Saving citrus from fruit fly
PAKISTAN is an important global producer and exporter of the fruit. In 2004, citrus production exceeded 167,000 tons with 95 per cent grown in Punjab. Most of the citrus output here (80 per cent) is reliant on mandarins.
Pakistan is the largest producer (95 per cent) of the world kinnow. In general 35 per cent of the produce is lost during pre- and post-harvest stages due to poor disease management, weather conditions, harvesting delays, poor harvesting practices, poor road conditions, lack of cold storage facilities and insect pest attacks specially fruit flies.
Fruit flies are present in most countries and attack many types of fruits, as well as fruiting vegetables, ornamental flowers and some nuts. Feeding by fruit fly larvae (maggots) damages the fruit internally, causing it to ripen prematurely and rot. Up to 100 per cent of fruit may be damaged by fruit flies when infestations remain uncontrolled. The presence of fruit fly can also result in loss of valuable interstate and export markets.
Fruit flies are serious agriculture hazard throughout the world and represent a threat to successful establishment of horticulture industry and trade. The existence of fruit fly also means s that crops that reach the market are not eligible for export due to quarantine regulations.
Lifecycle: Qfly and Medfly are most active from October to May. Some activity will continue in warmer periods during winter months. Adults of both species of the fly become active in spring and start laying eggs in mature fruit. For both species of the fly the preferred hosts are stone fruit that can support and buildup their populations before citrus fruits are available as cites for egg laying.
The adults can live for a few months and lay hundreds of eggs, a few millimeters deep inside the fruit. A Medfly may lay up to 1,000 eggs during her life. Eggs hatch in a few days and the larvae eat through the fruit, growing to about 9mm long when mature. Depending on temperature, this takes one to several weeks for Qfly and two to six weeks for Medfly.
Infested fruit often ripe prematurely and drop on the ground. Mature larvae leave the fruit, dropping to the ground and burrowing into the top few centimeters of soil to pupate.
The pupa stage lasts one to several weeks for Qfly and two to seven weeks for Medfly. When pupation is complete, the new adults emerge from the soil and take about a week to mate, feed and begin laying eggs.
Adult female Qfly and Medfly need a source of energy and protein before they can mature their eggs. For this, they may feed on nectar, honeydew from sap-sucking insects such as scales and aphids, bird droppings and bacteria. Qfly generally lays eggs in citrus that is at the ‘silver green’ stage or more mature, while Medfly prefers fruit that has started to color. Skin color may develop prematurely around the egg-laying site (the ‘sting’) and fungal decay can infect stung fruit under humid conditions. Stung fruit can fall, even if no fruit fly larvae develop. Populations of fruit fly continue to build up through successive generations over the spring and summer months until temperatures in autumn.
Strategies for the control of fruit flies should posses the following components: sustainable, suppression and environmental friendly. The management approaches may include physical control, cultural control, biological control, the sterile insect technique (SIT), male annihilation technique (MAT), protein bait technology and insecticides cover spray as there is no single, ‘one-answer’ solution to the fruit fly problem.
The following options for fruit fly management are available to organic producers and should be applied to home garden trees as well as commercial orchards.
Early harvest: As the season progresses, fruit fly populations, attractiveness of fruit to fruit flies and the risk of damage increase. Tall trees are more likely to carry un-harvested fruits that can act as infestation sites for fruit flies.
Trapping: Traps are generally considered useful for monitoring fruit fly populations rather than controlling them. Recent overseas research however indicates that high densities of traps can remove enough fruit flies to significantly reduce the level of fruit damage. Traps attract fruit flies by using pheromones, food scents or visual cues. Pheromone traps contain a sex pheromone that attracts male flies. Depending on the trap type, the flies drown in liquid bait, get caught on a sticky layer or are killed by a contact insecticide.
In the latter case, the insecticides commonly used are not permitted under organic standards. However, liquid and sticky pheromone traps suitable for use on organic properties are available commercially.
Biological control: Newly emerged flies need up to 24 hours for their wings to harden before they can fly, so are prone to predation on the soil surface by birds, ants, bugs and earwigs. Birds including domestic poultry may also contribute to the control of fruit fly larvae in fallen fruit and shallowly buried larvae and pupae. Cultivation would increase the exposure of larvae and pupae to these and other predators, but is not desirable where it would be needed – right under the trees.
Parasitic wasps and nematodes also attack various stages of fruit fly. While all of these natural enemies help to reduce fruit fly numbers, they are very unlikely to provide economic levels of control.
The destruction of fallen, damaged, over-ripe and excess ripe fruits is strongly recommended to reduce resident populations of fruit flies. Crop residues such as fallen, over-ripe or damaged fruits may be destroyed by deep-burying.