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 (Schinus nriolle) makes it especially worthy of praise, and the 

 question has frequently come up whether or not fumigation destroys 

 the Scutellista. Numerous observations and experiments respecting 

 this point have been made during this investigation indicating that 

 fumigation destroys many of the Scutellista 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 Scutellista 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 larvse, 

 and the gas does not penetrate such scales as easily as it does those 

 nonparasitized. 



One of the greatest benefits of the Scutellista 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 Scutellista 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, 



