46 BULLETIN 597, U. S. DEPARTMENT OF AGRICULTURE. 
wear halter appliances during the summer, it is necessary to treat 
the eggs during the autumn to prevent a late infestation from the 
well-incubated eggs after the protectors have been removed. ‘Then, 
too, the ease with which places so accessible to the horse’s mouth can 
be washed makes the use of washes a practical prevention in regions 
where bots are not so numerous. 
LARVZE REMOVED FROM EGGS PRIOR TO TREATMENT. 
Active larve were removed from well-incubated eggs and subjected 
to substances reported in Table X. Only larve in excellent condition 
were used, and these were observed in watch glasses, small tin boxes, 
and test tubes at short intervals until dead. When in doubt they 
were removed with a drop of the liquid to a microscope slide, and the 
warmth of one’s breath was sufficient to cause living ones to move. 
Larvee were killed instantly when placed in volatile liquids or gases 
of carbon disulphid and in absolute alcohol. 
TaBLe X.—Resistance of first-stage larve of Gastrophilus intestinalis, Aberdeen, 
S. Dak., 1916. 
Larvee placed in— Longevity. Larve placed in— Longevity. 
zi 5 
Drysbimsboxe ease eee 72 to 126 hours. || Borax, saturated solution. ----.- 40 minutes. 
Winter ies asa ee ie eee ee Raa 76 to 99 hours. 50 per cent alcohol. .....--....-- 30 minutes. 
Tincture quassia......-..:-.-..-- 24 to 36 hours. Petroleum, refined.-....-...---- 30 minutes. 
Beta-naphthol in alcohol. .....-. 20 to 28 hours. BO) Serene seas races 30 minutes. 
10 per cent oil of tar emulsion... | 41 to 48 hours. IBGHO BONG oj acbocaasSseecasaeece 13 minutes. 
Borax, saturated solution........- 28 to 41 hours. 334 per cent pine tar and 66% per | 1 minute. 
ID OF Rech eee eee eee eee 24 to 43 hours. cent kerosene. 
Dr. Guyot’s results compare favorably with those herein reported. 
His larve remained alive in water for 4 days, nearly a day in olive 
oil, and more than 14 hours in bichlorid of mercury solution 1 to 
1,000. 
The movement of freshly emerged larvee is very rapid upon moist 
surfaces, but upon a dry surface they seldom move from the original 
location, although they have been observed to live for 72 to 125 
hours. When placed in water the larvee became submerged with the 
exception of the posterior spiracles, which remained exposed at the 
surface. They are capable of living in this manner for 76 to 99 
hours. 
LARV REMOVED AFTER TREATMENT OF EGGS. 
Hundreds of eggs were collected from horses in pastures during 
the latter part of August and the early half of September. At this 
time the activities of adults of G. intestinalis were being directed to 
the manes of horses for oviposition, as in most cases the inside of the 
forelegs and sides immediately behind the forelegs were very grossly 
infested. These hairs were of sufficient length to render handling 
easy, and the eggs were about the same age. Except as otherwise in- 
