Apart from a couple of months in the middle of winter we have a very humid climate which is ideal for the Queensland fruit fly (Bactrocera tryoni) which is a native pest throughout eastern Australia.
The adult is wasp-like, red-brown with yellow marks, and about 8 mm long. The female stings the maturing fruit and lays its eggs just below the surface. Hatching takes place after two to three days and the then tunnel in the flesh. They carry bacteria that aid in fruit breakdown.
Larvae mature in seven to ten days in summer and emerge from the fruit to pupate in the soil. The pupa stage lasts about 10 days. The life cycle takes about 2.5 weeks during summer.
Affected fruit are readily recognised since rots develop rapidly and the skin around the sting marks becomes discoloured. Queensland fruit fly damage is more severe during mid and late summer than at other times. Large numbers of flies can be expected after good falls of summer rain; fruit flies become active after periods of rain or high humidity.
In an organic garden there are not many ways to control fruit fly; of course physical barriers such as mesh and cloth bags placed over the fruit will keep it safe however this is not practical when you have a number of crops to protect. I have been using Eco Naturelure which is an attractant containing Spinosad. I have painted a number of boards yellow and paint the Naturelure on these boards and hang them on various trees. I do not spray the plants directly.
The major problem with this is that the boards are washed clean in the rain and of course we seem to be getting rain nearly every second day! So it is a constant task to reapply the Naturelure solution after each day of rain.
You should always remove fallen or damaged fruit as soon as you can to avoid these being used to breed the next generation of fruit fly.
I am a member of the Brisbane Organic Gardening Inc and the following article was published in our newsletter with a recipe that I am told works.
Last weekend I made up a batch and have placed around my garden, it is too early to say whether it has worked for me but speaking to people at our last meeting it seems it has worked well for most.