Identifying soil beetle pests

Page last updated: Friday, 25 May 2018 - 10:23am

In the south-west of Western Australia, many types of beetles are found in pastures, broadacre and horticultural crops. As a first step to knowing whether or not a particular insect is a pest, it is necessary to identify it. The more common and damaging species of beetles are featured here as an aid to their identification.

How to distinguish between the beetle species

Species described

These insects are often found in the same situations and their feeding activity or damage may be confused with each other.

The beetles described include:

  • African black beetle
  • bronzed field beetle
  • pasture beetle (Aphodius)
  • vegetable beetle.

And beetles that are in the weevil group because they have a 'snout' include:

  • apple weevil (curculio beetle)
  • Fuller's rose weevil
  • garden weevil
  • sitona weevil
  • small lucerne weevil
  • spotted vegetable (desiantha) weevil
  • subterranean clover (sub-clover) weevil
  • vegetable weevil
  • whitefringed weevil.

Differences in morphology of adults and larvae

Adult beetles

Adults of these beetles differ markedly. While adult weevils have a very hard outer shell, are usually flightless and have a prominent snout on the head, the beetles are also 'hard shelled', are more active fliers and do not possess a snout. Further descriptions for each adult species can be seen below.

Beetle larvae

African black beetle and pasture beetle are typically known as 'cockchafers' with larvae having:

  • three pairs of legs on the thorax
  • a prominent brown head with black jaws
  • the body forming a C-shape with the end of the abdomen slightly enlarged.
Different sized cockchafer larvae
Different sized cockchafer larvae

Larvae of vegetable beetle and bronzed field beetle have the common name 'false wireworm' with larvae having:

  • three pairs of legs on the thorax
  • are not C-shaped
  • vegetable beetle larvae have a worm like shape with shiny hard skin
  • the larval stage of the bronzed field beetle are dark brown with upturned spines on the end of the body.
Life stages of bronzed field beetle, left to right, larva, pupa, adult that has just emerged from pupa, adult
Life stages of bronzed field beetle (left to right) larva, pupa, adult that has just emerged from pupa, adult
Vegetable beetle: larvae (left), pupa (middle), Adult (right)
Vegetable beetle: larvae (left), pupa (middle), adult (right)

Weevil larvae

Weevil larvae are legless, the abdomen is not enlarged and have either:

  • a white head, which makes the two black jaws very obvious (this includes whitefringed weevil, small lucerne weevil and Fuller's rose weevil).
White headed weevil larva
White headed weevil larva: typical of whitefringed weevil, Fuller's rose weevil and small lucerne weevil. Prominent black jaws, legless. All are soil inhabiting. Larvae longer than 10mm are white fringed weevil. Small larvae are difficult to identify.

or:

  • a brown head (this includes garden weevil, apple weevil, spotted vegetable weevil, vegetable weevil, sub-clover weevil and sitona weevil).
Brown-headed weevil larvae
Brown-headed weevil larvae: typical of garden weevil, apple weevil, spotted vegetable weevil and sitona weevil. Brown head, legless. All are soil inhabiting. Small larvae are difficult to identify.
Weevil larvae and corresponding adult - left to right apple weevil, garden weevil, whitefringed weevil, Fuller's rose weevil, vegetable weevil
Weevil larvae and corresponding adult (left to right) apple weevil, garden weevil, whitefringed weevil, Fuller's rose weevil, vegetable weevil

Contact information

Stewart Learmonth
+61 (0)8 9777 0167