Antennal tubercles are misnamed as they are not actually tubercles, but an integral part of the head. They are associated with the antennal socket and are not actually part of the antenna. In some aphids, there are projections on the first antennal segment, but these are not antennal tubercles in the sense used in aphid morphology.
These antennal tubercles diverge from one another and are smooth.
These antennal tubercles are parallel and scabrous.
In AphID, all tubercles, when well developed, are considered either 1) parallel to converging or 2) parallel to diverging. In no case in AphID are the antennal tubercles of an aphid species exclusively parallel. Thus, coding a specimen as habing parallel antennal tubercles will actually permit it to have any of the three.
These antennal tubercles are converging on one another and are scabrous.
Many aphid species have reduced antennal tubercles. These are obviously undeveloped and in AphID fall into the same category as those species that have no antennal tubercles at all.
Some aphid species clearly have no antennal tubercles at all.