Toxicological and biochemical studies with field populations of the Germancockroach, Blattella germanica

Topical bioassays with cypermethrin, lambda-cyhalothrin, permethrin, propox ur, 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 gs-fold for permethrin, 4- to 55-fold for lambda-cyhal othrin, 5- to 33-fold for propoxur, and 3- to 19-fold for chlorpyrifos. The synergists piperonyl butoxide (PBO) and S,S,S-tributylphoshorotrithioate ( DEF) affected cypermethrin resistance to varying degrees depending on the s train. Piperonyl butoxide pretreatment decreased cypermethrin resistance in only 5 strains, but caused an increase in resistance level in 7 strains. C onversely, DEF pretreatment reduced the resistance level in 10 of the strai ns and increased the resistance level in only 2 strains. Correlation analys is of resistance ratios for each strain and insecticide indicated a direct relationship between resistance lever of one insecticide and another, espec ially among the pyrethroids. All field strains exhibited significantly high er microsomal oxidase, glutathione S-transferase, and esterase activities t oward surrogate substrates as compared with the insecticide-susceptible str ain. However, levels of cytochrome P450 content, aldrin epoxidase activity, methoxyresorufin O-demethylase activity, and glutathione S-transferase act ivity were not correlated with pyrethroid resistance, suggesting that these activities are poor indicators of pyrethroid-resistance magnitude. Interes tingly, significant correlations were found between general esterase activi ty and cypermethrin (P = 0.002), permethrin (P = 0.007), cyhalothrin (P = 0 .002), and propoxur (P = 0.001) resistance levels. The data support the con clusion of esterase involvement in cypermethrin resistance determined by sy nergist (DEF) bioassay. However, the significance of this relationship, in the context of resistance detection, requires further examination. (C) 1998 Academic Press.