220 Journal of Agricultural Research voi.iv. N0.3 



When newly hatched, the larva is from 0.39 to 0.40 mm. in length and 

 from 0.09 to o.io mm. in width; when full grown it becomes about i.o 

 to 1.2 mm. in length. In general shape the body is fusiform, broadest at 

 the middle of the abdomen, and tapering to a point at the anal end. The 

 antennae are slender, their length being equal to one-sixth that of the 

 body; the bases of the segments are shaded and set in proximal tubercles. 

 There are no changes in the form during growth, except that the color be- 

 comes lighter during the last few days of the larval period. The larvae 

 become full grown in from 10 to 12 days and crawl down the plants into 

 the soil, where they pupate and transform to adults. There is no indica- 

 tion of the yellow color of the adult when the larv^ae enter the soil. The 

 pupal period lasts from 10 to 13 days, though no observations on this 

 stage have been noted. 



THE ADULT (PL. XXX, FIG. 3) 



The adult, which was described by Hood,^ may be readily recognized 

 by the fact that it is a wingless form and has a pronounced yellow color, 

 which distinguishes it from Euthrips tritici and other species of thrips 

 commonly found on wheat. 



NUMBER OF GENERATIONS ANNUALLY 



The complete life cycle from egg to adult requires from 30 to 35 days. 

 The egg hatches in from 6 to 10 days, the larval period occupies from 10 

 to 12 days, and the pupal period from 10 to 12 days, while the newly 

 issued female reqtiires but from two to three days to prepare for egg 

 laying. Although the length of life of an adult has not been definitely 

 determined, a few have lived eight months in the laboratory. 



The adults emerge from winter quarters as soon as the warm days of 

 spring arrive, and the females soon begin depositing their eggs. There 

 are from four to five generations each year. These overlap one another, 

 so that adults and larv^ae are present at all times, even in late winter. 

 Larvae are most numerous at heading time in the spring, also about the 

 time volunteer plants come up in late summer, and again in late fall, 

 when the wheat is getting a good start. They continue to feed until the 

 cold weather causes them to go into hibernation. 



CROPS AFFECTED 



Growing wheat is the only cereal that is known to have been damaged 

 by this insect, although certain species of grasses are sometimes injured 

 to a slight degree. Wheat plants furnish its principal food from the time 

 the volunteer plants sprout in August until the wheat crop is harvested 

 the following June. During the interval between wheat harvest and the 

 sprouting of volunteer wheat the thrips feed and reproduce on Agropyron 



' Hood, J. D. Op. cit. 



