LIFE HISTORY. 11 



a 2-acre field at intervals of 4 and 8 rods. The day following was 

 rainy and unfavorable to movement of the thrips, but the second fol- 

 lowing day was pleasant. In the afternoon of the second day an 



examination was made, and four plant- were found to have been cov- 

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

 remaining, 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 thrips commence feeding and breeding on the young plants 

 the lower or sand leaves receive the greatest amount of injury. From 

 the lower leaves they gradually work up the stalks to tin 1 leaves above, 

 until at harvesting time they have reached more than half way up. 

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

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

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

 and 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 thicken- 

 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 which the tobacco thrips belongs. 

 The motion seems to be produced by a combined movement of the 

 wings and abdomen. 



Flight. — The closely related wheat thrips takes flight readily, 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 {Rubus sp.), shepherd's purse 

 (Bur*,/ bnrsa-pastoris) , and mustard (Brassica sp.). Adults and 

 larva' were taken on oats, wheat, and cocklebur as well a- on tobacco. 



LIFE HISTORY. 



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

 thrips were confined in small wide-mouth vials on parts of tobacco 

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

 attempts failed to induce them to oviposit. The part- o( tobacco 

 leaves were thereupon replaced by -mall bean pod-, with the result 

 that oviposition soon took place. Absorbent cotton was used ;> a 

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



