The recent heavy rains in Australia have been hailed as a Godsend, providing much needed water and nourishing our plants and wildlife. But with these blessings comes a plague – the locust explosions. Neda Vanovac reports.

The locust plague descends. Image: Australian Plague Locust Commission

As one of the ten plagues of Egypt, locusts have struck fear into the hearts of landholders since biblical times and beyond.

“They can come in late in the afternoon and demolish your paddock overnight, and fly away the next morning,” says Charles Armstrong, head of the NSW Farmers Association.

But what exactly are these creatures and where does their power to devastate swathes of land come from? How are we preparing for the onslaught?

Rural regions in New South Wales are on an almost-constant plague locust alert, and warnings in early 2010 have been escalating with the fears that favourable weather conditions have aided the egg-laying and survival of these pests.

“A lot of country is in very good condition due to heavy rainfall. Locusts have responded very rapidly to that; they’ve been able to multiply,” says Chris Adriaansen, director of the Australian Plague Locust Commission (APLC). The APLC is responsible for strategically monitoring and managing locusts, and undertaking ground and aerial control of their numbers.

“We have a very large area that has a fairly sizeable population spread across it. Those locusts have been moving southwards over the past week or so and have been congregating in larger numbers at extreme ends of their habitats, where we’ve been seeing some fairly large swarms.”

According to the Department of Agriculture, Forestry and Fisheries’ online locust profile, rainfall between December and January has significantly improved pasture conditions in many areas of NSW, leading to a substantial increase in locust populations.

The Australian plague locust can reach plague proportions within a year if a sequence of widespread heavy rains occur in inland areas. This is particularly prevalent during summer as heavy rainfall allows the locusts to rapidly complete several generations of increase.

“Locusts have laid substantial numbers of eggs throughout the north west, central north, central west, Riverina and south western areas of the state. Many adult locusts have laid multiple times due to the excellent conditions,” according to the Department of Primary Industries’ March 2010 locust report.

Professor Steve Simpson, Laureate Fellow at the University of Sydney, has conducted extensive research into the swarming behaviours of locusts. Essentially two animals packed inside the same genome, Simpson says that environmental elements can turn locusts from solitary to gregarious, which shifts their entire behaviour and causes locusts to travel in plague-like proportions.

“When they’re born and live on their own; they’re shy solitary grasshoppers. But when they’re exposed to crowding then they quite quickly, within a matter of hours, flip into the gregarised form, which means they actually aggregate with one another. Having aggregated, if you get a critical number of them in a small area, when they’re juveniles they start to march collectively, and when they’re adults they’ll take off and fly.”

In their solitary condition, locusts are repelled from one another, Mr Simpson says.

“If they’re forced to come together, which happens when they’re either born in close proximity because the mothers laid eggs in a dense [quantity], or when the environment forces them together because, say, plants are rare and patchy, then they flip into this aggregative behaviour. … Close physical contact with one another stimulates a change in their nervous system that causes them to be attracted to one another.”

As locusts jostle against one another, they stimulate critical sense organs located in the hairs of their hind legs, which in turn releases the neurochemical serotonin into their central nervous system and causes the switch from solitary to gregarious.

“[Serotonin] acts upon their neural pathways and causes neural circuits to do different things. Instead of producing behaviour where they’re repelled by one another, they’re attracted,” says Simpson.

The Australian plague locust is one of three species of locust to be declared a pest under the Rural Lands Protection Act 1998, and is responsible for almost all of the locust damage in NSW.

Locust swarms in northwest NSW are extreme. Image: Australian Plague Locust Commission

The destructive potential that 2010’s plague of locusts could have is enormous. The APLC estimates that the 2004/2005 plague locust control program saved $20,000 worth of crops and pastures for each $1,000 spent in controlling locusts. In that period in excess of $1 billion worth of crops and pasture were saved during the locust control program.

“[Locusts can damage] fairly large amounts of both pastures and crops, particularly to grain crops. They eat the plant material. If you end up with locusts taking out a reasonable part of your crop, it could take years for that to recover,” says Mr Adriaansen.

Mr Armstrong from NSW Farmers Association, says that a plague “represents a complete loss of the seed, and diesel and time and general costs of putting the crops in.” He adds that there exists no insurance protection for farmers against these destructive pests.

Locust swarms can cover up to 50 km² at a time, doing widespread and severe damage to pasture, cereal crops such as wheat and oats, and to summer forage crops such as sorghum and lucerne.

According to the Department of Primary Industries website, locusts can migrate 500 to 600 km distances overnight which can lead to sudden infestations in areas that were previously unaffected.

The website says, “In closely settled districts, vegetables and even orchard trees can be badly damaged. Winter grain crops have usually hardened off by the time adult locusts are active in early summer. However, in dry weather less advanced and more open crops are highly susceptible to attack.”

Locusts are the swarming phase of short-horned grasshoppers, and can breed very rapidly, becoming migratory and travelling great distances, stripping and destroying large tracts of land.

The adult female locust is approximately 4 cm long and the male is usually about 3 cm long. Female locusts lay eggs in batches in the soil, each containing 30 to 60 eggs and one female may lay up to four batches. Autumn-laid eggs generally remain dormant through winter and resume development and hatch the following spring, which is the current situation in NSW.

Current locust numbers in the northwest are described in the report as extreme, with densities the highest seen in NSW for many years.

However, Mr Adriannsen says that the APLC are yet to refer to the numbers as a plague at this stage.

“What we have is a very large population spread out over a very large area. What will happen now is that these adults will lay eggs, those eggs will wait over winter and all hatch out in the spring. Provided that the conditions remain quite favourable as they are now, with the soil and vegetation, we will have a very large nymphal population come spring,” he says.

Almost all locust control is undertaken at the nymphal level, when locusts are young and not yet airborne.

Mr Adriaansen says that controlling the nymphs is easier than adults, as the young tend to congregate in larger concentrations.

“Because [adults are] spread out, by virtue of the fact that they need room to fly, then you will need to cover ten times the area, on average, to kill the same number of locusts. There are deficiencies associated with that, not least of which is the need to apply pesticides to a much larger area, which needless to say we prefer not to do. We prefer to be quite targeted in a direct application.”

The Department of Primary Industries’ report, notes that if ground control of locusts is unsuccessful, there will be an increasing number of locusts continually laying eggs over the winter which could result in a population explosion come spring.

The report predicts that once the adult locusts begin to fly, they will be very difficult, if not impossible to control.

Under the Rural Lands Protection Act 1998, landholders are required to report the presence of plague locusts to their local Livestock Health and Pest Authority, which provides them with insecticides to control locusts on their land.

“We [have done] quite a lot of aerial control,” says Mr Adriaansen.

“We use three different locust-control agents, one of which is a bio-pesticide, a naturally-occurring fungus that has been isolated from grasshoppers and locusts that we spray over the top of the locust nymphs, in addition to other standard pesticides for locust control.”

Swarms of locusts on the move are fiercely destructive.

Once locusts come together in large numbers they face a severe shortage of food. They require food with high protein sources, but often the nearest source of protein is other locusts.

“They’re cannibalistic,” says Mr Simpson.

“So when one moves nearby, they all move in parallel with their neighbours, because if they stop they’ll be attacked. They’re moving to get more food, but because the most available source of food might be the one in front, they all keep moving. They call it a forced march.”

For the farmers of NSW, Mr Armstrong says: “[They are] fairly vigilant, watching to find them, but sometimes [there is] a sense of hopelessness”.

Landholders are advised to report any and all locust activity and to cooperate in every way with their local Livestock Health and Pest Authority.