Although the pink bollworm, Pectinophora gossypiella (Saunders), remains a significant pest of cotton in the southwestern United States, the pest has not yet become established in southeastern US cotton. The objectives of this study were to determine how low temperatures and high soil moisture common to the southeastern US might affect mortality of diapausing and nondiapausing larvae of pink bollworm. In the laboratory at constant temperatures, moisture (0%), and darkness, nondiapausing prepupal larvae died more quickly as temperatures were lowered from 22 to 10 to 5°C. At 5°C, 90% of the population was dead after 12 days. Under similar experimental conditions, prepupal larvae reared under diapause inducing conditions (20°C, 10L:14D), but showing no developmental evidence of diapause, also died more quickly at lower temperatures. In this case, 26 days at 5°C were required to achieve 90% mortality. For diapausing, prepupal larvae collected from the field, mortality was greater at 5°C than at 20, 15, or 10°C, but larvae could withstand 5°C for 60 d before 90% of the population died. In response to moisture, as soils at 10°C became saturated (>165% gravimetric soil moisture), most larvae ( 60%) died within the first 10 d of the experiment. Diapausing individuals are more resilient to cold temperatures than nondiapausing individuals, but winter temperatures in the southeastern US are not sufficiently cold to completely preclude establishment of pink bollworm. Only northern Missouri has maximum air temperatures 5°C for enough time to significantly affect numbers of diapausing larvae.