# Investigating the Genetic Underpinnings of Ongoing Fall Armyworm (FAW) Range Expansion in Aotearoa New Zealand

## TL;DR

This study examines the genetic makeup of fall armyworm populations in New Zealand and other regions to understand their spread and resistance to insecticides.

## Contribution

The study provides new genomic data from the invasion front in Oceania and identifies insecticide resistance alleles in fall armyworm.

## Key findings

- New invasive fall armyworm populations in New Zealand conform to the population structure seen in Benin.
- Preliminary evidence suggests multiple introductions to New Zealand, increasing genetic diversity.
- Putative insecticide resistance alleles were detected in new samples, highlighting the need for ongoing monitoring.

## Abstract

Spodoptera frugiperda
(fall armyworm; FAW) is a major agricultural pest native to the Americas, with the first reported invasion of Africa in early 2016. Since then, FAW has spread rapidly across Africa and Asia before invading Australia (2020) and first being detected in Aotearoa New Zealand in February 2022. Here, we assessed the whole genomes of 34 novel FAW individuals along the invasion front (representing three new invasive populations from Cambodia, Australia, and New Zealand) with the largest publicly available global FAW genome dataset (n = 173), resulting in a dataset of 112 and 99 samples from the invasive and native range, respectively, to: (1) place the new invasive populations within the global invasion; (2) identify the potential geographic origin of the New Zealand invasion, including from a single or multiple incursion event; and (3) assess pre‐existing insecticide resistance potential at the invasion front. We confirm that these new invasions conform to the broad population structure of the initial invasive populations identified in Benin (West Africa), all of which belong to the invasive corn strain, as defined through previous triosephosphate isomerase (TPI) analysis and associated isolation from specific host plants. While we could not confidently assign the source population of the New Zealand invasion, we find preliminary support for a multiple introduction hypothesis in our data, which could contribute to increased genetic diversity within the New Zealand population. Further sampling is therefore required to fully characterise the origins of the New Zealand invasion. In novel samples, we detected putative insecticide resistance alleles previously reported in other invasive populations. These resistant loci should be tracked over time to understand the mechanisms enabling the invasion success of FAW in the Asia‐Pacific region. We emphasise that sharing of genomic resources between institutions and consortia is an essential first step in the control of this global invader.

We generated new genomic resources for the invasion front of fall armyworm in Oceania, confirming that the new invasions conform to the population structure initially identified in Benin. We also identified SNVs associated with insecticide resistance that should be a focus of future tracking of the invasion front and established populations.