THE GRAPE PHYLLOXERA IN CALIFORNIA. 



75 



The adult instar of the winged form shows what is probably the 

 most highly developed form structurally of the phylloxera. The 

 winged insect is, on the average, slightly shorter than the full- 

 grown nymph. The antennae are longer than those of the previous 

 instar and bear two sensoria of about equal size. The comparatively 

 large wings are weakly veined but necessitate strong muscles in the 

 interior of the thorax. The legs are quite long and the tibise exceed 

 the femora in length. As the migrant sheds the nymphal skin, push- 

 ing it back and moving about its appendages, the wing pads appear 

 as little white rolls; the mesothorax is shining green, the head and 

 abdomen bright orange. The wings unroll as the skin is being passed 

 off the abdomen. As soon as it is entirely shed the insect moves off 

 and then pauses while the wings assume their final shape and posi- 

 tion, but remain whitish, hyaline, and limp. Soon, however, the 

 wings dry and the thorax hardens and darkens until it is almost 

 black. The head, prothorax, and abdomen remain orange, the head 

 with a grayish luster. The molting process occupies about 50 

 minutes. 



The adult winged t form. 



PI. VIII, a-e. 



General color orange or yellowish brown or gamboge yellow; head a little 

 dusky on the anterior half, especially the cephalic margin (front) ; ocelli dark 

 red ; eyes brighter red than ocelli, compounded of many facets ; ocular tubercle 

 small ; antennas with three joints, not quite reaching the anterior margin of 

 the mesothorax, pale yellow, with apical fourth of joint 3 dusky gray ; third 

 joint much the longest, considerably over twice as long as first two combined, 

 somewhat constricted beyond the basal sensorium and at extreme base ; posterior 

 half of head, prothorax, and abdomen orange, yellowish brown, or gamboge. 



Thoracic lobes, scutellar lobes, scutellum, and mesosternum dark gray or 

 blackish ; legs pale yellow, tarsi duskier ; wing insertions, stigma, and veins 

 gray (at first greenish) ; stigma equal in length to about one- fourth of wing. 



First discoidal arising from subcosta not far from basal angle of stigma, 

 stout, not attaining the wing margin by a space equal to one-fifth its length; 

 second discoidal faint, arising from the first vein or discoidal a little before 

 its center and almost reaching the wing margin at a point a little nearer to 

 the apex of the third discoidal than to that of the first; third discoidal faint, 

 arising from first vein close to its base and continuing with a double shallow 

 curve almost to the wing apex (the basal half of this vein generally obsolete). 

 Lower wings with the costal vein running parallel to the anterior margin 

 for its whole length ; cauda bluntly rounded, bearing a fringe of hairs ; beak 

 slender, pale yellow, and almost reaching to second coxaa; two longitudinal 

 oval sensoria on the third antennal joint ; basal sensorium situated at basal 

 third of joint, apical sensorium close to apex of joint. Wings bome hori- 

 zontally, apparently the positions interchangeable, the right pair sometimes over- 

 lapping the left and vice versa. Abdomen widest at second and third abdominal 

 segments, where it is wider than the thorax, and about as long as head and 

 thorax combined. Body about as high as wide, not at all flat. 



Table XXVI gives the measurements from 8 individuals. 



