Left: Bug egg showing dark spot where Anastatus has pierced the egg shell with its ovipositor.

 

Send comments and bug observations to:
Richard Llewellyn
richard@bioresources.com.au

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Above: Parasitised bug eggs found on murraya inside a macadamia plantation at Bundaberg in mid June. So Anastatus adults are active in cooler weather.

So where to from here?


About a year ago I thought it would take at least a year before we would get any idea if Anastatus was able to make a useful contribution to bug numbers. In that time we have focussed on getting good numbers of wasps out onto lots of different farms using a “best bet” approach in order to see what happens as there is no other way to test it out.


We have had promising results at a good number of sites and we may also get season to season impact as overwintering bugs are likely to be reduced if there has been good Anastatus activity in late Autumn. We need to give it another two seasons before we can be really sure about whats going on.


Still with these good results under our belt we will move onto further developing the mass rearing and field release systems. We want to improve the consistency of parasitism rates on cards and maybe even despatch adult wasps during the cooler months. The development of the wasps inside the eggs is very slow when the temperature is below 20 deg C while the adults are okay at this temperature and in the sun it may be 5+ degrees higher. But this will take some time to figure out.


We also want to try and get a better handle on identifying the type of site where Anastatus will work best. The required release rates will vary and some sites may need more time than others. We need to consider size and position of bug breeding area/s in relation to the size of the crop.


There is a wide spectrum of situations. From a

small bug breeding area within a large crop up to a

large bug breeding area surrounding a small crop.

In the former, once bug numbers are reduced it is likely that the bugs will be slower to recolonise that area while in the later bug breeding area the bugs may be continually moving in. We don't know what the dynamic will be in such a case.


At some sites its likely that the adult bugs seen in the crop are a spill over from the forest while most of the bugs remain in the forest. A reduction in bugs numbers on the periphery of the forest could result in a disproportionally large reduction of bugs in the crop.


Anastatus behaviour

There are also lots of questions we have about the biology and behaviour of Anastatus wasps as well as FSB.


The good results so far indicate that the Anastatus have moved off into areas around the crops where bugs are breeding and laying eggs. To investigate how they do this we can study the scent preferences of Anastatus using an olfactometer.


Alana Danne at UQ has started this work. Various sources of scent (bugs, eggs, honey, damaged fruit etc) are placed in various combinations in the branches of the Y-tube while a constant flow of filtered air is sucked through the tubes. Wasps are released into the tube and their movement towards one or other scent is measured. This way its possible to get an indication of which combinations of scents most attract the parasitoids.




Anastatus is a very important parasitoid in China and a lot more research has been done on their local species. One study describes how the antennae of the wasps are finely tuned to detecting various types of cues and is asymmetrical to aid in determining direction and orientation. The various functions of different parts of the antenna enable the wasps to gradually find the host habitat, then the host plant, and finally search locally for the host. The interaction of right and left antennae enhances the searching ability as well as being vigilant for predators.


Asymmetrical Distribution of Antennal Sensilla in the Female Anastatus japonicus ZHAO JUN MENG et al. 2012


 
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