Optimizing pyramided transgenic Bt crops for sustainable pest management

Transgenic crop pyramids producing two or more Bacillus thuringiensis (Bt) toxins that kill the same insect pest have been widely used to delay evolution of pest resistance. To assess the potential of pyramids to achieve this goal, we analyze data from 38 studies that report effects of ten Bt toxins used in transgenic crops against 15 insect pests. We find that compared with optimal low levels of insect survival, survival on currently used pyramids is often higher for both susceptible insects and insects resistant to one of the toxins in the pyramid. Furthermore, we find that cross-resistance and antagonism between toxins used in pyramids are common, and that these problems are associated with the similarity of the amino acid sequences of domains II and III of the toxins, respectively. This analysis should assist in future pyramid design and the development of sustainable resistance management strategies

Supplementary raw data

Supplementary tables (1-5) and figure (1

Pollen-mediated gene flow of the <i>cry1Ac</i> transgene in non-Bt cotton fields, sample sizes, and field attributes.

1<p>Number of tested plants, including the total number of edge plants, the number of edge plants included in the paired analysis (where applicable), and the number of plants collected 20 m in from the field edge for paired analysis (where applicable).</p>2<p>Honey bee (HB) density from visual monitoring (honey bees/100 flowers).</p

Diagram of rings drawn around a hypothetical cotton field.

<p>The first ring is 250 m from the field edge, and each subsequent ring increases in radius by 250 m. The area of non-Bt and Bt cotton was measured at each increasing scale. Light and dark gray represent non-Bt and Bt cotton, respectively, and the black rectangle represents a monitored non-Bt cotton field. For actual monitored fields, some rings overlapped those of nearby monitored fields.</p

Range odds ratios¹ for the effects of the explanatory variables on outcrossing.

<p>From a simplified model without the interaction term (odds ratios of interactions are difficult to interpret). Results from models with and without fields <i>A</i> and <i>B</i> are given.</p>1<p>Range odds ratios estimate the change in the odds of an event (i.e., outcrossing) over the observed range of an explanatory variable <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0014128#pone.0014128-SAS1" target="_blank">[31]</a>. For instance, in the field with the most honey bees, plants had 6.4-fold higher odds of outcrossing than in the field with the fewest honey bees for the 15 field model.</p

Effect likelihood ratio tests for pollen-mediated gene flow of the <i>cry1Ac</i> transgene in monitored non-Bt cotton fields.

<p>Significance levels (<i>P</i>-values) for each factor from models with and without fields <i>A</i> and <i>B</i> (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0014128#pone-0014128-t001" target="_blank">Table 1</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0014128#pone-0014128-t003" target="_blank">Table 3</a>) are given. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0014128#pone-0014128-t002" target="_blank">Table 2</a> for details on the explanatory variables.</p>1<p>Area of Bt cotton fields within 750 m of the edge of monitored non-Bt cotton fields.</p

Uncertainty coefficient of determination (R²) for multiple logistic regression of pollen-mediated gene flow.

<p>The area of Bt cotton at various distances from the edge of monitored non-Bt cotton fields was considered in separate analyses for each scale. Honey bee density, the proportion of plants in the monitored non-Bt cotton fields that were adventitious Bt plants, and the interaction between Bt cotton fields and adventitious Bt plants were also in the analyses. Pollen-mediated gene flow of the <i>cry1Ac</i> transgene was the response variable for the analyses. Results with fields <i>A</i> and <i>B</i> (solid line) and without fields <i>A</i> and <i>B</i> (dashed line) are shown.</p

Summary of explanatory variables included in the full logistic regression analysis.

<p>Variables that were not significant (α>0.05) at any of the spatial scales in the model with all 15 fields were excluded from further analyses.</p

Seed-mediated gene flow of the <i>cry1Ac</i> transgene in monitored non-Bt cotton fields.

1<p>Percentage of plants that were adventitious Bt cotton plants in samples taken from the field edge or 20 m in from a field edge, if applicable.</p>2<p>Percentage of adventitious Bt cotton plants that were hemizygous for the Bt trait.</p>3<p>Putative source of seed-mediated gene flow.</p

Appendix B. A list of parasitoid species recovered from collections of Estigmene acrea (1996–2001) in southeastern Arizona.

A list of parasitoid species recovered from collections of Estigmene acrea (1996–2001) in southeastern Arizona