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. 



