The first signs of fruit fly damage are stung or infested fruit. Stinging is caused when the female lays eggs into unripened and ripened fruit.
Eggs laid into hard, green, unripened fruit are unlikely to hatch, though the fruit may become distorted or misshapen due to damage. Eggs laid later as fruit is maturing or ripening are more likely to successfully hatch.
Worldwide, Medfly has been recorded from over 260 plant species including fruits, vegetables and nuts. In WA, thin-skinned stone fruit (apricots, nectarines, peaches), mangoes, persimmon, apples, pears and mandarins are particularly susceptible.
Medfly will attack all citrus except some lemons and can breed in over-ripe or damaged fruit of less susceptible crops including tomato, eggplant and capsicum. When populations are very high, less preferred hosts such as olives may also be attacked.
It has been estimated that without control, Medfly would infest all susceptible fruit such as apricots, nectarines, peaches and mandarins and to a lesser extent, apples and pears.
All citrus is susceptible in warm winters. Only early maturing varieties of stone fruit or tolerant varieties such as some lemons and avocados can be grown without chemical control.
Medfly is thought to originate from Africa and is now endemic to WA. It was discovered in Claremont in 1895 and is found from Esperance through to Carnarvon. It is present in Broome and Derby, but absent from the Ord River Irrigation Area (ORIA, Kununurra). The main area of infestation extends from Perth through to Bunbury.
Queensland fruit fly (Bactrocera tryoni) is the main pest species in eastern Australia, but is not present in WA.