CAWTHRON INSTITUTE

Nelson Evening Mail, Volume LXVI, 21 April 1934, Page 6

CAWTHRON INSTITUTE

CONTROL OF BLOW-FLIES Though blow-flies may be a source of annoyance to the householder, the principal reason for their attracting the attention of the entomologist is that the maggots of certain species—known as sheep-maggot flies—attack and frequently destroy living sheep. The depredations of these species are so severe at times as to result in heavy losses reaching over a quarter of a million sterling. This problem is by no means peculiar to New Zealand ; it is one of the most outstanding problems in Australia. Normally blow-flies are of considerable importance in that their maggots act as scavengers by feeding upon decaying animal carcases and such like. The attack of the- maggots upon living animals is no new thing; it has been going cn for ages. But the development oi the livestock industry where animals aiv reared m excessive numbers on a given area lias offered greater opportunity for the animal infesting habit of some blow-fly species. In the entomological exhibition at the Cawtliron Institute, which closes to-day, the different species of blow-flies in New Zealand are shown, attention being drawn especially to the species that attack sheep. For some time past the Institute has been rearing and distributing a parasite to control these flies, and this parasite lias now become established in different parts of the Dominion where it is to be found busily at its work of control. A very popular feature of the blow-fly exhibit is this parasite—which is easily seen by the unaided eye—actively attacking the maggots. The parasite, which resembles a flying ant, captures a maggot and a tussle' begins, the maggot twisting and turning in an endeavour to dislodge its foe. Tile parasite maintains a hold of its- victim and manoeuvres for an opportunity to insert its needle-like egg laying apparatus into the maggot. When this is accomplished the maggot becomes temporarily paralysed, while tho parasite places an egg within its body. Shortly after, the paralysed maggot recovers and continues its activities, but the grub which has hatched from the parasite’s egg is busy devouring its victim. The final stage of the battle is reached when the maggot transforms to a pupa or resting stage from which u blow-fly would normally emerge; but it is at this stage that the parasite completes its destruction and nv place of a blow-fly, a fully developed parasite makes its way out of its victim’s pupa.