Physiological status of overwintering boll weevils, Anthonomus grandis Boheman, in Arizona.

Abstract

The overwintering physiology of boll weevils was evaluated using collections from a field in Laveen and 2 fields in Marana, Arizona, during the 1987-1988 winter and spring, and the 1988 non-cotton season, respectively. The objectives of the study were to determine if the strain of boll weevils, Anthonomus grandis Boheman, in Arizona enter true diapause, when diapause occurs, proportion of population entering diapause, and factors inducing diapause. Comparative studies were performed on 1987-1988 collections from both pheromone traps and bolls, to assess sex ratio, survival, reproductive behavior and adult longevity. Large numbers of weevils were caught in traps from September 1987 through April 1988, and there was no evidence of correlation of trap catches with prevailing temperatures. Hibernation cage studies also showed the absence of a sustained period of inactivity, and emergence was completed before the availability of squaring cotton. Significantly higher survival was observed among boll-enclosed weevils relative to the trap collected weevils, when placed in cages. Furthermore, moderate moisture was found to have a positive influence on survival. Studies on diapause and reproductive behavior revealed that a significant number of weevils in the trap collections was reproductive, whereas, a higher proportion of weevils collected from bolls seemed to be in a non-reproductive or diapausing condition. Subjecting weevil samples to three temperature/photographed regimes (25°C, 14L:10D; 20°C, 12L:12D; and 15°C, 10L:14D) showed that higher temperature/longer light cycle was more conducive to diapause completion and post diapause development. But, on transferring sub-samples to altered temperature/photoperiod regimes, temperature was determined to be the more important factor inducing diapause termination. Evaluations on longevity showed that 20°C 12L:12D photoperiod was optimal for survival of both fed and unfed weevils. Studies on weevil-samples collected from the two fields in Marana to evaluate the influence of plant phenology on overwintering status showed that the two populations were significantly different with respect to diapause status, reproductive behavior, egg lay, preoviposition period, moisture and fat content, and lipid composition. Higher proportions of weevils collected from the field with mature cotton bolls (Field 2) were found to be in a state of firm diapause, whereas those from a field with all stages of fruiting cotton (Field 1) were predominantly reproductive or intermediate.