Florivory is an alternative but suboptimal diet for an invasive leaf-feeding beetle

Authors: DESURMONT, GAYLORD - European Biological Control Laboratory (EBCL); BLANCHET, ARNAUD - European Biological Control Laboratory (EBCL)

Submitted to: Ecological Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2023
Publication Date: 3/22/2023
Citation: Desurmont, G., Blanchet, A. 2023. Florivory is an alternative but suboptimal diet for an invasive leaf-feeding beetle. Ecological Entomology. 1-4. https://doi.org/10.1111/een.13237.
DOI: https://doi.org/10.1111/een.13237

Interpretive Summary: The viburnum leaf beetle is an invasive species in North America native to Eurasia. It only feeds on viburnum shrubs, which are popular as ornamental plants and widespread in forests. Larvae and adult defoliate viburnums in natural and managed landscapes, leading to shrub death after repeated complete defoliations. This pest also indirectly impacts the fauna relying on viburnum fruits as a food source in American forests and has led to a decrease in populations of several resident birds. Viburnum leaf beetle larvae feed primarily on young viburnum leaves. However, larvae have been observing persisting in the field in Europe in the absence of young leaves. Here we tested the hypothesis that larvae can survive feeding on viburnum flowers instead of leaves. Results showed that larvae can indeed develop to the adult stage feeding only on flowers, but this diet is subpar compared to young leaves and leads to higher larval mortality and smaller adult size. This result shows that this insect can change its feeding strategy when experiencing a shortage of its normal food. Such dietary flexibility may allow it to adapt to novel host plants more quickly in its invasive range. This study has direct implications for pest management: the knowledge that larvae can 1) use and hide within flowers and 2) can to a certain extent survive in the absence of new leaves should be taken in consideration when devising pesticide application strategies.

Technical Abstract: 1. The viburnum leaf beetle (VLB) Pyrrhalta viburni is a specialist leaf-feeding insect native to Eurasia and invasive in North America. VLB is a univoltine species: eggs hatch during springtime, typically in synchrony with the burst of new leaves of Viburnum plants, and larvae feed on young leaves to complete their development. 2. In the southern extent of its native range, VLB occurs on Viburnum tinus, an evergreen host plant that does not necessarily produce new leaves in the spring. Here we explored the idea that VLB larvae could potentially survive on V. tinus in the absence of new leaves by feeding on V. tinus inflorescences, which are consistently produced during springtime. 3. Under laboratory conditions, VLB larvae could complete their development by feeding solely on V. tinus inflorescences, with a negative impact on performance: larval survivorship to adult stage and adult mass decreased and developmental time increased when larvae fed on inflorescences compared to young leaves. Survivorship was null when larvae were fed old V. tinus leaves. 4. These results illustrate the dietary flexibility of VLB, which may have helped it to adapt to novel host plants in North America. Exploring the drastic differences in larval performance between young leaves, old leaves, and inflorescences may lead to new developments in pest management research.