Degree

Doctor of Entomology (PENTM)

Document Type

Dissertation

Abstract

The effects of herbivory and chemical applications as potential inducers of resistance to herbivores in rice, Oryza sativa L., were explored through a series of field, greenhouse, and laboratory experiments. Studies were conducted to investigate the preference and performance of several herbivore pests of rice with a focus on, Lissorhoptrus oryzophilus Kuschel, the rice water weevil (RWW), under conditions where rice plants had been stressed by previous herbivory or chemical applications. The effects of defoliation by Spodoptera frugiperda (J.E. Smith), the fall armyworm, on resistance and tolerance of rice to RWW under field conditions were examined. Herbivory by fall armyworm on rice may indirectly affect RWW in rice fields in the southeastern United States via changes in rice resistance and tolerance. Hypotheses were that defoliation by fall armyworm would alter the resistance of rice to subsequent infestation by RWW, and that defoliation would reduce the tolerance of rice to subsequent RWW injury. Additional experiments probed the effects of larval and adult feeding on rice tissues by RWW on subsequent adult RWW preference. Hypotheses were that prior feeding by either stage would alter plant resistance to subsequent adult infestation. These studies provided strong support for larval induced resistance to aboveground conspecific adults, while providing weaker support for adult induced resistance to subsequent RWW adults. Investigations of the effects of methyl jasmonate, a derivative of the plant hormone jasmonic acid, which is involved in the mechanisms underlying induced resistance to herbivores, were also studied at the greenhouse and field level. It was hypothesized that methyl jasmonate seed treatments would increase resistance in rice to RWW. Results indicated that while the compound did not provide protection equal to pyrethroid insecticides, it was capable of inducing resistance to RWW at the cost of delays in plant growth and potential reductions in yield. Finally, herbicide-induced resistance to major herbivores in LA rice was investigated at the field level. These herbivores included the RWW, a complex of stemborers (Lepidoptera:Crambidae) including Diatraea saccharalis (Fabricius), the sugarcane borer, Chilo plejadellus (Zincken), the rice stalk borer, and Eoreuma loftini (Dyar), the Mexican rice borer, as well as the rice stink bug, Oebalus pugnax (Fabricius). Hypotheses were that there would be both direct and indirect effects of herbicides on insect and weed densities in rice, and that these effects would translate to differences in rice yields between treatments. Overall results from this series of experiments indicate that herbicides are capable of altering pest densities of both weeds and insects, and the resulting changes in these communities can have impacts on yields. Collectively, this work documents the potential of plant stressors including herbivory, hormone seed treatments, and herbicide injury to influence resistance of rice to insect herbivores. The broader implications of the work presented are significant due to the potential impact this information may have on IPM and future research. It is important to note that rice in the southern U. S. can be used as a model for developing countries where pest management options are limited and pesticide safety is frequently eschewed.

Date

10-23-2018

Committee Chair

Stout, Michael

Available for download on Wednesday, October 23, 2019

Included in

Entomology Commons

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