Effectiveness of insecto applied to shelled maize against stored-product insect larvae

Insecto, a marine diatomaceous earth, is recommended for grain application at 0.5-1 g of formulation per kilogram of grain to control stored-product insects, Mortality and adult emergence of the red flour beetle, 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 Insecto; at these rates, mortality of O. surinamensis and P. interpunctella Ist instars was 96-97 and 86-97%, respectively. The percentage of adults of the 3 species emerging from Ist instars exposed to treated maize was related inversely to Insecto rate. Complete suppression in emergence of T. castaneum and P. interpunctella adults was achieved at 1 g/kg; at this rate, suppression in emergence of O. surinamensis adults was 98%. Emergence of P. interpunctella adults from Ist, 3rd, and 5th instars exposed to Insecto-treated maize indicated that Ist and 3rd instars of P. interpunctella were more susceptible than 5th instars to Insecto. At 0.5 and 1 g/kg of Insecto, suppression in emergence of P. interpunctella adults from exposed Ist, 3rd, and 5th instars was 99-100, 73-92, and 6 -37%, respectively. A g-parameter negative exponential regression model best described the relationship between mean adult emergence and Insecto rate for the species and instars tested.