3 2 4 
The Two-winged Flies 
cisco peninsula, showed a peculiar stunting and gall-like swelling of the 
leaves. Since then this deformation has appeared so abundantly and widely 
within the range of this tree that the species is actually threatened with 
extinction, the shortened, swollen needles not being able to perform the 
essential food-assimilating functions of green leaves. This injury is due 
to a single species of Cecid fly known as Diplosis pini-radiata (Fig. 451), 
Fig. 451. —The Monterey-pine midge, Diplosis pini-radiata; eggs in upper left-hand 
corner; pupa, larva, breast-bone of larva, and adult female. (Much enlarged.) 
which lays its eggs at the base of the growing new needles and whose larvae 
hatching and lying here use up the sap necessary for the development of 
the needles. Hundreds of Monterey pines have been cut down, and unless 
the natural enemies of this little fly, of which two or three have been dis¬ 
covered, get the upper hand of the pest, this splendid species of pine may 
be wholly destroyed. A half-dozen other species of Diplosis are known 
in this country and Europe as pests of conifers, but no other pine species 
seems to have suffered quite so severely as this interesting Californian one, 
whose whole geographical range extends over but a thousand square miles, 
and which is thus specially liable to destruction by concentrated insect 
attack. 
If the collector will break up and examine carefully almost any old or 
partially decaying toadstools or shelf fungi from trees, he will find in the 
soft fungous body numerous small translucent white maggot-like larvae, the 
larvae of fungus gnats or members of the family Mycetophilidae. The gnats 
themselves are slender delicate flies, mostly with clear wings, though some 
common species have dark wings, with the basal segment (coxa) of the legs 
unusually long and the antennae in most cases free from the whorls of long 
hairs so characteristic of the Chironomidae, Culicidae, and other families of 
flies otherwise much resembling the fungus-gnats. The flies are to be looked 
for on decaying vegetable matter, especially fungi, and in damp places. 
The eggs are laid variously: on fungi, in decaying wood, among decom¬ 
posing leaves, in animal excrement, and under the bark of trees. The larvae 
