THE MEALY PLUM APHIS. 5 



THE SPRING FORMS. 



Six "wingless generations, in the maximum-generation series, were 

 bred from April to June during 1916. An unusually hot wave oc- 

 curred June 6, and killed all of the individuals of the seventh and 

 eighth generations in the cages. It has been determined, however, 

 that wingless generations may persist on the winter hosts through 

 the summer as late as September, but apparently they can not pro- 

 duce true sexes. In the maximum series all second-generation indi- 

 viduals were wingless, in the third generation 1 out of 29 was 

 winged, none of the fourth or fifth generations were winged, while 

 the majority of the sixth and seventh generations were wingless. All 

 the individuals in this series were bred on Mvrobalan plum. 



SPRING WINGLESS FORMS. 



Description. 



Newly hatched. — Pale yellowish-green ; eyes dark red ; rims of cornicles 

 dusky. Appendages hyaline greenish-white. Form elongate oval. 



Antenna? 5-jointed, half as long as body. Comparative measurements as fol- 

 lows: I, 0.03 mm.; II, 0.025; III, 0.11; IV, 0.06; V, 0.175 (0.05 plus 0.125). 

 Beak reaching third coxa?, 0.22 mm. long; cornicles wartlike, 0.025 mm. long. 

 Style rounded. Length of body, 0.50 mm. ; width of body, 0.22 mm. 



In the first instar the general color darkens, but it is never as dark as 

 that of the stem mother ; the tarsi, last antennal joint, and tip of beak become 

 dark grayish-black. After the first molt a conspicuous " meal " is secreted in 

 four longitudinal rows of circular areas on the body dorsum. This " meal " is 

 more abundant on the first and fifth abdominal segments than elsewhere. The 

 three longitudinal green stripes described in the stem mother appear less dis- 

 tinct in later generations. After the second molt the body is elongate oval. The 

 aphids have a carinated appearance following each molt. 



Adult. — Light green; eyes dark red to black; antenna? pale hyaline green, 

 apex gray ; legs hyaline greenish-white, tarsi and tibial apices gray ; cornicles 

 somewhat dusky in apical half ; cauda light greenish-white. Beak pale, tip 

 blackish. " Meal " as in larva, increasing with age of insect. Form elongate 

 oval. 



Antenna? on frontal tubercles, 6-jointed, two-thirds as long as body; com- 

 parative measurements as follows : I, 0.085 mm. ; II, 0.075 ; III, 0.39 ; IV, 0.24 ; 

 V, 0.225; VI, 0.445 (0.105 plus 0.340). In later generations filament of VI is 

 longer in proportion than in earlier. Beak reaching second coxa?, 0.30 mm. 

 long. Cornicles imbricated rather inconspicuously, constricted near base, some- 

 what enlarged in middle, mouth not flaring ; length, 0.115 mm. Cauda ensiform, 

 0.17 mm. long. Body length, 2.2 to 2.8 mm. ; width, 1.2 mm. Small, pale, bluut 

 lateral tubercles occur on the prothorax and on each abdominal segment. Body 

 armed with very few hairs. 



Duration of Nymphal Stages. 



Records of the development of the wingless forms were made both 

 •on caged trees and in the orchard. Myrobalan and Agen (French) 

 prunes were used for hosts. The development was similar on both 



