Response of Sitophilus oryzae (L.), Cryptolestes ferrugineus (Stephens) and Oryzaephilus surinamensis (L.) to different concentrations of diatomaceous earth in bulk stored wheat

Formulations of diatomaceous earth from different sources show variation ill toxicity and ill certain physical characteristics which call affect product efficacy. Also, different insect species show variation in their susceptibility to the product. Adults of Sitophilus oryzea (L.), Cryptolestes ferrugineus (stephens) and Oryzaephilus surinamensis (L.) were exposed to wheat kernels treated with a formulation of diatomaceous earth of Brazilian origin (Keepdry (R)), at concentrations of 250, 500, 750, 1000, and 1250g t(-1) during different exposition periods. The treated kernels, in four replicates of 100g per treatment, were poured in plastic vials and infested with the insects. The vials were placed in environmental chamber at 25 degrees C and 65% RH and the mortality was evaluated periodically. The number of dead insects per treatment was analyzed by the variance analysis and the differences between the means were determined by the Tukey test at 5%. The mortality of the three species was directly related to the diatomaceous earth concentration and to the exposition time, with the best results at concentrations above 500g t(-1). The most tolerant species was S. oryzae that reached 100% mortality only at the 14(th) day of exposition, at 750g t(-1). On the other hand, C. ferrugineus was the most susceptible species to diatomaceous earth; it reached 100% mortality at 500g t(-1) at the 4(th) exposition day. It was concluded that the diatomaceous earth used in these experiments presented a satisfactory control level, and that it represents a very efficient grain potector for using in stored wheat insect management programs.