Mediterranean fruit fly (Ceratitis capitat)a and Queensland Fruit Fly (Dacus tryoni)
Mediterranean fruit fly is a small insect similar in appearance to a housefly with a yellow and brown banded body (they are a true fly - ie a member of the order Diptera). The females have a clearly visible ovipositor behind the abdomen. Wings are held in the drooping position. They lay eggs in fruit, where they feed until they are ready to pupate. At this time they drop to the soil, where they remain buried 5 mm under the surface for a month (in ideal conditions) or longer.
Queensland fruit fly is larger and reddish brown with yellow marks on its abdomen. Its life cycle is similar to the introduced pest. Queensland fruit fly is found mostly around Sydney or further north. Mediterranean fruit fly is a major pest in Western Australia
Fruit flies should not be confused with the small black ‘vinegar fly’ which is attracted to fermenting fruit.
Evidence of fruit fly activity includes clearly visible puncture marks in the skin of fruit, sometimes associated with fruit rot which starts around the wound, or frass. . Fruit ‘stings’, where the adult has punctured the skin to lay eggs, appear as small holes which usually repair to small raised lumps in citrus and passionfruit, small T shaped marks of lumps in avocado or brown spots on persimmons, apples and pears. On stonefruit the stings are usually inconspicuous.
Larvae are creamy-white maggots which grow to about 8 mm in length. Maggots are clearly visible inside the fruit when opened.
They are a major economic pest and quarantine is an important method of control to limit their range.
Conventional sprays for fruit fly are usually based on fenthion, dimethoate and trichlorfon. Fention is very toxic to domestic animals especially poultry and other birds. Organic control methods include traps and baits and integration of poultry into the orchard.
Quarantine points are found on major roads around fruit producing areas and entry of potential host plants is not permitted without an inspection certificate from the Australian Quarantine Inspection Service. Generally this is granted only after dipping in a pesticide solution or cold storage although close inspection of fruit is an alternative option. Complete eradication is possible from areas where they are not well established, if strict surveillance can indicate their presence early enough. In fruit cropping areas where they have the potential to become established resources are devoted to trapping as a protective measure. When outbreaks occur all fruit is either sprayed or stripped and destroyed by burning or immersion in kerosene or pesticide.
Old neglected trees and over ripe fruit should be removed to reduce host sites. Fallen fruit should be removed and destroyed or fed to animals within 24 hours. Some benefit may be obtained from good pruning to open the tree to light, although this strategy is only useful when other methods are successful in reducing fruit fly to low numbers.
Control of aphids and scale may be of assistance as the adults are attracted to the sticky ‘honeydew’ which they produce.
Depending on where you live you may wish to seriously consider not growing the major host plants. Selecting early varieties of fruit may help to avoid the peak seasons, as numbers often build up after several generations (in each year). In Sydney Queensland fruit fly season starts in late August or September and gradually builds up until late January and February. Losses of main crops such as tomatoes will be tolerable in home garden situations before late January, without any spraying
Some fruits are much less attractive to fruit fly and can be grown successfully even in peak fruit fly areas - try mulberries and lemons. Some growers report that thick skinned varieties, such as Tom Thumb tomatoes are resistant - but they will still suffer some attack. In southern Australia loquat is a potential host which requires special attention because it provides a food source between winter crops (citrus) and summer crops (stone fruit etc). At the other end of the season late crops such as quince and medlar can extend the season of fruit fly.
Traps and lures or baits
The adult fly feeds and matures for about one week prior to mating. During this time it can be attracted to a bait and trapped. A range of baits are used. generally the strategy is to maintain a few baits before the fruit season to identify the first flight. When the first evidence of activity is discovered a full baiting schedule must begin immediately.
Some baits are indiscriminate, attracting useful insects such as bees, lacewings and hoverflies, so you will have to experiment to discover which ones are most effective in your area without causing too much damage to beneficial insects.
Traps can include small jars, plastic bottles and a range of other receptacles. You could also try good old fashioned fly paper - although it is indiscriminate and will stick anything that lands on it.
Dak pots are available in NSW for Queensland fruit fly, but they are only a monitoring tool and will not control the pest. They attract males only and are used to indicate flights and as a guide for when to spray.
Splash baits are made with a cup of sugar in one litre of water and 5-10 ml pyrethrum (conventional splash baits are made with maldison). Nicotine sulphate was used for this purpose and was once considered to be organically acceptable but it is now considered too toxic to be recommended in these pages especially when pyrethrum works well (if reapplied often). Walk around the orchard with the mixture in a bucket dipping the end of branches into the liquid.
A selection of bait recipes:
Kerosene, creosote and mothballs (camphor and naphthalene - but it is not ‘organic’) are deterrents but many stations will be required (at least three per tree). They mainly work by masking the fruit scent and they will make staying in the vicinity of orchard trees unpleasant for the gardener too.
Ants and predatory flies may take fruit fly but predation is insufficient to remove the pest from orchards or gardens.
Poultry are undoubtedly one of the most useful control methods for organic growers and home gardeners. They control maggots as they drop to the ground and scratch for pupae under the surface, thus reducing the number of adults in the next generation. Bantams are particularly effective at search and destroy techniques and contribute manure, eggs and a range of other services.
Sheep, wallabies and other grazing animals are also useful to remove fallen fruit from under orchard trees.
Cold storage of fruit will kill maggots.
Another effective technique is total exclusion, generally a fine polypropylene mesh or other material such as mosquito netting which is draped over small trees or fruiting vegetables.
I was most impressed when I met Brisbane gardener Muriel Chartris (see Acres Vol 2 no. 5). She covered fruit such as tomato and eggplant with cloth as they were growing. She had observed that the fruit fly likes to land on fruit from above and rarely finds its way underneath. Muriel also suspects that covering fruit helps to reduce ripening smells in the vicinity.
Fruit fly can be attracted to sugar and protein, and moist baits are generally more effective than dry ones. Here are a few favourite recipes, but you may try other ingredients and combinations.
Molasses, water and fruit juice - experiment with quantities, starting with one part molasses, two parts water and three parts fruit juice.
Equal parts of honey, laundry ammonia and vanilla essence diluted in water (you can use urine instead of ammonia).
Orange rind (one or two oranges) 150 ml ammonia and 250 ml water - dilute further as required.
Four parts protein bait such as corn meal and one part ammonia diluted in water.
equal parts of molasses and flour mixed in water.
Baits without poisons work by luring the adult away from the crop or by drowning them in the sticky solution, or by ingenious traps where the fly can easily get in but not easily escape.
Commercially available baits are available in eastern states (eg DAK pots). Most contain a poison and they are unacceptable in organic certification. Other growers may decide to use them and some use them only in windbreaks or non-cropping trees, but this will reduce their effectiveness.
Home made organically acceptable baits may use natural pyrethrum or borax powder (in dry baits or mixed with jam).
Molasses or honey can be replaced with treacle, golden syrup, jam or sugar syrup.
Sherry, port wine or brewing lees, yeast mixed in water and vegemite are effective when mixed with water.
Wheatgerm, bran or other protein meal can replace corn meal.
Detergent, soap or flour may help to ‘stick’ the insects and make it harder for them to emerge from the bait.