Chapter 9 - Arthropod Resistance to Crops

Abstract

This chapter describes different attempts by agriculturalists and entomologists to manage the resistance by host plants to deal with the real or potential evolution of counteracting resistance by arthropods. There are a wide variety of cases in which an arthropod species has overcome host plant resistance (HPR) designed by humans to control crop pests. Resistance by arthropods to HPR can occur to both traditionally bred crops and transgenic insecticidal crops. Much of the focus of HPR is on antibiosis, and more recently, production of extremely high doses of toxins in transgenic insecticidal crops. IRM will be needed whether the HPR is caused by antibiosis or by antixenosis. Major resistance genes have been identified, most notably in insects that are targets of transgenic insecticidal crops. These genes and the resistant insect colonies based upon them can be used to study the dynamics of resistance and the efficacy of various management strategies. Examples of this are M. destructor on wheat and P. xylostella on broccoli. The behavior of the arthropod influences how quickly it will evolve resistance to either antibiosis or antixenosis. An HPR variety that deters an herbivore is expected to exert less selection pressure for resistance than one in which the herbivore has no preference between it and the susceptible variety. This does not mean, however, that an herbivore will not evolve behavioral resistance. Indeed, T. urticae still evolved resistance to morphological features of tomatoes and broccoli previously shown to deter mites. S. graminum has evolved resistance to many sorghum and wheat cultivars, most of which have some level of antixenotic effect.