For the Love of Bees and Beekeeping
What Does Honey Bee IPM Look Like?
by Keith Delaplane
When it comes to honey bee health it’s almost become a platitude to extol the virtues of IPM – Integrated Pest Management – an approach to pest control that has dominated agricultural research, teaching, and extension since the 1960s. Over the years, IPM has made impressive advances into mainstream crop culture and animal husbandry. Its adherents can be found at all strata of agriculture from mega-farms to community farmers’ markets. The term began popping up in beekeeping magazines shortly after the arrival of Varroa mites in the 1980s, and today one can find IPM sections in beekeeping catalogs and copious literature about sustainable methods of controlling mites and keeping bees healthy. But it seems to me that there still remains no small confusion over what exactly IPM is. Or at least what it looks like in the case of beekeeping.
For starters, IPM is not the same thing as organic or natural beekeeping – philosophies of food production that, among other things, share an aversion to the input of toxic chemicals. It is not the same thing as let-alone beekeeping or the use of survivor stock. It does not mean an exclusive adherence to “soft” pesticides like formic acid or thymol. It’s almost, but not quite, synonymous with “sustainable” agriculture.
Now it’s true that IPM shares features of all of these, but what makes Integrated Pest Management distinctive is its, well, integration of multiple pest limiting tactics in an effort to keep pests at non-damaging levels. IPM is not explicitly anti-chemical but rather treats chemicals as a last resort after a string of prior measures. If the prior measures work, then there’s no need to use pesticides. If they don’t, then pesticides can always be called into service.
What all this means is that IPM leans heavily on the idea of treatment thresholds – research-derived pest levels that are known to represent the highest pest density that is tolerable without tipping over the crop – or bee colony in our case – into an irrecoverable decline. It’s at this point, and not before or after, that IPM says acute pesticides should be applied. But the emphasis – the whole point of it all – is on delaying that tipping point, ideally forever. It’s a subtle difference that, in my opinion, represents the most responsible way to include acute toxins in our modern food production system.
Now treatment thresholds are variable depending on time of year, location, and the past experience of scientists and beekeepers. Ideally, they are derived from experiments that set up a range of Varroa mite levels, monitor and treat at different times of the season, and retrospectively determine which mite levels and treatment episodes resulted in optimum colony strength and survival. In the table I have put together some published treatment thresholds for representative parts of North America. The most common values reported are number of mites counted from a 24-hour sticky sheet on the bottom board or else mites per 100 bees recovered from an alcohol-wash or sugar-shake method.
Once a beekeeper is armed with a locally-relevant treatment threshold, then the name of the game is to keep the treatment threshold from occurring. This is done by using those “prior measures” I talked about. Those prior measures in classical IPM, developed largely with crop plants in mind, have traditionally been lumped into three categories or triads: biological pest controls, cultural pest controls, and genetic host resistance. Biological pest control refers to the use of beneficial predators, pathogens, or parasites to control a pest, and in row crops they play a huge role in pest insect IPM. But except for some positive evidence with pathogenic fungi and a few anecdotes about pseudo-scorpions and predatory Hypoaspis mites, the literature on natural enemies of Varroa is pretty thin. With reflection this is not surprising, as the large nests of social insects constitute buffered safe habitats (sometimes called “homeostatic fortresses”) in which the parasites themselves may not have evolved many natural enemies.
But when it comes to cultural controls and genetic host resistance, beekeeping IPM fits well with the classical model. Cultural controls refer to steps a grower can take to create growth and rearing conditions that discourage pest populations. In the case of Varroa we have a couple examples. One group showed that ...