20 
NORTH AMERICAN FKYER TICK AM) OTHER SPECIES. 
Table III. Relation of temperaturt to period of incubation in Margaropus annulatus 
at Dallas, '/'< <.. 1905-1906. 
onto deposited. 
\ 
of 
lots. 
Incubation 
Incubation temperature. 
M 
nod. 
Mean. 
1 effective. 
Maxi- 
mum. 
.Mini- 
mum. 
Aver- 
- 
Maxi- 
mum. 
Mini- 
mum. 
Aver- 
age. 
Maxi- 
mum. 
Mini- 
mum. 
Aver- 
age. 
1905. 
2 
1 
.'. 
8 
7 
11 
13 
2 
Days. 
56 
:.l 
33 
28 
26 
32 
154 
139 
Days. 
i3 
39 
27 
21 
22 
23 
23 
135 
Days. 
19.5 
!•..: 
29 
24.8 
23. I 
24.9 
46.2 
137 
°F. 
62.6 
72. 6 
79.7 
80.5 
80.5 
79.7 
79.4 
53.4 
°F. 
62.3 
69.7 
73.5 
79.8 
79.8 
78.9 
54.6 
53 
°F. 
62.4 
71 .8 
77.6 
80.2 
80.2 
77.8 
70.7 
53.2 
°F. 
1,083 
1. L75.8 
1,103.-2 
1,046.6 
962.1 
1,169.3 
1,907.9 
1,600.6 
F. 
840.5 
1,139.1 
782.7 
•_ 
vv,7 
1,510.8 
- 
Apr 
1,286.4 
M;iv 
1,023 
.(uric 
Julv 
866. 5 
Aug 
904.4 
1. 127 


" Weighted. 
It will be noted that the total effective temperature necessary to 
cause eggs to hatch, varies from 866.5° to 1,555.7°. It would be of the 
greatest practical importance to formulate a rule which, on the basis of 
effective temperatures, would show the time when eggs will hatch at 
different seasons of the year. It is probable that the present data arc 
insufficient for this purpose, and special efforts will be made to add 
to them. However, with the data at present available the following 
tentative' law may be proposed: 
WTien the average daily mean temperature ranges less than 53.2°, at 
least 1,510.8 degrees of effective temperature must accumulate befort 
hatching will take place. When the mean daily temperature averages 
from 61 .4° to 77.8°, from 84-0.-5 to 1 ,139.1 degrees of effective tempi ratun 
will he required for hatching. VHten the mean daily temperatun aver- 
ages higher than 80°, between 782.7 and 8.24-3 degrees of effectivi tem- 
perature must he accumulated before hatching will take place. 
It is not our purpose to advise an attempt at the practical appli- 
cation of this rule at the present time, but it is supposed that such 
practical application can be ultimately made. To do so it would 
only be necessary for the stockman to have a set of self-recording 
maximum and minimum thermometers, such as can be purchased 
for S3. Or the data might be obtained from the nearest Weather 
Bureau station. By either of these means the average daily tempera- 
ture could be easily obtained. By summing up the daily effective 
temperatures— that is, the number of degrees above 43 — the stock- 
man, by reference to the minimum amount of accumulated effective 
temperature necessary for hatching with various average daily tem- 
peratures, could determine ai least within certain limits what time 
" This rule, of course, may nol apply in rare cases in which eggs are deposited where 
they will be subjeel to artificial heal rather than to weather temperature, ae in manure 
piles. Ii will apply, however, to the greal majority of pasture conditions throughout 
the infested area. 
