FERN-PESTS. 



169 



In fact, if the greenhouse is smoked lightly every 

 week, as it should be, very little trouble will be 

 experienced from this source. When house-plants 

 or ferneries are attacked by them, the Aphides may 

 be readily removed by using a soft brush. 



The Thrips {Heliothrips hcBmorrhoidalis^ PI. 22, 

 Fig. 2) is much harder to manage. These insects 

 generally collect unobserved on the under side of 

 the fern-fronds, where they increase greatly, and 

 injure many plants before their presence is sus- 

 pected. They live upon the cuticle of the frond 

 or leaf, causing it to turn brown or whitish. The 

 insects in the larval state are white, the adults 

 black or dark brown. These are so small, — being 

 only about the sixteenth of an inch in length, — 

 that they are hardly noticeable without a glass, 

 and are with difficulty removed by mechanical 

 means. Smoking which will keep the Aphis in 

 check will not dislodge the Thrips, while smoke 

 sufficiently strong to kill the Thrips will be sure 

 to injure the more delicate plants. The best 

 method is to select some time when dull weather 

 is expected, and give the house, three evenings in 

 succession, as much smoke as is safe. This will 

 usually dispose of the Thrips ; but, if unsuccessful, 

 repeat the operation soon. One gardener says 

 that he judges of the necessary quantity of smoke 

 by tasting the leaves of several plants : if the 

 tobacco is perceptible, he feels that the Thrips 

 must have been killed. 



