578 MISC. PUBLICATION 657, U. S. DEPT. OF AGRICULTURE 
structed in the ground or in decayed wood, although some may occur 
between leaves or in the galls. The adults emerge in April and May, 
and the females lay their egos in the tender leaves. Felt (153) listed 
many gall-making species known to occur in the United States in 1940, 
together with a key to their galls. The production of the galls on 
the leaves is the only injury caused by these insects, and apparently 
this is never of sufficient importance to warrant artificial control 
measures. 
The larva of the poplar leaf-folding sawfly (Pontania bozemani 
Cooley) is pale green and is found on the inner surface of a leaf fold, 
which it skeletonizes. This species occurs in the prairie region of 
Canada and southward into the United States. The adults emerge in 
May. In laying their eggs the females injure the tender leaves, ‘thus 
causing a part ‘of each to fold over. Egg laying continues through 
July. “The larva vacates the leaf fold at certain times and eats holes 
through the leaf. The injured portions of the leaves become black- 
ened, giving the infested trees an unsightly appearance. When full 
grown ’ the larva constructs its cocoon within the fold and dr ops to the 
ground with the leaf. 
Pontania populi Marlatt folds the edge of the leaf of big toothed 
aspen in May, and P. robusta Marlatt isa ‘leaf folder on quaking aspen. 
The full-grown larva of P. amentivora Roh., the willow-cotton saw- 
fly, is about 14 inch im length, the head is dark brown, the eye spots 
are black, and the body is “white, with faint grayish spots about the 
bases of the hairs. The last-named species occurs in some of the Mid- 
dle Atlantic States and its larvae infest the aments of willow (Salix 
humilis Marsh). ‘The adults appear late in March and early in April. 
The premature showing of “cotton” by infested aments (fig. 165), a 
characteristic of attack, generally occurs about the middle ‘of April. 
The larvae become fully grown during the latter part of April, and 
drop to the ground to spin their cocoons. Apparently there is one 
generation annually, and the winter is passed as prepupal larvae in 
cocoons. Although sometimes abundant locally, its damage probably 
is of little or no economic importance. 
As in the genus Pontania, the insects in the genus Hwura are small 
and are gall makers. The larva is usually yellowish or greenish white, 
with the head often tinted shghtly with brownish and with the eye 
spots black. ‘Those species that have been studied attack willow, and 
it is probable that some species occur throughout the entire range of 
their food plant. Ross (367) and Felt (153) “listed several species s that 
are found in the United States. The gall is usually a somewhat woody 
swelling of the twig, sometimes involving the entire shoot in a gradual 
enlar cement and sometimes being an abr upt swelling on one ‘side of 
the shaft. A few are formed on the leaf or the leat petiole (fig. 166). 
Buds may also be enlarged and the interior altered through occupa- 
tion by these insects. The galls are often smooth surfaced, but are 
sometimes cracked or seamed, and their color is usually that of the 
bark of the twig attacked. The inner structure is fleshy at least dur- 
ing the period of development. The growths these sawflies produce 
on willow shoots can cause economic losses where normal twig develop- 
ment of willow is important. 
These sawflies apparently have one generation a year. The adults 
emerge in the spring, and the species that have been observed lay 
