34 



THE MONTHLY BULLETIN. 



usually ascertained by the work, which consists m scarring the fruit in 

 such a way as to form nearly regular circles around the stem and blos- 

 som ends, although these scars may extend almost over the entire 

 surface. They also cause a characteristic crinkling and thickening of 

 the young citrus foliage, just as the buds are unfolding. 



Life History. — The winter is spent in the adult form, which hiber- 

 nates in various protected places. The thrips become especially abun- 

 dant about the time the citrus trees are in bloom and begin their work as 

 soon as the petals fall and continue throughout the summer. The eggs 

 are laid from May to August, hatching in six or ten days. The larvae 

 greatly resemble the adults but are at first somewhat lighter in color. 

 In from six to eight days they change into the pupal stage, and in 

 another three to five days become adult insects. The entire life cycle, 

 from the laying of the egg to the beginning of the egg-laying of the 

 adults of the second generation, is about twenty days. There are from 

 eight to ten generations a year in the San Joaquin Valley, as estimated 

 by Jones and Horton. 



Fig. .31 — Oranges showing the work of the citrus thrips. (LT. S. Dept. Agrcl.) 



Distribution. — Up to the present lime the distribution of the citrus 

 thrips is limited to the citrus sections in the San Joaquin Valley, along 

 the western border of the Sierra foothills. This includes the Porter- 

 ville and Bakersfield citrus belts. 



Food Plants. — Citrus, Funica (jranatum (pomegranate), Yitis vin- 

 ifera (European grape varieties), Schimis molle (California pepper 

 tree), "umbrella tree," Pyrus communis (pear), Pnonis armeniaca 

 (apricot), Prunus persica (peach). Primus domestica (European plum 

 varieties), Salix sp. (willow), Rumex sp. (dock), Porfulaca oleracea 

 (purslane), Olea europma (olive), Euhus idanis (European raspberry), 

 Rosa sp. (ro.se), Solmiimi sp. The work upon oranges sometimes results 

 in great losses. Fig. 31 shows characteristic chafing. 



