234 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



As a result of work at Qiiincy, Fla., the method of combating the 

 tobacco budworm by means of the arsenate of lead and meal mixture 

 has been perfected and this remedy now is used very generally. It 

 has effected a saving of at least $20 per acre over the method previ- 

 ously in vogue. 



It has been found that the tobacco thrips can be controlled fairly 

 well by the use of nicotine sulphate as a daytime spray. Heretofore 

 planters in Florida have had to use kerosene emulsion for the control 

 of this insect and could make the application only at night. By using 

 nicotine sulphate planters can employ their labor more efficiently 

 and obtain practically as good results as usually were obtained by 

 applications of kerosene emulsion at night. 



Insects affecting sugar cane. — Work on sugar-cane insects was 

 conducted on lines previously established. Experiments on control, 

 general observations, and life-history studies were continued. A 

 more efficient machine was devised for the application of poisons to 

 sugar cane. A search was made for parasites of the sugar-cane moth 

 borer in the Southeastern States and in Cuba. As a result of the 

 work in Cuba many individuals of one species were shipped to 

 Louisiana. Whether they have become established can not be de- 

 termined at this time. Methods of controlling the Argentine ant in 

 sugar fields were tested but on the whole the results were unsatis- 

 factory and considerable further work is necessary. 



INVESTIGATIONS OF INSECTS AFFECTING THE HEALTH OF MAN. 



The agricultural importance of malaria is shown by the fact that 

 the loss from this disease on a typical southern plantation culti- 

 vating 1,800 acres of land amounted during one season to $2,200 

 through loss of time and to $4,300 through inefficiency due to the 

 infection. 



Four species of mosquitoes of the genus Anopheles, namely, quadri- 

 Tnaculatus, punctipennis^ pseudopunctipennis, and crucians^ have 

 been encountered in the delta region of the lower Mississippi Valley 

 where the field work of the bureau is conducted. Intensive studies 

 on abundance and house habits showed that Anopheles quadri- 

 macidatus is the principal species concerned in the transmission of 

 malaria in this region. 



Large series of specimens were reared for experiments conducted 

 in New Orleans to test the resistance of the malaria parasites to low 

 temperatures while in the body of the mosquito. This work showed 

 that the tertian parasite is able to survive a temperature of 31° F. 

 for a period of four days. In a smaller series of tests the estivo- 

 autumnal parasite survived a temperature of 35° for 24 hours. This 

 work is preliminary to more detailed investigation to determine the 

 possibility of the malaria parasites surviving the winter months in 

 the body of the mosquito host. A long series of dissections of adult 

 Anopheles collected during the winter about habitations gave no 

 evidence of infection. 



Bearing on the question of infection in the mosquito host is the 

 food habit of the adult Anopheles. An examination of nearly 5,000 

 stomachs of Anopheles quadrimaculatus at Scott, Ark,, during the 



