Thrips 



Thrips are tiny insects seldom measuring more than 1/20 of an inch 

 in length. They are slender, and vary in color from green or white for 

 the young insects to brown or black for the adults. 



The injury caused by thrips is so characteristic that their presence 

 is easily recognized. They feed by scraping the epidermis of the leaf 

 and sucking the sap from bruised cells beneath. Injured tissues turn 

 gray or silvery colored and black specks of excrement are usually pres- 

 ent around the affected area. Older leaves are usually affected most. 

 With some plants the lower leaves first assume the symptoms previouslv 

 mentioned, then the leaves begin to take on a dried or burned appear- 

 ance. The gloxinia is damaged severely by thrips. The leaves assume 

 a rusty appearance first and eventually the buds may fail to open. 



Thrips multiply much more rapidly at warmer temperatures, so 

 when an infestation occurs it is well to move the plant to a cooler loca- 

 tion until the insects are under control. 



Other control measures are regular washing and contact sprays, if 

 it is possible to use them. Tartar emetic ( Vi teaspoon) and brown sugar 

 (2 teaspoons) mixed in 1 pint of water and sprayed on plants in a light 

 mist with a household fly sprayer is an excellent control. Very minute 

 quantities of this material are necessary because it acts as a bait and at- 

 tracts the thrips. Tartar emetic is a deadly poison, so should be used 

 with extreme care. Any control measure used for thrips should be re- 

 peated at short intervals, for all stages of the insect are present at one 

 time, and some stages are more susceptible to spray treatment than others. 



Scale Insects 



Scale insects are probably the most troublesome on ferns and foliage 

 plants. They are tiny insects that work under cover of a flattened scale 

 that is usually gray, orange, brown, or black in color. They feed by 

 inserting their mouth parts into the cells of the leaf and sucking out the 

 plant juices. The spot directly under one of these insects becomes brown 

 or yellow and eventually the entire leaf becomes lighter in color. A 

 sticky excretion from this insect is often present on the leaves with them. 



Fortunately, these insects are stationary, except for the first few 

 hours of their existence. Judicious pruning is helpful where the infesta- 

 tion is localized to a few leaves or stems. Where the infestation is se- 



Fig. 6a (left) — Thrips injury on gloxinia leaf. Fig. 6b (right) — Typical 

 thrips injury on an older leaf of browallia 



Eleven 



