198 PLANT LICE. 
female. In such cases she has departed for another leaf, or 
even another plant, to found another colony. In this way the 
melon fields become infested, and at that time of the year. Now 
if, during this period, we have a heavy, cold rain, and especially 
if it lasts more than a day, most of these migrating forms will be 
destroyed, and with them also a considerable portion of such 
young as have been deposited on the melon vines. For some 
reason it seems as if there were not much migration to melon 
fields after this time, and if no lice are found in the fields by the 
end of the first weeks of July, exemption will probably continue 
throughout the season. If circumstances favor, however, the 
insects multiply rapidly and spread from hill to hill, partially of 
their own motion, winged forms being developed and flying a 
short distance, and partially by the assistance of ants. These are 
usually found in great numbers in the fields in attendance on the 
Aphids, and without much doubt they carry specimens from one 
plant to another.”’ 
There are many other species belonging to the genus Aphis, 
that are found in our state, but it is not necessary to describe them 
here. 
The genus Myzus has the feelers about as long as the body, 
and they are situated on moderately distinct frontal tubercles, 
which are gibbous on the inner side, as are also the first joint of 
the antennz. Legs moderately long; honey-tubes cylindrical, 
rather long; body often more or less covered with capitate hairs. 
A number of very destructive-species belonging to this genus 
are found in Minnesota. 
Myzus cerast Fab. (The Cherry-tree Plant-louse). 
This is a shining black louse which appears as soon as the 
leaves of the cultivated cherries expand, being hatched from eggs 
which are deposited on the branches the previous autumn. The 
disgusting looking lice multiply so fast that before long the under- 
side of the young leaves is entirely crowded with them, turns 
yellowish, and in the case of a young tree the whole foliage looks 
sick and the tree suffers greatly. The species is also abundant 
on the sand-cherry. 
In extreme cases the lice crowd together in such dense masses 
that they stand, two deep, on each others’ backs, with just suffi- 
