The Medfly originated in sub-Saharan Africa and in the last 160 years has spread through most tropical and sub-tropical countries – Southern Europe, the Middle East, large parts of Australia, most of Africa, Southern and Central America and Hawaii.
In Spain, they are a huge problem throughout the south and along the Mediterranean coastline. Our habit of transporting fruits from one continent to another has given them a free ride! The Medfly has spread more than any other type of fruit fly and is now considered to be the biggest agricultural pest in the world.
It has achieved this position because it is more cold tolerant than most species and has a huge range of host fruits – over 260 fruits, vegetables and nuts. Thin-skinned ripe juicy fruits are preferred, especially citrus, stone fruits such as apricot and peach, fruits with small seeds such as apple and pear as well as peppers, tomatoes and figs.
The adult Medfly is somewhat smaller than the common house fly, measuring around 5mm long. It is yellowish in colour with a brown tinge to the lower abdomen and has wings with brown and yellow markings. The eyes are the most recognisable feature – brick- red in colour. They can fly short distances (and are often carried further by the wind) when searching for host fruit but, within an orchard situation with plenty of food possibilities, they will not normally move more than 150m. The female lays eggs in batches of around a dozen, just under the skin of the fruit, and, in a lifetime can lay 300 eggs. Under optimum conditions, a life cycle can be completed within 21 days. Activity will stop at temperatures below 10C.
Within a few days of egg laying the maggots or larvae will hatch out and it is their feeding on the fruit pulp that destroys our potential crops. The larvae will eat for two or three weeks, reaching 1cm long. Their tunnelling through the fruits allows entry to bacterial and fungal infections. The fruits slowly decompose. Once mature, the larvae they will come to the surface of the fruit, drop to the ground, tunnel under and pupate. This is when chickens are incredibly useful!! The adult fly will emerge with 8 to 45 days; they then require a few days to mature, copulate and start laying eggs.
There is evidence that the larval time varies from fruit to fruit. In a peach it is around 10 days but is considerably longer in citrus, reaching up to as much as 20 days in lemons and limes under the same climatic conditions. This is probably because the larvae need the sweetness of the fruit to mature sexually. They prefer thin-skinned succulent fruits, preferably yellow/orange colouring and they are very susceptible to lack of food, with some 50% of young flies dying within the first two months.
The sequence of attacks on fruits within Spain is: 1st generation in winter to oranges and mandarins; 2nd generation in spring to early apricots; 3rd generation in late spring/early summer to early peaches, nectarines. During summer, 4th generation attack late peaches, nectarines, pears, mangoes and papayas. The 5th generation, during September, attack figs, apples and grapes. During October, the sixth generation, attack prickly pear fruits, dates and early citrus. If the weather stays good, a seventh generation will attack persimmons (kaki) and citrus. Other fruits such as plums, loquats (nispero), cherries, pomegranate, avocadp, guava and custard apples are not immune either.
Commercially they are the most damaging pest. Huge sums of money have been and are being spent on control but, even so, in certain areas commercial growers avoid varieties of fruits that mature late because of the sheer numbers of Medflies. Damage to the environment and, of course, ultimately us, is immense and immeasurable.
As gardeners, we love to grow our own fruit and veg and nothing is more disappointing than cutting into freshly picked fruit and finding it inedible.
We have the answer and it’s environmentally friendly – the Ceratrap.
It’s a plastic pot that hangs in a fruit tree. It contains an attractant that the female flies find irresistible and they are drawn into the pot where they drown, unable to escape. The pots should be hung at a height of approximately 1.5m and on the sunny side of the tree. One pot will protect an area of approx. 150m2 and the effect will last for around three months. Then the pots can be refilled. Simple, clean and effective. Price €8.50 each pot at Viveros Florena.
Lorraine Cavanagh owns the specialist garden centre Viveros Florena, Competa, Malaga (garden centre, designers & landscapers) and is author of the best-selling Mediterranean Garden Plants and Citrus, The Zest of Life.
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