49 



plant was a small one, and the pot rested on the floor of the fumi- 

 gating box. It was observed that the fumes were very thin near 

 the bottom of the box, and in later experiments the pots were set on 

 a board raised about a foot from the floor. This insecticide is in- 

 expensive to use, and some who have had experience with it against 

 the insect claim that it is ineffective even for the adult. My own 

 experiments show that one or two ounces to 2000 cu. ft. of space, 

 according to the tightness of the house, should result in killing the 

 adults. The cost of fumigating a house containing 20,000 cu. ft. of 

 space at one ounce per 2000 cu. ft. of space would be $1.56. Ac- 

 cording to experiment 6 it would cost five times this amount to kill 

 one-half of the larvae and pupa; in a house of the same size. There 

 are many insecticides on the market which are used as fumigants 

 which have tobacco extracts as the active principle. Nicoticide may 

 be considered as a fairly representative type of the best of this class. 



Bush's Best Brand Fumigating Compound. — Nearly as effective, 

 ounce for ounce, as Nicoticide, but much more expensive. 



Thripscide. — The single experiment indicates that this material 

 is no more effective on the adult Aleyrodes than ordinary tobacco. 



•Carbon bisulfid. — Long exposure necessary for good results ; 

 too expensive for ordinary use. In a greenhouse containing 20,000 

 cu. ft. of space, the adults and a small percentage of the young could 

 be destroyed for $6.00, and the adults and about 50 percent of the 

 immature insects for about $10.00. 



Hydrocyanic Acid Gas. — Safe to use only by careful and intelli- 

 gent persons who appreciate its properties. Far cheaper and more 

 effective than any other fumigant known for use against the green- 

 house Aleyrodes. Cost for a house containing 20,000 cu. ft. of 

 space, using KCN at rate of .01 gm. per cu. ft., between 25 and 30 

 cents for each fumigation. Even plants as tender as tomatoes can 

 be fumigated without injury with the extremely small amounts of the 

 cyanide required. 



RECOMMENDATIONS. 



Fumigation. Bearing in mind the cost, labor involved and effect 

 on plants and Aleyrodes of the various materials used in these ex- 

 periments, hydrocyanic acid gas is pre-eminently the most deserving 



