# Landscape Genomics and Evolutionary History of Megamelus scutellaris, a Biocontrol Agent of the Invasive Water Hyacinth (Pontederia crassipes)

## TL;DR

This study explores the genetic diversity and evolutionary history of a biocontrol insect in South America to improve its use in controlling invasive plants in new regions.

## Contribution

The study combines genomic and environmental data to reveal how climate and geography shaped the genetic structure of M. scutellaris.

## Key findings

- Three genetic lineages of M. scutellaris are linked to river basins and ecoregions.
- Population divergence is associated with Pleistocene climate shifts and Holocene splits.
- Genetic differentiation is strongly tied to climatic variation and environmental resistance.

## Abstract

Understanding the evolutionary history of biological control agents in their native ranges is crucial for improving their selection, establishment, and performance across environmentally diverse regions. Phytophagous insects that specialize on aquatic plants offer particularly valuable models, as their evolutionary trajectories may be shaped by a combination of climatic variation, host plant availability, and the fragmented nature of aquatic habitats.
Megamelus scutellaris
is a monophagous planthopper native to South America that has been introduced into the United States and South Africa as part of biological control programs targeting the highly invasive aquatic plant, Pontederia crassipes. In this work, we combined nuclear SNP and mitochondrial sequence data to investigate the genetic structure, demographic history, and environmental drivers of population divergence in
M. scutellaris
across its native range in Argentina and Paraguay. We identified three main genetic lineages broadly associated with major river basins and ecoregions. Demographic modeling supported an early divergence, likely linked to Pleistocene climatic shifts and hydrological changes, followed by a more recent split dated to the early Holocene. Contemporary gene flow was asymmetric and varied in magnitude among lineages, reflecting differences in connectivity and environmental conditions. Lastly, landscape genomic analyzes revealed a strong association between genetic differentiation and climatic variation, supporting models of isolation by environment and resistance. These findings highlight the role of evolutionary and ecological processes in shaping the genetic landscape of
M. scutellaris
and provide key insights for selecting source populations better suited to different environments in introduced regions.