6 BULLETIN 165, U. S. DEPARTMENT OF AGRICULTURE. 



and in these experiments is used at the rate of 1-2,000. The nico- 

 tine sulphate used was standardized to 40 per cent and the solution 

 of quassiin was used so that it would correspond with the 40 per cent 

 solution of nicotine sulphate. For instance, instead of using 1 gram 

 of quassiin to 2,000 cubic centimeters of water, 0.4 gram was used 

 to 2,000 cubic centimeters of water. 



During the early part of the work it was discovered that the whale- 

 oil soap, even when used at the greatest dilution at which it had any 

 spreading effect (1 pound to 100 gallons), killed a certain percentage 

 of the aphides. Since a spreader is necessary, experiments were 

 inaugurated to find one that would have no effect upon the insects 

 treated. It was found that the soap bark solution which was being 

 used in some other work was an excellent spreader and did not affect 

 the insects in the least. In all of the following experiments a water 

 decoction of this material was used at the rate of 2 pounds of soap 

 bark to 100 gallons of water. 



In applying the solutions, a compressed-air spray machine (fig. 

 1) which maintained 50 pounds pressure and handled as small an 

 amount as 200 cubic centimeters was used. A fine mist nozzle was 

 so adjusted to this pressure of 50 pounds that a washing rather than 

 a mist spray was produced. 



In conducting the experiments detailed in Table II prune twigs 

 infested by the hop aphis (PJrorodon humuli Schrank) and the prune 

 aphis {Hyalopterus pruni Fab.) were brought from the field and, 

 after being sprayed with the solutions, were set in moist sand. 

 By placing the pots of sand containing the sprayed twigs on sheets 

 of paper the percentage of the insects that were killed by the solu- 

 tions were readily obtained. Check twigs were kept to make sure 

 that there was not a marked mortality from some other cause. 



Table II gives the results of the spraying experiments with quassiin 

 in aqueous solution and also in solutions of certain alkaline sub- 

 stances. 



Table II. — Results of experiments with quassiin as a contact insecticide. 

 SEMES NO. 1. WITH SOAP BARK IN LABORATORY. 



904 

 8, 060 

 1,119 



0.4 grams to 1,500 cc 1,310 



0.4 grams to 1,000 cc 1, 831 



0.4 grams to 3.000 cc. 

 0.4 grams to 2,000 cc. 

 0.4 grams to 1,S00 cc. 



Number of 

 aphides 

 sprayed . 



Per cent of 

 aphides 

 killed. 



85.1 

 93. 02 

 94.6 

 93.9 

 99.7 



SERIES NO. 2. WITH WHALE-OIL SOAP IN FIELD. 



0.4 grams to 2,000 cc. 

 0.4 grams to 1,800 cc. 

 0.4 grams to 1,500 cc. 



