Australian Plague Locusts – What to look for when locusts are flying in Victoria
All Victorians are working hard to mitigate the locust threat but it won’t be possible to eradicate every locust; there will be adult locusts that survive and lay eggs or swarm, and some may be blown in from interstate.
Landholders need to remain vigilant and be ready to treat locust hoppers after they have hatched and before they can fly. The most effective and efficient time to treat is when they form dense bands on the ground.
It is critical that landholders continue to report where adult locusts are active or laying to help landholders and agencies target the next generation of newly hatched nymphs.
The following information will help landholders recognise what locust egg laying and swarm activity looks like and what to do if they should see adult locusts laying eggs on their property.
Recognising an Australian Plague Locust
The locust is similar in appearance to grasshoppers. It can be identified by the large dark spot on the tip of the hind wings and the distinctive red shanks on the hind leg. The body colour varies; it can be grey, brown or green. Male locusts are 25-30 mm long while females are 30-42 mm long.
Immature plague locusts are referred to as hoppers or nymphs. Their wings are not fully developed and the red colour of the hindleg shanks is less developed than in adults. This makes it hard to distinguish them from immature stages of other locusts and grasshoppers.
Locusts are also hard to spot when they first emerge as young immature locusts (called hoppers). They are only about 3mm long and pale in colour. Newly hatched locusts can cause considerable damage and can consume half their body weight in food per day.
Hoppers, which are wingless and unable to fly, move as a ‘band’ or group on the ground, with up to thousands of hoppers for every square metre of the band. Spraying with insecticides at this stage is very effective and can greatly reduce numbers.
Reporting Adult Locusts Laying Eggs
Once adult locusts reach maturity and can fly they will begin to lay eggs. Monitoring your property for egg laying activity will better prepare you for treating a second generation of locust hoppers on your land.
|Adult Australian Plague Locust laying egg pod in soil|
Recognising locusts laying eggs and locust egg beds
Egg beds are difficult to detect unless female locusts are observed during egg laying.
Locusts usually lay eggs on bare damp dirt. Female locusts may crowd together and lay large numbers of eggs in a patch of soil suitable for egg laying. These areas are referred to as egg beds. The eggs are buried below the surface.
Egg beds are most easily detected while the locusts are laying eggs. While female locusts are laying eggs and have their abdomen poked into the soil they do not disturb and fly away as rapidly as normal. After laying, the pod is sealed with a frothy plug to protect the eggs from desiccation.
|Adult locusts laying eggs will leave drill holes in the ground|
Each female lays pods of about 30 eggs, sometimes laying only one pod per life time. However they can lay up to five pods, with pods laid at five to seven day intervals.
The full extent of egg laying does not become apparent until the eggs begin hatching and the hoppers, which are more easily detected, emerge from the ground and become active.
Where to look
The ground where the eggs have been laid looks like a sieve with lots of shallow holes that are very close together.
Locust eggs are usually laid in barer areas that are exposed to sunlight and often along fence lines, headlands or roadsides.
Female locusts will often make test drill holes in the soil without laying any eggs. When looking for egg beds, care needs to be taken to ensure that sites where locusts have been test drilling are not mistaken as egg beds. In this case, the actual extent of egg laying can be over-estimated. A frothy plug at the entrance to the egg bed is one indication that it is not a test drill.
Landholders trying to identify locust egg beds should therefore dig up clods of soil where locusts are seen drilling, or where holes are evident and directly inspect the actual density of locust eggs in the soil.
|Landholders should dig up the suspected egg bed to check for locust eggs|
Within the short period after egg laying, the holes created during laying may fill with loose dirt from the surface very quickly removing all traces of egg laying within as little as two to three hours after the event.
When the adults are in low density, and in some other situations, egg laying may be scattered across an area.
What you can do
Landholders should mark the location of known egg beds on their land when they witness egg laying activity. Over time, the drilled holes which are an indicator of egg laying activity become less obvious (through erosion or vegetation cover).
It’s important that landholders with known egg beds are aware of these sites so they can return later to monitor hoppers hatching.
Also, to help to reduce future damage caused by locusts, landholders should report egg laying activity to the DPI Locust Hotline on 1300 135 559 so that DPI can monitor activity, inform landholders of the best time to act in their region, and respond in the most strategic way to the locust threat.
|Diagram of Australian Plague Locust lifecycle|
Egg development occurs only in warm moist conditions. Given sufficient moisture and at a daily maximum of 35°C, egg development takes just over two weeks, while with a daily maximum of 25°C, it takes over a month. Egg development does not take place below about 15°C. Eggs laid in late autumn usually enter a diapause state which allows them to over-winter and hatch when temperatures increase in spring.
From each egg, an immature locust emerges, called a nymph or more commonly a hopper. As the hoppers grow and develop, they pass through five, and in some circumstances six, stages of development called instars.
The hoppers moult between each instar to enable their body to expand. In mid summer, the hoppers take around 20-25 days to complete their development before maturing to become adult locusts that are capable of flight.
|The best time to treat locusts is at the 2nd or 3rd instar stage when locusts form dense bands on the ground|
Hopper development is very dependant on the weather and can be delayed by wet, cool conditions.
The most effective and efficient time to spray locusts is approximately two weeks after they hatch, when the hoppers form dense, concentrated bands on the ground.
The development period between eggs hatching to an adult locust with wings takes around 6-8 weeks, depending on the temperature. Higher temperatures speed up the development process. Over winter, eggs can lay dormant in the ground for some months, and subsequently hatch with the onset of warm weather.
However, the adults still need to grow and accumulate fat before they start to migrate. Fat is needed as fuel for long distant flights.
The adult locust usually goes through three stages of development
- growth during which the wing muscles are developed and the exoskeleton hardens
- fat accumulation
- oocyte (egg) development.
Landholders should consider walking around their property and undertake a thorough inspection as locust hoppers (immature locusts) may not be immediately visible from a moving vehicle.
Flying adult locusts and locust swarms
|Spraying adult locusts is considered an ineffective and inefficient use of chemical|
DPI doesn't recommend spraying flying, adult locusts as it is very difficult to do safely and effectively. They will often move away from ground based equipment and also recolonise an area after spraying.
In order to treat the same number of locusts, you would need to spray 10 to 20 times the area of swarms as you do of nymphal bands.
There are increased risks associated with swarm control due to the larger areas which need to be treated.
This can increase the potential impact to environmentally sensitive and off-target areas.
Individual landholders may make a business decision to spray flying locusts for the protection of valuable crops - but must obey withholding periods and follow directions on the label of chemicals used.
In gardens it may be more effective to use shade cloth or netting (which is not green in colour, as green attracts locusts) to stop locusts getting to plants or choose a household or garden insecticide. Small numbers of locusts in gardens are unlikely to cause significant damage.
Staying safe when driving through locusts
|Consider attaching an insect screen (not green in colour) to your external radiator air-inlet for extra protection|
Locusts can impair your vision by splattering and sticking to your windscreen, which is why it’s important to be prepared and have special cleaning agent and a cloth/brush on hand.
Also, car radiators can become blocked and overheat. Monitor the temperature gauge on your dashboard – dead locusts can reduce air flow to an engine and cause overheating.
For more information please read the Staying Safe When Driving Through Locusts fact sheet on the DPI website www.dpi.vic.gov.au/locusts, or contact the DPI Locust Hotline on 1300 135 559 for more advice.
[Consider attaching an insect screen (not green in colour) to your external radiator air-inlet for extra protection.]
Information on the locust situation and locust biology and management can be found at www.dpi.vic.gov.au/locusts
Report locust hatchings or contact the DPI Locust Hotline on 1300 13 5559