Hymenoptera : Pergidae

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Image above: Sawfly Larvae

Sawfly larvae are the juvenile forms of adult sawflies of the family Pergidae. These sawflies are native insects related to wasps and are common throughout Australia. The common name ‘Sawfly’ comes from the saw-like appearance of the egg-laying apparatus (ovipositor) of female sawflies. The females use the ‘saw’ to cut slits in plants into which they lay their eggs. Sawflies do not sting.

Sawfly larvae superficially resemble caterpillars and they feed on the leaves of various native plants. The common name of some Sawfly species may derive from the native plant it feeds on, for example, ‘Callistemon Sawfly’. Some Sawfly larvae are called ‘spitfires’ because of their repulsive defence tactic of rearing up and regurgitating thick yellow fluid to drive away predators.

Best Treatment for Sawfly Larvae

The secret to pest control is to keep an eye on your plants, so that you can detect pest incursions early. This is certainly important for insects such as Sawfly larvae, especially if the plants are young. If you can find Sawfly larvae when they are small you can prune any infested leaves off and prevent a major defoliation of vulnerable young plants.

Long-tailed Sawfly larvae can even damage mature bottlebrushes and paperbarks. If this happens regularly to your bottlebrushes the trick is to keep an eye on the shrubs, and detect the larvae when they are immature. Young Long-tailed Sawfly larvae are likely to be feeding on the tips of branches and you may be able to prune most of them off. Even if the infestation gets away from you, the plants will recover if they are appropriately watered and fertilised.

If you see a large cluster of Sawfly larvae in a mature eucalypt, that is much less of a problem. The feeding activity of Sawfly larvae is unlikely to affect a healthy mature gum tree. Those large clusters only cause a problem when the larvae migrate down out of a tree and they are looking for a place to pupate. The larvae sometimes travel along fences and even cross driveways in their search for a pupation site. If the Sawfly larvae are large and they have come out of a gum tree they are likely to be ‘spitfires’ and should be handled with caution. If you don’t have any vulnerable young native plants in your garden, and you can tolerate a bit of damage, maybe those larvae can be left alone. 

If treatment is needed, control Sawfly larvae with Yates Baythroid Advanced Insect Killer for Gardens. Mix as directed and spray thoroughly. Repeat as needed, especially at the beginning of renewed pest activity.

What are Sawfly Larvae &
How to Get Rid of Them

There are about 150 species of sawflies in the family Pergidae in Australia. This family is a member of the large insect order Hymenoptera – the same insect order as ants, bees and wasps. Sawflies have a lifecycle of complete metamorphosis: egg, larva, pupa and adult.

Larvae of some sawflies – especially ‘spitfires’ in eucalypts – gather in large groups during the day for protection. When the larvae spread out at night to feed, they tap on the branches with their abdomens to let the rest of the group know where they are, so they can re-form their protective cluster before daylight. Callistemon Sawflies and other members of the Lophyrotoma genus don’t form large clusters, and may feed day or night.

Description

Larvae

Sawfly larvae grow from about 20 mm to 60 mm in length depending on the species. All species have six obvious thoracic legs near the head. The larvae of many common Sawfly species (e.g., Perga spp. or Pergagrapta spp.) that attack eucalypts have no abdominal prolegs, but other sawfly larvae such as Lophyrotoma spp. may have up to eight pairs. Prolegs are stubby fleshy appendages under the abdomen of larvae.

Callistemon Sawfly larvae and other members of the Lophyrotoma genus have long fleshy ‘tails’ and are sometimes called Long-Tailed Sawflies. Sawfly larvae may be blue-black, green, grey, brown or reddish depending on the species. Classic ‘spitfires’ tend to be very dark in colour with short white hairs.

Adults

Adult sawflies are insects related to wasps, but they lack the typical narrow ‘waist’ of wasps. Sawfly adults are typically inconspicuous insects about 20 mm to 30 mm long, brown or blue-black in colour depending on the species, and some species may have white or yellow markings.

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Image above: Adult Female Sawfly (Pergagrapta polita)
(image courtesy of Denis Crawford)

Life Cycle

Female sawflies use their ‘saw’, which is part of their ovipositor, to cut slits in leaves in which they lay eggs. The eggs are laid in batches and may be laid along the midrib of the leaf or along the leaf edge depending on the sawfly species. Female sawflies of the genus Pseudoperga are noted for standing guard over their eggs and larvae, whereas other Sawfly species lay their eggs and fly away.

Sawfly larvae grow through about six instars before pupating. Mature Sawfly larvae of some species climb down from trees in large groups to pupate in the soil, sometimes migrating along fences and across pathways in the process. Other sawfly larvae such as Long-tailed Sawfly larvae (Lophyrotoma spp.) simply drop to the ground.

Sawfly larvae that feed on eucalypts (i.e., ‘spitfires’), possess specialised mouthparts that separate toxic oils from eucalyptus leaves and pass them into an organ known as a diverticulum. The larvae regurgitate these stored oils just before feeding or during feeding, as well as when provoked by predators. The oils are toxic to the Sawfly larvae themselves so it makes sense that the diverticulum would have to be emptied when full.

Most sawfly larvae pupate in hard cocoons, while Long-tailed Sawfly larvae Lophyrotoma spp. pupate in soft cocoons. Most sawfly species complete their life cycle in one year, but Long-tailed Sawfly larvae can complete their lifecycle in about 12 weeks and may have more than one generation per year depending on the climate. Adult sawflies are short-lived, with a life expectancy of 7 to 9 days, and the adults of many species don’t feed.

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Image above: Sawfly larvae

What Plants are Impacted by
Sawfly Larvae

Bottlebrush (Callistemon spp.), native conifers (Callitris spp.), eucalypts (Angophora, Corymbia, Eucalyptus spp.), and paperbark (Melaleuca spp.). Sawfly species are usually host specific. The host plant’s name is often part of the insect’s common name for example ‘callistemon sawfly’ and ‘paperbark sawfly’.

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Image above: Steel Blue Sawfly (Perga dorsalis) larvae in a classic 'Spitfire' cluster
(image courtesy of Elise Dando)

Symptoms of Sawfly Larvae

Damage usually starts with the youngest leaves at the tips of the branches. When larvae are small they may skeletonise leaves, but as they grow larger often only the leaf stalks remain. Large numbers of grubs are capable of seriously defoliating young trees, and mature shrubs such as bottlebrushes and paperbarks.

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Image above: Long-tailed Callistemon Sawfly larvae (Pterygophorus sp.)
(image courtesy of Denis Crawford)

How to Prevent Sawfly Larvae Appearing

Monitor

  • Look for skeletonised leaves.
  • Serious damage can be prevented by detecting the presence of larvae early, look for clusters of small larvae on the youngest leaves (that is at the top of the tree).
  • Look for clusters of large caterpillar-like sawfly larvae on branches.

Prevent

  • Healthy trees will recover quickly from infestations. Make sure your trees and shrubs are watered and fed appropriately. For a soil conditioning fertiliser suitable for most plants, including natives, try Yates Dynamic Lifter Soil Improver & Plant Fertiliser.
  • Pick off any sawfly larvae you find - wear gloves if dealing with ‘spitfires’, or prune off small branches with spitfire groups.

Natural Enemies

  • Birds feed on larvae.
  • Several species of parasitic wasps (see beneficial wasps) and flies parasitise eggs and larvae.
  • Beetle larvae prey on Sawfly pupae in the soil.

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