Page:Encyclopædia Britannica, Ninth Edition, v. 24.djvu/571

Rh WHEAT 535 Orthoptera. It is a minute insect about 2 mm. long, with a black and brown coloration. The male is wingless ; the female bears four long narrow wings fringed with long hairs. The antenna? are eight- jointed. The legs terminate in characteristic swellings ; there are no claws. The insects are very active. The larvae are whitish yellow, with bright red eyes, and acquire their wings after the fourth casting of the skin. The damage done to corn crops by these minute insects is often very serious ; they secrete themselves under the paleae surrounding the seed, and feed upon the soft juices of the latter. In addition to this, they sometimes cause injury to the plant by attacking the stalk whilst it is soft and full of sap. Owing to their very small size it is ex ceedingly difficult to devise means for getting rid of them ; much may be done, however, to pre vent their appearance by keeping the land clean and free from weeds, which harbour them, and by destroying all refuse in which they may jjf breed, and ploughing in the stubble to a con- FIG. 2. Corn thrips siderable depth. (Thrips cerealium), The most injurious form amongst the Hcmi- female; magnified. ptcra is Siphonoplwra granaria (Ajihis granaria, Kirby) ; it attacks wheat chiefly in England, but is also found upon oats, barley, and rye. The young Aphides attack the leaf blades whilst young and tender, and when the ear begins to appear it is covered with numbers of these insects in every stage of development, from the young larva Fio. 3. 1, Siphonoplwra granaria, winged Aphis ; 2, natural size of same; 3, wingless form ; 4, natural size of same; 5, Aphidius avenue; 6, natural size of same ; 7, Ephedrus plagiator ; 8, natural size of same. to the perfect insect. The larva; are of a green or dark green colour, with brown antennae and yellow and black legs. The female, which produces the young viviparously, has a green abdomen, bearing two horns posteriorly ; the rest of the body is brownish green, the legs black and yellow, the eyes red. The winged females, which appear late in the season, lay eggs ; but whether these eggs serve to carry the species over the winter or whether this is done by hibernat ing larva; is not definitely known. Both larva; and females produc ing them have been found amongst the roots of the wheat plant during the winter. This Aphis is known to occur upon several of the common grasses of England ; hence any grasses growing in a wheat field should be destroyed as much as possible when the pest is in the neighbourhood. Deep ploughing and rotation of crops may also be recommended. In cases where the insects are noticed at an early stage, a dressing of soot or gas lime will serve to check them. Their numbers are kept down by lady-birds (Coccinclla), which should never be killed, and also by two species of ichneu mons (Aphidius i c?iand Ephedrua plagiator), which lay their eggs in the body of the Aphides. The order Diptera includes several insects which are very harm ful to corn crops. The frit fly, Oscinis vastator, is a very active small fly, with a greenish black metallic lustre, about 2 to 3 mm. in length. The larvae are yellow or light brown, pointed anteriorly. The flies emerge from the chrysalis about April, and the female deposits her little red eggs upon the under surface of the leaf of the wheat ; the larva when it is hatched creeps down and bores its way into the terminal bud of the plant, thus arresting all growth of the ear. The larva assumes the chrysalis state inside one of the outermost leaf sheathe. There are believed to be two broods each year. If, as seems probable, the pupoj pass the winter amongst the stubble or grass weeds, it is important that these should either be burnt or ploughed deeply in. Two closely allied species of flies also attack corn crops ; they are Chlorops tseniopus and Chlorops lincata. The former is of a light straw colour, with three longitudinal dark stripes, and a greenish black abdomen ; the antennae are black, the eyes greenish ; and the dark feet have a stripe of lighter colour. It is about 3 to 4 mm. long. The injury to the crops is caused by the fly laying its eggs between the leaves of the young plant ; the larvae which hatch out from these bore their way down the stem from the base of the ear to the first joint, and there they form swellings known to the farmer as the &quot;gout.&quot; The ear is aborted or misformed. The dampest part of the field is most subject to attack. Ch. lincata is about 2 mm. long ; the antennae have their two proximal joints yellow, whilst the third is black on its outer side ; in its habits this insect resembles Ch. tseniopus, but attacks chiefly barley crops. The daddy long-legs, Tipula oleracea, causes great damage to corn and other crops by the larvae gnawing the young plants whilst they are still below the level of the ground. The female deposits her eggs in the ground, or near it in some grass, &c., choosing as damp a place as possible. The larva is provided with a very tough skin and may measure 1J inches in length. It is apodal, and bores its way beneath the surface of the earth by alternately contracting and expanding. It assumes the pupal condition during the later half of the summer. The pupae are provided with backwardly directed spines, by means of which they raise themselves above the level of the ground. As a means of preserva tion against this pest, ditches and other damp places should be cleaned out. Rooks, which de vour the larvae at a great rate, should be encour aged ; and deep plough ing to bury the eggs and the larva; should be prac tised, and the land dressed with some such poisonous substance as gas lime be fore breaking up. Two species of Cecido- myia are most destruc tive to wheat. Cccido- myia tritici, the wheat midge, has been known in Great Britain for over a century. This fly is Fia 4. Daddy long-legs (Tipula oleracca). 1, a little over 2 mm. in Larva ; 2, pupa case ; 3, insect, natural size ; length, of an orange yel- 4 &amp;gt; eggs- low colour, with black eyes ; the female is provided with a long ovipositor, by means of which it deposits ten or more eggs in the ears of wheat. The lame hatch out in about ten days. They are at first transparent, but become yellow, and their colour gradually deepens. Most of the larvae fall off the plant and bury themselves in the ground, where they change into pupae ; some, however, re main in the ear and are found in some numbers in chaff. The perfect insect emerges from the pupa in the spring. It is probable that more than one brood is produced during the season. The damage caused to the crop is due to the larva feeding upon the soft tissue of the ear and thus causing the seed to be imperfect ; some authorities state that it also devours the pollen. Since the larvae exist in chaff, great care must be taken that this does not prove a source of infection, and land which has been badly affected must be ploughed deep, in order to bury them. C. destructor is well known under the name of the Hessian fly. It was first noticed in Great Britain during the summer of 1886, in Hertfordshire, and within a few months its presence was reported throughout the eastern half of England and Scotland, a circumstance which led some authorities to believe that it had existed in Great Britain for some little time ; there has been, how ever, no definite proof of this. The fly has been known in North America since 1776, where it has done very extensive damage, espe- Flo 5 .__ IIessian fly (Cccidomyia de- cially during warm moist sum- ttntctor). i, Insect; 2, larva; 3, pupa mers. It is known to occur or &quot;(lax seed.&quot; All magnified. throughout central Europe ; in 1879 it made its appearance in Russia, and in four years had spread over the greater part of that country. The female fly is about 3 mm. long, brownish in colour, but becoming black in the thorax and head. The wings are fringed, rounded at their ends, and the third nerve is branched. The an- tennte are also fringed and consist of two globular basal joints,