Redheaded pasture cockchafer is currently restricted to pastures in some areas on the Port Hills and Banks Peninsula, Canterbury, and also to amenity turf within Christchurch city
This insect has a two-year lifecycle so serious damage may only occur once every two years
The very large larvae (up to 30 mm long) of this pest can cause serious pasture damage during autumn and winter
Adult beetles are not known to cause any damage
Biology
The redheaded pasture cockchafer is an Australian species but has been present in Canterbury on the Port Hills and Banks Peninsula since the early 1960s. Only limited spread from the known infested areas has been observed to date. However, it is at serious pasture pest in Tasmania, South Australia, Victoria and parts of New South Wales and is possible it will eventually spread to pastures with similar characteristics in many areas of New Zealand
Adults are shiny dark brown/black robust looking beetles very similar in appearance to the African black beetle found in parts of the North Island. Both sexes are approximately 12 mm long and can be found close to the soil surface in pasture through early spring. The beetles undertake dispersal flights during warm evenings from September to mid-October. Eggs, about 2 mm long and ovoid to spherical in shape, are laid singly in soil 10 – 50mm deep in mid to late spring
The larvae pass through 3 stages during their first year before pupating and becoming beetles during the second summer of their two-year lifecycle. Beetles emerge from these pupae and spend the following autumn and winter deep in the soil before surfacing again as adult beetles in spring
The C shaped larvae appear superficially like common grass-grub but have a red head capsule and when full size, are up to four times the size and weight of a common grass grub
Impacts
Red headed pasture cockchafer larvae feed on organic matter and live root material present in the top 100 mm of soil.
Pasture damage is caused by large 3rd stage larvae feeding on plant roots in autumn and winter. If large numbers of larvae are present pasture root systems can be completely severed about 2.5 cm below the soil surface and the pasture can be rolled up like a carpet. If lower numbers are present pasture damage similar to that caused by the New Zealand grass grub can appear with patches of dead pasture becoming visible and pulled plants seen post grazing.
Shallow-rooted pasture plants are reported to be at most risk from cockchafer damage.
The damage threshold for redheaded pasture cockchafer larvae, reported in Australian literature, is about 70/m2 which is considerably lower than for the New Zealand grass-grub.
Beetles do not appear to feed so do not cause any damage.
Control
There are few options available to control the Australian redheaded pasture cockchafer.
No chemicals are registered in New Zealand for control of larvae or adults in established pasture or for pasture seedling establishment.
Off target use of insecticides registered for use against the common grass grub have been attempted with variable results. This pest prefers soils with high organic matter which may bind to insecticides and reduce their efficiency.
Redheaded pasture cockchafer larvae are not known to be affected by any currently available grass endophytes. The adult beetle does not feed so is unlikely to be directly affected by endophytes.
A biological control product based on a strain of the fungus Metarhizium anisopliae was developed and used in Australia in the 1990s but has since been removed from the market due to production problems.
Reports from Australia suggest vigorous top-working, such as using a rototiller, greatly reduces damage to resown pastures.
As this pest has a two-year lifecycle there may be a damaging population present in an area only each second year. Monitoring populations by spade sampling may allow a farmer to identify years in which new pastures could be established in the absence of potentially damaging populations.
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