Top-down cascading effects of seed-feeding insects and their parasitoids on plant responses and early season herbivores

Authors: CUNY, MAXIMILIEN - Neuchatel University - Switzerland; LA FORGIA, DIANA - Neuchatel University - Switzerland; DESURMONT, GAYLORD - European Biological Control Laboratory (EBCL); GLAUSER, GAETAN - Neuchatel University - Switzerland; BENREY, BETTY - Neuchatel University - Switzerland

Submitted to: Functional Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/2022
Publication Date: 4/7/2022
Citation: Cuny, M.A., La Forgia, D., Desurmont, G., Glauser, G., Benrey, B. 2022. Top-down cascading effects of seed-feeding insects and their parasitoids on plant responses and early season herbivores. Functional Ecology. 00, 1-13. https://doi.org/10.1111/1365-2435.14049.
DOI: https://doi.org/10.1111/1365-2435.14049

Interpretive Summary: Seed herbivores are insects that specialize in feeding on the seeds of plants. Sometimes seeds can withstand some damage and still germinate, but it depends on the extent of the damage. Parasitoids are insect that attack insect herbivores, stopping their development before it is completed. Here we show that seed herbivores that attack Lima bean decrease the germination success of the seeds, but seeds that are not too damaged actually germinate faster than undamaged seeds. In addition, a parasitoid that attacks the seed herbivore decreases the quantity of damage done on individual seeds, increasing the likelihood of a seed to withstand the attack of an herbivore. This research shows the importance of seed herbivores in plant populations dynamics and the importance of natural enemies such as parasitoids in regulating the impact of herbivores.

Technical Abstract: The effects of seed-feeding insects on plant populations extend beyond seed set reduction. Seeds affected by herbivory may still be able to germinate and thus contribute to seedling recruitment and subsequent insect-plant interactions. In this context, the action of natural enemies such as parasitic wasps may reduce the impact of seed predation on plant fitness. Here, we showed that bruchid seed predators had an overall negative impact on germination success of wild Lima bean seeds, which may have important consequences for the constitution of soil seed banks and population stability. Additionally, plants originating from damaged seeds suffered a decrease in performance and resistance against generalist herbivores. These seed-feeding insects season-long negative effects may play an important role in intraspecific variation of plant defense, which may in turn affect herbivorous insect populations. Finally, parasitoids significantly increased plant fitness by attenuating most of bruchids immediate and season-long detrimental effects.