Submitted to: Entomological Society of America Annual Meeting
Publication Type: Abstract only
Publication Acceptance Date: 8/15/2002
Publication Date: 11/17/2002
Citation: AVERY, P., JARONSKI, S. EFFECT OF INDUCED SYSTEMIC RESISTANCE ON THE SUSCEPTIBILITY OF INSECT HERBIVORES TO ENTOMOPATHOGENS. ENTOMOLOGICAL SOCIETY OF AMERICA ANNUAL MEETING. 2002. P. 39. Interpretive Summary: The theory we examined is that Induced Systemic Resistance (induced by the chemical harpin) may affect the susceptibility of insect herbivores to one or more insect pathogens through some form of indirect stress on the insect. Three model systems were used to examine this theory: grasshoppers, the European Corn Borer and Black Cutworm, all feeding of corn plants, and the fungal pathogen, Beauveria bassiana. Grasshoppers reared on harpin-induced corn did not display any adverse directed effects such as slowed developmental rate, or smaller adult body size. Nor did their susceptibility to the Beauveria fungus change. Both lepidoptera suffered high control mortality rendering any data essentially meaningless.
Technical Abstract: Induced systemic resistance and systemic acquired resistance in plants involve major biochemical changes resulting in resistance to pathogens, reduced disease expression, and direct effects on herbivores. Tritrophic effects on the pathogens of herbivorous insects have not yet been described, however. If an insect feeding on induced plants is stressed in some manner it may be more susceptible to pathogens. We are studying three model systems to examine these tritrophic effects: the susceptibility of the orthopteran Melanoplus sanguinipes, and the lepidotperans Ostrinia nubilalis and Agrotis ipsilon, all feeding on SAR-induced corn plants, to Beauveria bassiana Strain GHA. SAR was induced by application of a commercial preparation of harpin. Immature insects were reared on induced and corn plants and then bioassayed as young adults (M. sanguinipes) or 4th instar larvae (the two lepidopterans) with the fungus. No consistent effect was observed with the grasshopper species in terms of its susceptibility to the fungus. Severe control mortality of the lepidopteran larvae rendered data meaningless.