354 



PSYCHE. 



[March 1896. 



other winged generation is produced, 

 which migrates back to the plum (on 

 which account these forms are some- 

 times called return-migrants), where 

 each settles upon a leaf and gives birth 

 to three or more young that develop into 

 sexual oviparous females. About the 

 same time winged males are produced 

 upon the hops. They also migrate to 

 the plum where they mate with the 

 oviparous females. The latter deposit 

 the winter eggs upon tlie twigs about 

 the buds; and on the advent of cold 

 weather all forms but the eggs perisli. 

 There is no doubt that a considerable 

 number of the aphides commonly affect- 

 ing trees and shrubs have a somewhat 

 similar history. For instance our com- 

 mon apple aphis {A. mali ) spends the 

 summer upon grasses, where they con- 

 tinue breeding until autumn, when they 

 return to the apple, and the winged 

 females establish colonies of the wing- 

 less egg-laying form upon the leaves. 

 The males fly in from the summer 

 host-plant. The eggs are then laid on 

 the twigs and buds an.d the cycle for the 

 year is completed. 



The aphid commonly atl'ecting 

 cherrv trees ly]SIyzus cerasi) has a 

 similar history. It winters over on 

 the twigs in the egg state. Early in 

 spring the young aphides hatch and 

 crawl upon the bursting butls, inseit- 

 ing their tiny sap-sucking beaks into 

 the tissues of the unfolding leaves. 

 In a week or ten davs they become 

 full-grown and begin giving birth to 

 young lice, which also soon develop 

 and repeat the process, increasing 



verv rapidh . Most of the eailv spring 

 forms are wingless but during June 

 great numbers of the winged lice 

 appear, and late in June or earl}' in 

 July they geneially leave tlie cherry, 

 migrating to some other plant, although 

 we do not yet know what that plant 

 is. Here they continue developing 

 throughout the summer, and in autumn 

 a winged brood again appears and 

 migrates back to cherry. These 

 migrants give birth to young that 

 develop into egg-laying females which 

 deposit small, oval, shining black eggs 

 upon the twigs. 



While the aphides aflecting decidu- 

 ous trees commonly live upon the 

 leaves and deposit eggs upon the buds, 

 the rule is reversed in the case of 

 some species found upon conifeis. Foi 

 instance the large Lachnus {L. piul) 

 occurring upon the twigs of Scotch 

 Pine deposits eggs in longitudinal 

 rows upon the leaves. The handsome 

 White Pine Lachnus (Z. strobi) has 

 also a similar habit. Like most plant- 

 lice, this species reproduces vivipa- 

 rously, or by giving birth to living 

 young, during the summer, but on 

 the approach of cold weathei' the 

 sexual individuals are produced. Din- 

 ing October these are usually the 

 only forms present, the oviparous 

 females being congregated in great 

 numbers upon the bark of the smaller 

 branches, with their heads directed 

 towards the ti'imk of the tree. When 

 disturbed thev move about rapidly, 

 usually attempting to conceal them- 

 selves on the other side of the branch. 



