TJKK HISTORY. 11 



a '2-acio field a( intervals of 4 and S rods. Tlic day followino- was 

 rainy and nnfavorable to niovonient of the thrips. but the second fol- 

 lowino- day was pleasant. In (lie afternoon of the second day an 

 e.xaniination was made, and four plants were found to have been cov- 

 ered with dirt in the ridging for setting the field. Of the eleven 

 I'cniaining, four plants were found without thrips, five with one each, 

 one with two. and one with three. From this it would seem that the 

 thrips are quite strongly attracted from the weeds in the field to the 

 tobacco. 



As the tliri})s connnence feeding and breeding on the young plants 

 the lower oi- sand leaves receive the greatest amoimt of injury. From 

 the lower leaves they gradually work up the stalks to the leaves above, 

 until at harvesting time they have reached more than half way u[). 

 In attacking a leaf they first appear feeding near the tij), and grad- 

 ually work toward the stem. It may be Avell to note here that the 

 leaves are harvested by picking — called " priming " — as they ripen, 

 t;nd that the stalks often reach the slats or cloth 9 feet from the 

 ground. In the early stages of the tobacco the thrips are found on 

 that grown in sun and shade alike, but as the sun tobacco thickens 

 up they seem to leave it and are found in numbers only on the shade- 

 grown tobacco. In a field in which Cuba and Sumatra varieties 

 were grown together the thrips were found to be equally injurious to 

 both. 



Jumping. — When disturbed, the adults have the habit of jumping. 

 and have thus been mistaken by some for small fleas. This charac- 

 teristic is typical of the genus to wdiich the tobacco thrips belongs. 

 The motion seems to be i)roduced by a. combined movement of the 

 wings and abdomen. 



Fl'iijlit. — The closely related wheat thrips takes flight r-eadily, but 

 the tobacco thrips apparently does not do so. Notwithstanding all 

 the observations he has made, the writer has as yet failed to see it 

 take wing, and its power of flight must be limited. 



FOOD PLANTS. 



The tobacco thrips seems to be a general feeder, as adults were taken 

 in April on blooms of dewberry (Rithus sp.), shepherd's purse 

 (Biirm hiirm-pastoris). and mustard {Br<ixsiea sp.). Adults and 

 larva^ were taken on oats, wheat, and cocklebur as well as on tobacco. 



LIFE HISTORY. 



MctJiodn of study. — In order to determine the life cycle, adult 

 thrips wer^ confined in small wide-nu)uth vials on parts of tobacco 

 leaves for periods of twelve and twenty-four hours, but repeated 

 attempts failed to induce them to oviposit. The parts of tobacco 

 leaves were thereupon replaced b}' small bean pods, with the result 

 that oviposition soon took place. Absorbent cotton was used as a 

 stopper for the vial in order to keep the moisture from forming on 



