THE WHITE-FLY OF GREENHOUSES 



BY CLARENCE M. WEED AND ALBERT F. CONRADI 



During recent years greenhouse crops in this and other states 

 have been very commonly attacked by a tiny insect which has 

 received the common name of white-tly. It is a member of a 

 small and generally little-known famil}^ whose technical name 

 is Aleurodes. It accomplishes its injury by sucking the sap of 

 its food-plants, often appearing upon the leaves in enormous 

 numbers. A great variety of greenhouse crops suffer from its 

 depredations, although in New Hampshire cucumbers and 

 tomatoes growing under glass have been damaged the most. 



The white-flies as a family are tropical insects. In warm 

 climates man}" species are abundant out of doors, but in cold 

 regions onh^ a few sorts appear to be able to survive from sea- 

 son to season, except in the shelter of the heated greenhouse. 



LIFE HISTORY 



The egg of the white-fly common in our greenhouses is a 

 minute oblong object slightly pointed at one end. The rounded 

 end is attached to the under surface of the leaf so that the egg 

 hangs perpendicularly downward when the leaf is horizontal. 

 Its length is less than 1-4 mm. or about 1-100 inch. When 

 first laid the eggs are slightly greenish yellow, but they soon 

 become darker. Just before hatching the color is a dull o:lossv 

 brown. 



In a little less than two weeks (13 days according to our 

 observations) the eggs hatch into little nymphs, which move 

 about over the surface of the leaf for a few hours, perhaps a 

 day ; then they insert their tiny beaks into the succulent tissues 

 of the leaf and settle down, taking on the appearance of a 

 minute scale. 



The little scale remains in position two weeks or longer ; 

 then it is a tiny flattened object, with oval outline, of a slightly 

 greenish-yellow color, in size about 1 mm. by 1-2 mm. Under a 



