Location: Crop Protection and Management ResearchTitle: Resistance mechanisms against arthropod herbivores in cotton and their interactions with natural enemies Author
Submitted to: Critical Reviews in Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2013
Publication Date: 7/1/2013
Citation: Hangenbucher, S., Olson, D.M., Ruberson, J., Wackers, F., Romeis, J. 2013. Resistance mechanisms against arthropod herbivores in cotton and their interactions with natural enemies. Critical Reviews in Plant Sciences. 32:458-482. Interpretive Summary: Cotton possesses a broad range of powerful defensive mechanisms. Direct defense is provided by several morphological traits like trichomes. The most important mechanism of direct defense in cotton plants, however, is a group of closely related terpenoids: gossypol, hemigossypolone and the heliocides 1-4. These coumpounds help to control insect pests and additionally provide resistance against pathogens. The toxins are inducible and their distribution follows the optimal-defense theory. A range of minor toxins, like tannins and flavonoids also contribute to the direct defense. The plants possess several additional inducible indirect defense traits, like the emission of volatiles and production of extrafloral nectar that attract and sustain populations of beneficial insects. The effectiveness of these defense traits is influenced by environmental factors and crop management. Yet, cotton is attacked by a complex of arthropod pests and is one of the most heavily insecticide treated crops in the world. Therefore alternative methods of pest control should explore the wealth of defense mechanisms provided by the plant. This can be achieved by selecting for varities and cultivation methods that enhance the plants’ direct and/or indirect defense traits. This needs to be supplemented by cultivation methods that conserve predators and parasitoids through use of insecticides with a narrow target spectrum, low tillage to increase ant densities and landscape management to provide beneficial species with alternative food sources and overwintering sites. In this context the adoption of transgenic Bt cotton is an important tool to effectively control key Lepidoptera pests, and to reduce insecticide use, which helps to conserve the biodiversity and function of biocontrol organisms.
Technical Abstract: Cotton plants from the genus Gossypium are grown on more than 30 million hectares worldwide and are a major source of fiber. The plants possess a wide-range of indirect and direct-defense mechanisms against arthropod pests. Direct defense mechanisms include morphological traits such as trichomes and a range of secondary metabolites. The best known defense compounds are the terpenoid gossypol and it's derivates. In addition, a range of indirect defense mechanisms help defend the plant. These include volatiles and extrafloral nectaries that attract and sustain natural enemy populations. We discuss the different direct and indirect defense traits of cotton, their induction by pests, and their impact on herbivores and their natural enemies. In addition, we discuss the use of genetically engineered cotton plants to control insect pests and the influence of environmental factors on cotton’s defense traits .