Sustainable Management of Varroa Destructor Keith S Delaplane, Phd
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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.