THE THYSANOPTERA 



157 



The dark brown — almost black — adults (Fig. 150) appear early in 

 spring, coming out of the ground about the time the fruit buds are swelling 

 and opening, and as soon as these have opened slightly the insects work 

 their way into them and feed on the most delicate parts. The eggs are 

 laid mainly in the young leaf and fruit stems and young fruit and hatch 

 on an average after about 8 days. The nymphs (Fig. 151) feed on the 

 leaves and young fruit forming a sort of ''scab" on the surface of the latter, 

 and remain on the tree for 2 or 3 weeks, though from the first young to 

 appear to the last young to disappear, may be 

 more than 2 months. When through feeding 

 they fall to the ground, which they enter for a 

 varying distance, and there, after from 2 to 5 or 

 6 months, they transform to the last stage before 

 the adult, having previously molted once under- 

 ground. Late in the fall or winter the final 

 molt produces the adults which remain in the 

 ground till early spring. 



This remarkable life history, quite unlike 

 anything known for any other Thysanoptera, 

 permits but one generation a year, with active 

 injury during only a rather short period in the 

 spring. 



Control. — These insects can be destroyed by 

 spraying with Nicotine sulfate 40 per cent used 

 at the rate of 1 part to 800 parts of water, stand- 

 ard formula. Success with this treatment, how- 

 ever, is entirely dependent upon the thoroughness 

 of the application. The first treatment should 

 at once follow the discovery of the Thrips upon 

 the swelling buds and should be repeated at least 

 every 2 or 3 days until the buds are open or 

 the Thrips have become very few. No spraying 

 should be done from the time the blossoms open 



until the petals fall. Then, if Thrips are abundant on the remains of 

 the blossoms, another treatment should be given. 



The Citrus Thrips (Scirtothrips citri Moult.) is a rather serious pest 

 in California and Arizona. It feeds upon the tender stems, leaves and fruit 

 of citrus trees, and occasionally also attacks the grape, apricot and other 

 plants. With seedling plants the leaves and buds are injured and 

 growth is checked. The fruit is injured by scars and scabs caused by the 

 feeding, and greatly reduced in value, and some drops to the ground. 



The adult is one of the smallest of the Thysanoptera, varying from 

 one-fiftieth to one-twentieth of an inch in length, and is orange-yellow in 

 color. The young appear in April and May and gather on the leaves 



i^ 



Fig. 151. — Nymph of 

 Pear Thrips, greatly en- 

 larged. {From U. S. D A. 

 Bur. Ent. Bull. 68, Part 1.) 



