PestFacts WA

Australian plague locust: spring hatchings are predicted

An adult Australian plague locust. Photo courtesy of: DPIRD.

Australian plague locusts (APL) were active across grain growing areas of WA in autumn. The highest number of APL reports came in from the northern agricultural region, especially from the Beacon and Bonnie Rock. This APL activity is shown on DPIRD’s PestFax map below.

The PestFax map displaying Australian plague locust reports received over the past 8 months. Current to 19 August 2021. Map courtesy of: DPIRD.

Properties that had APL in autumn are most at risk of APL hatching this spring.

Predicted hatchings

An Australian plague locust egg bed. Photo courtesy of: DPIRD.

Adult APL had sufficient fat scores in autumn to lay a full complement of eggs in the WA grainbelt. High numbers of eggs can be laid in a small area, known as an egg bed, which is usually found on hard bare ground in soil that has not been cultivated, such as along fencelines and entrances to paddocks. 

Eggs laid in autumn undergo diapause and hatch as temperatures warm. Over-wintering eggs do not need spring rains to hatch.

Egg beds that have been underwater can have high mortalities. However, egg beds that have been waterlogged have been observed to hatch.

Entomologist Svetlana Micic (DPIRD) has run a model to determine the predicted hatching dates for APL eggs laid in mid-April. Hatching is predicted to start from mid-August in the northern agricultural region and in mid-September in the southern region of WA. For more information see the table below.

Thresholds

Pastures

Hoppers are the immature stage of APL. Hoppers take 6-8 weeks to become adults.

Hoppers and locusts can cause considerable damage to pastures. For example, 20 hoppers per square metre eat the equivalent of three sheep per hectare each day.

APL will feed on green pastures and pastures that have begun drying off. Control is considered economic if:

• Hopper densities exceed 20 per square metre and if the feeding value of pastures is equivalent to the cost of replacement feed for livestock.
• There are more than 10 APL adults per square metre.

Pastures that have completely dried off are not favoured by APL. APL and hoppers tend to move to adjacent green vegetation, such as tree lines and crops, at this stage.

Crops

Cereal crops are most susceptible to damage. Fortunately, established green crops tend to be avoided by hoppers but the edges of crops can be damaged.

Crops are most at risk when they are beginning to dry off and APL reach the flying growth stage.

The following crop stages are considered to be low risk for APL damage:

• Canola after leaf drop
• Lupins at pod bronzing
• Pulses at pod yellowing
• Completely dried off cereals.

Desiccated crops are not attractive to flying APL.

Effective control

To achieve effective control, the best time to apply an insecticide is when locusts are at the hopper stage and the majority are at the third and fourth growth stages (ie 1 to 1.3 cm long,  when the wing buds are as long as the collar on the back of the head (thorax).

For insecticide information, visit the department’s Australian plague locust control: registered insecticides.

Identification

Adult Australian plague locusts (left and centre). Note the dark spot on the wing and red coloured inner hind legs. Both adults and hoppers have a distinctive cross on the thorax (arrow indicates x-shaped marking; right). Photos courtesy of: DPIRD.

Hoppers and locusts can be easily confused with other native grasshoppers. Some grasshopper species have staggered hatchings, overlapping generations, hatch earlier than APL, and are present all year round. Grasshoppers, such as the wingless grasshopper, have more control options than APL, and other species, such as the spur-throated grasshopper, is not readily controlled by the application of synthetic pyrethroids which is registered for APL.  For tips on identifying APL, refer to DPIRD’s Australian plague locust: identification field guide. 

More APL information can be found at the department’s Diagnosing locusts and grasshoppers in crops and Australian plague locust: overview pages.

To read about previous APL activity this season, refer to DPIRD’s 2021 PestFax Issue 5 article Locusts are still on the move and Issue 1 article Locusts can damage emerging crops.

For more information contact Research scientist Svetlana Micic, Albany on +61 (0)8 9892 8591.

Article author: Svetlana Micic (DPIRD Albany).