SUSTAINABLE AND ORGANIC MANAGEMENT OF SELECTED FRUITS AND VEGETABLES
Title: Three Boll Weevil Diapause Myths in Perspective
Submitted to: American Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 17, 2008
Publication Date: March 23, 2009
Citation: Showler, A. 2009. Three boll weevil diapause myths in perspective. American Entomologist. 55(1):42-50.
Interpretive Summary: While research on the boll weevil has been copious, contentious myths persist about diapause. Boll weevil diapause myths analyzed in this study are: 1) diapause induction is governed by diet, 2) boll weevil diapause is universal, and 3) diapause can be determined by fat body size or lack of egg production. Existing scientific literature was examined and interpreted, and as a result, facets of boll weevil biology, ecology, and evolutionary principles were harmonized. Respective conclusions are: 1) diet should not be assumed to govern diapause; instead dietary deficits of key nutrients can alter metabolic processes, including egg production, without inducing diapause. 2) Diapause has not been reliably reported in subtropical and tropical habitats. Instead, survival modes in those areas appear to involve a combination of fully active but nonreproductive (able to reproduce with proper diet) adults reliant on commonly-found food sources, and immatures and adults that undergo quiescence in desiccated bolls. 3) Diapause should not be determined by few characters of poor quality, including fat bodies, absence of eggs, and atrophy of gonads.
The boll weevil, Anthonmus grandis grandis Boheman (Coleoptera: Curculionidae), originated in Mesoamerica but its contemporary distribution extends from the United States Cotton Belt to Argentina, throughout which it is a serious pest of cotton, Gossypium hirsutum L. While research on the boll weevil has been plentiful, contentious myths persist about its diapause which have clouded our ability to accurately characterize it and hindered progress toward developing suitable control strategies outside temperate areas. The boll weevil diapause myths analyzed herein are: 1) diapause induction is governed by diet, 2) boll weevil diapause is universal, and 3) diapause can be determined by fat body size or lack of egg production. The existing literature base was examined, interpreted, and facets of boll weevil biology and ecology were harmonized while bearing in mind the established definition and characters of diapause. Conclusions about each respective myth are: 1) diet should not be assumed to govern diapause, 2) diapause has not been reliably reported in subtropical and tropical habitats, and 3) diapause should not be determined by a select few characters of poor quality considered alone or in combination with one or two others, including fat bodies, absence of eggs, and atrophy of gonads. Survival modes in subtropical and tropical areas appear to involve a combination of fully active but nonreproducing (able to reproduce with proper diet) adults reliant on commonly-found food sources, and immatures and adults that undergo quiescence in desiccated bolls. Underpinning these conclusions is a paradigm, hitherto unrecognized, that nutrient deficits can resemble frequently-employed diapause markers without eliciting or involving diapause. The previously under-recognized role of nonreproductive host plants (plants that provide sustenance by supporting longevity but not egg development or oviposition), most notably cultivated citrus, in the spread of boll weevils into the United States is presented for the first time. Two important features involving investigations of boll weevil diapause are highlighted as well: definitions (Tauber et al. 1987, Taub-Montemayor et al. 1997) and characteristics of boll weevil diapause (Brazzel and Newsom 1959) should be viewed in their entireties, and caution should be exercised about reliance on non-refereed literature to establish broad biological and ecological principles.