Sampling date in 2009, corrected survival in bioassays, and history of planting in problem fields (P1–P4) and control fields (C1–C5) from 2003 to 2009.

a<p>Field history indicates the crop that was planted in a field each year: 1 = soybean, 2 = maize lacking rootworm active Bt, 3 = Cry3Bb1 maize, 4 = Cry34/35Ab1 maize, 5 = combination of Cry3Bb1 maize and Cry34/35Ab1 maize, 6 = research plots with non-Bt maize and several Bt maize hybrids (mCry3A <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0022629#pone.0022629-Walters1" target="_blank">[46]</a>, Cry3Bb1, and Cry34/35Ab1).</p

Correlation analysis for corrected survival of western corn rootworm.

<p>Correlations are shown for A) survival on Cry3Bb1 maize and Cry34/35Ab1 maize and B) survival on Cry3Bb1 maize and number of years Cry3Bb1 maize was planted in a field. Symbols in the graphs correspond to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0022629#pone-0022629-t001" target="_blank">Table 1</a>, which lists corrected survival for populations on Bt maize and the cultivation history of fields. For (A), no significant correlation was present between survival on Cry3Bb1 maize and Cry34/35Ab1 maize (r = 0.068; df = 6; P = 0.87). For (B), a significant positive correlation was present between corrected survival on Cry3Bb1 maize and the number of years Cry3Bb1 maize had been grown in a field (r = 0.832; df = 7; P = 0.005).</p

Distribution of sites sampled within Iowa during 2009.

<p>Sites beginning with C are control fields and were not associated with feeding injury to Bt maize, and sites beginning with P were problem fields, which were associated with farmer complaints of severe injury to Cry3Bb1 maize by corn rootworm. Codes correspond to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0022629#pone-0022629-t001" target="_blank">Table 1</a> where a field history is provided along with the corrected survival for these populations of western corn rootworm on Cry3Bb1 maize and Cry34/35Ab1 maize.</p

Survival of western corn rootworm on Bt and non-Bt maize.

<p>Data are shown for A) Cry3Bb1 maize and B) Cry34/35Ab1 maize. In both cases, survival also is shown for a non-Bt near isogenic hybrid. Bar heights are means and error bars are the standard error of the mean.</p

Up-regulation of apoptotic- and cell survival-related gene pathways following exposures of western corn rootworm to \u3ci\u3eB. thuringiensis\u3c/i\u3e crystalline pesticidal proteins in transgenic maize roots

Background: Resistance of pest insect species to insecticides, including B. thuringiensis (Bt) pesticidal proteins expressed by transgenic plants, is a threat to global food security. Despite the western corn rootworm, Diabrotica virgifera virgifera, being a major pest of maize and having populations showing increasing levels of resistance to hybrids expressing Bt pesticidal proteins, the cell mechanisms leading to mortality are not fully understood. Results: Twenty unique RNA-seq libraries from the Bt susceptible D. v. virgifera inbred line Ped12, representing all growth stages and a range of different adult and larval exposures, were assembled into a reference transcriptome. Ten-day exposures of Ped12 larvae to transgenic Bt Cry3Bb1 and Gpp34/Tpp35Ab1 maize roots showed significant differential expression of 1055 and 1374 transcripts, respectively, compared to cohorts on non-Bt maize. Among these, 696 were differentially expressed in both Cry3Bb1 and Gpp34/Tpp35Ab1 maize exposures. Differentially-expressed transcripts encoded protein domains putatively involved in detoxification, metabolism, binding, and transport, were, in part, shared among transcripts that changed significantly following exposures to the entomopathogens Heterorhabditis bacteriophora and Metarhizium anisopliae. Differentially expressed transcripts in common between Bt and entomopathogen treatments encode proteins in general stress response pathways, including putative Bt binding receptors from the ATP binding cassette transporter superfamily. Putative caspases, pro- and anti-apoptotic factors, as well as endoplasmic reticulum (ER) stress-response factors were identified among transcripts uniquely up-regulated following exposure to either Bt protein. Conclusions: Our study suggests that the up-regulation of genes involved in ER stress management and apoptotic progression may be important in determining cell fate following exposure of susceptible D. v. virgifera larvae to Bt maize roots. This study provides novel insights into insect response to Bt intoxication, and a possible framework for future investigations of resistance mechanisms