16 FIFTH REPORT OF THE ENTOMOLOGICAL COMMISSION. 
to a single species. Most ichneumons have bat a single generation; 
a few are double-brooded. In Germany, Katzeburg observed a brood 
Of Mierogaiter globatUS early in .May, and another early in August. 
Though there may be two broods of the hosts, there is, as a rule, but 
a single brood of iehneumons. Katzeburg, indeed, found that certain 
ichneumons of saw-fly larva* imitated the habit of the latter of living 
more than a year, I. 0., they did not develop until the greater number 
of saw-flies bad issued from the belated cocoons. On the other hand 
Pteromalu* pupanim undergoes an extraordinarily rapid growth; it 
stings early in June the chrysalids of Vanessa poli/chloros, and by the 
middle of July the adults appear. Teleas orulorum requires only four to 
six weeks to develop; it however flies somewhat later, so as to tind the 
suitable objects on which to lay its eggs. 
Ichneumons rarely develop in adult insects, but certain Braconids 
infest Coccinella beetles. The small Chalcids, i. e., Pteromali, mostly 
inhabit the tender pupse of bark-boring beetles and leaf-rollers. 
Among the smaller ichneumons several females usually inhabit a 
single host, while from 000 to 700 individuals of Pteromalus puparum 
may inhabit a single chrysalid, and 1,200 Apanteles a Sphinx larva. 
Most ichneumons develop within their hosts, but many species of 
Chalcids live on the outside and suck the blood of their host. The 
ichneumon Larvae living within their hosts often undergo the most 
remarkable transformation of their mouth-parts. In Microgaster globatus 
there are, at first, only the wart-like rudimentary sucking month-parts; 
but after the last molt the larva? acquire ordinary biting mandibles, 
with which they can gnaw through the skin of their host. However, 
the food of the ichneumon larvae is wholly fluid, their mouth-parts not 
allowing them to eat the fat-body of their host. 
Other parasitic insects are the larvae of the Tachina flies, a group 
closely allied to the common house-fly. The larvae are true maggots, 
footless, and take their food by suction through the mouth, the mouth- 
parts being very rudimentary. The Tachina (Senometopia) militaris 
has been observed by Riley to lay from one to six eggs on the skin of 
the army-worm, " fastening them by au insoluble cement on the upper 
surface of the two or three first rings of the body." The young mag- 
gots in hatching penetrate within the body of the caterpillar, and lying 
among the internal orgaus absorb the blood of their unwilling host, 
causing it to weaken and die. 
Other insectivorous insects are the Aphis-lions, the young of the lace- 
winged flies Ghrysopa and Hemerobius, which are frequently found in 
trees among plant-lice; also Carabid beetles. 
Artificial breedingof parasitic and predaceous insects. — Among the most 
important preventive measure against the wholesale ravages of insects 
is the artificial breeding of parasitic insects. We early advocated this 
in dealing with the Hessian-fly and wheat midge, suggesting the im- 
portation of the European parasites of the latter species in straw. Dr. 
Le Baron has experimented with the parasites of the apple bark-louse. 
