37 



Greenhouses in which vegetables are grown are liable to become 

 infested in two ways. First, there may be weeds, such as chick- 

 weed or other food plants of the species, growing in the house, under 

 the benches or other out of the way places, and on these the insects 

 may live during the summer months when the house is unused, and 

 in the fall spread to the new crops. Again, adults which have de- 

 veloped out of doors may fly into the houses. This is especially 

 liable to occur where there are infested plants in the vicinity. 



To prevent the first method of infestation, before starting a crop 

 in the fall, all weeds and vegetation of every kind should be re- 

 moved from the house. Eggs, larvae and pupae of the insect are thus 

 provided for. Adults may be killed by burning sulphur at the rate 

 of 6 oz. to iooo cu. ft. of space, or by hydrocyanic acid gas from .2 

 gram of Potassium cyanide (KCN) per cu. ft. of space, leaving the 

 house closed over night. The rate for the use of the cyanide, as 

 given above, is much greater than is absolutely necessary to destroy 

 adult Aleyrodes, in order that it may also be effective against thrips 

 and other pests. The effect of sulphur on other insects than Aley- 

 rodes is unknown to the writer. 



Whenever a first crop is entirely removed, the house should be 

 fumigated by one of these methods before starting a new crop. 

 This, of course, will not be possible where there is only one house, 

 and the new crop is under way before the old one is removed. 



To prevent the Aleyrodes from spreading into the greenhouses 

 from plants growing out of doors, little can be done except to see 

 that no infested plants are growing in the vicinity. Aleyrodes found 

 on strawberry plants, as will be seen later, need not be considered in 

 this connection. After the first few frosts in the fall there is little 

 danger of the insect getting into greenhouses from out of doors. 



REMEDIES. 



Various insecticides have been recommended and used for the 

 destruction of this insect. Ravenscroft (10), who was the first, as 

 far as I am aware, to recommend a specific treatment, says that " the 

 best remedy is to syringe with a solution of Calvert's Soft Soap." 

 Among the later recommendations are : Tobacco fumes in green- 

 houses, whale oil soap and kerosene emulsion out of doors (16); any 

 4 



