Christmas trees can carry a variety of live cargo with them when they travel… The Centre for Agricultural Biosciences International, a non-profit organization focused on science-based solutions for agriculture and the environment, lists the 12 pests of Christmas trees on its invasive species blog. The list includes the Western yellowjacket, a wasp native to western North America whose young queens spend the winter in species often exported as Christmas trees. This has caused a huge problem in Hawaii, which imports about 90,000 Christmas trees a year, mostly from Oregon. …One pest of concern that can move between Canada and the U.S. via Christmas trees is the LDD or spongy moth, formerly called the gypsy moth. It can also be a concern with trees moving between different parts of Canada; it caused the shutdown of at least two Christmas tree lots in Thunder Bay, Ont., last year.