10 THE TOBACCO THEIPS. 



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

 pale yellow: elsewhere pearly white. Head quadrate; eyes reddish. Antennae 

 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; fonrth 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; setae 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 iu length, 

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

 abdominal segment with longitudinal rows of setae, the ninth with two and 

 tenth with four spines that are four times the length of the seta 1 . 



Larva, second stage. — 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 setae increasing in length posteriorly : 

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

 others. 



The young nymph or prepupa. — Length. 0..~>2 to 0.62 mm.: width of meso- 

 thorax, 0.10 to 0.12 mm. Antennae translucent, extending forward, mucb short- 

 ened and composed of rive segments, rirst 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 being 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 

 are translucent white, stout. 



The full-grown nymph or i>»i>a. — Length. 0.68 to 1.22 mm.: width of meso- 

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

 antennae, wing pads, leu r s. and caudal segments of the abdomen varying to pearly 

 white. Antenna- extending to the middle of the prothorax. Three yellowish 

 ocelli between the eyes, the latter dark red. Wing pads so closely applied a- 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 sene. 0.078 mm. 



HABITS. 



Feeding. — When examination- were first made. April 17. the adult 

 thrips were found feeding in the -eed beds od the upper surface of 

 the young tobacco plant-, and in the held on the upper surface of the 

 leave- of young coeklebur weed-. In the larval stage they feed on the 

 lower surface of the leave> of tobacco and weed-, hut as they become 

 adult -ecm to prefer the upper surface, a habit which i- very favorable 

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

 by sprays. To determine the attractiveness of tobacco the experiment 

 was tried of transplanting young tobacco plant- into a field that had 

 been prepared ready for transplanting, but in which weed-, consisting 

 of eoekleburs and grass, were to be found. 



In order that thrips might not be accidentally taken from the >eed 

 bed <>n the plant-, the latter were dipped in a solution of kerosene 

 emulsion and tin- washed off with water. Fifteen plant- were set in 



