Cross-Resistance and Stability of Resistance to Bacillus thuringiensis Toxin Cry1C in Diamondback Moth (original) (raw)
Related papers
Cross-Resistance to Bacillus thuringiensis Toxin CryIF in the Diamondback Moth (Plutella xylostella)
Applied and Environmental Microbiology
Selection with Bacilus thuringiensis subsp. kurstaki, which contains CrylA and Cryll toxins, caused a >200-fold cross-resistance to CryIF toxin from B. thuringiensis subsp. aizawai in the diamondback moth, PluteUla xylosteUla. CrylE was not toxic, but CryIB was highly toxic to both selected and unselected larvae. The results show that extremely high levels of cross-resistance can be conferred across classes of Cryl toxins of B.
Applied and Environmental Microbiology, 2000
Four subpopulations of a Plutella xylostella (L.) strain from Malaysia (F 4 to F 8 ) were selected with Bacillus thuringiensis subsp. kurstaki HD-1, Bacillus thuringiensis subsp. aizawai, Cry1Ab, and Cry1Ac, respectively, while a fifth subpopulation was left as unselected (UNSEL-MEL). Bioassays at F 9 found that selection with Cry1Ac, Cry1Ab, B. thuringiensis subsp. kurstaki, and B. thuringiensis subsp. aizawai gave resistance ratios of >95, 10, 7, and 3, respectively, compared with UNSEL-MEL (>10,500, 500, >100, and 26, respectively, compared with a susceptible population, ROTH). Resistance to Cry1Ac, Cry1Ab, B. thuringiensis subsp. kurstaki, and B. thuringiensis subsp. aizawai in UNSEL-MEL declined significantly by F 9 . The Cry1Ac-selected population showed very little cross-resistance to Cry1Ab, B. thuringiensis subsp. kurstaki, and B. thuringiensis subsp. aizawai (5-, 1-, and 4-fold compared with UNSEL-MEL), whereas the Cry1Ab-, B. thuringiensis subsp. kurstaki-, and B. thuringiensis subsp. aizawai-selected populations showed high cross-resistance to Cry1Ac (60-, 100-, and 70-fold). The Cry1Ac-selected population was reselected (F 9 to F 13 ) to give a resistance ratio of >2,400 compared with UNSEL-MEL. Binding studies with 125 I-labeled Cry1Ab and Cry1Ac revealed complete lack of binding to brush border membrane vesicles prepared from Cry1Ac-selected larvae (F 15 ). Binding was also reduced, although less drastically, in the revertant population, which indicates that a modification in the common binding site of these two toxins was involved in the resistance mechanism in the original population. Reciprocal genetic crosses between Cry1Ac-reselected and ROTH insects indicated that resistance was autosomal and showed incomplete dominance. At the highest dose of Cry1Ac tested, resistance was recessive while at the lowest dose it was almost completely dominant. The F 2 progeny from a backcross of F 1 progeny with ROTH was tested with a concentration of Cry1Ac which would kill 100% of ROTH moths. Eight of the 12 families tested had 60 to 90% mortality, which indicated that more than one allele on separate loci was responsible for resistance to Cry1Ac.
Journal of Economic Entomology, 1996
Previous results have shown that diamondback moth, Plutella xylostella (L.), populations resistant to toxins from Bacillus thuringiensis subsp. kurstaki were susceptible to toxin CryIC. Use of commercial formulations of B. thuringiensis subsp. ai;:;awaithat contain CrylC has increased recently. Analysis of two commercial formulations by high pressure liquid chromatography showed that CryIC accounted for 26% of the CryI protein in the B. thuringiensis subsp. ai;:;awaiformulation, but did not occur in the B. thuringiensis subsp. kurstaki formulation. CrylAb was the most abundant Cryl protein in the commercial formulations of B. thuringiensis subspp. ai;:;awai and kurstaki. We found resistance to CrylC in a field population of diamondback moth from Hawaii that had been treated with B. thuringiensis subsp. aizawai. Leaf residue bioassays showed that, at 5 d after treatment with CryIC, LCsos for colonies derived from this population in 1993 and 1995 were ""20 times greater than the LC50 for a susceptible laboratory colony. For a nearby population that had not been treated with B. thuringiensis subsp. aizawai, responses to CrylC did not differ significantly from those of the susceptible laboratory colony. Resistance to CrylAb was lower in a CrylC-resistant colony than in a CrylC-susceptible colony that had been selected with B. thuringiensis subsp. kurstaki. These results suggest that the gene(s) conferring resistance to CrylC segregate independently from the gene(s) conferring resistance to CryIAb. In contrast with previous results with colonies derived in 1989, resistance to B. thuringiensis subsp. kurstaki in a colony derived in 1993 from the same field population did not decline when exposure to B. thuringiensis stopped. Thus, stability of resistance is not necessarily a fixed character, even for a specific population and pesticide. Despite substantial resistance to CrylC and B. thuringiensis subsp. kurstaki, resistance to a spore-crystal formulation of B. thuringiensis subsp. ai;:;awaiwas only 2-to 4-fold.
Different Mechanisms of Resistance to Bacillus thuringiensis Toxins in the Indianmeal Moth
Applied and Environmental Microbiology, 2001
Susceptibility to protoxin and toxin forms of Cry1Ab and the binding of 125 I-labeled Cry1Ab and Cry1Ac has been examined in three Plodia interpunctella colonies, one susceptible (688 s ) and two resistant (198 r and Dpl r ) to Bacillus thuringiensis. Toxicological studies showed that the 198 r colony was 11-fold more resistant to Cry1Ab protoxin than to Cry1Ab activated toxin, whereas the Dpl r colony was 4-fold more resistant to protoxin versus toxin. Binding results with 125 I-labeled toxins indicated the occurrence of two different binding sites for Cry1Ab in the susceptible insects, one of them shared with Cry1Ac. Cry1Ab binding was found to be altered in insects from both resistant colonies, though in different ways. Compared with the susceptible colony, insects from the Dpl r colony showed a drastic reduction in binding affinity (60-fold higher K d ), although they had similar concentrations of binding sites. Insects from the 198 r colony showed a slight reduction in both binding affinity and binding site concentration (five-fold-higher K d and ca. three-fold-lower R t compared with the 688 s colony). No major difference in Cry1Ac binding was found among the three colonies. The fact that the 198 r colony also has a protease-mediated mechanism of resistance (B. Oppert, R. Hammel, J. E. Throne, and K. J. Kramer, J. Biol. Chem. 272:23473-23476, 1997) is in agreement with our toxicological data in which this colony has a different susceptibility to the protoxin and toxin forms of Cry1Ab. It is noteworthy that the three colonies used in this work derived originally from ca. 100 insects, which reflects the high variability and high frequency of B. thuringiensis resistance genes occurring in natural populations.
One Gene In Diamondback Moth Confers Resistance to Four Bacillus Thuringiensis Toxins
Proceedings of the …, 1997
Environmentally benign insecticides derived from the soil bacterium Bacillus thuringiensis (Bt) are the most widely used biopesticides, but their success will be short-lived if pests quickly adapt to them. The risk of evolution of resistance by pests has increased, because transgenic crops producing insecticidal proteins from Bt are being grown commercially. Efforts to delay resistance with two or more Bt toxins assume that independent mutations are required to counter each toxin. Moreover, it generally is assumed that resistance alleles are rare in susceptible populations. We tested these assumptions by conducting single-pair crosses with diamondback moth (Plutella xylostella), the first insect known to have evolved resistance to Bt in open field populations. An autosomal recessive gene conferred extremely high resistance to four Bt toxins (Cry1Aa, Cry1Ab, Cry1Ac, and Cry1F). The finding that 21% of the individuals from a susceptible strain were heterozygous for the multiple-toxin resistance gene implies that the resistance allele frequency was 10 times higher than the most widely cited estimate of the upper limit for the initial frequency of resistance alleles in susceptible populations. These findings suggest that pests may evolve resistance to some groups of toxins much faster than previously expected. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked ''advertisement'' in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Journal of Economic Entomology, 2000
We studied mechanisms of resistance to Bacillus thuringiensis insecticidal crystal protein Cry1C in the diamondback moth, Plutella xylostella (L.). Binding assays with midgut brush border membrane vesicles prepared from whole larvae showed no signiÞcant difference between resistant and susceptible strains in binding of radioactively-labeled Cry1C. These results indicate that reduced binding of Cry1C to midgut membrane target sites did not cause resistance to Cry1C. Thus, the mechanism of resistance to Cry1C differs from that observed in several previously reported cases of resistance to Cry1A toxins in diamondback moth. We tested Cry1C toxin and Cry1C crystalline protoxin against resistant and susceptible larvae using leaf disk bioassays. After adjusting for the size difference between Cry1C toxin and protoxin, we found that with resistant larvae, toxin was signiÞcantly more toxic than protoxin. In contrast, with susceptible larvae, no signiÞcant difference in toxicity occurred between Cry1C toxin and protoxin. The resistance ratios for Cry1C were 19 for toxin and 48 for protoxin. These results suggest that reduced conversion of Cry1C protoxin to toxin is a minor mechanism of resistance to Cry1C. Because neither reduced binding nor reduced conversion of protoxin to toxin appear to be major mechanisms, one or more other mechanisms are important in diamondback moth resistance to Cry1C.
Journal of Economic Entomology, 2000
We studied mechanisms of resistance to Bacillus thuringiensis insecticidal crystal protein Cry1C in the diamondback moth, Plutella xylostella (L.). Binding assays with midgut brush border membrane vesicles prepared from whole larvae showed no signiÞcant difference between resistant and susceptible strains in binding of radioactively-labeled Cry1C. These results indicate that reduced binding of Cry1C to midgut membrane target sites did not cause resistance to Cry1C. Thus, the mechanism of resistance to Cry1C differs from that observed in several previously reported cases of resistance to Cry1A toxins in diamondback moth. We tested Cry1C toxin and Cry1C crystalline protoxin against resistant and susceptible larvae using leaf disk bioassays. After adjusting for the size difference between Cry1C toxin and protoxin, we found that with resistant larvae, toxin was signiÞcantly more toxic than protoxin. In contrast, with susceptible larvae, no signiÞcant difference in toxicity occurred between Cry1C toxin and protoxin. The resistance ratios for Cry1C were 19 for toxin and 48 for protoxin. These results suggest that reduced conversion of Cry1C protoxin to toxin is a minor mechanism of resistance to Cry1C. Because neither reduced binding nor reduced conversion of protoxin to toxin appear to be major mechanisms, one or more other mechanisms are important in diamondback moth resistance to Cry1C.