THRIPS INJUniNG THE FOLIAGE 203 



is recommended. The potato vines themselves, also, should be 

 burned. 



The Hop-aphis {Phorodon humuli Sclir.) 



Hops are subject to infestation by a green, soft-bodied louse, one eight- 

 eenth to one tweKth of an inch in length. The male plants in hopyards 

 always are infested first, and from these the lice spread two or three 

 weeks later to the female or fruiting plants. Their attack causes the 

 leaves to turn yellow, and seriously reduces the yield. 



Recent studies show that the winter may be passed in an egg stage 

 somewhere near or on the hop- vines, although it is known that the 

 same species winters also on plum trees. There are many generations 

 in the course of a summer. 



Thorough spraying with a contact insecticide, such as tobacco ex- 

 tract or 5 per cent kerosene emulsion, will kill the aphids. Remedial 

 treatments should be begun while the lice are still isolated on the male 

 plants, before spread has started. 



The Greenhouse Thrips {Heliothrips hwmorrhoidalis Bouch^) 



The foliage of plants in greenhouses sometimes is injured by a very 

 small, sucking insect properly known as a thrips. E\ddence of the 

 work is seen first in numerous whitish spots, where the juices of 

 the leaf have been sucked out. These spots show in the beginning 

 more plainly on the lower surface. As attack goes on, the spots 

 spread, forming blotches, dead areas appear around the edges of 

 the leaf, the fohage wilts, and finally drops off. The surface of the 

 leaf is covered with small drops of reddish fluid, which frequently 

 turns black. 



The adult insect is one fifteenth of an inch in length, dark bodied, and 

 though it has wings is not much disposed to fly. The young are lighter 

 colored, and have no wings. They suck the leaf juices just as do the 

 adults. Three or four weeks are required for a generation. 



Usually this pest is controlled successfully by fumigation with 

 tobacco. 



