Insecticidal effect and adherence of PyriSec® in different grain commodities

Exposure studies were carried out in the laboratory to assess the insecticidal effect of the formulation PyriSec((R)), which contains diatomaceous earth with natural pyrethrum and piperonyl butoxide, against Rhyzopertha dominica (F.). PyriSec((R)) was applied to eight grain commodities: wheat, whole barley, peeled barley, oats, rye, triticale, rice and maize, at three doses 0.75, 1 and 1.5 g/kg of grain. Dead R. dominica adults were counted after exposure to treated grain for 24h, 48 h, 7 d and 14 d at 26 degrees C and 55% r.h. After the termination of the 14-d-interval count, the treated quantities remained in the same conditions for an additional 60-d incubation period, and the progeny production was recorded. Mortality of R. dominica adults notably varied according to the commodity, but, in most cases more than 50% of the exposed adults were dead after only 24h of exposure. After 14d of exposure, adult mortality was >= 95 % in all grains treated with the highest PyriSec((R)) dose, with the exception of peeled barley, where the respective figure was 84.2%. No progeny was found in the grains treated with the highest PyriSec((R)) rate, but the number of F, individuals was low even in the case of the lowest PyriSec((R)) rate. Significant differences in the degree of PyriSec((R)) retention in kernels were noted among the eight grains tested. The highest retention level was noted for rice (91.4%) and the lowest for maize (10.1%). However, the degree of retention to a given grain was not indicative of the effectiveness of PyriSec((R)) against R. dominica. (c) 2005 Elsevier Ltd. All rights reserved.