Acanthoplus discoidalis
Encyclopedia
Acanthoplus discoidalis (armoured ground cricket, armoured bush cricket, corn cricket or ) is a species of katydid that is native to Namibia
, Botswana
, and South Africa
. They are wide-bodied, flightless and can grow to around 5 cm. Their thorax
is covered in sharp spines and they have a pair of strong biting jaws. They are able to defend themselves against predators in an unusual manner by squirting
haemolymph (insect blood) out of their bodies. Their populations peak in autumn
and their bodies often litter roads during this time. When deprived of protein
and salt
they can become cannibalistic.
nestlings. It is believed that they may be able to detect the location of nests using auditory signals.
. The mechanism used depends on the sex of the individual and the method of attack. When attacked from the side, males will stridulate and both sexes will attempt to bite the attacker. In around 50% of attacks from the side, both sexes will autohaemorrhage, squirting between 5 mg and 80 mg of toxic haemolymph at their attacker over distances up to 30 cm. When attacked from above and therefore less able to bite their attacker they autohaemorrhage more than when attacked from the side. Experiments have shown that the haemolymph is distasteful to at least two reptile
species, but the compounds that confer this are unknown. It has been hypothesised that they may be phytotoxin
s found in plants that the crickets eat and that they then sequester these to use as defensive compounds themselves. After autohaemorrhaging they clean themselves meticulously, this is thought to be done so that other members of the species do not cannibalise them. Bateman and Fleming, experts on the species, believe that autohaemorrhage is a carefully regulated defence response rather than an accidental consequence of being attacked. Another defensive response is to regurgitate
their stomach contents when attacked, this is used more often when the insect has already been attacked repeatedly.
pouch and an associated spermatophylax
(a body of food given to the female as a nuptial gift) - together termed the spermatophore
. They therefore cannot mate again for some time as they have to wait until a new spermatophore has grown. Females mate once before laying eggs, and then mate and lay eggs in a random order. This means that it is advantageous for males to mate with virgins over non-virgins as a higher proportion of the offspring will be their own. Males are able to discriminate between virgins and non-virgins and successfully complete more matings with virgins and they transfer their spermatophore more quickly when mating with virgins. Virgins are lighter than non-virgins allowing males to distinguish between virgins and non-virgins by determining the mass of the female when they copulate.
and millet
in Southern Africa and can cause decreases in yield of up to 40% in these crops in some years. Insecticide
s can be used, but as Acanthoplus discoidalis are flightless they can be controlled fairly easily by constructing a 50 cm deep trench around the field, poisoned baits can also be placed in the trenches. It has been suggested that the crickets could also be used as high protein chicken
feed.
Namibia
Namibia, officially the Republic of Namibia , is a country in southern Africa whose western border is the Atlantic Ocean. It shares land borders with Angola and Zambia to the north, Botswana to the east and South Africa to the south and east. It gained independence from South Africa on 21 March...
, Botswana
Botswana
Botswana, officially the Republic of Botswana , is a landlocked country located in Southern Africa. The citizens are referred to as "Batswana" . Formerly the British protectorate of Bechuanaland, Botswana adopted its new name after becoming independent within the Commonwealth on 30 September 1966...
, and South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
. They are wide-bodied, flightless and can grow to around 5 cm. Their thorax
Thorax (insect anatomy)
The thorax is the mid section of the insect body. It holds the head, legs, wings and abdomen. It is also called mesosoma in other arthropods....
is covered in sharp spines and they have a pair of strong biting jaws. They are able to defend themselves against predators in an unusual manner by squirting
Blood squirt
Blood squirt is the effect when an artery, a blood vessel in the human body , is cut...
haemolymph (insect blood) out of their bodies. Their populations peak in autumn
Autumn
Autumn is one of the four temperate seasons. Autumn marks the transition from summer into winter usually in September or March when the arrival of night becomes noticeably earlier....
and their bodies often litter roads during this time. When deprived of protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
and salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
they can become cannibalistic.
Diet
Acanthoplus discoidalis are omnivorous and will eat many different foods. One record documented them attacking Red-billed QueleaRed-billed Quelea
The Red-billed Quelea is the world's most abundant wild bird species, with an estimated adult breeding population of 1.5 billion pairs. Some estimates of the overall population have been as large as 10 billion...
nestlings. It is believed that they may be able to detect the location of nests using auditory signals.
Defense
Acanthoplus discoidalis have several defensive mechanisms that they use when attacked, as well as the innate defence provided by their armoured exoskeletonExoskeleton
An exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...
. The mechanism used depends on the sex of the individual and the method of attack. When attacked from the side, males will stridulate and both sexes will attempt to bite the attacker. In around 50% of attacks from the side, both sexes will autohaemorrhage, squirting between 5 mg and 80 mg of toxic haemolymph at their attacker over distances up to 30 cm. When attacked from above and therefore less able to bite their attacker they autohaemorrhage more than when attacked from the side. Experiments have shown that the haemolymph is distasteful to at least two reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
species, but the compounds that confer this are unknown. It has been hypothesised that they may be phytotoxin
Phytotoxin
Phytotoxin refers to a substance produced by a plant that is toxic or a substance that is toxic to the plant Many substances produced by plants are secondary metabolites and are the by-products of primary physiological processes...
s found in plants that the crickets eat and that they then sequester these to use as defensive compounds themselves. After autohaemorrhaging they clean themselves meticulously, this is thought to be done so that other members of the species do not cannibalise them. Bateman and Fleming, experts on the species, believe that autohaemorrhage is a carefully regulated defence response rather than an accidental consequence of being attacked. Another defensive response is to regurgitate
Regurgitation (digestion)
Regurgitation is the expulsion of material from the mouth, pharynx, or esophagus, usually characterized by the presence of undigested food or blood.Regurgitation is used by a number of species to feed their young...
their stomach contents when attacked, this is used more often when the insect has already been attacked repeatedly.
Reproduction
Acanthoplus discoidalis have a relatively long courtship period, it starts at sunset and is usually completed by sunrise. Males stridulate which attracts females to their location. Males produce a large spermSperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
pouch and an associated spermatophylax
Spermatophylax
A spermatophylax is a gelatinous bolus which some male insects eject during copulation with females through their aedeagi together with spermatophores, and which functions as a nutritive addition for the female....
(a body of food given to the female as a nuptial gift) - together termed the spermatophore
Spermatophore
A spermatophore or sperm ampulla is a capsule or mass created by males of various animal species, containing spermatozoa and transferred in entirety to the female's ovipore during copulation...
. They therefore cannot mate again for some time as they have to wait until a new spermatophore has grown. Females mate once before laying eggs, and then mate and lay eggs in a random order. This means that it is advantageous for males to mate with virgins over non-virgins as a higher proportion of the offspring will be their own. Males are able to discriminate between virgins and non-virgins and successfully complete more matings with virgins and they transfer their spermatophore more quickly when mating with virgins. Virgins are lighter than non-virgins allowing males to distinguish between virgins and non-virgins by determining the mass of the female when they copulate.
Control
Acanthoplus discoidalis is a pest of sorghumSorghum
Sorghum is a genus of numerous species of grasses, one of which is raised for grain and many of which are used as fodder plants either cultivated or as part of pasture. The plants are cultivated in warmer climates worldwide. Species are native to tropical and subtropical regions of all continents...
and 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...
in Southern Africa and can cause decreases in yield of up to 40% in these crops in some years. 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...
s can be used, but as Acanthoplus discoidalis are flightless they can be controlled fairly easily by constructing a 50 cm deep trench around the field, poisoned baits can also be placed in the trenches. It has been suggested that the crickets could also be used as high protein chicken
Chicken
The chicken is a domesticated fowl, a subspecies of the Red Junglefowl. As one of the most common and widespread domestic animals, and with a population of more than 24 billion in 2003, there are more chickens in the world than any other species of bird...
feed.