Baseline Susceptibility of European Corn Borer (Lepidoptera: Crambidae) to Bacillus thuringiensis Toxins

Marçon, Paula; Young, Linda J.; Steffey, Kevin L.; Siegfried, Blair D.

doi:10.1093/jee/92.2.279

Cited by 154 publications

(160 citation statements)

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“…It is well established for the impact of Cry1Ab on O. nubilalis larva, that growth inhibition data are much more sensitive than mortality data (i.e., EC 50 values are about one order of magnitude lower than LC 50 values) [14]. Further, it is well established that older larvae suffer less mortality from Cry1Ab compared to neonates, but show sublethal effects such as reduced growth.…”

Section: Discussionmentioning

confidence: 99%

Putative effects of Cry1Ab to larvae of Adalia bipunctata - reply to Hilbeck et al. (2012)

2012

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In their recent study, Hilbeck et al. (2012) report that Cry1Ab causes lethal effects on larvae of the ladybird beetle Adalia bipunctata when fed directly to the predator. Such toxic effects were not previously observed in a direct feeding study conducted by us (Álvarez-Alfageme et al. 2011). Because Hilbeck et al. (2012 claim that our study design did not allow us to detect any adverse effects we provide arguments for the value and relevance of our study in this commentary. Furthermore we discuss two additional published studies that have not revealed any direct effects of Cry1Ab on larvae of A. bipunctata and are not mentioned by Hilbeck et al. (2012). One of the studies was conducted in our laboratory under more realistic exposure conditions (Álvarez-Alfageme et al. 2011). Feeding A. bipunctata larvae with spider mites reared on Bt maize did not reveal any adverse effects on lethal and sublethal parameters of the predator. This was despite the fact that the larvae had ingested high amounts of biologically-active Cry1Ab protein. Thus, we do not see verified evidence that A. bipunctata larvae are sensitive to Cry1Ab at realistic worst-case exposure concentrations. This, together with the fact that A. bipunctata will be little exposed to Cry1Ab under field conditions, allows us to conclude that the risk of Bt maize to this predator is negligible. Support for this comes from the results of many Bt maize field studies that have not revealed evidence for direct Cry1Ab-effects on non-Lepidoptera species.

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Section: Discussionmentioning

confidence: 99%

Putative effects of Cry1Ab to larvae of Adalia bipunctata - reply to Hilbeck et al. (2012)

2012

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“…The second strain originated from a field collection of ϳ500 individuals from the Lombardia region of northern Italy and has been reared in the absence of selection for more than 100 generations (F100). Bioassay methods described by Marçon et al (12) were used to test the effectiveness of the three different Cry1Ab batches previously described with each quantified based on SDS-PAGE/densitometry. Neonate larvae (Ͻ24 h after eclosing) were exposed to seven concentrations of each Cry1Ab toxin (0.1, 0.3, 0.9, 2.7, 8.0, 24.0, and 72.0 ng/cm 2 ).…”

Section: Vol 74 2008 Methods To Quantify Cry1ab From Bacillus Thurimentioning

confidence: 99%

Comparison and Validation of Methods To Quantify Cry1Ab Toxin from Bacillus thuringiensis for Standardization of Insect Bioassays

Crespo

Spencer

Nekl

et al. 2008

Appl Environ Microbiol

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Standardization of toxin preparations derived from Bacillus thuringiensis (Berliner) used in laboratory bioassays is critical for accurately assessing possible changes in the susceptibility of field populations of target pests. Different methods were evaluated to quantify Cry1Ab, the toxin expressed by 80% of the commercially available transgenic maize that targets the European corn borer, Ostrinia nubilalis (Hübner). We compared three methods of quantification on three different toxin preparations from independent sources: enzyme-linked immunosorbent assay (ELISA), sodium dodecyl sulfate-polyacrylamide gel electrophoresis and densitometry (SDS-PAGE/densitometry), and the Bradford assay for total protein. The results were compared to those obtained by immunoblot analysis and with the results of toxin bioassays against susceptible laboratory colonies of O. nubilalis. The Bradford method resulted in statistically higher estimates than either ELISA or SDS-PAGE/densitometry but also provided the lowest coefficients of variation (CVs) for estimates of the Cry1Ab concentration (from 2.4 to 5.4%). The CV of estimates obtained by ELISA ranged from 12.8 to 26.5%, whereas the CV of estimates obtained by SDS-PAGE/densitometry ranged from 0.2 to 15.4%. We standardized toxin concentration by using SDS-PAGE/densitometry, which is the only method specific for the 65-kDa Cry1Ab protein and is not confounded by impurities detected by ELISA and Bradford assay for total protein. Bioassays with standardized Cry1Ab preparations based on SDS-PAGE/densitometry showed no significant differences in LC 50 values, although there were significant differences in growth inhibition for two of the three Cry1Ab preparations. However, the variation in larval weight caused by toxin source was only 4% of the total variation, and we conclude that standardization of Cry1Ab production and quantification by SDS-PAGE/densitometry may improve data consistency in monitoring efforts to identify changes in insect susceptibility to Cry1Ab.

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“…48 Thirty μl of water containing 0.1% Triton X-100 and an appropriate amount of Bt toxin were added to each well. After 7 d at 27°C, 24 D, and 80% RH, larvae were scored as dead if they died or if they had not grown beyond the first instar and did not weigh > 0.1 mg.…”

Section: O Nubilalismentioning

confidence: 99%

Efficacy of genetically modified Bt toxins against insects with different genetic mechanisms of resistance

et al. 2011

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Transgenic crops that produce Bacillus thuringiensis (Bt) toxins are grown widely for pest control, 1 but insect adaptation can reduce their efficacy. [2][3][4][5][6] The genetically modified Bt toxins Cry1AbMod and Cry1AcMod were designed to counter insect resistance to native Bt toxins Cry1Ab and Cry1Ac. 7 Previous results suggested that the modified toxins would be effective only if resistance was linked T A B A S H N I K E T A L ., N A T U R E B I O T E C H N O L O G Y 2 9 : 1 2 ( D E C E M B E R 2 0 1 1 )2 with mutations in genes encoding toxin-binding cadherin proteins. 7 Here we report evidence from five major crop pests refuting this hypothesis. Relative to native toxins, the potency of modified toxins was >350-fold higher against resistant strains of Plutella xylostella and Ostrinia nubilalis in which resistance was not linked with cadherin mutations. Conversely, the modified toxins provided little or no advantage against some resistant strains of three other pests with altered cadherin. Independent of the presence of cadherin mutations, the relative potency of the modified toxins was generally higher against the most resistant strains.The toxins produced by Bt kill some major insect pests but cause little or no harm to people and most other organisms. 8 Bt toxins have been used in sprays for decades and in transgenic plants since 1996 (ref. 6). Transgenic corn and cotton producing Bt toxins were planted on >58 million hectares worldwide in 2010 (ref. 1). The primary threat to the longterm efficacy of Bt toxins is the evolution of resistance by pests. [2][3][4][5][6] Many insects have been selected for resistance to Bt toxins in the laboratory, and some populations of at least eight crop pests have evolved resistance to Bt toxins outside of the laboratory, including two species resistant to Bt sprays and at least six species resistant to Bt crops. [2][3][4][5][6][9][10][11][12][13] The most widely used Bt toxins are crystalline proteins in the Cry1A family, particularly Cry1Ab in transgenic Bt corn and Cry1Ac in transgenic Bt cotton, which kill some lepidopteran larvae. 3 Cry1A toxins bind to the extracellular domains of cadherin, aminopeptidase, and alkaline phosphatase in larval midgut membranes. 14,15 Disruption of Bt toxin binding to midgut receptors is the most common general mechanism of insect resistance. 9 Mutations in the genes encoding midgut cadherins that bind Cry1Ac are linked with resistance in at least three lepidopteran pests of cotton, [16][17][18] but such cadherin mutations are not the primary cause of many other cases of field-and laboratory-selected resistance. 9,19,20 Although some aspects of the mode of action of Bt toxins remain unresolved, extensive evidence shows that after Cry1A protoxins are ingested by larvae, they are solubilized in the gut and cleaved by mid-gut proteases such as trypsin to yield activated 60-kD monomeric toxins that bind with membrane-associated receptors. 14,15 The signaling model suggests that after protease-activated monomeric toxins bind to ca...

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Baseline Susceptibility of European Corn Borer (Lepidoptera: Crambidae) to Bacillus thuringiensis Toxins

Cited by 154 publications

References 13 publications

Putative effects of Cry1Ab to larvae of Adalia bipunctata - reply to Hilbeck et al. (2012)

Putative effects of Cry1Ab to larvae of Adalia bipunctata - reply to Hilbeck et al. (2012)

Comparison and Validation of Methods To Quantify Cry1Ab Toxin from Bacillus thuringiensis for Standardization of Insect Bioassays

Efficacy of genetically modified Bt toxins against insects with different genetic mechanisms of resistance

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