Time-lagged intraspecific competition in temporally separated cohorts of a generalist insect
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Competition can have far-reaching consequences for insect fitness and dispersion. Time-lagged interspecific competition is known to negatively affect fitness, yet time-lagged intraspecific competition is rarely studied outside of outbreak conditions. We tested the impact of competition between larval cohorts of the western tent caterpillar (Malacosoma californicum) feeding on chokecherry (Prunus virginiana). We reared larvae on host plants that either had or did not have feeding damage from tent caterpillars the previous season to test the bottom-up fitness effects of intraspecific competition. We measured host-plant quality to test potential mechanisms for bottom-up effects and conducted field oviposition surveys to determine if female adult tent caterpillars avoided host plants with evidence of prior tent caterpillar presence. We found that time-lagged intraspecific competition impacted tent caterpillar fitness by reducing female pupal mass, which is a predictor of lifetime fitness. We found that plants that had been fed upon by tent caterpillars the previous season had leaves that were significantly tougher than plants that had not been fed upon by tent caterpillars, which may explain why female tent caterpillars suffered reduced fitness on these plants. Finally, we found that there were fewer tent caterpillar egg masses on plants that had tent caterpillars earlier in the season than plants without tent caterpillars, which suggests that adult females avoid these plants for oviposition. Our results confirm that intraspecific competition occurs among tent caterpillars and suggests that time-lagged intraspecific competition has been overlooked as an important component of insect fitness.
KeywordsPlant-mediated competition Amensalism Lepidoptera Malacosoma californicum Prunus virginiana
We thank Boulder and Jefferson Counties for funding and for their assistance on this project by issuing research permits. We also thank Robin Tinghitella, Julie Morris, Deane Bowers, the Murphy Lab Group, the University of Denver Organismal Biology Group, two anonymous reviewers, and the editor Jessica Forrest for their helpful comments on earlier versions of this manuscript.
Author contribution statement
EEB and SMM designed the experiments. EEB preformed the experiments, analyzed the data, and wrote the first draft. EEB and SMM wrote and edited the manuscript. Both authors gave final approval on the manuscript.
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