The Conundrum of Chemical Boll Weevil Control in Subtropical Regions

Abstract

Originally a Mesoamerican insect, the boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), has spread from the tropics, where it evolved on cotton, Gossypium hirsutum L., and other malvaceous plant species (Burke et al., 1986; Brubaker & Wendel, 1994; Showler, 2009b), north to temperate cotton producing areas of the United States and south to northern provinces of Argentina (Cuadrado, 2002; Showler, 2009b). The pest was first detected in United States cotton in 1892 (Parencia, 1978) and infested the Cotton Belt such that by 1917, every cotton-producing county in Georgia, for example, was infested (Hunter, 1917). Adults oviposit inside cotton buds or “squares” (usually one egg per square), and the hatched larva causes the square to abscise before it can flower (Showler and Cantu, 2005). If an egg is deposited within a young boll (older bolls become too hard to penetrate), or if mouthparts penetrate the rind of squares to the inner reproductive portion, fiber-producing locks can be injured or completely destroyed, but not necessarily all four locks (Showler, 2006a; Showler & Cantu, 2008). Boll weevil losses have been valued at $83.34 billion and insecticide-based control costs at $18.67 billion between 1893 and 1999, and infestations became so injurious that cotton-free winter periods were instituted by law in some areas (Haney, 2001). Later, insecticide-based eradication programs were launched in the United States and in Argentina (Dickerson & Haney, 2001; Haney et al., 2001; Johnson & Martin, 2001; Texas Department of Agriculture, 2002; Carmona et al., 2003). Natural enemies indigenous to the United States are not considered to be important as mortality factors against boll weevils (Jones & Sterling, 1979; Showler & Greenberg, 2003), although the imported fire ant, Solenopsis invicta Buren, native to South America (Buren et al., 1974; Lofgren, 1986), can account for up to 58% of boll weevil mortality in relatively wet regions where the predator thrives (Sturm & Sterling, 1990). In one study imported fire ant predation on immature boll weevils averaged 84% compared with 0.14% and 6.9% mortality caused by parasitism and desiccation, respectively (Fillman & Sterling, 1983). But in drier cotton growing areas, lack of sufficient predation to help govern populations in some new habitats outside Mesoamerica (Showler, 2007) permitted rapid dispersal (Burke et al., 1986; Showler, 2009a). While certain cultural practices, such as early planting (Showler et al. 2005) can help avoid large populations that typically accumulate in the summer (Showler, 2003, 2005), chemical intervention against building infestations has been the chief control tactic.