Liana Greenberg

Insects reproduce in landscapes where they encounter plant toxins, climatic extremes, predators, and parasitoids. My thesis asks how butterflies and their egg‑parasitoid enemies navigate this maze and what those decisions reveal about their intertwined evolution of mating, oviposition, and mortality. Focusing on Pieris butterflies and Trichogramma wasps, I combine broad literature syntheses with targeted experiments to trace how selection operates across life stages and trophic levels, and how today’s variation between and within species can reveal selection pressures from the past. In doing so, I treat each reproductive decision as the product of an ecological balancing act stretching from egg to adult and across generations.

I begin by developing a conceptual framework in which mating, oviposition, and enemy avoidance are inextricably entangled, between life stages and between herbivores (Pieris) and their enemies (Trichogramma). This opening review (Chapter 1) argues that the behaviour of mothers cannot be understood without simultaneously considering the sexual and natural selection imposed by their mates and their enemies.

Building on that foundation, Chapter 2 surveys how egg parasitoids locate hosts that are hidden, sparse, and short‑lived. This review explores how egg parasitoids use host- and plant-derived chemical cues to locate hidden host eggs. I show that cue use is used is highly variable across taxa and even among individuals, variation that reflects tuning to specific ecological contexts.

Chapter 3 narrows in on oviposition‑induced plant volatiles (OIPVs). This review focuses on oviposition-induced plant volatiles and shows that parasitoids use these reliably for long-distance host egg quality assessment. These reviews again emphasizes that cue-based strategies are context-dependent and labile.

The thesis then pivots to the butterflies themselves. Chapter 4 tests whether pierids can sidestep a potent plant defence—hypersensitive response‑like (HR) necrosis that kills their eggs. I found that all surveyed Pieris species lay eggs on HR-expressing leaves, and that HR-like cell death was frequently triggered, with no evidence of behavioral counter-adaptation in our sampled populations. In contrast, non-Pieris pierids preferentially oviposit on host tissues or species that do not express HR. These findings suggest that HR-like egg-killing remains an effective plant defense against Pieris butterflies, and that, at least in the populations studied, no clear behavioral counter-adaptations have evolved. This points to potential asymmetry in the evolutionary arms race and underscores the value of examining microevolutionary variation within species to detect emerging or context-dependent strategies of resistance.

In Chapter 5, I scale down to the microscopic architecture of eggs. This chapter investigates egg pore morphology in Pieris species and populations along a climatic gradient. I found that egg pores, aeropyles and micropyles that are key to gas exchange and fertilization, differed more between P. napi populations than between Pieris species. These traits correlated with the climates of origin rather than with egg size or phylogeny, suggesting local adaptation to abiotic stressors. This chapter highlights that even microscopic traits exhibit adaptive variation within species and may evolve rapidly in response to environmental pressures.

Chapter 6 revisits butterfly mating and incorporates the threat of egg parasitoids and predators as drivers of mating behaviors. This chapter focuses on Pieris post-mating odors and reframes them not only as anti-aphrodisiacs but as multifunctional ecological signals. These odors repel males, but also attract parasitoids, deter predators, and affect oviposition decisions. I found substantial variation within and among species in odor profiles, variation that tracks parasitoid pressure across populations rather than mating frequency or latitude. Disruption of odor detection altered oviposition behavior and susceptibility to parasitoids. These findings show how complex selection across interactions and environments can maintain chemical diversity within species.

Finally, Chapter 7 synthesizes these strands, arguing that what looks like maladaptive maternal behavior under a narrow lens often proves wise when viewed through the full, tangled web of selection. Maternal behavior in insects, and the (mis)alignment of preference and performance, reflects a dynamic compromise among competing pressures. These strategies are not static nor uniform. Variation within and between species, in behavior, morphology, and chemical signaling, offers a window into evolution in action, revealing the selective pressures insects face and the constraints they navigate. Looking ahead, this synthesis identifies several key directions for future research.

By combining reviews with novel data, and by highlighting intra- and interspecific variation, this thesis contributes to a more nuanced understanding of insect reproductive evolution. It shows that oviposition traits are rich with evolutionary complexity, making them ideal traits for studying adaptation, constraint, and trade-offs in a changing world. Ultimately, the findings reinforce a central message: mother does know best, and what she knows is shaped by the evolutionary legacy of diverse enemies, changing environments, and complex trade-offs.