RESUMO
Transgenic maize, Zea maize L., expressing the Cry1F protein from Bacillus thuringiensis has been registered for Spodoptera frugiperda (J. E. Smith) control since 2003. Unexpected damage to Cry1F maize was reported in 2006 in Puerto Rico and Cry1F resistance in S. frugiperda was documented. The inheritance of Cry1F resistance was characterized in a S. frugiperda resistant strain originating from Puerto Rico, which displayed >289-fold resistance to purified Cry1F. Concentration-response bioassays of reciprocal crosses of resistant and susceptible parental populations indicated that resistance is recessive and autosomal. Bioassays of the backcross of the F1 generation crossed with the resistant parental strain suggest that a single locus is responsible for resistance. In addition, cross-resistance to Cry1Aa, Cry1Ab, Cry1Ac, Cry1Ba, Cry2Aa and Vip3Aa was assessed in the Cry1F-resistant strain. There was no significant cross-resistance to Cry1Aa, Cry1Ba and Cry2Aa, although only limited effects were observed in the susceptible strain. Vip3Aa was highly effective against susceptible and resistant insects indicating no cross-resistance with Cry1F. In contrast, low levels of cross-resistance were observed for both Cry1Ab and Cry1Ac. Because the resistance is recessive and conferred by a single locus, an F1 screening assay was used to measure the frequency of Cry1F-resistant alleles from populations of Florida and Texas in 2010 and 2011. A total frequency of resistant alleles of 0.13 and 0.02 was found for Florida and Texas populations, respectively, indicating resistant alleles could be found in US populations, although there have been no reports of reduced efficacy of Cry1F-expressing plants.
Assuntos
Proteínas de Bactérias , Endotoxinas , Proteínas Hemolisinas , Spodoptera/genética , Animais , Toxinas de Bacillus thuringiensis , Frequência do Gene , Padrões de Herança , Resistência a Inseticidas/genética , Porto RicoRESUMO
Field tests of corn co-expressing two new delta-endotoxins from Bacillus thuringiensis (Bt) have demonstrated protection from root damage by western corn rootworm (Diabrotica virgifera virgifera LeConte). The level of protection exceeds that provided by chemical insecticides. In the bacterium, these proteins form crystals during the sporulation phase of the growth cycle, are encoded by a single operon, and have molecular masses of 14 kDa and 44 kDa. Corn rootworm larvae fed on corn roots expressing the proteins showed histopathological symptoms in the midgut epithelium.
Assuntos
Bacillus thuringiensis/química , Proteínas de Bactérias/farmacologia , Toxinas Bacterianas , Endotoxinas/farmacologia , Controle de Insetos/métodos , Zea mays/metabolismo , Animais , Toxinas de Bacillus thuringiensis , Eletroforese em Gel de Poliacrilamida , Proteínas Hemolisinas , Imunidade Inata , Immunoblotting , Larva , Modelos Genéticos , Plantas Geneticamente Modificadas , Transformação GenéticaRESUMO
A phagostimulant, 6,10,14-trimethylpentadecan-1-one (phytone), was isolated and identified from Bermuda grass,Cynodon dactylon (L.). The phagostimulant activity of this isoprenoid ketone was established from bioassays of fall armyworm larvae,Spodoptera frugiperda (J.E. Smith). Larvae displayed increased body mass accumulation as well as preference to diet supplemented with this molecule. Neonate larvae fed diet supplemented with chromatographic isolates of phytone-containing fractions from six Bermuda grass cultivars showed a 10-40% increase in body mass accumulation as compared with controls. This variation in larval body mass accumulation seems attributable to a differential concentration of phytone in the cultivars, which ranged from 0.5 to 43 ppm. Additionally, first-instar larvae responded preferentially to diet pellets topically treated with phytone in concentrations as low as 0.1 ppm.