50 FUMIGATION FOR THE CITRUS WHITE FLY. 
in the tables. It is evident from the results summarized in the fore- 
going table that prolongation of the period of exposure beyond 40 
minutes produces no noticeable increase in effectiveness. It is also 
evident that the dosage recommended for use with sheet tents of 
a good quality of 8-ounce duck is ample for bell tents of a good quality 
of 6^-ounce drill. The smaller amount of leakage surface with bell 
tents as compared with sheet tents may be entirely responsible for the 
apparently wide margin between the recommended dosage and the 
dosage actually required for efficiency, but it seems safe to conclude 
that the 6^-ounce drill used in the bell tent held the gas approxi- 
mately as well as the 8-ounce duck, the difference in leakage surface 
considered. 
MISCELLANEOUS EXPERIMENTS AND OBSERVATIONS. 
APPEARANCE OF LARV.E AND PUP^E OF THE WHITE FLY WHEN DE- 
STROYED BY FUMIGATION. 
The opportunities for studying the efficiency of the gas against 
citrus pests are far superior with the white fly as compared with 
the true scale insects. While it requires considerable skill in the 
examinations, the vital conditions of the larvae and pupae, both 
before and after treatment, can be recognized with practical cer- 
tainty without removing the specimens from the leaves. When in a 
normal condition the insects in the stages mentioned appear green, 
owing to their translucence, and paired yellowish spots, due to inter- 
nal organs, are sometimes visible in the abdominal region. As the 
pupa reaches maturity the reddish eyes of the adult become conspicuous 
and the location of the developing adult wings is indicated by whitish 
patches on either side of the body. T\ Tien destroyed by fumigation 
with hydrocyanic-acid gas the larvae and pupae usually turn more or 
less brownish in the course of a few days. This brownish discolora- 
tion is most pronounced along the middle of the body. Frequently, 
however, two or three weeks may elapse before they can be positively 
determined as dead. In the first examinations made by the author, 
pupae on fumigated trees were classed as alive, doubtful, and dead. 
It was afterwards determined that in practically every case those 
classed as doubtful were in reality dead. Examinations under a 
compound microscope were found to be of some assistance at times, 
but on the whole unsatisfactory. In such cases movements of the 
internal organs furnish positive proof that the insect is alive, but 
when these movements can not be detected there may still be doubt 
concerning the condition of the specimen unless granulation or dis- 
coloration of the body contents is evident. The most satisfactory 
method of observing the results of fumigation is to examine the 
insects with a hand lens of 1 or 1J inch focal distance without dis- 
