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Biological control of fruitspotting bug?

The text below is now somewhat out of date. We have progressed a lot since starting this work. To see the latest developments go to:

www.bioresources.com.au/anastatus

We at BioResources are often asked: What are the prospects for the biological control of fruitspotting bug, Amblypelta spp. (FSB)? Unfortunately there is no simple answer. Researchers at the Centre for Tropical Horticulture (CTH) in Alstonville have been investigating this perplexing subject for several years and have narrowed it down to several possiblities but unfortunately there is nothing yet that is a standout candidate.

Control of FSB to low levels and to a point where spraying is not required is very difficult and will involve the utilisation of a range of tactics. Whole farm spraying would need to be a last resort in such a system as broad spectrum sprays would potentially set back any natural enemies mass released and those already in the crop.

The options

We at BioResources are planning to collaborate in evaluating the options for biological control that are being investigated at CTH as part of a funded macadamia project. They include egg parasitoids and nymph/adult parasitoids.

There are question marks against all these options. Some relate to their in-field suitability for FSB and some relate to mass rearing issues and commercial viability.

The egg parasitoids need to be mass-reared on either FSB eggs (very difficult) or GVB eggs (difficult). These hosts are hard to rear efficiently and in high numbers so the cost of the end product would have to be much higher per individual than Trichogramma!

An area wide management program of FSB would be desirable. What we envisage (assuming we are able to mass rear a good parasitoid) are releases into areas where FSB are breeding - hot spots in the crop, along crop boundaries and alternative hosts nearby and purpose-grown trap crops which are being investigated at CTH.

FSB is a challenging pest - they are long-lived, very mobile (adults) and nymphs and adults are damaging at very low population densities, and at this stage we don’t know the level of impact of releases of egg parasitoids on FSB populations. Moderate levels of egg parasitism in breeding areas in spring may have a significant impact on the subsequent generations and their dispersal but we dont know whether this is achievable.

We are likely to have to use a combination of management tools (e.g. trap crops, varieties, biological control etc) to pull FSB numbers back enough to tip the balance in favour of a "minimum spray "(e.g. restricting spraying, one spray or spot spraying).

The above approaches need to be refined and tested. FSB breeding site maps could be developed with the help of growers and crop consultants.

Commercial mass-rearing of FSB natural enemies?

We at BioResources are interested in these possibilities - there is an obvious fit with MacTrix that has perhaps been more successful than originally expected. But these things take quite a while to work out and then test in the field. Nevertheless, we need to give it a go and the sooner we start the sooner we can either come up with something useful or else find out that this particular avenue is not going to make a useful contribution and/or be too difficult to commercialise.

Success in producing a useful biocontrol agent for FSB would be a significant advance for a number of horticultural industries and their growers affected by this pest. If this process was less than successful than we would like we would still learn a lot about managing FSB.

BioResources will be part of a HAL Research Funding Proposal to investigate "Biological Control Tactics for Fruitspotting Bugs". If accepted, this proposal would not start until July 2011. The details of the proposal will be developed over the next months.

BioResources would be involved in the development of a commercial mass-rearing systems for the short listed biocontrol agent(s) and in return provide significant quantities of biocontrol agents for large field trials in the various districts.

In the short term

Now that the MacTrix season is nearing an end and we are not so preoccupied we have started a small culture of FSB and hopefully with GVB and parasitoids to follow. This will enable us get a feel for how a larger scale system might work as well as to compliment the cultures at CTH Alstonville to produce material for small-scale collections and releases.

This would be a start before moving to the next phases – increasing culture sizes to enable field trials and then if the results are positive developing commercial scale mass-rearing systems and release programs.

Meanwhile, what about the other natural enemies of FSB?

There are a number of other natural enemies of FSB already in your crops - you have no doubt noticed some of these in your crops but it is hard to determine their respective contributions. Sometimes biological control works at a level hidden from casual or even close attention.

This is demonstrated when a secondary pest flairs after the application of a broad spectrum insecticide - we may not have noticed the natural enemies suppressing the secondary pest before the spray.

Natural enemies of FSB include ants (found in good numbers in macadamia farms), spiders (a significant predator in avocadoes), lacewings (late instar Green Lacewings have been observed predating on FSB nymphs), birds, micro bats while predatory bugs such as Assassin Bugs and Predatory Shield Bugs are likely to feed on FSB nymphs. Go to "other natural enemies" for more info.

Other tactics

Other tactics being investigated by DPI’s are pheromone lures and traps, canopy management, decoy crops, improving FSB monitoring especially in later developed nuts. Alternatives for Endosufan are being trialled at the Alstonville Research Station.

There is also scope to make the crop environment more favourable to natural enemies by providing habitat and alternative food sources to lure them into and keep them in the plantations.

Bugs wanted ALIVE

If you come across a concentration of FSB or GVB please let us know.

We have also found FSB on mulberries - both the white and black varieties.

We’ll let you know how we go with our part of the FSB project.

VC HAL Project Update

In order to get the ball rolling BioResources has lodged an application for a VC project with HAL with approvals to be notified in late April.

With short notice $10,000 was raised from about 50 growers and BioResources will contribute about $28,000.

Many thanks to all those that have pledged to make a contribution. It is very encouraging for us that there is so much interest in this project.

We'll keep you posted on the process.

In the meantime, we have started a FSB culture and Assassin bug with most of the bugs collected from our mulberry tree in the back yard (semi rural north-west of Brisbane).

Not only that, but we have collected our first egg parasitoids also from the backyard! Its an Anastatus species. Looks a bit like an ant when it moves over the leaves. Wings not prominent to naked eye. See pic to right.

For more on the biocontrol of FSB go to our web site at:

www.bioresources.com.au/FSBbiocontrol

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FSB eggs - 1 day old -
about 1 mm in diameter

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Assassin bug nymph attacking FSB nymph

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Hatched FSB egg

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FSB egg - 6 days old

FSB eggs - 4 days old

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FSB nymph - about 2 weeks old

FSB adult

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White spider - Thomisus species attacking
and killing BSB nymph in mulberry

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Anastatus egg parasitoid laying its egg into a FSB egg.