BUREAU or ENTOMOLOGY. 337 



for protection a<;;aiiist flies and mosquitoes. This experiment was 

 undertaken through cooperative arrangement with several State ex- 

 l>eriment stations, agents of the Bureau of Entomology, and other 

 agencies in al)out 14 sections of the country, the object being to gain 

 information as to the most economical and effective screen under 

 various climatic conditions. While this test must be continued for 

 several 3'ears longer to determine the durability of many of the kinds 

 of wire, some information of value is already obtained. It api^ears 

 that there is much variation in the durability of certain screenings 

 of the same class and cost, probably due to methods of manufacture. 

 It also api^ears that in some regions black wire (painted) is even 

 more durable than some kinds of the higher-priced galvanized 

 screens. 



Investigations of insects hreeding in human excreta. — Wilmington, 

 N. C, field station : Owing to lack of funds it was found necessary to 

 discontinue this project. The agent in charge of these investiga- 

 tions was transferred from the bureau on May 31. During the 

 time he was assigned to the project he did very efficient work in 

 rearing the various species of flies which breed in human excreta. 

 Shortly before he resigned from the bureau he had begun experi- 

 ments with chemicals for the prevention of fly breeding. There was 

 not enough time to reach definite conclusions as to the effect of the 

 chemicals. However, the greatest promise was shown by potassium 

 cyanide solution, sodium arsenate solution, and a pine-tar product 

 acid. 



TROPICAL AND SUBTROPICAL FRUIT INSECT INVESTIGATIONS. 



The work in tropical and subtropical fruit insect investigations 

 is under the charge of the Assistant Chief of the Bureau, C. L. 

 Marlatt. 



Investigations of insects affecting citrus fruits in Cali- 

 fornia. — Tlie research work of this station has been largely a con- 

 tinuation of the investigations of liquid hydrocyanic acid for the 

 fumigation of citrus trees. The use of this liquefied gas is largely 

 replacing and probably will ultimatel}' almost entirely replace the old 

 methods of citrus fumigation with gas developed under the tree at the 

 time of fumigation by a combination of the proper chemicals. The 

 special work of this year has been a study of the diffusion of lique- 

 fied hydrocyanic acid under various temperatures and the effect of 

 the gas on citrus insects as the temperature is reduced. Attention 

 has been given the subject of daylight fumigation, and it is evident 

 from the results thus far obtained that fumigation of doimant citrus 

 trees during the day is possible providing the proper dosage and 

 exposure are employed. 



The Argentine ant investigations referred to in the report for 

 the fi.scal year ended June 30, 1919, have been continued, owing to 

 the fact that some of the ant ])oisons recommended crystallized 

 during cold weather and soured in the presence of a humid atmos- 

 phere, and as a result it has been necessary to modify some of the 

 formula to meet winter conditions. Considerable time has also 

 been tlcvoted to instituting ant-control campaigns in citrus centers 

 where the Argentine ant is abundant. A number of papers dealing 



