4 86 
Saw-flies, Gall-flies, Ichneumons, 
comstockii , which infests various caterpillars. Its larvae are external para* 
sites clinging to the skin of the caterpillar. The chalcis-flies may usually be 
recognized by the characteristic branched single vein of the fore wings (Fig. 
673)- 
The economic importance of the hymenopterous parasites is obvious; 
from the point of view of the economic entomologist there are no other 
Fig. 686. —Larva of Xylina lacticinerea, green-fruit worm, killed by the parasitic grub 
of Mesochorus agilis, which has spun its cocoon beneath the caterpillar, fastening 
the latter to the leaf. (After Slingerland; natural size.) 
insects outside of the pests of such interest as these natural pest-fighters. 
Attempts have been made to make allies of them in man’s warfare against 
injurious insects by artificially disseminating them, even to the extent of 
colonizing bv importation from foreign 
countries various new species in partic¬ 
ularly pest-ridden localities. In Cali¬ 
fornia a constant and aggressive war has 
to be maintained by the fruit-growers 
against many insect pests, and particu¬ 
larly against the scale-insects. In this 
warfare a number of attempts have been 
made to introduce from other continents 
parasitic enemies of the scales. Unques¬ 
tionably considerable success has attended 
some of these importations, although as 
yet no other such signal overcoming of an 
insect pest by the use of these Hessians 
has occurred as attended the importation 
from Australia, several years ago, of the predaceous ladybird-beetle (Vedalia), 
enemy of the once dreaded fluted scale (see p. 189 for account of this). 
Any discussion of the parasitic families of Hymenoptera would be incom- 
Fig. 687.—A caterpillar of Xylina 
lacticinerea, green-fruit worm, from 
which the parasitic larva of Meteorus 
hyphantrice has just emerged and 
is spinning its cocoon. (After Slin¬ 
gerland; natural size.) 
