Pyrethroid Resistance in the Tobacco Bud worm (Lepidoptera: Noctuidae) Sterile Hybrid Strain

Abstract

A sterile back cross tobacco bud worm strain (TBW-BC) of Heliothts virescens (F.) was developed before extensive use of pyrethroid insecticides. Although this strain has been maintained free of pyrethroid insecticides, most tobacco bud worm populations have been exposed to pyrethroids and have demonstrated enhanced tolerance. Our estimated LD50 (cypermethrin) for third instars was significantly lower than tobacco bud worm from Mississippi. Thus, the TBW-BC strain could be at a disadvantage if exposed to pyrethroids after release. We developed a lineage of TBW-BC strain that is resistant to cypermethrin by repeatedly back crossing TBW-BC females to resistant tobacco bud worm males and selecting for tolerance. Resistant TBW-BC strain (R-TBW-BC) (LD50,638 μg per larva) should survive field applications that would kill most wild tobacco bud worm. Back cross mortalities were consistent with polygenic inheritance, but not with monogenic inheritance. Release of RTBW-BC strain cannot change tolerance in wild tobacco bud worm, because introduced resistance alleles will be carried only by individuals that also carry the sterility trait. Resistance of sterile insects would be diluted by outcrossingto wild tobacco bud worm, but sterile insects should remain significantly more tolerant than fertile insects for at least two generations. Use of R-TBW-BC strain could reduce costs in sterile-release programs.