Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 12/22/2004
Publication Date: 1/6/2005
Citation: Blanco, C.A., Sivasupramaniam, S., Ali, I., Luttrell, R., Martinez-Carrillo, J.L. 2005. Response of heliothin virescens and helicoverpa zea (lepidoptera: noctuidae) reference colonies to a homogeneous bacillus thuringiensis cry1ac-incorporated insect artificial diet. National Cotton Council Beltwide Cotton Conference. 1226-1233 Interpretive Summary: Monitoring susceptibility shifts through laboratory bioassays in these pests to the toxin(s) expressed by transgenic cotton is a way to measure if the insect resistance management strategy is effective. The strategy has two goals: a) to prevent the spread of resistant genes through early detection, and b) to satisfy regulatory requirements. To introduce new Bt-transgenic cotton varieties in other countries such as Mexico, besides satisfactorily meeting all the U.S. requirements, the registrants must demonstrate that resistance of target pest(s) to specific new Bt toxins does not exist prior to registration. Since the cost of development and registration for any new agricultural product is extremely high and time consuming, information generated in different countries is used to leverage local, specific data. This is important when the data of a registered, soon-to-be-registered product in a country considered of 'high registration standards' (e.g. the USA) is used to satisfy foreign requirements. Although the information exists, discrepancies in laboratory methodology have impeded researchers and regulatory agencies from closely comparing results from different areas. Therefore, in order to use the information generated elsewhere to fulfill registration requirements, it is very important to have homogeneity in the testing methodology. Three laboratories began testing the same insect colonies utilizing the same insect artificial diet finding that there are intrinsic experimental errors that produce discrepancies between laboratories. Some evaluation parameters have been identified as important in explaining such differences.
Technical Abstract: In order to assist the registrants of genetically modified cottons to fulfill their regulatory requirements in the U.S. and Mexico for Bacillus thuringiensis resistance monitoring, several. research institutions have conducted monitoring programs in different cotton regions of North America. Such requirements specify that monitoring testing should be done at a central. laboratory and duplicate population samples confirmed by a second facility. Without a standardized methodology to achieve this, several methodological aspects of obtaining the biological response of Heliothis virescens (Fabricius) and Helicoverpa zea (Boddie) to B. thuringiensis implemented by different laboratories might yield discrepancies when the same insect population is tested by more than one institution. This study, that obtained the biological response of a common H. virescens and H. zea reference populations with a common standardized Cry1Ac-incorporated insect artificial. diet in 3 different laboratories produced the following results: A) When the same common diet was tested by only one laboratory with 2 different insect colonies, mortality was significantly different among the tobacco budworm but not between bollworm colonies. B) When the same common diet was tested with the same insect colony in 3 different laboratories, no differences were found with H. virescens but the H. zea colony was significantly different in 2 of the 3 locations. C) When the same colony was tested with 3 different insect diets in 3 different laboratories, the tobacco budworm colony responded significantly different among all the locations but not the bollworm. Analysis of the biological response including first instar or first and second instars increased the discrepancies among the research institutions.