Plague Locusts - Information Sheet

The Australian plague locust is a native Australian insect that occurs naturally in the Channel Country of Queensland. Australian plague locusts have high rates of reproduction if conditions during spring, summer or autumn are suitable. A single female can produce between 100 and 200 eggs but many of these do not develop into adults because of the high mortality rate when in the first stages of life. Locusts are formidable eating machines that can rapidly damage pasture and crops. Immature locusts, commonly called hoppers, generally feed on pasture and developing (green) cereal crops. Controlling Locusts Locust control is the responsibility of the land manager on public land and roadsides, and landholders on private property. Hoppers are wingless and can move as a ‘band’ or group. This makes it easier to spray them with insecticides using standard farm spraying equipment. ‘No spray’ intervals between spraying chemicals on crops should be observed. Ground spraying is not effective when adult locusts fly. During the daytime locusts may fly at heights of three metres or more above the ground. Aerial spraying is a more effective means of control at this stage. In specific circumstances, the Victorian Government may undertake control activities on public and private land, but only with permission from landholders. Aerial spraying is not possible in many parts of Victoria because buffer zones are required to prevent off-target spraying of crops, livestock, houses, schools and waterways. The Australian Plague Locust Commission (APLC) has a mandate to minimise the risk of movement of plague locusts across state borders. The APLC has responsibility within the far north west of Victoria, and may undertake control in situations where movement of locusts into either South Australia or New South Wales could occur. Victoria invests $350,000 a year to support the APLC’s preventative controls. Since the APLC was formed in 1974, Victoria has invested more than $5 million on behalf of Victorian farmers. What Causes a Locust Plague The timing and quantity of rainfall is critical. Plagues occur when wide areas of inland Australia receive good rainfall, which stimulates grass growth (a food source and ideal breeding ground) through spring, summer or autumn. These conditions can support three to four generations of locusts, with each generation’s population increasing up to 10 times. Plague levels can be reached within a year. Lifecycle of a Locust Eggs Females drill holes in soil and lay eggs. Each female can lay 30-50 eggs in a batch and may lay several batches. Most eggs generally survive over winter, even in extreme conditions.

Australian Plague Locust Locust Eggs in an egg nest A dense swarm of locusts

Eggs resume their development midway through winter and hatch in spring, as wingless two millimetre long nymphs or ‘hoppers’. They get bigger through five growth stages (instars) and may group into ‘bands’ when in high density. Infestations of bands can cover areas of a few square metres to several hundred square kilometres. Up to 7,000 nymphs can populate one square metre.

Adults Developing from egg to adult takes six to eight weeks, depending on the time of year. Cool weather will slow maturity. Adults grow and fatten over about another week if green feed is available. Adults may fly individually or in small groups at heights of up to three metres during the daytime. Swarm Flights Day flights Swarms are low flying and during the day can fly 5-20 kilometres in suitable conditions, in their search for green vegetation. Night flights Sometimes whole swarms will migrate up to 700 kilometres at night. This usually occurs in strong warm winds associated with fronts or low pressure systems. Night flights usually only occur when surface temperature is more than 25 degrees. Night flight swarms may fly at a height of up to 3,000 metres. Food Hoppers and adults need fresh green vegetation to survive, develop eggs and fatten to fuel long night flights.

Image courtesy of the Australian Plague Locust Commission

Crop and Plant Damage

Adult swarms can cause severe damage to crops, especially if crops are greener than surrounding pasture.

Grain crops which are green just below the seed head are at risk. Locusts often chew through this and drop the seed head, ruining the crop. Locusts can eat dry grain crops but prefer grasses.

Young vegetables can be completely destroyed. Also, grape vines can be stripped of leaves causing grapes to drop.