|Description of adult|
Adult M. dorsalis are large insects up to 50 mm in length from the head to the end of the wings. The body is orange -brown in colour and they have long sucking mouthparts (proboscis) held flush up under the body when at rest. They are known for the distinctive noise they make when they gather in large numbers. They should not be confused with locusts (grasshoppers) that swarm and have chewing mouthparts.
The eggs are laid in slits in the bark of small twigs and branches. After the eggs hatch the young nymphs emerge and fall to the ground. They burrow into the soil and attach themselves to plant roots where they suck sap and extract nutrients. The nymphs are similar in shape to adults but lack of wings. Their sucking mouthparts distinguish cicada nymphs from beetles which have chewing mouthparts. Their cast 'skins' are common on the lower trunks of trees.
The egg stage lasts for several months. The nymphs stay in the soil feeding on sap sucked from roots for one up to 17 years depending on the species of cicada. They emerge from the soil in early summer usually after 25 mm or more of rain and climb a metre or so up some object. The nymphal skin splits down the back and the adult emerges. Adults mate and lay eggs and live for only a few weeks.
Cicadas are found throughout Queensland.
The smaller branches of many trees including coffee and eucalyptus are used for oviposition. Macrotristria prefer to lay eggs on dead dry twigs and even dead weed stalks.
A minor and sporadic pest. Good agronomic management will overcome most symptoms.
The major damage goes unseen in the roots but sap removal can stress trees. Oviposition has only been observed on dead twigs.
Sprays should not be required.
Sometimes, high incidence of cicadas in coffee has been linked to overuse of pesticides indicating that biological control may be important. Ants have been known to eat cicada eggs and young nymphs before they enter the soil.
Control of adults may not be effective as re-infestation after spraying can be a problem where large numbers of adult cicadas occur in a district. The use of pesticides can also be counterproductive, destroying natural predators.
Chemical registrations and permits
Check the Australian Pesticides & Veterinary Medicines Authority chemical database and permit database for chemicals registered or approved under permit to treat this pest on the target crop in your State/location. Always read the label. Always observe withholding periods.