Etofenprox guarding concrete for six weeks: immediate and delayed mortality of three major stored-product coleopterans

Abstract

This study addresses the residual efficacy of the pyrethroid insecticide etofenprox sprayed on concrete surfaces for the management of Prostephanus truncatus (Horn) (Coleoptera: Bostrychidae) adults, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) adults, and Trogoderma granarium Everts (Coleoptera: Dermestidae) adults and larvae, through a period of six weeks. Three doses of etofenprox (5 μg/cm2, 15 μg/cm2, and 45 μg/cm2) were tested to assess immediate (1, 2, 3, and 7 days of exposure) and delayed (7 days post-exposure) mortality. For P. truncatus, after 7 days of exposure, immediate mortality ranged between 35.6% and 53.3% the first week while the sixth week ranged from 12.2% to 27.8% after a gradual decrease the weeks in-between. Similarly, at the same exposure interval, the tested doses of etofenprox killed 36.7–62.2% of R. dominica the first week while 20.0–41.1% the sixth week. Etofenprox provided the highest mortality rates against T. granarium adults reaching 93.3–97.8% the first week. After a progressive decrease, mortalities ranged from 73.3% to 87.8% the sixth week. Regarding T. granarium larvae, 43.3–63.3% of the exposed individuals died the first week but during the last week mortalities decreased to 13.3–32.2%. Delayed mortality of all tested species/developmental stages was elevated the first week, reaching 100.0% for all tested doses against P. truncatus and T. granarium adults. During the last week, 45 μg/cm2 killed 100.0% of P. truncatus adults, 67.4% of R. dominica adults, and 42.9% and 31.1% of T. granarium adults and larvae respectively. The results indicate that the efficacy of etofenprox on concrete depends on the pest species/developmental stages that are exposed and/or the time that has passed since the application date.