Survival and Plant Injury of Cry2Ab2-susceptible and Resistant Sugarcane Borer (Lepidoptera: Crambidae) on Bt Corn Containing Single or Pyramided Transgenes

Abstract

The sugarcane borer (SCB), Diatraea saccharalis (F.) (Lepidoptera: Crambidae), is a target species of Bacillus thuringiensis (Bt) corn in South America and the mid-southern United States (Huang et al. 2007, Grimi et al. 2018). MON 89034 is a common Bt corn event targeting aboveground lepidopteran pests including SCB (DiFonzo 2020). MON 89034 contains genes for two proteins from Bt: Cry1A.105 and Cry2Ab2. Recently, resistance to Cry1F corn hybrids and crossresistance to the Cry1A.105 protein in MON 89034 have been reported in field populations of SCB in Argentina (Grimi et al. 2018). Thus, it is important to understand the potential for field-evolved resistance to Cry2Ab2 in SCB. Using a F2 screen, we isolated a Cry2Ab2-resistant SCB strain (Cry2A-RR) from a field population collected in Louisiana (Huang et al. 2015). The current study examines the performance of some common transgenic Bt corn traits containing one or multiple Bt genes against the Cry2A-RR. Two SCB strains, Cry2A-RR and a Bt susceptible strain (Bt-SS), were used in this study. The Cry2A-RR strain was developed from a F2 screen with a single two-parental family collected from a non-Bt corn field in Louisiana in 2011. It has been documented to be highly resistant to Cry2Ab2 protein and Cry2Ab2 whole corn plants (Huang et al. 2015). Bt-SS was originally obtained from non-Bt corn fields in Franklin Parish, Louisiana, in 2009. Thereafter, additional field-collected individuals were added into the Bt-SS strain to maintain its genetic diversity. BtSS was confirmed to be susceptible to purified Cry2Ab2, Cry1F, Cry1Ac, Cry1Ab, and Cry1A.105 proteins in diet, and to plant tissue expressing any of these Bt proteins (Ghimire et al. 2011, Wangila et al. 2012, Huang et al. 2015). To ensure a similar genetic background, the original Cry2A-RR described above was backcrossed with Bt-SS and the F2 populations of the backcrossed was reselected on Cry2A-Plant leaf tissue for three more generations as described in the F2 screen