A total of 385 alien insect species established on woody plants in Europe since 1800. Along with globalization, the rate of arrival of new species exponentially increased during the second half of the 20th century to reach an average of 6.7 species per year during the period 2000-2012. This trend mirrors the rapid increase in the import of live woody plants. Very large discrepancies were observed between alien establishments and interceptions at borders. An analysis of the temporal changes in colonization of trees species growing in Europe revealed that since 2000 the recruitment of alien herbivores increased more rapidly on deciduous trees and shrubs, especially of tropical/ subtropical origin such as palms and eucalypts, whereas this recruitment has decreased in Gymnosperms and slowered in fruit trees. Identifying appropriate and effective tools for the prior warning and early detection of alien insect arrivals is urgently needed but extremely challenging because most potential invaders do not cause significant damage in their native range, and even could be yet unknown to Science. A novel method consisting in sentinel plantings in other continents to detect potential invaders is discussed from the results of recent experiments carried out in China.