ABSTRACT

The evolution of wings has allowed insects to increase their powers of movement by several orders of magnitude. In large insects such as locusts and monarch butterflies, migratory flights of thousands of kilometers are the rule. G. E. Hutchinson has described the interaction of forces by which natural selection guides adaptation and speciation as the “ecological theater and the evolutionary play”. Forest bark beetles, Dendroctonus pseudotsugae and Trypodendron lineatum, are attracted to the phloem of host trees, and males to female-produced frass, only after a period of migratory flight. A major difference occurs between the two populations with respect to flight; in the migrant population there was an increase in migratory flights in the long-winged line, but there was no variation among lines in the nonmigrant population. The importance of migration to insect life histories means that in order to understand why animals migrate, we must place migratory behavior in the context of overall fitness.