Nicotine metabolism in the cabbage looper trichoplusia ni (Hübner)

Cabbage looper (Trichoplusia ni) larvae are generalist herbivores that feed on numerous cultivated plants. Consuming plant material from diverse plant species exposes these larvae to a wide variety of plant secondary metabolites involved in chemical defense against herbivory. The ability of the cabbage looper larvae to detoxify plant secondary metabolites, such as nicotine, has been attributed to the rapid excretion via the Malpighian (renal) tubules. However, the role of metabolism prior to excretion in the detoxification of nicotine in cabbage looper larvae has not been studied. The first objective of this thesis was to develop an accurate, precise, and sensitive method for the detection and quantification of nicotine and its major metabolites in tissues, blood and feces from insects. The second objective was to determine the appropriate nicotine dose to study the sub-lethal effects of nicotine in cabbage looper larvae. The third and final objective was to determine the metabolic fate of dietary nicotine in cabbage looper larvae. Previous studies have concluded that the cabbage looper does not metabolize nicotine. This thesis showed that the 4th instar larvae of the cabbage looper metabolized dietary nicotine into three distinct metabolites. In addition, the time course for nicotine metabolism and excretion was found to be more rapid than previously reported for other Lepidopteran insects. Taken together these data demonstrate that cabbage looper larvae are capable of efficiently metabolizing nicotine and excreting nicotine and these derived metabolites as a part of their xenobiotic coping mechanism.Arts and Sciences, Irving K. Barber School of (Okanagan)Biology, Department of (Okanagan)Graduat