38 



THE PRACTICAL ExNTOMOLOGlST. 



full of lice, some winged and some wingless, and 

 only differing from the Ap])le-tree Plant-lice in cer- 

 tain details of color, &c. The insect itself is called 

 the Currant Plant-louse (Aphis ribis,') and, like the 

 preceding, has in all probability been imported into 

 this country from Europe. 



If we examine a cabbage-plant towards the au- 

 tumn, we shall sometimes see all the outer leaves 

 covered by similar lice, except that they are dusted 

 over with a white powder, and differ from either of 

 the preceding in certain peculiarities of color, &c. 

 But never, under any circumstances, shall we see 

 the cabbage leaves curl up or bulge into blister-like 

 projections under the punctures of these insects, as 

 was found to be the case with the Plant-lice of the 

 Apple and the Currant. The cause of this differ- 

 ence can only be attributed to certain unknown pe- 

 culiarities of the plant which we call a cabbage. It 

 cannot be owing exclusively to the greater thick- 

 ness of the leaf of the cabbage, as compared with 

 the leaves of the apple or the currant, because there 

 are numerous plants with quite thin leaves which 

 are infested by Plant-lice, but which do not in con- 

 sequence thereof have their leaves curl up or bulge 

 out. The Cabbage Plant-louse is scientifically- 

 known as Aphis brnssii-x, and has likewise been in- 

 troduced among us from Europe. 



In the same way many other plants — for example, 

 the Plum, the Cherry, the Peach, the Grape-vine, 

 the Hose, the Willow, the Maize or Indian corn, 

 and the group of cereal plants known as Wheat, 

 Rye, Oats and Barley — are infested each by a ]ie- 

 culiar species of Aphis, and sometimes by several 

 distinct species ; and, as a general rule, a species 

 that inhabits one plant cannot live upon another, 

 but perishes if transferred to it by artificial means. 

 In the case of Wheat, Ilye, Oats and Barley, how- 

 ever, the same insect can live indifferently upon 

 either, as in the year 1861 the Farmers of New 

 York and New England and Pennsylvania ascer- 

 tained to their cost; the Grain Plant-louse (^l/;7u"s 

 nvenx) having in that year multiplied so prodigi- 

 ously in that section of country, as greatly to dam- 

 age the grain crop, and more especially the later- 

 maturing grain, such as Spring Wheat and Oats. 



Besides the genus Ajjhis, there are other genera 

 of Plant-lice belonging to the same Aphis family, 

 but diffiring in the veinlng of their wings and in 

 other minute particulars, and differing also more or 

 less in their habits. For example, the Woolly-Plant- 

 louse of the Apple-tree, {Eriaifoinalanifffira), belongs 

 to the genus Uriosoma, which has only one. instead 

 of two branches springing from the third vein in 

 its front wing, (see the above figure,) and inhabits 

 the limbs and trunk of the infested tree rather than 

 the leaves and small twigs. Again, the root Plant- 

 louse of the Apple-tree, {Pemphif/us pi/ri,) belongs 

 to the genus Pemphigus, which has the third vein 

 in its front wing perfectly simple, and not at all 

 I'orkod or sprangled, and inhabits the roots of the 

 infested tree exclusively. Trifling and unimportant 

 as such distinctions may appear to the general 

 reader, they are yet almost perfectly constant and 

 invariable. Take a hundred winged Plant-lice from 



the leaves of an Apple-tree, and every one of them 

 will have the third vein of the front wing twice 

 forked. Take a hundred winged Woolly-Plantlice 

 IVom the limbs of the same tree, and every one of 

 them will have the third vein once forked. Take 

 a hundred winged Root-Plantlice from the roots of 

 the same tree, and every one of them will have the 

 third vein devoid of any forks at all. AVhcre nature 

 is the workwoman, there are seldom any botches. 



Besides the genera of Plant-lice referred to above, 

 there are others which originate and inhabit curious 

 excrescences or "galls" upon different plants. But 

 in what I am now about to say, I shall, for the sake 

 of brevity, cortfine myself exclusively to the Plant- 

 lice belonging to the genus Aphis, none of which 

 inhabit galls, and but a single North American 

 species of which — the Maize Plant-louse (Aphis 

 maidis) — ever lives underground upon the roots of 

 the infested plant; and even that one occasionally 

 emerges into the light of day, and attacks the stems 

 of the roasting-ears. 



People are often puzzled at finding an Apple- 

 tree or other plant swarming with Plant-lice, when, 

 a week or ten days before, there was scarcely one 

 to be seen on it. The reason is the prodigious fe- 

 cundity and the very early maturity of these in- 

 sects. As a general rule, an Aphis in the summer 

 season attains complete maturity in ten or twelve 

 days, after which time it produces every day about 

 two young ones, which, contrary to the general rule 

 with insects, are born alive and not in the egg-state. 

 Hence, the English Entomologist, Mr. Curtis, has 

 calculated that from a single female, in seven ge- 

 nerations, 720 millions of lice may be produced. 

 ]jut in the case of the Grain Plant-louse, the pos- 

 sible rate of increase is more astonishing still ; for 

 Dr. Fitch ascertained, by actual experiment, that 

 one of the wingless females of this species becomes 

 a mother at three days old, and thereafter produces 

 four little babies every day ; so that even in the 

 short space of twenty days her descendants, if not 

 destroyed from extraneous sources, would number 

 upwards of two millions. If the human species in- 

 creased at the same prodigious rate, how rapidly 

 the land-speculators would make their fortunes ! 



The arithmetical reader may perhaps object, 

 that in the above calculations no allowance has 

 been njade for a certain per centage being males, 

 and consequently barren. But — strange to say — 

 all through the summer there are no males at all 

 born, all that are born, whether you choose to call 

 them females or not, being fertile individuals and 

 giving birth to others, and these to others still, and 

 so on indefinitely, without any intercourse with the 

 opposite sex. How, under these circumstances, the 

 process of generation is accomplished, is a curious 

 and at present an unsettled problem. Some distin- 

 guished German entomologists maintain that these 

 so-called females are neuters (Ammen), without any 

 regular ovaries developed, and that it is by a bud- 

 ding process, analogous to that of the l-'olyps, tliat 

 the young plant-lice are developed within the body 

 of the parent stock. I have just heard from Mr. 

 Darwin that it lias been demonstrated by Bal- 



