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Monitoring for egg parasitism

We suggest you employ a crop consultant to check for nutborer and other pests and for Trichogramma activity. Nevertheless, some smaller growers do it themselves. You may be able to get a consultant to give some hands-on instruction to get you going. It takes practice to do monitoring accurately and efficiently but it can save a lot of time and money in the long run.

See "Mac Pest Consultants" for a list of macadamia pest consultants in your area.

Monitoring procedures

Monitoring procedures for a range of pests are described in the "Macadamia grower's handbook" and see also the "Macadamia problem solver & bug identifier" both published by QDPI.

Typically, sampling for nutborer, is done by removing 100 to 320 nuts from trees (e.g. 10 nuts from 32 trees) and examining them for MNB eggs. Any eggs found are recorded and scored either: fresh, red, hatched, black or black with escape holes.

Nuts are also checked for damage, and any larvae and their size is recorded. This sampling is done fortnightly and weekly during pressure periods and gives a very good picture of what is going on, especially combined with results from previous weeks.

Spray decisions should not be made on egg and larvae pressure alone. Once parasitism builds up most of the "not black" eggs you find will actually be parasitised and spraying may not be necessary.

Ways of managing nutborer

The way the farm has decided to manage nutborer and MacTrix will have a bearing on the level of monitoring and decision making based on that monitoring.

For instance, a small farm may have decided that they will not spray for nutborer. In this case monitoring is not so important.

On the other hand, large farms may see the merit of a good monitoring regime and the savings in spraying that this is likely to bring. In such a case monitoring for parasitism and growing out "not black" eggs will be beneficial and potentially saving a lot of money and time spraying.

And again, another farm may decide to adopt a regular or strategically timed spray regime (either with Bulldock® and/or Mimic®) while still releasing MacTrix which will provide a "buffer" in the system and late season (post shell hardening) control.

So we suggest consultants and growers discuss the type of management they wish to adopt before the season gets going.

Monitoring for parasitism

There is a relationship between the number of black eggs found in the field and the rate of actual parasitism for a given egg pressure.

As a rule of thumb, once black eggs constitute over 40% of the total number of viable eggs, you can assume that a high percentage of the "not black" eggs are parasitised (unless the egg pressure is very high).

For a more accurate estimate of parasitism, especially when nutborer are just starting to show up, we recommend that nuts with viable, "not black" eggs are retained and examined a few days later to see if they yield larvae or go black. Don't just throw them away.

For example, if monitoring on Tuesday reveals low larvae numbers then wait until you have had a look at any retained eggs on Friday to see if they are parasitised before making a spray decision.

For instance, you may find 8 eggs all up, 3 may be already black and 5 not black. Keeping these 5 not black eggs for 3 more days is likely to reveal that 4 are already parasitised with only 1 of the 8 producing a larva.

Nuts with eggs on them can be placed in an egg carton to stop them rolling around and damaging the eggs. The carton can be placed in an esky in the ute until you get a chance to put them in a warm humid place and inside a plastic container to stop the nuts drying out and husks cracking but with a little ventillation to stop them going mouldy.

Further, how fresh the eggs are when the nuts were removed from the field will also influence your estimate of parasitism. Freshly laid eggs may be parasitised if left in the field for another day.

If you have a high level of parasitism in freshly laid eggs then this is a very good sign as there are high numbers of wasps in relation to fresh eggs. In this case, egg pressure could increase considerably and percent parasitism is likely to remain high.

See also "Environment" for factors influencing parasitism rates.

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A10 x hand lens is essential for monitoring
(Available from Bugs for Bugs, Mundubbera
Ph 07 4165 4663

Nutborer eggs - about 1 mm in diameter

Pink nutborer eggs - 2-3 days old

Red nutborer eggs - 4-5 days old

Nutborer larva head capsule in egg - 4 to 5 days old

Wasp escape holes - Wasps emerge about 9 to 10 days after eggs are parasitised

Parasitised egg just before wasp emergence

Clear empty shell of nutboreregg after larva has hatched.

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Nuts found with eggs on them can be placed in an egg carton to stop them rolling around and kept for a few days to see if larvae hatch or if the eggs go black indicating that they are parasitised.

Keep them in a warm humid place and out of the sun.

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For a closer look at parasitsed and un parasitised eggs as they develop click the image.