Abstract

Neighboring plants can influence a plant’s likelihood of receiving insect damage, and this may depend on how closely related the plant species are and the number of shared herbivores.

Based on preliminary field observations at local field sites around Miami University, three plant species in the Solanaceae family—Solanum carolinense, Physalis longifolia, and Physalis heterophylla—have different levels of herbivory when they co-occur versus when occurring alone. These three species receive leaf damage from both generalist and specialist herbivores, including the specialist Solanaceous moth herbivore, Manduca sexta. 

In order to better predict how insect damage is distributed in the field, we used greenhouse assays to examine differences in larval growth rate and M. sexta feeding preferences on leaves of these three host plant species. The results of feeding trials on individual leaves of these species indicated that M. sexta had a lower 24-hour growth rate when feeding on P. longifolia compared to S. carolinense and P. heterophylla. These results suggest that P. longifolia is more resistant to M. sexta herbivory. When given a leaf of each species in a 24-hour 3-way preference assay, M. sexta larvae mostly avoided P. longifolia and showed a preference for P. heterophylla and S. carolinense, with no preference between the two. With these results, the expected outcomes of upcoming summer 2025 field assays are that P. longifolia will receive lower levels of herbivory when co-occurring with S. carolinense and P. heterophylla, while these two species will show higher levels of herbivory when occurring alone in the field.  

Research Questions/Introduction

The level of insect damage (herbivory) a plant receives can be influenced by the identity and relatedness of neighboring plant species as well as the number of shared herbivores. Based on preliminary observations at field sites near Miami University, three Solanaceous plant species—Physalis longifolia, Physalis heterophylla, and Solanum carolinense—have different levels of leaf herbivory when co-occurring versus occurring alone (MK Huddleston, personal observation, 2024).

To better understand factors influencing the distribution of insect damage across host plant species, we conducted greenhouse assays measuring larval growth and feeding preferences of Manduca sexta, a specialist moth herbivore commonly found in the field.

Methods

• Plants were grown in the greenhouse at The Conservatory at Miami Hamilton from field-collected seeds of Physalis longifolia, Physalis heterophylla, and Solanum carolinense.

No-choice Feeding Assays

• Individual M. sexta larvae were placed in containers with a single leaf from one of the three Solanaceous species (N = 12 plants per species). 

• Larval weights were recorded before and after a 24-hour feeding period. Larval growth rates were calculated as                            log(final mass/initial mass) and averaged over two larvae per plant.

Choice Assays

• Individual leaves of the three plant species were placed equidistant from one another in circular arenas.

• One M. sexta larvae was placed in the middle of each arena and feeding choice was recorded after 24 hours                                        (N = 43 three-way choice trials). 

Conclusions

• These results suggest that P. longifolia is more resistant to M. sexta herbivory.

• In our summer 2025 field assays, we predict that P. longifolia will have lower levels of herbivory when co-occurring with S. carolinense and P. heterophylla, while these two species will likely have higher levels of herbivory when occurring alone.