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Number 7
Revised November 1992
By Charlma Phillips, Principal Forest Health Scientist

The Eucalyptus Weevil, Gonipterus scutellatus (Gyllenhal), is also known as the Eucalyptus Snout Beetle and the Gum Tree Weevil. It is a native insect and both adult and larval (immature) stages feed on the foliage of a wide range of eucalypts. It particularly favours Eucalyptus globulus and E. viminalis.
There have been few serious outbreaks of this insect and it is not regarded as a major pest of eucalypts in Australia. However, it has become a major pest in many overseas countries where eucalypts are grown as plantation trees.

Description

Adults: Adult weevils (Fig 1) are approximately 10mm in length. They vary considerably in colour from greyish to reddish brown with darker marking on the back. They are covered by small pale brown hairs which give a rough appearance to the body.

Eggs: The eggs are laid in a pod or capsule (Fig 2) on the surface of newly expanded mature leaves. These dark brown box-like pods contain from 3 to16 pale yellow eggs arranged in vertical layers. The pods are approximately 3mm in length, 2mm high and 1.5mm in width.

 
Figure 1 Adult Weevil

 
Figure 2 Egg Pod

 
Figure 3 Weevil Larvae

Larvae: larvae (Fig 3) are plump, legless, slug-like creatures. They are pale yellowish green in colour with black spots and a black stripe running along each side of the body. Mature larvae are approximately 10mm in length. They often have a characteristic long thread or filament of faecal material coiled up behind them.

Life History

Weevils are interesting insects in that the adults emerging in autumn delay their egg laying until the following spring and spend the winter hiding under bark or under debris on the ground. The general life history is given in Fig 4 and the seasonal cycle is shown in Fig 5.

There are two generations per year. Overwintering adult weevils reappear in spring (August/September) and begin egg laying. Egg laying by these adults continues until November.

The eggs hatch in 3-4 weeks. The first larva to emerge chews directly through the pod and the leaf surface on which the pod was laid making a hole through which all the other larvae emerge.

Figure 4 Eucalypt Weevil life history

There are four larval stages which last for a total of approximately 4-7 weeks depending on temperature. When fully fed, the larvae drop to the ground and pupate in the soil, forming small pupal cells or chambers made from soil particles cemented together just below the surface. The pupal stage lasts approximately 8 weeks.

Adults emerge from the soil in January for the second generation. Larvae of this generation mature and pupate in late summer with adult weevils again emerging in March/April.

Figure 5 Eucalypt Weevil seasonal cycle

Damage

Both adults and larvae are leaf feeders but it is the larval stage that does the most damage. Larvae damage leaves by eating one surface only and leaving characteristic "tracks" where they have been feeding (see Fig 6). Adult weevils chew the edges of the leaves giving them a ragged appearance. Both adults and larvae prefer the newly expanded adult leaves and shoots.

Trees that have had severe infestations and been defoliated many times are often bushy and stunted. Young trees are the most susceptible but seedlings may also be attacked.
 

Figure 6 Weevil larva showing characteristic feeding "track"

Control

Natural:

Eucalyptus Weevils are usually well controlled by natural enemies. Parasites include several species of small wasps which lay eggs inside the weevil egg pod. The wasp larvae feed on the weevil eggs, killing them in the process. Wasp and fly parasites have also been recorded as attacking the larval stages of the weevil. These lay their eggs in or on the weevil larvae. The resulting wasp/fly larvae feed on the weevil larvae and actually kill them.

Mechanical:

Egg pods and larvae are easily picked off small trees and destroyed.

Chemical:

Eucalyptus Weevil is not often a major pest but on occasions chemical control is warranted. The recommended chemicals are maldison, carbaryl or a synthetic pyrethroid.

Summary

When to look: 
Egg pods - look in spring and summer i.e from September to November and January/February.
Larvae - look from October to April/May.
Adults - present nearly all year but are not as easily detected as egg pods and larvae.

Where to look:
Egg pods - look on newly expanded adult leaves.
Larvae - look on adult leaves usually near the tips of branches.
Adults - look for them clinging to twigs and adult leaves.
NOTE: Adults are often hard to see as they are well camouflaged and rapidly drop to the ground if disturbed.

What to look for:
Egg pods - look for brown box-like pods.
Larvae - look for greeny yellow larvae with long filaments of faecal material curled behind. Also look for the characteristic feeding "tracks" of the larvae.
Adults - look for chewed, ragged leaves.
NOTE: Chewed leaves may also be due to a wide variety of other insects.

For further information please contact PIRSA Forestry

Disclaimer: While this publication may be of assistance to you, the government of South Australia and its officers do not guarantee that it is without flaw of any kind or is wholly appropriate for your particular purpose. The Government therefore disclaims all liability for any error, loss or other consequence that may arise from you relying on any information in this publication.