The experimental treatment of the blackfly, Simulium posticatum in the Dorset Stour using the biologically produced insecticide Bacillus thuringiensis var. israelensis.

Published online
11 Aug 1995
Content type
Journal article
Journal title
Journal of Applied Ecology

Welton, J. S. & Ladle, M.

Publication language
UK & England


Simulium posticatum causes a severe biting problem in the valley of the river Stour in Dorset, UK. Various control measures have been attempted including egg removal and weed cutting to remove associated larvae. Following a small-scale trial of the larvicide B. thuringiensis subsp. israelensis (Bti) in a side-stream of the Stour during 1989, permission was obtained to treat 4 sites on the main river between Blandford and Wimborne in 1991. The effect of Bti treatment (with Teknar HP-D) was monitored at sites up to 1300 m downstream of the application points. Mortality of S. posticatum was between 82% and 98% except for the site 1300 m downstream of Blandford where the kill was 68%. Extensive sampling of Chironomidae and other benthic invertebrates over a period of 84 days failed to show any effect of treatment on non-target organisms. Diurnal drift sampling was undertaken to assess any possible change in behaviour of invertebrates and to sample any dead animals in the water body. Again, no effect was found with the exception of dead larvae of S. posticatum within 1 day of treatment. By careful monitoring of simuliid populations it was possible to treat the river when only S. posticatum larvae were present, between winter and summer generations of other species.

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