THE HESSIAN FLY.

New Zealand Herald, Volume XXV, Issue 8985, 24 February 1888, Page 6

THE HESSIAN FLY.

DISCOVERY OF A DESTROYING PARASITE.

At the annual meeting of the Wellington Philosophical Society, on Saturday evening last, the following interesting paper on the Hessian fly was read by Mr. W. M. Maskell, F.R.M.S. :—The identification of the wheat fly sent down from the Rangitikei districb with the true Hessian fly (Cecidomyia destructor) is a matter of some importance ; for, although its mode of action might closely approximate to that of the European post, yet if there should be a specific difference we might hope that it would not really be as harmful. This identification depends chiefly upon some very minute characters. I have made careful microscopic examination, not, however, including dissection, of specimens of the insect in all stages; dissection is not necessary in this case, nor, indeed, would it be of any help in the absence of materials for comparison in that respect with the true Hessian fly. There is also unfortunately a want of full scientific description of the European insect. I have only been able to find notices of it in a few works and in articles in popular periodicals. These are, as usual, excellent up to a certain point, but they do not enter into sufficient detail. However, there is enough to enable me to say with almost positive certainty that the fly from Rangitikei is the true Hessian fly, or "corn scourge." The importance of this fact it is not necessary for me to dwell on at present. As regards the characters for identification : First, the fly is certainly a Cecidomyia, from' the general contour, the 17-jointed antenna?, the "legs without spines, the shape of tho head and eyes, &c., and tho form of tho larva or maggot. As to colour, it corresponds entirely with that of C. destructor, allowing for variations in sex, and the difference of terms used by writers. Thus, for example, one author says that the feet and antennae are pink " another says they are light brown." The venation of the wings in the perfect fly is an important point; and in this our fly corresponds with the European one. The form of the chrysalis or pupa, or I should rather say the " pupa-case," is exactly the " flax-seed " form of C. destructor. The true chrysalis or pupa resembles that of all cecidomyids in a general way, and I cannot take it as a character for identification of species. This pupa is, when nearly mature, quite loose inside the " flax-seed " case, and the general shape of the future fly can be readily distinguished in it. " As regards the larva, or maggot, it answers entirely to that of C. destructor, possessing the peculiar appendage beneath the head called the breastbone, characteristic of the Hessian fly. Indeed, I am not sure that this feature is not in itself sufficient for identification of the insect. The above characters, which require, indeed, somewhat close examination, but which are necessary for certainty, appear to me to be clear enough to settle the question. I had at first some doubt as to the veining of the wings, but have since been able to satisfy myself that there is no difference here; and coupling this, especially with the appendage to the head of the larva, I conclude that the real Hessian fly has reached these Islands. There is, however, a point to be noted which may lead to more satisfactory feelings. A good deal of interest has been taken, both in America and in England, in the fact that the Hessian fly is subject to much damage from the attacks of other insectsparasites, as they are called. In America several entomologists have recommended that such parasitic enemies should be introduced. In England also attention has been directed to this, and the exhibition of a parasite of the Hessian fly at the November meeting of the Royal Microscopical Society was considered as particularly gratifying. lam glad to report that in this country the pest has no sooner arived than it has been attacked by parasites. I placed in a glass box a number of pieces of wheat-straw from Rangitikei full of the " flax seed " pupa cases. In a couple of days three Hessian flies emerged from the pupa. But next day there came out also a much smaller insect, a Hymenopter, probably of the family Proctotrupidae. Now, these little .insects are essentiallyparasitic, they live and grow in the bodies of the larva? of other insects. This one, therefore, had in all probability emerged from a maggot of the Cecidomyia. I have been able to turn this probability into certainty, having yesterday, in examining some of the " flax seeds," come across one which contained the white skin of a dead maggot, and within this was the empty pupa-case of a hymenopterous parasite, the parasite itself having emerged. Whether or not this was the one I nad previously found I do not know. Anyhow, there are sure to be many similar cases. New Zealand contains several genera and species of hymenopterous insects which are thus parasitic on others. I have not at present sufficient material to determine whether the one thus found is identical with or different from the parasites in England or America. But it is probably a native of this country, and we may have therefore good grounds for hoping that the Hessian fly will be kept somewhat in check by our allies, the Hymenoptera, even without the trouble of importing parasites from Europe. I have brought here to-night specimens of the Hessian fly, its larva and its pupa, as well as the " flax seed " pupa cases ; and also a specimen of the parasite. He wished to point out that the insect was perhaps the worst pest that had yet arrived in New Zealand, and if it were not kept under either by the natural action of these parasites, or some official action on the part of the Government, or by some combination of the farmers of the colony—then, if they were to judge by what had been done in other countries—there would be great damage done to the wheat, oat, and barley crops of the colony. Sir James Hector explained that the life of the insect was an exceedingly interesting one. After the eggs were laid it rapidly grew into a crawling caterpillar, and worked its way into the bottom of the stubble, and then fastened its proboscis into the stem of the growing wheat. Numbers of the insects clustered round and extracted the juice of the stem, and finally the straw was eaten through, and the whole of the crop attacked was ruined. He wished to correct an erroneous impression that had got abroad, to the effect that the insect attacked grain. That was not true. There was a species of insect that attacked grain, but it had not yet made its appearance in this colony. He .suggested as a. means of eradicating the pest, that when a farmer observed indications of its presence in the crop he should cut the stubble as low as possible, and then burn it, after which the debris 'should be buried as deeply as possible. There seemed little doubt that the insect was introduced in tho straw that had been-used in packing some agricultural rfiachinery. It was a well known fact that the pest was introduced into England in some fodder which had come from Belgium. He thought that every step should be taken to keep the pest in check, and to prevent the recurrence of a fresh importation, not only of that, but of other pests more injurious. Had proper precautions been taken to have cases of live plants in Wardian cases disinfected when they were brought to this colony, the colony would not have been ravaged by insects.

Mr. Maskell said he hoped the newspapers would urge the people of the colony to combine in checking these pests, for what was the use .ftf one man doing his best to keep these pests down, while his neighbours did nothing to help him ? ' Mr. W. T. L. Traverß expressed the opinion that the man who industriously kept his orchard cleaned, and who suffered because his neighbours did not, should have some legal remedy. After some further remarks, the discussion closed. A number of specimens of the fly and the parasite in its various stages were exhibited by the microscopic section ( of the society.