Sawflies

Introduction

Sawflies are probably closest to the ancestral form that all hymenopterans (ants, wasps, bees and sawflies) evolved from. However, they are placed in a separate suborder, Symphyta (ants, bees and wasps belong to the suborder Apocrita) based on reproductive and other characteristics.

Identification

Sawflies do not possess the distinctive thin waist of the other hymenopterans, nor do they possess a sting. Their name comes from the female's saw-like egg-laying tube, which she uses to make a slit in a plant leaf or stem, into which she lays her eggs. The adult Steel-Blue Sawfly is usually a dark metallic blue, with a white spot on the thorax, and has a wingspan of about 4cm. The adult Bottlebrush Sawfly has an orange and black banded body, with a wingspan of about 2cm. Males have feathery (pectinate) antennae.

Habitat

Found on native trees and shrubs, such as eucalypts, paperbarks and bottlebrushes.

Feeding and diet

Sawfly larvae feed mainly on native trees and shrubs, such as eucalypts, paperbarks and bottlebrushes, although a small number of species are parasitic.

Eucalypt feeders

Larvae of sawfly species that feed upon eucalypts are often seen during the day in large closely packed groups on branches or on the ground. These larvae can cause extensive damage to their food plants. One very destructive genus is the Steel-Blue Sawfly (Perga sp.) which attacks eucalypts in south-eastern Australia. These larvae secrete an irritating or distasteful liquid from their mouths. With this defence, the sawfly larvae are usually avoided by predators. They are sometimes called 'spitfires', although they don't actually spit.

Melaleuca and Callistemon feeders

Sawflies are also found on Paperbarks (Melaleuca). A commonly occurring species is Pterygophorus facielongus, sometimes called the Long-tailed Sawfly. Unlike Steel-blue Sawflies, Long-tailed Sawfly larvae do not cluster in large numbers, but may sometimes cluster in small groups in the daytime. One of their favourite food plants is Melaleuca armillaris. At first the small larvae skeletonise leaves. The larger larvae eat whole leaves and can strip all the leaves from the top of the crown, feeding during both day and night.

The Bottlebrush Sawfly is another species of Pterygophorus, P. cinctus, which feeds on Bottlebrush (Callistemon).

Breeding behaviours

The sawfly's name comes from its ovipositor (or egg laying tube), which is saw-like. The female sawfly uses this ovipositor to saw a slit in plant leaves and stems, into which she then lays her eggs. The larvae of the Steel-Blue Sawfly pupate in a cocoon in the leaf litter, while Bottlebrush Sawflies pupate without a cocoon. When Long-tailed Sawfly larvae have finished feeding, they enter a mobile pre-pupal stage, seeking soft bark (such as a paperbark trunk) or soft timber in which to bore and pupate.

Danger to humans

Adult sawflies are not capable of stinging. However, the larvae may secrete an irritating liquid onto the skin or into eyes if disturbed.

References

• Jones, D. & Elliot, R. 1986. Pests, Diseases and Ailments of Australian Plants. Lothian Publishing: Melbourne. pp. 176 - 178.
• John McDonald, NSW Agriculture