PI.AXT LICE OR APHIDS. 



these insects are found in the sub family in the early part of the season always 



DiaspinK, — "the armoured scales," — 

 familiar species being the oyster shell 

 bark louse {Mytiluspis pomorum) ; the 

 "scurfy" bark louse {Chionaspis fur- 

 furus\ and the dreaded San Jose' scale 

 " Aspidiotus perniciosiis). These, like 

 the plant lice, are inconspicuous, and 

 extraordinarily prolific. The life histo- 

 ries vary somewhat, but the feeding 

 habits are much the same, and the prin- 

 ciples which govern the methods of 

 fighting the one, hold good also against 

 the other. 



The family Aphida; contains so 

 many species of plant lice that it is out 

 of the question to give even the briefest 

 description of many of them. Probably 

 the two best known to fruit growers are 

 the black cherry aphis (Myzus cerasi), 

 and the green aphis. Less familiar 

 species are the hop-louse, melon-louse, 

 cabbage-louse, etc. Some of these 

 species feed on an immense variety of 

 plants. A large number of species con- 

 cern themselves mainly with the roots of 

 plants, and are extremely difficult to 

 eradicate ; the corn-root louse and the 

 peach louse (aphis persica-niger ) are 

 examples. Then there are the gall pro- 

 ducing types, such as the " cock's 

 comb " gall, and finally the " woolly 

 plant lice," which are highly injurious, 

 and are typified in the •' whoolly apple 

 louse." 



The life history of most of the plant 

 lice is as follows : They winter in the 

 egg stage. Directly warm weather 

 arrives and growth commences, the eggs 

 hatch, and in a very short time the 

 wingless aphid gives birth to living 

 young. In five or six days the young 

 aphids are ready to reproduce, so that 

 by the end of a few weeks the progeny 

 of the original "stem-mother " mounts 

 well into the millions. All this time no 

 males have been produced ; plant lice 



breeding agamically, that is, without the 

 intervention of a male. If reproduction 

 is very rapid a scant food supply is 

 guarded against by the birth of winged 

 forms, which hie off to " fresh fields and 

 pastures new." As the cold weather 

 approaches, and growth of vegetation 

 ceases, the plant lice develop both sexes, 

 the female being wingless. A few eggs 

 are laid, sometimes very few, usually at 

 the ends of the twigs, or near buds 

 where vegetation is likely to start first in 

 the spring. The eggs are tough, and 

 resist successfully ordinary insecticides 

 and severe climatic conditions. The 

 lice, of course, live on the juices of the 

 plant or tree, the effect on the tender 

 growing shoots being woful. When sap 

 is abundant, and the lice are present in 

 great numbers, the '• honey dew " which 

 they excrete to ease themselves, glazes 

 all the adjacent foliage, and a fungus 

 disease develops which rapidly kills the 

 vegetable tissue. It has been thought 

 till quite recently that this " honey 

 dew " was ejected from two little tubes 

 frequently found on the upper part of 

 the sixth abdominal segment. Professor 

 Comstock Slates that this has been 

 found to be a mistake. The flow of 

 this sticky liquid is from the hind open- 

 ing of the alimentary canal. 



The relationship of ants to the plant 

 lice is now so well known that it is 

 hardly necessary to refer to it. Readers 

 of Sir John Lubbock's works, of Dar- 

 wins' " Origin of Species," etc., will 

 readily recall the interesting chapters 

 dealing with the relation of these insects 

 to each other. The principal food of 

 the ants seems to be this same " honey 

 dew," and though ants are not directly 

 injurious to vegetation, they are, un- 

 doubtedly, indirectly injurious, inas- 

 much as they protect and colonise the 

 various species of aphids. I look upon 



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