Senegalese grasshopper
Encyclopedia
Oedaleus senegalensis is a medium-sized grasshopper
species
found in the Sahel
region of Africa
, the Canary Islands
, Cape Verde Islands and West Asia. Although not called a locust
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.
, pronotum and femora
. The pronotum is tectiform, with an hour-glass shaped pattern on the dorsum
. The wing
s extend clearly beyond the abdomen
, 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.
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 the ones of real locusts.
. It consumes a fairly wide variety of grass
es, but in the Sahel, it has a preference for cram-cram (Cenchrus biflorus
). It generally attacks cereals, especially millet
and maize
. Grasses with a high silica content are avoided. Adults like to eat the soft unripe grains.
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
(ITCZ). The adults of the third generation follow the ITCZ on its 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 aggragation of grasshoppers around points of light at night might give the impression of swarms, Senegalese grasshoppers do not in fact form cohesive swarms like locusts do.
Egg
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
and survive the long dry season as a partly developed embryo
. 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.
ian countries such as Senegal
, Mauritania
, Burkina Faso
, Mali
, Niger
and Northern Nigeria
, especially during wet years following several dry ones.
As with many locust species, outbreaks may be controlled with insecticide
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
). 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.
Grasshopper
The grasshopper is an insect of the suborder Caelifera in the order Orthoptera. To distinguish it from bush crickets or katydids, it is sometimes referred to as the short-horned grasshopper...
species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
found in the Sahel
Sahel
The Sahel is the ecoclimatic and biogeographic zone of transition between the Sahara desert in the North and the Sudanian Savannas in the south.It stretches across the North African continent between the Atlantic Ocean and the Red Sea....
region of Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, the Canary Islands
Canary Islands
The Canary Islands , also known as the Canaries , is a Spanish archipelago located just off the northwest coast of mainland Africa, 100 km west of the border between Morocco and the Western Sahara. The Canaries are a Spanish autonomous community and an outermost region of the European Union...
, Cape Verde Islands and West Asia. Although not called a locust
Locust
Locusts are the swarming phase of short-horned grasshoppers of the family Acrididae. These are species that can breed rapidly under suitable conditions and subsequently become gregarious and migratory...
in English, this species shows gregarious behaviour and some morphological change (phase polymorphism
Polymorphism (biology)
Polymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...
) on crowding. In many parts of the Sahel, this species may cause greater year-on-year crop damage than better-known locusts.
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 will have varying degrees of green colouration, especially on the headHead
In anatomy, the head of an animal is the rostral part that usually comprises the brain, eyes, ears, nose and mouth . Some very simple animals may not have a head, but many bilaterally symmetric forms do....
, pronotum and femora
Arthropod leg
The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments are of Latin origin, and may be confused with terms for bones: coxa , trochanter , femur, tibia, tarsus, ischium, metatarsus, carpus, dactylus ,...
. The pronotum is tectiform, with an hour-glass shaped pattern on the dorsum
Dorsum (anatomy)
In anatomy, the dorsum is the upper side of animals that typically run, fly, or swim in a horizontal position, and the back side of animals that walk upright. In vertebrates the dorsum contains the backbone. The term dorsal refers to anatomical structures that are either situated toward or grow...
. The wing
Wing
A wing is an appendage with a surface that produces lift for flight or propulsion through the atmosphere, or through another gaseous or liquid fluid...
s extend clearly beyond the abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
, 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 nymphNymph
A nymph in Greek mythology is a female minor nature deity typically associated with a particular location or landform. Different from gods, nymphs are generally regarded as divine spirits who animate nature, and are usually depicted as beautiful, young nubile maidens who love to dance and sing;...
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 the ones of real locusts.
Biology
This grasshopper is essentially graminivoreGraminivore
In zoology, a graminivore is an herbivorous animal that feeds primarily on grass...
. It consumes a fairly wide variety of grass
Grass
Grasses, or more technically graminoids, are monocotyledonous, usually herbaceous plants with narrow leaves growing from the base. They include the "true grasses", of the Poaceae family, as well as the sedges and the rushes . The true grasses include cereals, bamboo and the grasses of lawns ...
es, but in the Sahel, it has a preference for cram-cram (Cenchrus biflorus
Cenchrus biflorus
Cenchrus biflorus is a species of annual grass in the Poaceae family. Common names include Indian sandbur, Bhurat or Bhurut in India, Haskaneet in Sudan, K 'arangiya in the Hausa language of Nigeria, and Ngibbi in the Kanuri language of Nigeria...
). It generally attacks cereals, especially millet
Millet
The millets are a group of small-seeded species of cereal crops or grains, widely grown around the world for food and fodder. They do not form a taxonomic group, but rather a functional or agronomic one. Their essential similarities are that they are small-seeded grasses grown in difficult...
and maize
Maize
Maize known in many English-speaking countries as corn or mielie/mealie, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Though technically a grain, maize kernels are used in cooking as a vegetable...
. Grasses with a high silica content are avoided. Adults like to eat the soft unripe grains.
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
Intertropical Convergence Zone
The Intertropical Convergence Zone , known by sailors as The Doldrums, is the area encircling the earth near the equator where winds originating in the northern and southern hemispheres come together....
(ITCZ). The adults of the third generation follow the ITCZ on its 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 aggragation of grasshoppers around points of light at night might give the impression of swarms, Senegalese grasshoppers do not in fact form cohesive swarms like locusts do.
Egg
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
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
Diapause
Diapause is the delay in development in response to regularly and recurring periods of adverse environmental conditions. It is considered to be a physiological state of dormancy with very specific initiating and inhibiting conditions...
and survive the long dry season as a partly developed embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
. 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 SahelSahel
The Sahel is the ecoclimatic and biogeographic zone of transition between the Sahara desert in the North and the Sudanian Savannas in the south.It stretches across the North African continent between the Atlantic Ocean and the Red Sea....
ian countries such as Senegal
Senegal
Senegal , officially the Republic of Senegal , is a country in western Africa. It owes its name to the Sénégal River that borders it to the east and north...
, Mauritania
Mauritania
Mauritania is a country in the Maghreb and West Africa. It is bordered by the Atlantic Ocean in the west, by Western Sahara in the north, by Algeria in the northeast, by Mali in the east and southeast, and by Senegal in the southwest...
, Burkina Faso
Burkina Faso
Burkina Faso – also known by its short-form name Burkina – is a landlocked country in west Africa. It is surrounded by six countries: Mali to the north, Niger to the east, Benin to the southeast, Togo and Ghana to the south, and Côte d'Ivoire to the southwest.Its size is with an estimated...
, Mali
Mali
Mali , officially the Republic of Mali , is a landlocked country in Western Africa. Mali borders Algeria on the north, Niger on the east, Burkina Faso and the Côte d'Ivoire on the south, Guinea on the south-west, and Senegal and Mauritania on the west. Its size is just over 1,240,000 km² with...
, Niger
Niger
Niger , officially named the Republic of Niger, is a landlocked country in Western Africa, named after the Niger River. It borders Nigeria and Benin to the south, Burkina Faso and Mali to the west, Algeria and Libya to the north and Chad to the east...
and Northern Nigeria
Nigeria
Nigeria , officially the Federal Republic of Nigeria, is a federal constitutional republic comprising 36 states and its Federal Capital Territory, Abuja. The country is located in West Africa and shares land borders with the Republic of Benin in the west, Chad and Cameroon in the east, and Niger in...
, especially during wet years following several dry ones.
As with many locust species, outbreaks may be controlled with insecticide
Insecticide
An insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
spray operations: usually at ULV
Ultra-low volume
The term Ultra-Low Volume is used in the context of pesticide application.Ultra-low volume application of pesticides has been defined as spraying at a of les than 5 L/ha for field crops or les than 50 L/ha for tree/bush crops...
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
Entomopathogenic fungus
An entomopathogenic fungus is a fungus that can act as a parasite of insects and kills or seriously disables them.-Typical life cycle:These fungi usually attach to the external body surface of insects in the form of microscopic spores...
(Metarhizium acridum
Metarhizium acridum
Metarhizium acridum is the new name given to a group of fungal isolates that are known to be virulent and specific to Acrididea. Previously, this species has had variety status in Metarhizium anisopliae and before that, reference was made to M. flavoviride.- Biology :M...
), is now available (see desert locust
Desert locust
Plagues of the desert locust have threatened agricultural production in Africa, the Middle East, and Asia for centuries. The livelihood of at least one-tenth of the world’s human population can be affected by this voracious insect...
). Large-scale field tests on O. senegalensis, by the LUBILOSA
LUBILOSA
LUBILOSA was the name of a research programme that aimed at developing a biological alternative to the chemical control of locusts. This name is an acronym of the French title of the programme: Lutte Biologique contre les Locustes et les Sauteriaux...
Programme in 1995-97, were amongst the first successful large-scale field tests using Metarhizium against Acridoid pests.