Contact and Fumigant Toxicity of Cyperus rotundus Steam Distillate Constituents and Related Compounds to Insecticide-Susceptible and -Resistant Blattella germanica

We assessed the toxicity of 17 steam distillate constituents of Cyperus rotundus (L.) rhizome, another seven known compounds of C. rotundus rhizome, and 14 structurally related compounds to females from an insecticide-susceptible KSS strain and two field-collected SEL and DJN colonies of Blattella germanica (L.). High contact + fumigant toxicity to KSS females was produced by p-cymene, nerol, linalool, o-cymene, (S)-(-)-citronellal, (1S)-(-)-camphor, terpinolene, and m-cymene (LD50, 0.29–0.47 mg/cm2). The toxicity of these compounds was virtually identical against females from any of the three strains, even though SEL and DJN females were resistant to six acetylcholinesterase inhibitors and three pyrethroids (resistance ratio, 9–154 and 12–195). These results indicate that the compounds and insecticides do not share a common mode of action or elicit cross-resistance. The test compounds were effective in closed but not in open containers against SEL females, indicating that their route of insecticidal action was largely a result of vapor action. Structure-activity relationship indicates that structural characteristics, such as types of functional groups, appear to play a role in determining the terpenoid toxicities to B. germanica. C. rotundus rhizome steam distillate constituents and related compounds described merit further study as potential fumigants for the control of resistant cockroach populations in light of global efforts to reduce the level of highly toxic synthetic insecticides in indoor environments.