Toxicity of boric acid (40–99% [AI]), silica gel, eugenol, and deltamethrin dust formulations to adult male German cockroaches, Blattella germanica (L.), was evaluated at five different relative humidities ranging from 0 to 100% and in the presence of 0 to 1 ml of water. Victor boric acid dust was generally the most toxic boric acid formulation at all relative humidities, despite having the lowest percentage (40%) of boric acid; however, this was the only formulation to have sucrose and other edible ingredients. There was no consistent effect of relative humidity on dust toxicity; LT50 values of Roach Prufe (98% boric acid), Victor, and Drione (silica gel and synergized pyrethrins) increased significantly linearly with relative humidity, whereas other formulations were unaffected. The LT50 values of all boric acid-based dust formulations declined exponentially when wetted with increasing volumes of water. Water did not affect the toxicity of deltamethrin and eugenol dusts, but it caused a linear decline in toxicity of silica gel (Dri-Die). The toxicity of a formulation containing silica gel and synergized pyrethrins (Drione) increased exponentially with increasing amounts of water. Moisture in the form of relative humidity does not strongly affect the toxicity of most insecticidal dust formulations. Presence of water, however, increases the toxicity of boric acid dusts and Drione. Toxicity of the hydrophobic deltamethrin (DeltaDust) and eugenol (EcoPCO D) dusts were unaffected by water.
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Vol. 97 • No. 3