The southward expansion of Anopheles farauti (Diptera: Culicidae) in Australia: a genetic and ecological niche modeling investigation.

The mosquito Anopheles farauti Laveran (1902) is a coastal malaria vector with a wide distribution throughout the Southwest Pacific. This species shows strong population genetic structure across Australia, New Guinea, and the Solomon Archipelago. In Queensland, Australia, its southern range limit has been the 21° latitude but, in 2023, it was detected in mosquito surveys 300 km further south, at 23° latitude. Additional collections undertaken in 2024 suggested that a population of An. farauti had established at this new southern limit. Sequencing of the mitochondrial cytochrome oxidase I (COI) gene revealed a single haplotype shared by all individuals, matching the nearest northern population. To investigate the suspected southward range expansion of An. farauti in Queensland, we performed machine learning ecological niche modeling using both MaxEnt and Random Forest approaches using historical collection data and WorldClim bioclimatic variables from that period. The model output indicated that the 23° latitude in Queensland is within the species' projected suitability range and identified temperature-related factors as the primary drivers of its distribution in Queensland. We hypothesize that the prolonged La Niña (2020 to 2023), and the 2023 global marine heatwave, which drove warmer ocean and coastal ambient temperatures, facilitated the latitudinal expansion of An. farauti in Queensland.