ENTOMOLOGY 265 



The White-Fly of Greenhouses. The white-flies as a family are 

 tropical insects. In warm climates many species are abundant out of 

 doors, but in cold regions only a few sorts appear to be able to survive 

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

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

 oblong object slightly pointed at one end. The rounded end is at- 

 tached to the under surface of the leaf so that the egg hangs per- 

 pendicularly 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 glossy 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 suc- 

 culent 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 MJ mm. Under a hand lens one 

 can see that it is scantily clothed with minute bristles, having a denser 

 fringe along the margins of the body. Finally a T-shaped rupture 

 appears in the back skin of the insect, and the adult white-fly emerges 

 to continue the propagation of the race. 



The mouth parts of both the nymphs and adults of the white- 

 fly are formed for sucking, and the insects are injurious in both these 

 stages. They insert their tiny beaks into the succulent tissues of the 

 under surface of the leaf ; the latter soon shrivels, dies, and later falls 

 to the ground. As the adults prefer to oviposit upon the younger 

 shoots the lower leaves of infested plants die first. 



Observations and experiments carried on very recently have 

 shown that by far the most harm was caused by the work of the 

 nymphs. Adults kept in breeding cages with plants lived a longer 

 time than those without food, yet in no case did the plants die where 

 adults alone were present. 



Some time after the leaves are infested the under surface is 

 covered with a sticky substance excreted by the insects. This not 

 only tends to close the pores of the leaf, but it supports a black fungus 

 which soon covers the entire under surface of the leaf, making it 

 appear as though it were covered with soot. In a badly infested 

 greenhouse the upper surface shows this fungus, but less so than the 

 under surface. 



The time required for this insect to complete all its life history 

 stages is not more than five weeks, allowing one week's time for ovi- 

 position. It follows that an indefinite number of broods are possible, 

 and if left unchecked their numbers may easily become most seriously 

 destructive. Hydrocyanic acid gas is the most successful, as well as 

 the most satisfactory, remedy. Before fumigating it is necessary to 

 know the amount of space contained in the house; this will enable the 

 operator to mix his chemicals properly. Hydrocyanic acid gas if 

 used too strong, or if left in the house too long, will seriously injure. 



