Synergism of Pyrethroids by Several Compounds Larvae of the Diamondback Moth (Lepidoptera: Plutellidae)

Abstract

Synergism of several pyrethroids in both susceptible (FS) and resistant (BC) Plutella xylostella (L.) larvae by several inhibitors of detoxifying enzymes and a compound reported to affect the insect nerves was determined. Only permethrin was synergized consistently and obviously in the resistant BC strain by the esterase inhibitors triphenyl phosphate and S,S,S-tributyl phosphorotrithioate. Piperonyl butoxide (pb), a microsomal oxidase inhibitor, synergized all four pyrethroids, although to different degrees, in both FS and BC strains. Pretreatment of the BC strain with pb increased the effectiveness of fenvalerate by 15-fold, deltamethrin 13-fold, permethrin 6-fold, and cypermethrin 3-fold. A tank-mix formulation of pb, Butacide, when mixed and applied simultaneously with these pyrethroids at varying ratios, also showed synergistic action. Among the four pyrethroids tested, fenvalerate was most drastically synergized by Butacide. A 1:1 to 5:1 ratio for Butacide and pyrethroids seemed optimal for the control of resistant P. xylostella. The response of the BC strain to deltamethrin and fenvalerate was affected somewhat by the pretreatment of 1,1-di-(4-chlorophenyl) ethanol. Finally, the possible consequences of large-scale applications of synergists, such as the appearance and intensification of certain resistance mechanisms and effects on mammals, are discussed.