Resource-seeking and oviposition behaviors in the monarch butterfly: Implications for habitat restoration across an agricultural landscape

Abstract

Habitat loss and fragmentation are major threats to wildlife biodiversity globally. Facilitating movement across such fragmented landscapes remains an ongoing challenge for wildlife conservation. Overcoming this challenge is particularly important for vagile insect species that search throughout a landscape for necessary resources. One such species, the North American monarch butterfly (Danaus plexippus), has faced substantial declines over recent decades. Extensive loss of monarch habitat across the U.S is implicated as a major contributor to population declines. Restoration of an estimated 1.3 to 1.6 billion stems of milkweed, the monarch’s obligate larval host species, across the breeding range of the North Central U.S is needed for recovery of the eastern North American population. Achieving this goal will require major restoration efforts into under-utilized, agriculturally dominated landscapes. Areas including, Conservation Reserve Program lands, rights of way and crop field margins are needed to reach habitat restoration goals. While the use of these acres is critical to ensuring enough milkweed stems are established, the ability of monarchs to detect these habitat patches and the potential exposure of monarchs to insecticides in agriculturally-adjacent areas has raised concerns about its benefit. Numerous risk assessments have been performed to understand monarch exposure risk in these areas, however, behavioral assays as to whether reproductive females will lay eggs on milkweed exposed to insecticides, has not been investigated. An understanding of the monarch’s movement and resource utilization patterns across such landscapes is therefore necessary to ensure habitat restorations that most effectively contribute to population recovery. I investigated these issues through two experiments. The first focused on testing the distance at which monarch butterflies can perceive habitat resources. For the second, I investigated whether egg-laying female monarchs can discriminate against milkweed exposed to a widely used neonicotinoid insecticide, imidacloprid. My findings indicate that resource-motivated monarchs display strong upwind orientation, regardless of resource presence, and that females do not discriminate against imidacloprid-treated stems, even at concentrations exceeding field-realistic rates. The implications of these findings for monarch conservation are discussed.