Differential effectiveness of deltamethrin dust on plywood, concrete, and tile surfaces against three stored-product beetles

Plywood, concrete, and the panels measuring 0.094 m(2) were treated with 0.05% deltamethrin dust at the rate of 3.54 g per m(2) and bioassayed each week for 21 weeks with Tribolium confusum (J. duVal), Tribolium castaneum (Herbst), and Rhyzopertha dominica (F.). Insects were exposed for 24 h, then either removed from the treated surface and held for 96 h (recovery study) or kept on the treated surface for an additional 96 h (residual study). Regression equations for T. confusum survival on plywood in the recovery study did not fit the data. Average survival at the 24- and 120-h mortality assessments was 56.8 +/- 3.8% and 14.8 +/- 2.8%. The LT95 on concrete, as determined by substituting a value of 5% survival (y) into the regression equation and solving for week (x), was 4.7 and 10.5 weeks for the 24- and 120-h assessments, indicating that mortality increased during the holding period. Toxicity was greatest on the, with LT(95)s of 9.7 and 10.8 weeks at 24 and 120 h, respectively, Survival of T. confusum on all three surfaces in the residual study was greater than in the recovery study. The LT95 for 24 and 120 h was 0.0 and 0.2 weeks for plywood, 3.2 and 4.3 weeks for concrete, and 6.0 and 6.4 weeks for the, Both T. castaneum and R. dominica were controlled by the deltamethrin dust, and there were no significant differences among the three surfaces or between the two methods of exposure. (C) 1997 Published by Elsevier Science Ltd.