Doctor of Philosophy (PhD)
Induced resistance to the rice water weevil, Lissorhoptrus oryzophilus, was assessed in greenhouse and field experiments. The fall armyworm,Spodoptera frugiperda, and an elicitor, jasmonic acid, were used to induce resistance. The effect of these treatments on rice resistance to oviposition varied between cultivar used, but significantly fewer larvae were found on plants exposed to S. frugiperda and jasmonic acid on both cultivars tested. Application of jasmonic acid significantly reduced the number of L. oryzophilus larvae per plant, and represents the first example of elicitor-induced resistance in rice in field experiments. Oviposition by the sugarcane borer, Diatraea saccharalis, induced resistance to further oviposition by D. saccharalis in several cultivars. Plants with egg masses present received 33- 50% fewer egg masses when exposed to gravid D. saccharalis. However, D. saccharalis oviposition on cultivar M202 rendered plants more susceptible to subsequent oviposition. M202 plants with egg masses present received 2-3 fold more egg masses when subsequently exposed to D. saccharalis. The rice stink bug, Oebalus pugnax, was reared on rice (Oryza sativa), barnyardgrass (Echinochloa crus-galli) and amazon sprangletop (Leptochloa panicoides) and the metathoracic gland (MTG) contents were analyzed using GC/MS. Quantities of three compounds ((E)-2- decenal, (E)-2-hexenyl acetate and n-dodecane) are significantly influenced by host-plant. Crude metathoracic gland extracts attracted O. pugnax at low concentrations, and attraction decreased as the concentration increased, suggesting a bifunctional role of metathoracic gland compounds. Field experiments using a synthetic mixture of the four most abundant MTG chemicals significantly reduced O. pugnax in plots sprayed with this mixture. In addition, the host-plant on which O. pugnax was reared was found to significantly alter the ratio of four MTG chemicals, as well as influence development time and adult weights. The biological activity of four common phenolic compounds in rice (ferulic, p-coumaric, cinnamic and caffeic acids) were evaluated for their effects on the growth rate of D. saccharalis and S. frugiperda larvae. Levels of these compounds were quantified and then incorporated into diet bioassays. Despite minor structural differences, these compounds were found to have widely divergent effects on the larval weights of D. saccharalis and S. frugiperda.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Hamm, Jason Charles, "Ecology and chemical ecology of plant-insect interactions in rice: implications for pest management" (2011). LSU Doctoral Dissertations. 2057.
Stout, Michael J.