tasks of medical en­ of exotic pests and pathogens has presented tomologists continue to be important. Arthro­ new problems in several countries, including pod systematics is important because the need the USA. For example, the year 1999 saw the for accurate identification of arthropods is vital invasion of the eastern USA by Aedes japonicus, to an understanding of natural disease cycles. an Asian mosquito, and West Nile virus, a mos­ Systematics has been made even more challeng­ quito-transmitted African arbovirus related to ing because of the current appreciation of the St. Louis encephalitis virus. number of groups of sibling species among vec­ At the same time old and new health prob­ tors of important disease pathogens. New mo­ lems with arthropods occur, the traditional ap­ lecular tools are assisting in separating these proaches to arthropod control have become forms.