INJURIOUS AND BENEFICIAL INSECTS uf CALIFORNIA. 



55 



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 esti- 

 mated by Jones and Horton. 



Nature of Work. — The presence of this insect is usually ascertained 

 by the work, which consists in scarring the fruit in such a way as to 

 form nearly regular circles around the stem and blossom ends, although 



Fig. 



48.— Oranges showing the work of the citrus thrips, Scirtothrips citri 

 (Moulton). (U. S. Dept. Agric.) 



these scars may extend almost over the entire surface. They also cause 

 a characteristic crinkling and thickening of the young citrus foliage, by 

 attacking the leaves just as the buds are unfolding. 



Distribution.— Up to the present time 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 Porterville 

 and Bakersfield citrus belts. 



Food Plants.— Apricot, citron, dock, grape, grapefruit, lemon, olive, 

 orange, pear, pepper tree, pomegranate, purslane, raspberry, rose, 

 Solatium, umbrella tree and willow are known food plants. 



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 results. Two sprays were used in the 

 work, lime-sulphur diluted at the rate of one part to eighty parts of 

 water and tobacco extract (40 per cent nicotine), diluted one part to 

 eighteen hundred parts of water. The lime-sulphur causes slight burn- 

 ings, but otherwise is as effectual and much less expensive than the 

 tobacco extract. Four applications are recommended: the first just 

 after most of the petals have fallen ; the second in ten or fifteen 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 



