APHIDES. 



APHIDES. 



also found another large species living on the 

 under side of the branches of various kinds 

 of willows, and clustered together in great 

 numbers. This species, the Doctor thinks, 

 cannot be identical with the willow-louse de- 

 scribed by Linnaeus. When crushed, it com- 

 municates a stain of a reddish or deep orange 

 colour. 



Some plant-lice live in the ground, and de- 

 rive their nourishment from the roots of 

 plants, which they often exhaust arid destroy. 

 Indian corn crops frequently suffer severely 

 from their depredations, especially when the 

 soil is light and reduced. They are generally 

 of a white colour, and are closely clustered to- 

 gether on the roots. Dr. Harris, from whose 

 Report all the information upon this subject is 

 obtained, says that he never has been able to 

 ascertain whether these are of the same spe- 

 cies as the root-lice described by European 

 writers. It is stated by those great entomolo- 

 gists, Kirby and Spence, that ants bestow the 

 same care upon the root-lice as upon their 

 own offspring, defending them from the attacks 

 of other insects, bringing them in their mouths 

 to the surface of the ground to give them the 

 advantage of the sun, &c. The sweet fluid 

 which exudes from them whilst pumping in 

 the sap of the roots, forms the chief nourish- 

 ment of the ants and their young. 



" The injuries occasioned by plant-lice are 

 much greater than would at first be expected 

 from the small size and extreme weakness of 

 the insects ; but these make up by their num- 

 bers what they want in strength individually, 

 and thus become formidable enemies to vege- 

 tation. By their punctures, and the quantity 

 of sap which they draw from the leaves, the 

 functions of these important organs are de- 

 ranged or interrupted, the food of the plant, 

 which is there elaborated to nourish the stem 

 and mature the fruit, is withdrawn, before it 

 can reach its proper destination, or is conta- 

 minated and left in a state unfitted to supply 

 the wants of vegetation. Plants are differently 

 affected by these insects. Some wither and 

 cease to grow, their leaves and stems put on 

 a sickly appearance, and soon die from ex- 

 haustion. Others, though not killed, are great- 

 ly impeded in their growth, and their tender 

 parts, which are attacked, become stunted, 

 curled, or warped. The punctures of these 

 lice seem to poison some plants, and affect 

 others in a most singular manner, producing 

 warts or swellings, which are sometimes solid 

 and sometimes hollow, and contain in their 

 interior a swarm of lice, the descendants of a 

 single individual, whose punctures were the 

 original cause of the tumour. I have seen 

 reddish tumours of this kind as big as a 

 pigeon's egg, growing upon leaves, to which 

 they were attached by a slender neck, and 

 containing thousands of small lice in their in- 

 terior. Naturalists call these tumours galls, 

 because they seem to be formed in the same 

 }ay as the oak-galls which are used in the 

 it kking of ink. The lice which inhabit or pro- 

 duce them generally differ from the others, in 

 having shorter antennae, being without honey- 

 tubes, and in frequently being clothed with a 

 104 



kind of white down, which, however, disappears 

 I when the insect becomes winged. 



" These downy plant-lice are now placed in 

 j the genus Eriosoma, which means woolly body, 

 and the most destructive species belonging to 

 it was first described, under the name of Aphis 

 lanigera, by Mr. Hausmann, in the year 1801, 

 as infesting the apple-trees in Germany. It 

 seems that it had been noticed in England as 

 early as the year 1787, and has since acquired 

 there the name of American blight, from the 

 erroneous supposition that it had been import- 

 ed from this country. It was known, however, 

 to the French gardeners for a long time pre- 

 vious to both of the above dates, and, accord- 

 ing to Mr. Rennie, is found in the orchards 

 about Harfleur, in Normandy, and is very de- 

 structive to the apple-trees in the department 

 of Calvados. There is now good reason to 

 believe that the miscalled American blight is 

 not indigenous to this country, and that it has 

 been introduced here with fruit-trees from Eu- 

 rope. Some persons, indeed, have supposed 

 that it was not to be found here at all ; but the 

 late Mr. Buel has stated that it existed on his 

 apple-trees, and I have once or twice seen it 

 on apple-trees in Massachusetts, where, how- 

 ever, it still appears to be rare, and conse- 

 quently I have not been able to examine the 

 insects sufficiently myself. The best account 

 that I have seen of them is contained in 

 Knapp's 'Journal of a Naturalist,' from which, 

 and from Hausmann's description, the follow- 

 ing observations are chiefly extracted. 



"The eggs of the woolly apple-tree louse are 

 so small as not to be distinguished without a 

 microscope, and are enveloped in a cotton-like 

 substance furnished by the body of the insect. 

 They are deposited in the crotches of the 

 branches and in the chinks of the bark at or 

 near the surface of the ground, especially if 

 there are suckers springing from the same 

 place. The young, when first hatched, are 

 covered with a very short and fine down, and 

 appear in the spring of the year like little 

 specks of mould on the trees. As the season 

 advances, and the insect increases in size, its 

 downy coat becomes more distinct, and grows 

 in length daily. This down is very easily re- 

 moved, adheres to the fingers when it is 

 touched, and seems to issue from all the pores 

 of the skin of the abdomen. When fully 

 grown, the insects of the first brood are one 

 tenth of an inch in length, and when the down 

 is rubbed off, the head, antennae, sucker, and 

 shins are found to be of a blackish colour, and 

 the abdomen honey-yellow. The young are 

 produced alive during the summer, are buried 

 in masses of the down, and derive their nou- 

 rishment from the sap of the bark and of the 

 alburnum or young wood immediately under 

 the bark. The adult insects never acquire 

 wings, at least such is the testimony both of 

 Hausmann and Knapp, and are destitute of 

 I honey-tubes, but from time to time emit drops 

 of a sticky fluid from the extremity of the 

 I body. These insects, though destitute of wings, 

 ! are conveyed from tree to tree by means of 

 I their long down, which is so plentiful and so 

 j light, as easily to be wafted by the winds of 



