igo8] Studies on Aphididac 261 



0.2934-0.45(34, average, 0.3328; IV, 0.1548-0.2934, average, 0.1913; V, 0.1222- 

 0.2282, average, 0.1462; VI, basal, 0.0815-0.1141, average, 0.0986; VI, filament, 

 0.2119-0.3423, average 0.2494; total (average), 1.1430 mm.; cornicles, 0.1032 

 mm.; style, 0.0788 mm.; hind tarsus, 0.1059. mm. 



Pupa. — Head and thorax with a pinkish tint, and somewhat mottled, or 

 pale green. Eyes black. Tip of beak black. Antennae pale, excepting the 

 last segment, which is dusky. Wing-pads pale with a greenish yellow tint. 

 Legs pale. Abdomen dirty greenish, and sometimes with a yellowish or pinkish 

 tint. Cornicles and style pale. 



Wingless viviparous female. — The general body color, when examined with 

 the naked eye, varying from dirty green or yellowish green to almost jet black. 

 Head and portion of the thorax pale to dark dirty green. Antenna; about one 

 half the body in length; the two basal segments dusky, the third pale, and the 

 remaining segments darkening to black. (PI. XXIII, fig. 25.) Eyes black. Legs, 

 except the articulations and the tarsi, concolorous with the Isody coloration. 

 Abdomen and posterior portion of the thorax dark dirty green to black green, 

 and covered with many fine dark spots, which are scattered more or less irregu- 

 larly over the dorsum. Around the cornicles is a semicircular immaculate area, 

 and upon each of the last four abdominal segments is a more or less distinct 

 transverse black band. Ventral sui-face of the abdomen immaculate, excepting 

 a black blotch at the extreme posterior end. Cornicles pale, imbricate, and 

 slightly flaring at the tips; subequal to the tarsus in length. The dorsallv 

 curved style pale, and with a dark margin, conical, and slightly less than the 

 cornicles in length. 



Measurements. — Length of bodv, 1.927-2.218, average, 2.127 mm.: width, 

 1.136-1.164, average, 1.146 mm.; antenna, I, 0.0621; II, 0.0516; III, 0.2282- 

 0.3097, average, 0.2681; IV, 0.1304-0.2119, average, 0.1850; V, 0.1059-0.1630, 

 average, 0.1418; VI, basal, 0.0733-0.0978, average, 0.0912; VI, filament, 0.1793- 

 0.2526, average, 0.2192; total (average), 1.019 mm.; cornicles, 0.1263 mm.; style, 

 0.1121 mm.; hind tarsus, 0.1141 mm. 



Sexual forms— The sexual generation has never been obtained, 

 and from the data above it is evident that this species can hiber- 

 nate in this latitude as viviparous individuals. Its alternate 

 food plant, the apple, may possibly be the host upon which the 

 sexual forms are produced, though Aphis bakeri has not as yet 

 been found on apple in Illinois. 



EXPLANATION OF PLATES. 



Myzus elasagni Del G. — Plate XXI, figs. 1-9. 



Figure 1, fore wing; 2, antenna of winged cJ* ; 3, of winged viviparous 9 ; 

 4, of wingless oviparous 9 : 5, of wingless viviparous 9 ; 6, head of winged vivi- 

 parous 9 ; 7, style of wingless viviparous 9 ; 8, cornicle of winged viviparous 9 ; 

 9, hind tibia of wingless oviparous 9 ■ 



Rhopalosiphum berberidis Kalt. — Plate XXI, figs. 10-11; Plate XXII, 

 figs. 12-18. 



Figure 10, hind tibia of wingless oviparous 9 ; H, cornicle of wingless vivi- 

 varous 9 I 12, fore wing; 13, style; 14, antenna of winged (J* ; 15, of winged vivi- 

 parous 9 ; 16, of wingless oviparous 9 I 17, of wingless viviparous 9 ; 18, head 

 of winged viviparous 9 • 



Callipterus trifolii Mon. — Plate XXII, figs. 19-21; Plate XXIII, 28-33. 



Figure 19, cornicle of winged viviparous 9 I 20, fore wing; 21, style of 

 winged viviparous 9 ; 28, head of winged viviparous 9 ; 29, antenna of winged 

 viviparous 9 ; 30, of wingless viviparous 9 ; 31, of winged J^ ; 32, of wingless 

 oviparous 9 ; 33, hind tibia of wingless oviparous 9 • 



Aphis bakeri Cowen. — Plate XXIII, figs. 22-27. 



Figure 22, fore wing; 23, head of winged viviparous 9 ; 24, antenna of 

 winged viviparous 9 ; 25, of wingless viviparous 9 ; 26, cornicle of winged vivi- 

 parous 9 ; 27, style of winged viviparous 9 • 



