192 : PLANT LICE. 
Aphis mali Fab. (The Apple Plant-louse). 
This is a little green louse, frequently so abundant in early 
spring on both leaf and fruit buds of the apple, that in seasons 
favorable to their development the entire tree becomes infested, 
though usually the injuries are confined to the terminal shoots 
of a few branches. The same species also occur on the crab- 
apple and the mountain ash. It is especially noticeable when the 
spring is cold and backward. Prof. Webster has studied this 
insect very carefully, not alone in the orchards, but also in his 
insectary, and has discovered some most unsuspected facts, or, 
as he expressed it: 
“Tt would appear almost visionary to advocate spraying apple 
orchards in midwinter to protect the wheat crop, but nevertheless 
one of the most serious enemies of young fall wheat passes its 
egg stage on the twig of the apple during the winter season. I 
refer to the Apple Leaf-louse, Aphis mali Fab. Soon after the 
young wheat plants appear in the fall the winged viviparous 
females of this species flock to the fields and on these give birth 
to their young, who at once make their way to the roots, where 
they continue reproduction, sapping the life from the young 
plants. On very fertile soils this extraction of the sap from the 
root has no serious effect, but where the soil is not rich, and 
especially if the weather is dry, this constant drain of vitality 
soon begins to tell on the plants. Though they are seldom killed 
outright, these infested plants cease to grow, and later take on 
a sickly look, and not until the Aphis abandons them in autumn 
to return to the apple, do they show any amount of vigor, It 
is very seldom that the affected plants fully recover, at least in 
autumn, and the result must be to reduce their productiveness the 
following year. 
“Tt seems that by the third week from the time the eggs 
begin to hatch the lice become winged, and then abandon the trees 
and fly to grasses and probably to.some of the common weeds. 
“Of the three principal species of aphides infesting our 
smaller cereals, this species occupies an anomalous and at 
the same time important position. In point of numbers it is very 
greatly in advance of Toxoptera gramineum, and, usually, of 
Siphonophora avene, and its effects on young wheat during the 
