NATURAL CONTROL. 41 
longevity experiments in the laboratory we have used test tubes with 
the bottoms removed and placed in trays with moistened sand. The 
mouths of the tubes are closed with absorbent cotton. Observa- 
tions can readily be made through the glass without disturbing the 
ticks and the air in the tube is kept moderately humid. For 
longevity experiments out of doors, we have made use of 14-inch 
glass tubing cut in lengths of about 10 inches. In one end of these 
tubes about 2 inches of moist sand and clay is firmly packed to 
prevent the escape of the ticks through the bottom. These tubes 
are then set in galvanized-iron cylinders which are sunk into the 
soil. The soil from the inside of the cylinder is removed to a suffi- 
cient depth to allow the surface of the dirt in the tube to be on a level 
with the surrounding earth. In place of an absorbent cotton stop- 
per a piece of bleached cotton was firmly tied over the top with rough 
cord, which would stand prolonged exposure without breaking. If 
exposed to rains but largely protected from the sun during the 
warmer months the longevity can be determined under normal but 
favorable conditions. The above methods have also been employed 
in obtaining preoviposition and oviposition records. Most of the 
longevity records here reported are based on tube experiments, 
but in work with Margaropus annulatus we have also placed engorged 
females collected within 24-hour periods in clumps of grass, about 
which screen cages were set to prevent intrusion, and determined 
the longevity by recording the dates seed ticks first appeared upon 
the grass and the dates the last could be found. 
NATURAL CONTROL. 
CLIMATIC CONDITIONS.” 
Cold appears to be the most effective check upon the spread of 
some species, while heat and a small or an excessive rainfall are 
equally effective with others. The effect of atmospheric humidity 
is undoubtedly an important factor also. Dr. Arnold Theiler (1908) 
has found the larve of Margaropus annulatus decoloratus to die within 
30 minutes when exposed to a temperature of —5° C. (23° F.) for 48 
hours, although they are not affected by an exposure to that tem- 
perature for 24 hours. We have found that with the cattle tick, 
engorged females kept in tubes without stoppers were killed at 
Dallas in October when the temperature fell to 13° F. for a few 
hours. Eggs of several species of ixodids have been found to be 
rendered nonviable by exposure to sun on bare ground for a few hours 
when the atmospheric temperature was about 101° I. The eggs of 
1 This can readily be done by running the bared hand and arm over the grass. 
2 The admirable studies of the cattle tick by Cotton and Voorhees (1911) have come to hand too late to 
note in this bulletin. Cotton reports that all adults of M. annulatus exposed at 14° F. were killed; that 
when unprotected all the larve are killed at 4° F. and all the eggs at 2°. It was found that when more 
than 25 per cent of the original weight of the eggs of this tick is lost they will not hatch. 
