174 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 11 
Within two or three days after the larvae attach themselves to the 
outside of the host, the latter dies, soon becomes flabby, and turns to 
an ashy gray color. The larva slowly absorbs the contents of the 
host skin, increases in size and finally nothing remains of the host 
but the empty skin, which is usually pushed into one end of the 
puparium. When the host is dead or in a partly desiccated condition 
at the beginning of the attack, the larva may live for a time but ulti¬ 
mately dies. 
The larval stage requires a period of 8 to 12 days for complete devel¬ 
opment. Near the end of this stage the alimentary canal becomes 
completely developed and the waste material accumulated in the 
ventriculus is voided into one end of the puparium. In less than a 
day after defecation occurs the larva transforms to the pupal stage. 
The Pupa 
© 
The pupa (Fig. 8, 6) is at first white, turning rather rapidly to pale reddish brown 
and light brown. It varies in length from 1.41 mm. to 2.50 mm., with an average for 
15 individuals of 2.08 mm. The head is slightly wider than the thorax, its greatest 
width averaging 0.58 mm. The pupa is slightly depressed and slightly concave 
ventrally. The ovipositor sheath is turned upward, but does not extend dorsad of 
the abdomen. 
The pupa stage requires 8-12 days in May and June, with an aver¬ 
age of about 10 days. In midsummer this stage is undoubtedly 
shorter. 
Number of Generations 
In the laboratory the average time required for development from 
egg to adult varied greatly with the season. In May it averaged 25 
days; in June, 24 days; in July, 18 days and in July-August 23 days. 
The shortest period of development recorded was 15 days during July. 
Most larvse which develop from eggs laid during the latter part of 
August and September remained over winter in the condition of mature 
larvse, emerging as adults the following May. The average period 
required for development in the overwintering generation, based on 19 
individuals, was 265 days. 
Five generations were reared in the laboratory in 1916 between 
April and September. A sixth generation overwintered, and emerged 
the following May. Thus it was possible to rear six generations in 
about a year. Under field conditions at Hagerstown, Md., hibernat¬ 
ing larvse were found in puparia late in the spring. Adults probably 
do not emerge outdoors before the middle of June at about the time 
puparia of the spring brood of the Hessian fly are appearing. In a 
season like 1916 there is time for four generations to develop during 
the summer, which with the hibernating generation, makes five gem 
