PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Scarab grubs
Scarab beetles, cockchafers, dung beetles
Scientific name
Scarab grubs belong to the Family Scarabaeidae
(scarab beetles, cockchafers and dung beetles), a
number of other members of this family also attack
growing plants including:
African black beetle (Heteronychus arator)
Argentinian scarab (Cyclocephala signaticollis)
Black beetle (Metanastes vulgivagus)
Blackheaded pasture cockchafer (Aphodius tasmaniae)
Blacksoil scarab (Othnonius batesii)
Cane grubs (Lepidiota spp.)
Christmas beetles (Anoplognathus spp.)
Greyback canegrub (Dermolepia albohirtum)
Pasture whitegrubs (Rhopaea spp.)
Pruinose scarab (Sericesthis geminata)
Redheaded pasture cockchafer (Adoryphorus couloni)
Wheat root scarab (Sericesthis batesi)
Brown cockchafer (Ataenius imparalis)
Dusky pasture scarab (Sericesthis nigrolineata)
Paspalum whitegrub (Lepidiota laevis)
Pasture whitegrubs (Rhopaea spp.)
See also page 100.
Host range
Adult beetles. feed on the young foliage of a
range of plants depending on the species.
Adults of some species feed on different plants
from the larvae, eg Christmas beetles feed on
eucalypt foliage, their larvae feed on grass roots.
Adults of some species, eg African black beetle,
feed on the same plants as the larvae.
Young larvae. feed on organic matter in the soil
and when older feed mainly on roots of:
Ornamentals, eg herbaceous perennials, potted
plants. Fruit, eg peanut, pineapple, strawberry.
Vegetable s,
eg potato. Field crops, eg maize,
sugarcane, winter cereals. Grasses, eg pasture,
lawns, turf, golf courses. Weeds.
Description & damage
Adult beetles are 2-70 mm long, body is
usually stout, chunky, convex and of various
colors. Forelegs strongly developed for digging.
They may be seen swarming on certain eucalypts
during December-January. Many scarab beetles eat
leaves but some feed on nectar. Some species fly at
night, others during the day. Larvae or ‘curl’
grubs are 20-70 mm long when fully fed, plump,
soft, gray to white in colour with a hard, shiny,
dark coloured head with prominent jaws. They
have well developed legs on the thorax and are
nearly always curled into a C-shape. Larvae have
3 stages or instars. Younger instars live closer to
the surface; older instars feed at a greater depth.
Turf/pasture. Adults burrow into fine grasses,
physically disturbing the surface, some feed on the
surface. Infestation tends to move outwards from a
central point where the eggs were laid.
Primary damage is caused by larvae chewing
on grass roots which leaves the plant prone to
water and heat stress. Damage is usually first
noticed in autumn when patches of turf or
pasture die and become soft and uneven.
Secondary damage is caused by birds
feeding on grubs particularly if the area is wet.
Turf can be rolled back like a carpet to reveal the
grubs. Stock may pull up pasture. Up to
250 scarab grubs/square metre have been
recorded in the ACT. In some species, eg
pasture cockchafer late instar larvae cause
further damage by harvesting leaves to take into
burrows below the surface.
Severe damage may result in bare areas allowing
weed invasion. Damage is very patchy.
Other hosts. Scarab grubs may be a sporadic
pest of some crops. The entire root system of
strawberries and pineapple can be eaten causing
plants to be deprived of water and nutrients, wilt
and die. Potato stems may be severed below
ground or round deep holes gouged in tubers.
Roots of potted plants in nurseries may be eaten
right up to the crown causing them to wilt and
wobble. Adults of some species chew stems just
below ground level leaving a frayed edge.
Diagnostics. Damage by larvae is often
misdiagnosed.
Adult beetles are more easily identified but may
not be available when identification is needed.
Larvae are often identified from the shape of the
anus and surrounding hairs.
Molecular diagnostics often are needed to
identify larval insects or adult members of a
species complex.
Do not confuse with damage caused by other
agents, eg root rot, etc. Scarabs are minor pests
of glasshouses. Damage is more likely to be
caused by BVW.
Lucid keys www.lucidcentral.com/
Key to the Flower Chafers of NSW
Key to the Christmas Beetles of NSW
Key to the Dung Beetles of Eastern NSW
Key to Adult Cane Beetles
If in doubt see advice (page xiv).
Typical larva Christmas beetle raster Pruinose scarab raster
Fig. 75. Scarab grub larvae (Scarabaeidae)
Left: Typical scarab grub (larva) up to 20-70 mm long, usually found in the soil.
Right: Rasters of Christmas beetle and pruinose larvae.
108 Insects and allied pests - Coleoptera (beetles, weevils)