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Richard Llewellyn

Top left: Two of the three wasps sitting on bug eggs.

Top: Bug nymph on pittosporum fruit at Duck Creek, Alstonville

Further, with MacTrix good levels of parasitism late in the season have reduced nutborer overwintering so that nutborer is now not the serious pest it was 10 years ago.

This also happens with Trichogramma releases in sweet corn which start early with the aim to get parasitised eggs on all the plants in the crop before the vulnerable silking stage so that emerging wasps don’t have to go far to find more eggs. Once at this stage, parasitism rates are likely to be very high even under heavy pressure from heliothis.

Likewise, releases of persimilis predatory mites feeding for TSM in strawberries. Initially, the predators are spread at points throughout the crop from where they disperse in search of infected plants where they then multiply quickly and reduce mite numbers.

With the regular Anastatus releases we are trying to increase the likelihood of the wasps getting to a bug breeding area while the bugs are laying plenty of eggs. Better still, if they get there early then progeny from those eggs may not have to move to another site to find more eggs - they may already be in the bug breeding area.

Bugs will feed on many species of plants but the number that are suitable for getting bugs through to adulthood are much fewer. I suspect that even where wasps releases are not made, most eggs laid by bugs never develop through to adulthood. Some eggs may be parasitised while the food for nymphs may not be good enough or else they have been picked off by predators like spiders, ants or predaceous bugs. This would mean that there are many more bug eggs out there than adult bugs.

Bugs eggs are fairly tough and it seems there are not too many predators that eat them. However, this may favour egg parasitoids as it may help get them to adulthood inside the bug eggs.

Putting all these things together, with mass releases of Anastatus, the egg parasitoids could get the upper hand and reduce bug numbers significantly. This maybe how it is happening at our promising sites.

Bug plant hosts at present

We are about an hour north of Brisbane and around here there are wild guavas fruiting, blue quandongs flowering, murraya flowering and fruiting. Harpulia are about to flower. Citrus fruiting. All good FSB foods.

Go to the bug host list

More on bug and wasp behaviour

As mentioned in previous blogs we seem to be making headway at a number of sites. So what would be the mechanisms or behaviour that would enable the Anastatus to reduce bug numbers?

Host insects need to evolve ways of keeping ahead of their predators or parasitoids. If they hadn’t done so they would have become extinct long ago. FSB feed in an area for a while if the food is good then move on to another patch.

This may help keep them ahead of the parasitoids. Anastatus for instance has a development time of around 3-4 weeks. So if a wasp finds a bug breeding area and parasitises some eggs, by the time the progeny emerge the bugs may have moved on and the wasps will have to track them down again.

If wasps arrive at a new bug feeding and breeding site early they are more likely to be emerging from parasitised eggs before the bugs have moved on to a new food source. This would compound their impact on the bug population.

This process happens with lots of beneficial insects  both natural occurring and when mass released. With Trichogramma for nutborer, “MacTrix”, for instance, release points may be 20 per hectare. Wasps disperse from these points and initially egg parasitism is typically highest close to these release points. Progeny from these eggs will be more dispersed. This process continues over a number of generations (just 9 days per generation) until eventually emerging wasps are more evenly distributed through the crop and present on many parts of each tree in the plantation and well located for an increase in nutborer egg lay.

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