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Binning R.R.,DuPont Company | Lefko S.A.,DM Crop Research Group Inc. | Millsap A.Y.,DuPont Company | Thompson S.D.,DuPont Company | Nowatzki T.M.,DuPont Company
Journal of Applied Entomology | Year: 2010

Susceptibility of Diabrotica virgifera virgifera (LeConte) larvae to DAS-59122-7 maize was evaluated using a laboratory technique that measures rootworm survival to adulthood on maize seedlings. This method produces direct measures of larval susceptibility using realistic exposure to the same range of insecticidal protein concentrations found in field-grown DAS-59122-7 maize roots. First, second and third instars were reared to adulthood on DAS-59122-7 maize seedlings or a non-transgenic, near-isoline maize. Data on survival, adult gender ratio, adult weight and median emergence were collected. Overall, larval susceptibility to DAS-59122-7 maize was lower than earlier predictions (Storer et al. 2006). Neonate survival on DAS-59122-7 maize was approximately 33% of isoline survival after 17 days, and the same 33% recovered and developed to adulthood when the isoline maize was substituted. Survival rate on DAS-59122-7 maize increased with instar. The mean survivorship was 0.5%, 26% and 65% when exposure to DAS-59122-7 maize began at the first, second and third instars, respectively. Exposure to DAS-59122-7 maize led to sub-lethal effects on adult gender ratio, weight and median emergence. These effects decreased when exposure to DAS-59122-7 maize began at later instars. The killing effect of DAS-59122-7 maize on rootworm larvae appeared to result from the combined chronic effects and absence of a suitable host as perceived by the larvae. The relevance of these data and the methodology of estimating rootworm susceptibility to plant-incorporated protectants are discussed in the context of the US Environmental Protection Agency's functional definition of 'high dose' and use of refuge for resistance management (EPA 1998a). Based on these results it is evident that DAS-59122-7 maize does not meet the functional definitions of high dose as described by EPA (1998a,b) and ILSI (1999), and the utility of refuge, refuge size and refuge placement for delaying rootworm resistance should be further investigated. © 2010 Blackwell Verlag, GmbH.

Clark T.L.,University of Missouri | Clark T.L.,Monsanto Corporation | Frank D.L.,University of Missouri | French B.W.,U.S. Department of Agriculture | And 4 more authors.
Journal of Applied Entomology | Year: 2012

Mortality of western corn rootworm (Diabrotica virgifera virgifera LeConte) due to feeding on MON863 transgenic maize (Zea mays L.) expressing the Cry3Bb1 protein was evaluated at three Missouri sites in both 2003 and 2004 and at one site each in South Dakota, Nebraska and Iowa in 2004. To do this, survivorship relative to survivorship on isoline maize (i.e. the same genetic background, but without Cry3Bb1) was evaluated. Comparisons were made using low (1650-2500eggs/m) and high (3300-3500eggs/m) western corn rootworm egg densities. Significantly fewer beetles were recovered from MON863 than from isoline maize. Emergence from MON863 as a percentage of viable eggs ranged from 0.02% to 0.10%, whereas percentage emergence from isoline maize ranged from 1.09% to 7.14%. Survivorship on MON863 relative to survivorship on isoline averaged 1.51% when averaged across all environments and both years, so mortality because of the Cry3Bb1 protein averaged 98.49%. The average time delay to 50% cumulative beetle emergence from MON863 was 18.3days later than from isoline maize. Females comprised 56% and 71% of total beetles recovered from MON863 in 2003 and 2004, respectively. Results are discussed in relation to insect resistance management (IRM) of western corn rootworm. © 2012 Blackwell Verlag, GmbH.

Frank D.L.,University of Missouri | Frank D.L.,West Virginia University | Kurtz R.,Syngenta Biotechnology | Kurtz R.,Cotton Incorporated | And 10 more authors.
Journal of Economic Entomology | Year: 2015

Seed blends containing various ratios of transgenic Bt maize (Zea mays L.) expressing the mCry3A + eCry3.1Ab proteins and non-Bt maize (near-isoline maize) were deployed alone and in combination with a soil applied pyrethroid insecticide (Force CS) to evaluate the emergence of the western corn rootworm, Diabrotica virgifera virgifera LeConte, in a total of nine field environments across the Midwestern United States in 2010 and 2011. Northern corn rootworm, Diabrotica barberi Smith & Lawrence emergence was also evaluated in four of these environments. Both western and northern corn rootworm beetle emergence from all Bt treatments was significantly reduced when compared with beetle emergence from near-isoline treatments. Averaged across all environments, western corn rootworm beetle emergence from 95:5, 90:10, and 80:20 seed blend ratios of mCry3A + eCry3.1Ab: near-isoline were 2.6-, 4.2-, and 6.7-fold greater than that from the 100:0 ratio treatment. Northern corn rootworm emergence from the same seed blend treatments resulted in 2.8-, 3.2-, and 4.2-fold more beetles than from the 100:0 treatment. The addition of Force CS (tefluthrin) significantly reduced western corn rootworm beetle emergence for each of the three treatments to which it was applied. Force CS also significantly delayed the number of days to 50% beetle emergence in western corn rootworms. Time to 50% beetle emergence in the 100% mCry3A + eCry3.1Ab treatment with Force CS was delayed 13.7 d when compared with western corn rootworm beetle emergence on near-isoline corn. These data are discussed in terms of rootworm resistance management. © 2015 The Authors.

Velez A.M.,University of Nebraska - Lincoln | Spencer T.A.,University of Nebraska - Lincoln | Alves A.P.,DuPont Pioneer | Moellenbeck D.,DM Crop Research Group Inc. | And 3 more authors.
Bulletin of Entomological Research | Year: 2013

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. Copyright © Cambridge University Press 2013.

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