Geography, opportunity and bridgeheads facilitate termite invasions to the United States

With the ever-increasing rate of globalization, port of entry data can be an important source of information for the introduction and spread of invasive species on a worldwide scale. Using a comprehensive dataset spanning records from 1923 to 2017, termite interceptions at US ports of entry were analyzed. We identified 906 non-native interceptions originating from outside the US, including four families, 32 genera and 75 different termite species. Non-native termites originated from 88 different countries and were intercepted in 29 different states. There was a strong regional bias, with termite-rich areas closest to the US—Central America, South America and the Caribbean—the greatest exporters of termite species to the US. Among the 75 non-native termites intercepted, 12 had already become established outside of their native range, with eight appearing to utilize bridgeheads to expand their global distribution. Additionally, the establishment probability of a species was positively influenced by the number of interceptions, as three of the most common non-native species intercepted at ports of entry are currently established within the US—Nasutitermes corniger, Cryptotermes brevis and Coptotermes formosanus. Our results reveal important insights into the global dispersal of invasive termites and contribute further evidence towards the importance of trade, increased propagule pressure and the bridgehead effect as drivers of global invasion rates.