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

Author

Tabashnik, Bruce E, primary, Huang, Fangneng, additional, Ghimire, Mukti N, additional, Leonard, B Rogers, additional, Siegfried, Blair D, additional, Rangasamy, Murugesan, additional, Yang, Yajun, additional, Wu, Yidong, additional, Gahan, Linda J, additional, Heckel, David G, additional, Bravo, Alejandra, additional, and Soberón, Mario, additional

Published
2011
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156. Larval distribution and survival of second generation European corn borer, Ostrinia nubilalis (H.ubner) (Lepidoptera: Crambidae) on Event 176 Bt Corn

Author

Zoerb, Amelia C., Spencer, Terrence A., Hellmich, Richard L., Wright, Robert J., Siegfried, Blair D., Zoerb, Amelia C., Spencer, Terrence A., Hellmich, Richard L., Wright, Robert J., and Siegfried, Blair D.

Abstract

European corn borer Ostrinia nubilalis Hubner (Lepidoptera: Crambidae) larvae that have completed development on Event 176 Bt corn hybids have either survived exposure to sublethal doses of Cry1Ab Bt toxin or exploited plant tissues that do not express the toxin. To evaluate the impact of such exposure on larval establishment and survival, Event 176 plants with and without tassels and a non-Bt isoline were infested with O. nubilalis egg masses during anthesis. On the non-Bt plants, larval establishment occurred primarily on pollen collecting in the leaf axils, silks and ears. In contrast, almost no larvae were recovered from leaf axils of the Bt treatments and at least 50% fewer larvae were recovered from the silks and ears during the first 2 weeks after infestation relative to the non-Bt plants. The larvae recovered from Bt treatments weighed significantly less than those observed in the non-Bt isoline at 4 weeks after infestation. By the eighth week, the larval weights of all three treatments were similar in three of four different field tests, suggesting that second generation larvae have the ability to compensate for initial exposure to sublethal doses of Bt toxin. In laboratory assays involving exposure of neonate larvae to silks of Event 176 and non-Bt corn, survival of neonate O. nubilalis was not different although larval weights were significantly reduced (2- to 6-fold). These results suggest that second generation larvae completing development on Event 176 corn do not completely avoid exposure to the Bt toxin, although those that do survive are able to compensate for these sublethal effects. The implication of these results is that Event 176 hybrids do not appear to satisfy requirements for high dose that are recommended for resistance management purposes.

Published
2003

157. In-Field Labeling of Western Corn Rootworm Adults (Coleoptera: Chrysomelidae) with Rubidium

Author

Nowatzki, Timothy M., Niimi, Bradley, Warren, Kelli J., Putnam, Sean, Meinke, Lance J., Gosselin, David C., Harvey, F. Edwin, Hunt, Thomas E., Siegfried, Blair, Nowatzki, Timothy M., Niimi, Bradley, Warren, Kelli J., Putnam, Sean, Meinke, Lance J., Gosselin, David C., Harvey, F. Edwin, Hunt, Thomas E., and Siegfried, Blair

Abstract

Field and laboratory studies were conducted in 2000 and 2001 to determine the feasibility of mass marking western corn rootworm adults, Diabrotica virgifera virgifera LeConte, with RbCl in the field. Results showed that application of rubidium (Rb) in solution to both the soil (1 g Rb/plant) and whorl (1 g Rb/plant) of corn plants was optimal for labeling western corn rootworm adults during larval development. Development of larvae on Rb-enriched corn with this technique did not significantly influence adult dry weight or survival. Rb was also highly mobile in the plant. Application of Rb to both the soil and the whorl resulted in median Rb concentrations in the roots (5,860 ppm) that were 150-fold greater than concentrations in untreated roots (38 ppm) 5 wk after treatment. Additionally, at least 90% of the beetles that emerged during the first 3 wk were labeled above the baseline Rb concentration (5 ppm dry weight) determined from untreated beetles. Because emergence was 72% complete at this time, a significant proportion of the population had been labeled. Results from laboratory experiments showed that labeled beetles remained distinguishable from unlabeled beetles for up to 4 d post-emergence. The ability to efficiently label large numbers of beetles under field conditions and for a defined period with virtually no disruption of the population provides an unparalleled opportunity to conduct mark-recapture experiments for quantifying the short-range, intra-field movement of adult corn rootworms.

Published
2003

163. Expressed sequence tags from larval gut of the European corn borer (Ostrinia nubilalis): Exploring candidate genes potentially involved in Bacillus thuringiensis toxicity and resistance

Author

Khajuria, Chitvan, primary, Zhu, Yu Cheng, additional, Chen, Ming-Shun, additional, Buschman, Lawrent L, additional, Higgins, Randall A, additional, Yao, Jianxiu, additional, Crespo, Andre LB, additional, Siegfried, Blair D, additional, Muthukrishnan, Subbaratnam, additional, and Zhu, Kun Yan, additional

Published
2009
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169. Fipronil metabolism, oxidative sulfone formation and toxicity among organophosphate- and carbamate-resistant and susceptible western corn rootworm populations

Author

Scharf, Michael E., Siegfried, Blair D., Meinke, Lance J., Chandler, Laurence D., Scharf, Michael E., Siegfried, Blair D., Meinke, Lance J., and Chandler, Laurence D.

Abstract

Fipronil toxicity and metabolism were studied in two insecticide-resistant, and one susceptible western corn rootworm (Diabrotica virgifera virgifera, LeConte) populations. Toxicity was evaluated by exposure to surface residues and by topical application. Surface residue bioassays indicated no differences in fipronil susceptibility among the three populations. Topical bioassays were used to study the relative toxicity of fipronil, fipronil. the mono-oxygenase inhibitor piperonyl butoxide, and fipronil's oxidative sulfone metabolite in two populations (one resistant with elevated mono-oxygenase activity). Fipronil and fipronil-sulfone exhibited similar toxicity and application of piperonyl butoxide prior to fipronil resulted in marginal effects on toxicity. Metabolism of [14C]fipronil was evaluated in vivo and in vitro in the three rootworm populations. In vivo studies indicated the dominant pathway in all populations to be formation of the oxidative sulfone metabolite. Much lower quantities of polar metabolites were also identified. In vitro studies were performed using sub-cellular protein fractions (microsomal and cytosolic), and glutathione-agarose purified glutathione-Stransferase. Oxidative sulfone formation occurred almost exclusively in in vitro microsomal reactions and was increased in the resistant populations. Highly polar metabolites were formed exclusively in in vitro cytosolic reactions. In vitro reactions performed with purified, cytosolic glutathione-Stransferase (MW=27kDa) did not result in sulfone formation, although three additional polar metabolites not initially detectable in crude cytosolic reactions were detected. Metabolism results indicate both cytochromes P450 and glutathione-S-transferases are important to fipronil metabolism in the western corn rootworm and that toxic sulfone formation by P450 does not affect net toxicity.

Published
2000

172. Transcriptional analysis of susceptible and resistant European corn borer strains and their response to Cry1F protoxin.

Author

Vellichirammal, Neetha Nanoth, Haichuan Wang, Seong-il Eyun, Moriyama, Etsuko N., Coates, Brad S., Miller, Nicholas J., and Siegfried, Blair D.

Subjects
EUROPEAN corn borer, GENE expression, INSECT genetics, PLANT genetics, PLANT resistance to insects, GENETIC transcription, TRANSGENIC plants
Abstract

Background: Despite a number of recent reports of insect resistance to transgenic crops expressing insecticidal toxins from Bacillus thuringiensis (Bt), little is known about the mechanism of resistance to these toxins. The purpose of this study is to identify genes associated with the mechanism of Cry1F toxin resistance in European corn borer (Ostrinia nubilalis Hübner). For this, we compared the global transcriptomic response of laboratory selected resistant and susceptible O. nubilalis strain to Cry1F toxin. We further identified constitutive transcriptional differences between the two strains. Results: An O. nubilalis midgut transcriptome of 36,125 transcripts was assembled de novo from 106 million Illumina HiSeq and Roche 454 reads and used as a reference for estimation of differential gene expression analysis. Evaluation of gene expression profiles of midgut tissues from the Cry1F susceptible and resistant strains after toxin exposure identified a suite of genes that responded to the toxin in the susceptible strain (n = 1,654), but almost 20-fold fewer in the resistant strain (n = 84). A total of 5,455 midgut transcripts showed significant constitutive expression differences between Cry1F susceptible and resistant strains. Transcripts coding for previously identified Cry toxin receptors, cadherin and alkaline phosphatase and proteases were also differentially expressed in the midgut of the susceptible and resistant strains. Conclusions: Our current study provides a valuable resource for further molecular characterization of Bt resistance and insect response to Cry1F toxin in O. nubilalis and other pest species. [ABSTRACT FROM AUTHOR]

Published
2015
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190. Impact of Bt corn pollen on monarch butterfly populations: A risk assessment

Author

Sears, Mark K., Hellmich, Richard L., Stanley-Horn, Diane E., Oberhauser, Karen S., Pleasants, John M., Mattila, Heather R., Siegfried, Blair D., and Dively, Galen P.

Subjects
Corn -- Breeding, Pollen -- Physiological aspects, Monarch butterfly -- Physiological aspects, Population research -- Analysis, Science and technology
Abstract

A collaborative research effort by scientists in several states and in Canada has produced information to develop a formal risk assessment of the impact of Bt corn on monarch butterfly (Danaus plexippus) populations. Information was sought on the acute toxic effects of Bt corn pollen and the degree to which monarch larvae would be exposed to toxic amounts of Bt pollen on its host plant, the common milkweed, Asclepias syriaca, found in and around cornfields. Expression of Cry proteins, the active toxicant found in Bt corn tissues, differed among hybrids, and especially so in the concentrations found in pollen of different events. In most commercial hybrids, Bt expression in pollen is low, and laboratory and field studies show no acute toxic effects at any pollen density that would be encountered in the field. Other factors mitigating exposure of larvae include the variable and limited overlap between pollen shed and larval activity periods, the fact that only a portion of the monarch population utilizes milkweed stands in and near cornfields, and the current adoption rate of Bt corn at 19% of North American corn-growing areas. This 2-year study suggests that the impact of Bt corn pollen from current commercial hybrids on monarch butterfly populations is negligible.

Published
2001

191. Monarch larvae sensitivity to Bacillus thuringiensis-purified proteins and pollen

Author

Hellmich, Richard L., Siegfried, Blair D., Sears, Mark K., Stanley-Horn, Diane E., Daniels, Michael J., Mattila, Heather R., Spencer, Terrence, Bidne, Keith G., and Lewis, Leslie C.

Subjects
Bacillus thuringiensis -- Health aspects, Pollen -- Health aspects, Monarch butterfly -- Health aspects, Larvae -- Health aspects, Science and technology
Abstract

Laboratory tests were conducted to establish the relative toxicity of Bacillus thuringiensis (Bt) toxins and pollen from Bt corn to monarch larvae. Toxins tested included Cry1Ab, Cry1Ac, Cry9C, and Cry1F. Three methods were used: (i) purified toxins incorporated into artificial diet, (ii) pollen collected from Bt corn hybrids applied directly to milkweed leaf discs, and (iii) Bt pollen contaminated with corn tassel material applied directly to milkweed leaf discs. Bioassays of purified Bt toxins indicate that Cry9C and Cry1F proteins are relatively non-toxic to monarch first instars, whereas first instars are sensitive to Cry1Ab and Cry1Ac proteins. Older instars were 12 to 23 times less susceptible to Cry1Ab toxin compared with first instars. Pollen bioassays suggest that pollen contaminants, an artifact of pollen processing, can dramatically influence larval survival and weight gains and produce spurious results. The only transgenic corn pollen that consistently affected monarch larvae was from Cry1Ab event 176 hybrids, currently [is less than] 2% corn planted and for which re-registration has not been applied. Results from the other types of Bt corn suggest that pollen from the Cry1Ab (events Bt11 and Mon810) and Cry1F, and experimental Cry9C hybrids, will have no acute effects on monarch butterfly larvae in field settings.

Published
2001

195. Transgenic Insecticidal Corn: The Agronomic and Ecological Rationale for Its Use

Author

Ortman, Eldon E., primary, Barry, B. Dean, additional, Buschman, Lawrent L., additional, Calvin, Dennis D., additional, Carpenter, Janet, additional, Dively, Galen P., additional, Foster, John E., additional, Fuller, Billy W., additional, Hellmich, Richard L., additional, HigginS, Randall A., additional, Hunt, Thomas E., additional, Munkvold, Gary P., additional, Ostlie, Kenneth R., additional, Rice, Marlin E., additional, Roush, Richard T., additional, Sears, Mark K., additional, Shelton, Anthony M., additional, Siegfried, Blair D., additional, Sloderbeck, Phillip E., additional, Steffey, Kevin L., additional, Turpin, F. Tom, additional, and Wedberg, John L., additional

Published
2001
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