Australian plague locust

Current locust risk and outlook

Victoria

Report and prepare for locust activity

How locusts affect crops and communities

Locusts can feed on fresh green vegetation and cause significant damage to:

• pasture and crops
• horticultural crops
• home gardens
• parks
• sporting grounds.

Adult locusts

Adult Australian plague locusts can be identified by:

• a large dark spot on the tip of their hind wings
• distinctive red hind legs (Figure 1)
• body colour can vary from grey and brown to green (Figures 2, 3 and 4)
• adult males are typically 25 to 30 mm long.
• females are 30 to 45 mm long.

Figure 1: Red hind legs

Figure 2: Grey variant

Figure 3: Brown variant

Figure 4: Green variant

Grasshopper or locust?

Grasshoppers and locusts look similar, but they behave differently.

Grasshoppers are solitary insects. Locusts can gather in large numbers, form swarms and travel long distances in search of food.

While some native grasshopper species in Victoria can occur in large numbers, they rarely form organised groups or swarms.

Image credits

Figure 1, 2, 4: Michael Moerkerk, Agriculture Victoria, Horsham
Figure 3: Agriculture Victoria

Locust life cycle

After hatching, locusts pass through 5 juvenile growth stages (instars) before becoming adults. Young locusts are known as hoppers or nymphs.

Locusts generally mature within 2 weeks of becoming adult, depending on weather and food availability.  In favourable conditions, locusts can produce 2 to 3 generations in a single year.

Egg laying and egg beds

Female locusts lay eggs in pods 2 to 10 cm below the soil. Each pod contains 30 to 60 banana-shaped eggs and is sealed with a frothy plug that helps protect the eggs and retain moisture (Figure 5). A single female locust can lay 2 to 3 pods during her lifetime.

Egg-laying female locusts keep their abdomen firmly in the ground (Figure 6). They are hard to disturb and rarely fly away when approached.

Egg laying locusts are often found in large numbers in open, sunny areas. Low-level flight activity is also commonly seen nearby.

Thousands of female locusts can gather in one area to lay eggs, forming a large egg-laying site known as an egg bed.

Fresh egg beds often look like a sieve, with many holes on the soil surface (Figure 7). The holes can be quickly covered by soil, making egg beds difficult to find. Egg beds are easiest to locate if egg laying has been observed previously. Finding egg beds usually involves digging through soil clods. Marking known egg-laying sites can help with future monitoring and management.

Female locusts will often drill test holes before laying eggs to check whether the soil is suitable. As a result, not all holes contain eggs, and the size of an egg bed can sometimes be overestimated.

Figure 5: Egg pod

Figure 6: Female laying eggs

Figure 7: Egg bed

Egg development and hatching

Locust eggs need warmth and moisture to develop in the soil. Warmer temperatures speed up development. At a daily maximum temperature of 35°C, eggs can develop in just over 2 weeks. At 25°C, hatching can more than a month. Egg development stops when temperatures fall below 15°C.

In Victoria, locust eggs usually occur from spring to autumn. In favourable conditions, 2 to 3 generations can hatch during this period.

Eggs may hatch at once at the same time during warmer weather, or over several weeks during cool, damp conditions.

Hoppers and hopper bands

After hatching, locusts undergo 5 juvenile stages. Young locusts are known as hoppers or instars. Newly hatched hoppers are about 4 mm long. They are white when they first hatch but quickly change to pale brown, dark brown or black (Figure 8).

Thousands of young hoppers can emerge from an egg bed. They often remain close to the hatching site for several days before moving into nearby vegetation.

As hoppers grow, they can form large groups called bands. These bands may stretch for several kilometres and may be visible from the air. (Figure 9).

Hoppers in bands usually move in the same direction. The leading edge of a band can contain 1,000 to 5,000 hoppers per square metre.

Hopper bands can cause significant damage because they feed on vegetation as they move.

The best time to spray hoppers is when hoppers are in their second or third growth stage, about 2 weeks after hatching. Management is most effective when band densities reach or exceed 80 hoppers per square metre.

Once locusts develop wings and become adults, they become very hard to manage. During mid-summer, hoppers can develop into a mature adult in as little as 20 to 25 days, making early detection and management critical.

Figure 8: First instar hopper

Figure 9: Hopper band moving across field

Locust swarms

Adult locusts are highly social and band together to form swarms. When locust numbers are high, swarms travel up to 20 kms during the day. These flights usually occur in light winds and temperatures between 20°C and 35°C.

Swarms typically fly 3 to 20 metres above the ground and can appear to roll across the landscape.

Large swarms usually originate in Queensland and northern New South Wales and generally head south on hot northerly winds. Given favourable conditions, they can move through New South Wales and into northern Victoria.

Swarms are most likely to reach Victoria during late spring, summer and autumn. While they mainly affect northern Victoria, outbreaks can occasionally occur in southern parts of the state.

Image credits

Figure 5: Australian Plague Locust Commission (APLC)
Figure 6: Michael Moerkerk, Agriculture Victoria, Horsham
Figure 7, 8: Agriculture Victoria
Figure 9: Lyn Jacka, Agriculture Victoria, Mildura

Locust migration

Locusts can travel much greater distances during migration.

These flights occur at night and are carried by strong, warm winds associated with fronts or low-pressure systems. Locusts can travel up to 800 km and can fly at heights of up to 1,000 metres.

Migration can result in large numbers of locusts appearing in a new area overnight. While migration can contribute to outbreaks, it does not always lead to successful breeding if they land in a spot where conditions are unsuitable. There have been reports of locust swarms flying too far and landing in Bass Strait.