The efficacy of Dryacide, an inert dust, against two species of Astigmatid mites, Glycyphagus destructor and Acarus siro, at nine temperature and moisture content combinations on stored grain

Dryacide, an inert silicaceous dust, was tested for efficacy on wheat after 14 and 28 days exposure against the mites Acarus siro and Glycyphagus destructor at doses of 1, 3 and 5 g kg(-1), moisture contents (MCs) of 14.5, 15.5 and 16.5% and temperatures of 10, 17.5 and 25 degrees C. After 28 days at 10 degrees C, all doses were effective against A. sire with the exception of the lowest dose at the highest MC, but against G. destructor complete control only occurred at 3 g kg(-1) and 14.5% MC and at 5 g kg(-1) and 14.5 and 15.5% MC. After 28 days at 17.5 degrees C, the dust was fully effective against A. sire at 3 and 5 g kg(-1) but only at 14.5% MC. Glycyphagus destructor was only completely controlled after 28 days at 5 g kg(-1) and 14.5% MC. After 14 days at 25 degrees C, A. siro was completely controlled at 3 and 5 g kg(-1) and 14.5% MC as was G. destructor after 28 days. Neither species appeared to ingest the dust but considerable quantities adhered to their cuticles. The high mortalities observed under the range of experimental conditions, particularly the lowest temperature, suggest that a dose of 3 g kg(-1) may be effective as a replacement for organophosphorous (OP) pesticide surface treatments in an integrated storage strategy based on grain cooling. Exp Appl Acarol 23: 51-63 (C) 1999 Kluwer Academic Publishers.