| Mermis nigrescens | |
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| Species: | M. nigrescens |
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| Mermis nigrescens Dujardin, 1842 | |
Mermis nigrescens is a species of nematode known commonly as the grasshopper nematode. [1] [2] It is distributed in the Americas, Europe, and Asia. It occurs in Tasmania, but it has not been observed on mainland Australia. It has been rarely observed in Africa. [1] It is a parasite of insects, especially grasshoppers. [1]
This is a very large nematode, the male about 4 to 6 centimetres long [1] and the female known to exceed 20 centimetres. [3] The size is unusual for entomopathogenic nematodes, which are generally almost microscopic. [2] The body is pale brown, [2] and the gravid female has a dark stripe down the length of its body due to the presence of up to 14,000 eggs. [1] The body surface is smooth. It tapers at the front end, and the head and tail are rounded. [3]
The adult female has a bright red [4] or orange-red [3] spot on its head. Early in studies of the nematode, this was called the "chromatrope", because it apparently had a function in the animal's response to light. [4] On closer examination it had the form of a hollow cylinder, [5] and the red pigment inside was determined to be hemoglobin. [4] This haemoglobin, generally as oxyhaemoglobin, is densely concentrated in crystalline form. [5] The cylinder was confirmed to be an ocellus, a form of eye. [6] Haemoglobin takes the place of melanin as the shadowing pigment of the eye, and plays a role in the nematode's sensation of light, a function not observed in any other organism. [5] Some other nematodes have eye structures, but that of the female M. nigrescens is unique. It has a single eye, where other nematodes have two. Only the female has an eye, where eyes are present in both sexes of other eyed nematodes. Its eye takes up the entire front end of the body, the cylinder filling the entire body cavity. It has a cornea, or a structure that acts as a cornea. All other eyed nematodes have melanin as the shadowing pigment. The unique eye of M. nigrescens probably evolved independently among nematode taxa. [7]
This and other Mermis species are sometimes mistaken for horsehair worms, but the latter are longer and uniformly dark in colour, and their bodies do not taper. [1]
The adult male and female nematode mate in spring or summer. The male then dies and the female remains in the soil through fall and winter. During the following spring or summer the female emerges after a rainfall event while the landscape is still wet, often early in the morning. It then climbs vegetation, sometimes reaching 2 or 3 meters above the ground. It lays its eggs on plants. The eggs are dark brown or reddish, and are about half a millimetre long. The eggs attach to the plant via filaments called byssi. They are consumed by herbivores along with the plant tissue. [1]
This nematode is most often associated with grasshoppers. High levels of parasitism have been reported in species such as the two-striped grasshopper (Melanoplus bivittatus), the red-legged grasshopper (Melanoplus femurrubrum), the migratory grasshopper (Melanoplus sanguinipes), the snakeweed grasshopper (Hesperotettix viridis), [1] and the desert locust (Schistocerca gregaria). [8] Once it is ingested by an insect such as a grasshopper, an egg hatches almost immediately, sometimes within an hour. The juvenile nematode pierces the gut with its stylet and enters the hemocoel, the blood-like fluid that fills the insect's body cavity, acting as a circulatory system. There the nematode absorbs the insect's nutrients, taking glucose directly through its cuticle. [8] It grows and develops over several weeks. The newly hatched nematode is about 0.24 millimetres long; by day 37 it has reached about 5 centimetres. The nematodes grow more rapidly and attain larger sizes in larger insect hosts. More females occur in larger hosts, as well. The nematode is still a juvenile when it emerges from the host insect, and finishes its development in the soil. The insect dies as the nematode exits its body, if not before. [1] The adult nematode does not feed. [9]
M. nigrescens exhibits positive phototaxis; when it senses light with its eye, it moves toward it. Other eyed nematodes have a negative phototaxis, moving away from light. The juvenile M. nigrescens also has a weak negative phototaxis before its eye has developed. This behaviour may guide the juvenile underground, and lead the adult female to the surface, where it lays its eggs on vegetation. [7]
The nematode moves in a unique fashion, as well. The anterior tip of the body containing the eye swings horizontally and vertically while the "neck" region just behind it bends slowly. [6] This is apparently a scanning behaviour, in which the nematode senses light and determines its direction. [7] Rather than undulating as nematodes generally do, this species moves its body as several independent sections, pushing off of objects with some sections while others loop upward. [9] It also crawls on its ventral surface "like a snake", [1] rather than on its side like a typical nematode. [9]
In naturally infected earwig hosts ( Forficula auricularia ) in New Zealand a prevalence of 7.8% was observed. With around 10% of individuals carrying multiple worms. The highest observed number of M. nigrescens in one host was 5. [10]
When infecting earwigs the parasite is able to induce positive hydrotaxis. Larger M. nigrescens are more likely to induce positive hydrotaxis which is probably related to maturation of the worms. [10]
Nematomorpha are a phylum of parasitoid animals superficially similar to nematode worms in morphology, hence the name. Most species range in size from 50 to 100 millimetres long, reaching 2 metres in extreme cases, and 1 to 3 millimetres in diameter. Horsehair worms can be discovered in damp areas, such as watering troughs, swimming pools, streams, puddles, and cisterns. The adult worms are free-living, but the larvae are parasitic on arthropods, such as beetles, cockroaches, mantids, orthopterans, and crustaceans. About 351 freshwater species are known and a conservative estimate suggests that there may be about 2000 freshwater species worldwide. The name "Gordian" stems from the legendary Gordian knot. This relates to the fact that nematomorphs often tie themselves in knots.
Ascaris lumbricoides is the "large roundworm" of humans, growing to a length of up to 35 cm (14 in). It is one of several species of Ascaris. An ascarid nematode of the phylum Nematoda, it is the most common parasitic worm in humans. This organism is responsible for the disease ascariasis, a type of helminthiasis and one of the group of neglected tropical diseases. An estimated one-sixth of the human population is infected by A. lumbricoides or another roundworm. Ascariasis is prevalent worldwide, especially in tropical and subtropical countries.
In humans and most mammals and birds, the iris is a thin, annular structure in the eye, responsible for controlling the diameter and size of the pupil, thus the amount of light reaching the retina. Eye color is defined by that of the iris. In optical terms, the pupil is the eye's aperture, while the iris is the diaphragm.
Earwigs make up the insect order Dermaptera. With about 2,000 species in 12 families, they are one of the smaller insect orders. Earwigs have characteristic cerci, a pair of forceps-like pincers on their abdomen, and membranous wings folded underneath short, rarely used forewings, hence the scientific order name, "skin wings". Some groups are tiny parasites on mammals and lack the typical pincers. Earwigs are found on all continents except Antarctica.
Forficula auricularia, the common earwig or European earwig, is an omnivorous insect in the family Forficulidae. The European earwig survives in a variety of environments and is a common household insect in North America. The name earwig comes from the appearance of the hindwings, which are unique and distinctive among insects, and resemble a human ear when unfolded; the species name of the common earwig, auricularia, is a specific reference to this feature. They are considered a household pest because of their tendency to invade crevices in homes and consume pantry foods, and may act either as a pest or as a beneficial species depending on the circumstances.
Grasshoppers are a group of insects belonging to the suborder Caelifera. They are among what is probably the most ancient living group of chewing herbivorous insects, dating back to the early Triassic around 250 million years ago.
Heterodera sacchari mitotic parthenogenic sedentary endoparasitic nematode. This plant-parasitic nematode infects the roots of sugarcane, and the female nematode eventually becomes a thick-walled cyst filled with eggs. Aboveground symptoms are species specific and are similar to those caused by other Heterodera species. Symptoms include: stunted and chlorotic plants, and reduced root growth. Seedlings may be killed in heavily infested soils.
The differential grasshopper is a species of grasshopper belonging to the genus Melanoplus. It is found throughout northern Mexico, the central United States and southern Ontario, Canada. It is considered a pest over most of its range.
The nematodes or roundworms constitute the phylum Nematoda, with plant-parasitic nematodes being known as eelworms. They are a diverse animal phylum inhabiting a broad range of environments. Taxonomically, they are classified along with insects and other moulting animals in the clade Ecdysozoa, and unlike flatworms, have tubular digestive systems with openings at both ends. Like tardigrades they have a reduced number of Hox genes, but as their sister phylum Nematomorpha has kept the ancestral protostome Hox genotype, it shows that the reduction has occurred within the nematode phylum.
Mermithidae is a family of nematode worms that are endoparasites in arthropods. As early as 1877, Mermithidae was listed as one of nine subdivisions of the Nematoidea. Mermithidae are confused with the horsehair worms of the phylum Nematomorpha that have a similar life history and appearance.
Phototaxis is a kind of taxis, or locomotory movement, that occurs when a whole organism moves towards or away from a stimulus of light. This is advantageous for phototrophic organisms as they can orient themselves most efficiently to receive light for photosynthesis. Phototaxis is called positive if the movement is in the direction of increasing light intensity and negative if the direction is opposite.
Labidura riparia is a species of earwig in the family Labiduridae characterized by their modified cerci as forceps, and light tan color. They are commonly known as the shore earwig, tawny earwig, riparian earwig, or the striped earwig due to two dark longitudinal stripes down the length of the pronotum. They are sometimes wrongly referred to as Labidura japonica, although said species is actually a subspecies, Labidura riparia japonica, found only in Japan. L. riparia are a cosmopolitan species primarily in tropical to subtropical regions. Body size varies greatly, ranging from 16 mm to 30 mm, with 10 abdominal segments. Males and females differ in forcep size, with males having much larger and stronger curve, while females have smaller, straighter forceps with a slight curve at the end. Earwigs use these forceps to assist in predation, defense, sexual selection, courting and mating, and wing folding.
The red-legged grasshopper is a species of grasshopper belonging to the genus Melanoplus. It is one of the most common grasshoppers found in Mexico, the United States, and Canada. This grasshopper is frequently used as a model organism in scientific studies, due to their abundance throughout North America and behavioral response to changes in climate.
Skrjabinoptera phrynosoma is a parasitic worm in the phylum Nematoda, the most diverse of pseudocoelomates. Like many other parasites, the life cycle of S. phrynosoma is complicated and it involves two hosts – a lizard and an ant.
Platynereis dumerilii is a species of annelid polychaete worm. It was originally placed into the genus Nereis and later reassigned to the genus Platynereis. Platynereis dumerilii lives in coastal marine waters from temperate to tropical zones. It can be found in a wide range from the Azores, the Mediterranean, in the North Sea, the English Channel, and the Atlantic down to the Cape of Good Hope, in the Black Sea, the Red Sea, the Persian Gulf, the Sea of Japan, the Pacific, and the Kerguelen Islands. Platynereis dumerilii is today an important lab animal, it is considered as a living fossil, and it is used in many phylogenetic studies as a model organism.
Gordius is a genus of worms in the phylum Nematomorpha, the horsehair worms. It was formerly treated as the only genus in the family Gordiidae, but the genus Acutogordius is now considered as distinct. The genus is distributed worldwide except for Antarctica, where no Nematomorpha have been recorded.
Paragordius varius is a parasite species in the horsehair worm group (Nematomorpha). They cycle between terrestrial and aquatic habitats and are most commonly known for their ability to manipulate their definitive host to jump into a pool of water, which allows them to complete their life cycle. Adults are over 10 cm long and 400 μm in diameter. P. varius is usually found in water or wet areas. The definitive hosts are mainly terrestrial arthropods, most often carabid beetles, crickets and praying mantids.
Steinernema scapterisci, the mole cricket nematode, is a species of nematode in the order Rhabditida. It is a parasite of insects in the order Orthoptera, the grasshoppers, crickets and their allies. Native to southern South America, it was introduced into Florida in the United States in an effort to provide a biological control of pest (Neoscapteriscus) mole crickets.
Caedicia simplex is a species of bush cricket, native to New Zealand. It is also found in Australia.
Nectonema is a genus of marine horsehair worms first described by Addison E. Verrill in 1879. It is the only genus in the family Nectonematidae described by Henry B. Ward in 1892, in the order Nectonematoidea, and in the class Nectonematoida. The genus contains five species; all species have a parasitic larval stage inhabiting crustacean hosts and a free-living adult stage that swims in open water.
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