INSECTICIDE RESISTANCE IN BLATTELLA GERMANICA (L.) (DICTYOPTERA: BLATTELLIDAE) FROM HOTELS AND RESTAURANTS IN MALAYSIA

Abstract:
Twenty three strains of field populations of the German cockroach, Blattella germanica (L.) collected from hotels and restaurants from various localities in peninsular Malaysia were tested for their susceptibility to commonly used insecticides (propoxur, bendiocarb, chlorpyrifos, fenitrothion, pirimiphos-methyl, cypermethrin, permethrin and deltamethrin) using a modified W.H.O. tarsal contact method at a standard concentration of 20 mg cm-2. Several strains were also tested against other insecticides (DDT, endosulfan, dieldrin, diazinon, chlorpyrifosmethyl, malathion, carbaryl, etofenprox, bifenthrin and acetamiprid). Susceptibility to hydramethylnon was evaluated using commercial baits with a feeding bioassay method. Low to high levels of resistance to carbamates were detected (1.8 – 65.2X) while resistance to organophosphates was low (1.1 – 4.3X). However, one strain demonstrated high resistance to malathion (>275X). Resistance to pyrethroids ranged from 1.1 – 17.6X. Eleven strains tested showed low to high resistance to DDT (1.3 – 40.7X). No resistance to hydramethylnon-based baits was detected in this study (<1.3X). Several strains were chosen for synergism studies using piperonyl butoxide (PBO) and S,S,S-tributylphosphorotrithioate (DEF). Resistance to carbamates was partially suppressed by PBO and DEF, suggesting possible involvement of monooxygenase and esterase in the resistance. However, organophosphate resistance was only negated by DEF. Resistance to pyrethroids in several strains which also demonstrated DDT resistance, was not suppressed by both PBO and DEF, indicating possible involvement of a non-metabolic resistance mechanism.