Pie-dish Beetles

Introduction

The pie-dish beetles' common name refers to their general pie-dish shape and broad body flanges (rims) around the edges of their thickened, hardened, fore wings (elytra) and the front part of the thorax or second body segment (prothorax). These flanges can often be quite large.

Identification

The flightless species have fused elytra and no hind wings. Pterohelaeus spp. are often dusty blue in colour, while Helea spp. are nearly always black.

The uniquely Australian pie-dish beetles are representatives of the large cosmopolitan darkling beetle family, Tenebrionidae. They were first discovered by Frenchmen François Péron and his companion Charles Lesueur on Kangaroo Island, South Australia, in 1803. Most Australian pie-dish beetles belong in the genera, Helea or Pterohelaeus. The genus Helea contains about 50 named species which are flightless, with deeper body flanges than those of Pterohelaeus. The genus Pterohelaeus contains both flightless and winged species.

Habitat

Adult pie-dish beetles forage on the ground at night, moving around quite quickly on long legs. Some species return to the same resting-place at dawn, often using mammal (mainly rabbit) burrows to shelter in. Other species are commonly found under pieces of wood, leaf litter, logs or stones. Some species in the genus Pterohelaeus are found under the loose bark of living and dead trees such as Eucalyptus. The adults are most active during the hottest months of the year.

The pie-dish beetles' flattened body form with expanded flanges may have been an evolutionary adaptation for living for living under the loose bark of Eucalyptus. In the more recently evolved species, the flanges are even more exaggerated, serving to deter predators and possibly to play a minor role in water collection.

Distribution

Pie-dish beetles in the genus Helea are found over the whole Australian continent, except for the highest rainfall areas in the south, east and north. Most species are found in the arid parts of Western Australia and South Australia, with a good representation in mallee as well as drier areas. Like many other in the family Tenebrionidae, they are well-adapted to arid environments. A few species occur at higher elevations in Victoria and New South Wales.

Feeding and diet

Pie-dish beetles mainly feed on decaying vegetation. They take water from their food, fresh animal dung and may also collect it from their built-in gutter or flange.

Other behaviours and adaptations

The flanges protect the underside of the beetle from predators, sheltering the head and legs from attack by spiders (particularly Redbacks), scorpions, ground beetles (Family Carabidae) and ants during extensive night-time foraging. If one side is being attacked, the beetle tilts its body, covering this side with the large flange. The beetle can also partially bury itself in sand, with the edges of the flange lying flat against the ground, presenting the attacker with only the tough upper shield.

Life history cycle

Pie-dish beetles lay their eggs in moist soil during summer and autumn, usually under clumps of rotting plant material, under which adults often shelter. Females of some species can lay up to 1000 eggs during their life spans. The rate of egg production appears to be related to temperature. So is the time of hatching, which ranges from seven to fourteen days after the eggs were laid.

After hatching, the larvae can be found in loose clusters on the top of moist soil, dispersing as they develop. When fully grown, they burrow deeper into wetter soil where they build a circular pupal chamber and change into pupae. One to three weeks later, the adults emerge. At first they are soft and light brown, but they harden after about a week and the body becomes dark brown or black, the colour depending on the species. Soon after emergence, mating occurs and eggs develop three or four weeks later. Adult pie-dish beetles can be relatively long-lived (up to a year).

The larvae of some small species of pie-dish beetles may feed on newly germinated seeds of various crop plants in Queensland, including maize, barley, sunflower, tobacco, soybean and tomato. These larvae are commonly known as false wireworms. They can be distinguished by their yellowish brown colour (sometimes with black markings), their smooth cylindrical bodies and the three pairs of legs on the thoracic segments behind a rounded head. True wireworms are the larvae of click beetles (Elateridae). Although similar in appearance to false wireworms, true wireworms have flattened, wedge-shaped heads, rather than rounded heads.

Economic impacts

Adult pie-dish beetles may damage plants by chewing stems at or below ground level, causing them to fall over or wither while standing.

References

• Allsopp, P. G. 1980. Identification of false wireworms (Coleoptera: Tenebrionidae) from southern Queensland and northern New South Wales. Journal of the Australian Entomological Society 18(1979): 277-286.
• Hawkeswood, T. 1987. Beetles of Australia. Angus and Robertson, Sydney.
• Lawrence, J. F. and Britton, E. B. 1994. Australian Beetles. Melbourne University Press, Melbourne.
• Matthews, E. G. 1985. Foraging activity of some Tenebrionid beetles in a South Australian mallee area. In 'Soil and litter invertebrates of Australain Mediterranean-type ecosystems'. (Eds P. Greenslade and J. D. Majer.) pp. 63-64. WAIT School of Biology Bulletin, No. 12.
• Matthews, E. G. 1993. Classification, relationships and distribution of the genera of Heleini (Coleoptera : Tenebrionidae. Invertebrate Taxonomy 7: 1025-1095.
• Matthews, E. G. 1998. Péron, Latreille and Pie Dish Beetles. Search 19(4): 215-217.