Borer Control in Your Garden

Coleoptera (Beetles) : Cerambycidae and Buprestidae
Lepidoptera (Moths) : Cossidae and Oecophoridae

There are many insects that can be described as borers. The insects that bore into the seasoned timbers of furniture and houses are different species to those that bore into trees. The most common borer insects found in gardens are the larvae of Longicorn Beetles. Larvae of Jewel Beetles are also quite common in gardens.

Wood boring moth larvae may also be of concern in gardens, including the larvae of Wood Moths and the Fruit-Tree borer Maroga melanostigma. All these borer insects have something in common - most of their life cycles are completed out of sight inside their target plants.

Best Treatment for Borers

The secret to pest control is to keep an eye on your plants, so that you can detect pest incursions early. Any control method you use is always going to be more effective if you detect pests early (i.e., when their numbers are low).

Keeping an eye on your plants is paramount with borers because by their very nature, borers are hidden inside the plants. You are most likely to see the tell-tale signs of borer activity (see Symptoms of Borer Activity below) before you see the insects themselves.

Some borers are more damaging than others so identifying them is very important. For example, Jewel Beetle larvae prefer to feed in weakened or damaged trees. In other words, if you find Jewel Beetle activity in one of your trees, that is a sign the tree may not have been in great shape in the first place.

Some plants are more susceptible to borer damage than others – wattles such as those in the ‘Black Wattle’ group are particularly susceptible. If borer damage occurs regularly in wattles in your garden perhaps you could try planting less susceptible species such as Cedar Wattle. You should also consider removing any infested wattles to break the life cycle of the borer insects and prevent a new generation emerging.

To improve the health of your soil and plants, fertilise with Yates Dynamic Lifter Soil Improver & Plant Fertiliser. Alternatively, as a fast acting liquid fertiliser that can be applied to the leaves and soil, try Yates Dynamic Lifter Liquid.

What are Borers &
How to Get Rid of Them

Longicorn Beetles (aka Longhorned Beetles) are members of family Cerambycidae. There are about 1,200 species native to Australia, and some species are common borers in home gardens. Longicorn Beetles are not necessarily pests. Most species attack weakened, dying or dead trees and as such are part of the decomposition cycle.

Jewel Beetles are members of the family Buprestidae and there are about 1,200 species native to Australia. Their bright colours make them the most recognisable of all beetles. Jewel Beetle larvae are wood borers, but once again most species are not pests as they tend to attack unhealthy trees.

Wood Moths (also known as Goat Moths) are members of the family Cossidae. There are about 200 species native to Australia, but only about half of them have been formally described. This moth family includes the Witchetty (‘Witjuti’) grub that is thought to be the larval form of moths in the genus Endoxyla.

There are more than 5,000 species of moths in the family Oecophoridae. The most common wood borer in this family encountered in gardens is the native Fruit-tree borer Maroga melanostigma, which is found in all states of Australia. Compared to other borer pests, the damage caused by this moth is minor.

Description

Larvae

Longicorn Beetle larvae are typically creamy-yellow grubs with dark heads bearing powerful jaws, and large thoracic segments or ‘shoulders’. Larvae of common Longicorn Beetle species are 30 mm to 50 mm long.

Jewel Beetle larvae are legless creamy grubs, with a wide flattened thorax and a long body giving them an almost cobra-like appearance. Jewel Beetle larvae resemble Longicorn Beetle grubs but can be differentiated by an inverted ‘V’ on the first segment of the thorax, which is lacking in Longicorn Beetle larvae.

Wood Moth larvae are usually very large from 50 mm to 150 mm long, and yellow, grey or pink in colour depending on the species. Larvae are mostly hairless with armoured thoracic segments and brown heads.

Fruit-tree Borer larvae are pale pinkish brown caterpillars with brown heads and they grow to about 50 mm long.

Adults

Adult Longicorn Beetles vary in size from a few millimetres to more than 80 mm in length, with conspicuously long antennae, which may exceed body length (hence, ‘longhorned’ or ‘longicorn’).

Adult Jewel Beetles are mostly brightly coloured metallic beetles from 2 mm to 60 mm long. They are elongated and flattened beetles with short antennae − unlike Longicorn Beetles that have very long antennae.

Adult Wood Moths are usually large grey or brownish moths. Some Wood Moths are truly enormous with wing spans of 250 mm.

The adult Fruit-tree Borer moth is satiny-white and has a 30 mm to 50 mm wingspan. The upper surface of the abdomen is black with an orange-coloured fringe of hairs. There is a small black spot located near the centre of each white forewing.

Life Cycle

Female Longicorn Beetles lay their eggs under the bark of host plants. Almost all Longicorn Beetle larvae feed on wood, feeding internally and creating tunnels in phloem, sapwood or heartwood depending on the species. Larvae pupate within the tree. Adult Longicorn Beetles emerge from distinctive oval holes. The life cycle is completed in one to two years depending on the species.

Female Jewel Beetles usually lay their eggs in sick or stressed trees. Larvae hatch and tunnel in the cambium region, growing through several moults and chewing a maze of tunnels packed with sawdust and frass (droppings). Jewel Beetle larvae pupate in sapwood and later emerge as adult beetles. The life cycle may take anywhere from several months to several years depending on the species.

Female Wood Moths usually lay their eggs in crevices in the bark of various native plants. Larvae hatch and bore into the heartwood of large stems, trunks and/or roots depending on the moth species. Larvae may live in vertical tunnels for a couple of years, before chewing an exit hole in the trunk or roots depending on the moth species. Larvae pupate in their exit tunnels until moths emerge and fly off to begin a new generation. Emerging moths leave pupal cases clearly visible protruding from tree trunks or out of the ground depending on the species. The life cycle takes several years to complete.

Female Fruit-tree Borer moths lay their eggs on the bark of the host tree, often at branch junctions or in the forks of trees. Larvae burrow into the wood, sheltering in tunnels during the day and emerging at night to feed on the bark. Tunnel entrances are covered with frass, webbing and chewed bark. Larvae pupate in their tunnels and adult moths usually emerge in summer.

Image above: Longicorn Beetle larva feeding and tunnelling in woody plant material
(Image courtesy of Denis Crawford)

What Plants are Impacted by Borers

Longicorn Beetles
Trees including coniferous trees (native and exotic), citrus, eucalypt, fig, pittosporum and wattle.

Jewel Beetles
Various native trees including eucalypts and wattles, and native shrubs including Parrot-peas (Dillwynia spp.), Tea-trees (Leptospermum spp.), Paperbarks (Melaleuca spp.), and Bush peas (Pultenaea spp). Some Jewel Beetle species target specific plants – for example, Jewel Beetles in the Diadoxus genus are pests of various introduced and native conifers.

Wood Moths
Eucalypts, angophora, wattle, Myoporum and Xanthorrhoea.

Fruit-tree Borer
Citrus, stone fruit, pome fruit, fig, grapes, wattle and elm.

Image above: Adult Longicorn Beetle
(Image courtesy of Denis Crawford)

Symptoms of Borers

• Longicorn Beetle larvae create oval-shaped tunnels packed tight with a mixture of droppings and sawdust. Wattles look particularly miserable when infested with Longicorn Beetle grubs. Wattles exude an enormous amount of sap to defend themselves, giving the appearance the tree is bleeding to death.
• Jewel Beetles larvae tunnel into bark, cambium and sapwood, and their tunnels are packed with a mixture of droppings and sawdust.
• The tunnelling of Wood Moth larvae may go unnoticed until exit holes are obvious. Black cockatoos may tear off large sections of bark and sapwood to feed on larvae in tunnels. Bird damage may be the most obvious and serious damage.
• Fruit-tree Borer tunnel entrances covered with frass, bark and webbing in forks of trees.

Image above: Adult Longicorn Beetle on a tree trunk oozing sap caused by larvae
(Image courtesy of Denis Crawford)

How to Prevent Borers Appearing

Monitor

• Look for sawdust on the ground or around the junction of branches.
• Holes with frass, webbing, bark or sawdust in and around them.
• Flowing sap – especially on wattles.

Prevent

• Appropriately fed and watered, healthy and vigorous plants are more likely to survive an attack than a stressed and weakened plant.
• Clear away frass to expose tunnels and stab grubs with a piece of wire.
• Prune off infested branches where practical. You need to make sure the borer larva is inside what you are pruning off. The simplest way to do this is check your cut for a borer hole or tunnel. If there is a hole where you have cut, you will need to cut again further along the branch towards the trunk. In some cases, you may find the borer has entered the trunk, which means the tree may have to be severely pruned to a stump or removed entirely.
• Consult a qualified arborist if a large tree looks sick and there are signs of borer activity.
• Consult a tree nursery and select trees that are less susceptible to borer attack.

Natural enemies

• Parasitic wasps and predatory beetles attack borer larvae and pupae in tunnels.
• Tiny parasitic wasps may attack the eggs of wood boring moths.