CHAPTER 29 



GREENHOUSE THRiPs {Heliotkrips hczmorrJioidalis 



Bou.). 



Greenhouse thrips often cause considerable 

 damage to ornamentals, while their presence may not 

 always be detected. The damage caused by thrips 

 is confined to the foliage. The adult and the larvse 

 of the thrips feed by puncturing and lacerating the 

 epidermis and by sucking the plant juices. The in- 

 jury at first becomes apparent on the older leaves, 

 and later spreads to the younger ones. The trouble 

 first appears on the under side of the leaves in the 

 form of minute white epidermal spots. Later, as 

 the spots become more numerous, they unite, form- 

 ing large blotches. At this stage, the injury becomes 

 apparent on the upper part of the leaves as a dis- 

 tortion between the lateral veins, and by wilting 

 and dying of the edges. Both sides of the infested 

 foliage soon become covered with minute drops of 

 a reddish fluid which finally changes to black. These 

 drops are voided by the thrips. Affected foliage be- 

 comes white and drops off prematurely. In the 

 greenhouse, thrips may attack azalea, aspidium, cro- 

 ton, dahlia, phlox, verbena, pink, ferns, palms, ficus, 

 and fuchias. 



Control. The easiest way to keep this pest iu 



369 



