Aphis (Zyxaphis)

This subgenus name is used for a group of presumably related species that feed on sagebrushes (Artemisia) and rabbitbrushes (Ericameria, Chrysothamnus). There are several accepted species names, but I don’t use any of them due the common problem in aphid taxonomy — none of the existing keys are adequate for recognition of the full range of variation in the groups that may be species. One issue affecting this subgenus is that the apparent species are extremely variable in body size, pigmentation, and gross morphology. This is often evident in a single aggregation on a single branch, with some adults twice to three times the length of others. For some time I was thinking that body colors and host plants might be diagnostic but 2020 experience has cast that idea into doubt. Bottom line: I have accumulated quite a lot material, completely unsorted and without species names, with the intent of sitting down some long weekend to attempt a clean sort unencumbered by knowledge of existing species names. Then, I hope to have an estimate of how many species I have seen in all these years and figure out whether any existing names can be applied to my hypothesized groups. All that said, below are some photos of Zyxaphis species I’ve grabbed over the years.

Aphis (Zyxaphis) feeding on grey rabbitbrush (Ericameria nauseosa) in central Washington State. Note the bizarre curled siphunculi, which are not normal for the group but represent one of the many morphological idiosyncrasies of this subgenus.
This is the most common appearance of Aphis (Zyxaphis) on Artemisia tridentata: black and shiny with grey waxy reticulations. This is a viviparous female from central Washington State in May.
Here is another example of the shiny black Aphis (Zyxaphis) from Artemisia tridentata. This is an oviparous female in September in southern Oregon. These oviparae are unusual in having only a few scent plaques on the hind tibiae, which are not at all swollen.
Aphis (Zyxaphis), like some other aphids that feed on sagebrushes, are unusual among aphids for laying eggs in massive clusters like this, with many females contributing just a few eggs each.