270 



Plant-lice. - 



-INSECTS.- 



-COCCID^. 



over the kingdom ; so that a supply could not be 

 obtained for the navy. 



Plate 8, figs. 16 and 17, shows the Aphis rosa; ; the 

 former figure represents the male, the latter the female 

 of that species ; the figures, of course, are very highly 

 magnified. 



Eriosoma. — This genus, so called by Loach from its 

 seemingly vfoolly body, has no tubercles at the end of 

 the body for the secretion of honey-dew. The antennie 

 are short and the fore wings have simple oblique dis- 

 coidal nerves. 



To this genus belongs the Ap/iis lanata or A. lani- 

 gera of authors, which is so destructive to the stems of 

 apple trees. Mr. Ktiapp has given a most excellent 

 account of this insect* as observed in one of the western 

 English counties. Ho says — "Our apple trees here 

 are greatly injured, and some annually destroyed, by 

 the agency of what seems to be a very feeble insect. 

 We call it, from habit or from unassigned cause, the 

 ' American blight,' this noxious creature being known 

 in some orchards by the more significant name of white 

 blight.' In the spring of the year a slight hoariness is 

 observed upon the branches of certain species of our 

 orchard fruit. As the season advances this hoariness 

 increases; it becomes cottony, and towards the middle 

 or the end of summer the under sides of some of the 

 branches are invested with a thick, downy substance, 

 so long as at times to be sensibly agitated by the air. 

 This substance on close examination is found to conceal 

 a great number of small wingless ci'eatures, busily 

 engaged in sucking the juice of the tree. This they 

 effect by means of a beak ending in a fine bristle. This 

 is insinuated into the bark and the sappy part of the 

 wood, and through it the creature extracts, as through 

 a syringe, the sweet liquor that forms as it were the 

 life-blood of the branch. This long bristle is not to 

 be seen in every specimen. In those possessing it, it 

 is of difi'erent lengths, and is usually kept closely con- 

 cealed under the breast. In the younger specimens it 

 may be seen protruding like a fine termination to the 

 anus ; hut as the bodies lengthen, the bristle is soon 

 concealed from view." 



Mr. Knapp continues as follows: — " The alburnum, or 

 sapwood, being thus wounded, rises up in excrescences 

 and nodes all over the branch and deforms it; the limb, 

 deprived of its nutriment, grows sickly ; the leaves turn 

 yellow, and the part perishes. Branch after branch 

 is thus assailed, until they aU become leafless, and the 

 tree dies." 



The Eriosoma, not having wings, is dispersed by 

 means of this downy covering, which is wafted by the 

 winds in small tufts, so that the creature is conveyed 

 with it from tree to tree throughout the whole orchard. 

 In the autumn this substance is generally long, and the 

 insects being dispersed by the winds and rains which 

 are then prevalent, try to secrete themselves in any 

 crannies they can find. There are no data to tell 

 us when first this noxious insect visited us. America, 

 Normandy, and the Netherlands have all been sup- 

 posed to be the sources whence it was derived. Our 

 climate, at all events, seems to be very favourable to 

 its increase. 



* Journal of a Naturalist, p. 337. 



In 1745 Bonnet published his wonderful observa- 

 tions on the reproduction of the Plant-lice,* and proved 

 that the mother produced her young when no male 

 insect was present. " He isolated the young Aphis as 

 soon as it was hatched. On the eleventh day the Aphis 

 produced a young one alive; another succeeded, and 

 another. Every four-and-twenty hours the brood was 

 increased by three, four, and even ten arrivals. At the 

 end of twenty-one days ninety-five young ones were 

 produced from this single Aphis. Carrying further his 

 observations, Bonnet found that the virgin offspring of 

 this virgin parent also became parents ! We know 

 that this reproduction often goes on till the eleventh 

 generation ; then this process ceases, the last genera- 

 tion is of perfect insects, with separate sexes, and these 

 produce ova which next year become the productive 

 virgins we have just been reading of." The rate of 

 increase may be conceived by the following calculation. 

 The Aphis produces each year ten larviparous broods, 

 and one wdiich is oviparous ; and each generation 

 averages one hundred individuals. 



Generation. Produce. 



1st, 

 2iid, 

 3rd, 

 4tli. 

 5lh, 

 6lh, 

 7th, 

 8th, 

 9th, 

 10th, 



1, aphis. 



100, a hundred. 



10,000, ten thousand. 



1,000,000, one million. 



100,000,000, one hundred millions. 



10,000,000,000, ten billions. 



1,000,000,000,000, one trillion. 



100,000,000,000,000, hundred trillions. 



10,000,000,000,000,000, ten quatrillions. 



1,000,000,000,000,000,000, one quintillion. 



Professor Huxley has made some very curious re- 

 searches on the reproduction of the Aphides,f in which 

 lie ascertains that the virgin viviparous aphis produces 

 its broods of young from unfertilized ova, while the 

 female ovijiarous aphis produces her j'oung from ova 

 fertilized by spermatozoa, and that both broods in their 

 early stages are similar. 



On the family Aleykodid^, which is so prolific, 

 I have neither room nor time to enter. 



Family— COCCIDiE. 



This family of insects, which contains the well-known 

 Cochineal, is a most anomalous one. The females are 

 alwaj's wingless, and in their last state deposit their 

 eggs and very speedily perish ; their dried up bodies 

 serving as a cover and protection to the eggs. The 

 mates of these insects are small fellows, not at all 

 resembling their females in any particular either of 

 form or habit. They are active, and have only two 

 wings developed, which they use by flying about in 

 the bright sunshine ; the place of the second pair 

 of wings is supplied by two small projections some- 

 what like the poisers of flies. But to return to the 

 females, Mr. Westwood,J speaking of the whole family, 

 says, that without referring to their singular habits, " we 

 find some of them on arriving at their last state so far 

 departing from the typical characters of the winged 

 insects, as to prove that Ptilota may exist, which in the 

 imago state are not only wingless, but also footless and 



* Insectotheologie, vol. i. 



t Proceedings of the Linnrean Societ}', Nov., 1857. 



i Arcana Entomologica, vol. i. p. 21. 



