Use of a pyrethrin larvicide to control Culicoides variipennis (Diptera: Ceratopogonidae) in an alkaline lake.

Laboratory bioassays with Culicoides variipennis larvae from Borax Lake, CA, indicated an LC90 of 16.8 ppb for pyrethrins at 23 degrees C. A field test in a pond adjoining the lake reduced adult C. variipennis emergence greater than 99% for over 30 days after treatment at a rate of 131 ppb pyrethrins. Further small scale field tests indicated that C. variipennis could be controlled in the lake at a rate of 701 g/ha pyrethrins applied as a peripheral treatment. The first lake treatment resulted in a 99.3% decrease in the density of C. variipennis larvae along the shoreline. Four treatments resulted in a 98.5% decrease from non-treatment years in the number of adult cumulative insect-days during May and June.