Fruit fly battle: Gene control years away

IT IS likely to be several years before South Australia’s proposed mass-rearing facility begins producing male fruit flies that have been genetically manipulated to suppress infestations of Mediterranean and Queensland fruit flies.

Under the microscope: Key research is being carried out in laboratories around the world to control pests such as the varieties of fruit fly that are threatening Sunraysia’s multi-million-dollar horticulture industry.

Under the microscope: Key research is being carried out in laboratories around the world to control pests such as the varieties of fruit fly that are threatening Sunraysia’s multi-million-dollar horticulture industry.

Mourquong citrus grower Vince Demaria, a member of the new committee that will co-ordinate fruit fly control in the Greater Sunraysia Pest Free Area, said last week the technology was still being developed.

Until the facility begins operating, the citrus, table grape and summer fruits industries will need to hold the line with conventional suppression techniques that rely on baiting, trapping and killing fruit flies, according to Mr Demaria.

Several novel technologies are emerging for insect control that render current radiation-induced sterile-male insect technology obsolete.

Two promising techniques rely on a time-bomb effect, where male flies are genetically modified to transmit a gene that leaves male flies unaffected, but blocks the development of female fruit fly larvae into adult flies.

Radiation-sterilised male insects have been used to control pests like Medfly in California, and screw-worm fly, a serious pest of the beef cattle industry, in the southern US. But radiation sterilisation is obsolescent, because it is inefficient. 

The radiation not only sterilises the males, it causes other genetic­ damage that compromises their ability to compete successfully against wild males to mate with wild female flies.

In the 1970s, before the advent of recombinant DNA technology – genetic engineering – CSIRO researchers developed a novel genetic technique that relied on a laboratory-bred, mutant strain of the sheep blowfly, Lucilia cuprina.­

The laboratory strain had several fused chromosomes; males carrying the defect could mate with female compound-chromosome (CC) flies, but produced no offspring if they mated with chromosomally normal wild female flies. The technique was field-trialled­ in the Brindabella Valley near Canberra in 1979-80, but was unsuccessful. 

The CC flies tended to mate among themselves, rather than with wild flies, and did not persist in the field.

The new recombinant DNA techniques promise to overcome the problem of the modified strains being at a disadvantage against wild-type flies in competition for matings. 

All techniques are dependent on the wild-type females mating only once in their lifetime, and maximising the likelihood that the one-off mating will be with a modified male fly.

Oxford Insect Technologies’ Oxitec system is likely to be a leading contender for controlling fruit fly in Australia. 

It’s potentially applicable to any species of fruit fly, or any insect pest, and has the major advantage that it produces only male flies – female larvae die before completing development – and the few females that do manage to pupate and hatch are severely compromised and unlikely to produce female offspring in the field.

It employs an ingenious technique is called RIDL, which stands for Release of Insects carrying a Dominant Lethal (gene).

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