90 INSECTS INJURIOUS TO VEGETABLES 



cucumber, squash, turnip, cauliflower and strawberry, and does 

 more or less damage to nasturtium, mignonette, carnations, 

 candytuft, four-o'clock and rudbeckia. 



The female thrips cuts a slit, in a leaf or stem usually, to 

 deposit her eggs. In a few days the young thrips work their 

 way out and begin to feed. They suck the juices of plants and, 

 as they feed continuously, their growth is rapid. The entire 

 life cycle from the time of the deposition of the eggs until the 

 maturing of the adult is passed under favorable coalitions, in 

 a warm atmosphere, in three weeks. Out-of-doors in a cooler 

 atmosphere a longer period would be required for the life cycle. 



The minute size of thrips, with their habits of feeding by 

 suction, in concealment in their host plants, renders it difficult 

 to treat them successfully. The best contact poisons are dilute 

 kerosene-soap emulsion, applied as for aphides (p. 361). It 

 is practicable in some cases to dip whole plants, when being 

 transferred from the hothouse to the field, in kerosene 

 emulsion. 



For fumigation, hydrocyanic-acid gas, carbon bisulphid and 

 different preparations of tobacco are useful. Tobacco prepara- 

 tions, containing about 40 per cent, nicotine, have been found 

 effective at the rate of 5 or 6 teaspoonfuls to i J/2 pints of water 

 when vaporized in a space of 5,000 cubic feet. This method does 

 not injure cucumbers w^hile nearly all the thrips on plants thu, 

 treated are killed. 



In the field drenching affected plants with a hose will kill 

 many of the pests. Clean methods of farming is a necessity, 

 as thrips develop largely in grasses, weeds and other vege- 

 tation in and near onion fields. All other infested plants should 

 also be treated with kerosene-soap emulsion, and the weeds 

 burned where possible. 



The Wheat Thrips {Thrips tritici Fitch).— This native spe- 

 cies, also called the strawberry midget, has been reported as 



