding’ the adult) to be the “best” method. Our two recommended methods are the use of powdered sugar or using alcohol (or a non-sudsing soap). Use of powder sugar allows return of adult bees back into their colony whereas the alcohol/soap kills the sampled bees. See Tools for Varroa Guide on website www.honeybeehealthcoalition.org

Generally a sample size of 300 adults, collected from a brood frame, is recommended. The adult bees can be collected directly into a wide-mouthed sampling jar, previously marked (by sample counting) to indicate 300 bees or the brood frame can be shook into a bucket or plastic container and a ½ cup size measuring cup filled with the bees to dump into the sampling jar. The solid lid of the sample jar is replaced by a 5-mesh screen.

If using powder sugar, a generous amount of powdered sugar (confectioner’s sugar) is sifted onto the sample and the jar vigorously shaken for a minute to thoroughly distribute the sugar and then left to stand for a minute or more to allow heat to build up in the 300 bees. If alcohol is used, add enough iso-propyl (rubbing) alcohol to cover the bees. The liquid is swirled and the bees thoroughly washed for at least a minute. DO NOT RUSH SAMPLING. The mites between the body segments of bees need to separate from their host’s body to get an accurate count. See accompanying photos.

USING powder sugar mite monitoring           Using alcohol wash mite monitoring

The sample jar with powdered sugar is then inverted and excess powdered sugar shaken out, along with the mites that had been on the adults. With the alcohol/soap, the mites will be in the liquid portion which can be poured from the sample through a filter, such as a coffee filter, for counting or simply counted in the bottom of liquid with adult bees held above the liquid at base.

The number of mites washed/sugared from the bee bodies is then converted to per cent number of mites for 100 bees (6 mites on 300 adults = 2% for example). The ‘threshold’ for decisions on continuation or initiation of control is currently 2-3% – this number too has been steadily decreasing. Some beekeepers like to keep the number below 1%. Repeat sampling can be done to confirm accuracy. When the sample is below 2-3% monitoring should be repeated to confirm mite population remains at a low level.

BOTTOM LINE: Washing adults collected from a brood frame using powdered sugar or alcohol/soap is the faster and most accurate mite monitoring method for assessment of mite population in colony

In 4 survey years the percent of OR/WA individuals using sticky boards as their monitoring tools has steadily decreased (from 37% of individuals using them in 2015 to currently 25% of respondents using them in 2018 survey response) while alcohol wash as a monitoring method has increased from 5% of reported use in 2015 survey to 14% in most recent survey.  Use of powdered sugar to monitor mites has also steadily increased although more modestly. These trends are shown in graph below for 4 survey years.

With our pnwhoneybeesurvey we ask percentage of OR hives monitored for mites, whether sampling was pre- or post-treatment or both and, of the 5 possible mite sampling methods, what method was used and what month(s) was it employed.  184 individual respondents (63%) said they monitored all their hives. When those individuals monitoring all their colonies was equated to the loss they reported, the loss rate was 38. Sixty-one (22%) individuals reported no monitoring and when paired with their loss had a loss level of 49% , 9 percentage points higher [43 individuals reported monitoring some of their colonies; they had a 26% loss]. Numbers are shown in Figure below.

Comparing the last 2 survey years there was a lower loss level, better winter survival difference of 8 percentage point lower losses (48.5% no monitoring vs 40.5% loss total monitoring all colonies.) This means a 17% advantage.

In the 2017-18 season, 68% of Oregon individuals used more than one sampling method. 32% of individuals used a single monitoring method (23 individuals used alcohol wash, 19 used sticky board and 18 powder sugar). Of those using multiple sampling methods, 39% used 2 methods, 24% used 3, 5% (10 individuals) used 4 and 1 individual used all 5. Sticky boards were used 108 times, at least once in each month. Alcohol wash was used the fewest times, 51 total and only 11 months with little utilization in an additional 3 months. Most sampling to monitor mites was done in July – September, as might be expected since mite numbers change most quickly during these months and results of sampling can most readily be used for control decisions. See graphic below illustrating monthly use for each of the 5 sampling methods.

Summary: Monitoring colonies for mites helps inform the beekeeper on HOW MANY mites (size of mite population) and with repeated sampling if the number is increasing or remaining level. This can key a decision on risk of doing nothing about mites (i.e. not using a mite control) and also can help confirm that a treatment (when sampled post-treatment) was effective in reducing the mite population. Of the several sampling methods the recommendation is to wash adult bee bodies, collected from the brood area of the colony, with powdered sugar or alcohol/soap. Mite number in sample should be below the 2/3% level to confirm there is a low risk of mite damage to the colony. Consult the Tools for Varroa Guide information on the website www.honeybeehealthcoalition.org for further information on sampling, the meaning of mite sample numbers and for information on mite control.

Download the PDF report here

Survey mite assumptions & failed inventions

There is no selection in mite control for none as an answer it assumes all do mite control and I do not.
RESPONSE – We have a none for non-chemical treatment controls. Then a screen did you use a control – clicking none takes you past the specific controls to section 9 on queens. We do have another for all multiple answer choices and you can put none in there.

My bees are in a hard to feed area and I do well except in wintering. This year I moved them in to their bee house and failed to connect the entrance I invented with nosema and blocking the hive entrance. When I realized my mistake my hives were doomed to fail. Mostly my fault I should have 6 strong hives right now. I lost two hives in late September 15 airplane spray of some type then seven in January 16 I think five I killed with my invention 2 hard cold killed, I lost 2 in February march 16 hard cold snap week hive but one with brood and 3 frames of bees just died I think it should have made it.
Response – The main thing is to learn from the mistake – you had a good idea but it didn’t quite work out as intended. The losses you describe are too common for our area however so maybe it wasn’t just your management (or lack thereof) that was the issue. I trust this season will be different – at least the chance to make a different mistake with the bees.

“…mite control has no effect on survival!”

I’ve tried several different methods of mite control, feeding etc. and it has no effect on survival!

RESPONSE: Mites are a really tough pest to control.  You should be monitoring and use more than one control option. We have to mix up our options. Sorry you have not found the formula of what works best for you yet. Check out the Tools for Varroa Control on the Honey Bee Health Coalition websitewww.honeybeehealthcoaltion.org/varroa

Confusing sanitation question

I don’t understand the sanitation question (maybe the 3rd or 4th)

RESPONSE: thank you for your comment. Apiary site selection means we can reduce drifting and help our bees stay in their proper hives by how we site our hives in the apiary. I am working on further explanation to help better explain – I think we do too little on basic sanitation with our bees and that makes mites stronger and more of an issue in our high colony losses.

Early spring swarming altering counts?

On section 11: I wanted to reply 3-4 colonies, based on my current hives swarming. Went from 2-3 hives due to a swarm from one of my hives this April 2016. Questions about packages of bees vs. swarms of bees might be of use in terms of overwintering, Queen health and survival. With regard to varroa control, allowing for natural swarming to break the mite cycle might be an informative category. In terms of learning beekeeping, my best source has been the online Warre listserv. Might want to include such a category (yahoo groups) in your questions. Thanks so much for doing this! I look forward to seeing the results.

RESPONSE: That you for your comments although we do get at many of them within survey questions.  Allowing annual swarming might be a good response option to split out. I think online sources should be an option – will see about adding it & we do have category other which is where you would state this. We will transfer it from here this year.

Varroa mite control – what works ! By Dewey M. Caron

The pnwhoneybeesurvey received responses from 250 backyard beekeepers in 2015. Overall overwinter losses of individuals with either 8- or 10-frame Langstroth bee colonies was 27%; factoring in total backyarder losses for beekeepers entering winter with Langstroth, Top Bar, Warre, 5-frame nucs or other hive types was 29%. Our annual OSU survey of commercial and semi-commercial beekeepers (13 OR individuals maintaining some 60% of the estimated total colonies in the state) was 14.2%, somewhat below the commercial/semi-commercial beekeeper loss rate in the Pacific Northwest states of OR, WA and ID combined (=15.7%).The BIP national survey that included both backyarder and commercial beekeepers, reflecting survey responses from more backyard individuals but the majority of colonies were those of commercial beekeepers, reported a slightly lower overall loss of 23.2% . This is shown graphically as Figure 7 below.v1
Mite Monitoring
One hundred sixty three (163) individuals reported that they monitored for mites during some of the previous year (see pnwhoneybeesurvey.com for information on monitoring and when the monitoring was doneseparated by method of monitoring). The graph below shows the method used expressed as percent of individuals with number of individuals shown in ( ) within the graphic. One hundred individuals (37%) used sticky board mite drop, slightly over 100 (41% total) used visual inspections of either adult bees (54 individuals) or drone brood (55 individuals), while 45 individuals (17%) used sugar shake. Fourteen (14) individuals did an alcohol wash (5%) of total. The total is greater than 250 since
44% of responding individuals used more than one monitoring technique (both visual inspection methods were often checked for example).v2
We know the most reliable technique for examination of mite populations within a bee hive is via use of alcohol washing or powdered sugar shake. When we compared the individuals who used each technique (whether singly or in combination with another technique) and the reported loss by the same individuals, the result illustrates how significant monitoring with sugar shake was as this group had significantly lower overwintering losses (22%) compared to those who did not monitor (89 individuals – 31% loss) or used visual monitoring (29% and 31% loss rates -see graphic below). Those who checked sticky board also had significantly lower losses (22.5%). Individuals (14 total) who used alcohol washing did not show reduced losses, in part, because the variation among those 14 individuals was large.

Use of a Non-Chemical Control
We asked in the survey about control, both with a varroa control chemicals and via use of a non-chemical technique. In the options for non-chemical control, we received 406 responses from 75% of the individuals – 25% (49 individuals) did not indicate use of any of the choices nor fill in the other selection opportunity. Ninety-seven individuals (51%) ireported use of 2 (56 individuals) or 3 or more techniques (41 individuals). The graphic below shows the percent loss response for the alternatives offered, minus the 150 individuals (37%) of responses who checked use of screen bottom board (which is reported in a different report on the pnwhoneybeesurvey.com website – under Screen bottom boards.) Losses for each alternative are irregardless if they used only that technique alone or used it along with another/other methods.v4

There is no statistical difference between the data points. None were widely used. Individual selections varied from 49 individuals who checked nothing used to 21 individuals who said they used the technique of requeening. Numbers were relatively small and variation was large. The only value that was below the 27% average loss was use of small cell/natural comb (24% – most responses seemed to be the natural comb choice). Largest loss values were for requeening (36%) and brood cycle interruption (39%), the two techniques that are usually listed as viable, useful non-chemical controls. Why they are on the high end of the loss scale is unknown.
Chemical Control
For the users of 8 and 10 frame Langstroth hives, we compared the percent loss of individuals who used a chemical control for varroa mites (142 individuals) to those who did not. The loss rate of those using a chemical control were one-third as large as the overall group and were nearly double for those who did not use a chemical control. Results were statistically significant from the total loss of this group of 27%. v5
Examining individual choices (50 individuals reported use of more than one chemical) show use of three materials,resulted in significantly lower overwintering losses. Graph below. v6
Beekeepers have various options for Varroa control. The key to better overwintering is to monitor using sugar shake or alcohol wash to determine infestation level of a colony and then depending upon the season deciding on what might be an appropriate chemical or non-chemical technique to use to reduce mite populations. In this survey response we were unable to demonstrate the usefulness of non-chemical use to reduce overwintering losses. The BeeInformed Survey  2014-2015 preliminary results  does support our belief that non-chemical approaches can be useful and the Honey Bee Health Coalition website Tolls for Varroa Management guide Varroa management guide provides information on usefulness of an integrated non-chemical and chemical control approach to varroa mite population management.
Dewey M. Caron Sept 2015

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Screen Bottom Boards by Dewey M. Caron

Screen Bottom Boards (SBB) have a number of uses in our bee stewardship. They are widely substituted for a solid bottom board.  A 1939 Delaware beekeeper removed his solid bottom and left his colony open at the bottom, which he termed bottomless beekeeping. There truly is nothing “new” in our beekeeping practice of using a screened bottom on hives. Although many beekeepers use SBB to control varroa, BIP and PNW surveys clearly point out they are not a very effective varroa mite control tool.

In our national BIP surveys, fully 95% of respondents indicate they have modified the colony bottom board and now use a screen bottom board. sbb1 Our PNW Honey Bee Survey also asked respondents about screen bottom board use. Among Oregon and Washington hobbyist (backyarders or small-scale beekeepers), 79% of the 250 respondents said they used screened bottoms; 66% used them on all their hives with the remaining 13% using them on a percentage of their hives (See figure right).

Comparing overwinter loss percentage, there was no difference for the 21% who did not use SBB (27% loss rate , same as tsbb2he overall 250 respondent base) compared to the79% who did (25% middle column in left graphic  – column on right of graphic is overall loss rate for those beekeepers using either 8-frame or 10 frame Langstroth hives – when the data for individuals who used other hive types besides Langstroth is included, the overall overwinter loss rate for backyarders was 29%).

We also asked whether they blocked colony SBBs during the winter. The majority (51%) left them open over the winter period sbb3(never response). 19% sometimes blocked them and 31% said they closed them (always response) during the winter (see graphic right). When we examined winter losses for this response, there was no statistical dfference in loss, although the trend was for lower losses when the SBB were closed  (24% vs 31%).

As stated above, SBB are not an effective mite control tool, although most beekeepers state they are using them for that reason. In our PNW survey, respondent beekeepers who said they used bottom boards as a non-chemical treatment option for varroa mites, had no statistical improvement in survivability.  Langstroth 8-frame beekeepers who listed SBB use, entered winter with 97 colonies losing 25 by the spring (=25% loss rate) and Langstroth 10-frame beekeepers entered winter with 596 colonies of which 440 survived ( =26% loss rate); other hive types included in the survey (5-frame nucs, top bar hives or Warre hives) do not easily lend themselves to bottom modification with screening, although some individuals with such hives may use a partial bottom screen in place of a solid bottom.

With our Bee Informed National survey (www.beeinformed.org), use of SBB did not improve winter survival rate in any of our survey years when we directly compared their use with loss rates. However in survey year 2013-2014, northern beekeepers did have about a 10% decrease in losses when SBB were used compared to southern beekeepers. Experimental studies on SBB and mite population levels show either no or this slight ~10% improvement in reducing mite population levels when SBB are used.

So what can SBB do to benefit our bees?

Using a screen bottom aids greatly in hive ventilation. sbb4 It can be used with upper entrances at the covers or with ventilation ports added to hive bodies. Air circulation for better ventilation can be further aided by pushing the outer frames inward a bit to allow air circulation upward between the outer frame and box wall. Heavy burr and brace combs, sometimes due to incorrect bee spacing between the hive boxes, when both the bottom bar and the dropping of the top bars below the rim creates a ½ inch of larger space, and heavy propolis use in the fall, may reduce good air circulation in the boxes.

During winter, beekeepers at more northerly locations or higher elevations often close or reduce the screen opening beneath their colonies. It is not advisable to have wind blowing into the bottom of a winter colony but an air space beneath the colony, with screen bottom board left open, is not detrimental to colony wintering. The dead air space and moderating soil temperatures may be helpful. Often this dead space beneath a screened bottom can be created with hive stand configuration.

Another advantage of a screen bottom board is that it provides for a convenient garbage pit to remove debris and fallen mites from a colony. The original Langstroth hive had such a feature but it was discontinued when the hive construction was simplified. They were thought to promote wax moth with the design Langstroth used.

Screen Bottoms may offer some improvement for some beekeepers, particularly where winter confinement period is long and when mite populations are lower. In is not clear if this improvement is due to mites alone or to the other effects a screen vs closed bottom may have on colony survivability (see below). As regards varroa mites they should be considered a tool that may reduce winter losses when used in combination with other mite control treatments and tools.

August 2015 Dewey M. Caron

To download a copy of this report click here