324 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 



