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Beware: Locusts are not the docile-looking grasshoppers we see in our gardens

The South African government spends millions of rands to control the infestations of the brown locust annually with many initiatives reporting successes in limiting true swarming phases. Picture: Nicolas Lindsay/UnSplash

The South African government spends millions of rands to control the infestations of the brown locust annually with many initiatives reporting successes in limiting true swarming phases. Picture: Nicolas Lindsay/UnSplash

Published Apr 28, 2022

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Durban - Swarms of locusts continue to wreak havoc in parts of the Western Cape province, with some regions experiencing severe drought, exacerbating the already dire situation.

Experts are calling for an urgent intervention to prevent possible short-term food insecurity.

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The Western Cape Department of Agriculture said swarms within the province were dominant in three districts, but mostly affecting areas such as Calitzdorp, Ladismith and Oudtshoorn, putting pressure on farmers and agricultural groups.

What are locusts and where did they come from?

These are not the docile-looking grasshoppers we see in our gardens. Locusts are grasshoppers that are able to exist in two phases, a solitary and a gregarious phase.

The gregarious (sociable) phase lives in swarms, are able to migrate over large areas and may even darken the sky in this stage.

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The brown locust is an agricultural pest in southern Africa, with populations reaching plague proportions as seen in the Western Cape currently.

It is known to cause significant damage to crops and pastures in parts of southern Africa, including Namibia, Botswana, Zimbabwe and South Africa, where the main outbreaks area are in the semi-arid Karoo region

According to the South African National Biodiversity Institute, the brown locust is a medium-sized insect characterised by classic gregarious behaviour with a discontinuous genetic variation resulting in the occurrence of several different forms on crowding.

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This basically means that locusts change their appearance and become ravenous when within close proximity to large numbers of their own species, forming destructive swarms.

The two known forms of the brown locust include the gregaria or migratory form, which is the larger form with a body length of 41 to 51 mm, changing colour from yellowish grey to yellow when sexually mature. The solitary form is smaller with a body length of about 26 to 36 mm. Adults are green, mottled with brown and black.

The mature locust has four wings, six legs with the hind pair large and strong, and modified for jumping. It has two large eyes on the sides of its head, and three tiny bead-like eyes on the front of the head. The female has four hard, horny points on the end of the abdomen, while the male has smooth, round tips on his abdomen, with a pair of very small feelers on it.

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Grasshoppers usually move by walking or jumping, but most adults fly. Their adaptations for movement include strong fore-wings and hind legs.

Brown locusts have a rather peculiar way of flying, they almost always soar upwards and then dip and swerve before settling down, a sort of evasive manoeuvre, if you will.

The male locust makes a chirping sound by rubbing its hind legs against its wings, very much like a cricket.

The brown locust is native to the semi-arid Karoo, which includes parts of South Africa and Namibia but, due to their ability to travel long distances when swarming, they have been known to frequent most parts of Southern Africa.

Brown locusts live in areas with shorter grass, bare ground for basking in the sun and enough moist soil in which to lay eggs.

One of the favourite breeding spots for brown locusts, according to SANBI, are the south-western corners of the Free State where the rainfall is slight and the veld consists of short grass mixed with short Karoo bush.

The solitary grasshoppers are found in the veld where there is an outcrop of white limestone in the red sand. The brown locust feeds mainly on grasses.

When rains are good, the brown locust can produce up to three generations in a single season, laying up to 160 eggs at a time which hatch within 10 to 20 days.

The fully gregarious adult brown hoppers are extremely active, flying both day and night and laying eggs in vast egg beds, which may hatch to cause major swarms.

True solitary forms of the brown locust are relatively sedentary and only undertake night flights. They do not form swarms and are thought to only lay diapause eggs.

These eggs accumulate on the soil in a stage of dormancy and only hatch after adequate rainfall, causing unexpected swarms. Another super interesting quality is that the eggs are able to survive repeated unexpected dehydration and rehydration.

The species is one of the known agricultural pests in South Africa, attacking mainly cereals and pastures.

The South African government spends millions of rands to control the infestations of the brown locust annually, with many initiatives reporting successes in limiting true swarming phases.

In South Africa, strides have been made in controlling the outbreaks of these locusts.

However, there is a lack of research on the impacts of the application of insecticides to human health and livestock, as well as risks to the environment in terms of pollution and ecosystem benefits in terrestrial as well as aquatic ecosystems.

For example, a 1998 study reported that non-target grasshopper populations decreased following the application of chemicals used for brown locust control in the Karoo.

The brown locust is an amazing survivalist that would give even Bear Grylls a run for his money. They can withstand the arid conditions of the Karoo by using a number of cool strategies.

The eggs have an impermeable cuticle, are drought resistant and may live in the soil for about three years. These eggs only hatch when the moisture content of the soil is suitable. Once diapause is completed eggs, may enter a stage of dormancy, which can last for several years.

Why do these grasshoppers swarm?

The gregarious phase in locusts is a strategy born out of desperation and driven by hunger, and swarming is a response to find new pastures for feeding.

Additionally, the gregarious locusts are reported to have high levels of serotonin in their bodies, which regulates moods and social behaviour, appetite and digestion, sleep, memory, sexual desire and depression in humans.

Grasshoppers and locusts are both components of healthy and disturbed grassland ecosystems. They are known to stimulate plant growth, participate in nutrient cycling and play an important role in food chains. Some grasshoppers are proposed as ecological indicators of ecosystem quality and efficacy of ecological networks.

Plagues of locust outbreaks date back to biblical times. In Africa, locusts form part of the human and livestock diet. Sheep grazing creates shorter and sparser grasses preferable for brown locusts and this in turn promotes outbreaks, very much like the ones we’re seeing engulfing the fields and pastures of the Western Cape.

Although South Africa has succeeded in managing the locust outbreaks in the past, the challenge lies in the changing climate, which might promote outbreaks.

SANBI believes that the country would benefit greatly from detailed studies focusing on understanding the impact of land use change, climate change and other global change challenges in relation to brown locust.

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Related Topics:

Climate Change

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