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Hassanpour Farshour, Nazli

University of British Columbia

The cabbage looper, Trichoplusia ni (T. ni) is a generalist insect (Lepidoptera: Noctuidae) that is an agricultural pest of crucifers and other crops of economic importance. In fact, over 70% of all agricultural pest insects are Lepidopterans. Although insecticides are effective at controlling insect populations by targeting the nervous system, they can have negative off-target effects. Cytochrome P450s (CYPs), glutathione S-transferases (GSTs), UDP-glucuronosyltransferases (UGTs), and carboxylesterases (CEs) are metabolic enzymes frequently implicated in insecticide resistance. These enzymes work in concert with transport genes such as ATP-binding cassette transporters (ABCs), organic cation transporters (OCTs) and multidrug resistance proteins (MRPs). Upregulation of detoxification enzymes and inhibited binding of insecticides due to target-site mutations are the main mechanisms causing insecticide resistance. Enriched metabolic detoxification of xenobiotics along with the subsequent development of insecticide resistance have been linked to the overexpression of CYPs in insects. Previous studies have suggested that generalist insect herbivores’ (e.g. T. ni) growth and development are inhibited by exposure to the plant alkaloid nicotine, whereas specialist insect herbivores (e.g. tobacco hornworm) are not affected. However, it has been shown that the Malpighian (renal) tubules of T. ni actively excrete nicotine. Recent research has shown that T. ni do in fact detoxify nicotine into the three major metabolites; cotinine, cotinine-N- oxide, and nicotine-N-oxide. The objective of this thesis was to utilize next-generation sequencing methods to establish a greater understanding of how nicotine, a model plant alkaloid, is detoxified by a generalist insect such as T. ni. This thesis showed that dietary nicotine exposure in T. ni resulted in the increased expression of a number of metabolic detoxification and transport-related gene candidates. CYPs in particular showed increased expression in response to nicotine in both midgut and renal tissues. A number of these showed high sequence similarity to previously published CYPs in other insect pests. Taken together these data provide further insights on how nicotine is metabolized and excreted by T. ni. This research will increase opportunities for the development of new biochemical and physiological targets for the control of insect agricultural pests and disease vectors which are economically, environmentally, and medically significant.

Text

2021-06-23

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/78772

Biology

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/