DNA Screening Reveals Pink Bollworm Resistance to Bt Cotton Remains Rare After a Decade of Exposure

Tabashnik, Bruce E.; Fabrick, Jeffrey A.; Henderson, Scottie; Biggs, Robert W.; Yafuso, Christine M.; Nyboer, Megan E.; Manhardt, Nancy M.; Coughlin, Laura; Sollome, James; Carrière, Yves; Dennehy, Timothy J.; Morin, Shai

doi:10.1603/0022-0493-99.5.1525

Cited by 45 publications

(31 citation statements)

References 37 publications

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“…In particular, the laboratory selection experiments with Cry2Ab in diet started with a hybrid strain of pink bollworm (BX-H) that had close to 10% survival at a diagnostic concentration of Cry1Ac (10 g toxin/mL diet) ( Table 1). In contrast, after a decade of exposure to cotton producing only Cry1Ac, survival at the diagnostic concentration of Cry1Ac was essentially 0% in field-derived strains of pink bollworm (24,25). Second, laboratory-selected strains of pink bollworm showed recessive inheritance of resistance to high concentrations of Cry2Ab (Fig.…”

Section: Discussionmentioning

confidence: 98%

“…Both Cry1Ac and Cry2Ab are active against some key lepidopteran pests, including pink bollworm (Pectinophora gossypiella), a major cotton pest in the southwestern United States and in many other countries (21). Bt cotton producing only Cry1Ac has been exceptionally effective against pink bollworm in Arizona; susceptibility to Cry1Ac has not decreased in field populations of this pest despite more than a decade of exposure (22)(23)(24)(25). Previous work showed that laboratory selection of pink bollworm with Cry1Ac yielded high levels of resistance to Cry1Ac, but little or no cross-resistance to Cry2A toxins (26-28; http://www.epa.gov/scipoly/sap/meetings/ 2006/october/unnithan et al 04 cry2ab baselines.pdf).…”

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confidence: 99%

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Asymmetrical cross-resistance betweenBacillus thuringiensistoxins Cry1Ac and Cry2Ab in pink bollworm

Tabashnik

Unnithan

Masson

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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115

106

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Transgenic crops producing Bacillus thuringiensis (Bt) toxins kill some key insect pests and can reduce reliance on insecticide sprays. Sustainable use of such crops requires methods for delaying evolution of resistance by pests. To thwart pest resistance, some transgenic crops produce 2 different Bt toxins targeting the same pest. This ''pyramid'' strategy is expected to work best when selection for resistance to 1 toxin does not cause cross-resistance to the other toxin. The most widely used pyramid is transgenic cotton producing Bt toxins Cry1Ac and Cry2Ab. Cross-resistance between these toxins was presumed unlikely because they bind to different larval midgut target sites. Previous results showed that laboratory selection with Cry1Ac caused little or no cross-resistance to Cry2A toxins in pink bollworm (Pectinophora gossypiella), a major cotton pest. We show here, however, that laboratory selection of pink bollworm with Cry2Ab caused up to 420-fold crossresistance to Cry1Ac as well as 240-fold resistance to Cry2Ab. Inheritance of resistance to high concentrations of Cry2Ab was recessive. Larvae from a laboratory strain resistant to Cry1Ac and Cry2Ab in diet bioassays survived on cotton bolls producing only Cry1Ac, but not on cotton bolls producing both toxins. Thus, the asymmetrical cross-resistance seen here does not threaten the efficacy of pyramided Bt cotton against pink bollworm. Nonetheless, the results here and previous evidence indicate that crossresistance occurs between Cry1Ac and Cry2Ab in some key cotton pests. Incorporating the potential effects of such cross-resistance in resistance management plans may help to sustain the efficacy of pyramided Bt crops.evolution ͉ genetically engineered crops ͉ transgenic crops ͉ Bt cotton

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Section: Discussionmentioning

confidence: 98%

mentioning

confidence: 99%

Asymmetrical cross-resistance betweenBacillus thuringiensistoxins Cry1Ac and Cry2Ab in pink bollworm

Tabashnik

Unnithan

Masson

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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115

106

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“…Resistance genes of lepidopteran and coleopteran populations exposed to Bacillus thuringiensis spraying or to Bt-transgenic crops have been investigated, and the frequency ranges from 10 Ϫ5 to 10 Ϫ1 (1, 2, 5, 6, 14, 16,19,35,36). Global monitoring data on resistance have shown that the frequency of resistance alleles has not increased in pest insects from Bt crop areas, and it is likely that the high-dose refuge strategy has contributed to delaying resistance (21,34).…”

Section: Discussionmentioning

confidence: 99%

“…Most studies used the F2 screen to estimate the frequency of resistance alleles, which is a method based on the bioassay of F2 neonates obtained from isofemale lineages. Recently the first DNA screening for mutants of the cadherin gene associated with Bt cotton resistance of the pink bollworm Pectinophora gossypiela (Lepidoptera: Gelechiidae) was performed, but those alleles were not present in a sample of 5,571 insects from Arizona (36). A similar screening of a retrotransposon insertion in the cadherin gene (HevCaLP) associated with B. thuringiensis resistance of the lepidopteran Heliothis virescens did not detect this insertion among 7,000 individuals, and its frequency was estimated to be 7 ϫ 10 Ϫ5 (13,14).…”

Section: Discussionmentioning

confidence: 99%

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Detection of an Allele Conferring Resistance to Bacillus sphaericus Binary Toxin in Culex quinquefasciatus Populations by Molecular Screening

Chalegre¹,

Romão²,

Amorim³

et al. 2009

Appl Environ Microbiol

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The activity of the Bacillus sphaericus binary (Bin) toxin on Culex quinquefasciatus larvae depends on its specific binding to the Cqm1 receptor, a midgut membrane-bound ␣-glucosidase. A 19-nucleotide deletion in the cqm1 gene (cqm1 REC ) mediates high-level resistance to Bin toxin. Here, resistance in nontreated and B. sphaericus-treated field populations of C. quinquefasciatus was assessed through bioassays as well as a specific PCR assay designed to detect the cqm1 REC allele in individual larvae. Resistance ratios at 90% lethal concentration, gathered through bioassays, were close to 1 and indicate that the selected populations had similar levels of susceptibility to B. sphaericus, comparable to that of a laboratory colony. A diagnostic PCR assay detected the cqm1 REC allele in all populations investigated, and its frequency in two nontreated areas was 0.006 and 0.003, while the frequency in the B. sphaericus-treated population was significantly higher. Values of 0.053 and 0.055 were detected for two distinct sets of samples, and homozygote resistant larvae were found. Evaluation of Cqm1 expression in individual larvae through ␣-glucosidase assays corroborated the allelic frequency revealed by PCR. The data from this study indicate that the cqm1 REC allele was present at a detectable frequency in nontreated populations, while the higher frequency in samples from the treated area is, perhaps, correlated with the exposure to B. sphaericus. This is the first report of the molecular detection of a biolarvicide resistance allele in mosquito populations, and it confirms that the PCR-based approach is suitable to track such alleles in target populations.Bacillus sphaericus Neide is considered the most successful microbial larvicide to date for the control of mosquito species from the Culex pipiens (Diptera: Culicidae) complex (20). B. sphaericus biolarvicides commercially available are based on highly toxic strains characterized by their ability to express the binary (Bin) protoxin, a crystal protein produced in large amounts during sporulation (7). This heterodimer is formed by the BinA (42-kDa) and BinB (51-kDa) subunits that act in synergy to produce larvicidal activity upon Culex larvae (3, 23). The BinB subunit is responsible for the recognition and binding of the toxin to specific receptors on the midgut epithelium surface, while BinA is primarily responsible for the toxic effects, but first the crystal has to be ingested by the larvae and the protoxin must be processed into toxin by the midgut (7). The Bin toxin receptor in C. pipiens (Cpm1) and Culex quinquefasciatus (Cqm1) is a 60-kDa ␣-glucosidase attached to the epithelial cell membrane by a glycosylphosphatidylinositol anchor (9, 30, 31). The action of the Bin toxin on Culex larvae relies on its specific binding to those membrane-bound receptors (24). Disruption of the interaction between the toxin and the midgut is the major mechanism underlying resistance, and it has already been reported from different laboratory-or fieldselected colonies (25,26,27,3...

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Field‐evolved resistance to Bt toxin Cry1Ac in the pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), from India

Dhurua

Gujar

2011

Pest Management Science

288

185

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The data reported here constitute the first evidence of field-evolved resistance of pink bollworm to Cry1Ac. This initial evidence spurred more extensive evaluations during the 2009-2010 growing season, which confirmed field-evolved resistance to Cry1Ac in Amreli. The lack of cross-resistance to Cry2Ab2 suggests that plants producing this toxin are likely to be more effective against resistant populations than plants producing only Cry1Ac.

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DNA Screening Reveals Pink Bollworm Resistance to Bt Cotton Remains Rare After a Decade of Exposure

Cited by 45 publications

References 37 publications

Asymmetrical cross-resistance betweenBacillus thuringiensistoxins Cry1Ac and Cry2Ab in pink bollworm

Asymmetrical cross-resistance betweenBacillus thuringiensistoxins Cry1Ac and Cry2Ab in pink bollworm

Detection of an Allele Conferring Resistance to Bacillus sphaericus Binary Toxin in Culex quinquefasciatus Populations by Molecular Screening

Field‐evolved resistance to Bt toxin Cry1Ac in the pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), from India

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