Effectiveness of Insecto Applied to Shelled Maize Against Stored-Product Insect Larvae

Abstract

Insecto, a marine diatomaceous earth, is recommended for grain application at 0.5-1g 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 1st instars to shelled maize, Zea mays L., treated with different rates of Insecto were evaluated in the laboratory. For each species, mortality of 1st instars increased with Insecto rate. All 1st 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 1st instars was 96-97 and 86-97%, respectively. The percentage of adults of the 3 species emerging from 1st 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 1st, 3rd, and 5th instars exposed to Insecto-treated maize indicated that 1st and 3rd instars of P. interpllnctella were more susceptible than 5th instars to Insecto. At 0.5 and 1 g/kg of Insecto, suppression in emergence of P. interpllnctella adults from exposed 1st, 3rd, and 5th instars was 99-100, 73-92,and 6-37%, respectively. A 2-parameter negative exponential regression model best described the relationship between mean adult emergence and Insecto rate for the species and instars tested.