Injurious Insects (continued)
( Originally Published 1915 )
Crane Flies; the Pear Midge; the Celery Fly; the Cabbage Root Fly; the Onion Fly; the Narcissus Fly; the House Fly.
In this lecture we are concerned with the order Diptera which comprises the true Flies. These Insects can be recognised by the presence of a single pair of wings, the hinder pair being absent, and only represented by curious knobbed organs known as halteres or balancers. The larvae of the Diptera are devoid of true limbs and are commonly known as maggots. A pupa stage is always present and, in a very large number of species, the skin of the larva is retained, forming a hardened case or puparium enclosing the true pupa. Although no adult Flies are directly injurious to vegetation, certain kinds such as Mosquitoes, Sand Flies, and Tsetse Flies are injurious to man. They pierce the skin in order to suck his blood and thereby act as carriers of the organisms of some of the most virulent diseases.
Some of the most familiar of the larger Flies are the " Daddy Long Legs," or Crane Flies (Tipula oleracea and allied species) (T3). Although they are commonly pests of our meadows and cereal crops nevertheless they not infrequently injure turnips, peas, beans, cabbages, hops, dahlias, carnations and other garden plants. Their larvae are commonly known as " leather jackets," and when fully grown they attain a length of 1 1/2in. In colour they are dull grey or brown and are not unlike fragments of small dark twigs. They live exclusively beneath the soil and, although they devour a considerable amount of dead vegetable matter, their staple diet seems to consist mainly of the roots of various plants. They are specially common in damp parts of meadows, wherever there is rank herbage, especially grass. Leather jackets feed mostly at night when they often come to the surface of the soil. When fully fed they turn to elongate pupa which force their way to the surface of the soil, where they may be often seen projecting for about half their length vertically out of the ground. The Crane Flies issue late in the spring and lay their black spindle-shaped eggs on or near the surface of the ground. These eggs give rise to the Leather Jackets which eventually transform into a second brood of Flies appearing in great numbers during August and September. The late brood of Crane Flies is always more abundant than the spring one, and their eggs develop into larvae which remain beneath the soil all through the winter. They are often abundant in garden lawns in low-lying districts, and it is advisable in such cases to roll heavily and keep the grass closely cut. Rolling at the proper seasons crushes the pupae and if done regularly after dark a large number of the larva would probably also be destroyed. When present in large numbers thorough turning of the soil in the autumn and winter renders the larve accessible to rooks, starlings, and other birds which prey upon them in large numbers. A good soil dressing is 1 to 2 cwts. of nitrate of soda to the acre, and although Leather jackets are susceptible to its effects, they are by no means always eradicated. Gas lime is only doubtfully effective. Theobald advises the use of traps of partially buried turf as a device for enticing the Flies to lay their eggs, and also to. attract the larvae from the adjacent soil. To arrest local attacks in parts of lawns and beds 1/2 oz. of carbon bisulphide to each square yard injected by means of a Vemorel injector, or other suitable instrument, to a depth of about 6 inches is usually quite effective.
The Pear Midge (Diplosis pyrivora) is one of the worst enemies of pear growers. All varieties appear to be attacked by this Insect, but it is not known to affect any other kind of fruit. The adult Midge is only about kin. long and is blackish-grey or black in colour; the female can be distinguished from the male by the abdomen terminating in a long pointed egg-laying instrument or ovipositor. The Flies or Midges first appear during April just about the time when the pear blossoms commence to show their petals, and are to be found up to about the middle of May. The eggs are laid within the blossoms, and when the latter are unopened the petals are stated to be pierced by the ripositor and the eggs deposited on the anthers. In opens flowers the pistil is pierced and the eggs inserted their in. The larvae are very minute white or pale yellow maggots and only attain a length of about inch when fully grown. They feed within the developing fruitlets eating out their centres and leaving behind them a mass of ecomposing tissues. As many as ten, twenty, or even thirty of these maggots may be found within a single fritlet. The attacked fruits usually swell more rapidly that sound ones, and can be readily recognized on the tree by being often twice the size of the latter and more or les distorted. When mature the maggots leave the fruitls either before or after the latter have fallen. In either case they crawl out from their shelter and exhibit cupus jumping movements until they bury themselves in to ground beneath the trees. Here they spin delicate coons of a dirty creamish colour, and hibernate there throughout the rest of the year until the following spring. Unfortunately there is no universal measure for copeing with this Insect. All infested fruitlets should be collected and destroyed before the larvae leave them. Lvery bad infestations it is better to, gather and destroy the whole crop. If an orchard be well stocked with poultry in the spring when the Flies appear and also in June when maggots reach the earth, material benefit is very often attained. Removal of the surface soil contaning the larvae is scarcely a practicable measure. In America the application of Kainit is recommended. If well spread at the rate of half a ton to the acre around the trees it is said to destroy the larvae and pupae in the soil.
When the large are leaving the fruitlets 5 cwt. to the acre is said to be sufficient to destroy them. In this country Kainit has been very little used, and reports as to its value are conflicting, nevertheless, it fully merits a fair trial.
The Cely Fly (Acidia heraclci) is a pretty brownish beet with mottled ornamental wings. It may appearat the end of April but is commonest: in June and the are several broods in the year. The eggs are laid on he leaves of celery and also parsnips. The larva are white or greenish maggots which mine the leaves of those plants. There may be sever larvae in a leaf and by their devouring the middle layers of tissues transparent patches result, covered only by the upper and lower epidermis. After a while these patch become brown and the functions of the leaves are very gatly reduced. The larvae turn into yellow or yellow-brown pupae shaped some-what like minute barrels, and are found sometimes in the leaves but mostly in the soil. The .sect winters in the pupa buried a few inches beneath the round. This fact is of value with regard to preventiveneasures and deep trenching in winter between the origin, rows and burying the soil therein containing the pupae will destroy many of the Flies which would otherwise purge. The mixing of gas lime with the soil adds to the effectiveness of this measure. Screening the young plants with cheap muslin when first put out protects them from t Flies until they are well established, and less liable to suffer severely from the Insect. Picking off and burning the mined leaves will destroy the larva, but in bad attacks the depletion of the foliage by this method would be too great. All infected celery tops should be burnt and not ca aside on refuse heaps. Theohald recommends spraying with nicotine; a useful formula is oz. of 98 per cent nicotine, and lb. of soft soap to 10 gallons of water. Various preparations of nicotine are obtainable and so long as be above proportions are maintained it matters very little which is used (15). It is best to spray in the evenir and when the foliage is not too dry, the spray is said to soak through the epidermis and kill a large number of the larvae.
The Cabbage Root Fly (Cliortophila rassicae) is one of the worst pests of cabbage and culiflowers, and may also attack radishes, turnips, sweets and stocks. Growth of the affected plant is checked, the leaves flag and discolour, the roots are largely destroyed, and the plants die. The Fly is an ashy-grey Insect not mike the House Fly in general appearance and measures about 1 in. long. The winter is passed through in the pupatage and the first brood of Flies appear in April or the beginning of May and there are most probably three generations in a year. The eggs are visible to the naked eye and are laid close to, or on the plant, usually just below the surface of the soil. The larva are typical FIy magots white or pale yellowish, and about 1/4tin. in length when mature.
They commence in jury by gnawing the outer layers of the young roots, afterward making tunnels inside the main root; they may also rade the lower part of the stem. The pupe are about 1/5in. long, oval in form, a light or dark brown and are found in the soil close to the plants. As regards preventive asures early plants have the best chance of success as the become well set before the bulk of the Flies appear. 1rthing the soil around growing plants is valuable as it,auses the. development of fresh rootlets, which serve toeplace those already destroyed by the maggots. A cu-ul of paraffin well mixed with each bucketful of sand,prinkled round the plants once a week until good growl is made, is to be recommended and it acts as a deterrt, driving the Flies elsewhere. Dusting the young plantwith soot is said to be effective and is well worth trial. 'America tarred felt paper discs, slipped round the stems t the young plants and pressed Rat on the ground are stiigly recommended. They are said to afford efficient prc.ction to. young plants against the Flies laying eggs thon, Experiments are being conducted under my direon to test the value of these discs, and if they prove isfactory, their low cost and the simplicity of the meth. will argue strongly in their favour. When the crop is Tested much benefit is derived by pulling up and burningll infected plants as soon as noticed. Furthermore, all bbage stumps should be up-rooted straight away and of left to decay ; by these means large numbers of lar are destroyed which would otherwise escape into the so to pupate. In very severe infestations I would strongl advise discontinuing growing cabbages for one year, td replacing with peas and beans or other distantly rcla l crops. Unless some such course be taken bad infestatts may continue for several years in succession, owing tthe large number of pupa" the soil contains during the wter, after the season is over. Such pupa, are very hard toot rid of as soil dressings such as lime or gas lime arc orery little value. Digging over the soil exposes considtble numbers of pupoe to the attacks of insectivorous his, while over large areas deep ploughing might possib effectively bury a large proportion of them.
The Onion Fly (Hyleniilz !petvrzim) (17) is closely related to the Cabbage Fly and a common pest wherever onions are grown; it is a gr4sh Insect very like the Cabbage Fly. The Flies are common in April and May 'laying their eggs on the necks of lions or on the leaves .just above the soil surface. After aout a week, the eggs hatch into larvae which become full grown in three to four weeks, and are then about 1/3in. long They turn to brown pupae in the soil, though a few may remain in the bulbs, and the Flies commence to appier about fourteen days later. There are several broodsh the year though the exact number has not been detremined ; the winter is passed as pupae which give rise of the early Flies of the next year. In the earliest indications of an attack the first leaves become yellow and then wtish, followed by other leaves behaving in a similar manner. Very young plants are usually nearly eaten through just above the forming bulbs, and the larvae; migrate t fresh plants. As the onions shelter a number of maggots and render it rotten. As are insecticides are useless against their burrowing habits. All pulled up and burnt. Earth valuable as it protects the for is also to be recommended in started before the Flies a,ppea under glass February and p1 mg and burying the soil cont the case of the Celery Fl Various substances are also females from laying their eggs following methods are usefij Watering, or better still, spraying the bases of two to three pints of dissolved. in one gallon of seven to eight gallons of soap while the soap solution is h thoroughly by syringing it paraffin remains on the sur of soot to two of finely mended. In America the acid and lime. Three pints water and a tablespoonful wards.
The length of the complete life cycle depends very largely upon temperature, and during hot weather it may only occupy three weeks from the time the eggs are laid up to the time when the resultant Flies emerge. Certain of the late autumn Flies survive the winter and give rise to the maggots in the following spring; the Flies appear in their greatest profusion during August and September. The House Fly is injurious to man in acting as a carrier of disease germs, and it is specially concerned with the spread of infantile or summer diarrhoea and typhoid fever. It is, therefore, of prime importance to give the Insect no opportunities for breeding and thereby providing a check upon its abundance. All accumulations of manure and refuse should be removed at least once a fortnight, or more often if possible. The adoption of closed ash-bins excludes the access of the Flies to their contents, and are most effective in this respect. Accumulations of farm manure provide nutriment for enormous numbers of House Fly maggots. Experiments on a large scale arc being conducted both in this country and America for the purpose of rendering manure heaps repellant to the Flies and their maggots and, at the same time, still retaining their valuable fertilising properties. When troublesome in houses the House Fly can be readily poisoned by using one teaspoonful of formalin added to a teacupful of water poured into a soup plate. The mixture should be sweetened with a little sugar or should contain about 25 per cent. of milk. If placed at night large numbers of the Flies will partake of it in the early morning and are poisoned thereby. The mixture also has the advantage of being too weak to be harmful to human beings or domestic animals.