Origins and Coadaptation of Insect Pests from Wild to Domesticated Host Plants: Examples from Maize, Cotton, and Prickly Pear Cactus

Abstract

This chapter presents examples of how human activities have modified the distribution, ecology, and genetics of selected insect species. The first three examples involve how the key Mexican crops lead to the origin of important crop pests, whereas the last example is a case of an intentionally introduced beneficial insect turned exotic invasive pest of a cultivated crop. The first example is a comparative ecological and genetic analysis of how the corn leafhopper (Dalbulus maidis Delong and Wolcott) emerged as an herbivore specialist on the teocintle, the progenitor of maize, to become an important pest of modern maize. The second example concerns a highly generalist lepidopteran herbivore, the fall armyworm (Spodoptera frugiperda). This is a ubiquitous pest of maize in Mexico and the Americas that has been favored and adapted to modern maize monocultures. In 2014, the species began an unprecedented worldwide expansion into Africa, Asia, and Australia where it has caused great damage to a wide range of crops. The third example is that of a key cotton pest originating from Mexico and Central America, the boll weevil (Anthonomus grandis). This species illustrates how ancestral pest lineages on wild host plants constitute important sources of biological control agents, and information contributes to our understanding regarding the history and sources of pest lineages. Finally, we present the cactus moth (Cactoblastis cactorum), an exotic insect which is threatening wild and cultivated cactus populations of Mexico whose invasion could be catastrophic for prickly pear cacti (Opuntia), which represents a fundamental component of arid ecosystems of Mexico and is an important crop and food resource that is intricately linked with Mexican culture. These examples emphsize that efforts are needed to conserve in situ populations of both the wild host plants and their insect associates as well as increase efforts to prevent invasions of new crop pests.