78 HYDROCYANIC-ACID GAS FUMIGATION IN CALIFORNIA. 
decided benefit. The prevalence of the black scale on many other 
hosts offers a wide range of activity for the parasite, and it is on these 
noncitrus plants that our little friend does some of its very best work. 
If it did nothing else, its work against the black scale on the pepper 
tree (ScMnus molle) makes it especially worthy of praise, and the 
question has frequently come up whether or not fumigation destroys 
the ScuteUista. Numerous observations and experiments respecting 
this point have been made during this investigation indicating that 
fumigation destroys many of the ScuteUista in its adult and pupal 
stages. The majority of the parasites, however, are unaffected, even 
when schedule No. 1 is used. Parasitized scales have been removed 
the day following such treatment and placed in vials, with the result 
that some adults would immediately issue and others continue to 
issue for many days afterwards. The adults of ScuteUista in the open 
are destroyed by a weak dosage. The reason they escape beneath 
the scales is that such parasitized scales are tightly sealed to the 
leaf or branch, apparently by some secretion produced by the larvae, 
and the gas does not penetrate such scales as easily as it does those 
nonparasitized. 
One of the greatest benefits of the ScuteUista is its work in trees 
which have been fumigated. The eggs of the black scale to a large 
extent survive the gas treatment. This leaves abundant oppor- 
tunity for a future infestation on trees treated when eggs are present. 
If ScuteUista occurs in the orchard, these undestroyed eggs are 
devoured, thus completing a treatment for which fumigation itself 
is only partially successful. 
THE COST OF FUMIGATION. 
The cost of fumigating an orchard depends principally on the size 
of the trees and the dosage-rate used. The average California citrus 
orchard requires an average expenditure of from $25 to $40 per acre 
for one fumigation treatment. Large seedling trees are much more 
expensive, while young trees cost considerably less. 
The directors of fumigating outfits base their estimates on two 
distinct considerations: The chemicals and covering the trees. Con- 
tract fumigators usually furnish the cyanid at 30 cents per pound, 
which also includes the sulphuric acid necessary for generation of the 
gas. The price of covering trees varies with their size, number, 
location, topography of land, etc. The fumigator will charge more 
per tree where the orchard consists of a half acre than if it has 50 
acres. Trees that require a 45-foot tent usually will cost more to 
cover than those requiring a 36-foot tent. The average price of 
covering in commercial work where nothing larger than 45-foot tents 
is used is from 10 to 12 cents per tree. Large seedling trees whose 
covering requires derricks may cost from 40 to 50 cents, or even more, 
