[Insects know no border.].

One of the major consequences of the joined action of demographic pressure and evolution of human activities lies in enormous increase of transportation, both in frequence and speed; taking advantage of these facilities, some arthropods could increase their geographical distribution and create new health threats. Several demonstrative examples are exposed in order to illustrate this anthropic dissemination of the vectors : the introduction of Anopheles gambiae s.l. in Mauritius Island between 1850 and 1865, in north-east of Brazil in 1930, and in the Nile valley in 1942, these three phenomena being followed by great malaria epidemics; the arrival and dissemination in Africa of chigoe (Tunga penetrans) and, more recently, of the human flea (Pulex irritans); the propagation, in the west Indies, of the african cattle tick Amblyomma variegatum; finally, the expansion of two mosquito species, Aedes aegypti and Ae. albopictus, with real or potential consequences in the field of yellow fever and dengue transmission. These facts, among many others, attest of the constant evolution of epidemiological situations, and of the necessity of a permanent entomological surveillance in order to be able to take adequate measures in time.