Abstract

The fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is currently the most important maize pest in Mexico. Its control is mainly based on the use of conventional insecticides. Additionally, Bt-maize expressing Cry1F protein represents an alternative to control this pest. We estimated the baseline susceptibility in Mexican populations of S. frugiperda to Cry1F protein. Twenty-eight geographical populations were field collected from Baja California Sur, Chihuahua, Coahuila, Durango, Sinaloa, Sonora, and Tamaulipas states. The F-1 neonate larvae of each population were subjected to diet-overlay bioassay. After 7 d of Cry1F exposure, the percent mortality and the percent growth inhibition with respect to the untreated control were recorded (S-LAB). The LC50 ranged from 14.4 (6.3-24.0) (Cajeme 1, Sonora) to 161.8 ng/cm(2) (92.0-320) (Ahumada 2, Chihuahua), while the LC95 was between 207.1 (145-363) (Obregon, Sonora) and 1,217 ng/cm(2) (510.8-7,390.0) (Rio Bravo 2, Tamaulipas). The sensitivity ratios at 50% mortality, (LC50 field/LC50 S-Lab) and 95% mortality were <= 6.45 and <= 5.05-fold, respectively. The 50% growth inhibition (GI(50)) ranged from 2.8 (0.008-9.3) (Obregon, Sonora) to 42.4 ng/cm(2) (3.6-147.0) (Cajeme 1, Sonora). The GI(95) was between 75.4 (San Luis Rio Colorado, Sonora) to 1,198 ng/cm(2) (Cajeme 1, Sonora). The relative inhibition at 50% of the growth, (RI50 = GI50 field /GI(50) S-LAB) was <= 3.5 and at 95% (RI95) was <= 1.91-fold. These results indicated susceptibility to Cry1F protein in the evaluated populations of S. frugiperda.