EFFECTIVENESS OF INSECTO APPLIED TO SHELLED MAIZE AGAINST STORED-PRODUCT INSECT LARVAE

Insecto, a marine diatomaceous earth, is recommended for grain applica tion at 0.5-1 g of formulation per kilogram of grain to control stored -product insects, Mortality and adult emergence of the red flour beetl e, Tribolium castaneum (Herbst); sawtoothed grain beetle, Oryzaephilus surinamensis (L.); and Indianmeal moth, Plodia interpunctella (Hubner ), exposed as Ist instars to shelled maize, Zea mays L., treated with different rates of Insecto were evaluated in the laboratory. For each species, mortality of Ist instars increased with Insecto rate. All Ist instars of T. castaneum were killed at 0.5 and 1 gl kg rates of Insec to; at these rates, mortality of O. surinamensis and P. interpunctella Ist instars was 96-97 and 86-97%, respectively. The percentage of adu lts of the 3 species emerging from Ist instars exposed to treated maiz e was related inversely to Insecto rate. Complete suppression in emerg ence of T. castaneum and P. interpunctella adults was achieved at 1 g/ kg; at this rate, suppression in emergence of O. surinamensis adults w as 98%. Emergence of P. interpunctella adults from Ist, 3rd, and 5th i nstars exposed to Insecto-treated maize indicated that Ist and 3rd ins tars of P. interpunctella were more susceptible than 5th instars to In secto. At 0.5 and 1 g/kg of Insecto, suppression in emergence of P. in terpunctella adults from exposed Ist, 3rd, and 5th instars was 99-100, 73-92, and 6 -37%, respectively. A g-parameter negative exponential r egression model best described the relationship between mean adult eme rgence and Insecto rate for the species and instars tested.