ERADICATION OF THE ROOKY MOUNTAIN SPOTTED FEVER TICK. 9 



gorging. The last female on sheep No. 10 would probably have 

 become engorged had it been fertilized, for fertilized females engorge 

 rapidly, whereas with infertile females engorgement is slow. 



THE APPLICATION OF THE INFORMATION OBTAINED TO PRACTICAL 



ERADICATION. 



The main point to be considered in the last experiment is the fact 

 that of 33 females put on sheep No. 10, only 1 fed sufficiently to lay 

 eggs. There were in all, however, 6 females which stood a fair 

 chance of engorging, so that it is difficult to say what percentage of 

 females that get on a sheep in nature will enggrge to repletion. If 

 we assume that 6 females would have fed to repletion in nature, we 

 find that 5.5 per cent of those females which got on the sheep became 

 engorged. In the experiment with 2 sheep, at the end of 6 days these 

 animals had picked up at least 19 females, of which 13 females at- 

 tached. At the same rate in 30 days sheep No. 10 would have had at- 

 tached 80 females and would have picked up 94 females. If we take 

 5.5 per cent of 94 we have 5.17 females which would engorge to reple- 

 tion in a month. We would have to assume this many to be the maxi- 

 mum for the sheep with heavy wool in the experiment. The mini- 

 mum would be 0, since there were 2 sheep which had no females at- 

 tached at the examination. It would be impossible to strike -an aver- 

 age, but let us assume that each sheep would breed, on an average, 2 

 ticks per month. We would then have, for a her<ji of 1,000 sheep, 

 2,000 ticks per month during the tick season. Each female means 

 about 4,000 larvae. This would make 8,000,000 larvse, which is a 

 rather large number, though, it is of course impossible to estimate 

 what percentage of these would ever reach maturity. It might, how- 

 ever, be possible to eliminate the sheep which are likely to breed the 

 majority of the ticks. Could this be done, it would be possible to 

 use sheep in the destruction of ticks without dipping them. Until 

 that fact is demonstrated, however, it would seem necessary to dip 

 sheep along with other live stock in case they were allowed to run in 

 " ticky " country. Even if it were not necessary to dip sheep with heavy 

 wool, it would certainly be necessary to dip lambs or sheared sheep. 

 A mere glance at the table will show that lambs or sheared sheep will 

 breed a considerable number of ticks and kill but few. The only pos- 

 sibility, therefore, of employing sheep in the work of tick eradication 

 would be the using of wethers of other sheep with heavy wool. It 

 does not appear practicable to attempt to use wethers alone, under 

 any circumstances, as a means of ridding the Bitter Root Valley of 

 spotted fever ticks. Nevertheless it would appear to be possible to 

 use sheep as one means of reducing the numbers of the ticks, although 

 in this connection several considerations must be mentioned. 



