How to Make a Queensland Fruit Fly Trap and Bait

Angelo (admin)

2 years ago

One of the most damaging pests of fruit and vegetables in Australia is the Queensland fruit fly or Qfly (Bactrocera tryoni). To control this pest, you can make your own home made traps using empty clear plastic bottles, and also make the homemade bait lure liquid to put into them, as described in this article.

Queensland Fruit Fly Trap Construction

To construct this trap you will need:

An empty, clear plastic water or soft-drink bottle with a lid
Real 100% fruit juice (1 cup)
Cloudy ammonia or wheelie bin cleaner (1 tablespoon)
A short length of stiff (2mm thick) wire (25-30cm) or a length of string

The diagram below shows the construction steps, with the explanation following.

Remove the label from the clear plastic bottle first, as it may deter the flies, they are repelled by white objects!
Mark the positions of five holes near the ‘shoulders’ of the bottle, 10cm from the top, but on the front half of the bottle only.

To do this, mark the first two hole positions on opposite sides of the bottle, then mark the remaining three between them. Use a permanent marker, felt-tip marker, wax pencil or anything else that will write on the plastic.

Note – There are no holes in the back half of the bottle to allow us to pour the liquid out of the bottle!
Drill, punch or burn the five holes at their marked positions, they should be 6-8mm in size.
To be able to hang up the trap, attach a length of string around the neck of the bottle, or make a wire hanging loop by piercing the lid and pushing a short length of stiff 2mm wire through it. Bend a small loop at the lower end to prevent the wire slipping out, and make a larger hook at the top to allow easy hanging.
To make the bait lure mixture in the bottle, pour in 1 cup of 100% fruit juice (which includes the pulp) and 1 tablespoon of cloudy ammonia (or wheelie bin cleaner). This should fill the bottle so it is around 1/3 full.
Hang the trap from a tree branch using the string or wire loop, and attach it 1m to 1.5m above the ground, on a shaded branch on the eastern side of the tree that receives morning sun only.

The bait lure mixture can last up to 3 weeks, but should be changed weekly for best results.

There’s no need to use fresh fruit juice. Spoiled fruit juice that has begun to ferment can be used in this trap along with the cloudy ammonia. If it’s available for free from a shop, grocery or supermarket, that would be great way to reuse food (drink) waste.

How Many Queensland Fruit Fly Traps Does My Garden Need?

The commercial Queensland fruit fly traps, which work exactly the same way, are set up with 1 trap per tree or 1 trap every 20m² when trees are touching. With one trap every 20 square metres, three or four traps would adequately cover a 60-80m² garden planted up with fruit trees.

When to Install Queensland Fruit Fly Traps

Place the trap in the garden spring, before fruit flies start attacking the fruit, when the fruit are small and still developing. Ideally, hang the traps when fruit reaches approximately one third its final size.

To reduce pest numbers, it is essential to install the traps at least 45 days prior to fruit ripening.

How the Queensland Fruit Fly Trap Works

The trap exploit the pest’s requirement for sugars and protein, and will capture both male and female Queensland fruit fly.

Fruit juices naturally contain sugars, and we use a fruit juice with the pulp for the protein component. The instructions specify 100% fruit juice for this reason. The term ‘fruit juice drink’ on labels describes a product that has a very small amount of fruit juice in it, no pulp[, with sugar and artificial flavour added – which is useless for this type of trap and bad for your body, so don’t use it.

The cloudy ammonia is added because it releases an ammonia smell, which the pest associates with rotting fruit, making the bait more attractive to them.

In the trap design, I’ve used 6-8mm holes for a specific reason. The documentation from the government agriculture departments suggests cutting three holes about the size of a 10-cent piece, 10cm from the top, but warns that the traps may attract and catch beneficial insects also.

The large holes are meant to allow the scent of the bait to drift out easily, but they create a problem. They allow larger insects to enter, including larger beneficial insects, or they may just fill up with nasty European wasps.

Since the Queensland fruit fly (QFF) is approximately 6-8mm long, and much narrower than that, it doesn’t need a huge opening, and a hole around 6-8 mm wide is sufficient to allow it to enter the trap, but keep larger insects out.