Spotlight on the monitoring of the invasion of a carabid beetle on an oceanic island over a 100 year period

The flightless beetle Merizodus soledadinus, originating from the Falkland Islands, was introduced to the sub-Antarctic Kerguelen Islands. We compiled the existing information on ship visits and landings on these islands to confirm the introduction date of M. soledadinus. Using data available in the literature, in addition to collecting more than 2000 presence/absence records of M. soledadinus over the 1991-2018 period, we tracked changes of its abundance and geographical distribution. The range expansion of this nonflying insect was initially slow, but has accelerated over the past two decades in parallel to local increased abundances of the insect s populations. Human activities may have facilitated colonization of some localities by M. soledadinus which is now widely present in the eastern part of the Kerguelen archipelago. This predatory insect represents a major threat for the native invertebrate fauna; in particular, the wingless flies Anatalanta aptera and Calycopteryx moseleyi which are locally displaced and/or eliminated by the beetle. If no control measures, let alone eradication, are practicable, it is essential to limit the transport of this invasive insect along with human activities. Since 2006, the Kerguelen Islands have had the status of a nature reserve, making these results of significant interests for the management of this archipelago, and more generally, emphasizing the importance of long-term biomonitoring programmes for assessing and predicting changes in the distribution of invasive organisms. Strict biosecurity measures have now been established at the Kerguelen Islands, with even greater attention paid to visits to remote sites not yet colonized by M. soledadinus.