260 ANNUAL EEPOKTS OF DEPARTMENT OF AGRICULTURE. 



worked out by Dr. Hopkins, the chief of this section, in rehation to 

 forest and other injurious insects. It has proved, however, of such 

 wide application that he has worked upon its various aspects with 

 much assiduity. Extensive studies of tlie advance of the spring 

 season were carried on over a large portion of the United States, and 

 over 19,000 records of periodical events in pknts and insects were 

 made in the East. The most important result of this special study 

 of the advance of spring is in .the almost complete verification of 

 evidence in support of the law that has been formuhited from a 

 preceding study of 40,000 records of reported dates of wheat harvest 

 and of records of altitude limits of life zones. Applications of this 

 law appear to be of great value in the study of all problems relating 

 to periodical farm practice, the warfare against insects among others. 



TROPICAL AND SUBTROPICAL FRUIT INSECT INVESTIGATIONS. 



This branch of the bureau's investigations is under the charge of 

 the assistant chief of the Bureau, Mr. C. L. Marlatt, 



Investigation: s of insects affecting citrus fruits in Califor- 

 nia. A considerable portion of the time of the investigators as- 

 signed to this project has been devoted to extension Avork in connec- 

 tion with the efforts to stimulate production as a war measure. The 

 research work of this station has been continued with respect to 

 the investigation of the availability of liquid hydrocyanic acid 

 for the fumigation of citrus trees and the control of citrus mealy- 

 bugs and the Argentine ant. For the purpose of experimentation 

 Avith the liquid hydrocyanic acid, a 600-acre citrus ranch at Orange 

 was placed at the disposal of the agents of this department, and 

 veiy careful records have been kept on the subject of dosage, ex- 

 posure, and effect of meteorological and soil conclitions, and also of 

 previous insecticiclal treatments. Paralleling these orchard experi- 

 ments, certain necessary physical and chemical examinations have 

 been made of the liquid cyanid, involving the examination and analy- 

 sis of over a hundred clifferent samples to determine variation in 

 the chemical composition and the causes of such variation, involving 

 both methods of production and impurities. This investigation has 

 resulted in the determination of proper dosage tables for effective 

 use against the different scale insects infesting citrus trees under the 

 different conditions outlined tables which have been published and 

 are now available and are being generally followed in orchard work 

 in southern California. 



The control of the Argentine ant, which has rapidly spread dur- 

 ing the last few years in the citrus districts in California with the 

 resultant large increase of damage by mealybugs, which it harbors 

 and distributes, has been continued and a more efficient ant poison 

 has been developed especially in its application to the dryer condi- 

 tions. of California. Demonstrations with this poison in the control 

 of ants and the attendant mealybugs have been made at the various 

 places in the principal citrus-producing counties of California. A 

 method of control of the citrophilus mealybug, which has recently 

 become a very serious pest in limited regions of the citrus belt of 

 California, by banding and the use of ant poisons, has been de- 

 veloped which has resulted in one of the most notable successes in 



