26 



Toward midsummer many of the lice on the twigs crawl down into the 

 ground and locate upon the roots. 



APPLE PLANT-LICE. 



The foliage of apple trees, particularly of young trees, often appears 

 curled, and sometimes discolored. This curling is produced by colo- 

 nies of plant-lice. These lice secrete a sticky liquid known as honey- 

 dew, which falls on the leaves below. A black fungus grows upon the 

 leaves covered by the honey -dew, and this checks their growth. There 

 are several of these plant-lice that attack the leaves of apple; two of 

 them are greenish in color, another has a reddish tinge. 



The commoner of the two green species is known as Aphis mali 

 Fitch, (probably Aphis annuBe Oest). Its life history is about as fol- 

 lows: The eggs are laid on the tree in the fall, partly hidden in crev- 

 ices of the bark; the young hatch from these eggs in early spring, and 

 grow into wingless and sexless lice, known as "stem-mothers," which 

 produce living young; these young become winged, and, in the early 

 summer, migrate to grasses, where they increase during the summer. 

 In the fall they develop a set of winged, sexless lice, which migrate 

 back to the apple and give birth to sexed individuals; these pair, and 

 the female lays her eggs. 



The other green .species is Aphis mali Koch. It passes its entire 

 life history upon the apple. The eggs are laid in the late fall. They 

 are black, and occur generally on the trunk and branches. In early 

 spring the young hatch from these and grow into stem-mothers. These 

 produce living young for a number of generations. Many of these of 

 the first two generations become winged, fly to other apple trees, and 

 there start colonies. In October sexed specimens are produced, and 

 the female lays the eggs that are destined to pass the winter. 



The other apple plant-louse is A. sorbi Kalt. It is distinctly tinged 

 with red, and the wingless forma have a whitish powdering on the 

 body. This species has a life history similar to that of Aphis maU 

 Fitch., but it is not known what plants serve as its summer hosts. 



THE PLUM PLANT-LOUSE. 



(Hyalopterus pruni Fabr.) 



This insect winters in the egg state. The young on hatching in 

 spring go to the under surface of the leaf and there multiply rapidly. 

 Their bodies are covered by a bluish-white mealy powder. Winged 

 specimens are occasionally developed which migrate to other trees. 

 They feed on the plum all summer, but some specimens are said to 

 migrate to grass in early summer. In the fall the winter egg is 

 attached to a plum twig, usually at the base of a bud. At times they 

 do considerable damage to young plum stock. 



