20 



FARMERS BULLETIN 804. 



SEASONAL HISTOKY. 



The eggs of the rusty plum aphis hatch early in the spring and 

 the normal life period of the stem-mother is about a month. Dur- 

 ing this time she produces young 

 at the rate of four to six a day. 

 In a little over a week these young 

 are mature and reproducing, so 

 that large colonies soon result. A 

 few winged forms occur in the 

 early generations, but it is not 

 until late spring that a large per- 

 centage of spring migrants is 

 found. These winged forms fly 

 from the plum and settle upon 

 various grasses, where they pro- 

 duce colonies throughout the sum- 

 mer around the crowns of the 

 plants. In October the fall mi- 

 grants are produced upon the 

 grasses, return to the plum, and 

 there give birth to the egg-laying 

 wingless females. The males, also 

 produced upon the grasses, mi- 

 grate to the plum in order to locate 

 and fertilize the egg-laying fe- 

 males. In some regions the spe- 

 cies seemingly lives on the plum 

 throughout the year. 



THE LONG-BEAKED THISTLE APHIS.i 



In some localities the long- 

 beaked thistle aphis is abundant 

 on plum trees. In structure this 

 species most closely resembles the 

 rusty plum aphis. The insects are 

 shiny green and black, some of the 

 wingless ones and all of the winged 

 ones having a large black patch 

 on the abdomen, 

 ^ery abundant on the trees, it does 



Fig. 15. — The rusty plum aphis (Apliis 

 setariae) : Colony on shoot and foliage 

 of plum. (Original.) 



Although this species becomes 

 not curl the leaves to any extent. Trees have been observed in the 

 vicinity of Washington with the underside of nearly every leaf 

 thickl}^ covered with the insects, and yet these leaves were rolled only 

 slightly from the edges. The insects always feed on the underside 



Aphis cardui L. 



