10 THE TOBACCO THEIPS. 



General shape fusiform. Color of posterior part of thorax and entire abdomen 

 pale yellow ; elsevA'here pearly white. Head quadrate ; eyes reddish. Antennse 

 0.15 mm. in length ; distinctly four-segmented ; basal segment cylindrical, 

 short; second ovate, slightly shorter than the third; third slightly conical, 

 the apex joining the second ; fourth fusiform, widest near the basal fourth, 

 about equal in length to the other three. The fourth segment is distinctly 

 annulated, the second and third indistinctly so; seta^ are present on all seg- 

 ments, most numerous on the fourth. Legs translucent white, stout. Abdomen 

 tapering posteriorly ; with ten segments, the first eight nearly equal in length, 

 the ninth twice and tenth three times the length of the preceding. Each 

 abdominal segment with longitudinal rows of seta^, the ninth with two and 

 tenth with four spines that are four times the length of the seta>. 



Luna, scco)i(l stofic. — Length from 0.6 to 1.17 mm. ; width of mesothorax from 

 0.14 to 0.2 mm. ; shape same as in first stage. Color of thorax and abdomen 

 yellowish, with exception of the last abdominal segment. Head quadrate ; 

 antennae with four segments, the fourth being more distinctly annulated than in 

 the first stage. Abdomen with the set:e increasing in length posteriorly; ninth 

 and tenth segments about equal in length, each less than twice the length of the 

 others. 



77(C yoinnj in/iiii)]i or prcinipa. — Length, 0.r>2 to 0.C>2 mm.; width of meso- 

 thorax, 0.10 to 0.12 mm. Antenn;e translucent, extending forward, much short- 

 ened and composed of five segments, first two cylindrical and very short, third 

 and fourth globose, fifth tapering to the apex. The last segment of the abdomen 

 is set with four spines by use of which the young nymph seems to protect itself, 

 when approached by another the abdomen l>eing turned upon it. The wing 

 sheaths are very noticeably separated, the upper one extending to the middle of 

 the second segment, the lower one to the middle of the third segment. The legs 

 ai'e translucent white, stout. 



TJie 'fuU-yroini Hi/Diph or i>iii>(>. — Length. 0.(i8 to 1.22 nun.; width of meso- 

 thorax, 0.15 to 0.20 mm. Shape similar to the adult. Color yellowish; head, 

 anteiniie. wing pads, legs, and caudal segments of the abdomen varying to pearly 

 white. AntenuiB extending to the middle of the prothorax. Three yellowish 

 ocelli between the eyes, the latter dark red. Wing pads so closely applied as to 

 appear single, extending to the middle of the fifth abdominal segment; length 

 from head to tip of wing pads 0.39 mm. The abdomen is noticeably contracted 

 longitudinally; greatest width, 0.24 mm.; longest setie, 0.078 mm. 



HABITS. 



Feeding. — When examinations Avere first made. April 17. the adult 

 thrips Avere found feeding in the seed beds on the upper surface of 

 the young tobacco plants, and in the field on the upper surface of the 

 leaves of young cocklebur weeds. In the larval stage they feed on the 

 lower surface of the leaves of tobacco and weeds, but as they become 

 adult seem to prefer the upper surface, a habit which is very favorable 

 for remedial treatment, as they can then be reached much more readily 

 by sprays. To determine the attractiveness of tobacco the experiment 

 was tried of transplanting young tobacco plants into a field .that had 

 been prei)ared ready for transplanting, but in which weeds, consisting 

 of cockleburs and grass, were to be found. 



In order that thrips might not be accidentally taken from the seed 

 bed on the plants, the latter were dipped in a solution of kerosene 

 emulsion and this washed off with water. Fifteen plants Avere .set in 



