The founding of new, geographically isolated populations is a process central to many issues in evolutionary biology. One aspect of this process that has received much attention is the reduction in population size that accompanies the founding of a new population. Colonization by a small number of founders is a recurrent theme in both speciation theory (Bush, 1975; White, 1978; Templeton, 1980) and some theories of macroevolution (Eldredge and Gould, 1972). Current interest in such population can be traced to Mayr's (1954) theory of speciation via the founder effect, and ultimately to Wright's (1932) shifting balance theory. Despite their theoretical importance, there are few studies of the genetic effects of colonization and population bottlenecks in nature. There is no shortage of work in which assumed bottlenecks are invoked to explain results, but studies of known bottlenecks are few indeed (Taylor and Gorman, 1975; Schwaegerle and Schaal, 1979; Bryant et al., 1981). One underexploited source of data on bottlenecks is introduced insects. The presence of an important pest is usually noticed soon after its introduction into a new area, and its subsequent spread is documented. Furthermore, pest insects are the subject of control measures which may generate secondary post-introduction bottlenecks. Although the exact size of the initial population is not known, the wealth of other data on introduced pest populations makes them well worth studying.