The synthetic pyrethroid isomers .2. Biological activity

Pure optical isomers of phenothrin, permethin and cypermethrin were synthesised and tested on a wide spectrum of insects (Blattella germanica, Leptinotarsa decemlineata, Tribolium confusum, Oncopeltus fasciatus, Musca domestica, Aedes aegypti). Our results suggest that in the structurally related series phenothrin, permethrin and cypermethrin the chemical modifications had only a small influence on intrinsic activity of the compounds at the target site. The activity of piperonylbutoxide synergised 1Rtrans phenothrin and 1Rcis permethrin (LD(50)=1.2 ng/fly in both cases) is in a similar range to the most active 1RcisS cypermethrin isomer alone or with PB (LD(50)=0.9 and 0.4 ng/fly, respectively). Some cypermethrin isomers considered previously to be totally inactive show significant activity depending on the tested insect species. The 1RcisR and 1RtransR isomers proved to be as active as the most potent isomers on mosquito. A similarly unexpected result was that in the case of mosquito all four trans isomers were significantly more active than the corresponding cis isomers.