Field OPS & Areas
– Life-Cycle
– Identification
There are two fruit fly species of economic importance on deciduous fruit:
Mediterranean fruit fly and Natal fruit fly.
Their biology and life-cycle are virtually identical.
Life-Cycle
Under favourable conditions female fruit flies become sexually mature and capable of laying eggs about 5 days after they emerge. After mating they actively seek out ripening fruit, and deposit their banana-shaped eggs in a small cavity just below the skin. Oviposition (sting) sites appear as small brown spots on the surface of the fruit, under which is a cavity with one to more than 20 eggs.
After 2 to 3 days in favourable conditions the minute, transparent larvae hatch and start feeding on the flesh of the fruit, slowly tunnelling towards the core. The larvae have a sharply-pointed front end with no obvious head, and a blunt rear end, and become cream-coloured as they get older. Early infestation is often indicated by a brown colouration of the fruit flesh in the area of feeding due to oxidation of the tissues. From about 7 to 40 days later, depending on fruit kind and temperature, the larvae reach maturity (8 to 10 mm long), when they leave the fruit, fall to the ground and pupate just below the surface of the soil. About 8 to 40 days later, depending on temperature, the adult flies emerge from the pupae, crawl up to the soil surface, and the cycle is complete.
During warm conditions and in ripe fruit, the life cycle can be completed in as little as 3 to 4 weeks. This duration can increase to about 2 or 3 months in winter or where eggs are laid in greener fruit.
Identification
Mediterranean fruit fly
Eggs are white and banana-shaped, about 1 mm long. Mature larvae are creamy-white, legless, 7 to 9 mm long, and the body tapers from a blunt rear end. Pupae are reddish-brown, cylindrical with rounded ends, and 4 to 6 mm. Pupation usually occurs in the soil. Adults are slightly smaller than a housefly, about 3 to 5 mm in length, yellowish orange-brown in colour, with some orange-brown markings on the wings. The eyes are reddish purple with a green fluorescence.
Natal fruit fly
Immature stages are very similar to Medfly, but slightly larger. The adult is about the size of a housefly, up to 8 mm in length, and more brown than Medfly. The eyes are reddish purple, usually with a blue fluorescence. The male has black ‘feathering’ on the lower end of the middle legs. As in Medfly, wings are also patterned but wing bands are brown and generally darker than on Medfly.
African invader fruit fly
A new species of fruit fly, the African invader (or Asian) fruit fly Bactrocera invadens, has recently invaded Africa from Sri Lanka. It had spread to more than 10 countries in Africa, including Mozambique and Namibia, where it is reported as an extremely serious fruit pest.
This fruit fly is highly invasive with a high reproductive potential, and has a long list of host plants, including citrus, mango, cashew, papaya, guava, pepper, and several wild host plants. The main pathway for fruit flies to spread from one country to another is through the international movement of infested fruits.
Specimens of this invasive pest were intercepted in South Africa, but timely intervention has led to successful eradication from South Africa.
Fruit Fly Africa has a network of traps deployed throughout South Africa to enable early detection and further action.
