12 



SUMMARY. 



As thrips take their food by suction, stomach poisons are not 

 available, and contact poisons and fumigation are the only methods 

 of value. 



Spraying with contact poisons, however, is only a partial success 

 at best, as many of the insects escape, being protected by the leaf 

 veins, spines, and grooves of the stem of the plant. Dipping the 

 whole plant into the poison, as was the case with experiments 3 and 

 4, would avoid this difficulty, but as this is only possible in the case 

 of potted plants, fumigation appears to be the most successful 

 method of dealing with these insects in greenhouses. 



Of the materials tried in fumigation — Rose-leaf Tobacco Extract, 

 Carbon disulphide, Nikoteeu Aphis Punk, Nikoteen and Hydrocy- 

 anic acid gas — the carbon disulphide fumes were so heavy that they 

 settled to the bottom of the case, leaving the insects on the upper 

 parts of the plant uninjured, while if a sufficient quantity of fumes 

 should be produced to fill the greenhouse, it is probable that in the 

 lower parts they would necessarily be so dense as to kill the plants. 



Nikoteen Aphis Punk proved ineffective for thrips though strong 

 enough to destroy plant lice. 



Rose-leaf Tobacco Extract, though a success in killing the thrips, 

 as shown by experiments 14 and 15, is more expensive for the work 

 than Nikoteen, which when vaporized in the proportions given in 

 experiments 21, 22 and 23 gave about the best results of anything 

 tried, though the results from Hydrocyanic acid gas were also suc- 

 cessful. If the extremely dangerous character of this gas and also 

 the fact that in some cases the plants were injured by it, be taken 

 into account, however, the Nikoteeu appears to have been the most 

 successful substance for fumigation, used in these experiments. 

 The Nikoteen used was manufactured by the Scabcura Dip Co. of 

 Chicago. 



