RESUMO
We evaluated the effects of Bacillus thuringiensis (Bt) toxin CrylAc on survival and development of a susceptible strain and laboratory-selected resistant strains of pink bollworm, Pectinophora gossypiella (Saunders). For susceptible and resistant strains tested on artificial diet, increases in CrylAc concentration reduced developmental rate and pupal weight. In greenhouse tests, survival of resistant larvae on transgenic cotton that produces CrylAc (Bt cotton) was 46% relative to their survival on non-Bt cotton. In contrast, Bt cotton killed all susceptible larvae tested. F1 hybrid progeny of resistant and susceptible adults did not survive on Bt cotton, which indicates recessive inheritance of resistance. Compared with resistant or susceptible larvae reared on non-Bt cotton, resistant larvae reared on Bt cotton had lower survival and slower development, and achieved lower pupal weight and fecundity. Recessive resistance to Bt cotton is consistent with one of the basic assumptions of the refuge strategy for delaying resistance to Bt cotton. Whereas slower development of resistant insects on Bt cotton could increase the probability of mating between resistant adults and accelerate resistance, negative effects of Bt cotton on the survival and development of resistant larvae could delay evolution of resistance.
Assuntos
Bacillus thuringiensis , Proteínas de Bactérias/farmacologia , Toxinas Bacterianas/farmacologia , Endotoxinas/farmacologia , Gossypium , Mariposas/efeitos dos fármacos , Controle Biológico de Vetores/métodos , Animais , Toxinas de Bacillus thuringiensis , Proteínas de Bactérias/genética , Toxinas Bacterianas/genética , Endotoxinas/genética , Feminino , Proteínas Hemolisinas , Masculino , Mariposas/crescimento & desenvolvimento , Plantas Geneticamente Modificadas , Pupa/efeitos dos fármacos , Pupa/crescimento & desenvolvimento , Razão de MasculinidadeRESUMO
Fitness costs associated with resistance to transgenic crops producing toxins from Bacillus thuringiensis (Bt) may have important effects on the evolution of resistance. We investigated overwintering costs in pink bollworm, Pectinophora gosypiella (Saunders), strains with different degrees of resistance to Bt cotton. Frequency of resistant individuals in a strain was not associated with induction of diapause or emergence from diapause in early winter. Emergence from diapause in the spring was 71% lower in three highly resistant strains than in two heterogeneous strains from which the resistant strains were derived. This underestimates the overwintering cost because the frequency of the resistance allele was relatively high in the heterogeneous strains. Emergence in the spring in hybrid progeny from crosses between the resistant and heterogeneous strains was greater than in resistant strains but did not differ from susceptible strains, showing that the overwintering cost was recessive to some extent.
Assuntos
Bacillus thuringiensis , Proteínas de Bactérias , Toxinas Bacterianas , Endotoxinas , Gossypium , Mariposas , Controle Biológico de Vetores/métodos , Animais , Toxinas de Bacillus thuringiensis , Proteínas de Bactérias/genética , Endotoxinas/genética , Feminino , Proteínas Hemolisinas , Resistência a Inseticidas , Masculino , Plantas Geneticamente Modificadas , Estações do AnoRESUMO
Transgenic cotton producing a Bacillus thuringiensis (Bt) toxin is widely used for controlling the pink bollworm, Perctinophora gossypiella (Saunders). We compared performance of pink bollworm strains resistant to Bt cotton with performance of their susceptible counterparts on non-Bt cotton. We found fitness costs that reduced survival on non-Bt cotton by an average of 51.5% in two resistant strains relative to the susceptible strains. The survival cost was recessive in one set of crosses between a resistant strain and the susceptible strain from which it was derived. However, crosses involving an unrelated resistant and susceptible strain indicated that the survival cost could be dominant. Development time on non-Bt cotton did not differ between the two related resistant and susceptible strains. A slight recessive cost affecting development time was suggested by comparison of the unrelated resistant and susceptible strains. Maternal effects transmitted by parents that had eaten Bt-treated artificial diet as larvae had negative effects on embryogenesis, adult fertility, or both, and reduced the ability of neonates to enter cotton bolls. These results provide further evidence that fitness costs associated with the evolution of resistance to Bt cotton are substantial in the pink bollworm.
Assuntos
Bacillus thuringiensis , Proteínas de Bactérias/farmacologia , Toxinas Bacterianas/farmacologia , Endotoxinas/farmacologia , Mariposas/efeitos dos fármacos , Controle Biológico de Vetores/métodos , Zea mays , Adaptação Fisiológica , Animais , Toxinas de Bacillus thuringiensis , Feminino , Proteínas Hemolisinas , Resistência a Inseticidas , Masculino , Mariposas/crescimento & desenvolvimento , Plantas Geneticamente ModificadasRESUMO
Strategies for delaying pest resistance to genetically modified crops that produce Bacillus thuringiensis (Bt) toxins are based primarily on theoretical models. One key assumption of such models is that genes conferring resistance are rare. Previous estimates for lepidopteran pests targeted by Bt crops seem to meet this assumption. We report here that the estimated frequency of a recessive allele conferring resistance to Bt toxin Cry1Ac was 0.16 (95% confidence interval = 0.05-0.26) in strains of pink bollworm (Pectinophora gossypiella) derived from 10 Arizona cotton fields during 1997. Unexpectedly, the estimated resistance allele frequency did not increase from 1997 to 1999 and Bt cotton remained extremely effective against pink bollworm. These results demonstrate that the assumptions and predictions of resistance management models must be reexamined.
