The Senegalese grasshopper (''Oedaleus senegalensis'') is a medium-sized

grasshopper Grasshoppers are a group of insects belonging to the suborder Caelifera. They are amongst what are possibly the most ancient living groups of chewing herbivorous insects, dating back to the early Triassic around 250 million years ago. Grassh ...

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

found in the

Sahel The Sahel region (; ), or Sahelian acacia savanna, is a Biogeography, biogeographical region in Africa. It is the Ecotone, transition zone between the more humid Sudanian savannas to its south and the drier Sahara to the north. The Sahel has a ...

region of

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

, the

Canary Islands The Canary Islands (; ) or Canaries are an archipelago in the Atlantic Ocean and the southernmost Autonomous communities of Spain, Autonomous Community of Spain. They are located in the northwest of Africa, with the closest point to the cont ...

Cape Verde Islands Cape Verde or Cabo Verde, officially the Republic of Cabo Verde, is an island country and archipelagic state of West Africa in the central Atlantic Ocean, consisting of ten volcanic islands with a combined land area of about . These islands ...

, and

West Asia West Asia (also called Western Asia or Southwest Asia) is the westernmost region of Asia. As defined by most academics, UN bodies and other institutions, the subregion consists of Anatolia, the Arabian Peninsula, Iran, Mesopotamia, the Armenian ...

. Although not called a

locust Locusts (derived from the Latin ''locusta'', locust or lobster) are various species of short-horned grasshoppers in the family Acrididae that have a swarming phase. These insects are usually solitary, but under certain circumstances they b ...

in English, this species shows gregarious behaviour and some morphological change (phase polymorphism) on crowding. In many parts of the Sahel, this species may cause greater year-on-year crop damage than better-known locusts, attacking crops such as the

pearl millet Pearl millet (''Cenchrus americanus'', commonly known as the synonym ''Pennisetum glaucum'') is the most widely grown type of millet. It has been grown in Africa and the Indian subcontinent since prehistoric times. The center of diversity, and ...

.Maiga, I. H., M. Lecoq, and C. Kooyman. 2008. Ecology and management of the Senegalese grasshopper, Oedaleus senegalensis (Krauss 1877) (Orthoptera: Acrididae) in West Africa: review and prospects. Annales Societe Entomologique de France 44: 271–288.

Description

Adults

The basic colour of adult insects is a mixture of light beige and brown, but if they have grown up in green vegetation, a large proportion has varying degrees of green colouration, especially on the

head A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple ani ...

, pronotum, and femora. The pronotum is tectiform, with an hour glass-shaped pattern on the dorsum. The

wing A wing is a type of fin that produces both Lift (force), lift and drag while moving through air. Wings are defined by two shape characteristics, an airfoil section and a planform (aeronautics), planform. Wing efficiency is expressed as lift-to-d ...

s extend clearly beyond the

abdomen The abdomen (colloquially called the gut, belly, tummy, midriff, tucky, or stomach) is the front part of the torso between the thorax (chest) and pelvis in humans and in other vertebrates. The area occupied by the abdomen is called the abdominal ...

, the hind wings bearing a black, curved bar running from the front to the back with only a very slight interruption. This is the easiest character distinguishing this species from related ones found in the same distribution area. The bar of '' O. nigeriensis'' has a large gap in the middle, while the one of '' O. johnstoni'' is only present on the posterior part of the wing.

Nymphs

The colour of immature insects or

nymph A nymph (; ; sometimes spelled nymphe) is a minor female nature deity in ancient Greek folklore. Distinct from other Greek goddesses, nymphs are generally regarded as personifications of nature; they are typically tied to a specific place, land ...

s is largely the same as that of the adults with green being predominant in green vegetation. Under crowded conditions, the nymphs develop increasingly extensive black markings. They can even form hopper bands like locusts, but these bands are not as cohesive as those of real locusts.

Biology

This grasshopper is essentially graminivore. It consumes a fairly wide variety of

grass Poaceae ( ), also called Gramineae ( ), is a large and nearly ubiquitous family (biology), family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos, the grasses of natural grassland and spe ...

es, but in the Sahel, it has a preference for cram-cram ('' Cenchrus biflorus''). It generally attacks cereals, especially

millet Millets () are a highly varied group of small-seeded grasses, widely grown around the world as cereal crops or grains for fodder and human food. Most millets belong to the tribe Paniceae. Millets are important crops in the Semi-arid climate, ...

and

maize Maize (; ''Zea mays''), also known as corn in North American English, is a tall stout grass that produces cereal grain. It was domesticated by indigenous peoples in southern Mexico about 9,000 years ago from wild teosinte. Native American ...

. Adults like to eat the soft unripe grains. Grasses with a high

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...

content are avoided. This species generally has three generations per year during the rainy season, but evidence for the occasional fourth generation has been found during years of exceptionally longs rains. A number of adults of the first and second generations migrate north following the

Intertropical Convergence Zone The Intertropical Convergence Zone (ITCZ , or ICZ), known by sailors as the doldrums or the calms because of its monotonous windless weather, is the area where the northeast and the southeast trade winds converge. It encircles Earth near the t ...

. The adults of the third generation follow the zone on their way back to the south. At that time, populations have often greatly increased leading to the southward migration of huge numbers of grasshoppers, often at the time that millet is ripening in the fields. These can then cause serious damage to the crop. Though the aggregation of grasshoppers around points of light at night might give the impression of swarms, Senegalese grasshoppers do not, in fact, form cohesive swarms as locusts do.

Egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the ...

s are laid in sandy soil in small packets of about 20–40 eggs called egg pods. Practically all eggs laid by the first and second generations hatch during the same season, usually within two weeks. However, most eggs of the third generation enter into

diapause In animal dormancy, diapause is the delay in development in response to regular and recurring periods of adverse environmental conditions.Tauber, M.J., Tauber, C.A., Masaki, S. (1986) ''Seasonal Adaptations of Insects''. Oxford University Press It ...

and survive the long dry season as a partly developed

embryo An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...

. Within two weeks of the first substantive rain (≥10 mm), about 60% of the eggs hatch, with the remaining 40% hatching after subsequent showers. This is an obvious adaptation to the erratic rains in the Sahel. In some years, the first hoppers that emerge perish because of lack of subsequent rain.

Outbreaks and control

Outbreaks are frequent in Sahelian countries such as

Senegal Senegal, officially the Republic of Senegal, is the westernmost country in West Africa, situated on the Atlantic Ocean coastline. It borders Mauritania to Mauritania–Senegal border, the north, Mali to Mali–Senegal border, the east, Guinea t ...

Mauritania Mauritania, officially the Islamic Republic of Mauritania, is a sovereign country in Maghreb, Northwest Africa. It is bordered by the Atlantic Ocean to the west, Western Sahara to Mauritania–Western Sahara border, the north and northwest, ...

Burkina Faso Burkina Faso is a landlocked country in West Africa, bordered by Mali to the northwest, Niger to the northeast, Benin to the southeast, Togo and Ghana to the south, and Ivory Coast to the southwest. It covers an area of 274,223 km2 (105,87 ...

Mali Mali, officially the Republic of Mali, is a landlocked country in West Africa. It is the List of African countries by area, eighth-largest country in Africa, with an area of over . The country is bordered to the north by Algeria, to the east b ...

Niger Niger, officially the Republic of the Niger, is a landlocked country in West Africa. It is a unitary state Geography of Niger#Political geography, bordered by Libya to the Libya–Niger border, north-east, Chad to the Chad–Niger border, east ...

, and northern

Nigeria Nigeria, officially the Federal Republic of Nigeria, is a country in West Africa. It is situated between the Sahel to the north and the Gulf of Guinea in the Atlantic Ocean to the south. It covers an area of . With Demographics of Nigeria, ...

, especially during wet years following several dry ones. As with many locust species, outbreaks may be controlled with

insecticide Insecticides are pesticides used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. The major use of insecticides is in agriculture, but they are also used in home and garden settings, i ...

spray operations: usually at ULV rates of application and often via government or donor-aid sponsorship. A biological pesticide product called 'Green Muscle', which is based on an entomopathogenic fungus ('' Metarhizium acridum''), is now available (see

desert locust The desert locust (''Schistocerca gregaria'') is a species of locust, a periodically swarming, short-horned grasshopper in the family Acrididae. They are found primarily in the deserts and dry areas of northern and eastern Africa, Arabia, and ...

). Large-scale field tests on ''O. senegalensis'', by the LUBILOSA Programme in 1995-97, were amongst the first successful large-scale field tests using ''Metarhizium'' against acridoid pests.

Gallery

File:OSE_Niger.JPG, Brown colour phase File:Oedaleus senegalensis L3 female.jpg, Third instar female File:Oedaleus senegalensis L4 male.jpg, Fourth instar male File:Oedaleus senegalensis L5.jpg, Green fifth instar File:Oedaleus senegalensis L5 brown.jpg, Brown fifth instar

References

External links

AcridAfrica

Names in Dogon languages, with images from Mali
{{Authority control Oedipodinae Locusts Agricultural pest insects Insect pests of millets