TRIBES OF APHIDIDAE 53 
Thomas (1879) named the tribe Lachnini. Mordwilko (1895-1908) 
first clearly indicated the limits of the group under the term Lachninae 
which he later changed to the better term Lachnina. 
Morphological characters. Head transverse, with frontal margin 
broad and straight. Antennae have six segments, rarely only five; 
usually less than half the length of the body; spur of the terminal seg- 
ment short and undeveloped; segments of the flagellum provided with 
numerous long, spreading hairs; secondary sensoria mostly large and 
circular, but variable in number and position; marginal sensoria more 
or less scattered and not forming a compact group. The rostrum is 
usually long, sometimes as long as or longer than the body. In the 
Lachnini the rostrum is distinctly 5-jointed. Legs long and slender, 
the hind pair especially so; they are usually provided with long and 
spreading hairs like those on the body. Wings are large and the 
venation is typical of the family; stigma long and slender, rarely short 
and broad; stigmal vein (Rs) originating from the distal end of the 
stigma and runs as a straight vein to the margin, or, when originating 
some distance from the apex of the stigma, it is more or less curved; 
the media is a very faint vein in the Lachnini, but more distinct in the 
Pterochlorini. The cornicles are short, often mere pores, situated on 
conspicuous cone-shaped, hairy tubercles which are seldom much re- 
duced or wanting. The cauda is short and broad and not conspicu- 
ous. 
Biological characters. It becomes apparent from extended mor- 
phological and biological studies on the family that the Lachnina rep- 
resent the most generalized and primitive forms of the Aphididae that 
are in existence at the present time, and that they give the key to the 
phylogenetic understanding of the family. This is indicated by their 
size, form of the antennae, the structure of the sensilla and sensoria, 
the long rostrum with the free distal segment, the venation, and the 
form of the cornicles and cauda. But more so does the habitat of 
the group, as bark feeders on conifera and deciduous trees, indicate 
that they are a remnant of a group that in the past predominated and 
gave characters to the family. Paleontology also, as far as known, 
points to similar conclusions. 
KEY TO THE TRIBES OF THE LACHNINA 
1. Stigma long and stigmal vein takes its origin from the distal end of the 
truncate stigma and runs as a short, straight vein to the margin; media appears as an 
indistinct vein. They are found.feeding on the bark of coniferous trees. 6 
1. Tribe LACHNINI 
—Stigma long or sometimes short, with the stigmal vein arising some distance 
back from the apex of the stigma and curved more or less before reaching the margin; 
media slender but distinct. They are found feeding on the bark of deciduous trees 
and woody plants. ... 2. Tribe PTEROCHLORINI 
