Oral toxicity and repellency of borates to German cockroaches (Dictyoptera: Blattellidae).

Abstract

The oral toxicities of boric acid and disodium octaborate tetrahydrate (DSOBTH) in dry-mixed, wet-mixed, and water-based solution baits were determined for German cockroaches, Blattella germanica L., in choice and nonchoice experiments. In dry-mixed, nonchoice bait tests, all cockroaches died within 1 wk. Time to mortality decreased as the concentration of boric acid increased. The LT50s for DSOBTH were not significantly different for any concentrations tested. In choice tests, the order of LT50s of boric acid and DSOBTH were 6.25% = 12.5% > 25% = 50% and 25% > 12.5% > 50% > 25%, respectively. Consumption of treated and control baits and the differences between the LT50s of the nonchoice and choice tests indicate repellency of the toxicants. Most German cockroaches died in 3-6 d in wet-mixed nonchoice tests, but all cockroaches survived the wet-mixed choice tests except at the lowest concentration of boric acid. This result indicated repellency. In nonchoice tests with water-based solutions, all cockroaches died in 5 d. In choice tests with boric acid solutions, mortality did not increase at concentrations > 1%. Choice/nonchoice ratios indicate no repellency of water-based solutions. In addition, consumption of treated and blank solutions was not significantly different for any concentration except 4% DSOBTH.