1.

This year the beekeepers Ive interviewed are much more confident. Most are using some combination of mite control agents and being proactive. The advice from successful beekeepers is that regular monitoring of mite levels is critical. If you wait until you are seeing mites on your bees, youre starting too late!

Eric Mussen points out that you should not forget to deal with tracheal mite and Nosema disease if necessary, since hes seeing a fair share of colonies damaged by each. If colonies are stressed by mites and disease in Fall, your Fall colony count may have little relationship to the number of strong colonies youll have in February! Indeed, many mite-stressed colonies simply collapse in the orchard the first week of bloom.

Most successful beekeepers in pollination feed their colonies with syrup and pollen supplement to boost colony strength in late Summer. If you want big bees in February, you need to go into Winter with a large cluster of well-fed young bees free of disease (for great info, search Eric Mussens web pageshttp://entomology.ucdavis.edu/faculty/mussen/news_index1.html).

2.

The European honey bee has not yet reached a stable relationship with its relatively new parasite, the varroa mite. In a typical, untreated colony, the mite level is at its lowest point about Christmas time. The mite population increases through the spring, reproducing especially in drone brood (a key point to remember). The colony generally tolerates the mites during this time, since the bees are reproducing faster than the mites, and drone brood is more expendable than worker brood. Then in late July or August (depending on your area) three things happen: the bees stop raising drones, they cut back on brood rearing, and the mite population peaks. At this point in time, there are a large number of mites relative to the small amount of worker brood to parasitize, and the developing workers are either killed outright, stressed to the point that they are susceptible to viruses (especially Deformed Wing Virus), or too weakened to become productive workers. Unfortunately, this is the generation of workers that must support the colony through winter. The result is that the Varroa-stressed colony collapses sometime between fall and early spring. Commonly, the beekeeper observes an active colony in the fall, then some weeks later, there are absolutely no bees, and an abandoned hive full of honey. To make matters worse, as the colony collapses, other colonies will rob it out, and in the process carry mites back to the robbing colonythis is the main mode of dispersal of the mite to new colonies (Goodwin 2006).

3.

In preparing for our brass-knuckled assault on our enemy, we must know its weak spots (Ive put them inboldface). Unfortunately, during the period that mite populations are building, about two thirds of the mites at any time are safely hidden in sealed brood, protected by the silken bee pupal cocoon. Only a few volatile miticides can penetrate the cocoonnotably formic acid and thymol. In the process, however, these two treatments also kill a percentage of the bee brood.

So, other than using a cocoon-penetrating fumigant, we must hit the mite when it is mostvulnerablein the phoretic (hitchhiking) stage.There are two times to do that:when the colony is broodless(during winter, or made broodless by manipulation), or when the mite is feeding on adult bees prior to entering a cell.

Heres the biology: a female foundress mite enters a cell when (or just before) the bee larva is in the propupal stage, but before it spins its cocoon. This occurs about day 8-10 after the bee egg is laid. The foundress mite and any mature daughters emerge with the adult bee on day 21 (if the bee survives until then). Therefore, the mite is hidden for only about 10-12 days. The adult female must then spend from 4 to 15 days sucking the blood of adult bees (usually on nurse beesin the brood nest area) before she is ready to enter a cell and start egg laying. A female mite can live for 3-4 breeding cycles. Reproductive success averages roughly 1-2 viable offspring in worker cells, and2-3 in drone cells.Because of this low rate, in order for the mite population to increase, femalemites must invade a cell and reproduce more than onceduring their lifetimes. Most all methods of beating up the mite focus on its vulnerability during the phoretic stage.

The varroa life cycle takes about 11-12 days in the cell, then several days in the phoretic stage on adult bees. Credit needed.

One other aspect of mite biology is of note: the foundress mite is moreattracted to, and successfully rears more offspring in, drone broodthan in worker brood (on its natural host, Apis cerana, the mite reproduces only on drone pupae), due to the drones larger size and longer developmental period. We can use this fact against our enemy.

Another biological aspect of varroa worth noting is its amazing ability to quickly develop genetic resistance to chemical miticides (at least the synthetic ones that have only one mode of action). Once in a cell, the foundress mite lays a male egg first, then female eggs thereafter. The male mite mates with his sisters, and dies when the cell is opened. This inbreeding locks in successful genetic mutations that might have allowed a particular foundress mite to survive a chemical treatment.

You may have noted that I have not discussed our allies in this battlethe bees (who have a vested interest in surviving). I will cover their contributions further along.

Our Contribution to the Problem

Youre all familiar with selective breeding for better bees. Be aware that we have also been breeding for better mites. That is, mites that can survive our repeated Silver Bullet attacks. Specifically, we have been applying selective pressures to favor mites that:

1. Evolve resistance to miticides

2. Rebuild populations quickly in mite-depopulated colonies (mites with low reproductive success cannot recover from regular treatments)

3. Kill colonies, rather than coexist with them, since colonies that collapse best disperse mites.

In other words, weve been inadvertently selecting for the most virulent, rather than the most benign mites.One could argue that it would be better to change our strategies to reverse the above selective pressures, and promote mites that are less virulent, and that can coexist at a low level in our colonies.

Our Fighting Strategy: Integrated Pest Management

I already mentioned that the Brass Knuckles approach means that were going to accept the mite as a permanent resident in our hives, but were sure going to make its life miserable. If it starts to build up to a level that hurts our bees, were going hit it from several directions, so that it doesnt have a chance to build a defense (resistance) against any single tactic or weapon. The strategy were going to use is called Integrated Pest Management (IPM).

An Overview of IPM for Varroa

O.K., so what does IPM mean for the beekeeper? In a nutshell, learn about varroas strengths and vulnerabilities. Then develop a strategy to thwart its strong points (especially its ability to evolve resistance to miticides), and exploit its weak points, attacking it from several different directions. Allow me to give you an overview of the rest of this series:

First, you dont have to fight the mite single-handedly. There are bees out there with the genetics to fight the mites themselvestheyll just need your help sometimes.

Second, stop freaking out if you see a mite! Understand your enemy, so youre not irrational with fear. The bees can handle a certain level of mites fairly well. Find out for your area, just what load of mites your colony can safely carry at any time of the year. The level that starts to hurt the colony is called the Economic Injury Level. So monitor your mites to make sure they stay below that level. If the mites are at a lower level, relaxyou can sleep at night. However, if they are starting to approach injury level, start hitting them softly. Only if they are over that level would you consider hitting them hard with some sort of strong chemical (you want to save your strong chemicals like a pistol in your back pocket, just in case things start to get out of hand).

Third, lets make it generally miserable for the mite to survive, reproduce and disperse; and do all we can to help our bees fight the mite on their own. These tactics fall underBiotechnical Methods.

One biotechnical method is trapping mites in sacrificial drone brood. Im inserting a drone trap frame in February in an almond orchard.

Fourth, now that youve done the first three steps, that may be all you have to do to maintain a truce with varroa! Unfortunately, most of us will still have to keep fighting. The next step in IPM isSoft Treatments, i.e., chemicals that kill a moderate proportion of the mites, are gentle on the bees, and unlikely to contaminate the combs.

ApiLife Var was one of the first soft treatments. Its main active ingredient is thymol, along with eucalyptol, menthol, and camphor.

Fifth, if soft treatments still havent done the job, and you need to do something drastic to keep your colony alive, then pull out aHard Treatment. The temptation may be to just go straight to hard treatments each year, but in the long run that would just put us back on the Silver Bullet treadmill, since the mites will likely develop resistance to any hard treatment used yearly. So we will use hard treatments sparingly.

The mites success is based upon four main tactics:

1. It hides in the brood (where its hard for us, or the bee, to hit it).

2. It inbreeds, which lets it quickly lock in miticide-resistance mutations.

3. It reproduces relatively slowly, but exponentially, especially in the drone brood. (A weakness: this requires female mites to invade cells multiple times, and thereby expose themselves).

4. It spreads by weakening or killing the colony so that it can hitchhike on robber bees to infest new colonies.

Since we humor ourselves to be smarter than the mite, lets throw a stick into the gears of each of its tactics. What we want to do is to punch the mite from several directions, with each blow coming from a different brass knuckle that only kills, say half of them, so there is less selective pressure for the mite to evolve resistance to any one of our methods. The rationale for this is:

1. There is usually a trade off in overall fitness or vitality involved in the mite changing a behavior, or gaining a biochemical resistance (miticide resistance comes at a cost), and

2. There would be little pressure for the mite to adapt to any one particular threat, since enough mites survive each punch that change is not worthwhile.

3.Remember that varroa peacefully coexists with Apis cerana, and evolved to become less, rather than more, virulent to its original host. So our model is not to exterminate the mite, but rather to just keep it subdued.

So were going to choose a medley of methods and treatments, alternating among them, to keep the mite off balance, and unable to fight back. The key thing to remember is Rule No. 1 of varroa IPM:

DO NOT BECOME COMPLACENT!

Many beekeepers have fallen into this trapyou figure out a great seasonal strategy that gives you good mite control for two years in a row. You pat yourself on the back, and lean back in your easy chair, proud of your victory over those dumb mites. Ive got news for youthe mites never relax. The next year (or the next) those mites come back with a vengeance, and bam!, you feel like youre back on Square One. Join the crowdweve all been there!

So what do I mean by Do not become complacent? Beekeeping was easy in the Good Old Days before varroa. You could figure out a seasonal management system, and repeat it successfully year after year. No morenow youve got to spy on the mite regularly, both at home, and elsewhere. Keep abreast of what its doing in the next state, because it will soon be doing it in your apiary! Monitor mite levels regularly. Some years mites will have low populations for no apparent reason; other years theyll roar into battle like a horde of Mongols. Youve got to be ready to adapt. More importantly, be proactive, and keep one step ahead of them (easy to say, huh?).

That said, the Europeans, who have had the mite much longer than us, have come to the conclusion that IPM is the only way to go (they also tend to run small, labor-intensive operations). I will list a number of useful papers and manuals available on the Web at the end of this series of articles. For the hobbyist, with isolated small beeyards, and the ability to spend a little time with each colony, organic IPM is clearly the way to go, and he/she can then charge accordingly for their honey. The sideliner (which is the most difficult way to keep bees, since your day job pulls you away from critical beekeeping tasks), is going to need a labor-effective strategy.

4.

5.

Both the mite and bee population are at their lowest just before the first brood emerges in spring. The bee population climbs at a quicker rate than the mite population until midsummer, when the bees start to ramp down. The mites get off to a slower start, and then hit their stride during drone rearing season in spring and summer. Note how the mite to bee infestation ratio climbs dramatically in early September. When that occurs, the bees really feel the impact of varroabrood is stressed or dies, viruses run rampant, and the generation of bees that will form the winter cluster is weakened and vulnerable. For a review of the insults that varroa parasitism visits upon a honeybee colony, see the excellent New Zealand guide cited at the end of this article.

A key point to remember is that the relative infestation (percent, or mites per 100 bees) is more important than total mite populationa large colony can handle more mites than a small one. At much above a 2% infestation in spring, honey production drops off severely. At much above 5% in fall, colony winter survival suffers (although the fall economic injury threshold numbers by various authors range from 1% to 11%) (Currie & Gatien 2006). We will return to percent infestation, and economic injury levels in my next article.

Unchecked, varroa can really multiply! A 12-fold increase is typical in a short season consisting of 128 days of brood rearing (Martin 1998). However, its population can increase 100- to 300-fold if broodrearing is continuous! (Martin and Kemp 1997).

There are also major confounding factors. Some years, mite populations are low across the board (possibly due to hot, dry weather) and no treatment is required (Harris, et al 2003; and personal observations). In any apiary, there is usually huge colony-to-colony variation in mite levels, especially if one is using a variety of queen lines. If there is a reservoir of collapsing colonies nearby, mite invasion can make your best mite-fighting efforts moot. Finally, tracheal mites, nosema, viruses, and chemically contaminated combs can cause even relatively low mite levels to be fatal to the colony.

6.

Any general would be foolish to commence a battle without first assessing the strength of his enemy. A beekeeper practicing integrated pest management against varroa is no different. The problem with varroa is thatby the time you start to notice mites on the bees during normal colony management, they may have already built up to a damaging level.That is, varroa are rather inconspicuous due to the fact that about two thirds of them are hidden in the brood, and the phoretic (hitchhiking) mites are usually hiding on the undersides of bees, where the beekeeper cant see them. One must also add the unspoken fact that Joe beekeeper doesnt really want to see mites, since if he doesnt see any, he can enjoy the pleasant fantasy that they are under control.

Because of the difficulty of gauging the degree of varroa infestation during normal colony inspection, the vigilant beekeeper must sample his colonies for mites in a timely manner in order to determine what efforts he needs to be making to keep the mite population at a tolerable level.By tolerable, I mean below the level at which mites are likely to cause, or are on track to cause, economic injury to the colonyslower buildup, less honey production, a viral epidemic, poor wintering, or at worst, colony collapse. That level will vary greatly by time of season, as detailed in my previous article on mite population dynamics.

There are three main ways of sampling the mite population:

1. Natural mite fall caught on a stickyboard under a screen

2. Jar samplesether roll or powdered sugar shake; alcohol or detergent wash

3. Brood sampling with a cappings fork

Each way has its own advantages and disadvantages, and is each most accurate at different times of the year.

Stickies

Stickyboards are generally the most accurate and consistent method of estimating the total mite population, since they monitor the entire colony, rather than just a sample of the bees. They are used to estimate the total mite population by catching the natural fall (drop) of (live and dead) mites from the bees. The natural fall is assumed to be a proportion of the total population. Therein lies the rub: the proportion of mites that fall each day depends upon whether the colony is broodless, beginning broodrearing, broodrearing in earnest, or shutting down broodrearing. According to Martin (1998), one can estimate the total mite population by multiplying the daily drop by 250-500 when the colony is broodless, or by 20-40 when brood is present. Other authors come up with a spectrum of different conversion factors. Luckily, you dont really need to know the total mite populationyou only need to know if the natural daily drop indicates that the mites are at a tolerable level on their growth curve. Note that stickyboard readings can be wildly inaccurate at the beginning or ending of broodrearing, as mites transition from the adult bees to brood, or vice versa.Stickies are the best sampling method during normal broodrearing periods while brood is emerging.

There is no clear harmful threshold at which a mite population suddenly causes harm. A mite population that causes no obvious damage to one colony may prove very damaging to another (from Managing Varroa). Well spoken! Most of us have a hodgepodge of bee genetics in our apiaries, and every colony has a unique combination of genes involved in mite resistance, and susceptibility to viruses and other diseases. This variability problem will likely decrease as we continue selecting for robust and resistant queenlines. You already know what Im going to say: Dont coddle wimpy bees!

Some colonies in some areas will collapse once the total mite population gets much over 1000. Other colonies in other areas can handle 4000 to 5000 mites, and a few have survived 10,000! You can use the U.K. interactive varroa calculator to estimate your total mite population based upon stickyboard counts

http://www.nationalbeeunit.com/public/BeeDiseases/varroaCalculator.cfm

It appears that the best time to do mite control is in winter and spring to nip the exponential growth of mites in the bud. The gist of the European literature supports this, with recommendations to keep mite levels below seasonal thresholds by the use of oxalic acid dribble on the broodless winter cluster, and drone brood removal throughout spring buildup (Ill cover this in my next article). Colonies are monitored in August to see if they need a summer treatment.

VarroaPop modeling suggests that that the critical time for last-ditch mite treatment is August 15th (DeGrandi-Hoffman & Curry 2005). Waiting until September 15th results in a winter cluster of only half the size (18,000 vs. 35,000 bees). This means that the beekeeper has a very narrow window in which to initiate effective mite treatment! If you delay, your bees will pay. My own treatment records confirm this pointyards that I treat in mid August go into winter strong and healthy. Yards that I delay treatment by a month are puny. You may have to pull off honey supers and treat if you want the colony to survive the winter! California beekeepers, due to lack of pollen in late summer and fall, will likely want to give their colonies pollen supplement in late summer to promote broodrearing, and to fatten up their bees after the August treatment.

Rather than thinking of when to apply your last-ditch treatment in late summer, perhaps you should be thinking about the effects of mites hammering your bees earlier in the seasonthat is, during the buildup and honeyflow. Currie & Gatien (2006) compared honey production in Manitoba between colonies that received spring mite treatment vs. those that didnt. Colonies with 2% mite infestation in spring (mid April to mid May in Manitoba) produced only half the honey one year, and only 1/37th as much another year, as did those that received treatment! Not only that, but increased mite levels also increase the transmission rate of viruses between bees within a hive, potentially leading to an irreversible epidemic later in the season. It would be wise for the beekeeper to concentrate upon reining in varroa in the springtime.

Admit that the only way for the mite to sneak up on you, is if youre not watching. Thats why we sampleto avoid surprises. The concept to grasp is that varroa populations do not really explode (except by robbing of collapsing colonies). The population actually grows steadily, just like compound interest in a bank account. The growth rate is about 2% per day. Your best strategy is to retard their growth by various methods during spring buildup, to avoid them ever reaching high populations.Sample during buildup to make sure levels are low before you put your honey supers on.

Unchecked, the mite population will double roughly every month during broodrearing. Understand the concept of doubling. If the mite population doubles from 200 to 400 in May, the colony will barely notice; doubling from 400 to 800 in June will start to stress the bees. The July mite population doubles again from 800 to 1600, and now the bees are definitely stressed, honey production is hurt, and viruses start to spread.What youre most concerned with, is any further doubling once the total mite population passes the 1000 mark (a daily sticky count of around 25, or 4-5 mites in a 300-bee jar sample).Once they pass this level, they appear to explode. If you reach this level in mid August, just before the mite population peaks, no problem. But if you reach it in early July, youd better pull your honey supers and knock em back!

The current level of viruses in bees will often lead to a colony collapse at a total mite level of only 1000 mites.

Based upon the fact that mite-tolerant races of bees rarely allow varroa to exceed a 2% infestation, my current recommendation is :

As a general goal, try to keep the mite level below a 1% infestation of adult bee at any time

24-hr natural sticky fallabout 10 mites

Ether roll or sugar shake of 300 bees about 3 mites

10-min sugar dust dropabout 5-10 mites

7.

Drone Brood Management and Trap Combs

The first punch that were going to hit the mite with is based upon the fact that varroa reproduces rather poorly in worker brood, but is nearly three times more successful in drone brood, due to its longer postcapping period. Its not surprising then, that female mites prefer drone brood by a factor of roughly 10 to 1 (reported figures range from 4:1 12:1). The mites, being tiny and blind, apparently recognize nurse bees by odor (Dillier 2004), and ride around on them until they smell a drone larva of the right age. Since nurse bees spend much more time feeding drone larvae than worker larvae (Calderone & Kuenen 2003), the mites have ample opportunity to come into contact with drone larvae.

A feral colony of bees builds about 17% drone comb (Seely 2002). Rapid mite reproduction in this amount of drone brood largely accounts for the decimation of the feral bees by the mite. The stimulus to build drone combs is good forage (at any time of the year), with a negative feedback from drone brood already existing (Charriere, et al. 2003). Beekeepers, by using worker-sized foundation, can typically keep drone cells down to about 4% if they regularly cull old combs. However, colonies will normally produce temporary drone cells in the space between the brood chambers in spring. Indeed, a quick inspection of the exposed drone brood when you break the brood chambers apart can give you an indication of varroa infestation level.

The beekeeper practicing varroa IPM can minimize varroa reproduction by managing the amount of drone comb in his colonies. This is especially important since hygienic bees remove only infested worker pupae, not drone pupae. Ive already mentioned the importance of culling old combs with drone cells. Wilkinson and Smith (2000, 2001) modeled the effects of drone brood management. They state: At 5% drone brood, as many mites are emerging from 50-60 drone cells as from 1000 worker cells. This certainly emphasizes the importance of drone brood in mite population growth, and the need for beekeepers to prevent large quantities of drone brood being reared unnecessarily and being left to emerge in the hive. They suggest regular and ruthless culling of the old combs and the badly built combs.Their model predicted that reducing drone brood from 4% to 3.2% would reduce the mite population growth rate by 25%!They suggest that drone brood is more important to mite growth at low mite levels, since drone brood capacity for mites reaches its limit before that of worker brood.

Clearly, the beekeeper should cull frames containing drone comb. However, we can go even a step further, and use drone comb to trap mites, and then remove those mites from the colony. This process is called drone comb trapping, and is widely used with great success in other parts of the world. The concept is simple: insert a frame of drone comb into a colony at the edge of the brood nest, allow the queen to fill it with drone eggs, wait while the mites infest the cells, then remove the frame before the mites emerge. Theoretically (Wilkinson & Smith 2002), trapping with one deep drone frame once a month for four months will delay the mite population from reaching a damaging level for 2-4 months; two frames monthly will delay it for a year.

In his study (Calderone 2005), two combs were replaced monthly from June through September. Mite levels were kept to about 2.5% (ranging from 0-7%)up to 10 times less than control colonies! The drone-trapped colonies also made more honey!

Here are the advantages of this design:

1. It takes only about 15 seconds per colony to open the lid, remove the comb, cut out the drone comb with your hive tool, replace the frame, and close the lid. Its so fast that we dont even close the door to the truck when we hit a yard! No freezing or extra work is required.

2. Since the bees must build comb from scratch, the queen can only lay so many drone eggs per day. This restraint extends the period that the combs are actually trapping mites.

3. Since the combs are returned to the same hive, there is no spread of disease from colony to colony.

Points to remember:

1. A full comb removed monthly will generally keep mite levels below threshold.

2. Two full combs would be even better.

3. Two combs, alternately removed every other week, would likely be best.

4. Do not forget to remove the combs at 4 weeks, or youll be breeding mites!

Powdered sugar dusting

Mites are only phoretic for about 5 days during broodrearing (a range of 4-15 days, dependent upon a number of factors (Harbo and Harris (2004)). Therefore, one would expect about a 20% turnover of phoretic mites every day, as older ones reenter brood cells, and new ones emerge. Knowing this, even if you had some new wonder chemical that killed 100% of the phoretic mites one day, youd still have a 20% return of the phoretic mite population the next day, 40% by the second day, and back to the pretreatment level within a week!If you were to take a stickyboard count a week after the 100% kill, you would see zero effect from the dusting!

What I realized was that the problem wasnt that sugar dusting didnt work, but that I was not measuring its efficacy the right way! So I looked to the literature for measured levels of efficacy of an in-hive sugar dusting. To my surprise, there werent any. Fakhimzadeh had only measured the increase in daily mite drop and Aliano and Ellis (2005) had recorded a 75% mite drop only from caged bees. I contacted every researcher and beekeeper I could for an in-hive efficacy figure, but no one had one. So I collected the hard data myself, by dusting three test colonies (one, two, and three story), measuring the mite drop for the first hour, and then sacrificing all the bees in the colonies and washing the mites from them. I will write up a full version of the results when we complete testing, but in short,about a third of all phoretic mites in a colony drop in the first hour after dusting!

I set up a simple mite population growth curve based upon a starting population of 100 mites, and a reasonable 2.4% daily mite growth rate (Martin 1998). Then I killed 1/6 of the total mite population at each dusting, based upon killing half of the one-third of the total mite population that is phoretic at any given time during the treatment period of March 1 through September 1. This model is very crude, and doesnt account for amount of drone brood, multiple infestation, or other variables, and should only be used to give us a rough idea of the feasibility of the technique. I must admit, the results surprised me in how closely they reflected field experience! Clearly, powdered sugar dusting as a mite control measure has proven field efficacy, plus a mathematical model to support it.

The estimated effect of powdered sugar dusting over a screened bottom on mite population growth, based upon a starting population of 100 mites, a daily growth rate of 2.4%, and an estimated kill of 50% of the phoretic mites per dusting treatment. Note that weekly dustings would result in a decrease in the mite population. These curves are based upon very crude math, and are only for general illustrative purposes, although they confirm field experience.

Note that the control curve reaches a devastating mite level by September 1st. Monthly dusting in this model keeps the mite population below a moderate threshold of 3000 mites, and bimonthly dusting keeps em below 1000a load that is considered acceptable by most all authorities. The weekly dustings actually decreased the mite population over the treatment period.

Not only that, but the illustrated curves likely underestimate the effect of sugar dusting, since even though it effectively kills only a sixth of the mites, the mites killed are those that would have been most likely to survive to reproduce. That is, once a mite is in the phoretic stage, its natural mortality rate is very lowabout 0.6% (6 out of 1000) per day, as compared to the 20 30% mortality of those first emerging from cells (Martin 1998). Although about two-thirds of the mites are under cappings and thereby protected from dusting treatments, that proportion is tempered by the fact that a quarter of them will not survive through emergence. This makes the mortality of the phoretic mites more important than their proportion might indicate. Recall from my discussion of mite population dynamics that that a female mite needs to average 2-3 reproductive cycles for varroa populations to grow at the pace that we see in the field. If sugar dusting knocks a mite down early in her life, she will be unable to complete multiple cycles.The surprising effectiveness of sugar dusting may due to its impact on the average number of reproductive cycles that a mite can complete.

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