The relationships of Drosophila obscura fallén and D. subobscura collin to naturally-occurring fruits.

The relation between British woodland Drosophila and naturally-occurring fruit was examined in three ways: (1) Field observations show D. subobscura emerging in large numbers, and D. obscura and D. ambigua in much smaller numbers, from rowan and woody nightshade, but not other fruits. D. subobscura used rowan inefficiently; its peak of emergence is in mid-November. (2) Microbial studies suggest that adult flies do not feed on naturally-occurring fruit in the wild, and that laboratory-rotted fruit supports a yeast flora similar to but not the same as naturally-rotted fruit. (3) Laboratory tests using D. subobscura and D. obscura show low adult longevity on fruit; an ability to oviposit on fruit, especially with an alternative food source, which varies with the softness of the fruit; and an ability of larvae to develop on fruit. The implications of these three lines of evidence are discussed.