THE PARASITE OF THE SHEEP-MAGGOT FLY.

Otago Witness, Issue 3205, 18 August 1915, Page 12

THE PARASITE OF THE SHEEP-MAGGOT FLY.

The blowfly is a source of much trouble and loss, more particularly in Australia, and for some years search has been made for some natural enemy of the pest. In this connection the Sheep-maggot Fly Government Experiment Station, New South Wales (says the Pastoral - Review), recently made an important discovery. This parasite—the Chalcid wasp (Nasonia brevicornis) —was first found under a dead foal at Yarrawin, and some very interesting particulars on the subject are given in a bulletin entitled “ Sheep-maggot .Flies” by Mr W. W. Froggatt, F.L.S., New South Wales Government Entomologist. The perfect chalcid wasp is just onc-twelfthT of an inch in length, of a dull metallic green colour, and in general appearance looks like a tiny winged ant. About 20 colonics of these parasites, containing some thousands of spec,mens each, have been forwarded for liberation in suitable localities in infested areas in all parts of New South Wales, and it is to be hoped that something will be heard of their appearance next summer. After the discovery, Mr Froggatt brought back to Sydney with him a number of parasitised fly pupae for the purpose of ascerta.'n.ng as far as possible their methods of parasitism and life history. The pupae were those of the green and blue sheepmaggot fly (Calliphora rufifacics). They “ were placed in a glass jar,” says Mr Froggatt, “ and in about 24 hours the small anthke wasps began to make their appearance in large numbers. The tiny insects were transferred to ordinary circular glass lamp chimneys, plugged at both ends. In the meantime, to obtain material in which the wasps might oviposit, several pieces of meat were left exposed in the laboratory, and were soon infested with the eggs or maggots of several species of flies, which included the common blowflies (Calliphora viilosa and C. ocean;as), the green bottle fly (Lucilia soricata). Sarcophaga aurifrons, and several smaller flies. As soon as infested the meat was placed in glass jars, and the maggots allowed to develop and pupate. The life-history of the parasite being unknown, it was at first attempted to parasitise the maggots, and although the parasites made several attempts to insert their ovipositors into the bodies of the maggots, they were prevented from doing so by the constant wriggling of the maggots. Some fresh pupce were then placed within the tube, and were quickly settled upon by the parasites, which immediately began tp lay their eggs within the pupm by inserting their ovipositor through the pupal covering. Their sense of location is evidently very acute, as pupae exposed anywhere in the laboratory were always found and attacked by parasites which had accidentally escaped from their tubes. The only evidence of a puncture remaining is a small bead of clear liquid at the point of insertion, but she almost immediately turns round and sucks up the liquid, and thus leaves no visible signs of her work, -Tins licjuicl is probably used in the first case as a lubricant by bathing the styles as they work in the sheath while puncturing. The time occupied in the whole process of insertion and partial withdrawal and the deposition of the eggs is variable, and was found to range from four to 25 minutes. The young larvae hatch in about three days’ time, when they bite through the fly integument, insert the head. and. while their bodies remain outside, feed upon the juices of the fly pupae. As the larvae develop the unfortunate pupae are gradually eaten, until the full-grown parasitic. larvae occupy the space once occupied by the fly pupae, nothing of the latter finally remaining except the shrivelled integuments. The period of development of the larvae occupies about seven days from the time of hatching, the full-grown larva being a cylindrical, dirty white, legless grub. The pupal stage occupies about five days, and the adults usually gnaw one hole in the pup.arium and escape, although two may sometimes be made. The time occupied from oviposition to the emergence of the adult is' 15 days, but there are indications that this varies with temperature. The males characteristically appear a little before the females, and are active little creatures, continually running over and over the empty pupal cases. As soon as the females emerge copulation bcghis, the females being ready at nneo to receive the males. The number of broods.in a year has yet to he determined, hut between December and May 10 broods developed under artificial conditions; these, however, may be more favourable to the parasites. "Whether the number of broods would he doci'cnsefl under natural conditions, as seems likely, lias yet to be determined. The parasites, on the. whole, are very hardy little creatures, and under careful treatment should live several weeks. In conclusion, it should be understood that, while this parasite should act as an important aid to our artificial methods of control, adverse weather conditions, failure of food; supplies, and other limitations may reduce their value, so, that wo cannot hope for a complete annihilation, but should

reasonably expect a considerable reduction in the blowfly pest.