HortFACT
Identification
The adults are shiny black-dark brown beetles about 12mm long. They are found close to the surface in the soil of pastures.
The spherical white eggs are 1.5-2.0mm in diameter and are found singly in the soil at a depth of 10-50mm.
The larvae are white, curled up grubs 5-25mm in length. There are six legs on the thorax and the dark gut contents are visible in the swollen abdomen. The head of the grub is reddish-brown and the anal cleft forms a horizontal arc at the rear.
The ginger brown pupae are found in earthern cells at 100-300mm depth in the soil.
Host plants
The larvae feed on the roots of grasses, rushes and thistles in hill pastures. The adults do not feed.
Damage
Destruction of the pasture sward may occur in autumn through the feeding activity of large larvae when these are present at densities of 200-500 per square metre. Heavy infestations can result in the roots of pasture plants being severed to such an extent that the pasture can be rolled back in sheets.
Distribution
The redheaded cockchafer is an introduced insect of Australian origin. It is a native of South Australia, Victoria, New South Wales and Tasmania. The beetle was first recorded in New Zealand in 1963 in a small area of the Port Hills near Christchurch. Its distribution is presently restricted to about 3000 ha of hill country around the Port Hills and northern Banks Peninsula including a 5km coastal strip from Purau to Camp Bay. It is found in well drained loamy soils.
Life cycle
| Egg |  |
| Grub | |
| Pupae | |
| Adult | |
| Month | |
| Note: Coloured bars indicate periods of peak activity in each of the life cycle stages | |
In Canterbury the life cycle lasts 2 years. Eggs are laid singly in the spring, October-November, and the larvae hatch out after 5-6 weeks. The grubs moult twice before becoming nearly full grown in the following winter. In their second year, the larvae move downwards in the soil, form an earthen cell and pupate in late summer. The adult emerges from the pupa after 3 weeks. Its body is initially reddish-brown but darkens to black as the exo-skeleton hardens. The beetles move up to within 1-10cm of the surface where they remain over winter neither eating, mating nor emerging.
In September the beetles emerge at dusk and fly for a brief period, usually returning to the pasture where they burrow themselves in. Mating takes place in the soil and each female lays about 20 eggs. Some fertilized females and males make flights of up to several kilometres and so although most eggs are laid in the home pasture, some are laid at other sites and may establish new infestations.
The two-year life cycle results in the occurrence of two broods of this species. Adults and mature larvae occur together in winter while eggs and larvae are found together in spring. The proportion of the total population in each brood can vary from 1:1 to the near absence of one brood.
J. FARRELL