Hi Dale, In reply to your comments. First, The main Bt corn includes borer and root worm protection (yielgard plus) while earlier yieldgard was borer or root worm specific. My understanding is that root worm protection generally involves both Bt and soil insecticide treatment. http://www.uky.edu/Agriculture/Entomology/entfacts/fldcrops/ef147.htm "The grower may apply insecticide treatments for control of corn root worm larvae with the refuge corn " http://apply-mag.com/mag/farming_corn_rootworm_technology/ "The corn refuge can be treated with a non-Bt insecticide to control late-season pests such as corn borer; however, the YieldGard Rootworm corn also must be treated". My comment that Canada does not allow chemical insecticide treatment of the refuge was this year changed in Ontario to allow insecticide. "http://www.gov.on.ca/OMAFRA/english/crops/field/news/croptalk/2004/ct_0104a6.htm Soil-applied insecticide treatments for control of corn rootworm larvae may be applied to the refuge area. Insecticide use for adult control is not permitted." My understanding is that chemical insecticide use is costly but used a great deal to market corn from the refuge. Nest,turning to your comment about registering Bt corn with levels sufficient to eliminate heterozygous resistant insects.In genetic terminology, the corn insects are described as being recessive meaning that the resistant allele was quite (not expressed) in the heterozygote. If the allele was partially expressed the heterozygote would be called partially dominant.Corn resistance to Bt has been described as recessive while cotton resistance was observed to be recessive at high toxin levels but to be partially dominant in strains expressing low toxin levels. I disagree with your view that the study I mentioned could not detect resistance in a short time span. The study was capable of detecting resistance but failed to mention that refuges were sprayed with chemicals that likely killed the resistant individuals. Finally, both borer and root worm corn have used chemical insecticides that certainly render the "refuge" more public relations than resistance control. The promoters of gm corn for used in developing countries seem to ignore the need for chemical insecticides and costly licenses for using gm corn. Dale Wilson wrote:
Joe,The paper below proclaims that GM crops bearing insecticidal proteins have been used for a number of years without giving rise to resistant insects. The report deals with the refuge strategy and the use of high toxin dosage along with pyramiding toxin genes as factors preventing insect resistance from arising.I take this paper with a grain of salt simply because 8 years is too short a time to draw any conclusions about the success or failure of resistance managment.However, the main reason that insect resistance has not been detected was not mentioned in the article. The main reason that insect resistance has not appeared is that the US EPA allows the gm crop and refuge to be sprayed with chemical insecticides. The refuge strategy of insect resistance provides crop areas in which the target insect pest may thrive and breed with resistant insects from the gm crop (insect genes for resistance are usually recessive). Spraying chemical insecticides allows taking damage free crops from the refuge but it also rubs out any resistant insects.That might be true in theory, but in the case of European corn borer, the insectidal remedies are not very effective. Plus, most growers use standard economic thresholds to decide whether to spray. Since corn tolerates a fair amount of ECB, many refuge fields will not be sprayed. Plenty of moths will be produced in areas under conventional insecticidal control, especially first generation.Another unmentioned factor that effects resistance is the use of synthetic toxin genes in the various commercial gm crops that vary in both toxin production and the actual sequence of the toxins.The strategy has been to register only Bt corn with sufficiently high toxin production to kill ECB heterozygous for the resistance gene. I think this is a sound strategy.However, that factor is far less imposing than the combination of GM crop toxin and chemical insecticides.Bt corn is far more effective than insecticide for control of ECB. Spraying insecticide onto Bt corn is a waste of money. Dale __________________________________ Do you Yahoo!? Yahoo! Mail - Find what you need with new enhanced search. http://info.mail.yahoo.com/mail_250 ******************************************************** To unsubscribe from SANET-MG: 1- Visit http://lists.sare.org/archives/sanet-mg.html to unsubscribe or; 2- Send a message to <listserv@sare.org> from the address subscribed to the list. Type "unsubscribe sanet-mg" in the body of the message. Visit the SANET-MG archives at: http://lists.sare.org/archives/sanet-mg.html For more information on grants and other resources available through the SARE program, please visit http://www.sare.org.
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