Seasonal patterns in host-free survival of the boll weevil (Coleoptera: Curculionidae) in the subtropics

The overwintering ecology of the boll weevil, Anthonomus grandis Boheman, in the subtropics is poorly understood. Knowledge of seasonal patterns of host-free survival may be important to eradication efforts in the Lower Rio Grande Valley of Texas. The host-free survival of weevil cohorts emerging between 1 June and 3 November 1994 was examined. Weevils were fed either outdoors for 21 d (9 cohorts), outdoors for 28 d (6 cohorts), or under controlled conditions (29.4 +/- 1 degrees C, 13:11 [L:D] h photoperiod; 5 cohorts) for 21 d. Weevils were fed cotton (Gossypium hirsutum L.) squares or bolls, depending on availability in the field, and were subsequently held without food in the same environment in which they were fed. Survival of weevils fed outdoors exhibited a marked seasonal pattern in which greater survival was associated with the later cohorts. However, survival of cohorts fed and held under controlled conditions exhibited no seasonal pattern. When survival was adjusted for degree-day accumulations, using a base temperature of 12.8 degrees C, differences in survival curves of weevils fed outdoors were reduced but not eliminated. During the periods of highest degree-day accumulations, most cohorts fed outdoors for 21 d exhibited greater survival than those fed outdoors for 28 d, and survival tended to be greater for weevils fed under controlled conditions than for weevils fed outdoors. These observations suggest the feeding period duration influenced subsequent survival. The observed influence of temperature on host-free survival suggests the opportunity to reduce overwintering weevil populations in subtropical regions through a delayed planting tactic.