131 
_ was an active, winged creature, capable of extended flight, he con- 
cluded that remedial work was useless, since the flies could, and doubt- 
less would, deposit their eggs over the entire surrounding country. 
AS a consequence the worms were allowed to travel to the adjoining 
fields and the injury thus increased through ignorance of the fact that 
the Tachina flies were the most important of the parasitic enemies of 
the worm. Formany years well-informed gardeners in parts of Europe 
have practiced collecting ladybirds and some of the ground beetles to 
liberate upon plants infested by plant-lice or by cutworms. The char- 
acteristics of these two families, Coccinellide and Carabide, should be 
taught in our schools, as a definite knowledge of certain species, which 
is readily acquired, may often be turned to account in a limited way by 
the cultivator. 
In a few cases like this there is no reason why the farmer should not 
be taught with advantage to discriminate between his friends and his 
foes, and to encourage the multiplication of the former; but for the 
most part the nicer discriminations as to the beneficial species, some 
of the most important of which are microscopically small, must be left 
to the trained entomologist. Few of the men practically engaged in 
agriculture and horticulture can follow the more or less technical 
characterizations of these beneficial species, and where the discrimi- 
nating knowledge is possessed it can, as just intimated, only excep- 
tionally be turned to practical account. Thus our literature on this 
subject in the past has been of interest from the entomological rather 
than from the agricultural point of view, as most writers on economic 
entomology have contented themselves with describing and illustrating 
such beneficial species. 
In other cases much good may be done without any special knowl- 
edge of the beneficial forms, but as a result of a knowledge of the 
_ Special facts which enables the farmer to materially encourage the mul- 
tiplication of parasitic species while destroying the plant-feeding host. 
The Rascal Leaf-crumpler (Mineola indiginella Z.), a common insect 
_which disfigures and does much damage to our apple and other fruit 
trees and which hibernates in cases attached to twigs, iS a case in 
point. Many years ago I urged the importance of preserving the sey- 
eral parasites known to prey upon it, in the following language:* 
. 
' 
The orchardist has but to bear in mind that it (the leaf-crumpler) is single- 
brooded and that it passes the winter in its case, and he will understand that by 
collecting and destroying these cases in the dead of the year when the tree is bare, 
he effectually puts a stop to its increase. * * * Whether collected in winter or 
pulled off the trees in spring or summer, these cases should always be thrown into 
some small vessel and depasited in the center of a meadow or field away from any 
_ fruit trees. Here the worms will wander about a few yards and soon die from 
exhaustion and want of food, while such of the parasites, hereafter mentioned, as 
are developed or in the pupa state will mature and eventually fly off. In this 
“manner, as did Spartacus of old, we swell the ranks of our friends while defeating 
our foes. 
« 
ir 
*Fourth Report, Insects of Missouri, 1871, p. 40. 
