Abstract
The economic entomologist is concerned with the eradication or control of insect infestations, or with the restriction of spread of pest-species. In the course of such work, he is often confronted with the appearance of new infestations in cleared or virgin areas. These infiltrations from other source regions originate, in part, from the gradual extensions of other foci by flights or migratory movements, and, also from the intervention of air currents.