Transactions of RHASS Volume 1940 - Page 057
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| Year | 1940 |
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102 INSECT AND OTHER PESTS or 1939. The eggs, which resemble minute seeds, are 3:. in. long, oval, shiny black, with one end slightly rounded, the other conical. The period of incubation is about fourteen days, and the majority of the grubs hatch about the middle of September. The newly hatched grubs differ from those of later stages in the absence of four pairs of fleshy conical projections at the hind-end of the body. Instead, there are two tufts of bristles. Although the Leather Jacket is such a common insect it is interesting to learn that the number of its moults and the duration of its various larval stages have not been definitely decided. All that can be said is that there are at least three stages. The grubs continue in the larval stage from September to July, so that there is but a single generation of Crane Flies per annum. The newly hatched grubs burrow down to the roots of plants, on which they feed until they enter upon hibernation. It is these young grubs which are so susceptible to injury as a result of exposure to drought and sunlight, and this is the reason why an abnormally dry autumn is usually followed by a year in which damage due to the Leather Jacket is relatively slight. Incidentally, drought has a lethal effect on the early stages of other soil pests such as Wire- worms, Surface Caterpillars, and Slugs. Full-grown grubs (Fig. 6) are about 1% inches long, with a wrinkled, tough, leathery skin. In July or August the grub Inoults for the last time and changes to a Chrysalis which lies erect in the ground with its front end projecting slightly above the surface. After ten to fourteen days the Crane Fly pulls itself free of the chrysali‘s skin and is almost immediately ready to take wing. Pairing occurs shortly after the flies emerge, and egg- laying begins and is practically completed on the first day of their winged existence. In this regard it is interesting to note that Crane Flies which are captured at light-traps are mostly individuals which have completed egg-laying. Lovi- bond (loo. oil), from an examination of Crane Flies taken at a light-trap exposed at Rothamsted over a period of four years, found that 95 per cent of the eggs had been laid before the flies were caught. This, combined with the fact that only 23 per cent of the common T. paladosa were females, rather indicates that light-traps would be quite ineffective in coping with crane-fly infestations. Symptoms and Damage.—In pastures and cornfields infested with Leather Jackets bare patches appear in spring where the plants have been attacked and destroyed. The grubs feed just below the surface of the soil on roots and underground stems, but on warm damp nights they are attracted to the surface to feed, when they sever the plants at soil level just as Cutworms do. INSECT AND OTHER PESTS or 1939. 103 Control on Arable Land—(1) The most effective remedy for Leather Jackets on arable land is the application of a poison bait, the same as that which is used in eradicating Surface Caterpillars. It is made by mixing together on a concrete floor 25 lb. of bran and 1 lb. of Paris green. Sufficient water is then added, a little at a time, to make the whole mass damp but not sodden. All the time it is thoroughly stirred With a stout stick to ensure that the ingredients are uniformly mixed. The bait is broadcast by hand in the late afternoon or evening at the rate of 25 lb. per acre. In that Paris green is a (leadly poison it is enjoined that the bait should be used with all due precautions. (2) We have seen that egg-laying of Crane Flies occurs in Fig. G.——Lcatlm Jackets, lam-(r of Tipula paludosa. From nature. Slightly enlarged. August in leys and pastures. Therefore grass land that is marked for cropping should be ploughed in July and the sod turned completely over. The land should be well consolidated after ploughing and a good tilth produced so as to give the crops a good start and enable them the better to withstand attack. Natural Enemies—It is well known that Leather Jackets form a substantial part of the dietary of lapwings, rooks, starlings, pheasants, and gulls in spring and early summer, when the insects are brought to the surface in the course of cultivation. Yet another bird enemy is the little owl which, according to Lovibond, is active in hunting and devouring the adult flies. |
| Title | Transactions of RHASS Volume 1940 - Page 057 |
