John T. Lill

My research interests focus on the ecology and evolution of plant-herbivore interactions. More specifically, I am interested in understanding the joint impacts of host plant traits and natural enemies (insect predators and parasitoids) on insect herbivore life history traits, behavior, population dynamics, and host plant ranges. Most of the abundant literature in this field has focused on single trophic level interactions (i.e., between insect herbivores and their host plants or between insect herbivores and their natural enemies) and has failed to adequately address the complex multi-trophic level interactions thought to characterize both natural and agricultural systems. Along with students, I am also investigating the effects of climate change on species interactions.

Evolutionary Ecology of Tritrophic Interactions

I investigate how seasonal changes in host plant quality and the risk of attack from natural enemies jointly shape the diet breadth, behavior, phenology, and life history traits of Lepidoptera. Many species of Lepidoptera exhibit wide variation in the timing of critical interrelated life cycle events (egg hatch, larval feeding, diapause), yet the genetic basis of and the fitness consequences for individual variation in these traits are poorly understood. This information is essential to understanding the potential role of natural selection in shaping insect morphology, behavior, and life history. Over the last decade, I have used three main systems, slug caterpillars (Limacodidae), fall webworms (Erebidae) and silver-spotted skippers (Hesperiidae), to experimentally investigate the ecological consequences of feeding on alternative host plants.  

Periodical Cicadas

Together with my long-term collaborator, Dr. Martha Weiss (Georgetown University), and my former postdoctoral associate, Dr. Zoe Getman-Pickering, we have been investigating the ecological impacts of the 2021 Brood X periodical cicada emergence on the trophic dynamics of a local forest food web. The goal of this research is to document the direct and indirect effects of a massive pulse of insect biomass on the trophic interactions and resulting population dynamics of insectivorous birds, caterpillars, parasitoids, and plants in a local oak forest.

Arthropod Community Ecology

I have been involved in several projects that have a common goal: to understand the role that species interactions play in structuring the arthropod communities associated with different tree species.

Leaf shelters. In my collaborative research with Dr. Robert Marquis (University of Missouri-St. Louis), we demonstrated that leaf-tying caterpillars on white oak (Quercus alba L.) act as physical ecosystem engineers by constructing habitats (leaf shelters) that are subsequently colonized by an array of other leaf-tiers, non-tying herbivores, scavengers, and predators. The results of this study indicated that both the abundance and composition of the oak arthropod fauna changed dramatically when leaf shelters were experimentally removed. Recent work in my lab has focused on testing for priority effects on the community assembly process and examining competitive interactions among leaf-tying caterpillars within leaf ties.  I am looking for students interested in ecosystem engineering and arthropod community ecology who might be interested in further exploring this study system.

Induced responses. Early-season damage has been shown to induce changes in various plant traits including chemistry, morphology, and phenology. I am interested in how early-season defoliation by eastern tent caterpillars (Malacosoma americanum) influences the abundance and composition of leaf-chewing herbivores occupying black cherry trees (Prunus serotina) later in the season.

Species Interaction Webs. Having spent the last two decades rearing large numbers of wild-collected herbivores from the field, I am excited to begin constructing and analyzing the structure of plant-herbivore-natural enemy interaction webs that include both parasitoids and arthropod predators.

Climate Change

Research into the effects of climate change on species distribution and range has moved beyond single-species studies to focus on species interactions.  Recent research in my lab has focused on experimentally examining the effects of climate warming on the phenology of spring-feeding folivores (eastern tent caterpillars) and their egg parasitoids, as well as the fitness consequences of asynchrony for both hosts and parasitoids. My recently graduated Ph.D. student, Ryan Spahn explored how experimental warming altered plant-caterpillar-parasitoid interactions in Brassica agroecosystems.