1118 



PRACTICE OF AGRICULTURE. 



Part III. 



7682. The A'phides or plant lice, next to locusts, are tlie most universal devastators of the vegetable 

 world : almost every plant has its peculiar species ; their fecundity is so prodigious, that Reaumur has 

 calculated that in five generations one A^his may be the progenitor of 5,904,9UO,000 descendants; and 

 it is supposed that in one year there may be twenty generations ! Those which attack the different kinds 

 of grain seldom multiply so fast as to be very injurious ; but those peculiar to pulse increase rapidly, 

 and take such possession, that the plants are greatly injured and frequently destroyed before the seeds 

 are matured. 



7683. These insects are equaUy injurious in their winged 

 {,fi^. 972. / magnified) and in their larva or apterous state (m m '.e- 

 iiified) ; they are a favourite food of sparrows and other birds, 

 who destroy numbers : they are likewise exposed to other deadly 

 and cruel enemies ; one of these is a small hymenopterous insect, 

 which deposits its egg in the body ; it is there hatcned, and feeds 

 upon the intestines ; in a short time the A'phis swells, becomes 

 hard, and, from being green, changes to a dark red colour. The 

 artful destroyer within, when lie finds his victim dying, eats a 

 hole through its belly, and fastens the A'phis, by that part, to a 

 leaf or twig. When the parasite has thus devoured the inside, 

 and is ready to emerge as a perfect insect, he opens a passage 

 for himself by cutting out a round hole in the side, leaving the 

 piece, like a door on its hinges, adhering to the body (m). 

 But the most inveterate and destructive foe to the plant-lice is 

 the lady-bird or lady-cow (Coccin^Ua L., fg. 974. a), which, 

 in its larva state (b), feeds entirely upon these insects; and 

 the havoc made among them may be conceived, from the 

 myriads upon myriads of these jiretty little creatures which 

 are usually seen in years when the plant-louse abounds ; 

 every one, probably, destroying tens of thousands of A'phides 

 before he becomes a beetle. On this account the lady -bird is 

 the greatest friend to the gardener and farmer ; and could there 

 be any method devised of increasing these useful insects at 

 will, our hot-houses, gardens, fields, and hop plantations. 



would soon be cleared from the ravages of plant-li( 



The 



974 



larva; of several bee-like flies (S^r- 

 phus F., c) are no less useful in 

 this respect. Their form very much 

 resembles that of the leech, having 

 no apparent head. Some species 

 are green, with a white stripe down 

 the middle; others brown, variegat- 

 ed with darker shades. They are 

 always found upon those plants most 

 infected by A'phides, upon which 

 they solely depend for nourishment ; 

 heiice they become most beneficial, 

 and should on no account be de- 

 stroyed. As palliative measures, 

 the ajiplication of powdered quick- 

 lime may be resorted to ; or the in- 

 fected shoots may be topped off before 

 the insects are greatly multiplied, 

 re))eatiRg the same operation before 

 the time that the winter stock of 

 eggs are deposited. By the first 

 pruning a very numerous present increase will be prevented ; 

 and by the second, the following year's breed may, in a great 

 measure, be destroyed. (Phil. ra;is. 41. p. ISl.) 



7684. The wire-wor^n is a name that has been given, without discrimination, to the larvaj or grubs of 

 various insects, totally different from each other : hence it is, that much confusion and contradiction will 

 be found respecting it in agricultural books. The true wire- worm is the grub of a small beetle (E'later 

 segetis Marsham), and it derives its name from its slender form and uncommon hardness. It lives in the 

 larva state nearly five years; during which time it is supported by devouring the roots of wheat, rye, oats, 

 and grass, which it attacks indiscriminately, and causes annually a large diminution of produce : it 

 abounds chiefly in newly broken-up land, and is particularly destructive in gardens recently converted 

 from pasture land. In the larva state it may be decoyed by offering it more tempting food ; but no method 

 has yet been devised for destroying the perfect insect. 



768.5. The grub is a general name for several larvas of crane flies ( Tlpiilada;), called by the country 

 people long-legs, or gaffer long-legs. 



7686. One of ihe mofl ietlrueiive among these insects to the 

 roots of grass and grain is the Tfpula oleracea. The larva is 

 said, by some authors, merely to loosen the roots by burrov.ing 

 among them ; but others assert, that it likewise feeds upon the 

 fibres. However this may be, the evil produced is evident ; for 

 in many parts of England it cuts off a large proportion of the 

 wheat crops, especially if sown upon clover-lays. Reaumur 

 informs us, that sometimes in France, particularly in marshy 

 lands, the grass of whole districts has been so destroyed by it, 

 as not to produce the food necessary for the sustenance of the 

 cattle. No effectual remedy has yet been discovered for this 

 evil ; and Steckney observes, that the insect is not killed by 

 lime, even when applied in much larger doses than usual. 



7687. There are several other species of a large size, as the 

 Tfpula crocata {Jig. 975. a), and Tfpula riv6sa (c), which, in a 

 less degree, are also injurious to such lands as are moist and 

 humid. 



"7688. Another mimile species is particularly destructive to 

 com, and is generally known as the wheat-fly (Tlpulatrftici, h): 

 its history and economy has been ably investigated by Mr. 

 Marsham and Mr. Kirby. The injury first appears in the 

 ear, several of which, on being opened, will be found to contain 

 an orange-coloured powder ; in this are concealed very minute 

 larvse (/), which, on being magnified (,?), are seen to be thick 

 at one end, extending and contracting themselves at plejisure. 



and frequently jumping half an inch at one spring ; they take 

 their station in the longitudinal furroMr of the giain, and b^ 

 sucking its milky jxiice causes it to shrink up, and become 

 what the farmers call punf^led: the last sown wheat always ap- 

 pears the most infected. In the beginning of June the per- 

 fect insect (i) may be seen in innumerable multitudes, flying 

 in the evening in all directions over tlie corn-fields; but during 

 the day not one is to be perceived. The female lays her eggs 

 (d e magnified) by means of a retractile tube, which encloses a 

 very long and acute sting resembling a hair ; but this can only 

 be distinctly seen when the insect is magnified (A). Tlie wheat- 

 fly would soon become a formidable enemy to mankind, were 

 not its race exposed to an inveterate foe, scarcely larger than 

 themselves ; this is the /chneiimon T^pulae, the female of which 

 carefully searches out the grubs of the wheat-fly, and deposits 

 in each one of her eggs : these are hatched, and ultimately the 

 larva devours the body Avhich gave it life. One ichneumon 

 will thus cause the death of many dozens, and prevent the fu- 

 ture multiplication of thousands. The only palliative that has 

 been recommended for stopping the progress of this insect has 

 originated in Mr. Kirby ; this consummate naturalist thinks 

 much benefit would be derived by fumigating the com with 

 tobacco and sulphur, when the wind is in a favourable quarter : 

 this must be done as soon as the ear begins to shoot from the 

 leafy stalk. {Linn. Trans.) 



SuBSECT. 5. Insects injurious to Food, Clothing, ^c. 



7689. The manufactured produce qf our fields and gardens, whether as food or clothing, is still 

 exposed to the ravages of other tribes of insects, which take up their residence in our dwellings, and on 

 every thing about us. Fortunately, however, these domestic enemies are much less numerous and hurtful 

 in this country than in the tropical regions of America, India, and Africa, where their devastation is 

 almost incredible. Amongst the few that are indigenous, or that have been naturalised in Britain, the 

 principal are the cock-roach, the house-cricket, and the bacon-grub. 



