Red locust
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| Nomadacris septemfasciata Audinet-Serville, 1883 |
The red locust is a large species found south of the Sahara in Africa. Outbreak areas have been identified in Zambia, Tanzania, Malawi and also Madagascar and Reunion. In the Sahel, the species is observed on a more incidental basis in Cape Verde, the central Niger River delta in Mali and around Lake Chad.
This locust is sometimes called the Criquet nomade in French, due to its nomadic dry season movements, and the Red Locust (Criquet rouge in French) in reference to the colour of its hindwings.
Nomadacris septemfasciata shares the subfamily Cyrtacanthacridinae with other locusts, e.g. the desert locust (Schistocerca gregaria (Forskål, 1775)), the tree locust (Anacridium melanorhodon (Walker, 1870)) and the bird locust (Ornithacris cavroisi (Finot, 1907)) for which it is often mistaken.
Moisture is a crucial factor for red locusts. They actively seek moist environments in seasonal flood plains with large grassy lowlands and some tree cover of Acacia farnesiana or Mangifera indica to satisfy their semi-arboreal behaviour. They are generally graminivorous. Their biotopes are mixed herbaceous formations with Hyparrhenia, Echinochloa and Cyperus in the upper stratum and Cynodon etc. in the lower stratum. In farming zones, they often colonize mesohygrotrophic grain crops, especially when the fields are hedged in with bush and when waste and fallow lands are interlaced between the fields. Red locusts become sedentary when shelter, perches and food are available.
N. septemfasciata produces one generation yearly, with an imaginal diapause period triggered by reduced daylength in the dry season. Sexual maturity and egg laying are achieved over quite a long period at the beginning of the rainy season, resulting in staggered hatching. The eggs incubate for about one month and hoppers take two months to complete their moulting. There are 6 - 8 instars depending on the sex and phasal state of the individual. Emerging imagos remain immature until the following rainy season.
Gregarious capabilities are less pronounced in red locusts than in desert locusts and migratory locusts. Outbreak areas are reactivated during dry years in response to the reduced colonizable surface area available to this hygromesophilic locust, thus increasing population densities to above the critical phase transformation threshold. In invasion years, swarms can be distributed over a few hectares and up to hundreds of km². The locusts fly quite slowly with the wind during daylight hours when air temperatures are above 26°C. They never move more than 20 - 30 km per day. Mature swarms then break up before egg laying, which often occurs at night with eggs being laid in moist sandy-clayey soil. Females congregate in limited areas and lay 70 - 90 eggs/pod. Hatched bands of young hoppers are then capable of travelling hundreds of metres daily in open areas. The imagos remain grouped thus binding the swarms.
Compared to solitarious forms, gregarious red locusts do not live as long, they develop through 6 instars rather than 7 and sexual maturation takes longer. Gregarious females lay fewer eggs and less frequently, but the emerging hoppers are larger and heavier. Gregarious red locusts have more markings than the solitarious forms.
Almost all of southern Africa was invaded during the last great widespread plague (1930-1944). Mesohygrotrophic crops cultivated in breeding biotopes were often attacked: maize, rice, sugarcane, fruits, wild herbaceous species and trees such as acacias, eucalyptus and pines. Ecological control was attempted in central Africa, involving environmental modification of outbreak areas, but the project was unsuccessful. Chemical control is currently being used. Research should now be directed towards improving spraying techniques and selecting better acridicides. A biological product based on a pathogenic fungus is now available (see desert locust). It has been successfully tested on both nymphs and adults of the red locust.
The red locust is easily identified by its typical body colour. The overall colour is a mixture of light beige and brown. It is never green. There are seven clear transversal brown bands on the elytra (thus explaining its species name "septemfasciata") and its hindwings are red at their base. There are two typical wide lateral brown bands on the pronotum.
The hoppers can also be recognized by their colouring, but there is a broad range of phase-related colour differences. Solitary hoppers can be green or brown and gregarious hoppers are bright yellow and red-brown with black markings.
[edit] General morphology
- Size
males 60 - 70 mm long, females 60 - 85 mm long,
- Overall body colour
The species is easily identified by its overall colour which is a mixture of light beige and brown. There is no green form. There are 7 clearly distinguishable transversal brown bands on the elytra. The hindwings are reddish basally. There are 2 characteristic wide lateral brown bands on the pronotum. Gregarious locusts become dark red with age. Solitary hoppers are an overall green or brown and they are solid red-brown, yellow and black in the gregarious phase.
