Susceptibility of Spodoptera frugiperda collected from multiple locations to purified Cry1F protein using diet-incorporated bioassays.

Larval mortality was calculated as the number of dead larvae divided by the total number of larvae in the test. During this study, three Cry1F-susceptibile (SS) strains (SS-FL, SS-LA, and SS-TX) were used as references. SS-FL was initiated from larvae collected from Hendry Co., FL in 2011; SS-LA was established from insects collected from Franklin Parish, LA in 2008; and SS-TX was developed from insects collected from Hidalgo Co., TX in 2013. All three SS strains were highly susceptible to both Cry1F maize plants and Cry1F protein in diet. Because the overall performance on maize plants and diet were similar among the three strains, SS was used to denote all three strains unless mentioned specifically. FL-HD-nBt-12 was collected from a heavily infested non-Bt sweet corn field that was close to an early-planted Bt maize field. The Bt maize field was heavily damaged by S. frugiperda and the population infesting the non-Bt sweet corn was believed to be the progeny of moths that came out of the Bt maize field. LA-RD-24 and FL-39 were two resistant families isolated from populations from Rapides Parish, LA and Collier Co., FL, respectively, using the F2 screen. FL-CL-nBt-12, FL-CL-nBt-13, FL-CL-Bt-12, and FL-CL-Bt-13 were collected from non-Bt and Bt plants in two field trials in Collier Co., FL in 2012 and 2013. LA: Louisiana, FL: Florida, GA: Georgia, NC: North Carolina. NBt: non-Bt maize, Bt: Bt maize. The LC50 value of a population was considered to be greater than the highest Cry1F concentration tested if its larval mortality was 50 of the field populations divided by that of the SS strain. Analysis of variance for growth inhibition: F14,46 = 59.75, PSusceptibility of Spodoptera frugiperda collected from multiple locations to purified Cry1F protein using diet-incorporated bioassays.