840 
[Assembly 
every kind of tree and plant appears to have one or more species 
of aphis infesting and blighting it, each species of aphis seems to 
have a particular parasite preying upon and devouring it; for 
each kind of aphis from which I have reared these insects has 
furnished a species differing from all the others, and in some in¬ 
stances two species have been obtained from one kind of aphis. 
The British entomologists enumerate upwards of fifty species of 
these insects, which is nearly equal to the number of their aphides. 
They differ from all the other insects of the family to which they 
pertain, by having commonly a very large triangular stigma to 
the fore wings, and very few veins, and these commonly end 
abruptly without reaching the apical or inner margins. Hence 
there are but few if any closed cells or panes to the wings. One 
of our species having the wings more fully veined and forming 
complete cells may be met with accompanying what appears to be 
an undescribed species of aphis which infests the stalks of lettuce 
in our gardens. This in my manuscripts is named 
The Lettuce-louse Apuidius (A. Lactucaphis ). It is deep black with legs tinged 
with brownish, their bases and knees very slightly paler; the abdomen long obovate, 
flattened, rather narrower than the thorax, its apex rounded; antenna: almost as 
long as the body, 19-jointed, second joint smallest, globular, third joint longest with 
a slight constriction in its middle, the succeeding joints successively shorter, the last 
scarcely longer than the preceding one, long ovate; wings slightly smoky, outer 
marginal vein and the vein bordering the cell beyond the stigma black, the outer 
veins brown, stigma dusky white. Length 0.06 to the tip of the abdomen. 
One of the prettiest species which I have met with was bred 
from aphides upon the spotted knot-weed {Polygonum persicaria), 
and may be named 
The Knot-weed Aphidius (Praon Polygonaphis). It is black and shining with 
a slender elliptical abdomen of a bright sulphur-yellow color tinged with dusky above 
and at its tip beneath, with broad clear yellow bands at the anterior sutures, its base 
being narrowed into a short cylindrical pedicel, which with the legs and bases of the 
antennse are of a bright reddish or beeswax yellow color, the tips of the feet being 
black; its antennae arc inserted on slight broad elevations upon the front of the head 
and are 17-jointed, the two short basal joints beiDg a third thicker than the following 
ones, which are equal, cylindric, four times as long as they are thick, the last rather 
longer than the preceding, its apex abruptly rounded. Length 0.08, wings ex¬ 
pand 0.16. 
Another species is a common destroyer of a species of aphis 
which infests the fruit stems of the high cranberry, (Viburnum 
