Abstract
Many herbivorous insects die of pathogen infections, though the role of plant traits in promoting the persistence of these pathogens as an indirect interaction is poorly understood. We tested whether winter leaf retention of bush lupines (Lupinus arboreus) promotes the persistence of a nucleopolyhedroviruses, thereby increasing the infection risk of caterpillars (Arctia virginalis) feeding on the foliage during spring. We also investigated whether winter leaf retention reduces viral exposure of younger caterpillars that live on the ground, as leaf retention prevents contaminated leaves from reaching the ground. We surveyed winter leaf retention of 248 lupine bush canopies across twelve sites and examined how it related to caterpillar infection risk, herbivory, and inflorescence density. We also manipulated the amount of lupine litter available to young caterpillars in a feeding experiment to emulate litterfall exposure in the field. Greater retention of contaminated leaves from the previous season increased infection rates of caterpillars in early spring. Higher infection rates reduced herbivory and increased plant inflorescence density by summer. Young caterpillars exposed to less litterfall were more likely to starve to death but less likely to die from infection, further suggesting foliage mediated exposure to viruses. We speculate that longer leaf life span may be an unrecognized trait that indirectly mediates top-down control of herbivores by facilitating epizootics.
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Data availability
The data and code are deposited on Dryad and Zenodo respectively. Pan, Vincent; Pepi, Adam; LoPresti, Eric; Karban, Richard (2023), The Consequence of Leaf Life Span to Virus Infection of Herbivorous Insects, Dryad, Dataset, https://doi.org/10.25338/B8PD2K.
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Acknowledgements
We thank Harry Kaya, Danielle Rutkowski, Vinay Mase, Michael Turelli, and Jenny Cory for helping with the identification of the virus, Neal Williams for sharing microscope equipment and freezer, Jay Rosenheim for sharing incubators and lab space, Claire Beck and Jasmine Daragahi for help with rearing caterpillars, Jackie Sones for aiding access to the Bodega Marine Reserve, the joint-insect ecology lab group at UC Davis for providing feedback, Hanna Kahl and Emily Meineke for commenting on our manuscript, and the anonymous reviewers for providing constructive comments.
Funding
VSP, AP, and RK were funded by NSF-LTREB (1456225) and an NSF-REU supplement (DEB-2018169). EFL was funded by start-up funds from Oklahoma State University.
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VSP, AP, and RK conceived the study and collected the data. VSP and AP conducted the analysis. VSP wrote the manuscript. AP, EFL, and RK provided editorial support. All authors contributed critically to the drafts and approved final publication.
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Communicated by Caroline Müller.
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Pan, V.S., Pepi, A., LoPresti, E.F. et al. The consequence of leaf life span to virus infection of herbivorous insects. Oecologia 201, 449–459 (2023). https://doi.org/10.1007/s00442-023-05325-w
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DOI: https://doi.org/10.1007/s00442-023-05325-w