Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2002
Publication Date: N/A
Interpretive Summary: Efforts to plan and conduct boll weevil eradication or suppression programs could be greatly improved by the ability to accurately predict winter mortality of adult boll weevils. It is generally assumed that many overwintering weevils are killed as a result of freezing. However, very little is known about the temperatures (supercooling points) required to freeze weevils and even less is known about the factors influencing supercooling points of weevils. We examined the impact of food in the gut and fat present in weevils on supercooling points of adult boll weevils. We found that weevils that had food in their guts froze at much higher temperatures than those that had empty guts. The sex, age, and amount of fat present in weevils did not appear to influence supercooling points of weevils. Because the temperatures at which weevils froze in our study were much cooler than what overwintering weevils would normally encounter in the field, our results suggest that other mechanisms in addition to acute freezing are important in determining overwintering survival of boll weevils. These results also indicate that the recent feeding history and gut content of weevils should be considered or documented in future supercooling and overwintering survival studies.
Technical Abstract: Cold bath studies were conducted to examine the impacts of midgut content and fat body condition on supercooling points of adult boll weevils, Anthonomus grandis Boheman. The presence of solid food in weevil midguts significantly raised the supercooling points of weevils. Supercooling points of recently fed weevils with solid food present in their midguts ranged from -6.2 to -16.0 C, with a mean +/- SD of -10.9 +/- 1.9 C, whereas supercooling points of unfed weevils with empty midguts ranged from -10.2 to -20.2 C, with a mean +/- SD of -16.0 +/- 2.1 C. The mean supercooling point of weevils whose midguts contained colored traces of food from previous feeding was between those of recently fed weevils containing solid food and those having empty midguts. These findings indicate that the influence of feeding on supercooling points of weevils is related to the quantity and/or condition of midgut contents in weevils. No relationship was detected between the supercooling capabilities of weevils and amounts of hypertrophied fat bodies present for either fed or unfed weevils. Additionally, there was no significant difference in mean supercooling points between male and female weevils, and no relationship was detected between the supercooling points of weevils and their age. These results show that presence of food residues in the boll weevil midgut can have a pronounced affect on supercooling points of weevils, and indicate that the recent feeding history and midgut condition of weevils should be considered or documented in future supercooling and overwintering survival studies.