Toxicity of amorphous silicas and silica-pyrethroid mixtures to Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Abstract

The toxicity of some pyrogenic and precipitated amorphous silicas to Tribolium castaneum (Herbst) was assessed in admixture with wheat grain. A good correlation ( r 2 = 0.82, n = 7) was found between the 48 h LC50 of the toxic dusts and their adsorption capacity for a saturated hydrocarbon oil. The pyrogenic silicas Cab-O-Sil M5 and Aerosil R972 were used as carriers to prepare dust formulations of permethrin, cypermethrin and deltamethrin at various concentrations, and 48 h (Cab-O-Sil M5 and Aerosil R972) and 168 h (Cab-O-Sil M5) LC50s were determined using the same bioassay system. Low and intermediate concentrations of the pyrethroids substantially reduced the 48 h LC50s of these silicas while high concentrations antagonised their toxic action due to knockdown effects. The 168 h LC50s of Cab-O-Sil/permethrin formulations were approx 15 and 150 × lower than those of talc/permethrin formulations at 2% w/w and 0.1% w/w respectively. The 168 h LC50 of the Cab-O-Sil/cypermethrin formulation was comparable with that of the talc/cypermethrin formulation, and that of the Cab-O-Sil/deltamethrin formulation was about 5 × less than a talc/deltamethrin formulation, at 2 and 0.2% w/w pyrethroid respectively on the dust carrier.