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Title: Host-free Survival of Boll Weevils (Coleoptera: Curculionidae) from Two Regions of Texas.

Author
item Spurgeon, Dale
item Sappington, Thomas
item RUMMEL, D. - RETIRED TEXAS A&M

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2008
Publication Date: 7/23/2008
Citation: Spurgeon, D.W., Sappington, T.W., and Rummel, D.R. 2008. Host-free Survival of Boll Weevils (Coleoptera: Curculionidae) from Two Regions of Texas. Southwest Entomol. 33:151-152.

Interpretive Summary: The boll weevil overwinters in most U.S. cotton production areas in a state of dormancy called diapause. This diapause state permits the weevils to survive the non-cropping season without feeding on cotton. New information regarding diapause could be useful to efforts to improve the efficiency of ongoing eradication programs. Some reports have suggested that diapause is controlled differently in weevil populations from different geographical areas. However, more recent reports for two widely-separated weevil populations in Texas do not support these conclusions. In laboratory studies we stimulated weevils from the Lower Rio Grande Valley (LRGV) and High Plains of Texas to enter diapause by manipulating their food supply, and then compared their survival in the absence of food. Examinations of weevils at the beginning of the survival period indicated about 90% were in diapause. Average (4 to 6 weeks) and maximum (12 to 16 weeks) survival was similar for the two weevil populations, and statistical tests did not indicate differences in their respective patterns of survival. Therefore, our results did not provide any evidence to suggest the diapause state differs between these two weevil populations. Our results also suggest that efforts to understand apparent differences in boll weevil overwintering between temperate and subtropical regions should focus on influences of the overwintering environment, such as weather, rather than on differences in diapause.

Technical Abstract: New information regarding boll weevil (Anthonomus grandis Boheman) overwintering, and especially diapause, is important to efforts to improve the efficiency of eradication programs. Some published reports suggest the diapause response differs among geographically separated populations of the boll weevil. However, recent experimental evidence failed to indicate such differences between two populations in Texas. We used dietary methods to induce diapause in weevils from the Lower Rio Grande Valley (LRGV) and High Plains of Texas, and compared their subsequent host-free survival under controlled conditions (23.9 +/- 1 degree C). Dissections confirmed high levels of diapause at the initiation of the host-free period (females, 91-98%; males, 84-93%). Survival analyses indicated median longevities of about 4 wk for High Plains weevils, and nearly 6 wk for weevils from the LRGV. Maximum longevities were 12 and 16 wks (LRGV and High Plains, respectively). No statistical differences were detected between survival curves for the two populations. Therefore, our results did not indicate fundamentally different responses to our experimental conditions by weevils from the Texas High Plains and LRGV. These results suggest that efforts to interpret apparent differences in the dynamics of boll weevil overwintering between temperate and subtropical regions should focus on influences of the overwintering environment rather than on differences in the diapause response.