Progress 12/01/05 to 11/30/10
Outputs
OUTPUTS: To determine the affects of Bt-transgenic corn on pest damage and aflatoxin in a new fused-gene Bt corn hybrid, Gary Odvody and I examined insect whorl, shank, stalk, and ear injury as well as aflatoxin level and yield on 6 replicate plots of 3 different corn lines at Corpus Christi and Beeville, TX from 2005-2007. Each line included 1 fused-gene (Cry1Ab+Cry2Ab2), one Mon810 (Cry1Ab), and 1 non-Bt hybrid, and comparisons between hybrids within each line were made to determine the efficacy of the fused-gene hybrid. Insect damage included whorl (0-9 rating / 10 plants) and ear injury (cm / 10 ears) by corn earworm and fall armyworm, with no shank or stalk damage by any pest. In 2005, there were significant interactions between location and hybrid type for all dependent variables except yield, whereas in 2006 and 2007 there were no interactions. Each year, whorl and ear injury were significantly less and yield greater in the fused-gene hybrids than in Cry1Ab and non-Bt hybrids. Also, aflatoxin was lower in the fused-gene hybrids then in the Cry1Ab and non-Bt hybrids in 2005 and 2006, but there were no differences in 2007. In conclusion, compared to similar conventional Non-Bt and Cry1A corn hybrids, those with the fused gene proteins had significantly lower insect injury and aflatoxin content, and higher yield. In a study of sugarcane borer (SCB) damage to corn, in 2006 I found that for 400 plants both the proportion of stalks damaged and cm of SCB tunneling were positively correlated with kernel weight per ear, i.e. yield actually increased with stalk damage. However, in 2007 I found that there was no relationship between stalk damage and yield. Also, in a project with Fangneng Huang at LSU, we found that SCB from the Coastal Bend of Texas were more susceptible to Bt toxins than SCB from Louisiana. I also worked with Roy Parker examining relationships between cotton fleahopper densities on 5 dates (9 May to 12 June) during cotton square development and fruit numbers, retention, and yield. Fleahopper densities on all 5 dates were significantly and negatively correlated with yield (r2≈0.36 each date) as well as with most crop data. As an example, on 12 June, fleahopper densities were negatively correlated with squares per plant (r2=0.58), green bolls per plant (r2=0.34), green bolls on branches 1-5 and 6-10 (r2=0.28 for each), and at positions 1, 2, and 3 (all r2≈0.31), as well as % fruit retention per plant (r2=0.72), % fruit retention on branches 1-5 (r2=0.51), 6-10 (r2=0.85), and 11-15 (r2=0.51), and at positions 1, 3 (r2=0.56 for each), and 2 (r2 = 0.77). Also, fleahopper densities were positively correlated with fruit abscised (r2=0.5) and plant height at harvest (r2=0.76). Examining the relationship between cotton yield and plant variables, we found that yield was positively correlated with squares per plant (r2=0.31), as well as % fruit retention per plant (r2 = 0.34), % fruit retention on branches 6-10 and 11-15, and positions 1, 2, and 3 (r2≈0.25 for each). Also, yield was negatively correlated with plant height at harvest (r2=0.23). PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Overall, my project helped growers to increase the use of environmentally sound, sustainable, insect control methods, as well as providing them with the information to make informed decisions on the importance of controlling new crop pests and choosing crop varieties that reduce insect pest damage and aflatoxin while maximizing yield in South Texas. My project also benefited grower's economically by suggesting cost-effective solutions and techniques to integrate pest control based on economic damage thresholds and pest resistance management, increasing their profits by maximizing their yields while reducing expensive chemical inputs, reducing fungal toxin accumulation, and preventing the development of resistance to control measures by pests.
Publications
- No publications reported this period
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Progress 01/01/07 to 12/31/07
Outputs
To determine the affects of Bt-transgenic corn on pest damage and aflatoxin in a new fused-gene Bt corn hybrid, Gary Odvody and I examined insect whorl, shank, stalk, and ear injury as well as aflatoxin level and yield on 6 replicate plots of 3 different corn lines at Corpus Christi and Beeville, TX from 2005-2007. Each line included 1 fused-gene (Cry1Ab+Cry2Ab2), one Mon810 (Cry1Ab), and 1 non-Bt hybrid, and comparisons between hybrids within each line were made to determine the efficacy of the fused-gene hybrid. Insect damage included whorl (0-9 rating / 10 plants) and ear injury (cm / 10 ears) by corn earworm and fall armyworm, with no shank or stalk damage by any pest. In 2005, there were significant interactions between location and hybrid type for all dependent variables except yield, whereas in 2006 and 2007 there were no interactions. Each year, whorl and ear injury were significantly less and yield greater in the fused-gene hybrids than in Cry1Ab and non-Bt
hybrids. Also, aflatoxin was lower in the fused-gene hybrids then in the Cry1Ab and non-Bt hybrids in 2005 and 2006, but there were no differences in 2007. In conclusion, compared to similar conventional Non-Bt and Cry1A corn hybrids, those with the fused gene proteins had significantly lower insect injury and aflatoxin content, and higher yield. In a study of sugarcane borer (SCB) damage to corn, in 2006 I found that for 400 plants both the proportion of stalks damaged and cm of SCB tunneling were positively correlated with kernel weight per ear, i.e. yield actually increased with stalk damage. However, in 2007 I found that there was no relationship between stalk damage and yield. Also, in a project with Fangneng Huang at LSU, we found that SCB from the Coastal Bend of Texas were more susceptible to Bt toxins than SCB from Louisiana. I also worked with Roy Parker examining relationships between cotton fleahopper densities on 5 dates (9 May to 12 June) during cotton square development
and fruit numbers, retention, and yield. Fleahopper densities on all 5 dates were significantly and negatively correlated with yield (r2≈0.36 each date) as well as with most crop data. As an example, on 12 June, fleahopper densities were negatively correlated with squares per plant (r2=0.58), green bolls per plant (r2=0.34), green bolls on branches 1-5 and 6-10 (r2=0.28 for each), and at positions 1, 2, and 3 (all r2≈0.31), as well as % fruit retention per plant (r2=0.72), % fruit retention on branches 1-5 (r2=0.51), 6-10 (r2=0.85), and 11-15 (r2=0.51), and at positions 1, 3 (r2=0.56 for each), and 2 (r2 = 0.77). Also, fleahopper densities were positively correlated with fruit abscised (r2=0.5) and plant height at harvest (r2=0.76). Examining the relationship between cotton yield and plant variables, we found that yield was positively correlated with squares per plant (r2=0.31), as well as % fruit retention per plant (r2 = 0.34), % fruit retention on branches 6-10 and
11-15, and positions 1, 2, and 3 (r2≈0.25 for each). Also, yield was negatively correlated with plant height at harvest (r2=0.23).
Impacts
Overall, my project helps growers to increase the use of environmentally sound, sustainable, insect control methods, as well as providing them with the information to make informed decisions on the importance of controlling new crop pests and choosing crop varieties that reduce insect pest damage and aflatoxin while maximizing yield in South Texas. My project also benefits grower's economically by suggesting cost-effective solutions and techniques to integrate pest control based on economic damage thresholds and pest resistance management, increasing their profits by maximizing their yields while reducing expensive chemical inputs, reducing fungal toxin accumulation, and preventing the development of resistance to control measures by pests.
Publications
- Chilcutt, C. F., Odvody, G. N., Correa, J. C., Remmers, J. (2007) Effects of Bacillus thuringiensis transgenic corn on corn earworm and fall armyworm (Lepidoptera: Noctuidae) densities, Journal of Economic Entomology, 100: 327-334.
- Chilcutt, C. F., Matocha, J. (2007) Effects of crop rotation, tillage, and fertilizer applications on sorghum head insects, Journal of Economic Entomology, 100: 88-94.
- hilcutt, C. F. (2007) Bt gene flow to corn refuges: pest behaviour, mortality, and resistance evolution (abstract), Resistance 2007, Rothamsted Research, Harpenden, Hertfordshire, UK.
- Chilcutt, C. F. (2007) Effects of proportion and configuration of Bacillus thuringiensis cotton on pest abundance, damage, and yield, Journal of Economic Entomology, 100: 1428-1434.
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Progress 01/01/06 to 12/31/06
Outputs
To determine the affects of Bt-transgenic corn on pest damage in a new fused-gene Bt corn hybrid I examined insect densities, whorl, shank, stalk, and ear injury as well as yield on 6 replicate plots of 3 different corn lines at 2 locations. Comparisons between fused-gene-Bt, Mon810-Bt, and non-Bt hybrids within each line were made to determine the efficacy of the fused-gene hybrid and elucidate interactions between insect densities, damage and yield. Results are pending. In another experiment to determine both the effects of sugarcane borer (SCB) larvae on corn yield, and the relative benefits of reducing this damage with Bt hybrids, I examined the effects of Bt corn on stalk and shank damage by SCB and whorl and ear damage by corn earworm larvae as well as yield differences between Bt and non-Bt corn. I also examined the effects of SCB stalk and shank damage on kernel weight per ear of non-Bt corn. To accomplish this I used side-by-side 24-row plots of Bt and non-Bt
corn replicated 4 times- collecting data from 25 plants from each of the center 4 rows for a total of 400 Bt and 400 non-Bt plants. Whorl injury on a scale of 0-9 was assessed and plants were cut above the roots at harvest time and taken to the lab where ear tip injury by corn earworm was assessed and ears were threshed to obtain weight. For each plant, SCB damage was measured on shanks and in stalks by plant node. I found that Bt corn had higher yield than non-Bt corn and that Bt corn almost eliminated shank and stalk damage by SCB and reduced whorl and ear damage by corn earworm. However, for non-Bt plants, both the proportion of stalks damaged and SCB tunneling were positively correlated with kernel weight per ear-yield actually increased with stalk damage. But, I also found that both kernel weight and stalk damage increased from one end of the field to the other suggesting that insects may have been preferentially feeding on corn with higher yield potential. I also collected SCB
larvae and pupae and sent them to Fangneng Huang at LSU as part of a study to detect resistance to Bt. Fangneng is currently mating pairs of these insects to produce lines for testing Bt resistance and compare them with his own lines from Louisiana. In another study, to determine the effects of Bollgard and Bollgard II Bt cotton on control of lepidopteran pests, I placed 3rd instar budworm and bollworm larvae from a lab colony singly on cotton fruiting structures (squares, flowers, and bolls) from 3 non-Bt cotton varieties, 6 Bollgard varieties (one Bt toxin) and 3 Bollgard II varieties (2 Bt toxins). I found that larvae of both species developed slower on Bt varieties than on conventional varieties. For each species, final prepupal weights for larvae reared on Bollgard and Bollgard II fruiting structures were not different, but were about 25% less than larval weights when reared on the same structures from conventional cotton. However, prepupal survival of both species was similar on
Bt varieties compared with conventional varieties suggesting that larvae that move to Bt plants from non-Bt plants can survive and reduce yield if Bt plots are close to non-Bt plots.
Impacts
Overall, my project helps growers to increase the use of environmentally sound, sustainable, insect control methods, as well as providing them with the information to make informed decisions on the importance of controlling new crop pests and choosing crop varieties that reduce insect pest damage while maximizing yield in South Texas. My project also benefits grower's economically by suggesting cost-effective solutions and techniques to integrate pest control based on economic damage thresholds and pest resistance management, increasing their profits by maximizing their yields while reducing expensive chemical inputs, reducing fungal toxin accumulation, and preventing the development of resistance to control measures by pests.
Publications
- Chilcutt, C. F., G. N. Odvody, J. C. Correa, J. Remmers, and R. D. Parker. 2006. Decreased whorl and ear damage in nine Mon810-Bacillus thuringiensis corn hybrids compared with their non-Bt counterparts. Journal of Economic Entomology 99: 2164-2170.
- Chilcutt, C. F. 2006. Cannibalism of corn earworm from Bt and non-Bt corn. Journal of Economic Entomology 99: 728-732.
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Progress 01/01/05 to 12/31/05
Outputs
To determine Yieldgard-YG and Herculex-HX Bt corn hybrids effects on pest damage (previously reported) and aflatoxin we planted 4 groups of related YG, HX, and non-Bt hybrids. HX and YG did not reduce ear damage or aflatoxin and despite differences in ear damage between hybrids, hybrid type did not affect yield. To determine the affects of maternal and paternal corn trait inheritance on pest damage and aflatoxin we examined ear injury on 4 corn hybrids hand-pollinated by selfing and with 2 other hybrids. Ear injury measurements were made on 10 ears per treatment plot of 6 replicates. Overall, ear damage to N79-P4 (6.1 cm) was significantly >than OPQ (3.9 cm), DK269 (4.3 cm) and P32R25 (4.6 cm), which were not different. Also, ear damage was > when the pollen source was N79-P4 (5.5 cm), than the other 3 pollen sources, and > when the pollen source was OPQ (4.8 cm) than DK269 (4.3 cm) or P32R25 (3.9 cm). Kernel damage to N79-P4 (3.1 cm) was significantly >than the other
3 hybrids, and P32R25 (2.2 cm) was >than DK269 (1.5 cm) and OPQ (1.2 cm). Also, kernel damage was significantly > when the pollen source was DK269 (2.4 cm) than the other hybrids, and > when the pollen source was OPQ (2.1 cm) then P32R25 (1.8 cm) or N79-P4 (1.6 cm). Aflatoxin was significantly affected by maternal hybrid, but not pollen source. Aflatoxin content of N79-P4 (398 ppb) was significantly > than OPQ (219 ppb) and DK269 (104 ppb), but not P32R25 (301 ppb), and P32R25 was > than DK269. Aflatoxin content was not significantly correlated with kernel damage, or ear damage, maternal hybrid was the most important factor affecting aflatoxin, whereas ear damage was affected by maternal and paternal inheritance. Also, experimental Bt-stacked gene hybrids from Monsanto were evaluated for insect and aflatoxin control, but results are pending. To evaluate the effects of gene flow from Bt to non-Bt plantings on pests I planted 2 yellow Bt hybrids adjacent to a white non-Bt hybrid, using
color as a marker to estimate gene flow and measure effects on earworm and borer feeding. The proportion of yellow kernels in white ears decreased in a reciprocal fashion with increasing distance from Bt plots. Both earworm and borer larvae were placed singly on ears with various proportions of yellow-Bt and white-non-Bt kernels in containers in the lab to observe behavior and mortality. Increasing distance from Bt plots (decreasing yellow-Bt kernels) was significantly positively correlated with mortality of both both pests. The proportion of time each pest spent feeding on yellow kernels was correlated with the proportion of yellow kernels, indicating that neither species abandoned nor avoided feeding on Bt kernels. Finally, the proportion of time spent moving was not correlated with the proportion of toxic kernels, indicating that searching time for non-toxic food sources did not increase. These results indicate that gene flow from Bt plots to non-Bt plants can decrease refuge size,
reduce control in Bt plots, and increase pest resistance. Lastly, I measured Bt toxin levels, bollworm and tobacco budworm mortality on fruiting structures from Bollgard and Bollgard II Bt cotton with results pending.
Impacts
Overall, my project helps growers to increase the use of environmentally-friendly insect control methods, as well as providing them with the information to make informed decisions on crop varieties to use in our area. My project also benefits growers economically by suggesting cost-effective solutions and techniques to integrate pest control and pest resistance management, increasing their profits by maximizing their yields while reducing expensive chemical inputs, reducing fungal toxin accumulation, and preventing the development of resistance to control measures by pests.
Publications
- Chilcutt, C. F., L. T. Wilson, R. Lascano, K. F. Bronson, and J. Booker. 2005. Sampling and effects of plant, soil, and landscape characteristics on sap-feeding herbivores in cotton. Environmental Entomology 34: 75-86.
- Chilcutt, C. F. 2005. Chaperone effects on bollworm survival and Cry1Ac levels in Bt cotton flowers and squares. Proceedings of the Beltwide Cotton Conferences, New Orleans, LA, Jan. 5-8, 2005 (abstract).
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Progress 01/01/04 to 12/31/04
Outputs
To determine the affects of maternal and paternal corn inheritance on pest ear damage and aflatoxin we examined 4 hybrids, each self-pollinated and pollinated with 2 other hybrids. Ear damage measured on 10 ears / plot was greater when the pollen source was N79-P4 than the other pollen sources, and greater with Opaque than DK269 or P32R25 pollen. Kernel damage was greater with DK269 pollen than the other hybrids, and greater with pollen from Opaque then either P32R25 or N79-P4. Aflatoxin was significantly affected by maternal hybrid, but not paternal, and mirrored results on kernel damage. However, aflatoxin content was not correlated with damage. To determine the effects of hybrid type, Yieldgard-Cry1Ab, Herculex-Cry1F, and non-Bt corn hybrids on pest damage and aflatoxin, 4 groups of related hybrids were used. Ear damage to Herculex was greater than to Yieldgard in one group, for another group Herculex was greater than for Yieldgard and non-Bt, while for the other 2
groups, hybrid type did not affect ear damage, although for one of these aflatoxin was greater for Herculex then for Yieldguard. Herculex and Yieldgard did not reduce ear damage or aflatoxin and did not affect yield. In other experiments, Bt gene flow to non-Bt corn plants was examined. This consisted of different Bt/nonBt refuge structures and planting sorghum or sunflower between Bt and non-Bt corn. Non-Bt corn planted upwind and either adjacent or diagonal to Bt plots reduced Cry1Ab and %Cry1Ab kernels. Also, planting 15-row sunflower barriers between Bt and non-Bt plots reduced gene flow to < 1% in all refuge rows, and all but the closest row with 7 row barriers. Except for the closest non-Bt row with the 7-row barrier, using either the 7 or 15-row barrier had the same effect on Cry1Ab. Also, 2-40 row plots of yellow Bt hybrids, adjacent to 40 row plots of a white non-Bt hybrid were planted to use yellow color as a marker to estimate Bt gene flow to non-Bt refuges, observe the
pattern of Bt and non-Bt kernels produced and H. zea feeding. The proportion of yellow kernels in white ears decreased with increasing distance from Bt plots. H. zea were placed singly on ears with various proportions of yellow Bt and white non-Bt seeds in containers in the lab to observe behavior and mortality. Increasing distance from Bt plots (decreasing proportion of yellow Bt kernels) was positively correlated with mortality of H. zea. Finally, effects of the cotton growth regulator, Chaperone, on Bt levels and mortality of H. zea feeding on cotton flowers and squares was examined by placing 10-2nd instar H. zea separately on caged cotton squares and 10 on caged flowers at 5 and 10 days after Chaperone treatment. Mortality of H. zea on flowers after 48 h increased from 6% on untreated to 12% on Chaperone. On squares, mortality of H. zea decreased from 20% and 45% on untreated to 10% and 25% on Chaperone 5 and 10 days after treatment, respectively. ELISA measurements of Cry1Ac in
squares and flowers mirrored the results for bollworm mortality. Cry1Ac levels were not significantly different between flowers of Chaperone and controls, but in squares was lower in Chaperone.
Impacts
Overall, my project helps grower?s to increase the use of non-chemical insect control methods that are less destructive to the environment, as well as providing them with the information to make informed decisions on crop varieties to use in our area. My project also benefits grower?s economically by suggesting cost-effective solutions and techniques to integrate pest control and pest resistance management and increasing their profits by maximizing their yields while reducing expensive chemical inputs and preventing the development of resistance to Bt toxins by pests.
Publications
- Chilcutt, C. F. and Tabashnik, B. E. 2004. Contamination of refuges by Bacillus thuringiensis toxin genes from transgenic maize. Proceedings of the National Academy of Sciences USA 101: 7526-757529.
- Chilcutt, C. F. and Tabashnik, B. E. Gene flow from transgenic corn to non-Bt corn refuges. ISB News Report, July 2004.
- Chilcutt, C. F. 2004. Contamination of refuges by Bt toxin genes from transgenic corn. XXII International Congress of Entomology, Brisbane, Australia, August 16-21, 2004 (abstract).
- Chilcutt, C. F. 2003. Gene flow from Bt transgenic corn to non-Bt corn: can refuges speed the evolution of pest resistance? Pp. 765-770. In The BCPC International Congress, Crop Science and Technology 2003: Congress Proceedings. Nov. 10-12, 2003. The British Crop Protection Council, Alton, Hampshire, UK.
- Chilcutt, C. F. and Johnson, M. W. 2004. Development of resistance in pests to transgenic plants: Mechanisms and strategies. Pp. 177-217. In: O. Koul and G. S. Dhaliwal (eds.), Transgenic crop protection: concepts and strategies. Science Publishers Inc., USA.
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Progress 01/01/03 to 12/31/03
Outputs
Movement of Bt genes from Bt cotton to adjacent nonBt refuge plants was measured using ELISA. Treatments included natural pollination of nonBt flowers at 3 distances from the Bt plots, nonBt plants artificially pollinated with Bt pollen, and caged plants in adjacent Bt and nonBt plots. Cry1Ac levels were 3000 ng/g in seeds from Bt plants and about 40 ng/g in nonBt seeds at all distances. In nonBt plants hand-pollinated with Bt pollen, Cry1Ac in seeds was 500 ng/g. Cry1Ac was zero in nonBt plants caged with adjacent Bt plants. This demonstrates that Bt pollen is spread to nonBt plants which then produce Bt toxic seed. Gene flow from Bt corn to nonBt corn refuges was measured using ELISA to determine Cry1Ab levels in nonBt corn at increasing distance from Bt plots. Results indicate that Bt genes are spread for 30 m from Bt plots to nonBt refuges with Cry1Ab concentrations decreasing in a quadratic fashion with distance. The effects of a 16 m blank area between Bt plots
and nonBt refuges was also examined and indicated that Cry1Ab concentrations in refuges were more than 2 times as high as in refuges adjacent to Bt plots. These results cast doubt onto the use of adjacent areas nonBt corn as refuges. To test the effects of different agronomic practices on insect densities in sorghum comparisons of continuous sorghum versus sorghum/ cotton rotation, conventional versus reduced tillage, and fertilization were examined. The effects of the different treatments on rice stinkbug and H. zea densities varied, although no insects were affected by fertilizer. H. zea were only affected by rotation (during one year) being higher on continuous sorghum (6 per 10 head sample) than on sorghum that had been rotated with cotton (2). Stinkbugs were affected by rotation and tillage. During 2 years stinkbug densities were higher on sorghum that had been rotated with cotton (33 and 6 per sample) than on continuous sorghum (14 and 4), but in the third year were higher on
continuous sorghum (9) than on sorghum rotated with cotton (6). Tillage affected stinkbug densities during one period each year, being higher on conventional tillage than reduced tillage. From these results, the only conclusions possible are that fertilizer treatments do not affect the insects measured and rotation of sorghum with cotton could reduce H. zea. Effects of the growth regulator Actigard (believed to increase plant defensive proteins) on H. zea damage to corn indicated that it did not affect ear damage. Effects of a cotton growth regulator, Atonic, on mortality of H. zea feeding on cotton flowers and squares of Bt and nonBt plants was found to increase mortality of H. zea on flowers from 6% on untreated to 12% on Atonic treated. However, on squares, Atonic decreased mortality of H. zea larvae from 20% on untreated to 10% on Atonic-treated at 5 days after treatment, and from 45% on untreated to 25% on Atonic treated 10 days after treatment.
Impacts
Overall, my project will help grower?s to increase the use of non-chemical insect control methods that are less destructive to the environment, as well as providing them with the information to make informed decisions on crop varieties to use in our area. My project will also benefit growers economically by suggesting cost-effective solutions and techniques to integrate pest control and pest resistance management and increasing their profits by maximizing their yields while reducing expensive chemical inputs.
Publications
- Chilcutt, C. F., L. T. Wilson, and R. J. Lascano. 2003. Field evaluation of a Helicoverpa zea (Lepidoptera: Noctuidae) damage simulation model: effects of irrigation, H. zea density and time of damage on cotton yield. Journal of Economic Entomology 96:1174-1183.
- Chilcutt, C. F. and M. W. Johnson. 2003. Development of resistance in pests to transgenic plants: Mechanisms and strategies. In: O. Koul (ed.), Transgenic crop protection: concepts and strategies. Science Publishers Inc., USA.
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Progress 01/01/02 to 12/31/02
Outputs
Comparing whorl and ear injury, and aflatoxin levels in Bt versus nonBt corn we found that Bt hybrids consistently had lower whorl injury and generally lower ear injury. However, these lower levels of insect injury did not translate into lower aflatoxin. In 2002 (as in 1999) many Bt hybrids actually had higher aflatoxin than nonBt hybrid pairs despite lower levels of ear injury. These results varied between years and were not consistent across hybrid pairs or sites in 2002. In a separate test we inoculated corn with high levels of Mexican rice borer. Despite the fact that Bt plants almost completely eliminated borer injury while nonBt plants had high levels, we still found equal levels of aflatoxin on Bt versus nonBt hybrids. In 2001 and 2002 I examined the effect of both irrigation and Bt refuges on sap-feeding insect densities in cotton and found that both aphids and whitefly were affected by irrigation but not refuge. While whitefly were at higher densities in
irrigated plots, aphids were at higher densities in dryland. Thrips were only affected by refuge; densities were higher in mixtures than other plots, and higher in plots of continuous Bt and alternating strips of Bt and nonBt than nonBt plots. To determine Bt-transgenic corn effects on pest densities we counted the numbers of insects on 30 ears of corn from each of 17 Bt-hybrids and their 17 isogenic non-Bt counterparts. For the 3rd straight year we found that all instars of fall armyworm were at lower levels on Bt than nonBt plants, but that early instar corn earworm numbers were higher on Bt hybrids than on their nonBt counterparts. To better understand this we also compared oviposition preference of corn earworm adults on Bt versus nonBt plants and found that there was no difference in the number of eggs laid. To determine if the higher corn earworm numbers were due to reduced cannibalism of Bt intoxicated larvae I removed different instars of corn earworm from Bt and nonBt plants.
Next I placed all pairs of instars from nonBt plants together on media, and pairs of instars from Bt plants on media. I then observed cannibalism and found that cannibalism of Bt collected larvae was actually slightly higher than for nonBt collected larvae. In a study of the effects of rotation, tillage, and fertilizers on sorghum pest and predator densities over a 3-year period, the effects of the different treatments on rice stinkbug and corn earworm densities varied, although predators were unaffected by any of the factors examined. Corn earworm were only affected by rotation in 2000; earworm densities were higher on continuous sorghum than on sorghum rotated with cotton. This difference was actually only significant during the sampling period with the highest density, but wasn?t seen in 2001 or 2002. In 2000 and 2001 stinkbug densities were higher on sorghum rotated with cotton than on continuous sorghum, but, in 2002 stinkbug densities were higher on continuous sorghum than on
sorghum rotated with cotton. Tillage affected stinkbug densities during one period in each of 2000 and 2001; stinkbug densities were higher on conventional than reduced tillage plots.
Impacts
Overall, my project helps grower?s to increase the use of non-chemical insect control methods that are less destructive to the environment, as well as providing them with the information to make informed decisions on crop varieties to use in our area. My project also benefits grower?s economically by suggesting cost-effective solutions and techniques to integrate pest control and pest resistance management and increasing their profits by maximizing their yields while reducing expensive chemical inputs.
Publications
- Matocha, J. E., C. F. Chilcutt, M. P. Richardson, and S. G. Vacek. 2002. Impact of cotton rotation and tillage intensity at varying phosphorus fertility on certain sorghum insects and grain yield. Pp. 180-183. IN Proc. 25th Southern Conservation Tillage Conference for Sustainable Agriculture, Auburn, AL.
- Odvody, G. N., and C. F. Chilcutt. 2002. Aflatoxin and Insect Response in South Texas of Near-isogenic Corn Hybrids with Cry1Ab and Cry2Ab Events. Mycopathologia 155: 107.
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Progress 01/01/01 to 12/31/01
Outputs
Tests with different Cry1Ab events and corn hybrids showed that all Bt corns are not equal in level of insect pest control or yield. Also, hybrid background had more affect on aflatoxin infection than did the presence of the Bt gene which either increased or decreased aflatoxin levels. In 2000, insect injury to corn ears and fourth instar fall armyworm numbers were both positively correlated with each other and with aflatoxin. Increasing fourth instar armyworms increased damage increasing aflatoxin. Results in 2001 were similar except that total fall armyworm numbers replaced fourth instar numbers in the relationships. In another experiment we compared caged corn ears versus uncaged ears and found that caging reduced ear damage and reduced aflatoxin, although the proportional reduction was the same for Bt and non-Bt hybrids. To determine the affects of Bt-transgenic corn on pest densities we counted insect numbers on 45 corn ears (9 replicates) from 9 Bt-hybrids and
their 9 isogenic non-Bt counterparts. Results for 2000 indicated that all instars of fall armyworm (except first) were reduced by half on Bt plants, whereas there were twice as many first instar corn earworm on Bt plants than on non-Bt plants. Also, second instars were at a higher level on Bt-plants, third instars were equal in number and fourth and fifth instars were at higher levels on non-Bt plants. Results for 2001 were similar, with trends being the same as for 2000. Also, in 2001 we looked at insect densities during 3 time periods and found that differences were mainly significant only during the time period that coincided with the highest pest density. We also collected and reared approximately 2000 corn earworm and fall armyworm from several Bt and non-Bt corn hybrids to determine the affect of transgenic corn on parasitism levels. However, low percentage parasitism, <2% in 2000 (17 parasitoids from 600 larvae) and 0% in 2001 (1 parasitoid from 1370 larvae) made it
impossible to determine any treatment differences. Another experiment was performed to evaluate refuge type using 2 Bt transgenic cotton lines and 2 non-Bt lines. Results indicate that neither mixtures nor stands had an advantage in controlling pests. Both demonstrated levels of insect damage and yield intermediate between the values for the different varieties used in mixtures and stands. The same refuge experiment was performed with corn and results were similar. In another experiment we found that headworms and predators were at higher densities in continuous sorghum plots than rotation plots during the first year of the study, whereas in the second year headworms were found in higher numbers in the cotton/sorghum rotation plots and predators were unaffected by rotation type. Stinkbugs were found at greater densities in cotton/sorghum rotation plots in the first year whereas in the second year rotation alone had no affect. On this and other experiments, more data is needed to make
conclusions.
Impacts
Overall, my project helps growers to increase the use of non-chemical insect control methods that are less destructive to the environment. My project also benefits growers economically by suggesting cost-effective solutions to pest control and increasing their profits by maximizing their yields while reducing expensive chemical inputs.
Publications
- Garcia, M. C., P. S. Leung, C. F. Chilcutt and B. Tabasnik. 2000. Short-term economic analysis of control of diamondback moth in Hawaii with Bacillus thuringiensis and other insecticides. Journal for Hawaiian and Pacific Agriculture 11:29-40.
- Odvody, G.N., C. F. Chilcutt, R. D. Parker, and J. H. Benedict. 2000. Aflatoxin and insect response of near-isogenic Bt and Non-Bt commercial corn hybrids in South Texas. Poster presented atp. 121-122 in USDA-ARS Aflatoxin/Fumonisin Workshop, October 25-27, 2000. Yosemite, CA
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