The vast improvements in the ease and convenience of international travel have not aided the situation. Customs departments usually examine closely and often quarantine plants before allowing them to enter a country, but checking thoroughly each specimen naturally is impossible, and pests invariably find a way to slip in.
現代交通方便，國與國之間的距離相形縮短，往來頻繁，一不小心，專吃農作物的昆蟲就由這些管道，被帶到沒有天敵的地區。