1494 



ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 



of the egg-laying of the adults of the sec- 

 ond generation, is about 20 days. There 

 are from eight to ten generations a year 

 in the San Joaquin valley, as estimated 

 by Jones and Horton. 



Food Plants 



Citrus, pomegranate, European grape 

 varieties, California pepper tree, "umbrel- 

 la tree," pear, apricot, peach, European 

 plum varieties, olive, European raspber- 

 ry, rose. The work upon oranges some- 

 times results in great losses. 



Control 



So far the best results in controlling the 

 citrus thrips have come from spraying, 

 experiments being conducted in California 

 and Arizona with very good lesults. Two 

 sprays were used in the work, lime-sul- 

 phur diluted at the rate of one part to 

 80 parts of water, and tobacco extract 

 (40 per cent nicotine) diluted one part 

 to 1,800 parts of water. The lime-sul- 

 phur causes slight burnings, but other- 

 wise is as effectual and much less ex- 

 pensive than the tobacco extract. Four 

 applications are recommended: the first 

 just after most of the petals have fallen; 

 the second in ten to 15 days after the 

 first; the third from three to four weeks 

 after the second and the fourth during 

 the months of August or September, when 

 the thrips are numerous on the foliage. 

 In spraying for this insect it is advisable 

 to use angle nozzles and from 175 to 200 

 pounds pressure, care beinj? taken that 

 every portion of the tree is thoroughly 

 drenched. 



Citrus White Fly 



Aleyrodes citn Riley and Howard 



General Appearance 



The adult white flies are about one- 

 tenth of an inch long; have yellow bodies 

 and opaque wings covered with a fine 

 white powder. The males have a charac- 

 teristic tuft on the under side of the ab- 

 domen. The pale yellowish-green eggs 

 are suspended on short stalks. The first 

 hatched young have legs and antennae 

 like a small scale insect, but after moult- 

 ing these disappear and the body becomes 

 flat, greatly resembling a soft scale. The 

 development of the insect takes place in 



the flattened shell, which gradually be- 

 comes raised, showing segmentation and 

 yellowish color. The adult emerges by 

 breaking through the top of the skin. 



Life History 



The winter is passed in the mature lar- 

 val stage on the under sides of the leaves. 

 Early in the spring the pupae appear and 

 in March and April the adults emerge. 

 The eggs are deposited upon the foliage, 

 the larvae beginning to hatch in about 

 three weeks. The first hatched have legs 

 and appendages and greatly resemble a 

 young scale They soon settle to feed and 

 after several months move no more until 

 the adult stage is reached. There are 

 several overlapping broods each year. 



Food Plants 



The principle food plants of economic 

 importance are citrus trees. 



Control 



By far the most effectual control meas- 

 ure is fumigation, as used for scale in- 

 sects, two-thirds of Schedule No. 1 being 

 recommended, see p. 1499. Emulsions and 

 x'esin sprays are also effective remedies. 



Cottony Cnsliion or Fluted Scale 



Icenja purrhasi Mask. 



General Appearance 



The adults are distinguished by large, 

 white, fluted cottony masses with distinct 

 red or yellow bodies, varying from one- 

 fourth to one-half inch in length and 

 three-fourths as wide. There are two va- 

 rieties, as follows: Icerya purchasi var. 

 OraiDtt Ckll., of which the body proper is 

 yellow or light brown, and Icerya pur- 

 chasi var. MasJcelU Ckll., the body of 

 which is very dark brown or almost black. 

 The eggs and young are bright cardinal 

 red. 



Life History 



The large cottony masses are the egg- 

 sacs of the females, and may contain 

 from 400 to 1,000 eggs. The males soon 

 after hatching secrete themselves in a 

 white cocoon for transformation, which 

 requires nearly one month. The females 

 are matured in from three to four months. 

 There are several broods during the sum- 



