Some pyrethroid insecticides have in the past been considered safe for bees because they have a repellent effect which is thought to keep the bees away from insecticide-covered flowers. The chemical drives them off. But it has been known that when pyrethroids are applied in the presence of foraging bees this results in a reduction in their activity (1). Scientists have now found that the affected bees slow down markedly, travel less and spend less time interacting with other bees – vital for bee colonies. They used video-tracking software to quantify these differences in bee behaviour (2).
In the USA, honey bees are carted about the country in vast numbers, to ‘service’, i.e. pollinate, a wide variety of crops like almonds, sunflowers, oil seed rape, apples, grapes and so on. Most crops in fact. A market that was worth an estimated $626 million dollars in 2012 (USDA: Link 3).
The bees didn’t get a penny! In fact, nearly 40% of these American colonies died off last year (2015), although they are quickly replaced with new ones (4). Many of the colonies are placed in orchards which have been sprayed with pyrethroids. Over one million acres of U.S. orchards are sprayed with pyrethroids (5). Whilst the bees are not killed outright by the insecticides, it is now becoming clear that they suffer sub-lethal effects. And although these effects don’t kill them, they definitely don’t make the bees stronger either! Although the link is not proven, it does not seem surprising to me that many of them die after suffering this stress, particular if they experienced heavy doses; together with the additional stress of being transported for thousands of miles on the back of lorries (3).
This study carried out in Nebraska, showed that the effects of the chemicals we put into the environment can be subtle; more subtle that was at first thought and shows that the risks need to be assessed carefully to pick up these sort of low-level effects. In this case it took careful experiments using video-tracking and computer software to quantify differences that might not be obvious to the unaided eye. After all, we can’t ask the bees how they are feeling! Or more accurately, they cannot reply.
It would of course be better if all of our crops round the world were pollinated by native wild pollinators; some of them are, but we need a more sustainable type of agriculture that focuses more on the impact of farming practices on the environment and less on maximizing profit. But farmers have to make a living and we might have to pay more for such a system? Or accept less production. In the meantime, spare a thought for the bees which gave their lives so that we can could enjoy our Californian grapes and cherries!
- Ingram, E. M., Augustin, J., Ellis, M. D., & Siegfried, B. D. (2015). Evaluating sub-lethal effects of orchard-applied pyrethroids using video-tracking software to quantify honey bee behaviors. Chemosphere, 135, 272-277.
I am a retired entomologist with a background in quarantine pests and invasive invertebrates. I studied zoology at Imperial College (University of London) and did a PhD on the population dynamics of a cereal aphid (Metopolophium dirhodum) in the UK. I spent 5 years with the British Antarctic Survey studing cold hardiness of Antarctic invertebates and 17 years with the Food and Environment Research Agency. My main interests now are natural history, photography, painting and bird watching.