Agenda: Why should we tolerate a diet of weak poisons?

The European Food Safety Agency spent months evaluating evidence and concluded that neonicotinoids pose unacceptable risks to the pollinating insects vital to our food supplies. Westminster's Environmental Audit Committee agreed. Other European countries including France, Germany and Italy have banned them because they think there is enough evidence. And there's been a growing body of support from groups like the Scottish Wildlife Trust, Friends of the Earth and the RSPB.

Since January last year I've been calling for a moratorium, so I'm glad the chemicals will at last be banned, for two years, starting in December.

But what are neonicotinoids and why is their restriction a victory? Well, they're used by farmers to help protect crops like oilseed rape and potatoes from unwelcome insects including aphids. They work on the insect's nervous system, causing paralysis and death.

Usually, seeds are coated with the insecticide before being drilled into the ground. This contaminates the pollen and nectar, resulting in what you might call collateral damage. Non-target insects such as honey bees, bumblebees, hoverflies and butterflies are exposed to the very powerful toxins. In tests half the honeybees died from a dose that was only about four-billionths of a gram.

While most pollinators are only exposed to not-quite-fatal doses, this appears to be enough to interfere with their foraging behaviour. Investigations in the field have shown honeybee nests treated with neonicotinoids grew more slowly and produced fewer queens.

When treated seeds are drilled into the ground, the coating loosens and can become airborne. Researchers have found neonicotinoids in soil from unplanted fields and in plants near treated fields. They're also highly soluble, so remain in the ground for a long time. What long-term effect are they having on our soil? They can get into vegetation around fields and into water courses. But while pollinating insects are important, is there a bigger picture we can't yet see?

Pollinating insects provide a vital service worth at least £43 million a year to Scotland's economy. It's particularly important to our fruit growers. In Scotland 10% of crop production relies on pollination. Insects also form a crucial part of the food chain for birds and other animals. We could see a collapse across our natural and agricultural landscape if pollinators become scarce.

Comments about a "precautionary approach" by Scotland's Environment Secretary, Richard Lochhead, at the weekend were incredibly frustrating. He wanted the ban delayed by two years to allow for more research, patronisingly describing the issue as "emotive" when, quite clearly, it is a rational one about evidence, economic cost and risk. What would be the point of implementing a ban after potentially years' more damage?

Of course, there's concern that not using insecticides could lead to a fall in yields but in many cases treatments are applied as insurance, a belt and braces approach. It's also said the alternatives are worse. But studies from the US show some crops don't benefit from the use of these chemicals at all. You have to remember that farming businesses rely on pesticide manufacturers for technical advice, so there are commercial pressures at play here.

Neonicotinoids only account for one per cent of treatments in Scottish farming so the ban can surely be managed with minimal disruption.

There is the wider issue of chemical control of pests. There are other measures including crop rotation, encouraging natural predators and growing pest-resistant varieties. Perhaps we should be doing more to promote these options.

As Rachel Carson said in that perennial reminder of the folly of chemical treatments, Silent Spring: why should we tolerate a diet of weak poisons? Who would want to live in a world which is not quite fatal?

A new daily column for outside contributors. Contact: agenda@theherald.co.uk

Alison Johnstone is the Green MSP for Lothian.