When and where to lay your eggs

A substantial portion of the millions of insect species on earth are phytophagous, and the great majority of these species is oviparous—they reproduce through larvae or nymphs that hatch from eggs laid by female insects on specific host plant species. When a female insect lays their eggs, however, she is repeatedly faced with the decision problem of ovipositing on lower-quality host plants or waiting out for higher-quality ones. Since her offspring develop differentially well depending on which host plant species they are raised upon, a mother’s oviposition decisions carry significant fitness costs and benefits. At the same time, females are pressed for time and for eggs in every oviposition decision they make—if they are too picky, they may run out of lifetime before all eggs have been laid and thus become “time-limited”; if they are not choosy enough, they may run out of eggs before their lives are over and thus become “egg-limited”. This thesis employs diverse theoretical approaches to examine how decision problems arise during the oviposition of phytophagous insects and how they are solved by female insects in their oviposition strategies. I begin by using analytical optimization models to show how the well-known life-history trade-off between survival and reproduction may lead to widely varying evolutionarily stable levels of egg and time limitation, the quantitative details of which depend on the trade-off’s shape and parameters. These findings also demonstrate that, while the risks of both egg and time limitation need to be evaluated on a case-by-case basis, neither phenomenon can be safely ignored in evolutionary studies of strategic insect oviposition. I then employ more schematic models to examine whether partitioning the fitness costs and benefits of each oviposition decision into opportunity costs mediated by time and by eggs is a useful practice to analyze oviposition strategies. I find that, in general, schematic time and egg costs will have to be conceptualized with great care to deliver insightful results, and that detailed evolutionary models may therefore represent more fruitful tools to study strategic insect oviposition. After studying the basis of the insects’ oviposition decision problems, namely how egg and time limitation may come about, I examine how generalist oviposition strategies can evolve from more specialist ones. Since most insects are specialists, but since generalism is a necessary intermediate step in the many host switches that have occurred over evolutionary time, the evolution of generalism is of key interest in the oviposition of phytophagous insects. My results confirm that unreliability of host plant availability may lead females to become more generalist and include novel hosts in their diet breadths on which larvae develop less successfully than on ancestral hosts. Using a combination of optimization and population genetic models as well as individual-based simulations, I show that generalism only evolves under restrictive conditions if host availability varies spatially but more readily when it varies temporally. This is because spatial variation in host availability can lead to emergent source-sink dynamics which favor specialist oviposition strategies adapted to highly productive habitats with more-than-average high-quality hosts. Conversely, temporal variation in host availability favors generalist strategies that fare well also in times with lower-than-average high-quality hosts. I explore the latter scenario using a simulation study of the orange tip butterfly (Anthocharis cardamines), a species whose larvae are phenologically specialized on flowers and seeds but whose females are oviposition generalists. My results suggest that this oviposition generalism may indeed result from the larvae’s phenological specialism which reduces host availability because it shortens the time windows during which individual host plants are suitable for successful larval development. Taken together, the approaches presented in this thesis showcase the usefulness of different theoretical methods to examine strategic oviposition in phytophagous insects. The resulting findings have consequences for empirical studies of insect oviposition, for instance with regard to which factors insects include in their oviposition decisions or how insects respond to geographically varying host plant abundances. Moreover, I discuss