Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/12/2007
Publication Date: 3/27/2007
Citation: Blanco, C.A., Perera O. P., Boykin D., Abel C.A., Gore J., Matten S. R., Ramirez-Sagahon J. C., Teran-Vargas A. P. 2007. Monitoring Bacillus thuringinesis-susceptibility in insect pests that occur in large geographies: How to get the best information when two countries are involved. J. Inv. Pathol. 95:201-207 Interpretive Summary: There is a common conception in agricultural areas near the US-Mexico border about insecticide resistance management. When insect resistance is detected in pests on either side of the border, it is usually ‘the neighbor’s fault’. Indeed, inappropriate resistance management programs and/or practices can create this situation. Migratory insecticide-resistant pests move across international borders and they could become established elsewhere. Although there are laboratory methods to evaluate insect resistance, these can vary greatly yielding different results. Therefore, one laboratory could report insecticide resistance with an insect sample while another might report susceptibility to insecticide on the same insect sample due to discrepancy of methodology. In this study we present a method to reduce potential variability on methodology. A sample of ready-to-use diet can be sent and/or received from a different laboratory and test with it a known insect strain. This diet can be produced several days before its use and can be subjected to different temperatures. This method proved that ready-to-use diet produced in USDA-ARS Stoneville can be stored either in a freezer, refrigerator or left to ambient temperature without losing its biological activity against an important cotton pest (tobacco budworm) for up to nine days, granting the possibility to collaborate on resistance management program with other counties e.g. Mexico.
Technical Abstract: The adoption of Bacillus thuringiensis-expressing cotton around the world has been proven to be beneficial for growers and the environment. The effectiveness of this important genetically-modified crop can be jeopardized by the development of B. thuringiensis-resistance in pests, with the possibility that this phenomenon could develop in one country and spread to another by means of insect migration. To preserve the effectiveness of this agricultural biotechnology, regulatory agencies have developed plans to mitigate the development of resistance, and research institutions constantly monitor for Bt-susceptibility shifts in important pests. If Bt-resistance is detected, this finding needs to be corroborated by an independent laboratory according to current regulatory requirements; a process that presents numerous challenges. We investigated the biological activity of Bt-incorporated diet after it was stored for several days at different temperatures. Diet stored up to nine days at different temperatures (-14 to 27 ºC) produced the same biological response as freshly-prepared diet. Elevating the temperature of Bt stock solution to 76 ºC as compared to 26 ºC yielded significantly higher concentration of Cry1Ac but not enough to elicit a significant biological response when these stock solutions were incorporated into insect artificial diet. These findings are important particularly when the confirmation of resistance is done at a distant location or when diet is shared and must be stored for later use, as in the case of international collaboration.