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Macadamia nutborer

Scientific name

Cryptophlebia ombrodelta

Description of adult

The moth is reddish-brown and measures 23-25 mm across the extended wings. The male is smaller than the female, which has a large dark triangular blotch two thirds of the way along the hind margin of each forewing.

Immature stages

The scale-like eggs, which are laid singly on the fruit, are oval, approximately 0.8 mm long, and change colour from ivory-white when first laid, to pink then black just prior to hatching. Fully-grown larvae are up to 20 mm long, and pinkish with discrete, dark green spots. Three or four days before pupation they construct tightly woven silken cocoons that are sealed with an unobtrusive flap, providing an exit for the emerging moth. Pupation occurs in damaged fruit, and sometimes in sheltered sites in other parts of the tree. When the moth emerges, the pupal case is left protruding from the exit hole.

Life history

The eggs are laid singly on or near the fruit. During summer they hatch in 4-6 days. The larval stage lasts 3-4 weeks, and moths emerge after a pupal period of 8-10 days. The life cycle, from egg-laying to moth emergence, takes about five weeks.

Distribution

All lychee, longan and macadamia districts in Queensland.

Host range

Lychee, longan, macadamia and many exotics grown as ornamentals including bauhinia, bird of paradise tree, the native cupania, easter cassia, golden rain tree, mimosa bush, poinciana, schotia and tamarind. Orchards near townships, where such hosts are plentiful, are likely to suffer more damage than orchards in more remote areas.

Damage

Macadamia nutborer is a major pest of lychee and longan fruit, and significant infestations occur in most seasons.

On hatching, larvae bore through the skin and into fruit in search of the seed. When this occurs in green fruit, the fruit will drop, however the larva will most likely still develop to maturity in the fallen fruit, if ground predators don't discover it. Ripening fruit generally does not fall, and the larva often drowns in the juice if the skin is penetrated in the equatorial region where the flesh is thickest.

The rind tissue around the entry hole may appear to be scalded, and such damage is sometimes wrongly attributed to fruit fly, which rarely attacks lychees and longans. Entry on the shoulder or near the peduncle is more likely to ensure survival of the larva enabling it to reach the seed. Mature fruit damaged by macadamia nutborer may weep and stain other fruit in the cluster or those hanging below. One larva can cause perhaps 10% more damage through this secondary staining effect.

Control options

Examine five fruit panicles on 20 trees widely spaced throughout the crop, commencing when green fruit are 20 mm long (for lychee and longan). Spray if more than five out of 100 panicles are infested with live, unhatched and unparasitised eggs. Check developing fruit weekly for larval entry holes and/or frass. Infestation levels increase as the fruit mature due to immigration of moths from alternative hosts. Oozing juice from maturing fruit may also indicate a nutborer infestation.

Biological

The egg parasitoid, Trichgrammatoidea cryptophlebiae, which is a native of Africa, has become established in Australia and provides excellent biological control of the macadamia nutborer, especially in longans later in summer. Numerous native larval parasites that attack the borer include the braconid wasps, Apanteles briareus Nixon, and Bracon sp., the ichneumonid wasp, Gotra bimaculatus Cheesman, and an unidentified tachinid fly parasite.

Chemical

In lychee and longan, spray with a suitable insecticide when 5% of panicles have fruit with fresh, unparasitised eggs. These will be white or pink, as opposed to parasitised eggs, which are black.

Chemical registrations and permits

Check the Australian Pesticides & Veterinary Medicines Authority chemical database and permit database for chemicals registered or approved under permit to treat this pest on the target crop in your State/location. Always read the label. Always observe withholding periods.