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Spotting Bugs In Macadamias

Article by: Kevin Quinlan, Supply Chain Manager – NIS, MPC, Craig Maddox I&I NSW, Centre for Tropical Horticulture.
Ruth Huwer I&I NSW, Centre for Tropical Horticulture.

This article provides a brief overview of the management of spotting bugs (Amblypelta spp.) in macadamias, including the identification of the pest, the types of damage caused and the control strategies used.

Key points are:

  • adult spotting bugs can feed on fully mature nuts, as they secrete enzymes when feeding that allows them to penetrate the shell;
  • late season damage often does not show up on macadamia shell, but the kernel has been damaged. This late season damage is often called “blind stings”;
  • a good monitoring program is critical allowing you to determine when there is activity occurring in your orchard and apply control strategies as needed;
  • spotting bugs will continue to feed in an orchard until there isn’t any food available or a more appealing food source emerges;
  • you only need small numbers of spotting bugs to have significant amounts of damage;
  • the aim of a spotting bug management program is to reduce the population early in the season, so numbers do not build later in the season.

Introduction

Spotting Bug is the general name used to describe the fruit-spotting bug (Amblypelta nitida) and the banana-spotting bug (A. lutescens lutescens). Both of these insects attack a wide variety of horticultural crops, including avocado, custard apples, lychee, mango, passionfruit and pecans, as well as many native and ornamental fruit and nuts. Spotting bugs are not the only bug species that attack macadamia but they are the most perennial problem in all growing areas.

Spotting Bug feeding on Murraya paniculata berries NSW (courtesy I&I NSW)

Spotting Bug feeding on Murraya paniculata berries NSW (courtesy I&I NSW)

What do they look like?

Adult spotting bugs are yellow-green-brown in colour and about 15mm long. There are 5 nymph stages (called instars), with the early stages being ant-like, orange-brown in colour and with prominent antennae. Later stages are greener in colour and have wing buds. A distinctive feature of the nymphs is that the second last joint of the antenna is black and flattened. It is rare to see spotting bugs in trees, as both adults and nymphs are very alert and if they fear being seen they will hide behind fruit or leaves. They also have the ability to drop down to the ground quickly to avoid being found.

Life cycle stages of fruit spotting bug nymphs and adults. From Macadamia problem solver and bug identifier © The State of Queensland, (2003)

Life cycle stages of fruit spotting bug nymphs and adults. From Macadamia problem solver and bug identifier © The State of Queensland, (2003)

banana-spotting-bug-nymph

Banana spotting bug nymph. From Macadamia problem solver and bug identifier © The State of Queensland, (2003)

When are they present?

Most damage to macadamias occurs between September and February, with some of the thinner shelled and later varieties being attacked all year if spotting bug is left unmanaged. Spotting bugs are able to penetrate fully hardened shells due to the long stylet (microfine syringe like feeding tube) and powerful enzymes they release while feeding. This late damage can show up as a ‘blind sting’, as you can not see the damage on the outside of the shell but the kernel is damaged. Blind stings are difficult for growers and processors to detect until after the shell is cracked.

Research by Industry and Investment NSW (I&I NSW) at the Centre for Tropical Horticulture (CTH) Alstonville, over several seasons and on several crops, has been able to link chemicals in flowers with movement of female fruit spotting bugs. These chemicals are known as “semio-chemicals or karimones” and they signal to the adult bug populations that the macadamias are about to develop nutlets. This is very important as the semio-chemcials allow the spotting bugs to know that if they now enter a macadamia orchard and lay eggs, food for their developing nymphs will be plentiful.

Eggs have been collected in spring from the flowers of many crops, including mango, lychee, and avocado but none more than macadamia.As very few eggs are laid, a small number of spotting bugs can do considerable damage. This makes an effective monitoring program a crucial part of spotting bug management.

Eggs of fruit spotting bug laid on early stage macadamia florets August/September 2009 at CTH Alstonville (courtesy I&I NSW)

Eggs of fruit spotting bug laid on early stage macadamia florets August/September 2009 at CTH Alstonville (courtesy I&I NSW)

Typical fruit spotting bug cycle for macadamias. Note the months indicated for a particular active can vary depending upon seasonal weather conditions and crop growth stages.

Typical fruit spotting bug cycle for macadamias. Note the months indicated for a particular active can vary depending upon seasonal weather conditions and crop growth stages.

There are two to three generations of spotting bug during the macadamia nut development. The first egg laying usually occurs in August/September and the second in October/November, with it taking approximately 42 days for a spotting bug to develop from an egg to an adult.

Once an adult, spotting bugs can live for up to six months. During the main summer period the adult bugs are far more mobile in the orchard and can invade and leave areas quickly. As a few spotting bugs can do considerable damage, this makes breaking their breeding and feeding cycles crucial.

Normally two applications of a registered insecticide 4 weeks apart during the spring build up and one just prior to Christmas removes the threat for the older Hawaiian varieties. However when poor nutset occurs in the September flowering we often get a season with summer and/or autumn flowering (like 2010) which can immediately start another cycle for the spotting bug. This virtually keeps them in the macadamia orchard all year resulting in higher damage.

Once adult spotting bugs enter your orchard (or are bred in your orchard) they will not move onto another crop until the food source dries up (i.e. nuts start to fall at harvest) or they find an alternative food source that is more attractive.
If your early season management stops the nymphs from maturing and the adults from reproducing and feeding, you will reduce the potential for late season damage, which is very difficult to see or remove from your nut in shell (NIS). Good monitoring is crucial to ensure you detect any populations of spotting bug and so apply control strategies only when necessary.

What does the damage look like?

Damage caused by fruitspotting bug depends upon the stage of development of the nuts. I&I NSW carried out a series of experiments between 1997- 2005 at CTH Alstonville, where they caged macadamia nut racemes for an entire season. Fruit spotting bugs were released into the cages at different stages of the season, to ensure nut damage.

This series of experiments showed that all early season damaged nutlets basically dropped from the raceme up to November. After this time nuts continued to be damaged but less and less fell off the tree. The visible symptoms of damage follow this same pattern, with less and less damage obvious until late in the season spotting bug damage is only visible in the kernel. There are also occasions where small nymphs feed only on the husks. The following photos show the damage caused at different stages of development.

Typical fruit spotting bug damage symptoms

All images below are form Macadamia problem solver and bug identifier© The State of Queensland, (2003)

Spots on a young nut.

Spots on a young nut.

Sectioned nut showing lesions on the inside of the husk (nut removed)

Sectioned nut showing lesions on the inside of the husk (nut removed)

Sectioned developing nut showing damage to soft shell and developing kernel

Sectioned developing nut showing damage to soft shell and developing kernel

Shell damage

Shell damage

Kernel Damage

Kernel Damage

 

Can spotting bugs feed on fully mature nuts?

Unfortunately yes. Due to the long proboscis (feeding tube) that fruit spotting bugs have and the secretions they exude from it, they can penetrate fully mature nuts. In some orchards they attack late in the season (January to early February) and damage the kernel.

Caged racemes from 344 and A16 trees with fruit spotting bug introduced for a weeks feeding during the month labeled. January feeding on both varieties left dark welts in the forming shell, March feeding still visible in the kernel but not on the shell. (courtesy I&I NSW).

Caged racemes from 344 and A16 trees with fruit spotting bug introduced for a weeks feeding during the month labeled. January feeding on both varieties left dark welts in the forming shell, March feeding still visible in the kernel but not on the shell. (courtesy I&I NSW).

The damage does not show up on the outside of the shell, but the kernel is damaged. This makes it difficult to remove these damaged nuts on a sorting table. (

Green vegetable bug (Nezara viridula) is also able to feed on mature nuts, although it will not usually breed in the crop (like fruitspotting bug). Green vegetable bug has even been found to feed on dropped nut if left unmanaged. Green vegetable bug invade from pasture legumes, soybean or passionfruit crops and also have many weed hosts (especially black berry nightshade). It is much easier to control if the weed management is good on your farm. This damage also does not show up on the outside of the shell.

Both types of bugs have the potential to make significant proportions of the crop worthless quickly, and as a result, careful monitoring is required to determine if late season bug activity is present in your orchard so that appropriate control strategies can be carried out.

Fruit spotting bug feeding directly through the shell to create a blind sting (left) (courtesy I&I NSW). and the typical blind sting damage found in macadamias (right). Note the absence of damage on the shell (courtesy MPC).

Fruit spotting bug feeding directly through the shell to create a blind sting (left) (courtesy I&I NSW). and the typical blind sting damage found in macadamias (right). Note the absence of damage on the shell (courtesy MPC).

Are there variety preferences?

Research at CTH Alstonville has found that there are varietal differences in the levels of fruit spotting bug damage found. Generally, thinner shelled varieties have been found to suffer higher levels of damage than thicker shelled varieties. This means that you’re monitoring and control strategies may need to be different for particular varieties, especially late in the season. In thin shelled varieties, if spotting bug is not controlled, crop losses over 80% per tree are not uncommon, with an average of around 30-50% being observed most years.

Monitoring and action levels

A small number of adult and nymphs can do a lot of damage. This makes monitoring and timely control strategies crucial for spotting bugs. It is best to monitor trees from all areas of the orchard, but it is important to pay particular attention to trees adjacent to bushland and ‘known hotspots’. Experienced scouts and many researchers have found that spotting bugs will infest the same areas consistently each year. Most orchards tend to have these areas, but only good spatial crop records will provide this information.

The conventional approach is to look for green fallen nuts with internal fresh damage. From December onwards it is important to collect nuts from the tree for damage, as nuts damaged from this time onwards will not be aborted.
The current protocol is as follows:,

Early in the season, sample at least 10 freshly fallen nuts from each tree (and from December onwards sample nuts from the tree). The number of trees examined will vary, but you need to ensure you sample enough trees to determine if spotting bugs are present or absent. One option is to monitor 10 trees in known hotspots and then examine trees randomly across the remainder of the block. You must ensure a minimum of 35 trees are monitored in this arrangement.

To monitor for damage, cut open the nut and separate the husk, shell and kernel. Examine each part for damage. Spotting bug damage appears as a brown lesion on the inside of the husk. There may also be crinkled areas on the developing shell or the kernel is shrunken. The following photos show some typical damage symptoms seen while monitoring.

Some typical damage symptoms seen while monitoring

Sectioned developing nut showing damage to soft shell and developing kernel

Spots on a young nut.

Sectioned nut showing lesion on inside of husk (nut removed) and Nut with glucose rich exudates on the surface that appears after fruit spotting bug feeding

Note figure above shows the glucose rich exudates which osmotically flows to the surface of the nut after the fruitspotting bug has fed on the macadamia nutlet (courtesy I&I NSW). (Other images from Macadamia problem solver and bug identifier © The State of Queensland, (2003)).

Control options

Unfortunately there aren’t any effective bio-control agents commercially available, but research work has commenced into this area. The aim of the research work is to reduce our dependence on chemical control for this pest.

Chemical Control

The currently registered chemicals for the control of fruit spotting bugs are shown in the table over (correct as of 22nd September 2010). Please note that the listing of a chemical here does not mean that MPC or I&I NSW endorses its use or recommends the product. All users of agricultural chemicals must be trained and all applications must be made in accordance with label directions.

Currently Registered chemicals for spotting bug(s) control.

Chemical

Critical use comments

Acephate (i.e. Orthene®) Broad spectrum organophosphate, should not be used at flowering. (not compatible with Trichogramma wasps (Mactrix).
Azinphos-methyl (i.e. Gusathion®) Broad spectrum organophosphate, should not be used at flowering. Best used as part of a bulldock resistance management program (not compatible with Trichogramma wasps (Mactrix).
Beta-cyfluthrin (i.e. Bulldock®) Only 2 applications per season of Bulldock should be made.
Should not be used at flowering (1 spray is compatible with Trichogramma wasp use (Mactrix).
Endosulfan (i.e. Thiodan®) The APVMA has cancelled the active constituent approvals for endosulfan effective from the 12th October 2010, but use of cancelled product containing endosulfan in accordance with label instructions is permitted until 12 October 2012.
Methidathion (i.e. Supracide®) Methidation is a broad-spectrum insecticide and should be used sparingly not compatible with Trichogramma wasps (Mactrix).
Trichlorfon (i.e. Lepidex®) Trichlorfon suffers from alkaline hydrolysis. If using this product ensure you add a buffering solution to your tank (eg LI700).

What about biological control?

There are some known predators and parasitoids of spotting bugs. Unfortunately there aren’t any effective biological control agents commercially available, but research has commenced into this area. The aim of the research is to find a way to establish both parasitoids/predators for the adult and nymphal stages and also the eggs.

A multi facetted approach to spotting bug management will be the topic of future research and a proposal is currently being developed with a number of horticultural industries. This project will look at a range of issues surrounding bio-control, including the mass rearing of a range of egg parasitoids and adult and nymph predators that are known to attack spotting bug (or potentially attack them) but haven’t been successfully reared in large numbers.

As a precursor to this project, a small Voluntary Contribution (VC) project is being undertaken by Bio-resources PTY LTD to look at mass rearing systems for fruit spotting bug. Mass rearing spotting bugs is crucial because many of the known parasitoids are spotting bug specific. To be able to rear the parasitoids in large enough numbers for release into orchards, you therefore need a good supply of spotting bugs. Spotting bug has proven difficult to rear in captivity and so this project will look to find ways to improve this situation.

Where can I access further information?

The following is a list of information sources:

Macadamia Growers Handbook

This reference book contains a large amount of information on all aspects of macadamia production. The section on spotting bugs is very useful.

Macadamia problem solver and bug identifier

This book contains high quality photos and information regarding the identification of nearly all problems encountered in a macadamia orchard.

BioResources Pty Ltd

This website provides information on the new research project investigating the feasibility of a range of parasites for fruit spotting bug. There are some excellent photos on this website. www.bioresources.com. au/FSBbiocontrol

References

Brimblecombe AR (1948) Fruitspotting Bug as a pest of macadamia or Queensland nut. Queensland agriculture Journal 67: 206-211.

Ironside DA (1981) Insect pests of Macadamia in Queensland QDPI publication 81007.

Miles PW (1987) Plant sucking bugs can remove the contents of cells without mechanical damage. Experimentia 43. 937-939.

Miles PW & Taylor (1994) Osmotic pump feeding by coreids. Entomologia experimentalis et applicata 73: 163-173.

Huwer R.K., Maddox, C.D.A. and Purdue, I.M. (2008). Workshop – Pest & Disease Management: Progressing IPM and tackling options for FSB – the next big problem Proceedings of the Australian Macadamia Society Conference 30 October – 1 November 2008.

Acknowledgements

Photographs of fruit-spotting bugs and nut damage by courtesy of Agri- Science Queensland, Dept of Employment, Economic Development and Innovation, www.dpi.gov.au (formerly DPI&F, QLD); © The State of Queensland, (2003).