Dataset of observations of Trichocera maculipennis (Diptera) in Navarino Island (Cape Horn Biosphere Reserve), Chile

During the 2022/23 austral winter, large swarms of Trichocera (Saltrichocera) maculipennis Meigen, 1818 (Diptera: Trichoceridae) were observed around house roofs in Puerto Williams (Navarino Island, southern Chile, 54°S). In January 2023, the presence of this species was also confirmed in Punta Arenas (53°S), with specimens collected within Chilean Antarctic Institute (INACH) warehouse facilities. No swarms or individuals have yet been observed in other urban or rural areas around Punta Arenas. Trichocera maculipennis is native to the Holarctic region and became established on King George Island (South Shetland Islands, Maritime Antarctic) over 15 years ago. The source of the King George Island population has not yet been confirmed, although a South American logistics hub is regarded as the most plausible. However, the species has not previously been reported from South America. Taxonomic and molecular identification techniques were used to confirm the identity of the new specimens obtained from Navarino Island and Punta Arenas. Preliminary observations of the fly’s habitat preferences and swarming behavior in Puerto Williams are provided, as well as comparisons in wing morphometrics between flies from Puerto Williams and King George Island. The fly's extensive distribution and high abundance in Puerto Williams are consistent with human-facilitated introduction and several years’ establishment. The most likely source of colonization event(s) to Puerto Williams is/are from an as yet unreported southern Chilean source population, with the new observations of small numbers of individuals in Punta Arenas being consistent with this. Such a source is also most plausible for King George Island. An alternative, less plausible, hypothesis is of ‘back transfer’ from King George Island to continental South America, although this does not give a clear direct link with Puerto Williams. These new observations highlight the urgent need for survey work particularly around human settlements in the Cape Horn archipelago and elsewhere in southern Patagonia and Tierra del Fuego, to better understand the invasive potential and possible routes for colonization of this species. These findings emphasize the importance of implementing robust management strategies and biosecurity measures, particularly during transportation between logistical hubs in southern South America and the remote areas of the Cape Horn Biosphere Reserve and Antarctica.