The Plant Louse, or Green Fly. 573 
Those of the rose-tree have been particularly noticed, 
and of ten generations produced in one spring, summer, 
and autumn, the first nine were viviparous, and the last 
oviparous. The first nine generations consisted of 
females only ; but in the tenth' there were males. In 
this singular aberration from the common laws of nature 
this insect is a remarkable anomaly. They multiply at 
such an extraordinary rate — the whole ten generations 
within three months — that from a single Aphis ten 
thousand million millions may be produced in that short 
period, and it has been calculated that the progeny of a 
single Aphis during a single summer, supposing its mul- 
tiplication to be subject to no check, might exceed in 
weight the entire human population of China. 
The moss-rose, the hop, the vine, the apple-tree, the 
bean, the willow, and privet, are all particularly liable 
to be infested with this insect ; the various species of 
which take their names according to the plants on which 
they are usually found. The red tumours, commonly 
called galls, which are seen on the surfaces of leaves, 
especially on those of the willow, varying from the size 
of a ladybird to that of a pigeon's egg, are produced by 
Aphides, and contain thousands of small lice. From a 
pair of small tubes placed near the end of the body of 
these insects exudes a saccharine fluid, of which ants 
are very fond; and it is this fluid dropped upon the 
adjacent leaves, or the extravasated sap flowing from 
the wounds caused by the punctures of the insects, 
which is known under the name of honeydew. 
After a mild spring, most of the species of Aphis 
become so numerous as to destroy all the young shoots 
of the plants on which they are found. No successful 
mode of destroying them has yet been discovered, but 
the best remedy against them is to wash the infested 
shoots with tobacco water or soap lees ; and to repeat 
the operation when any Aphides are seen. 
