14 FIF1II REPORT OF THE ENTOMOLOGICAL COMMISSION. 
parent. A teoond generation of sexiest individuals tlms results, jrhicfa is succeeded 
bj a third, fourth, fifth, and even a ninth generation, the process being only termi- 
nated by the approach of oold vreather, when ;i last brood of males and females ap- 
pear. By this anomalous, asexual mode ot reproduction, a single Aphis may hecome 
the parent of millions of yonng. 
Certain plant-lice occur on the roots of plants, others on the stems or twigs; others 
puncture leaves, eau-dng them to roll or crumple, or to form galls. Ants are fond of 
the sweet excretions from the " honey tabes," and often keep them captive in their 
ike herds of cattle. The maggots of Syrphus flies, lady-birds (Cocoinella), and 
the larva- of the lace-winged fly, besides small ichneumons, destroy great uumhers of 
them and keep them within due limits. 
To the plant-lice family belong the species of Adelges and Cln>rmes which produce 
cone-like swellings on the new-grown twigs of spruce; alsc of Pemphigus, which pro- 
duce gall-like swellings on poplars, etc. 
Bark-lice. — In the species of Coccidce, the males alone are winged, 
having but a single pair, while the females are wingless, scale-like and 
do great damage by puncturing the bark of trees. 
Dipterous or tic<> winged gallflies. — Maples, wild plums, poplars, and 
other trees have numerous leaf-galls of varied form made by little gnat- 
like flies belonging to the dipterous family Cecidomyidce. These flies 
are minute, most of them smaller than a mosquito. The females lay 
their i^g^s in the stems, leaves, and buds of various plants and trees, 
thus producing galls, a common example being the willow dipterous 
gall-fly ( Cecidomyia strobiloides). There are thirteen other species found 
by Mr. Walsh to raise galls on eight different kiuds of willow, the dif- 
ferent kinds of galls being readily distinguished, while the flies them- 
selves and their maggots are closely similar. The maggots of the 
Cecidomyiaus are usually minute orange, pinkish, or yellowish worms 
without feet, and with the body pointed at each end. 
Insectivorous or parasitic insects. — While the undue increase of forest 
insects is largely prevented by iusectivorous birds, their numbers are 
especially reduced by the attacks of parasitic or carnivorous insects. 
Of these the most efficient are the ichueumou flies, which are wasp- 
like insects forming a large group of the order Hymenoptera, belonging 
to the families Ichneumonidce, Proctotrupithc, and Ghalcididw. Of the 
ichneumons there are probably from 4,000 to 5,000 species. Many of 
the species of Proctotrupidce oviposit in the eggs of Lepidoptera and of 
dragon flies, etc. The largest species belong to the first named family. 
They are recognized by their long, slender body and long, external 
ovipositor. The larva is like the maggot of a bee or wasp, being foot- 
less, soft, and white, and with a smaller head. 
"When about to enter the pupa state the larva spins a cocoon, 
consisting in the larger species of an inner deuse case and a looser, 
thinner outer covering, and escapes as a fly through the skin of the 
caterpillar. The cocoons of the smaller genera, such as Cryptus and 
Microgaster, may be found packed closely in considerable numbers, 
side by side, or sometimes placed upright within the body of cater- 
pillars."* 
* Packard's "Guide to the Study of Insects," p. 193. 
