Master of Science (MS)
Insect herbivores can induce a range of plant defenses. Signal pathways can be activated that result in the production of secondary metabolites. Many of these compounds can reduce insect fitness, deter feeding, and attract beneficial insects. Additionally, organic and inorganic chemicals applied as a foliar spray or soil drench can activate these plant responses. Azelaic acid, benzothiadiazole (BTH), gibberellic acid (GA3), harpin, and jasmonic acid (JA) are thought to mediate plant response to pathogens and herbivores. The effects of these elicitors on the induction of plant defenses were determined by measuring the weight gain of fall armyworm (FAW), Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) on four important crops, cotton, corn, rice, and soybean, treated with elicitors, under greenhouse conditions. JA consistently induced cotton and soybean resistance to FAW. In contrast, azelaic acid, BTH, and harpin treated plant material increased weight gain of FAW, suggesting negative crosstalk between the salicylic acid and JA signaling pathways. No induction of defense was observed in corn and rice, and the lack of spray mixture adhesion to those crops inspired a second experiment in which four adjuvants were co-applied with a reduced rate of JA (0.25X) to corn and cotton. Corn was more responsive to the use of an adjuvant than was cotton. The differential effectiveness of two elicitors, JA and BTH, was investigated on FAW and another noctuid species, the soybean looper (SBL), Chrysodeixis includens (Walker). Weight gain of FAW offered JA-treated soybean was significantly lower than FAW offered non-treated soybean in all trials, whereas growth of SBL was significantly reduced in only one trial. BTH was not effective in reducing weight gain of SBL offered plant material treated at the 1X or 5X rates. BTH reduced weight gain of FAW only in trial 2, at the 5X rate. The findings presented herein provide further support that foliar applications of JA increase resistance to arthropod herbivores, and that this relationship between plant and herbivore could be transitioned to the field, with the ultimate goal of using elicitor-induced defense as a part of an integrated pest management program.
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Gordy, John, "A survey of chemical elicitors and their effectiveness as promoters of plant defense against herbivory by Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae)" (2013). LSU Master's Theses. 246.