affecting the Corn-Crops. 
505 
growth, from minute ones that were just born to the full-sized 
and winged parents. I observed that all which had not arrived at 
their last stage had shorter legs than the others ; the largest ones 
were of a dull orange-colour ; the antenna?, except at the base, 
the eyes and abdominal tubes, the extremity of the tibiae and the 
tarsi were black, and tlie thighs pitchy towards their apex (fig. 1 1 ; 
s, showing the natural size). \N ith them were multitudes of dead 
Aphides, whose history I shall now relate. 
Opportunities have repeatedly been afforded us in the course of 
these investigations, of showing the wonderfid ways bv which 
Providence has provided agents to restrain the ravages of noxious 
insects, which without such checks would frequently render man's 
greatest efforts abortive; and as there is no tribe of insects more 
subject to parasitic enemies than the Aphides, we may reasonably 
infer, indeed it is proved by experience, that when such checks 
are withheld, oiu* crops will suffer severely from the super- 
abundance of insect tribes. The wheat-ears this year afforded a 
beautiful illustration of the economy of parasitic insects and the 
benefits resulting from their agency : on some wheat which we 
examined, not a singly Aphis had escaped the searching vigilance 
of its enemies, and the husks were spotted with immovable black 
shining globules, as represented in plate O, fig. 20, b : on a closer 
examination it w as evident that these w ere Apliides which had 
been punctured by minute parasitic flies, and diat as they in- 
creeised in bulk, the little internal maggots fattened upon their 
muscles, until the Aphides died from exhaustion, their bodies 
being gummed by a natural secretion to the chaff and stalks, their 
antennae and legs remaining just as they were during life, and 
likewise retaining their natural colours. I placed these infested 
ears in a box, and after a short time I bred from them two distinct 
species of parasitic flies, as well as a third from another wheat -ear, 
all of which 1 will now describe. 
They belonged to the Order Hymenoptera, the Family Ich- 
NEUMONIDES ADSCITI ; aiid the first to the Genus Aphidils : 
the Species is named by Mr. Haliday 
7. A. Avenae.* In the 3Iale the antennae are dull black, filiform, 
compressed, inserted in front of the face, scarcely so long as the 
body, and composed of twenty joints, the two first forming an oval 
shining mass : head and thorax smooth, shining black, the former 
transverse oval ; eyes rather small, and somewhat lateral ; ocelli 
large, forming a triangle on the crown : thorax w ith a double 
channel down the fore part of the disc; collar very short and nar- 
row ; scutellum semiovate ; postscutellum and abdomen with a 
few whitish hairs as well as the thighs ; pedicle rather long, nar- 
*■ Ent. Mag., vol. ii. p. 99. 
