Atrusca cubitalis

This short-winged species, cubitalis, is the producer of all the oak apples found in Colorado west of the Continental Divide. There is no species of the Atrusca bella complex in that area. On the eastern slopes of the Colorado Rockies oak climbs hardly above 6,000 feet, falling some 4,000 feet short of most of the passes. On the western slopes, another oak of the Gambelii complex climbs much higher, reaching to about 9,500 feet, although it also falls short of the passes. The Western Colorado cynipids are, in consequence, well isolated from the Eastern Colorado species by a considerable oak-free area which extends over the Divide and well down on the eastern slopes of the range. cubitalis is best distinguished by its nearly closed areolet and by the fusion of the marks in the cubital cell which form a line parallel to the cubital vein. Although the insect is in other respects hardly separable from brevipennata, the characters noted are constant throughout the several localities, well distributed over the western half of Colorado, from which we have bred insects.