Insect Pollinators in Trouble


Professor Stuart Reynolds, University of Bath

28 January 2016


In recent years, populations of honey bees, bumble bees and other insect pollinators have experienced unexplained declines. The problem is real, although the way it is reported is sometimes hysterical. Documenting it is made difficult by the fact that wild pollinator populations experience marked year-to-year variation following environmental factors like the weather. And when economists look at the problem, they notice that domestic honey bee colony numbers have frequently declined when imports of honey went up. What looks like an ecological problem turns out in some cases therefore to be an economic one.

Green pressure groups blame chemical companies and farmers for pollinator troubles; farmers naturally disagree. Some countries including the UK have banned some pesticides. In the USA, interest centres an unexplained syndrome called “colony collapse disorder” (CCD). A virus is thought to be responsible but this has not yet been proved. And some North American commercial bee keeping practices look distinctly unhelpful to honey bee heath. Moreover, “CCD” is frequently supposed to be a worldwide problem, but it is not at all evident that bees in other parts of the world suffer from the same problem.

In fact, it isn't at all clear that all the finger pointing is supported by good evidence.

It would be nice if science could give strong recommendations on how to ameliorate the troubles that evidently beset insect pollinators, but actually the usual methods of science turn out to be not very well suited to solving what is almost certainly a multi-factorial problem. Science is good at solving clearly defined problems, but here we appear to be faced with what is probably many problems all at once, all of which have the same effect - to cause declines in pollinator populations.

In his talk Professor Reynolds examined the extent to which it is possible to tease out the reasons for pollinator declines.

Probably foremost among these is the ever-increasing intensification of farming, which leaves agricultural landscapes with fewer and fewer wild flowers. These are necessary for insect pollinators to prosper - feeding from crops is not enough because the crops are not available all through the pollination season. Moreover, monoculture pollination may result in nutritional problems for bees.

Second, the modern worldwide trade in bees has resulted in the worldwide spread of bee pathogens and parasites. These spread rapidly among pollinators (not necessarily only among honey bees) when they visit flowers previously and promiscuously visited by other pollinators; this is in fact rather similar to the spread of sexually transmitted diseases in humans. The fact that some bee diseases and insecticides equally depress bee immune systems doesn’t help. In fact in comparison with “bee AIDS” may be appropriate here.

Third, honey bees and bumble bees may be particularly susceptible to insecticide problems. Eusocial bees are particularly important as pollinators; this is because their sophisticated communication and navigation systems enable them to share information about flower locations among close relatives (nestmates). Because of this, these insects may suffer behavioural disruption when exposed to sub-lethal doss of insecticides in the field; these are doses that would appear harmless when tested by normal acute safety-testing methods.

The insecticides most often blamed are the neonicotinoids, mostly used as systemic seed treatments in crops like oilseed rape, sunflowers and soya beans. Professor Reynolds reviewed the evidence that that these chemicals are indeed capable of haring bees, and also discussed the EU and UK moratoriums on using them.

But insecticides are an easy and popular target for Green pressure groups. The chemicals that get most blame may not turn out to be the important ones. And what about the notoriously impossible problem of pesticide mixtures? And anyway, beekeepers themselves use pesticides to control infestations of Varroa mites. In the end, it is possible that chemicals may not be very important at all.

Finally, and importantly, the peculiar sex determination genetic system of bees leaves them more than usually susceptible to inbreeding depression (an example of what is sometimes known as the Wallace effect). Once a bee population falls below a certain size, it suffers a descending spiral of fitness loss.

And of course, some people even blame mobile phones… despite the popularity of this idea on the Internet, Professor Reynolds dismissed it for lack of supporting evidence.

Everything points to a multifactorial problem. Given this, how can bee research help regulators and beekeepers? Mostly, said Professor Reynolds, by restraining the enthusiasm of commentators for over-simple solutions.