Biology subjects

Rousseau, R.

Publications and source records attributed to Rousseau, R..

3 recordsLinked to original sources

bioRxiv2025

An integrative field and modelling study of the bottom-up, top-down and indirect effects of native species on invasive insects and their biological control : the case of the worldwide chestnut tree pest, Dryocosmus kuriphilus, in the French Eastern Pyrenees

Insect pests invading an ecosystem typically face various forces regulating their population growth and spread. While the resources they feed on and their natural enemies have bottom-up and top-down effects on insect invasion success, other native species, more distant in the local trophic network, can have indirect effects on the ecosystems susceptibility to invasion. Resolving the mechanisms underlying these naturally occurring indirect interactions and their impact on invasion dynamics is a key challenge toward risk assessment and environmental management. In this contribution, we investigated how indirect interactions with several native species contribute to variations in Dryocosmus kuriphilus infestation level in 24 natural chestnut tree populations of the French Eastern Pyrenees. This invasive gall-forming hymenopteran parasites cultivated and wild Castanea sativa stands, and its hymenopteran parasitoid, Torymus sinensis, is world widely used as a control agent. We combined ecological, molecular and statistical approaches to quantify the effects of Quercus pubescens, Fagus sylvatica and the parasitic fungus Cryphonectria parasitica on the pest oviposition rate (effect i), its host detection capacity (effect ii), the production of native parasitoids (effect iii) and in providing alternative hosts for the control agent (effect iv). The integration of these effects into a specifically designed D. kuriphilus - T. sinensis dynamical model, provided clear evidence of the quantitative impacts of Q. pubescens and C. parasitica on the invasion potential of the pest and its biological control.

ecology↗

bioRxiv2025

Source-sink dynamics explains the co-existence of the invasive pest Dryocosmus kuriphilus and its biological control agent Torymus sinensis across French Eastern Pyrenees.

Biological invasions have become a major cause of ecological and economic costs in many (agro-)ecosystems. Understanding the regulation of their local dynamics by resources limitation and natural enemies, i.e. bottom-up and top-down determinants, through inherently heterogenous environments stands as a critical challenge to provide efficient risk assessments and management measures. Here, we propose an unprecedented integrative modelling approach based on a spatial extension of the seminal Nicholson-Bailey model parameterized by a comprehensive field assessment of all the bottom-up and top-down determinants affecting the spread of a worldwide invasive pest, Dryocosmus kuriphilus, in 23 natural chestnut tree populations of the French Eastern Pyrenees. The analysis of the within-site dynamics allowed to quantify the spatial heterogeneity in the two types of regulatory forces across the study area, and to identify 16/23 sites where the control agent, Torymus sinensis, is expected to persist and control the invasive pest. The comparison of these predictions with the levels of D. kuriphilus hyperparasitism by T. sinensis, observed in all 23 forest sites, suggested hidden source-sink dynamics within the study area. The investigation of such dynamics by the coupling of any two local dynamics predicted in each of the 23 sites showed that i) low rates of D. kuriphilus and T. sinensis dispersal lead to a synchronization to the dynamic expected in the site with the highest chestnut tree frequency, while ii) higher rates typically allow for a stable equilibrium. Those predictions provide quantitative evidences for the persistence of T. sinensis in the 7 predicted sink sites sustained by its local 16 source populations. Dispersal then tends to homogenize the local efficiencies of the control agent while decreasing its global impact on the pest invasion. Overall, this pioneer spatial modelling of D. kuriphilus - T. sinensis interaction suggests that both introduced species are likely to persist in the European forest environments in a co-invasion scenario.

ecology↗

bioRxiv2024

Unravelling the bottom-up and top-down control of a worldwide chestnut tree pest invader through integrative ecological genomics

Biological invasions have become a major threat to all agro-ecosystems. Estimating the bottom-up and top-down forces controlling the spread of invasive insects is a key challenge to lessen their burden on crops, forestry, and biodiversity. We combined ecological, metabarcoding and population genomics analyses with an integrative modelling of the invasion of a global insect pest to identify the impacts of its chestnut tree resource, natural enemies and biological control agent in Eastern Pyrenees. The host tree frequency and genomic variation associated with common resistance pathways had effects 4-10 times greater than the native hyperparasite community on the pests invasion potential (R0). The >90% field rates of hyperparasitism by the control agent and the associated 80% reduction in pest infestation are likely to be deceptive as our modelling consistently predicts their long-term coexistence with periodic re-emergences. Such a persistent co-invasion scenario calls for a thorough assessment of the impact of these global pest and control agent on natural forest ecosystems.

systems biology↗