8 
In common with other sawflies, however, they rarely leave their larval 
food-plants, and to be collected successfully a knowledge of their habits 
in this respect is very desirable. 
In number of broods great diversity is found, and the normal rule of 
most Tenthredinide, of a single yearly brood, is frequently deviated 
from. Some species are known to be limited in number of broods only 
by the length of the season, as, for example, Pteronus ventralis Say, the 
common willow species. Two annual generations are common, but 
many species are single brooded, the larvie entering the soil or other 
material or remaining in their galls at the completion of growth and 
continuing in dormant condition until the following spring, when shortly 
before they emerge as perfect insects the change to the pupal condition 
takes place. The males normally appear a few days before the females, 
and the duration of the life of the adults of both sexes is short, not 
often exceeding a week or ten days. Of alarge percentage of the species 
no males are known, and in the case of many species careful and 
repeated breeding records indicate that males are very rarely produced. 
In some species parthenogenesis is complete; that is, the eggs from 
unimpregnated females produce other females. In other instances of 
parthenogenesis, however, either males only are developed from unfer- 
tilized ova or females very rarely. 
The union of the sexes takes place very shortly after the appearance 
of the females and egg deposition closely follows. The eggs are inserted 
either singly or a number together in the young twigs, larger veins, 
petioles, in the surface parenchyma, or in the edges of the leaves, the 
single exception being the case of the gooseberry sawfly (Pteronus 
ribesii), which merely glues its eggs to the leaf without making any 
incision whatever. 
Most of the species are external feeders on the foliage of plants, but 
the species of two genera, Huura and Pontania, so far as their habits 
have been studied, are gall makers, and pass their early life in the 
interior of the plants, either in the stems without causing abnormal 
growths or in the excrescences or galls on the stems and leaves. At 
least one American species develops in the rolled or folded edge of the 
leaf. The larvie are 20-footed, some solitary, others gregarious—the 
latter usually more brightly colored and possessing means of protec- 
tion in glands secreting a noxious fluid. Most of the solitary ones are 
green and not readily observed. They usually feed from the underside 
of the leaves, eating from the edge or cutting circular holes in the gen- 
eral surface, and in some cases taking everything but the stronger 
veins. Many species rest quietly during the day, feeding only at night. 
Some have the habit of throwing the posterior segments violently 
upward to frighten away parasites or enemies; others adhere to the 
leaves or twigs by the thoracic feet only, coiling the posterior segments 
under the middle ones. 
