peratures after 2L, to 60 days. Whereas an occasional female dies 

 as soon as oviposition is completed, others may survive for a few 

 days or, exceptionally, for a month. One tick deposits from 2^00 

 to ^300 eggs. 



In nature, the yellow dog-tick doubtless may produce two 

 generations a year. Lounsbviry reared three generations a year 

 in an incubator. Taking average figures for ticks raised under 

 favorable conditions, the cycle may be completed in 123 days, 

 as follows: 



PERIOD DAYS 



123 



Ecology 



The distribution of H. 1. leachii has been determined for 

 South Africa by Theiler a!nd Robinson (1953A) . The most important 

 factor in limiting this tick's spread there is increasing aridity. 

 Twenty inches of annual rainfall, irrespective of vegetation type, 

 appears to be the critical level there. 



However, in northern Sudan, where rainfall is absent or 

 considerably less than ten inches annually, H. 1. leachii is 

 still fairly common on foxes. 



In the Nile Valley of Egypt, where rainfall is nil to ex- 

 ceedingly low, the tick thrives. But, it should be stressed, the 

 microhabitats of its larval and nymphal host, the grass rat, Arvi- 

 c ant his n. niloticus, are more humid than elsewhere, situated as 



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