Survival of Diapausing and Nondiapausing Boll Weevlls (Coleoptera: Curculionidae) Subjected to Freezing Temperatures

Abstract

Boll weevils, Anthonomus grandis grandis Boheman, were subjected to freezing temperatures of 0.0, −2.5, −5.0, −7.5, and −10.0°C in a cold bath. Survival of diapausing and nondiapausing adults was compared after exposures of 2-, 4-, 6-, and 8-h duration. Diapausing and nondiapausing individuals could be separated by exposure to −7.5°C for 6 h; diapausing adults were alive and able to walk after this treatment, whereas nondiapausing adults were dead or unable to stand. In the diapausing group, young boll weevils (36 d old) were more tolerant of freezing conditions than were older (110 d old) boll weevils. In a 2nd test, diapausing adults were exposed to these 5 temperatures for 8–72 h. Boll weevils did not survive exposures ≥40 h duration at −1O.0°C. In a 3rd test, diapausing boll weevils were subjected to temperatures of 0.0, −2.5, −5.0, and −7.5°C for 4, 8, 16, and 24 h/d for 2, 6, 10, 14, and 18 consecutive days. At the end of the daily freezing exposure, adults were removed from the cold bath and held at 4.4°C. No boll weevils survived the treatment combinations of −5.0°C for 24 h/d for 14 d and of −75°C for 16 and 24 h/d for 10, 14, or 18 d. However, temperatures this low for this length of time are not common in the Texas Rolling Plains. In the regression equation relating survival with the various exposure conditions, the linear and quadratic components for temperature were primary variables affecting survival in each of the 3 tests.