From the Wikipedia entry on Cyhalothrin:
Pyrethroids such as cyhalothrin are often preferred as an active ingredient in agricultural insecticides because they are more cost-effective and longer acting than natural pyrethrins. λ-and γ-cyhalothrin are now used to control insects and spider mites in crops including cotton, cereals, potatoes and vegetables.
Lambda-cyhalothrin Cyhalothrin gamma.svg λ-cyhalothrin (racemic)
Compounds Lambda: λ-Cyhalothrin (RS)-α-cyano (1RS,3RS): Cyhalothrin Gamma: γ-Cyhalothrin
Gamma-cyhalothrin and lambda-cyhalothrin1 are the active ingredients in the current commercial products based on cyhalothrin. Both are cyanohydrin esters of cis-3-[(Z)-2-chloro-3,3,3-trifluoropropenyl]-2,2-dimethylcyclopropanecarboxylic acid. All of the insecticidal activity is due to the proportion of absolute stereochemistry (1R) in the mixture. The active isomer of deltamethrin, (1R)-cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropanecarboxylic acid, has the same stereochemistry.
Cyhalothrin and deltamethrin acids. γ-cyhalothrin (a single chiral isomer) is indeed twice as active as λ-cyhalothrin on a weight-for-weight basis. The latter is racemic and contains the (1R) and inactive (1S) isomers in equal amounts.
I have tried and tried on my own to find out what lowercase gamma and lowercase delta could mean here, but I can't find an answer...
Also what does, AND Enantiomer mean? Or, A.N.D. Enantiomer?