Mediterranean fruit fly
Mediterranean fruit fly (Ceratitis capitata) is a serious horticultural pest in Western Australia (WA). It attacks a range of cultivated fruits and some fruiting vegetables.
Medfly, as it is commonly known, costs the WA horticulture industry millions of dollars annually in lost production and control costs.
Growers use a range of methods to combat fruit fly, including pesticides, baiting and orchard hygiene. The withdrawal of organophosphates from use in commercial orchards has led to renewed interest in innovative solutions against fruit fly.
The current technique - SIT
Sterile Insect Technique (SIT) involves sterilising male Medfly using radiation. The sterile male flies are then released in targeted fruit growing areas that have large wild populations of the pest. The sterile flies mate with wild females, but no offspring are produced. This reduces the pest population over a series of releases.
It is a clean, environmentally-friendly method of pest control, but its success is limited because the sterile flies are less vigorous than wild flies. Radiation can weaken the newly sterilised insects, making them less able to compete with wild males.
The technique is generally used in conjunction with other control methods.
A new technique
A Medfly strain was sourced from University of Oxford spinout company Oxitec, based in the United Kingdom. The approach is similar to SIT but instead of using sterilising radiation, pest control is achieved by using a self-limiting gene along with a colour marker to track and trace the insects in the environment.
The males pass on the ‘self-limiting gene’ causing the female offspring to die before they can reproduce and sting the fruit. The male flies are expected to be free of the adverse effects of sterile male flies weakened by radiation under conventional SIT methods.
The trial
The trial, conducted by the Department of Agriculture and Food, Western Australia tested whether purpose-bred male fruit flies can be reared successfully and cost-effectively in a controlled laboratory environment and whether they can successfully compete with pest males and SIT males.
The flies were imported into Western Australia from the United Kingdom under permit at the egg stage and reared at approved research facilities operated by DAFWA.
Department and Oxitec scientists undertook glasshouse studies comparing the performance of the Oxitec flies against the sterile flies.
Replicates were run with 21 mating trials in total, under strict regulatory conditions. Each replicate involved either Oxitec or sterile male flies, competing with wild male flies, to mate with females.
During the trials each mating pair was collected and checked to determine the males’ genotype.
The sterile males were irradiated at either a high dose, providing a better guarantee of sterility, or a low dose. The Oxitec males outperformed the sterile males treated with a high dose. The mating performance by the Oxitec males was comparable with the sterile males irradiated at low levels.
The research found the Oxitec male flies are compatible with wild female flies and their mating performance is promising.
The Department is now in consultation with Australian Government regulatory bodies including the Office of the Gene Technology Regulator for the next phase of testing.
Legislative requirements
The trial is subject to quarantine and regulatory conditions required by the Australian Department of Agriculture and Water Resources, Australian Department of Environment and the Office of the Gene Technology Regulator.
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