SUSCEPTIBILITY OF FOUR HELIOTHIS VIRESCENS AND HELICOVERPA ZEA REFERENCE COLONIES TO A HOMOGENEOUS CRY1AC-INCORPORATED INSECT DIET: IMPLICATIONS FOR AN AREA-WIDE MONITORING PROGRAM

摘要

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 susceptibility monitoringprograms in different cotton regions of North America. Current monitoring is done at a central laboratory and duplicate population samples sent a second facility. Without a standardized methodology to compare or corroborate results across laboratories and scientists, several methodological aspects of obtaining the biological response of Heliothis virescens (Fabricius) and Helicoverpa zea (Boddie) to B. thuringiensis might yield discrepancies when the same insect population is tested by more than one institution / researcher. This study compared the biological response of 2 H. virescens and H. zea reference colonies from 2 different laboratories using a common standardized Cry1Ac-incorporated insect artificial diet. Mortality was significantly different among two tobacco budworm colonies but not between two bollworm colonies when tested in only one laboratory. When a common diet was tested with the same insect colony at three different laboratories, similar results were found with H. virescens, an insect species much more susceptible to Cry1Ac than H. zea, a more tolerant species, especially when mortality analysis included surviving first or second instar larvae. When the same colony was tested with 3 different insect diets in 3 different laboratories, the tobacco budworm colony responded significantly different among locations; on the other hand, more pronounced significant differences were found in the bollworm colony. Analysis of the biological response including first instar or first and second instars increased the discrepancies among the research institutions. For accurate comparison purposes among laboratories, the inclusion of a common diet and a common reference laboratory insect colony is recommended.