48 THE WHITE-FLY OF GREENHOUSES 



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 prop- 

 agation of the race. 



INJURIES TO THE PLANT 



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 during the past 

 season showed that much 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. 



HIBERNATION AND BROODS 



We have no evidence in our New Hampshire studies that the 

 white-flies can pass the winter out of doors. On those plants 

 that were infested in the open last summer and since brought 

 into the greenhouse, none of its life-history stages can be found. 

 The treatment given those in the greenhouses subdued their 

 numbers and at the approach of cold weather the few that 

 remained were less active. Some adults linger among the 

 leaves of yourg beets in the greenhouse during the colder wea- 

 ther, occasionally appearing on young tomato plants. Adults 

 captured on January 14 and put in vials containing no food 

 died in three days, others kept in bell jars with plants survived. 

 No nymphs could be found at this time, and it is probable that 



