Author: Alana WilcoxPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
The eastern North American monarch butterfly (Danaus plexippus) has undergone large-scale declines over the last two decades and no clear single cause to explain the decline has yet been identified. In Chapter 2, I assess the contribution of potential threats on eastern population of monarch butterflies. I found that declines in suitable environmental conditions and overwintering and breeding habitat loss are likely the leading threats to the eastern population of monarch butterflies, but that risks imposed by contaminants, predation, and parasitism may also contribute. Agrochemical exposure, specifically from neonicotinoids, is a leading concern due to the potential lethal and sublethal effects on development and behaviour on non-target species, such as monarchs. I also conducted two experimental studies on monarchs reared on milkweed grown in soil treated with field-realistic levels of clothianidin at a low (15 ng/g of clothianidin) or high (25 ng/g of clothianidin) dose levels, or in a control (0 ng/g of clothianidin). In Chapter 3, I provide experimental evidence that late instar caterpillars reared on clothianidin-treated milkweed were smaller and weighed less than controls. Nonetheless, clothianidin treatment was also associated with larger adult monarch butterflies, but did not influence the egg size or the number of eggs laid. In Chapter 4, I show that clothianidin did not influence orientation, vector strength, or the rate of travel of adult migratory monarch butterflies. Lastly, in Chapter 5, I investigate whether captive rearing, often used as a conservation and educational tool for this species, influences migratory behaviour. While captive-reared migratory monarchs tested in the flight simulator did not show a normal directional flight response, individuals released in the wild and radio-tracked showed proper orientation and flew in a southward direction towards their Mexican overwintering grounds. Collectively, my thesis contributes to a broader understanding of the potential causes underlying declines in monarch butterflies, most notably from neonicotinoids, and offers important insight into viability of captive rearing as an important conservation and educational tool.