A REVISION OF THE APHID GENUS ESSIGELLA (HOMOPTERA, APHIDIDAE, LACHNINAE) - ITS ECOLOGICAL ASSOCIATIONS WITH, AND EVOLUTION ON, PINACEAE HOSTS

This revision recognizes 13 species, 2 subspecies, and 3 subgenera of Essigella aphids of the lachnine subtribe Eulachnina. Essigella (Arche oessigella) NEW SUBGENUS, Essigella (Lambersella) NEW SUBGENUS, E. (L. ) eastopi NEW SPECIES, E. (L.) hillerislambersi NEW SPECIES, E. (E.) c ritchfieldi NEW SPECIES, and E. (L.) fusca voegtlini NEW SUBSPECIES ar e described. The taxonomic status is changed for E. (E.) knowltoni bra ggi Hottes NEW STATUS, E. agilis Hottes NEW SYNONYM, E. claremontiana Hottes NEW SYNONYM, E. cocheta Hottes NEW SYNONYM, E. gillettei Hottes NEW SYNONYM, E. maculata Hottes NEW SYNONYM, E. monelli Hottes NEW SY NONYM, E. oregonensis Hottes NEW SYNONYM, E. palmerae Hottes NEW SYNON YM, E. patchae Hottes NEW SYNONYM, E. pergandi Hottes NEW SYNONYM, E. pineti Hottes NEW SYNONYM, E. robusta Hottes NEW SYNONYM, and E. swain i Hottes NEW SYNONYM. A phylogenetic tree for the genus is reviewed; t hat estimate, which used Pseudessigella as a outgroup and employs evol utionary quantitative genetic rationales, was produced using discrimin ant function analysis and a maximum-likelihood net-working algorithm, because conventional cladistic characters were inadequate within the g enus. The phylogeny is corroborated because it closely reflects the ge netic relationships of the aphid's Pinaceae hosts, and their biogeogra phic origins. Essigella appear to have evolved with their hosts, or in a resource-tracking fashion, and seem to display instances of charact er-displacement among closely related species in (or near) sympatry, p resumably as a result of competition of their host pines as resources.