Ongoing invasions of old-growth tropical forests: establishment of three incestuous beetle species in southern Central America (Curculionidae: Scolytinae)

Old-growth tropical forests are widely believed to be immune to the establishment of alien species. Collections from tropical regions throughout the world, however, have established that this generalization does not apply to inbreeding host generalist bark and ambrosia beetles. Scolytine saproxylophages are readily spread by shipping, inbreeders can easily establish new populations, and host generalists readily find new breeding material, apparently regardless of stage of forest succession. Consequently, many inbreeding scolytines are globally distributed and abundant in all forest types, often being among the dominant species in their wood-borer communities. We report the recent introductions to lower Central America of two Old World inbreeding ambrosia beetles: Xylosandrus crassiusculus, which breeds primarily in smaller diameter trunks, small branches, and twigs, and Xyleborinus exiguus, which is apparently not size selective. We also document the establishment of Euwallacea fornicatus in the region, known previously from a single collection in Panama. Xylosandrus crassiusculus and E. fornicatus are notorious agricultural and forestry pests, as are several previously established alien species in the region. Studying the spread of species such as these three new arrivals into millions of years-old faunas could help us to understand if the saproxylic communities of old-growth tropical forests are peculiarly vulnerable to invasion.