Pyrethrin II, cinerin II, allethrin II, pyrethrin II isomer, and allethrin II isomer were prepared by esterification of rethrolons with (+)-trans-pyrethric acid and (+)-trans- methyl-2, 2-dimethyl-3-(2'-carboxy-l'-propenyl) cyclopropanecarboxylate and their relative toxicities to pyre-thrin I, cinerin I and allethrin I against houseflies were measured by counting “mortality” and “knock-down percent”