Even at low doses, an insecticide banned in the European Union kills insect brain cells and could contribute to bee population decline.
The European Union agreed to ban neonicotinoid insecticides including imidacloprid in 2018 to help protect bee populations.
At high doses insecticides do what it says on the label, but research from Australia shows that exposure at low levels can cause oxidative stress in the brain resulting in reduced energy levels, the death of brain cells, blindness and impacts on metabolism in insects.
“We were able to attribute this oxidative stress to the binding of imidacloprid to receptors in the brain,” said Philip Batterham, an emeritus professor at the University of Melbourne.
For bees, this could explain why their guidance system is thrown off course by imidacloprid which could cause a decrease in reproductive capacity.
While insecticides probably contribute to insect population declines, other factors including climate change and habitat destruction play a major role, Prof Batterham said.
These different factors may synergise, and the cost-benefit analysis of certain agricultural practices should be examined.
“We know that many insect species provide vital services, and those services can be in agriculture like pollination, and we’re very focused on that because we realise that the loss of honey bees would be quite devastating,” he said,
“But there are also ecosystem services, there are food chains, and if you begin to lose species then you’re playing a game of Jenga and you don’t know how many species you can lose before ecosystems would be under threat.”
A series of recent papers in the scientific journal Proceedings of the National Academy of Sciences of the USA examine the health of insect populations around the world.
Many are decreasing at a rate of one to two per cent annually, which is concerning in light of the increasing demand for land and food by a rising human population.
However, the decline is not universal and the papers identified species that are increasing in both number and distribution, especially in temperate and Arctic regions traditionally impacted by harsh winters.
There are non-chemical alternatives for pest control including genetic modification and the use of bacteria to specifically impede the reproduction of pests, and Prof Batterham said all options must be on the table.
“We need to assess them all, and do the complete cost-benefit analysis and ask what is the best option in terms of crop yields and environmental health,” he said.
“Two world clocks are ticking, with every passing minute the global human population is increasing, while the available land useful for agriculture is decreasing.”