Reprint from CMS 1973

Many insects attack macadamias and a number of these are capable of causing severe crop loss.

During the past decade, Macadamia nut growing in Queensland has expanded considerably. Many grafted plantings are now coming into hearing and the need for efficient pest control is assuming greater importance.

The major insect pests include Macadamia flower caterpillar, fruit spotting bug and banana spotting bug, Macadamia nut borer, Macadamia twig girdler, Macadamia leaf miner, and Macadamia felted coccid.

Other species are mentioned but are of lesser importance because they are more sporadic, or their damage is less severe or confined to young trees.

The incidence of pests varies with different districts and seasons. It is therefore important that growers learn to recognize the pests and their damage so that appropriate insecticides can be applied only as needed.

MAJOR PESTS

HABITS AND DAMAGE. The flower caterpillar is a common and widespread pest of Macadamias in Queensland extending from the border north to Cairns, it limits production by destroying flowers and, following heavy infestations, few nuts are set. In southeast Queensland, it is less severe in elevated and inland areas. Varieties, which flower early, that is, during winter months (June, July), frequently, set a crop before heavy infestations occur in August-September.

LIFE CYCLE STAGES. The adult stage of the Macadamia flower caterpillar is a small, grey moth. It lays small, white to yellowish eggs anywhere on the flower racemes. The larvae tunnel into buds and develop a striped green, brownish or grey color. A larva finally grows to 12 mm long. Larvae festoon the flowering parts around the raceme stem with webbed frass and other debris and may completely destroy the flowers, preventing nut set. Most fully-grown larvae leave the racemes to pupate in debris on the ground.

CONTROL. The Macadamia flower caterpillar can be satisfactorily controlled with sprays of trichlorphon 0.05% active constituent. Spraying should be directed particularly at racemes and must be carried out thoroughly. Correct timing of spray application is important in obtaining effective control. For this reason, the developing flower buds should be regularly examined for newly laid eggs and signs of young larval activity in the buds. Commence spraying when 50 to 80% of the racemes are found to be infested with these early stages so as to kill as many young larvae as possible.

The number of sprays needed will depend on when the infestation occurs in relation to bud development. An infestation early in the development of the buds may require two or three sprays at 10 to 14-day intervals. A later infestation may require only a single spray just before full bloom. Control is more readily achieved where all the trees flower together.

The insecticide trichlorphon is relatively non-toxic to honeybees. However, when honeybees are working the flowers, spraying should be done at a time of day when the bees are least active.

HABITS AND DAMAGE. The fruit spotting bug is more prevalent in southeast Queensland and the banana spotting bug is mainly a pest in central and northern areas. Distribution of the two species can overlap and both may occur together on Macadamias. Both bugs feed on the nuts and cause serious premature nut fall and nut malformation. Greatest crop loss occurs from September to January.

External evidence of damage to the nuts is often, though not always, discernible as dark, sunken spots on the green husk at the point of injury. Internal damage is shown when nuts are sectioned and includes breakdown of plant cells, brown calluses on the inner husk and shell and the kernel may be misshapen and translucent instead of the normal milky white color. As the nutshells harden, damage shows as separate, light brown, sunken spots on the shell with an ingrowth of husk tissue at these points. The banana-spotting bug feeds also on young shoots and causes splitting, dieback and multiple shooting.

Life cycle stages. The adult stages of both species are elongate, about 12-mm long, and light green in color. They are difficult to distinguish from each other, but the fruit spotting bug adults are usually a little darker in color than those of the banana spotting bug.

The greenish, triangular-shaped eggs of the two species are similar and are usually laid singly on nuts or foliage. The younger stages or nymphs are wingless and ant-like in appearance but more closely resemble adults as development proceeds and wing buds become visible.

The nymphs of the fruit-spotting bug are orange to greenish orange in color with black legs and antennae and two small black spots on the abdomen. Nymphs of the banana spotting bug are readily distinguished from those of the fruit spotting bug by their red legs and antennae and reddish orange abdomen; the two black spots on the abdomen are larger and more defined.

CONTROL. When either of the bugs is causing nuts to fall, control can be achieved with a spray of trichlorphon or endosulfan 0.05% active constituent. Usually two thorough applications about 3 weeks apart in November or December will be sufficient to control fruit spotting bug, but whether this is also adequate for the banana spotting bug has still to be determined. Additional sprays may be necessary if reinfestation occurs or if foliage damage is severe.

HABITS AND DAMAGE. Macadamia nut borer occurs widely throughout coastal Queensland, but is not a serious pest in elevated areas of the southeastern part of the State. It is the larva of a reddish brown moth, which lays its eggs on the nuts. The larva tunnels into the husk or kernel and develops into a light pinkish grub with dark spots that grows to 17 mm long. Pupation occurs within the damaged nut or husk and the moth emerges leaving the pupal case protruding from the cocoon. Spread of the insect is slow and new plantings, especially if isolated, can be relatively free of damage for a long time.

Larvae can be found in nuts all the year round, but most severe infestations take place from December to April. Crop loss is caused by direct feeding in the kernel and subsequent invasion by secondary organisms, and by premature nut fall.

As the nuts mature, the shells become hard and resist entry by the larvae. Feeding is then confined to the husk, and kernel loss is reduced. Among varieties with thin shells or with an open micropyle, kernel damage is greater than in those with shells of even medium thickness and with a closed micropyle. Selecting varieties, which mature early, can therefore reduce crop loss and with nuts having shells of even medium thickness and closed micropyle.

Control. Sprays of carbaryl 0.1% at intervals of 2 to 3 weeks have been found to give economical control of nut borer. If severe infestations are indicated, four applications or more may be required, usually between late November and January. Effective control during this period can be most difficult if prolonged wet season rains occur.

HABITS AND DAMAGE. The twig girdler is the larva of a satiny white moth. The insect so named because of its habit of girdling or ringbarking twigs, also destroys foliage and tunnels into nuts. Damage is most severe in young trees and in southeastern Queensland. The heaviest infestations are found in elevated areas such as the Blackall Range.

The larva, which grows to 20 mm in length, is mottled brown with black spots and a dark brown head. It draws leaves together into webbed and frass-cluttered shelters and numerous larvae of different sizes can be found in one cluster of damaged leaves. The development of the insect from egg to adult bred on foliage takes from 3 to 5 months in summer.

Control. The twig girdler is usually controlled in the course of spraying for other pests, but specific control of this pest can be necessary particularly on young trees. Carbaryl 0.1% spray, thoroughly applied, will give control. Two sprays a year, one in spring and one in autumn, may be needed.

HABITS AND DAMAGE. The adult of the leaf miner is a tiny moth with brown and white, barred wings. The minute, transparent glistening eggs are laid on the surfaces of young leaves. The larvae mine under the leaf cuticle and, when fully grown, are distinguished by transverse red stripes on the body. Mature larvae move out of the leaves to pupate in debris on the ground.

Only flush or new growth is attacked. The narrow, meandering mines are the first easily recognized signs of activity. These are quickly extended to blisters, which may destroy the whole leaf. Continuing heavy infestations may repeatedly destroy flushes of young growth, giving the tree a ragged and scorched appearance. Leaf miner is most severe in elevated areas as on the Blackall Range, and is most active in sheltered situations.

Damage is more severe on young trees. This is particularly so if heavy pruning is carried out in tree training operations. The aim of this pruning is to produce a tree with a single leader and suitably placed laterals with wide-angle crotches. No assessment has been made on the effect of the pest on hearing trees but repeated attacks retard growth and probably depress yields.

CONTROL. Leaf miner can be controlled with sprays of azinphos-ethyl 0 025% active constituent. A higher concentration of 0.05% active constituent may be necessary if a heavy infestation is involved. During peak summer activity, repeated spray applications may be needed every 2 or 3 weeks. Young growth must be wet thoroughly. It is important that growers, in areas subject to leaf miner, make regular inspections of new growth on young trees for leaf miner activity. This enables timely spraying to be carried out and destruction of new growth avoided.

HABITS AND DAMAGE. The Macadamia felted coccid occurs widely on cultivated Macadamias in southeastern Queensland and has also been recorded from naturally growing macadamias in the Maryborough district.

The adult female of this scale insect is about 1 mm long and is enclosed in a white to yellowish felted sac. The winged adult male emerges from a smaller white, elongate, rigid felted covering.

Infestations are usually first noticed by the severe twisting and distortion of young shoots or flower racemes. Infested parts are stunted and often die. On older foliage, chlorotic spots appear at feeding points. Severe infestations can cause dieback on older trees and death of young nursery trees. Although the effect of the insect on nut yields has not been investigated, it is apparent that considerable yield reductions can occur as a result of destruction of racemes and young nuts.

CONTROL. As part of a control program, careful attention should be given to the means of preventing the spread of the Macadamia felted coccid. Scion wood and young trees to be transferred to the field should be carefully inspected.

If heavy infestations build up on nursery trees, the trees should be disposed of by burning. The remainder of the nursery should be sprayed with white oil or superior oil at strength of 1 part of oil in 100 parts of water. Effective control depends on thorough coverage. When spraying, it is important to obtain thorough wetting of all plant material.

Some young stages concealed under scale clusters or in leaf folds may survive one spraying. For this reason two follow up treatments at intervals of 3 to 4 weeks should be made to kill any survivors. Nurserymen and farmers need to be constantly on the watch to prevent the spread of this pest on young trees.

When it is necessary to use scion wood from an infested source, the scion wood should be dipped in 1 part of oil in 100 parts of water and allowed to dry in the shade before grafting. Follow up sprays after the grafts have taken is advisable to ensure eradication of any surviving coccid.

Field treatment has not been fully investigated but, if the need arises, an oil spray of 1 part of oil in 100 parts of water applied to wet the tree thoroughly will reduce damage. This spray can be applied at flowering in combination with the Macadamia flower caterpillar spray.

The larvae of a number of lycaenid butterflies attack the buds of Macadamia racemes. One of the most common of these is a light green to pinkish colored slug-like larva of the hairy line blue butterfly. The spherical, slightly flattened, finely sculptured white eggs are laid anywhere on the raceme. On hatching, the larva moves from bud to bud and eats out the floral parts leaving a neat round hole in the bulbous end of each bud. The larva is difficult to find because it is similar in color to the raceme on which it is feeding. This pest can at times be severe enough to warrant insecticidal control on autumn and early winter flowers.

The Macadamia lace bug is a tiny, elongate sucking insect. The adult stage is light to dark brown in color. Younger stages or nymphs are oval in shape and vary in color from light yellowish to pink. Colonies of nymphs and adults feed on racemes and progressively kill all the buds or flowers present. The most severe infestations occur on the Blackall Range, particularly in closely planted stands of Macadamias. Young shoots are also destroyed.

Control of the lycaenid larvae and Macadamia lace bug has not been investigated but trichlorphon 0.05% sprays should be satisfactory.

Black citrus aphids sometimes cause severe damage to developing racemes. However, natural enemies usually control infestations.

Red shouldered leaf beetle may attack flowers, young nuts and young foliage. Infestations are usually sporadic and patchy and may occur in winter, spring or summer. The beetles are about 6 mm long and 3-mm wide, light yellow with a light, cherry-colored band across the wing covers and a pair of similarly colored spots on the back towards the end of the body. Beetles are often attracted to the flowers during full bloom and severe damage occurs when there is a heavy infestation.

Sprays of trichlorphon, or carbaryl 0.1% readily control it. Carbaryl should not be used on flowers, as it is very toxic to bees. A follow-up spray may be needed if reinfestation occurs.

The larva of the yellow peach moth damages nuts in a similar way to that of the Macadamia nut borer. The pinkish larva resembles the nut borer larva, but grows slightly larger and the dark spots on the body are larger and more oval. Nuts borne in tight clusters are more prone to attack and the larva characteristically fills the spaces between nuts with frass.

The lycaenid fruit borer is the larva of the cornelian butterfly. The stout-bodied, slug-like larva grows to 25 mm long and is a purplish brown with orange and green markings. It tunnels into the nut making a clean circular hole which is neatly "plugged" by the flat anal segment of the larva. One larva is capable of destroying the kernels of several nuts. Nuts from 8 mm in diameter to full size are attacked from November to March.

Control measures recommended for the Macadamia nut borer should be satisfactory for the yellow peach moth and lycaenid fruit borer.

Numerous lepidopterous larvae destroy foliage on macadamias. The Macadamia cup moth larva is an oval, flattish, green, slug-like larva. It has a prominent mid-dorsal yellow stripe, which resembles the midvein of a leaf. The full-grown larva is about 3.5 cm long and 1.5 to 2 cm wide. Insecticide treatment may sometimes be required for the variegated hairy caterpillar, the brown tufted caterpillar, the macadamia-tufted caterpillar and the brown looper when they occur on young trees. A carbaryl 0.1% spray gives satisfactory control.

The orange fruit borer is a common and persistent pest of macadamias. The larva is a leaf roller but also infests flowers, erodes nut husks and occasionally tunnels into the nuts. It can be necessary to control this light brownish, striped larva in nurseries where its leaf rolling damage to terminal shoots promotes the growth of undesired multiple shoots. A carbaryl 0.1% spray is effective.

The larvae of two moths are commonly found in nuts stored on the farm. One of these, the Macadamia kernel grub Cateremna sp., infests nuts in the field when there has been damage to the shell by other insects or when there is access to the kernel through an open micropyle. Over 30 white to creamy colored larvae can be found on one kernel. Kernels are soon destroyed and the larvae pupate within the nut.

The tropical warehouse moth, a common pest of stored products, also infests stored Macadamia nuts. Like Cateremna sp., it also depends on a hole in the shell to gain access to the kernel. No direct control can be employed against these insects. It is obviously advantageous to minimize shell damage and avoid nuts of the type that has an open micropyle. Farmers should give attention to hygiene and dispose of all old or damaged nuts likely to be a harborage for these pests. Nuts should be forwarded for processing as soon after drying as possible.

CONCLUSION

The insects referred to be a small proportion of the many species (approximately 150) recorded feeding on and damaging macadamias. Many parasitic and predatory insects that effect considerable control over some of the pest species are also associated with Macadamia nut trees.

The relative importance of the various species may well change as Macadamia growing expands and if insecticide usage becomes more widespread. Insecticides should be used as little as possible because many of the chemicals reduce the number of parasites and predators. Research continues to improve understanding of the pest complex, to find non-chemical means of controlling pests and to determine what pest infestation levels can be tolerated before chemical control is required.

Growers should seek to understand their pest situations and apply insecticide sprays only at the recommended rates and only when pest incidence is such that spraying is warranted. The addition of a wetting agent in appropriate quantities in all sprays except those containing white oil will aid in obtaining a uniform wetting with insecticide solution.

People involved in mixing and applying insecticides should read the label on the insecticide container and carefully follow all safety precautions.

Scientific names of insects, in order mentioned in the text, are:

Macadamia flower caterpillar Homeosoma vagella Zell.

Fruit spotting bug Amblypelta nitida Stal

Banana spotting bug Amblypelta lutescens lutescens (Dist.)

Macadamia nut borer Cryptophlebia ombrodelta (Low.)

Macadamia twig girdler Neodrepta luteotactella (Walk.)

Macadamia leaf miner Acrocercops chicnosema Turn.

Macadamia felted coccid Eriococcus sp.

Hairy line blue butterfly Erysichton lineata lineata (Murr.)

Macadamia lace bug Ulonemia sp.? concava Drake

Black citrus aphid Toxoptera aurantii (Boy. de Fonsc.)

Red shouldered leaf beetle Monolepta australis (Jac.)

Yellow peach moth Dichocrosis punciferalis (Guen.)

Lycaenid fruit borer Deudorix epijarbas diovis flew.

Macadamia cup moth Comana fasciata (Walk.)

Variegated hairy caterpillar Anthela varia (Walk.)

Brown tufted caterpillar Olene mendosa (Hubn.)

Macadamia tufted caterpillar Orgyia australis Walk.

Brown looper Lophodes sinistraria Guen.

Orange fruit borer Isotenes miserana (Walk.)

Macadamia kernel grub Cateremna sp.