Coleoptera : Heteronychus arator
There are two damage causing stages of the African Black Beetle life cycle, including the adult beetle stage and the juvenile (larval) ‘Curl Grub’ stage. Lawns and turf are notoriously impacted by pest attack, however, garden and potted plants are also significantly affected. Some of the risks of pest attack to plants and lawns include stunted growth, water stress and death. To avoid such damage to lawns and plants it’s important to be vigilant of the signs and symptoms of pests, quickly treat with a suitable control and implement preventative strategies.
For the control of African Black Beetle (adult stage) in lawns and turfed areas try Yates Baythroid Advanced Insect Killer for Lawns. Also controls Mole Crickets, Couch Mite, Ants, Armyworm, Cutworm, Webworm and the adult beetle stage of Billbug, Argentine Stem Weevil and Scarab.
When digging in the garden collect any larvae or adults and either feed to the birds or place pests into a bucket of soapy water. Drain off the excess water, place dead pests in a plastic bag and place into the rubbish bin.
If you have chickens or other fowl allow them to roam freely in and amongst the garden, lawn and turfed areas to feed on adults and first larval instar.
For large vegetable garden beds, allow beds to rest for a period, turning over the soil every now then exposing larvae and adults to predators such as birds.
For particularly infested beds, to prevent adults from laying eggs into the soil, plant crops in mid-summer to winter; and to prevent adults from feeding, plant crops in winter. Alternatively, plant an overabundance of crops at any time of year.
Plant a wide variety of crops as pests often preferentially feed on some crops and not others - this will reduce the effects of monoculture.
To prevent plant death of ringbarked woody plants slightly mound the soil over damaged stem or trunk.
Prune the foliage of trees and shrubs which have had their roots chewed and thereby root system reduced. Prune up to a third of the total foliage as this will help to rebalance the root-to-shoot-ratio.
Keep plants, lawns and turfed areas well-watered and fertilised until adequately recovered from attack. Yates Dynamic Lifter is an excellent organic fertiliser, which also improves the soil and enhances pest and disease resiliency.
The African Black Beetle (Heteronychus arator), also known as the Black Lawn Beetle or Black Maize Beetle, is an introduced pest species from Africa and is found in most parts of Australia (excluding Tasmania).
The adult beetles are glossy black, oval-shaped and generally 12 - 15mm long. On the underside of most of the body are light-brown bristle-like structures (setae). At the front of the body is the head, which is short, broad and angles downwards. At the front of the head are chewing mouthparts. On either side of the head are a pair of compound eyes and short, golf-club-like antennae. Behind the head, on the upper side of the body, is a large trapezoid-shaped plate (pronotum) which is the front segment of the middle section of the body (thorax).
Attached to the underside of the thorax are 3 pairs of legs which are lightly covered in spines. The upper portion of the leg is slightly flattened while the lower leg is thinner and thread-like. However, in males, the lower portion of the front legs are also slightly flattened. At the tips of the legs are claws. The hindlegs are the largest pair which are used for digging.
Adults have 2 pairs of wings, the outermost wings are hardened forewings (elytra) and used to protect the delicate membranous hind-flight-wings. While at rest, forewings fold down over the flattened hindwings and meet in the centre of the body, forming a distinct straight line. At the top of this line is a small triangular-shaped plate known as the scutellum. Along the length of the forewings are straight, mostly parallel indented lines.
The grub-like larvae have a creamy-white body with an orange-to-brown rounded head capsule and black jaws. The hind section of the body is generally swollen, baggy and grey-blue to green in colour due to the visible contents of the gut. The body is long, tubular, C-shaped and heavily segmented, growing up to 25mm long. At the front, along either side of the body, at each segment are a pair of orange-brown spots which are used for breathing (spiracles). On either side of the head are a pair of compound eyes and at the front of the head are chewing mouthparts. Antennae are small and generally inconspicuous. Attached to the underside and middle section of the body are 3 pairs of thin 5-segmented legs. Larvae are wingless.
Normally, there is just one generation of African Black Beetle per year, however, depending on the environment it may take up to 2 years to complete the entire lifecycle.
In spring, after mating the female adult lays eggs just underneath the surface of vegetation. Eggs are small (1.8 mm), round and cream-coloured. Females lay between 6 and 12 eggs individually, laying approximately 30 eggs in her lifetime.
After 2–5 weeks, eggs hatch and grub-like larvae emerge. Larvae develop through 3 larval stages (instars) where they grow then shed their exoskeleton (a process known as moulting) at each stage. After hatching, the first instar is 5mm long. At the second instar larvae burrow into the soil. After developing into the third and final instar stage, fully mature larvae are typically 25 mm in length and ready to pupate. Larvae are generally active throughout most of spring and summer.
In late summer to early autumn, mature larvae dig a chamber in the soil to create an ‘earthen cell’. Larvae ‘clear their guts’ of food and become a pale-yellow colour. As pupae develop, they become slightly darker and redder in colour and shorter (15 mm long) and more rounded in appearance. During the pupal stage, pupae do not feed, are mostly inactive and gradually transform into the adult form.
After pupating for approximately 2 weeks, adults emerge in late summer and autumn. Over winter, adults become less active and in cold conditions hibernate in the soil until emerging in spring where they are mature and ready for mating. Adults generally survive for 10 months, dying soon after reproducing in spring.
Behaviour and habitat
At the first instar stage, larvae feed on decaying organic matter just above the soil surface. At the second and third instar stage larvae exclusively feed below ground on plant and grass roots and other below-ground parts of plants. Adults mostly feed on plant and grass shoots just above or below the soil surface (up to 15 cm deep).
Adults are slow walkers and crawl mostly during the breeding season. Flying mostly occurs at night – particularly in autumn, less often in spring - where they are especially drawn to and fly towards artificial lights.
Birds, foxes, rats and mice, nematodes, and some microorganisms.
Lawns and turfed areas:
Further evidence of African Black Beetle includes physical signs of eggs, larvae, pupae and adults - see description and lifecycle for identification.
Avoid using bright outdoor lighting at night as this may attract flying adults into the garden.
Most turf varieties are highly susceptible to pest attack, severely impacting lawns and turfed areas. Examples include:
Both potted plants and plants in the ground, especially young plants, seedlings, small growing and thin-wooded plants are particularly vulnerable to pest attack. Edible plants including vegetables, herbs, tomatoes, citrus and fruiting trees may be impacted. Examples include:
Non-edible (ornamental) plants including flowering plants, roses, natives, succulents, tree and shrubs may also be impacted. Examples include: