THE HESSIAN FLY.

Temuka Leader, Issue 1704, 28 February 1888, Page 3

THE HESSIAN FLY.

The following description of the Hessian fly, taken from a Fifeshire paper, may be of interest to our readers just now, when the pest is . attracting so much attention, in New Zealand:— “ The Hessian fly is a family relation of the daddy longlegs, the common •- gnat, the water gnat, and the midge, ■ which, like itself, are included in the family Tipuildce, of the order Diptera. The female fly is a creature about an eighth of an inch long. Its body is of - a dark-brown color, shading into black; its wings are of dusky gray, fringed, and rounded at the yips. It - is characterised by long fringed darkcoloured antennae, bufc bead-like - points. The male fly, which is much less abundant than the female, is said to be smaller, but bas longer antenna?. The insect seems to prefer a warm moist climate, and generally attacks plants in a poor, thin, gravelly soil, probably because these are less able to resist its encroachments, It generates twice a year—in the spring and early autumn —the first generation injuring wheat and barley plants, the second attacking young wheot-plants directly they come up. The autumnal attack is, according to Dr Fitch, the more deadly, being ‘ in a double sense a radical one. Each particular shoot at whose root one or more of these larva is, is commonly destroyed by the time the worm has attained its growth. The presence of these worms is, therefore, readily detected by an examination of the small wheat in October or November. Individual shoots will be found here and there in the "field Withered and changed to a light color, strongly contrasting with the rich green of the vigorous uninjured plants.’ The effect of the insect on the plants is much like that of the disorder known as ‘ gout ’ or * rootfalling,’ only that, instead of giving way at the roots and various parts of the stem, the plants attacked by the Hessian fly are crippled and bent sharply down just above the second joint ; while the stems are so weakened and ‘ scrawled ’ that there is little or no corn in the ears, and the straw is broken, discolored, and stunted. Each female Hessian fly lays from 80 to 100 eggs, •xd places from 20 to 40 upon a single leaf in the creases of the upper parts of the blades of the young corn plants. I he eggs are quickly hatched, taking from four to eight days, according to the weather. From the egg . laid in the spring comes a wrinkled u . yellowish maggot--the larva—without .' legs, having 14 joints. It is close upon an eighth of an inch in length when full grown, being then of a clouded white hue, and showing faint greenish lines under the skm. After the larva has been hatched it almost invariably proceeds from its birthplace to the second joint of the stem, at the base of the blade, or leaf, and absorbs the juices of the plants. About five or six weeks after the larva, still in its position close to the second joint of the plants, gradually puts on a bright chestnut color, and ■ at this time or shortly afterwards, casts this embrowned skin. This skin is not cast in the ordinary meaning ef the term, as the larva remains within

it contracted in size and free to move. This is the flax-seed stage. The larvae in these puparia are fixed so very tightly in the straw, which has ripened and hardened around them, that it is frequently difficult to extract them from it. The pupa eventually breaks open and crawls from its puparium and works its way upwards within the sheath of the leaf until it arrives at some cleft in the now dead and brittle straw; through this cleft it gradually crowds its body until all except the tip of the abdomen is protruded into the air, the elasticity of the straw causing it to hold the pupa in this situation secure from falling, 'thus fixed the fly gradually emerges from the case. The Hessian fly attacks the young corn plants in the autumn as well as in the spring. In America, where it is necessary to sow the autumn wheat early in consequence of the continuous frost, serious injury is often done. In this country it may be hoped not so much harm will be effected in the autumn-sown crops, as immediately the frost comes the lame assumes the flax-seed cases in which they pass the winter, and the crops, which without such timely aid would soon turn yellow and die, are for a time safe.

“Mr Charles Whitehead, of the Agricultural Department, in a valuable report prepared by him on the subject, recommends that in localities where there is a suspicion of fly, wheat should be put in late, certainly not before the 20th October, in order that there may be no plants showing upon which the fly could deposit its eggs. Great care should also be taken to extirpate all self-grown wheat and barley plants round fields and near fields that have been infested during summer, and late developed plants of the first crop, as these will serve to carry on the insects during the winter. When wheat and barley plants have been intested with the fly it would be well not to sow wheat or barley in the ensuing autumn and spring near the affected fields. After an attack, and when the “ flax-seeds ” or chestnut-colored puparia, are seen in the straw of wheat and barley plants the straw should be cut high above the second joint, in which, and in the second joint, they are almost invariably located. This may be done by setting the reaping machines high, or by putting men on to reap in very bad cases. Then the land should be immediately cultivated with a scarifier, or broad share, and the stubble raked or harrowed together and burnt. Or the land may be deeply ploughed with close furrows in order to bury every particle of stubble. All straw that has come from infected fields, or from those where there is any suspicion that the insect has been present should be closely examined for “ flaxseeds.” If they were found in large quantities a public-spirited farmer would make a bonfire of the whole of the straw. The least that could be done would be to stack it as tightly and closely aa possible, and to guard it jealously that none is sold, and that it is all used in the winter, and that all passes through the mixen.

“ The Hessian fly has for its natural enemies at least five kinds of parasitic insects. The most destructive is one known as Platygaster error. This is a shiny black four-winged fly, smaller than the Hessian fly. It places its eggs with the eggs of the Hessian fly, ■’Trie victims arrive at the pupal state but no further, for the larvae of the Platygaster devour the contents of the puparia, and, wrapping themselves in cocoons, use them for their own purposes, It is devoutly to be hoped that these parasites may have accompanied the Hessian flies to the United Kingdom. If not, steps must be taken to introduce and colonise them at once.”