Master of Science
Jeremy N. McNeil
Keith A. Hobson
A number of lepidopteran agricultural pests cannot overwinter in Canada and the annual populations each summer are the result of immigration. In most years densities are low but sporadically there are major outbreaks resulting in serious economic losses. Currently, the detection of potential epidemics is based on pheromone trap catch data in the spring, which leaves a very short window for farmers to intervene if there are high numbers of immigrants. It is accepted that immigrant moth species originate from the USA but we are unsure of whether they originate from one geographic source area every year or if it varies considerably between years. Recent advancements using stable isotopes as endogenous markers offers a new approach to more effectively address certain questions about insect migration. I used the true armyworm, Mythimna unipuncta (Haworth), a spring immigrant into Canada to determine the validity of using stable hydrogen isotope measurements from wing chitin (δ2Hw) to infer the natal origin of adults captured in London. I first examined the isotope profiles of moths captured from April to October in 2016, and the results provide strong evidence that the moths captured in spring are immigrants, while adults captured in summer and fall are generally locally derived populations. Furthermore, data from moths captured in Texas early in the fall of 2012 were of northern origin, confirming the hypothesis of a return fall migration. I then compared the δ2Hw values of individuals captured in London throughout four years, 2008, 2013, 2015, and 2016. There was considerable intra- and inter-year variability, and while stable isotopes clearly provide insight into patterns of insect migration, significantly more data are required to refine the model and to allow greater precision when assigning the geographic origin of individuals. Furthermore, including information on other stable isotopes, such as carbon or nitrogen, could be used to determine whether immigrants come from natural or agroecosytems.
Doward, Kyle, "Migratory movements of the true armyworm (Mythimna unipuncta) (Haworth): An investigation using naturally occurring stable hydrogen isotopes" (2018). Electronic Thesis and Dissertation Repository. 5364.