Prevalence of corn earworm in late season volunteer corn in Mississippi and its implications on Bt resistance development

The southern United States has a long frost-free period after corn harvest and late season volunteer corn which germinates soon after harvest will have a long growing period, sufficient for corn earworm to develop on these volunteer corn plants. During Fall 2011 and 2012, field surveys were carried out to estimate the density of late season volunteer corn where corn had been grown earlier in the season. Volunteer corn seeds obtained from non-Bt x non-Bt cross were planted at three locations over 3 planting times to study the prevalence of corn earworm on late season volunteer corn. To study the development of corn earworm on volunteer plants resulting from different Bt and non-Bt crosses, 4 different crosses (Bt X Bt, Bt X non-Bt refuge, Non-Bt refuge X Bt and Non-Bt refuge X non-Bt refuge) were carried out and seeds from these crosses were planted in the field and greenhouse. Results from leaf tissue bioassays and ear infestations with corn earworm indicate sublethal Bt expression in Bt positive volunteer corn. Occurrence of a high density of late season volunteer corn revealed by the survey, coupled with sublethal Bt exposure to corn earworm suggests that late season volunteer corn could act as a potential source for Bt resistance development.