Evaluation of a new, enhanced diatomaceous earth formulation for use against the stored products pest, Rhyzopertha dominica (Coleoptera: Bostrychidae)

Abstract

Laboratory bioassays were carried out with DEBBM, a new enhanced diatomaceous earth (DE) formulation that contains the plant extract bitterbarkomycin, against adults of Rhyzopertha dominica (F.). Three series of tests were conducted. In the first, R. dominica adults were exposed on wheat treated with DEBBM at three dose rates, 50, 100 and 150 ppm, and mortality was measured after 7 and 14 days of exposure, at three temperatures (20, 25 and 30°C) and 65% R.H. Mortality increased with increasing temperature; at temperatures ≥25°C, after 14 days of exposure, mortality exceeded 98% even at 50 ppm. In the second series of tests, the same doses were assessed at 25°C and at two levels of R.H. (55 and 75%). In this case, relative humidity did not seriously affect the insecticidal effect of DEBBM, at the doses tested. All adults were dead after 14 days of exposure at 55% R.H. at doses ≥100 ppm. In the third test series, 50 and 150 ppm of DEBBM were added to wheat, barley, maize and rice, in order to evaluate the impact of grain type on the effect of this DE. No significant differences were noted in mortality levels among different grains. With the exception of maize, after 14 days of exposure, all adults were dead. This new enhanced DE formulation is shown to be effective at dose rates that are considerably lower in comparison with older DE formulations.