Arghghgh -- black fly is back!

Thu 22 May 2014, 11:23

Tony, (just made the name connection!) I don't think the EA would let you go anywhere near the river without a consent which would have to be the result of an comprehensive impact assessment/ survey.

Are there more bites because its a mild spring so people are clothed differently?
Is there any increase in population?
Where locally does the larvae grow?
What other larvae might be affected by treatment?

Just some questions that spring to mind, I would have thought it would be best to focus on speaking to the EA over the issue and asking for their advice on at the cost/ extents of a survey as this might work in the US or the River Stour but be totally unsuitable here.

FYI I'd prefer to use a more local reference than looking across the Atlantic for advice, see below extract from the BBC website:

Control of the fly is difficult and early attempts were limited to habitat modification by cutting or dragging out river weed. However, this was both labour intensive and ineffective. In the late 1980s, scientists from the Centre for Ecology and Hydrology (formerly the Freshwater Biological Association) suggested using a biological insecticide, Bacillus thuringiensis israelensis (or Bti for short). Bti is a naturally occurring bacterium which produces spores which, when they are eaten by blackfly larvae, rapidly kill the insects. The spores carry a toxin which destroys the gut walls of Simuliidae (blackflies) and Chironomidae (midges).

It was, of course, necessary to assess the environmental impact of such a treatment and in 1989 permission was obtained for the trial treatment of a side-channel of the River Stour at Blandford. Detailed monitoring of this showed that Bti successfully killed larvae of the Blandford Fly while having no other effect on other river life. By careful application of the treatment, it was possible to target only the larvae of S. posticatum, leaving even the larvae of other blackfly species (which are vital to the ecology of the river) unharmed.

In 1991 the first large scale treatment of the river was carried out and annual applications of Bti have continued ever since; resulting in the destruction of 80-90% of the Blandford Fly larvae and a corresponding reduction in the numbers of people bitten. Indeed, it is reported that the number of people bitten has dropped to less than one hundredth of those affected in 1989.

It is considered that this use of Bacillus thuringiensis israelensis in Blandford is probably the best example of the use of an eco-friendly biological pesticide, anywhere in the world.