If species divergence is to occur the new adaptation must lead to reproductive isolation. Insects feeding on different host plants are often confined to specific hosts dependent on the species of insect. Experiments have shown that females who developed successfully on a new host plant often return to that host plant type when they lay their own eggs. The offspring produced are exposed to different conditions and, after several generations, they are likely to acquire a range of adaptive features to cope with the new host. Such individuals are said to be ecologically isolated from the rest of the population.
Divergence can then occur.