The Formosan subterranean termite, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), is primarily reported from subtropical and warm temperate regions, whereas Coptotermes gestroi (Wasmann) is reported from many areas of the tropics. Taiwan is one of a few areas where the distributions of the two species overlap. By analyzing partial mitochondrial sequences of COII, 12S rRNA, and 16S rRNA, we found that most Taiwanese C. formosanus populations were closely related to Japanese and some Chinese populations and that Taiwanese C. gestroi populations were most closely related to those from the Philippines and Hawaii rather than populations from Thailand, Malaysia, Singapore, and Indonesia. The intraspecific variation of C. formosanus was 0.7–0.8% for three genes among seven Taiwanese populations, whereas all Taiwanese C. gestroi populations had identical sequences. The results support that Taiwan may be a center of origin for C. formosanus, but a recent introduction site for C. gestroi.

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Ambrosia beetles frequently invade non-native regions but are typically of no concern because most species live in dead trees and culture nonpathogenic symbiotic fungal gardens. Recently, however, several ambrosia beetle-fungus complexes have invaded non-native regions and killed large numbers of host trees. Such tree-killing invasions have occurred unexpectedly, and the mechanism of the ecological switch from dead trees to live trees has been left unexplained, or termed an "evolutionary mismatch." We demonstrate that the mismatch hypothesis is not supported in the redbay ambrosia beetle, Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae), because this beetle is able to colonize live trees also in its native range and its symbiotic fungus acts as a pathogen in some native hosts. We further synthesized findings from recent literature and unpublished observations on several other invasive fungus-associated beetles such as Euwallacea fornicatus (Eggers) (Coleoptera: Curculionidae), Platypus quercivorus Murayama (Coleoptera: Curculionidae), and Pityophthorus juglandis Blackman (Coleoptera: Curculionidae) to present an alternative to the "evolutionary mismatch" hypothesis. The revised hypothesis is that the majority of destructive ambrosia beetle species that have invaded new regions are already capable of colonizing living tree tissues in their native habitats. Furthermore, associated fungi are typically mildly to strongly pathogenic to native host tree species. A predisposition to colonize living tree tissues occurs in very few ambrosia beetle species, but these species predictably act as pests in invaded regions. Thus, simple screening of ambrosia beetle-fungus pairs for this particular ecological trait-colonization of live tree tissues-in their native habitats could help discriminate future tree-killing invasive pests from the majority of species that likely remain harmless.

Abstract:The Asian subterranean termite, Coptotermes gestroi, is a tropical species but has increasingly been collected from the subtropics in recent years, making it sympatric to the Formosan subterranean termite, C. formosanus in at least three areas, Taiwan, Hawaii, and Florida. Simultaneous flights by these two species were observed since 2013 in South Florida, during which interspecies tandems were observed. Laboratory mating of C. formosanus and C. gestroi alates produced hybrid incipient colonies of larger population size. Studies are underway to examine the presence in the field of hybrid colonies in sympatric areas of Taiwan and Florida. Other biological characteristics of C. formosanus × C. gestroi hybrids being studied include temperature tolerance and preference, colony growth rate, wood-consumption rate, and reproductive fertility. This current research aims to determine the potential establishment of a hybrid termite population in south Florida and Taiwan. It investigates the risk of introgressive hybridization in field populations, with an emphasis on its potential ecological, evolutionary, and economic consequences.