47 



other plants showed no injury ; on the contrary, a cheek cucumber 

 plant, which was practically a duplicate of the one fumigated in re- 

 spect to size, vigor and infestation, was dead two days later, while 

 the fumigated plant rapidly improved in health. Of the Aleyrodes, 

 all the adults, larva? and pupa? were killed; eggs apparently killed. 

 The red spiders on the cucumber plant were all killed. 



DISCUSSION OF RESULTS. 



Contact Insecticides. Few contact insecticides were used, but 

 these were varied enough to indicate that in general they are destruc- 

 tive to larva? and young pupa?, and more or less so to nearly mature 

 pupa?. They proved useless, however, for the eggs, and not practical 

 for use against the adults of this insect. The statements of those 

 who have had practical experience with Aleyrodes in greenhouses 

 shows that syringing the plants does not seem to lessen the numbers 

 of the adults. In these experiments especial attention was given to 

 the destruction of the adults, but not more than two-thirds of them 

 were killed in any case. At the most, one could not expect to kill 

 more than one-half the adults by an ordinary syringing, which would 

 be sufficient to destroy 90 per cent of the young. The most expert 

 growers of tomatoes in greenhouses tell us that these plants should 

 not be syringed except when it is absolutely necessary, for a damp 

 atmosphere promotes rot and interferes with pollination. It is de- 

 sirable, therefore, to depend as much as possible on fumigation for 

 the control of the greenhouse Aleyrodes, at least on those plants 

 which are liable to be injured in any way by the application of a 

 contact insecticide. These latter, however, may be used to advan- 

 tage in many cases. 



The following comments will aid in showing the relative value 

 of each of the contact insecticides used in the experiments: 



Lemon Oil Insecticide. — The cost of this material precludes its 

 use on a large scale, but it is easy to prepare, has a not unpleasant 

 odor, and the experiments show it to be effective on the larva? and 

 pupa? when the plant is dipped in a solution of one-half pint in one 

 gallon of water. Chiefly commendable for the treatment of house 

 plants. 



Laundry Soap. — Cheap; fairly effective on the insects when 



