Sustainable Management of Varroa destructor Keith S Delaplane, PhD

As varroa's resistance to fluvalinate spreads, we must turn to alternative control methods

NOT LONG ago I was conducting training workshops for beekeepers in Honduras. The routine was to travel from village to village and give day-long PowerPoint lectures covering everything from bee biology to genetics to breeding to pest control. I consider myself a moderately engaging lecturer, but on most days my audience would begin fading as the afternoon hours dragged on. The scene always changed at the point when I announced I would now talk about drugs and miticides. Eyes popped open, backs straightened, notebooks emerged and my audience was transformed in an instant from so many vague forms melting in their seats to attentive cadets, pencils ready. ‘Now for something important’, you could

read in their expressions. Claire Waring Beekeepers like using remedial chemicals which are quick BEEKEEPERS LIKE CHEMICALS and easy, so what is the problem? That experience taught me something. Beekeepers like to use remedial chemicals. I have seen that truth confirmed string of prior control measures. many times the world over. And I understand why. There is LOSS OF VIGOUR something proactive about inserting a miticide strip in your hives to knock back varroa. Something responsible. ‘I’m not In much of the developed world there is a sense that the leaving anything to chance,’ one says to himself, ‘This is vigour and productivity of honey bees have declined in the right thing to do.’ I know this warm feeling because I’ve recent decades. I will not stir that pot other than to offer my experienced it myself when I slide a fluvalinate strip prediction that if and when a research-based catalogue of between the combs. causes emerges, it will include pesticides – and these will also be ones designed for use inside beehives. It’s also easy to understand because, well, miticides work. They kill mites. And they kill them quickly with no obvious There are data to support this. Certain formulations of formic acid increase adult bee mortality and interrupt brood harm to the bees. So what’s the problem? rearing(1). One study found a downward trend in lifespan A DEFENCE and sperm loads of drones reared in the presence of fluvalinate(2). Another study showed a reduction in body So what is the problem with pesticides? This is not a trivial weight, ovary weight and stored sperm in queens reared in question and the answer is neither trivial, nicely-packaged, the presence of coumaphos(3). Yet another study showed a nor simple. But the fact is there are problems with acute 50% worker rejection rate of queen larvae reared in wax toxins in bee hives. Our search for these problems has cups laced with 100 mg/kg of coumaphos and those been a natural outcome of a sea change in society’s way of queens that survived to adulthood had lower body weight (4) thinking about land use and food production. This shift than the control group . transcends the scope of this paper, but suffice it to say we What makes these latter results so striking is that live in a time of heightened awareness of the subtle – 100 mg/kg is the legal tolerance level recognised by the some would say insidious – effects of pesticides in the US Environmental Protection Agency for coumaphos in environment. beeswax. Although this position can be pushed to irrational ends, I NON-TARGET EFFECTS think its basic premise is right: pesticides, although expedient and effective, have unavoidable, negative and It is worth stating that the non-target effects of pesticides unknowable consequences far down the cause-and-effect on a host (bees in our case) are always neutral at best. The chain. It is best to think of pesticides as a last resort after a default setting is negative. In the absence of evidence, we

Page 8 Bee Craft November 2007 can rationally presume that phenomenon, to say and disease organisms and pollinators(5). This result whatever biological system nothing of imaginative enrich rural economies for contradicts conventional we choose to examine will scientists to take an interest present as well as future thinking that would have be compromised if it is in the first place. The point generations. This is done in opted for maximum acres breached by a pesticide. is – such unpredictable part by incorporating, not under cultivation and secondary effects do exist ignoring, concepts normally It is also worth stating that demonstrates the economic and possibly explain many read about only in ecology thenon-targeteffectsof value of an ecosystems of the mysterious books: nutrient cycles, pesticides are not only approach to food morbidities that afflict predator/prey relationships, harmful at worst, neutral at production. beekeeping. pollinators, habitat best, or unknown – but the complexity and species At this point we must leave extent of their effects is WHY NOT WIN/WIN? richness. a general discussion of unknowable. Cause-and- sustainable agriculture to effect is not so much a No one seriously disputes The boundary between focus on that subset chain as a web. The the notion that pesticides agriculture and ecology concerned with sustainable ultimate outcomes of are inherently hazardous, so grows fuzzy because varroa mite management. inserting a pesticide, say for much of the modern era, ecology is recognised as a flumethrin, into a system as farmers and policy makers player in the game. And APRIMER have used models that complex as a honey bee because ecology is given weigh the risks to the host colony are so numerous as economic value, there is an Sustainable agriculture was and environment against preceded by a movement to approach infinity – and ethic of environmental the benefits realised by that started gaining voice in therefore the reaches of stewardship permeating the controlling a pest. the1960s.Thiswasatime scientific detection. movement. when the popular press was To offer a purely fictional But such an approach beginning to expose some example, let’s say that presumesthatwemust ECONOMIC VIABILITY of the excesses of flumethrin interacts with the take the bad with the good. This is all fine and good – if chemo-centric pest control. Why should we settle for terpenes in pine lumber it works. It is unreasonable this? Why not invest rather used in beehives to impair to ask farmers to practise One of the driving in management practices motivations for change was the expression of genes environmental stewardship that deliver pest control a realisation that repeated responsible in worker bees at the expense of profits. for recognizing queen without jeopardising the applications of the same Fortunately, available pheromone. Such a colony health of the host or its pesticide quickly select for evidence is promising. I would be handicapped at environment? Why not pesticide resistance. It was cannot disclose many levels. More to the invest in a pest recognised that resistance pre-publication details, but point, this fictional management philosophy could be reduced or my lab is preparing a paper cause-and-effect chain is that rejects a risk/benefit reversed if farmers that documents economic relatively simple because it approach in favour of a expanded their pest control involves only one primary win/win approach? viability of a sustainable measures to include cause, two intermediary varroa management system. non-pesticide practices such This is the sort of thinking causes and one effect, but as crop rotation, beneficial that animates a movement In a more general example, even this simple chain organisms and genetic host known broadly as it was shown in Alberta, poses a formidable resistance. sustainable agriculture. It’s Canada, that yields and challenge to scientific all in the name. Agricultural profits in canola (oilseed It was further recognised detection. practices that are rape) were maximised when that control was optimised It would take years of sustainable are ones that 30% of the land within 750 when more than one experiments and preserve land fertility, metres of field edges was measure was employed, serendipitous observations maintain plant and animal left uncultivated as preferably at different points to discover the productivity, control pest sanctuary for wild in the pest’s life cycle.

Fig 1. A bottom board sticky sheet is generally regarded as the most reliable estimator of colony varroa mite populations. A sticky sheet of paper is placed under a screen which protects bees from entanglement in the adhesive. The whole assembly is inserted onto the hive floor. After 3–7 days the screen is removed, mites counted and the average mite drop per day calculated Photos by Keith S Delaplane Bee Craft November 2007 Page 9 It is this integration of many the level at which the It is generally believed that as possible, preferably control strategies, in favour farmer is justified in themostreliablesampling forever. This can be done by of dependence on any one, applying a pesticide in method is that involving a using a number of that gives the approach its order to prevent a growing screen device on the hive non-pesticide practices name – integrated pest pest population from floor that traps and collects developed over the years, management, or IPM. Today achieving the economic mites when they fall off keeping in mind that one of IPM is recognised as a injury level. bees (Fig 1). The beekeeper the tenets of IPM is to central pillar of sustainable That intermediate level is can remove the screen after attack a pest at as many agriculture. called variably the Economic 3–7 days, count the mites different points in its life threshold, Action threshold andderiveavalueformite cycle as possible. IPM drop per day. or Treatment threshold. I will now talk about some The first step in developing Treatment thresholds are In my country we recognise of these IPM practices. The an IPM programme against sometimes derived by a late season (August) volume of published a particular pest is to grower experience or expert treatment threshold for the determine what density of opinion, but the best ones research on varroa IPM is Southeast as 60–190 mites the pest warrants control. are derived by controlled large and the references per day(6) and for the Pacific This implies that certain research – the more that follow are by no means Northwest, 23 mites per exhaustive. pest levels are region-specific the better. (7) non-damaging and do not day . Early season values warrant a pesticide TREATMENT are more congruent at 1–12 GENETIC HOST application. It also THRESHOLDS in the Southeast and 12 for RESISTANCE recognises that certain pest the Pacific Northwest. levels are damaging and if We who keep bees in the One hallmark of IPM is left uncontrolled will cut into UK or USA are fortunate to UK ON-LINE genetic host resistance. In the grower’s profits. The have some of the world’s CALCULATOR the case of varroa, it has trick is to determine that best developed treatment been slow-going to derive Beekeepers in the UK are pest level in the middle – thresholds for varroa mite. lines of Apis mellifera that fortunate to have an on-line demonstrate measurable Fig 2. Hygienic behaviour is one of the most important calculator that derives a resistance to this heritable honey bee traits for mite and disease resistance. treatment recommendation non-natural parasite. But One way to select for it is to freeze-kill brood in the field based on the month the potential advantages with liquid nitrogen and measure the percentage removal sampled, length of brood areenormousandwell rates by bees. rearing season in one’s worth the pursuit. In this figure, a metal canister is screwed into a patch of area, quantity of drone For one thing, genetic host sealed brood (top left), liquid nitrogen poured in to kill brood present and number brood, the frame returned to the colony and the frame resistance is active around of mites found in one of removed after 24 hours to calculate the percentage of the clock and year-long. It two sampling methods. freeze-killed brood cells removed by the bees. In the requires no more labour bottom right image, the bees are expressing a moderate This is quite simply the than the beekeeper would degree of hygienic behaviour, while expression is 100% in most user-friendly yet realize in ordinary the bottom left image sophisticated model of its requeening schedules. And kind and I recommend it finally, the last ten years highly for beekeepers in the have seen the development British Isles. This resource is of honey bee stocks that available at the National significantly limit varroa Bee Unit (NBU) website: populations by way of http://beebase.csl.gov.uk/ specific heritable attributes. public/BeeDiseases/varroa GENETIC RESISTANCE Calculator.cfm So-called hygienic bees are BELOW THE able to detect abnormalities THRESHOLD in sealed brood, open the cells and remove the Once armed with a compromised contents region-specific treatment (Fig 2). threshold, a beekeeper’s goal in sustainable varroa This behaviour is useful management becomes against brood diseases as clear: to keep mite levels well as varroa(8) and has below the threshold as long been shown to delay

Page 10 Bee Craft November 2007 Fig 3 (right). Varroa mites enter drone brood in preference removal rate of over 76% to worker brood. Beekeepers can insert whole frames of with this method. drone cells into colonies during periods of drone rearing. Once these cells are filled and capped, the frame can be SUNNY APIARY removed and frozen to kill a disproportionately large fraction of the colony’s varroa mite population LOCATIONS Thereisevidencethatby Fig 4 (below). The majority of experimental evidence simply placing an apiary in suggests that mesh floors, compared to solid, increase a sunny instead of a brood production and reduce varroa mite populations shaded location, a beekeeper can expect drone-rearing season. Bees Sincetheireffectsare significantly reduced rates will fill the cells with drone innocuous or good, they are of varroa mite population brood, mites will enter them considered one of those growth(17). in large numbers and once IPM practices – like genetic the cells are capped, the host resistance – that INTEGRATION beekeeper can remove the represent zero additional It is important that an IPM comb and freeze it, killing a labour inputs by the practitioner understands disproportionately large beekeeper. Or almost zero. what to expect from any of fraction of the resident mite It is generally recommended the components highlighted population. that beekeepers in cold above. It is simply this: to significantly onset of climates close the screens Of course, drones are killed delay or prevent onset of treatment threshold(9). over winter. too and critics of the the treatment threshold. Another heritable behaviour method complain that it POWDERED SUGAR is self-grooming by which a An IPM arsenal is useful bee removes a mite from represents a large energetic DUSTING only in the context of a cost to the colony. However, her body and gives it a It has been shown that sampling scheme that (10,11) this cost can be offset lethal bite . coating varroa-parasitised reliably informs the partially by returning the bees with powdered beekeeper of the mite A further success story is the freeze-killed brood to the confectioner sugar elicits a density in his/her hives. As search by the US colony where the bees will rapid mite fall(15).Alianoand long as IPM is keeping Department of Agriculture in subsequently cannibalise it, Ellis(16) expanded on this mites below the treatment the1990sforavarroa- regaining some of their knowledge by developing a resistant population of threshold, there is no need nutrient investment. method to dust an entire honey bees in far-east to apply an acute toxin. colony. Russia. This search was This technique has been Now a criterion like this aided by local scientists and shown to significantly A screened box with solid leaves room for many beekeepers – and was reduce colony mite floor is attached to the front possibilities. It’s possible (12) ultimately successful . density(14). ofahiveandacommercial that IPM could fail, Ô Subsequent field trials in bee repellent (Bee Go ) exercising no impediment theUShaveconfirmed MESH FLOORS applied to run bees into the whatsoever on mite lower varroa densities in box (Fig 5). The box with population growth. It’s colonies headed by In North America there has bees is then removed, possible that IPM could Russian queens(13) and been a resurgence of closed and the bees dusted succeed spectacularly, these now constitute a interest in a technique with 225 g powdered sugar exercising enough restraint growing fraction of the originally documented in and gently rolled to ensure on mites that they never queens used by American Europe – the use of mesh an even distribution of achieve treatment threshold. beekeepers. floors (Fig 4). sugar (Fig 6). It’s possible that IPM could DRONE BROOD In another paper, my After 20–30 minutes, during succeed partially, delaying TRAPPING colleagues and I reviewed which bees are grooming treatment threshold but not some of this literature and themselves, the box is preventing the need for a gently bounced over white This technique relies on the contributed additional rescue pesticide application paper to dislodge and fact that varroa mites evidence in support of the at some point. preferentially reproduce in (9) remove mites from the mix practice . In general, drone brood over worker (Fig 7). Then the bees are bottom screens ‘exert a RAISING THE ODDS brood (Fig 3). returned to their colony by modest restraint on mite dumping them into an But the important point It involves inserting a comb population growth and a emptyhivebodyplaced here is that the IPM of drone cells into the modest stimulus to brood over the brood nest (Fig 8). practitioner raises the odds brood nest during normal production’. The authors report a mite for success with each

Bee Craft November 2007 Page 11 Fig 5. Nick Aliano and Marion Ellis at the University of Nebraska (USA) have developed a way to dust a colony’s entire adult bee population with powdered sugar to induce varroa mite drop and removal. A screened cage is first attached to the colony entrance. A commercial bee repellent, used to remove bees from honey supers at harvest, is applied to run bees into the box Fig 6. 225 grams of powdered sugar are applied to the bees. The box is gently rolled to ensure complete coverage of the sugar

additional IPM component because IPM’s principles 8 Spivak, M (1996). Honey Apidae) in the northeastern he adds to the mix. This is make sense bee hygienic behavior and United States. JEcon 98 the ‘I’ in IPM – the powerful environmentally, defense against Varroa Entomol, (3): 645–50. 27 principle that control is economically and ethically – jacobsoni. Apidologie, : 15 Fakhimzadeh, K (2001). optimised when the pest is and socioeconomic forces 245–60. Effectiveness of confectioner sugar dusting to knock attacked at more than one will continue pushing 9Delaplane,KSet al (2005). Integrated pest management down Varroa destructor point in its life cycle. This beekeeping in that direction. u against Varroa destructor from adult honey bees in idea is even more attractive reduces colony mite levels laboratory trials. Apidologie, when one considers that 1 Satta, A et al (2005). Formic and delays treatment 32:139–48. some IPM components acid-based treatments for threshold. JApiculturalRes, 16 Aliano, NP & Ellis, MD 44 represent zero additional control of Varroa destructor (4): 157–62. (2005). A strategy for using labour and work in a Mediterranean area. 10 Peng, C (1992). Honey bee powdered sugar to reduce around-the-clock. This is J Econ Entomol, 98(2): grooming behavior in Varroa varroa populations in honey true, for example, for an 267–273. mite resistance. Bee Sci, bee colonies. JApicultural 2 IPM beekeeper who uses 2 Rinderer, TE et al (1999). (4): 200–1. Res, 44(2): 54–7. sunny apiaries, resistant Varroa in the mating yard: I. 11 Mondragón, L et al (2005). 17 Rinderer, TE et al (2004). A multifactorial study of the queens and mesh floors. The effects of Varroa The effects of co-mingled jacobsoni and Apistan on resistance of honeybees Russian and Italian honey Experimental support for the drone honey bees. Am Bee J, Apis mellifera to the mite bee stocks and sunny or principle comes from 139: 134–9. Varroa destructor over one shaded apiaries on Varroa (17) year in Mexico. Apidologie, Rinderer and co-workers , 3 Haarmann, T (2002). mite infestation level, et al 36: 345–58. who showed enhanced mite Effects of fluvalinate and worker bee population and 12 Rinderer, TE et al (1997). An control with sunny apiaries coumaphos on queen honey production. Am Bee J, importation of potentially honey bees (Hymenoptera: 144(6): 481–5. and resistant queens, and Varroa-resistant honey bees [Keith Delaplane is Professor of work by my colleagues and Apidae) in two commercial from far-eastern Russia. (9) EntomologyandHeadofthe myself which showed queen rearing operations. Am Bee J, 137(11): 787–9. J Econ Entomol, 95(1): Honey Bee Research and enhanced mite control with 13 Tarpy, DR et al (2007). 28–35. Extension Unit at the University Comparison of parasitic mites resistant queens and mesh of Georgia, USA.] floors. It is my belief that as 4 Pettis, JS et al (2004). in Russian-hybrid and Italian Effects of coumaphos on IPM gains adoption among honey bee (Hymenoptera: queen rearing in the honey beekeepers and as genetic Apidae) colonies across bee, Apis mellifera. three different locations in varroa resistance becomes Apidologie, 35: 605–10. North Carolina. JEcon more prevalent in honey 5 Morandin, LA & Winston, ML Entomol, 100(2): 258–66. bees, that the onset of (2006). Pollinators provide 14 Calderone, NW (2005). treatment thresholds will economic incentive to Evaluation of drone brood become increasingly rare. preserve natural land in removal for management of agroecosystems. Agric, Varroa destructor (Acari: GUARDEDLY Ecosyst Environ, 116:289–92. Varroidae) in colonies of OPTIMISTIC 6 Delaplane,KS&Hood,WM Apis mellifera (Hymenoptera: (1999). Economic threshold I am guardedly optimistic for Varroa jacobsoni Oud in about the future of IPM and Fig 7 (above). After 20–30 the southeastern USA. minutes the box is gently sustainable beekeeping in Apidologie, 30:383–95. general. Guarded, because bounced over white paper 7 Strange,JP&Sheppard,WS to dislodge and remove theeaseandefficacyof (2001). Treatment thresholds mites from the mix pesticides are powerful and timing for the control of Fig 8 (left). Bees are then incentives for individual Varroa destructor in honey returned to the colony by beekeepers to sacrifice bee colonies in Washington pouring them into an long-term ideals for state. J Econ Entomol, 94: empty hive body placed short-term gains. Optimistic, 1324–33. over the brood nest Page 12 Bee Craft November 2007