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. 



LARViE REMOVED FROM EGGS PRIOR TO TREATMENT. 



Active larvae were removed from well-incubated eggs and subjected 

 to substances reported in Table X. Only larvae 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. 

 Larvae were killed instantly when placed in volatile liquids or gases 

 of carbon disulphid and in absolute alcohol. 



Table X. — Resistance of first-stage larvw of Gastrophilus intestinalis, Aberdeen, 



8. Dak., 1916. 



Larvae placed in — 



Longevity. 



Larvae placed in— 



Longevity. 



Drv tin box 



72 to 126 hours. 

 76 to 99 hours. 

 24 to 36 hours. 

 20 to 28 hours. 

 41 to 48 hours. 

 28 to 41 hours. 

 24 to 43 hours. 



Borax, saturated solution 



50 per cent alcohol 



40 minutes. 





30 minutes. 





Petroleum, refined 



30 minutes. 



Beta-naphthol in alcohol 



10 per. cent oil of tar emulsion 



Borax, saturated solution 



Do 



Do 





Boric acid 





33i per cent pine tar and 66| per 

 cent kerosene. 



1 minute. 







Dr. Guyot's results compare favorably with those herein reported. 

 His larvae 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 larvae 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 larvae 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. 



LARVAE 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- 



