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Evaluating the impacts of refuge width on source-sink dynamics between transgenic and non-transgenic cotton.

Caprio MA, Faver MK, Hankins G - J. Insect Sci. (2004)

Bottom Line: In 1996, eggs of H. virescens from H. zea were not distinguished, but a significant increase in the density of eggs and a significant decrease in relative yield (refuge yield compared to the yield from immediately surrounding Bt-cotton) was found as refuge width increased.The density of H. virescens eggs increased with increasing refuge width, and there was a significant decline in density of H. virescens eggs with increasing distance from the refuge.We suggest that these differences reflect differences in the biology of the two insects.

View Article: PubMed Central - PubMed

Affiliation: Department of Entomology and Plant Pathology, Mississippi State, Box 9775, MS 39762, USA. mcaprio@entomology.msstate.edu

ABSTRACT
Resistance management for Bt-transgenic crops relies in part on the production of sufficient numbers of susceptible insects in non-toxic refuges. Simulation models suggested that source-sink dynamics could interact with the structure of refuges to impact the production of insects in these areas. We tested the hypothesis that altering isolation between refuges and transgenic cotton by manipulating the width of refuges embedded within cotton fields would alter the density of Heliothis virescens and Helicoverpa zea eggs oviposited in refuges. Three categories of refuge widths were tested over two years: they included narrow (16-24 m wide), medium (32-48 m wide) and wide (80-96 m wide) refuges. Isolation between the two habitats increased as refuge width increased. In 1996, eggs of H. virescens from H. zea were not distinguished, but a significant increase in the density of eggs and a significant decrease in relative yield (refuge yield compared to the yield from immediately surrounding Bt-cotton) was found as refuge width increased. In 1997, eggs from H. virescens were analyzed separately from H. zea using an ELISA test. The density of H. virescens eggs increased with increasing refuge width, and there was a significant decline in density of H. virescens eggs with increasing distance from the refuge. In contrast, there was no impact of refuge width on the density of H. zea eggs, nor was the slope of a regression of egg density and distance from the refuge significantly different from zero. We suggest that these differences reflect differences in the biology of the two insects.

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The change in mean (±SEM) egg density as a function of embedded refuge width for three farms in 1996. The small refuges were 16–24 m wide, the medium width refuges were 32–48 m wide, and the wide refuges were 80–96 m wide.
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i1536-2442-004-03-0001-f01: The change in mean (±SEM) egg density as a function of embedded refuge width for three farms in 1996. The small refuges were 16–24 m wide, the medium width refuges were 32–48 m wide, and the wide refuges were 80–96 m wide.

Mentions: A significant effect of refuge size on combined H. virescens and H. zea egg density was observed over the 1996 sample periods (F=5.49; df=2,30; p=0.026). Wider refuges had higher relative densities of eggs than narrow refuges (Fig. 1). No decline in egg density was recorded with increasing distance from the refuge for the distances sampled in this year (F=0.102; df=1,34; p=0.75; r2=0.003; Fig. 2). There was a significant decline in the relative yield of the refuge cotton compared with the surrounding Bt-cotton as the refuge width increased (F=8.67; df=2,56; p<0.001). The yield in the narrowest refuges was 81% of the yield of surrounding Bt-cotton, while the largest refuges yielded only 71% (Fig. 3).


Evaluating the impacts of refuge width on source-sink dynamics between transgenic and non-transgenic cotton.

Caprio MA, Faver MK, Hankins G - J. Insect Sci. (2004)

The change in mean (±SEM) egg density as a function of embedded refuge width for three farms in 1996. The small refuges were 16–24 m wide, the medium width refuges were 32–48 m wide, and the wide refuges were 80–96 m wide.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC455677&req=5

i1536-2442-004-03-0001-f01: The change in mean (±SEM) egg density as a function of embedded refuge width for three farms in 1996. The small refuges were 16–24 m wide, the medium width refuges were 32–48 m wide, and the wide refuges were 80–96 m wide.
Mentions: A significant effect of refuge size on combined H. virescens and H. zea egg density was observed over the 1996 sample periods (F=5.49; df=2,30; p=0.026). Wider refuges had higher relative densities of eggs than narrow refuges (Fig. 1). No decline in egg density was recorded with increasing distance from the refuge for the distances sampled in this year (F=0.102; df=1,34; p=0.75; r2=0.003; Fig. 2). There was a significant decline in the relative yield of the refuge cotton compared with the surrounding Bt-cotton as the refuge width increased (F=8.67; df=2,56; p<0.001). The yield in the narrowest refuges was 81% of the yield of surrounding Bt-cotton, while the largest refuges yielded only 71% (Fig. 3).

Bottom Line: In 1996, eggs of H. virescens from H. zea were not distinguished, but a significant increase in the density of eggs and a significant decrease in relative yield (refuge yield compared to the yield from immediately surrounding Bt-cotton) was found as refuge width increased.The density of H. virescens eggs increased with increasing refuge width, and there was a significant decline in density of H. virescens eggs with increasing distance from the refuge.We suggest that these differences reflect differences in the biology of the two insects.

View Article: PubMed Central - PubMed

Affiliation: Department of Entomology and Plant Pathology, Mississippi State, Box 9775, MS 39762, USA. mcaprio@entomology.msstate.edu

ABSTRACT
Resistance management for Bt-transgenic crops relies in part on the production of sufficient numbers of susceptible insects in non-toxic refuges. Simulation models suggested that source-sink dynamics could interact with the structure of refuges to impact the production of insects in these areas. We tested the hypothesis that altering isolation between refuges and transgenic cotton by manipulating the width of refuges embedded within cotton fields would alter the density of Heliothis virescens and Helicoverpa zea eggs oviposited in refuges. Three categories of refuge widths were tested over two years: they included narrow (16-24 m wide), medium (32-48 m wide) and wide (80-96 m wide) refuges. Isolation between the two habitats increased as refuge width increased. In 1996, eggs of H. virescens from H. zea were not distinguished, but a significant increase in the density of eggs and a significant decrease in relative yield (refuge yield compared to the yield from immediately surrounding Bt-cotton) was found as refuge width increased. In 1997, eggs from H. virescens were analyzed separately from H. zea using an ELISA test. The density of H. virescens eggs increased with increasing refuge width, and there was a significant decline in density of H. virescens eggs with increasing distance from the refuge. In contrast, there was no impact of refuge width on the density of H. zea eggs, nor was the slope of a regression of egg density and distance from the refuge significantly different from zero. We suggest that these differences reflect differences in the biology of the two insects.

Show MeSH
Related in: MedlinePlus