Genetic insights into the first detection of Paracoccus marginatus (Hemiptera: Pseudococcidae) in Australia.

Species spread in a new environment is often associated with founders' effect, and reduced effective population size and genetic diversity. However, reduced genetic diversity does not necessarily translate to low establishment and spread potential. Paracoccus marginatus Williams and Granara de Willink is a polyphagous pest that has invaded 4 continents in around 34 years. It was first detected in the Northern Territory, Australia in July 2023. Following this, we collected 45 specimens from 20 suburbs across 3 regions. Using mitochondrial cytochrome oxidase I and nuclear ribosomal RNA genes (18S and 28S), we examined molecular diagnostics robustness, genetic diversity, haplotype network, and demographics (Tajima D) of the recently detected Australian population. We compared our samples with publicly available sequences deposited on GenBank. All 3 genes were suitable for molecular diagnosis with a 100% identity score. For all 3 genes, we found low nucleotide diversity, haplotype diversity, and negative Tajima D in the newly detected P. marginatus population, suggesting a recent single founder event by a few individuals. Comparing our study's sequences with global sequences showed low haplotype diversity, nucleotide diversity, and Tajima's D, suggesting that despite low genetic diversity at the 3 genes, P. marginatus has successfully invaded South America, Africa, Asia, and Oceania. Our study highlights the role of demographic and life history traits in the species' invasion success. We provide a baseline dataset from the first detection of P. marginatus in Australia. Further analysis of the spread can provide insights into invasive species' adaptation in a novel environment.