550 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



Should the ground squirrels prove to be the chief host for the tick 

 which disseminates the dreiuled fever, it is believed their extermina- 

 tion within the limits of the valley can be accomplished without undue 

 expenditure of labor and money. 



CALIFORNIA GROUND SQUIRREL. 



Recent investigations by the Public Health and IMarine-Hospital 

 Service in California show that the infection of ground squirrels 

 with plague is more widespread in the State than was at first sup- 

 posed, and infected squirrels have been found in ten counties: Ala- 

 meda, Contra Costa, Merced, Monterey, San Benito, San Joaquin, 

 San Luis Obispo, Santa Clara, Santa Cruz, and Stanislaus. As yet, 

 however, very few of the several thousand ground squirrels exam- 

 ined from those sections show infection, the total number up to June 

 30, 1910, being 381. The infection, therefore, while somewhat wide- 

 spread, is by no means general, and it is believed that a well-organized 

 campaign of destruction in the counties where infected rodents have 

 been found will go far toward eliminating the danger of the plague's 

 becoming endemic generally among the rodents of California and 

 spreading to other States. 



When 2:)oisoning operations must be conducted on the large scale 

 necessary in the case of an animal so numerous and widely distributed 

 as this, cost is a prime factor of the problem. Accordingly during 

 the 3^ear careful experiments wath poisons have been conducted in 

 several parts of California to determine the cheapest and most effect- 

 ive method of use. Green barley heads and whole barley have been 

 found to be the best baits, and strychnine to be the cheapest and most 

 certain poison, provided a good quality be employed. Unfortunately, 

 some of the strychnine bought by farmers is poor, and hence yields 

 a minimum of effectiveness at a maximum of cost. 



The best time for poisoning operations has been found to be during 

 the late summer and fall months before the winter rains begin, not 

 only because the animals will more readily eat poisoned bait at this 

 time of year, but because this is the season for preventing increase, 

 the young appearing as early as March in the southern part of the 

 State. 



Hundreds of poisoned squirrels were examined with a view to ascer- 

 taining how many young they have. They were found to be very 

 prolific, having from 4 to 11 at a birth, or an average of 6 or 7. This 

 prolificness goes far to explain the quickness with which a locality 

 where a part of the squirrel population is destroyed is repopulated. 



DIKE BORERS. 



During the year demonstrations of methods of poisoning gophers 

 with strychnine and catching them by means of improved traps were 

 made in California, Arizona',^ and Nevada by assistants of the Survey. 

 At Banning, Cal., by cooperation with ranchers and fruit growers, 

 these destructive rodents were so reduced in numbers that their depre- 

 dations in many localities ceased. A report from the engineer in 

 charge of the reclamation project at Fallon, Nev., states that whereas 

 in 1906 over 50 expensive breaks in the canals occurred in consequence 

 of tunneling by gophers, during the past year, as a result of the adop- 



