Roles of host plants in boll weevil range expansion beyond tropical mesoamerica

Abstract

New findings about the food habits of the boll weevil, Anthonomus Brandis Brandis Boheman (Coleoptera: Curculionidae), refine current theories about range expansion beyond its tropical Mesoamerican origin. The weevil co-evolved with perennial host plants including cotton, Gossypium hirsutum L.,and patches of host plants were reached by flight, likely instigated by competition for limited resources. Boll weevils might have sought nectar, pollen, or both for energy to facilitate searching for patches of host plants. Range expansion was facilitated by shifts to new host plants, and in its dispersion north, the insect reached the subtropical Lower Rio Grande Valley of Texas, becoming established only when the citrus industry first boomed in the early 1890s. Commonly grown subtropical citrus species bear fruit containing sugars and other nutrients that can sustain active boll weevils over winter in spite of a 5-mo mandatory fall cotton plowdown. Feeding on citrus and cactus fruit, and possibly on nectars and pollens, makes nonreproductive host plants (used only for foraging) important for dispersal to and establishment at new latitudes. Once in south Texas, the pest moved rapidly through the Cotton Belt during warm seasons. To cope with cold temperate winters, the insect resorted to a poorly adapted dormancy response whereby mortality at study sites is often 100%. Extensive cotton monocultures support the buildup of large enough summer populations to increase the chance that a few survive and infest the spring crop. Establishment in temperate fringe areas (central Texas, southern Arizona, and California) and the pest's range expansion into subtropical northern Argentina are discussed in terms of associations with reproductive (plants that confer sufficient nutrients for boll weevil reproduction) and nonreproductive, indigenous, and exotic host plants.