Beetles - Pests

Beetles are insects belonging to the order Coleoptera.

It is estimated that there are 30,000 species of beetles in Australia representing 110 families. many new species and even some new genera are discovered each year.

One reason for the success of beetles is there hard outer covering. All winged insects except flies have two pairs of wings. It flies the front pair has been modified into a specialised flight organ. In beetles the front pair have been modified into hard coverings called �elytra�. This protective armour helps to protect them against predators, but does make it more difficult to fly, as they have to be carried open and raised in front of the true wings. Beetles are therefore generally not strong fliers.


Weevils are beetles too! They belong to the largest animal family known - the Curculionidae, and are generally recognisable by there long �nose� or �snout� called a rostrum, complete with a strange sent of articulated antennae. They also have a very hard and often spiky outer covering. Weevil larvae are different from the young stage of other beetles in having no legs. Over 3,000 Australian weevil species are known, from a world total of over 60,000.


Pea Weevil Bruchus pisorum, (not a true weevil). It only reproduces if eggs are laid on green pods in the field (ie not a pest of stored grain). Adults hibernate in autumn and winter in sheltered spots such as under bark or in cracks in fence posts. They resume their activities when temperatures rise to 18 degrees. Adults feed on pollen for 3 - 10 days before laying eggs and can fly for at least five kilometres to search for pea crops. Single eggs are visible on the exterior of green pods in spring, as the flower starts to wither. They are yellow and cigar-shaped (about 0.6 mm x 1.5 mm). Larvae hatch after about 14 days and bore into the pod, and then into the seed, where they feed for about 40 days. The larvae then chew their way out of the seed to pupate for two weeks.

Sitona weevil Sitona discoideus, a pest of annual medics and lucerne. The adult weevil is dark grey-brown and about 5 mm long, with three white stripes on the thorax. They emerge in mid spring to feed and become inactive in summer, when they shelter in cracks in soil, under bark or under the base leaf of plants. They start to feed again in autumn and mature in April. Egg laying can continue through the winter if food sources are available. The white-cream larvae (about 4 mm long) live just under the soil surface and pupate in the soil.

They adults produce characteristic scalloping marks on the leaf margins on annual medic or lucerne. Larvae will feed on nodules and may reduce nitrogen production.

Vegetable weevil Listrodere obliquus, a pest of cruciferous plants , especially cabbage and turnip; also celery, potatoes, tomatoes, lettuce, silver beet, spinach and winter flowers. Larvae feed on marshmallow and capeweed. Adults are about 9 mm long and greyish-brown. Larvae grow to 12 mm and are creamy in colour, turning green as they mature. They shelter in the ground during the day and emerge to feed at night. Adults are inactive in the soil over summer and lay eggs in late autumn. the larvae feed over winter and pupate in early spring.

Blackheaded Pasture Cockchafer Aphodius tasmaniae, a pest of pastures and lawns. Adult beetles are 8-12 mm in length and dark brown or black. They emerge from the pupae in the ground from January to March, usually at dusk and two or three days after rain. If conditions are favourable (warm and humid) they will swarm and fly off to new areas. If conditions are too cool they will mate immediately and burrow into the soil to lay eggs.

Because they burrow, they tend to avoid both very sandy and heavy clay soils. Adults feed on dung and prefer horse, cattle and sheep manure. If they can find food they will lay several batches of eggs.

The larvae are creamy to yellow with a dark brown head. They are susceptible to drying out and many die in the soil during drought, therefore they have a high egg production, laying 25 - 40 in the first batch and 15 -20 in a second laying, if conditions are favourable.

The young larvae dig vertical tunnels and feed on organic matter for about three weeks before moulting. The second instar will eat organic matter but is also capable of eating pasture top growth. The third instar have blue-grey bodies and a brown or black head. Each instar deepens and widens the tunnels until they are ready to pupate in the spring.

Redheaded Pasture Cockchafer Adorphorus coulone, a pest of subterranean clover and native pasture grasses. Adults are about 12 mm long by 8 mm wide. They fly during the period September - October in south - east Australia. and deposit eggs (one at a time) in the soil. The larvae feed on organic matter until April, May or June, when they become dormant. They resume feeding in the spring, when they are also capable of taking plant roots. In early summer they burrow deeper into the soil and pupate. When the adults emerge, they will lie dormant in the soil until the following spring.

African black beetle or Lawn beetle Heteronychus arator, a pest of lawns, maize, tomato, and other vegetables and grasses.

Shiny black adults are oval in shape and 12 mm long. Grey-white eggs are laid in soft soil in the spring. Larvae are white with a brown head, to 25 mm long and can be seen curled up in soil. Adults emerge from the pupae in mid summer - early autumn, and become dormant as the weather cools.

Elateroidea is a large family containing click beetles and wireworms. They can effect root crops, including onions or a variety of tubers, including flowering ornamentals. The adult click beetle makes a very loud clicking sound when disturbed. It is elongated, usually dark brown of black and flies into the house on summer evenings, or lone click beetle will be found crawling on the floor of around window sills.

Treating beetle pests

Beetle are difficult to destroy because of their hard outer covering. They are often nocturnal and may live for a large part of their life cycle hidden under the soil or under bark. Remember that many beetles are beneficial and may play a useful role in the farm or garden.

Use any knowledge you have of their life cycle or habits in order to control them. For instance lawn beetles live mostly underground. They still require oxygen underground. Changing the setting on the irrigation, so that they are flooded out over night, will force them to the surface in search of air, where they easily fall prey to the early birds. This technique may also work with beetle pests of potatoes or other tubers.

Beetle damage will often be seasonal, and the lawn (or crop) may recover without problems , so the concept of a �damage threshold� should be applied before considering using an insecticide.

Population numbers may also be limited by good rotation practice. Some beetles which damage underground parts can be lured away from crops with a decoy planting of mustard.

If they have to be sprayed, beetles may succumb to pyrethrum or derris

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