Larval movement between transgenic corn and non-transgenic plants: possible threat to high-dose resistance management strategy Karla A. Walker Department of Entomology, Iowa State University, Ames, IA 50011 Richard L. Hellmich (state representative to NCR-148) USDA-ARS, Corn Insects and Crop Genetics Research Unit Department of Entomology, Iowa State University, Ames, IA 50011 Overview: Research has shown that European corn borer (ECB), Ostrinia nubilalis (Hübner), larvae, particularly 4th and 5th instars, readily move between weeds and Bt corn hybrids. A combination of declining Bt expression and higher tolerance of Bt toxins by late instars results in ECB damage and survival of larvae. These conditions could be problematic for the high-dose strategy for managing ECB resistance to Bt corn. This would occur if larvae moved from non-transgenic plants to transgenic plants and survived differentially. *Results:* The transgenic corn hybrid that expresses CryIA(b) protein of Bacillus thuringiensis (Bt) subsp. kurstaki and a similar hybrid that did not express the Bt protein were used in this experiment. The corn hybrids were interplanted with weeds in screen cages. Four treatments were conducted in a two (type of corn hybrid: Bt and non-Bt) by two (type of weed: smartweed and pigweed, Amaranthus retroflexus L.) factorial design. Each treatment was replicated eight times, and the experiment was conducted for whorl and anthesis corn. More corn borers moved to Bt corn from smartweed than from pigweed during both whorl and anthesis corn. During anthesis the Bt corn and smartweed treatment had 26 corn borers that survived on a total of 128 corn plants. The non-Bt corn and smartweed treatment had 380 corn borers that survived on a total of 128 corn plants. In another experiment fourth instar larvae were confined to corn stalks with screen mesh cages during R1 (silking), R3 (milk) and R5 (dent) stages of development. Corn varieties included three Bt hybrids: MON810 (Monsanto, YieldGard), BT-ll (Monsanto/Northrup King, YieldGard), Event-176 (Novartis, Maximizer) and a non-Bt control B73xMo17. Each event was replicated six times for each corn developmental stage. Tunnel damage results suggests differences among the Bt events. The 176 event was particularly vulnerable to late-instar ECB at the R3 (milk) and R5 (dent) stages of corn. Discussion: Late-instar ECB movement could be an important factor for resistant management programs. The cage experiments we conducted with mixed plantings of transgenic corn and weeds suggest that late-instar ECB will move from weeds into transgenic corn. This phenomenon could be problematic to corn producers and could result in faster selection for corn borers that are resistant to transgenic corn hybrids. The research also suggests that not all weeds will be problematic. We have identified three weed species to date, cocklebur, Pennsylvania smartweed and fall panicum, that support the complete development of ECB. Other common weeds such as pigweed and water hemp do not have the architecture to support ECB neonates. These plants only support tunneling larvae and, consequently, should not be problematic in transgenic cornfields. The second experiment suggest that tolerance to late instar challenges varies among Bt corn events. Feeding preferences of European corn borer, Ostrinia nubilalis, neonates. Colothdian D. Tate, Department of Entomology, Iowa State University, Ames, IA 50011, and Richard L. Hellmich, USDA-ARS, Corn Insects and Crop Genetics Research Unit, Department of Entomology, Iowa State University, Ames, IA 50011. Choice tests were conducted to determine feeding preferences of European corn borer, Ostrinia nubilalis (Hübner), neonates for plants commonly found in Iowan cornfields. A two-choice arena was set up by placing an egg mass in the center of a petri dish. Two types of plant leaves were put into each arena. High humidity was maintained with a damp piece of filter paper. Number of neonates on each leaf type was counted 24 hours after eclosion. Eleven plants were tested which included: fall panicum, Panicum dichotomiflorum Michx., annual smartweed, Polygonum pensylvanicum L., pigweed, Amaranthus retroflexus L., yellow foxtail, Setaria glauca (L.) Beauv., green foxtail, Setaria viridis (L.) Beauv., giant foxtail, Setaria faberi Herrm., cocklebur, Xanthium strumarium L., german foxtail millet, Setaria italica (L.) Beauv., proso millet, Panicum miliaceum L., Bt corn, Zea mays L., and non-Bt corn. Smartweed and cocklebur were the most preferred plants followed by yellow foxtail. The other plants including Bt corn and non-Bt corn were fed upon at low levels. Using satellite DNA to evaluate population structure of Agrotis ipsilon and Pseudaletia unipuncta in North America Brad S. Coates, Department of Entomology, Iowa State University, Ames, IA 50011 Richard L. Hellmich, USDA-ARS, Corn Insects and Crop Genetics Research Unit Department of Entomology, Iowa State University, Ames, IA 50011. Primers have been developed to PCR amplify repetitive DNA of the black cutworm, Agrotis ipsilon (Hufnagel) and true armyworm, Pseudaletia unipuncta (Haworth). Several variable regions of DNA have been detected despite the fact that these primers were originally developed for European corn borer, Ostrinia nubilalis (Hübner). Preliminary data suggest that populations of true armyworm in Iowa, Indiana and Georgia have different allelic frequencies. We would appreciate any help to attain additional adult samples of true armyworm and black cutworm from other regions in North America. [ 1997 Research Index ]
Last updated 1 June, 2007 This page was constructed by Gail Kampmeier at gkamp[at]uiuc.edu Please direct questions of content and prospects of collaborative research to respective scientists. Research reports do not constitute publication and results may be preliminary. They are included here for informational purposes only. You should contact the authors for further information. Any references to commercial products do not constitute endorsement. [ NCR-148 \| Movement & Dispersal Index \| News Index ]

Larval movement between

transgenic corn and non-transgenic plants:

possible threat to high-dose

resistance management strategy

Karla A. Walker
Department of Entomology, Iowa State University, Ames, IA 50011
Richard L. Hellmich (state representative to NCR-148)
USDA-ARS, Corn Insects and Crop Genetics Research Unit
Department of Entomology, Iowa State University, Ames, IA 50011

Overview: Research has shown that European corn borer (ECB), Ostrinia nubilalis (Hübner), larvae, particularly 4th and 5th instars, readily move between weeds and Bt corn hybrids. A combination of declining Bt expression and higher tolerance of Bt toxins by late instars results in ECB damage and survival of larvae. These conditions could be problematic for the high-dose strategy for managing ECB resistance to Bt corn. This would occur if larvae moved from non-transgenic plants to transgenic plants and survived differentially.

Results: The transgenic corn hybrid that expresses CryIA(b) protein of Bacillus thuringiensis (Bt) subsp. kurstaki and a similar hybrid that did not express the Bt protein were used in this experiment. The corn hybrids were interplanted with weeds in screen cages. Four treatments were conducted in a two (type of corn hybrid: Bt and non-Bt) by two (type of weed: smartweed and pigweed, Amaranthus retroflexus L.) factorial design. Each treatment was replicated eight times, and the experiment was conducted for whorl and anthesis corn. More corn borers moved to Bt corn from smartweed than from pigweed during both whorl and anthesis corn. During anthesis the Bt corn and smartweed treatment had 26 corn borers that survived on a total of 128 corn plants. The non-Bt corn and smartweed treatment had 380 corn borers that survived on a total of 128 corn plants.

In another experiment fourth instar larvae were confined to corn stalks with screen mesh cages during R1 (silking), R3 (milk) and R5 (dent) stages of development. Corn varieties included three Bt hybrids: MON810 (Monsanto, YieldGard), BT-ll (Monsanto/Northrup King, YieldGard), Event-176 (Novartis, Maximizer) and a non-Bt control B73xMo17. Each event was replicated six times for each corn developmental stage. Tunnel damage results suggests differences among the Bt events. The 176 event was particularly vulnerable to late-instar ECB at the R3 (milk) and R5 (dent) stages of corn.

Discussion: Late-instar ECB movement could be an important factor for resistant management programs. The cage experiments we conducted with mixed plantings of transgenic corn and weeds suggest that late-instar ECB will move from weeds into transgenic corn. This phenomenon could be problematic to corn producers and could result in faster selection for corn borers that are resistant to transgenic corn hybrids. The research also suggests that not all weeds will be problematic. We have identified three weed species to date, cocklebur, Pennsylvania smartweed and fall panicum, that support the complete development of ECB. Other common weeds such as pigweed and water hemp do not have the architecture to support ECB neonates. These plants only support tunneling larvae and, consequently, should not be problematic in transgenic cornfields. The second experiment suggest that tolerance to late instar challenges varies among Bt corn events.

Feeding preferences of European corn borer, Ostrinia nubilalis, neonates.

Colothdian D. Tate, Department of Entomology, Iowa State University, Ames, IA 50011, and Richard L. Hellmich, USDA-ARS, Corn Insects and Crop Genetics Research Unit, Department of Entomology, Iowa State University, Ames, IA 50011.

Choice tests were conducted to determine feeding preferences of European corn borer, Ostrinia nubilalis (Hübner), neonates for plants commonly found in Iowan cornfields. A two-choice arena was set up by placing an egg mass in the center of a petri dish. Two types of plant leaves were put into each arena. High humidity was maintained with a damp piece of filter paper. Number of neonates on each leaf type was counted 24 hours after eclosion. Eleven plants were tested which included: fall panicum, Panicum dichotomiflorum Michx., annual smartweed, Polygonum pensylvanicum L., pigweed, Amaranthus retroflexus L., yellow foxtail, Setaria glauca (L.) Beauv., green foxtail, Setaria viridis (L.) Beauv., giant foxtail, Setaria faberi Herrm., cocklebur, Xanthium strumarium L., german foxtail millet, Setaria italica (L.) Beauv., proso millet, Panicum miliaceum L., Bt corn, Zea mays L., and non-Bt corn. Smartweed and cocklebur were the most preferred plants followed by yellow foxtail. The other plants including Bt corn and non-Bt corn were fed upon at low levels.

Using satellite DNA to evaluate population structure of
Agrotis ipsilon and Pseudaletia unipuncta in North America

Brad S. Coates, Department of Entomology, Iowa State University, Ames, IA 50011
Richard L. Hellmich, USDA-ARS, Corn Insects and Crop Genetics Research Unit
Department of Entomology, Iowa State University, Ames, IA 50011.

Primers have been developed to PCR amplify repetitive DNA of the black cutworm, Agrotis ipsilon (Hufnagel) and true armyworm, Pseudaletia unipuncta (Haworth). Several variable regions of DNA have been detected despite the fact that these primers were originally developed for European corn borer, Ostrinia nubilalis (Hübner). Preliminary data suggest that populations of true armyworm in Iowa, Indiana and Georgia have different allelic frequencies. We would appreciate any help to attain additional adult samples of true armyworm and black cutworm from other regions in North America.

[ 1997 Research Index ]