Laboratory evaluation of diatomaceous earths, when applied as dry dust and slurries to wooden surfaces, against stored-product insect and mite pests

The efficacy of Silico-sec® and Diasecticide™ applied as dry dust and slurry applications to wooden surfaces was assessed in the laboratory against adult Sitophilus granarius, and Lepidoglyphus destructor and against larvae of Ephestia kuehniella. Wood was used as the test substrate as it was considered to present a realistic challenge to efficacy due to its 3-dimensional structure. Against the insects, doses of 10 g/m2 Silico-sec® and 20 g/m2 Diasecticide™ were evaluated. Against the mite 1 and 3 g/m2 of the respective Silico-sec® and Diasecticide™ dry dusts and 20 g/m2 of the slurries were assessed. The effects on the insects and mites were assessed one day, 4 weeks and 12 weeks after treatment of the wood. Mortalities were evaluated after exposure times of 24 h and 7 days for the mite and insects, respectively, at conditions of 15 °C and 80% r.h., chosen to represent typical UK conditions after harvest. Of the four treatments, the Silico-sec® dry dust was the most effective against all the pest species, producing 80–95, 100 and 93–100% mean mortalities of S. granarius, E. kuehniella and L. destructor, respectively, over the 12-week experimental period. The Diasecticide™ dry dust produced <11, >99 and 68–93% mortalities of the respective species. The slurry treatments were less effective than the dry dusts with the Silico-sec® slurry producing 29–46, 83–97 and <8% mortalities of the respective species and the Diasecticide™ slurry being ineffective against S. granarius and L. destructor and producing 34–61% mortality of E. kuehniella. This study built on information gained from preliminary work and assessed DEs against tolerant pests on a surface where control was expected to be difficult, in order to provide dose recommendations which would encompass a range of infestation situations in the field.