BUREAU OF ENTOMOLOGY. 235 



active summer season showed that less than 50 per cent had taken a 

 blood meal, and, of those that had, only 20 per cent had fed upon 

 human blood. It appears from this work that the g^reat reduction 

 in the abundance of Anopheles with the advent of the colder tem- 

 peratures of fall operates against the infection of the mosquitoes 

 that enter the more inactive period of winter. 



A survey of malaria cases and infection on a plantation, in relation 

 to sources of Anopheles and environmental conditions that favor con- 

 centration about habitations, showed that, even within the limits of 

 a single plantation, the location of the houses in respect to breeding 

 places of Anopheles has an important influence on the number of 

 cases of malaria. Where drainage is not possible in the delta 

 country it has been found practical to impound the surface water 

 in a portion of a bayou under conditions unfavorable for the de- 

 velopment of Anopheles larvae, thus creating a favorable zone for 

 the location of cabins for the tenants. 



Cooperation with various agencies interested in the reduction of 

 malaria has been continued. The Bureau of Fisheries has made 

 progress* in the study of fish that feed upon mosquito larvse. 



The work on the control of the house fly was continued at the 

 Bethesda, Md,, Experiment Farm of the department through experi- 

 ments with manure pits with flytraps attached. A practical type of 

 manure pit was devised. The experiments with maggot traps in co- 

 operation with the Maryland Agricultural College were completed. 



Many experiments with certain common baits were carried out, 

 with the result that much more exact information has been obtained 

 •as to the stage of fermentation most attractive to flies and the length 

 of time each remains attractive. Some progress was made in the 

 study of the reactions of flies to pure isolated chemical compounds. 

 Poisoned baits made with sodium arsenite, calcium arsenite, and 

 formalin were tested and compared. 



Further observations and experiments on the overwintering of 

 house flies lead to the conclusion that in the latitude of Washington, 

 as well as farther south, the house fly overwinters in the larva and 

 pupa stages. The fly was found also to breed continuously during 

 the winter in heated buildings, such as houses used for breeding of 

 guinea pigs, where there was food for the adult flies and materials 

 on which the eggs could be laid and in which the larvae could de- 

 velop. Exact data were obtained on the seasonal occurrence of cer- 

 tain common flies. Studies were made on the life history and habits 

 of the cluster fly, which is often a nuisance in houses, and trapping 

 as a control measure was tried. 



The work on the eradication of the Rocky Mountain spotted-fever 

 tick was continued successfully in Montana in cooperation with the 

 State board of entomology. Many observations were made on biting 

 flies and other insects of importance in connection with the health 

 of man, local outbreaks were investigated, and a special circular on 

 important insects which may affect the health of men or animals 

 engaged in military operations was printed in a large edition. 



A special feature of the work was the completion of a large mono- 

 graphic treatment of the mosquitoes of North and Central America 

 and the West Indies, published by the Carnegie Institution of Wash- 

 ington. 



