350 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 10 



THE REDDISH-BROWN PLUM APHIS (RHOPALOSIPHUM 

 NYMPHE^ LINN.)^ 



By W. M. Davidson, Deciduous Fruit Insect Investigations, Bureau of Entomology, 

 U. S. Department of Agriculture, Sacramento, Cal. 



Distributed in many of the plum and prune districts of California 

 is a plump reddish-brown aphid. This aphis is generally confined to 

 a few trees in an orchard and occasionally infests apricots and almonds. 

 It. attacks plums of the domestica type along with the Mealy Plum 

 Aphis {Hyalopterus arundinis Fabr.), and those of the Asiatic type 

 along with Aphis cardui L. In the East it also occasionally infests 

 peaches. 



The insect is apparently of European origin and was known to Lin- 

 naeus. Well-known to later European and American entomologists, 

 it has been recorded from many parts of Europe and from Maine, 

 New York, Maryland, District of Columbia, Virginia, Pennsylvania, 

 Nebraska, Illinois, Iowa, Colorado and California and is probably dis- 

 tributed throughout the United States. It also occurs in Ontario 

 and Japan. 



The species is of especial interest in that it is double-hosted, spend- 

 ing the winter and spring on fruit trees and the summer and early fall 

 on a large variety of water plants, leading on them a semi-aquatic 

 existence. In California summer forms have been recorded from 

 Polygonum, Typha, and an unidentified pondweed, elsewhere they 

 have occurred among others on water-lily {Nymphea), pondweed 

 {Potamogeton) , Calla and water-plantain (Alisma). 



Biology and Habits 



The stem mothers hatch from winter eggs unusually early in the 

 season, sometimes before the buds of the trees perceptibly swell. In 

 1916 at Walnut Creek, Cal., hatching began about February 10, on 

 Myrobalan plums, and the earliest aphids matured before February 

 26. The year following at Sacramento eggs hatched as early as Feb- 

 ruary 15 on seedlings whose buds were swelling, and the aphids ma- 

 tured March 6. Hatching on French prunes occurs at about the time 

 the buds swell perceptibly, the early stem mothers maturing at the 

 time of full bloom. Eggs continue to hatch for two or three weeks, 

 the young stem mothers exhibiting a gregarious tendency. The sec- 

 ond generation aphids mature about as early as the stem mothers of 

 the Mealy Plum Aphis {Hyalopterus arundinis Fabr.), roughly between 

 March 20 and April 15. The spring forms feed chiefly on the tender 



Published with the permission of the Secretary of Agriculture. 



