Patterns and causes of oviposition in monarch butterflies: implications for milkweed restoration
Effective habitat restoration requires an understanding of species habitat preferences and the associated mechanisms driving those preferences. We examined the patterns and causes of oviposition preference in the monarch butterfly, a rapidly declining species, in southwestern Ontario at multiple spatial scales. Oviposition preference was dependent on both the size and density of the milkweed patch, as well as landscape type. Small (<16 m2), low-density (0-2 milkweed per m2) milkweed patches in agricultural landscape had the highest egg density compared to all types of milkweed patches in non-agricultural and roadside landscapes. Medium-sized patches had the highest predator abundance. Variation in the diversity of predators and parasitoids, abundance of parasitoids, and occurrence of parasites of monarch eggs and larvae did not appear to coincide with preferred egg laying habitats. Our results have important implications for restoring milkweed as an approach to counteract monarch butterflies declines.