52 HYDROCYANIC-ACID GAS FUMIGATION IN CALIFORNIA. 
rather than from actual experience in the field. 1 The practice among 
commercial fumigators has been to absolutely ignore these tables, 
depending, instead, on their own judgment. The result is that 
their scheduling differs markedly from that of the published 
schedules. 
FACTORS WHICH AFFECT THE DOSAGE. 
Although citrus-fruit growing in southern California is restricted 
to a limited area the climatic conditions are not uniform in all sec- 
tions. The region adjacent to the coast generally is cooler and much 
damper at night than in the interior valleys. This situation has led to 
a diversity of opinion among fumigators as to the comparative 
dosage for the two sections. Some hold that a heavier dosage is 
required near the coast on the ground that the gas is absorbed by 
the dampness; others, that the drier and lighter air in the interior 
valleys allows a more rapid escape of gas through the tent, which 
necessitates more cyanid than for the heavier air of the coast. Set- 
ting aside these opinions and examining the situation as it actually 
is, we find that the general dosage strength for a particular insect is 
approximately the same throughout southern California regardless 
of nearness to or remoteness from the ocean. Of course, there are a 
few striking individual variations from this general statement, but 
these variations are as noticeable in one place as in another. 
Personal experience in all sections has taught the writer that the 
leakage of gas is for the most part noticeably greater in the dryer and 
warmer interior sections than near the coast. Despite this condition 
any given dosage appears to be as efficient in one place as in another. 
This marked efficiency in the dryer and warmer sections regardless 
of the greater leakage might possibly be due to the fact that the scale 
insects are more susceptible to the gas in the higher temperatures 
general there than in the cooler temperatures of the coast. It is 
known among entomologists that insects are active at high tem- 
peratures but become dormant at low temperatures and in the latter 
condition are more difficult to destro}^. Prof. Woodworth, of the 
University of California, has informed the writer that laboratory 
experiments performed by him have shown this condition to exist 
among scale insects and that the temperature at which they become 
dormant is relatively high. This interrelation of temperature and 
activity has a very important bearing on the fumigation treatment 
and demands much further experimentation in the field as well as in 
the laborafcny. 
The old conception that an increase of dosage was required near 
the coast to offset the loss of gas from absorption by moisture is also 
no longer tenable. Experience has shown that the results during 
i Bui. 79, Bur. Ent., U. S. Dept. Agr., pp. 20-22, 1909, 
