580 MISC. PUBLICATION 657, U. S. DEPT. OF AGRICULTURE 
their eggs in the shoots. Since the growth of the gall apparently 
begins before the larva hatches from the egg, it is probable that the 
stimulus for abnormal growth is introduced into the plant principally 
as the egg is laid. A g eall develops also when the egg apparently fails 
to hatch. In some instances the full: grown larvae vacate the galls 
and construct thin cocoons in the gr ound in which they pass the winter, 
whereas in other species they remain in the galls and emerge as adults 
the following spring. The most practical method for combating these 
cawflies is to cut and destroy the infested twigs while the larvae are 
in the galls. 
The full-grown larva of the dusky birch sawfly (Croesus latitar- 
sus Nort.) 1s about 7% to 1 inch in length. The head is shiny black, 
the body yellowish green shaded with black, and on each side is a 
subdorsal row of more or less distinct black blotches, and in the sub- 
spiracular area a series of black spots. In the earlier instars the larva 
is fuscous, with few or no distinct dark markings. This species is 
generally common through New England and the Lake States. Its 
preferred food plant is gray birch, “although other birches (black, 
paper, red, and yellow) have also been recorded as hosts. Undoubt- 
edly this insect may be found over the entire range of the gray birch. 
The larvae are eregarious (fig. 167) and often are found defoliating 
small saplings, but there 
are no records to indi- 
cate that this species has 
ever defoliated exten- 
sive areas. There may be 
two complete generations 
or one and a partial sec- 
ond annually. The win- 
ter 1s passed as a pre- 
pupal larva in its cocoon 
in the topsoil. This 
larva transforms to the 
adult stage during May 
or the first half of June. 
Adults of the next gen- 
eration may emerge from 
the middle of July to 
the middle of Septem- 
ber, or in May or June 
of the following year; 
FicurE 167.—Larvae of Croesus latitarsus 
on birch leaf. (Courtesy Conn. Agr. Expt. 2 
Sta.) therefore the genera- 
tions overlap, and larvae 
may be found from early in June until late in the fall. 
SusFrAMILY ALLANTINAE 
The full-grown larva of the curled rose sawfly (A//antus cinctus 
(Ia) ais about 34 inch in length. The head is yellowish brown, with 
a brownish-black stripe on the middle of the fac e, and the eyes are 
black. The body is metallic green above and is marked with white 
dots, and the lower surface, including the legs, is grayish white. This 
species is found from Minnesota to Maine and as far south as northern 
