Southern African desert locust (Schistocerca gregaria flaviventris)

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The southern African desert locust, Schistocerca gregaria flaviventris, is treated as a subspecies of the plague desert locust, Schistocerca gregaria gregaria, which ranges from North Africa through the Arabian Peninsula into Southwest Asia. The southern form is geographically isolated in Southern Africa, can hybridize with the northern form but produces sterile offspring, and only occasionally swarms. In these rare swarms, hoppers become gregarious and show the black–yellow pattern typical of northern phase gregaria, yet remain unusually sedentary, and adults from both swarming and low-density populations retain the characteristics of solitarious northern locusts.

Taxonomy

For full nomenclature and taxonomic details of this taxon, see Orthoptera Species File

Identification

The southern African desert locust Schistocerca gregaria flaviventris (Burmeister, 1838) is a subspecies within the Cyrtacanthacridinae subfamily, which includes many of the world's most destructive locusts. These grasshoppers are typically large-bodied and powerful fliers, though S. g. flaviventris rarely forms swarms or exhibits full phase polyphenism unlike its northern relative S. g. gregaria. Closely related species in the subfamily include the desert locust (Schistocerca gregaria) and the South American locust (Schistocerca cancellata), alongside other African pests like the brown locust (Locustana pardalina) and red locust (Nomadacris septemfasciata).

Morphologically, Cyrtacanthacridinae species are distinguished by the presence of a prosternal spine and robust hind femora adapted for jumping. Southern African desert locust adults are pale brown or grey with a head stripe, spotted front wings, and yellow hind-wing bases. Solitary hoppers are green; gregarious ones turn orange-brown striped or (in labs) black with yellow-orange marks. Although it is capable of expressing both solitary and gregarious phases, a fully developed gregarious swarming phase has not yet been documented under natural conditions.

Identification details

S. g. Flaviventris can be recognized by its small, sharp prosternal tubercle (throat spur), which is straight, blunt-tipped, and slightly directed backwards. Hoppers in the solitary phase are usually light green, whereas more gregarious, transient marching hoppers in the field are often more yellow and orange with black/brown stripes; under dense crowding in laboratory cages they turn black with striking yellow and orange markings, but it is unlikely that this form has been seen in the field.

Adult females are about 70–90 mm long and males 60–75 mm, with irregularly spotted forewings and semi-transparent hindwings that are yellow at the base. Solitary adults are light brown or pale grey with a pale longitudinal stripe from head to pronotum. Swarming adults seen in 1934 were reported as deep yellow, resembling swarming S. gregaria gregaria from North Africa.

Highlighted resources

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  Southern African Desert Locust fact sheet 2024PDF · 5 pages · 3.9 MB

Distribution

The solitary phase of S. g. flaviventris is widely distributed across the semi-arid and arid regions of Namibia, South Africa, Botswana, Angola, and the Ascension Islands. Outbreaks of S. g. flaviventris primarily occur in the Kalahari sand-dune areas of southeastern Namibia, southern Botswana, and South Africa's Northern Cape Province (Gordonia district), where they occasionally overlap with brown locust outbreaks and lead to misidentification. in Solitary adults are powerful fliers, occurring widely across the Nama Karoo and parts of the Succulent Karoo in the Northern and Western Cape Provinces, as well as in southern Namibia, where they may be abundant in some seasons. These solitary-phase adults migrate at night and may cover long distances on disturbed weather systems, and are occasionally encountered at lights in Karoo towns across the Northern Cape. This locust occurs less commonly across the Bushmanland and Nama-Karoo regions of the Northern Cape Province, though it can be abundant at times in croplands around Calvinia, Kenhardt, and Hopetown. Hopper bands are seldom observed beyond the core breeding zone in the Kalahari sand dune areas.

Biology

The southern African desert locust is a subspecies of the notorious plague desert locust, S. g. gregaria, which occupies a broad belt from North Africa through the Arabian Peninsula into southwest Asia, and is separated from the southern African form by the equatorial forest and woodland savanna zones. Experimental cage crosses have shown that it can hybridize with the true desert locust, but the resulting progeny are sterile. The behavior and body proportions of S. g. flaviventris differ markedly from those of S. g. gregaria, suggesting that the two populations have been isolated for a long period.

A study of S. g. flaviventris populations showed broad genetic and morphological uniformity across their range, despite lacking the phase polymorphism and swarming of northern S. g. gregaria. Genetic diversity is moderately lower than in the northern subspecies, but populations remain highly homogeneous, similar to northern patterns, likely due to seasonal migrations that track rainfall.

Morphometric analyses of forewing length, femur length, head capsule width, and derived ratios reveal significant differences between southern African (S. g. flaviventris) and northern (S. g. gregaria) desert locust populations. Southern locusts have smaller mean measurements and greater inter-population distances, with southern males and females more similar to each other than to northern forms; this suggests an evolutionary split that may justify recognizing them as distinct species.

Walloff and Pedgley reviewed the biogeography and biology of S. g. flaviventris, see their paper for more details.

In years with above-average summer rainfall S. g. flaviventris can complete two generations, yet adults are capable of persisting in very arid environments receiving less than 100 mm of rain annually. Females of S. g. flaviventris mature in spring and oviposit only in moist sandy soil following good rains, with two generations possible annually under optimal conditions.

Each S. g. flaviventris female produces 2–3 egg pods lifetime, with solitary-phase pods holding 95–158 eggs and transient/gregarious-phase pods fewer than 80. Eggs typically hatch in 14–27 days, varying with temperature and soil moisture. Eggs are sausage-shaped, about 7 mm long and 1.5 mm wide, laid in pods whose tops are sealed with a hardened frothy plug, and they dry out quickly in dry soil. Hoppers pass through five instars, lasting 60–80 days total before fledging. Adults overwinter in reproductive diapause. Nymphs are typically lethargic and can easily be collected by hand, though loose, transient-phase bands may occasionally be seen moving in loose formations along the dune “streets” between Kalahari sand dunes. Adults are most often encountered as solitary individuals.Solitary-phase adults are powerful fliers that migrate long distances at night during summer. in

Habitat and ecology

This locust favors native semi-arid plants such as Tribulus species ('dubbeltjies'), wild pumpkin, and tsama melon (Citrullus).

Few details exist on natural enemies of this desert locust subspecies, but predators of brown locust outbreaks (birds, meerkats, bat-eared foxes, jackals, scorpions, and lizards) likely prey on it as well.

Management

There is no formal monitoring program, but in South Africa plague locusts are classified as a notifiable national pest, so farmers and residents are expected to report hopper bands or newly fledged swarms to their nearest Agricultural Extension office. When such reports indicate a potential economic threat to rangeland or crops, dedicated locust control teams may be deployed. Localized infestations are managed by Department of Agriculture locust officers using the same methods employed against the brown locust, primarily ultra-low-volume synthetic pyrethroid insecticides applied with motorized knapsack or vehicle-mounted sprayer.

Pest status

This locust seldom forms swarms, with just two major outbreaks documented (1934–35 and 1948–49). Localized transient-phase hopper bands needing chemical control emerge roughly once every ten years following good rains in the Northern Cape and southeastern Namibia’s Kalahari sand-dune areas, where they are mainly regarded as a curiosity.

Migrating adult swarms have historically invaded irrigated farmlands along the Orange River, damaging crops including citrus, cotton, tobacco, vines, and vegetables.

Outbreaks

Outbreaks of the southern African desert locust are generally treated as curiosities, and broad chemical control has seldom been used, with only two major campaigns recorded in 1934–35 and 1948. in Transient-phase hopper bands form sporadically (once or twice per decade) after good rains in the Kalahari sand-dune region. Rare adult swarms stay low to the ground in loose formations and avoid long flights. in

In 1934, around 100 groups of young adults were controlled in southern Namibia, with some invading South Africa that winter and damaging citrus and other crops. Small swarms were later noted at Calvinia and even Worcester in late 1934, while hopper bands were treated in Calvinia, Kenhardt, and Prieska areas in 1935. in

In 1948, 469 early hopper bands and 4 swarm groups were controlled from March to April. Hopper bands were treated again in 1951 and 1964 , along with bands and at least 25 fledgling groups from February to April 1994 (Department of Agriculture: Directorate Resource Conservation locust control records). in

In 2011, solitary adult aggregations were reported from a Calvinia district farm, far from core breeding areas, but no control action was taken. South Africa's National Department of Agriculture (Directorate: Climate Change and Disaster Management) holds no desert locust control records for the past 10–15 years. Hopper bands and small swarms have been chemically controlled during outbreaks in Namibia's Aroab, Karasburg, and Warmbath areas (eastern Karas region), with additional outbreaks noted westward at Aus (Luderitz District) and western Karasburg near the Namib Desert edge.

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