Crowding reduces per-capita parasite infection risk in a butterfly host

Crowding can result in greater disease transmission, yet crowded hosts may also remove infectious propagules from the environment, lowering the encounter rate and infectious dose of conspecifics. We combined experimental and modeling work to examine the impact of crowding of butterfly larvae on per-capita infection risk by a protozoan that is transmitted via the larval food plant, and the resulting infection load in adult butterflies. We reared larvae at different densities and mimicked low and high doses of parasites. We modified an existing model to include effects of conspecific density on food (and thus parasite) consumption rate and infected adult mortality rate. Experimental work indicated that infection rates on plants with ten caterpillars were reduced by at least 50% compared to single caterpillars. High density reduced individual infection risk and parasite load and extended the lifespan of all hosts, as crowded hosts removed parasites from the environment. Modeling suggested ..., , , # Crowding reduces parasite infection risk and virulence in a butterfly host

[https://doi.org/10.5061/dryad.8sf7m0czp](https://doi.org/10.5061/dryad.8sf7m0czp)

## Description of the data and file structure

This dataset includes the necessary data and code to reproduce the analyses in the manuscript entitled \"Crowding reduces parasite infection risk and virulence in a butterfly host\". In this study, we combined experimental and modeling approaches to investigate how crowding of butterfly larvae affects their infection risk from a protozoan parasite transmitted through the larval food plant, as well as the resulting infection load in adult butterflies. We reared larvae at varying densities and simulated different transmission rates by exposing them to low and high doses of parasites. An existing model was modified to account for the effects of conspecific density on food and parasite consumption rates, as well as infected adult mortality. All missing data are represented as NA.

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