The tobacco budworm, Chloridea virescens (F.) (Lepidoptera: Noctuidae), once a major insect pest of tobacco, Nicotiana sp., and cotton, Gossypium hirsutum L., in the Americas, has decreased in abundance, especially in cotton fields, during the past 2 decades. Little is known of the biological factors, crop management techniques, and effect that ample planting of cultivars of cotton expressing Bacillus thuringiensis Berliner (Bt-cotton) might have had on their reduction, nor of changes in the conditions of the ‘source’ areas that produce migrant populations of tobacco budworm. Detailed knowledge of its population dynamics is lacking. This work proposed a mathematical model considering only seasonal changes in temperature as the driving factor to explain variations of tobacco budworm during a 20-year collection of males in pheromone traps in Washington County, MS. Tobacco budworm dynamics according to the model suggested the stability of the population of the geographical area did not depend on immigration and that larvae of the last generation of the year that survive winter temperatures better explain the dynamics, contrary to what was commonly assumed that larvae in the area could not survive prolonged wet and cold winter weather. The Mississippi Delta has planted Bt-cotton in high proportions, however, this might be a more reasonable force behind reduction in abundance of tobacco budworms.