692 RoBertT MATHESON 
fertilized eggs of this species will over-winter and hatch in the following 
spring has not been determined. 
As to the proportion of the eggs that actually hatch, no very definite 
data can be given, as most workers content themselves with general 
statements. Gillette and Taylor (1908) report that in eastern Colorado 
not over one per cent of the eggs hatch. Brittain (1915 a) reports, in his 
work in Nova Scotia, 11.5 per cent hatching, and he states that other 
workers record as high as 30 per cent. Tho these statements refer to 
Aphis pomi, yet the eggs of Aphis avenae and Aphis sorbi must have been 
included, and this of course would vitiate the results. As the writer’s 
observations were made under similar conditions it is not necessary to 
present them. 
The stem mother 
The young lice which hatch from the eggs are all females and are 
generally referred to as stem mothers (Plate XVIII). The stem mothers 
are wingless, viviparous females reproducing without the intervention of 
males. The lice, when they leave the eggs, are active creatures with 
long legs, capable of crawling rapidly over the limbs and branches of the 
trees. They settle on the green tips of the opening buds (Plate VII), and, 
inserting their tiny beaks, begin at once to pump out the plant juices. 
In company with the grain aphis they may completely cover the green 
tips of the buds, often as many as sixty or seventy being present on a single 
bud. As the buds open and as more lice hatch, their numbers increase 
greatly, and it is not uncommon to find every bud completely covered. 
With the opening of the buds the lice penetrate in among the young 
and tender leaves and are soon almost completely hidden among the 
plant hairs. The lice attack also the flower buds, frequently congregating 
in them in such numbers as to prevent them from. unfolding. They 
attack also the young flower stalks, which they weaken, causing the flower 
to fail to develop normally. 
The young lice develop rapidly provided weather conditions are favor- 
able. As they grow they shed their skins at irregular intervals, passing 
thru four molts before reaching maturity. A detailed description of the 
stages is given below. In the writer’s cages the first eggs hatched on April 
21 (in 1915) and the stem mothers began producing young on May 10, 
a period of twenty days being required in this case for them to reach 
maturity. As that spring was very cold the development of the insects 
