Pests

Fruit flies a major problem that can be managed

Details: By AgNova Technologies

Effective field pest management only can be achieved when strategies are based on an understanding of fruit fly field biology (ecology).

Fruit fly biology
In Australia, over six decades of ecological research has provided an excellent foundation for control strategies that can be applied in most production systems.
Some of the key ecological features of major pest species such as Queensland fruit fly are:

Tropical fruit flies such as Queensland fruit fly originated in tropical and subtropical regions, so there are more species and larger populations in subtropical and tropical Australia.
The Queensland fruit fly has a high reproductive rate, building into large populations in short periods of time. This is because it has a short life cycle of about one month in optimum climatic conditions, uses a wide range of host plants for breeding and the females produce a large numbers of eggs.
Cities and towns have the largest populations because breeding takes place in many host plants in backyards, parks and forests.
The adult flies are extremely mobile. Our mark-recapture studies with Queensland fruit fly show that adults can disperse from 20 to 90 km.
Host plants are vital to the survival of the fly population. When fruit begins to ripen, flies are attracted in large numbers whereby the immature flies feed on surface nutrients to develop eggs. Mature egg laying flies also arrive in the tree and begin laying eggs into fruit as they do not need to feed on protein at that stage.

Field control strategies
Here is a summary of the potential pest management options for fruit flies:
Insecticide cover sprays – We now have limited options. The value of the systemic insecticides that have been withdrawn from use is that they attacked the egg laying females and the eggs deposited in fruit. Attacking this stage of the life cycle is the most important strategy we can develop. Currently available cover sprays can reduce the resident fly population in an orchard but cannot fully protect the fruit from damage caused by the mature egg laying females that fly in.
Physical control – Fruit bagging and exclusion netting. This is a good strategy for backyard growers but is impractical and too expensive for commercial producers.
Cultural control – Crop hygiene and early harvesting. In some areas of south-eastern Australia, cleaning up infested fruit and destroying it would be beneficial but will not cause a major reduction in fly populations unless it is carried out over large areas, and in cities and towns. For most of eastern and northern Australia, crop hygiene is not economically and biologically beneficial.
Biological control – Fruit flies have a wide range of parasites and predators, particularly in their native rainforest environment. Some of these have been researched for over 60 years and proven not to be useful for commercial levels of pest management.
Behavioural control - Strategies that use the biology of the fly.
Visual responses – Different pest species are attracted to different colours by responding to UV radiation of different wavelengths reflecting off the surfaces. Coloured traps can play a role in fruit fly management but must be designed for the target species.
Protein baits – These are food baits that meet the need of immature female flies to ingest protein for development to sexual maturity. They were first developed in the early 1950s as acid hydrolysates. Although effective, they were extremely phytotoxic due to a high salt content and level of acidity. In the past three decades in Australia, yeast autolysates have been produced. There are a number of these baits on the market which are used in fruit fly control programs. However, it is important to realise that protein bait sprays need to be applied correctly for achieving maximum efficacy, and that they only attract and kill immature flies. Because mature egg laying female flies are not responsive to protein, a high failure rate can be experienced, particularly in highly susceptible crops where there are large fruit fly populations.
Male lures – Queensland fruit fly males are attracted to Cue Lure, which was discovered by an industrial chemist in the early 1960s. Suppressing male fly populations using this method is an important strategy, but the application methodology is important. Because these flies are highly mobile and disperse across large distances, Cue Lure baits must be distributed in a high density per hectare and over very large areas.
Female lures – To date, the only female lures available are protein based, either as bait sprays or in traps. As discussed above, it is important to realise that protein targets immature flies, not the mature egg laying females that do the damage.
Conclusion
While there are strategies available to manage the fruit fly problem, there must be the industry and political will to develop and apply a new IPM program. In particular, we urgently need a new technique that targets that part of the life cycle that was hit by systemic insecticides, the mature egg laying females and their eggs.
AgNova Technologies has been supporting and collaborating with researchers at Griffith University for the past five years to achieve this goal.

Article written by Emeritus Professor Dick Drew who has spent more than 40 years involved in fruit fly research and is currently investigating the use of attractant baits for field control of fruit fly to reduce pesticide levels in food crops and the environment.