PLANT Lice InguRING FOLIAGE AND FRUIT OF THE APPLE 693 
was retarded. In the experiments of the preceding year the stem mothers 
that hatched first also required twenty days to reach maturity. Lice 
hatching at later dates, such as from April 26 to April 30, required from 
twelve to fifteen days to reach maturity, the stem mothers beginning 
to produce young from May 10 to May 12. In general it may be said 
that for the year in question (1915) the stem mothers reached maturity 
and began producing young from May 11 to May 14. At that time 
the trees were coming into full bloom and conditions were ideal for the 
young lice to cluster on the opening flowers as well as on the tender leaves. 
Activities 
After the last molt, the stem mothers become mature and begin pro- 
ducing young within a very short time, in many cases within twenty-four 
hours after the last molt or even within a shorter period. This time, 
however, varies greatly, apparently being dependent on weather conditions 
and particularly on moisture. In these experiments reproduction was 
delayed for several days in some instances, and several of the stem mothers 
died without producing any young. In the case of stem mothers placed 
on caged trees in the outdoor insectary, reproduction began, when the 
weather was clear (tho cool), usually within twenty-four hours after the 
last molt. Owing to the lack of necessary equipment it has been imposs‘ble - 
to study the relation of moisture or temperature to the activities of any 
stages of this insect, or the effect of these factors on the predacious or 
parasitic enemies. General observations have been made, but it seems 
unwise to include them here as no accurate experimental data are at hand. 
After reaching maturity the stem mothers do not move about over 
their host plant to any extent except when they become overcrowded 
or are disturbed. Under such conditions they seek new quarters and 
may spread generally over the tree on which they are located. 
Reproductive capacity 
As has already been pointed out, in 1915 reproduction was just becoming 
general when the apple trees were coming into full bloom. Many stem 
mothers, thru unknown causes, began reproducing later. Why certain 
stem mothers should begin reproducing considerably later than others 
under apparently similar conditions is unknown to the writer; tentatively 
several causes appear operative, but none of these have been determined 
