Seasonal Patterns in Host-Free Survival of the Boll Weevil (Coleoptera: Curculionidae) in the Subtropics

Abstract

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°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°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.

Temperature Influences on Diapause Induction and Survival in the Boll Weevil (Coleoptera: Curculionidae)

“…This improved survival may indicate that fat is more effectively accumulated at the lower temperatures because of reduced baseline metabolic rates, compared with higher temperatures. These observations were consistent with those of Spurgeon (2008) regarding survival patterns of cohorts of weevils fed and held under ambient conditions. Spurgeon (2008) was able to explain differences among survival functions of most weevil cohorts on the basis of temperature during the host-free period, except for the latest cohorts which experienced markedly cooler temperatures during the feeding period.…”

“…These observations were consistent with those of Spurgeon (2008) regarding survival patterns of cohorts of weevils fed and held under ambient conditions. Spurgeon (2008) was able to explain differences among survival functions of most weevil cohorts on the basis of temperature during the host-free period, except for the latest cohorts which experienced markedly cooler temperatures during the feeding period. Numerous other reports have indicated an association between increased overwintering survival of the weevil and late entry into overwintering quarters ( Hinds and Yothers 1909 , Gaines 1935 , Reinhard 1943 , Taft et al 1973 , Rummel and Carroll 1983 , Parajulee et al 1996 ).…”

“…The lower survival in association with feeding at higher temperatures observed in this study, combined with reduced post-feeding survival with increased temperature ( Spurgeon 2002 , 2008 ), suggest limited host-free survival potential of the boll weevil in subtropical and tropical regions. These observations accentuate the importance of thorough crop destruction and maximization of the host-free period to boll weevil management and eradication.…”

“…The higher host-free survival rates of males compared with females are difficult to interpret unambiguously, especially considering that several previous studies using either vegetative stage cotton as food ( Esquivel et al 2004 , Suh and Spurgeon 2006 ) or observations of survival under ambient conditions ( Westbrook et al 2003 , Spurgeon 2008 ) did not report similar differences. Regardless, differences observed in this study occurred early in the host-free survival period.…”

“…Based on their synthesis of the literature, they concluded the nature of adult diapause in the subtropical weevil was poorly understood, although extended host-free survival in the subtropics was clearly demonstrated. A subsequent survival study failed to detect differences in host-free survival between boll weevils from the Lower Rio Grande Valley and weevils from northern Texas when diapause was induced by manipulating the diet of the adult ( Spurgeon et al 2008 ). In addition, Spurgeon and Raulston (2006) conducted extensive studies with both southern temperate and subtropical weevils and failed to demonstrate any effect of photoperiod on diapause induction in either population.…”