Determination Of Baseline Susceptibility To Cry1Ie And Cry1Ah Proteins, A Preliminary Reseach Of Diagnostic Concentration For Cry1Ah And Dominant Natural Enemies For Overwintering Larvae For Ostrinia Furnacalis (Guenee)

The Asian corn borer (ACB), Ostrinia furnacalis (Guenee), is one of the most destructive pests of corn in China. Transgenic Bacillus thuringiensis (Bt) maize provide an effective mean to control this insect pest. However, evolution of resistance by target pests will be the great threat to the continued success of Bt toxins used in insecticide formulations or expressed by transgenic maize. It is necessary to investigate the mortalities of ACB caused by parasitism and infection especially Bt in the field, establish baseline data to enable the detection of changes in susceptibility in the field populations and monitor the resistance by using diagnostic concentration method after prolonged exposed to Bt crops.By the dose-mortality data for 15 populations of ACB exposed to the Cry1Ie and Cry 1 Ah toxins, there were significant differences in the susceptibility among the populations. The LC50S (Leathal Concentration 50s)ranged 0.18～3.42 μg/g (Cry1Ie protein/diet) and 0.34 μg/g～3.87 μg/g (CrylAh protein/diet). Meanwhile, by the growth inhibition data for ACB to Cry1Ie and Cry1Ah, the EC50S (Effect Concentration 50s) ranged 0.07-1.04 μg/g for Cry1Ie and 0.08 ～0.64 μg/g for Cry1Ah. Although the different times of collecting the ACB, the data for the dose-mortality and growth inhibition were different, the regions of ACB for the susceptibility to Crylle protein were similar. The LC50 values of the populations from the Huanghuaihai Summer Corn Region were higher compared to those from the Northeast Spring Corn Region. The susceptibilities to Cry1Ie and Cry1Ah in ACB populations collected in the summer of 2012 were lower than those collected in the autumn and winter of 2012. Those results indicate that the variations of susceptibility to Cry1Ie and Cry1Ah among the geographical populations of ACB are significant. The populations from the northeastern spring corn region are more susceptible than those from the summer corn region.Determinated the diagnostic dose (60 μg/g) of CrylAh by the bioassay of the seven populations of ACB collected in 2012. It could be useful to monitor susceptibility in ACB populations and determine the resistance of the field frequency for the future.There were 14984 diapausing larvae of ACB collected from 20 locations in 14 Provinces in the falls of 2011 and 2012. Averaged across locations mortalities caused by Bt and Beauveria bassiana were 36.2% and 14.4%, respectively. The epidemic of Bt and B. bassiana were inconsistent among years in northeastern spring maize area. However, the mortality resulted from Bt was significantly higher in summer maize region as well as other regions. Macrocentrus cingulum and Lydella grisescens were the dominant braconid wasp and the tachinid fly distributed in all locations. Averaged across locations parasitism were 7.0% and 5.1%. The ichneumon wasp, Eriborus terebranus, was mainly distributed in the north spring maize area and rarely found in summer maize region. The parasitism was as low as less than 1.0%. The mortality caused by two entomopathogens was generally higher compared with parasitism of three parasitoids although it varied greatly among the years, In conclusion, B. thuringiensis and B. bassiana were dominant natural biological control factors of O. furnacalis overwintering larvae, and the Bt is the main lethal factor as the mortality infected by Bt is higher than B. bassiana, but it varied greatly. M. cingulum and L. grisescens could result in a relatively lower, but more consistent parasitism throughout the country.