Toxicological and Biochemical Studies with Field Populations of the German Cockroach,Blattella germanica

Abstract

Topical bioassays with cypermethrin, λ-cyhalothrin, permethrin, propoxur, and chlorpyrifos were conducted on 12 German cockroach strains recently collected from the field. Resistance levels ranged from 3- to 159-fold for cypermethrin, 2- to 88-fold for permethrin, 4- to 55-fold for λ-cyhalothrin, 5- to 33-fold for propoxur, and 3- to 19-fold for chlorpyrifos. The synergists piperonyl butoxide (PBO) andS,S,S-tributylphoshorotrithioate (DEF) affected cypermethrin resistance to varying degrees depending on the strain. Piperonyl butoxide pretreatment decreased cypermethrin resistance in only 5 strains, but caused an increase in resistance level in 7 strains. Conversely, DEF pretreatment reduced the resistance level in 10 of the strains and increased the resistance level in only 2 strains. Correlation analysis of resistance ratios for each strain and insecticide indicated a direct relationship between resistance level of one insecticide and another, especially among the pyrethroids. All field strains exhibited significantly higher microsomal oxidase, glutathioneS-transferase, and esterase activities toward surrogate substrates as compared with the insecticide-susceptible strain. However, levels of cytochrome P450 content, aldrin epoxidase activity, methoxyresorufinO-demethylase activity, and glutathioneS-transferase activity were not correlated with pyrethroid resistance, suggesting that these activities are poor indicators of pyrethroid-resistance magnitude. Interestingly, significant correlations were found between general esterase activity and cypermethrin (P= 0.002), permethrin (P= 0.007), cyhalothrin (P= 0.002), and propoxur (P= 0.001) resistance levels. The data support the conclusion of esterase involvement in cypermethrin resistance determined by synergist (DEF) bioassay. However, the significance of this relationship, in the context of resistance detection, requires further examination.