Given the diverse climates within Australia the activity of fruit flies varies from state to state and region to region. Factors like temperatures, moisture availability and host fruits all play a part in influencing how fruit flies behave in a region. Understanding how fruit flies behave in your local area will be important in implementing a control strategy. While many of the specific activities will be similar, the timing of these can vary significantly.
In the southern regions of Australia, fruit flies have a distinctive pattern whereby the adult flies that have survived winter will start to become active in the warmer spring or early summer temperatures. Egg laying follows as host fruits become available and if there temperatures are high enough. By autumn, fruit fly activity is slowing and ceases altogether. In contrast, the warmer temperatures in Queensland and the north of Australia may mean fruit flies are active throughout the year. In these northern climates availability of fruiting hosts may be the limiting factor. In some locations, fruit fly activity will be very low or close to zero throughout the winter months, while at other locations, fruit flies may be active throughout the year.
Choosing and developing an effective fruit fly control strategy at home requires some thought about what fruits and vegetables you want to grow, where you live, and what measures you are prepared to undertake. Some of the decisions include:
Exclusion or control?
For small areas and high value crops, surrounding your fruit trees and other crops with a fine mesh that excludes fruit flies may be worthwhile. Provided that the mesh is fine and free from large holes it can completely prevent fruit flies from accessing your crop. However, it can be difficult to fully enclose large trees and you will need to only put the mesh up after pollination. This technique can be labour intensive and more expensive, but can be very effective.
Alternatively, there are a range of fruit fly baiting and trapping options available and while these are not difficult to use, they do take a sustained effort throughout the growing season.
Do I want that plant?
Fruit flies can affect a wide range of fruits and fruiting vegetables. Unintentionally, that unwanted or abandoned fruit tree could be providing a habitat for fruit fly populations to build up on before they move into your prized tomatoes and capsicum. If you have a fruit fly host plant that you don’t want, replacing it with a a purely ornamental plant could make a big difference.Fruit Fly Host List (agriculture.vic.gov.au)
What control methods am I prepared to use?
Increasingly many of the older chemical pesticides are being withdrawn from use meaning that the available control options are already less toxic to beneficial insects and many fruit fly control options are considered “organic”. However, some traps and lures still use chemical killing agents. While these chemicals are contained within the trap or lure and will never contact your plants, if you have young children or pets, you may be reluctant to use them.
Having thought about the measures you are willing and able take throughout the year, the next step is to implement the control measures.
1. Monitor for fruit fly activity.
Using fruit fly traps with an attractant (pheromone) in your backyard and checking it daily will let you know whether fruit flies are active in your area and when they have first emerged after winter. Male fruit flies are strongly attracted to these pheromones and this will then alert you when to use other control methods. With experience you will also learn when fruit flies are active in your region.
These traps are long-lasting, but while they do capture some male fruit flies, they will not remove the egg laying females. They need to be used as part of a broader strategy.
2. Apply bait sprays or use protein traps before fruit starts to ripen (and start early)
Female fruit flies need to feed on protein in order to develop their eggs. In nature, fruit flies get this protein by feeding on bacteria and other sources. However, this feeding need can be utilised to the gardeners’ advantage. From the moment you observe any fruit fly activity in a monitoring trap, use protein baits or traps to attract and kill flies.
The first option is to use a protein bait spray like Yates Natures Way Fruit Fly Control or Eco Naturalure. These products contain protein and an organic insecticide that fruit flies will feed on and subsequently die. Depending on the crop, these are sprayed on foliage.
The second option is to use a trap that contains a liquid protein source which female fruit flies are attracted to. The flies enter the trap and get stuck in the liquid where they eventually drown. Products like CeraTrap fulfill this need, though there are also alternative like BioTrap with Fruit Fly Attractant Gel. You can also make a liquid protein trap cheaply at home using an old soft drink bottle and the following directions from the Department of Agriculture and Food Western Australia. While the directions are focussed on Mediterranean fruit fly they are also relevant to other fruit fly species.Home made fruit fly trap (agric.wa.gov.au)
Protein bait sprays need to reapplied weekly and liquid protein traps refreshed with new liquid every week or whenever they dry out.
3. Remove fallen or rotting fruit
Fallen and damaged fruits provide a refuge for developing fruit fly maggots. Remove this risk by picking up all fallen fruit and any damaged fruit from the tree and dispose of them properly. The best option is to place them in a black plastic bag and leave them in the sun for a week to “cook”. This is vital if you have seen fruit fly maggots or have experienced problems with fruit flies in the past. You should do the same with any fruit you harvest that you find maggots in.
An alternative for small quantifies of fruit is to microwave it. Just placing fruit into the compost bin is not enough. The temperature in most compost bins is not enough to kill fruit flies.
For more information on specific fruit fly control strategies see:Control strategies for home gardeners