Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Biology

Supervisor

McNeil, Jeremy N.

Abstract

The wings of true armyworm (Mythimna unipuncta) are metabolically inactive tissue and as their isotopic profiles are determined by resources obtained during larval development, they provide information on natal origin of immigrants. The majority of female immigrants are mated so could the isotopic profiles of spermatophores dissected from her reproductive tract provide information about the natal origin of her mates? However, as spermatophores are produced by metabolically active male accessory glands and could use resources obtained from larval and adult feeding I conducted experiments to determine the relative importance of these two dietary sources on the isotopic profiles of spermatophores. Laboratory results showed H from both dietary sources affect the isotopic profiles of spermatophores so they provide no reliable information about the origin of the female’s mates. However, this could be a model system to examine turnover rates of resources obtained during larval and adult stages in a migratory species.

Summary for Lay Audience

When habitat quality declines, insect species either enter a dormant state until conditions improve or migrate to more favorable sites. The true armyworm moth, Mythimna unipuncta, is a seasonal migrant, passing the winter in southern United States and moving northward in summer to avoid high temperatures at overwintering sites. Populations of this species occur annually in eastern Canada and may in some years cause considerable crop losses. However, we know little about the natal origin of these immigrants or if they come from the same site every year. These questions are now being addressed using naturally occurring chemical signatures that are based on stable isotopes of H and C (depicted as 𝛿2H and d13C) in wings.

The majority of spring immigrant females captured in London, ON, are mated, as evidenced by the presence of one or more spermatophores in her reproductive tract. The spermatophore, a structure containing sperm and nutrients, is transferred from the male to the female at the time of mating. While wing tissue composition does not change after emergence and is a reflection of larval diet, the spermatophore is formed at least several days after adult emergence so its isotopic profiles could be influenced by both larval and adult dietary sources.

Controlled laboratory experiments using individuals reared on different combinations of control and 𝛿2H / d13C spiked larval and adult diets, found that (i) both larval and adult diets affect the isotope composition of spermatophores, and (ii) while the spermatophores are formed within the female’s reproductive tract her contribution to the spermatophore’s isotope profile was small. Overall, my findings suggest that the isotopic profiles of spermatophores do not provide any reliable information about male natal origin due to the effects of adult diet. However, this system could be used to examine the turnover of larval and adult dietary foods in metabolically active tissues, and future studies should include factors such as sustained flight and male mating history on spermatophore isotope composition.

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