June, '17] DAVIDSON: REDDISH-BROWN PLUM APHIS 351 



stems, and later on the leaf and fruit petioles and during April mul- 

 tiply rapidly. Winged forms appear first the second week in April 

 and may be found until July. The colonies decline throughout May 

 and June, both through the production of winged migrants and through 

 the increasing activity of natural enemies. 



Summer colonies are found from May to October and are often very 

 large, the individuals being very prolific. Natural enemies again 

 exact heavy toll. 



Fall migrants are produced from the middle of October to early 

 December, the majority during the first half of this period. In 1915 

 at Walnut Creek, Cal., these began to arrive on the winter host Octo- 

 ber 25, in the following year on October 20. The fall migrants feed on 

 twigs and petioles and deposit the sexed females. Winged males 

 arrive while the females are growing and settle down on the twigs 

 beside them. After a development period of about 20 days the females 

 mature, copulation occurs and shortly after the females place winter 

 eggs in the axils of the buds of the following year. The egg is rather 

 elongate, bare, at first shining green, in a few days turning jet black. 



This aphis is preeminently a twig-feeder and the fact that the stem 

 mothers hatch so early and feed exposed points to an easy control 

 should the species ever become of sufficient economic importance to 

 warrant combative measures. Even on many of the summer hosts 

 the twigs and flower stalks are preferred to the leaves. 



Recognition Characters 



General Color. — Reddish-browTi varying to dark olive and dark greenish-brown. 

 Newly-hatched stem mothers are green, soon changing to a dark slate-colored hue, 

 hghtly dusted with gray pruinose meal. Aphids of the second generation are yellow- 

 ish-brown when born, reddish-brown in later stages. Sexual females crimson. 



The head and abdomen of the pupa bear white pulverulence. 



In the winged forms the head, thoracic lobes, scutellum and sterna are shining 

 black, prothorax brown with yellowish sutures. The stigma and insertions of the 

 wings are yellowish gray, the veins brown; the first and second discoidals thicker 

 than the other veins. Many individuals have a series of lateral sub-circular brown 

 areas, and besides these the males have brown cross-bands on the abdomen. 



The base of the third antennal joint, basal beak joints, extreme base of femora, 

 basal half to three quarters of tibiae are yellowish-gray, elsewhere the appendages 

 are dark gray, dark brown or black. Cauda gray, cornicles brownish-black with 

 base paler. 



Structure. — Antennae placed on short frontal tubercles, shorter than the body 

 (except in the male); joint III about four-fifths as long as the spur of joint VI, but 

 in some instances III is but three-fifths as long as spur and again they are sub-equal; 

 in apterous forms there are no sensoria except the usual terminal on joints V and VI; 

 in the winged spring migrants joint III has from 17 to 22 circular sensoria distribu- 

 ted almost the whole length of the joint and joint IV has from to 3 circular sensoria. 

 In the winged fall migrant the number of sensoria on joint IV varies from 2 to 11, the 

 usual number being 3. The male antenna bears on joint III about 30, on IV about 



