Neonicotinoids - insecticide problems

Maanantai 30.4.2018 klo 17.07 - Mikko Nikinmaa

In 1962 Rachel Carson wrote the book Silent Spring. It started the modern nature conservation era, and in the end led to banning of DDT. DDT was earlier considered to be an excellent insecticide - only slightly toxic to humans but effectively killing insects. It only had the unfortunate side effect that it disturbed the calcium metabolism of birds and accumulated in the food chain. Therefore especially the eggshells of birds of prey got thinner, and easily broke whereby the number of offspring decreased markedly. However, other insecticides are also a problem for birds, because insects are the major food of many birds. Recent reports have indicated marked decreases of bird populations in Europe. The reasons are easy to see: since insecticides kill insects, there is less food available for birds, and also the toxins usually accumulate in birds, which catch the poisoned insects more easily than unaffected one. In contrast to us humans, birds cannot read and thus don't realize that insects of a certain field should not be eaten because of insecticide application.

Recently, among insecticides, neonicotinoids have attracted the most attention, as they are now banned in European Union. Their development started from the observation that tobacco fields were virtually insect-free. Nicotine is a very effective insecticide (and poisonous to all animals). Thus development of nicotine derivatives, neonicotinoids, was started in various chemical companies. The attention on neonicotinoids stems from the correlations between their use and diminishing bee populations in some studies. For me it is not at all surprising that beneficial bees are affected as much as the insect pests, after all they are also insects. Hitherto one has not been able to develop any insecticide that would only kill insect pests, but leave beneficial insects such as pollinators in peace. I think that will be quite unlikely also in the future. The reason why neonicotinoid use was thought to be useful for agriculture is that oil plant seeds were treated with the neonicotinoid, and the coated seed killed the insect pests during germination. Although neonicotinoids are highly toxic to all insects, it was thought that the concentration would decrease enough during growth, so that flowering oil plants would not be toxic to pollinating insects any more. However, recent results have suggested that this is not the case.

In Finland, the most important group lobbying against neonicotinoid ban has been agricultural producers (MTK). This goes beyond my understanding, since the oil seeds can only be produced, if the flowers are pollinated by insects. If the insecticide kills the pollinators, the production of plant oil ceases. Because of this, one would think that the agricultural producers would be the ones lobbying for, not against, the ban. 

Pollinators, agriculture and insecticides

Lauantai 8.4.2017 klo 13.28 - Mikko Nikinmaa

The production of virtually all vegetable oils depends on plants, which need to be pollinated by bees and other insects. Similarly apples, cherries and most berries are produced only if insects pollinate the plants effectively. Thus, to a large part agricultural production needs insects such as bees. Against this background it is very surprising that especially farmer lobbying groups are strongly against banning of some insecticides such as neonicotinoids - if bees die, much of agriculture becomes impossible.

As such, it should not be a surprise that bees are killed by insecticides: they are as much insects as the harmful insect pests. If insecticides kill the latter, they also kill bees. To my knowledge nobody has been able to produce an insecticide which would kill pests and not harm the beneficial pollinators. With regard to the neonicotinoids, the problem is the following: the seeds are often treated with them, whereby the insecticide is released out of the growing plant, and kills the insects that would be disturbing plant growth. When the plants flower, the insecticide producers have estimated that the excreted amount of neonicotinoid is small enough not to be lethal to pollinators. Some recent results suggest that this is not the case. However, since it is clear that time of plant growth is a significant factor in affecting insectiside excretion, it is to my mind quite surprising that it has not been studied in detail, how the excretion depends on time. Another poorly known question is how long the excreted neonicotinoid remains poisonous in soil. Also this point would need time-course studies. Since such studies are for direct importance to agriculture, funding them should be done by diverting a small amount of agricultural subsidies to toxicological research needed for profitable future cultivation of oil plants.