Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) Immune System Responses to Variation in Nutritional and Plant Defensive Environments
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Date
2021-04-16
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Abstract
Insects challenged with a pathogen must respond with the appropriate level and type of immune response to maximize the likelihood of survival. They exhibit behavioral defenses, as well as humoral and cellular defenses, which are regulated by signal induction pathways. Extensive research has been done to understand the signaling pathways that elicit different immune responses; however, most of the research has been conducted in model organisms. Little is known about the immune system of Helicoverpa zea, possibly the most important crop pest in the New World. Even less is known about the nutritional behavioral changes within this species, or the effects of inducible plant defenses on altering pathogen susceptibility in H. zea. The first objective was to assess variation in the immune response of H. zea to four different entomopathogenic microbes throughout the infection cycle. The immune response differed based on pathogen type and time post-inoculation. Bacillus thuringiensis bacteria induced the strongest immune response, upregulating Relish, the transcription factor for the IMD pathway. The second objective was to determine whether nutritional variation affected the immune response to Helicoverpa armigera nucleopolyhedrovirus (HearNPV). Insects have been found to alter their intake of proteins and carbohydrates to off-set costs associated with activating immunity, while others have been shown to actively self-medicate to survive the infection. However, in this study H. zea did not exhibit compensatory feeding or self-medication; rather the pathogen could be manipulating the host. The final objective was to understand the effects plant defenses have on HearNPV virulence in previously-infected H. zea larvae. Plant defenses had an effect on healthy larvae, while infected larvae were not affected. Control larvae reared on plants with induced systemic resistance (ISR) upregulated did not survive as well as larvae on Control plants or plants with systemic acquired resistance (SAR) upregulated. Together, these data illuminate how H. zea responds to pathogenic infections and the constraints imposed by nutritional and plant defensive environments.
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Immunology, Nutritional Immunology, Cotton Bollworm, Entomopathogen, Biopesticide