Cyclocephala signaticollis

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Beetle Larvae

Curl Grubs are the larvae of beetles in the family Scarabaeidae i.e. scarab beetles. This family is one of the largest beetle families in the world, with more than 2,200 species native to Australia. The larvae of various scarab beetles are known by several common names including ‘curl grubs’, ‘white curl grubs’ and ‘cockchafers’.

The African Black Beetle (Heteronychus arator) is an introduced scarab pest, and is one of the ‘curl grubs’ that damages lawns.

The Argentinian Scarab (Cyclocephala signaticollis) is another introduced scarab pest, which became established in Sydney suburbs in the 1940’s but has since spread to Canberra, northeast NSW, and SE Queensland. Recently several specimens have been identified in Adelaide and Melbourne.

Several native cockchafer species (Adoryphorus spp., Aphodius tasmaniae, Sericesthis spp.) are serious pasture pests in southern Australia. Christmas Beetles (Anoplognathus spp., Calloodes spp., Repsimus spp.) and Rhinoceros Beetles (Xylotrupes ulysses) are also scarab beetles.

Curl Grubs, especially the larvae of African Black Beetle and Argentinian Scarab, can be serious pests of lawns if they become established. Some Curl Grubs may also be pests of other garden plants and potted plants.

Best treatment for Curl Grubs including Argentinian Scarabs

Try Yates Grub Kill and Protect for the control of Curl Grubs (specifically Argentinian Scarab larvae and African Black Beetle larvae) in lawns. The product also controls other lawn beetle pests including Argentine Stem Weevil larvae and Billbug larvae; and lawn caterpillar pests including Lawn Armyworm, Sod Webworm, and Black Cutworm.

The secret to pest control is to keep an eye on your plants, including your lawn, so that you can detect pest incursions early. It pays to know what to look for so check out Symptoms of Curl Grubs including Argentinian Scarab Damage. If you find damage look closer to see if you can find grubs and identify them from the Description below.

Prevention is always better than cure, and you are more likely to be able to achieve that if you are out and about in your garden regularly. There are several things that you can do to prevent serious damage from beetle larvae (see How to Prevent Curl Grubs including Argentinian Scarab Appearing).

Regular monitoring of your lawns will ensure that a major infestation of Curl Grubs including Argentinian Scarab larvae doesn’t appear ‘overnight’. All treatments are way more effective if you can catch an infestation in its early stages.

Well cared-for lawns are more likely to resist, and recover from, beetle larvae attack than neglected ones.

What are Curl Grubs & Argentinian Scarabs and How to Get Rid of Them

Curl Grubs, including African Black Beetle and Argentinian Scarab, are the larvae of different scarab beetle species. The adults are different in appearance and behaviour, but what they have in common is how their larvae are usually curled up into a ‘C’ shape when we find them. The larvae of these scarab beetle pests are always found underground - you won’t find them climbing in plants feeding on leaves.

Description:

Larvae:

Curl Grubs generally have distinct ‘C’ shaped pale cream or white bodies, six prominent legs and usually have a swollen darker tip to the abdomen. Larvae grow to 20 – 60 mm long depending on the species. The heads of larvae may be black, brown, red or yellow depending on the species.

African Black Beetle larvae are ‘C’ shaped, about 25 mm long with a brown head, pale cream body and six prominent legs.

Argentinian Scarab larvae are also ‘C’ shaped and grow to about 25 mm long with a yellowish to light brown head, pale cream body and six prominent legs.

It is extremely difficult to differentiate between African Black Beetle larvae and Argentinian Scarab larvae. You need to find the adult beetle stage to identify them.

Adults:

The adult stage of Curl Grubs varies considerably depending on the species, but they are usually shiny, brown or black, robust beetles. The beetles are about 12 to 25 mm long depending on the species.

African Black Beetle adults are robust, shiny, black beetles about 12 mm long.

Argentinian Scarab beetles are soft-bodied beetles about 15 mm long. They are light brownish-beige in colour with distinct, complex, and symmetrical dark brown markings on their backs. Other Curl Grub adults do not have these patterns.

Life Cycle:

The life cycles of Curl Grubs vary in length from one year to every two or three years depending on the species. Because of these varying generation lengths you may find Curl Grubs in the garden at any time of the year, depending on which species is involved. Female beetles lay eggs in the soil, which hatch and pass through about three moults feeding on plant roots, before pupating in the soil. Adult beetles emerge from the soil and may be drawn to lights at night.

The African Black Beetle has a one-year life-cycle with the most damaging grubs being active in late spring and throughout summer. Adults may be present from late summer and autumn to late spring. Adults overwinter in soil or debris.

The Argentinian Scarab has a one year life cycle. They spend about 10 months underground as larvae or pupae. Research shows that larval feeding occurs during autumn, through winter and into early spring. Adult beetles are active from late November to February, with peak activity in late December.  Beetles fly at dusk and are attracted to lights, especially after rain.

 

African Black Beetle Larvae

Image of Argentinian Scarab Larvae courtesy of Syngenta

What Plants are Impacted by Curl Grubs & Argentinian Scarabs

Curl Grubs can cause serious damage to turf grasses by nipping off the roots. Larvae of African Black Beetles may also infest the roots of potted ornamentals, or damage a range of garden and edible plants by nibbling on roots. They cause severe damage to root vegetables, especially potatoes, by severing stems and gouging deep holes into tubers.

Argentinian Scarab larvae seem to only damage turf grasses in Australia. Note this pest is known to infest garden plants and potted plants in other countries.

Symptoms of Curl Grub & Argentinian Scarab Damage

  • Root damage underground causes turf to die off leaving brown patches.
  • Patches can be rolled back like a carpet because the larvae have nipped off all the roots.
  • Holes gouged in potato tubers.
  • Roots of potted plants nibbled resulting in plants looking dried out.

Image of Argentinian Scarab Larvae courtesy of Syngenta

How to Prevent Curl Grubs & Argentinian Scarabs Appearing

Monitor

  • Watch for brown patches appearing in lawns.
  • Check lawns if large birds like magpies are pecking at the ground.
  • Be extra vigilant if there are many adult beetles drawn to lights at night.

Prevent

  • Don’t stress your lawn by mowing it too closely.
  • A healthy lawn can recover easily from mild pest infestations. Help your lawn recover by watering and feeding appropriately.
  • Throw any Curl Grubs you find while digging in the garden onto the lawn for visiting birds, or your chooks, to feed on. This breaks the life cycle, preventing the next generation of egg laying beetles from emerging.
  • Check for grubs when re-potting plants.

Natural enemies:

  • Parasitic wasps such as female flower wasps (Scoliidae and Tiphiidae) burrow underground looking for scarab larvae to lay their eggs in.
  • Currawongs and magpies along with ibis and other birds. Unfortunately their pecking may cause some damage, but the lawn will recover if appropriately fed and watered.
  • Treat lawn with beneficial nematodes. Nematodes are roundworms which live in soil and kill beetle grubs by penetrating their bodies and breeding inside them. Beneficial nematodes are available commercially and can simply be watered into the lawn.

Recommended products to control Curl Grubs & Argentinian Scarabs


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