Decrease in the resistance level of Blattella germanica (Linnaeus) (Blattodea: Ectobiidae) to insecticides after being reared without selection pressure for ten years

This study aims to investigate changes in resistance insecticides over a ten-year period five strains of German cockroaches, Blattella germanica (Linnaeus), which had previously shown deltamethrin, propoxur, and fipronil 2012. The were reared laboratory without exposure for ten years. In 2022, they tested the same using topical application method. ratio (RR50) was calculated each strain determine level insecticide. found that initially resistant, became less resistant or even susceptible after being insecticide decrease observed all strains, but reduction pattern varied, apparently influenced by type For instance, MDN2 strain, very high (RR50: 1019.74 -fold) 1 -fold). Similarly, ACH2 classified as highly propoxur 48.64 -fold), with 12.21 fipronil, both susceptible. also discussed potential mechanisms resistance, including reduced frequency genes fitness costs. findings suggest rearing cockroaches treatment can lead commonly used insecticides. These be develop more effective methods controlling cockroaches.