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item Spurgeon, Dale

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/11/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary: Previous studies have shown that death of boll weevils in the winter is related to the occurrence of sub-freezing winter temperatures. However, these relationships are of little use for predicting survival in areas where freezing temperatures seldom occur. The relationships between temperature and boll weevil survival were evaluated at four temperatures ranging from 55 to 85 degrees F. No differences in survival of male and female weevils were observed regardless of temperature. Temperature strongly influenced survival, but these relationships changed over time. Weevil survival was consistently lowest at 85 degrees F and tended to increase as the temperature was lowered to 65 degrees F. Survival at 55 degrees F was very high at first, but after several weeks survival at this temperature was lower than that at 65 degrees F. This decrease in survival at 55 degrees F shows that low temperatures above freezing are harmful to overwintering boll weevils. These findings provide an explanation for boll weevil mortality during the winter months in areas where freezing temperatures seldom occur. The relationships between temperature and survival can be used to develop predictive models that will help improve the timing of control practices such as delayed planting and diapause (hibernation) sprays.

Technical Abstract: Most studies of boll weevil overwinter survival have focused on the effects of severe winter temperatures. Consequently, little is known regarding the temperature dependence of such survival in locales where sub-freezing temperatures infrequently occur. The temperature dependence of host-free survival of diapausing weevils was examined at four constant temperatures ranging from 12.8 to 29.4 degrees C. No differences in survival were detected between weevil sexes. Significant influences of temperature on survival were observed, but these relationships changed over the course of the survival period. Survival was consistently lowest at 29.4 degrees C. Survival rates at 12.8 and 18.3 degrees C were initially higher than those at 23.9 degrees C, but after the 20th week survival at 12.8 and 23.9 degrees C were similar. From week 21, until week 40 when the numbers of live weevils remaining were low for all temperatures, survival at 18.3 degrees C remained higher than survival at other temperatures. The lower than expected survival at 12.8 degrees C suggests the occurrence of a chronic low-temperature injury not previously recognized. These results provide additional insight into the dynamics of boll weevil overwintering and should be useful in developing models to predict weevil survival in areas where sub-freezing temperatures seldom occur.