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item Spurgeon, Dale

Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2006
Publication Date: 11/2/2006
Citation: Spurgeon, D.W., Raulston, J.R. 2006. Boll weevil (Coleoptera: Curculionidae) adult diapause responses to selected environmental and dietary conditions. Annals of the Entomological Society of America. 99:1085-1100.

Interpretive Summary: Diapause is a state of dormancy used by the boll weevil to survive the winter in many U.S. cotton production regions. A sound understanding diapause is essential to maximizing population suppression efforts in eradication programs. Although it is widely regarded that day length and nighttime temperatures control the onset of diapause, the true nature of the diapause remains a contentious issue. In laboratory studies involving carefully controlled diets and weevils from distinctly different geographical areas (Lower Rio Grande Valley and Brazos Valley of Texas) we found no evidence that day length influenced the occurrence of diapause. Nighttime temperature influenced the timing of appearance of both reproductive and diapause characters, but did not determine the occurrence of diapause. However, a high incidence of diapause was consistently associated with groups of weevils feeding on cotton buds stripped of their protective bracteoles, compared with weevils fed as individuals on intact buds. Fundamental differences in the diapause response were not observed between weevil sexes or geographical origins. These results suggest improved understanding of the dynamics of adult diapause could be achieved through continued investigation of the effects of adult diets.

Technical Abstract: Diapause in the boll weevil (Anthonomus grandis Boheman) remains a contentious issue despite intense investigation. In particular, the roles and interactions of photoperiod, temperature, and adult diet are poorly understood. We re-examined the influences of these factors using a feeding regime typical of previous studies (group, 1 square per 5 weevils/d) as well as one known to promote reproductive development (single, 1 square per weevil/d). Three separate studies each incorporated all combinations of the following: photoperiod (short day, 11:13; long day 13:11 [L:D] h), temperature regime (warm night, 29.4°:29.4°C; cool night, 29.4°:10°C [day:night]), feeding regime, and age at dissection (3, 6, 9, and 12 d after adult eclosion). Studies differed in the source of weevils (Lower Rio Grande Valley, Brazos Valley of Texas), and the photoperiod used to rear weevils to adulthood (11:13 or 13:11 [L:D] h). Interpretable effects of photoperiod on diapause induction were not observed. Cool nights delayed development of fat bodies, oocytes with yolk, and the occurrence of diapause, especially in weevils fed in groups. However, these effects were not apparent by day 12. The most marked responses were to feeding regime. Hypertrophied fat bodies and diapause generally occurred more often, and oocytes with yolk less often, for weevils fed in groups compared with those fed singly. Fundamental differences in diapause response corresponding to rearing conditions or source of weevils were not observed. These results suggest improved understanding of the dynamics of adult diapause could be achieved through continued investigation of the effects of adult diets.