October, ’24] 
turner: tule billbug 
531 
spring and summer among the tules in which the immature stages have 
developed. 
Characteristic cavities are made by the adult in feeding on the tule 
stems. The incision is elliptical in shape, nearly a quarter of an inch 
long and half as wide, readily recognized after once having been seen. 
Underneath this comparatively small opening examination will show 
that a cavity has been excavated in the coarsely cellular body of the 
stem, often an inch in length and half as wide. Evidently the adult eats 
out all the tissue within reach of its proboscis from the original incision. 
Caged adults were voracious feeders on the green tule stems with which 
they were provided. 
We have some evidence to indicate that the rootstocks of tules which 
are standing in water all or a considerable part of the time do not 
become infested. 
Life History 
The eggs require from 10 to 13 days for hatching. The average period 
for incubation for 30 eggs under observation during May and early 
June, 1922, in an unheated room at Sacramento, was 11 days. 
Larvae reared in the laboratory attained their full development in 
about 100 days, during which period they molted four times, including 
the last cast on entering the pupa stage. An average larval period of 
98.4 days is afforded by the records of fifteen larvae reared in the 
Sacramento laboratory during the summer and fall of 1922. 
The pupal period of specimens reared in cages in an unheated room 
during the fall of 1922 averaged 20 days, varying greatly. Thirty-six 
pupae in the rearing cages, from which the above average was computed, 
varied from 10 to 31 days. Five became adult in 18 days, five in 23 
days, three in 15, three in 16, three in 17 and three in 22 days, the re¬ 
mainder in from 10 to 31 days. One month is not the maximum pupal 
period, however, since our observations show that under natural con¬ 
ditions a large proportion of individuals hibernate as pupae. 
Seasonal History 
There is but one generation a year. The earlier maturing individuals 
spending the winter months as adults in the pupal cells, and the later 
maturing ones hibernating as pupae or even larvae. We have no evi¬ 
dence to indicate that adults winter over outside the tule roots, or to 
show the proportion of hibernating larvae and pupae which mature 
successfully after hibernation. In the field adults which evidently had 
