To measure is to know: Molecular tools help to map the distributions of invasive shothole borers (Euwallacea fornicatus species complex) in Hawaii, and beyond

The Euwallacea fornicates species complex consists of at least four highly invasive species of ambrosia beetle (Coleoptera: Curculionidae: Scolytinae). The most authoritative means of identifying the species in this complex is using DNA sequences. Only one member of the complex, E. perbrevis (tea shothole borer; TSHB), was thought to have established in the Hawaiian Islands, but in 2016 a DNA sequence of a second species, E. fornicates (polyphagous shot hole borer; PSHB) was belatedly deposited in the public repository GenBank, indicating that it had also been detected on at least one occasion. In response, we sought to survey shothole borer populations on the two most-populous islands of Hawaiʻi, Big Island and Oʻahu, and confirmed that populations of TSHB and PSHB are indeed established on both. Given the damage that invasive populations of PSHB (in particular) are inflicting on agricultural- and natural ecosystems in areas as disparate as the U.S. mainland, Israel, and South Africa, confirmation that it is established in Hawaiʻi raises concerns about its potential impact on native Hawaiian species, highlights a need for more expansive monitoring, and may further inform pest management decisions. Since sequencing DNA is itself a relatively costly affair, we describe a simple molecular tool for identifying individual members of the species complex based on high-resolution melting analysis. The Euwallacea fornicatus species complex consists of at least four highly invasive species of ambrosia beetle (Coleoptera: Curculionidae: Scolytinae). The most authoritative means of identifying the species in this complex is using DNA sequences. Only one member of the complex, E. perbrevis (tea shothole borer; TSHB), was thought to have established in the Hawaiian Islands, but in 2016 a DNA sequence of a second species, E. fornicatus (polyphagous shot hole borer; PSHB) was belatedly deposited in the public repository GenBank, indicating that it had also been detected on at least one occasion. In response, we sought to survey shothole borer populations on the two most-populous islands of Hawaiʻi, Big Island and Oʻahu, and confirmed that populations of TSHB and PSHB are indeed established on both. Given the damage that invasive populations of PSHB (in particular) are inflicting on agricultural- and natural ecosystems in areas as disparate as the U.S. mainland, Israel, and South Africa, confirmation that it is established in Hawaiʻi raises concerns about its potential impact on native Hawaiian species, highlights a need for more expansive monitoring, and may further inform pest management decisions. Since sequencing DNA is itself a relatively costly affair, we describe a simple molecular tool for identifying individual members of the species complex based on high-resolution melting analysis.