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Romanomermis culicivorax

By Jeanette Cruz

Geographic Range

Romanomermis culicivorax is naturally found in the United States, particularly in Louisiana, Florida, and Utah. However, humans have distributed the species around the world. (Levy, et al., 1979; Nickle, 1984)

Habitat

Romanomermis culicivorax live in slow-moving freshwater and in the substrate at the bottom of these bodies of water. These include ponds and lakes (Levy et al. 1979). Larval stages parasitize larval mosquitoes. (Levy, et al., 1979)

  • Aquatic Biomes
  • benthic
  • lakes and ponds
  • rivers and streams
  • temporary pools

Physical Description

These parasitoids range in size from 5-25 mm (Nickle 1972). They are colorless except when food is present in their intestinal tract. They are unsegmented and bilaterally symmetrical with a circular cross section. The circular body is bluntly rounded anteriorly and tapers posteriorly. Regions are not easily divided into head, neck, and truck or tail. The oral opening is terminal and is followed by the stoma, esophagus, intestine, and rectum. Females have separate genital and digestive tract openings. In males, the reproductive system joins posteriorly with the digestive tract to form a cloaca. Romanomermis culicivorax also have a protoplasmic extension from the somatic muscles that reaches for synapses with the central nervous system (Maggenti 1997). (Maggenti, 1997; Nickle, 1972)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Range length
    5 to 25 mm
    0.20 to 0.98 in

Development

Eggs develop within 7 to 10 days at 26°C. Egg development is temperature dependent, and it may take several months for eggs to develop if the temperature is less than 10°C. Eggs inhabit temporary bodies of water that dry up periodically. Mature eggs in a moist environment devoid of free-water hatch and remain in a latent stage until they are exposed to the free-water. Eggs that mature in free-water hatch as they mature. Upon hatching, the preparasite is active and swims around until it finds a host, a larval mosquito. Upon successful contact with a host, it uses its stylet to attach to it and then enters the host's hemocoel via the hole made in the host's cuticle. The preparasite stage lasts less than 9 minutes. The parasitic stage begins when the nematode enters the host. It remains inside the host for 7-9 days and continues to develop. Afterwards, it molts into the postparasitic stage. In the postparasitic stage, the nematode ruptures the host's cuticle and emerges. This is fatal to the host. The nematode then burrows into the substrate and remains there for seven or more days to mature into the adult stage. After molting, the adults mate, and the females lay their eggs. They can lay 2,500 eggs within a time-span of 10-15 days. This life cycle occurs in 3-6 weeks (Nickle 1972; Nickle 1984).

R. culicivorax undergo four molts between the first stage and the adult. At each molt, the cuticle of the body, esophagus, and the rectum is shed (Maggenti 1997). (Maggenti, 1997; Nickle, 1972; Nickle, 1984)

Reproduction

R. culicivorax have separate sexes, with females being oviparous. R. culicivorax undergo four molts between the first stage and the adult(Maggenti 1997). After molting to the adult stage, the adults mate, and the females lay the eggs in the substrate at the bottom of a body of water. They can lay 2,500 eggs within a time-span of 10-15 days. This life cycle occurs in 3-6 weeks (Nickle 1972; Nickle 1984).

Studies support cross-fertilization is the only mode of reproduction of R. culicivorax. They also have no distinguishable sex chromosomes (Hendry et al. 1986). (Hendry, et al., 1986; Maggenti, 1997; Nickle, 1972; Nickle, 1984)

  • Range number of offspring
    2,500 (high)
  • Parental Investment
  • pre-fertilization
    • provisioning
  • pre-hatching/birth
    • provisioning

Lifespan/Longevity

The entire life cycle may take 3-6 weeks, depending on water temperature. (Nickle, 1972; Nickle, 1984)

Behavior

In the parasitic stage of the nematode, six stages can be identified. The first stage is host detection. R. culicivorax cannot detect the host from relatively remote distances. The second stage is orientation to the host, a larval mosquito. The third stage is attachment, and this is aided by secretion of an adhesive material from the anterior region of R. culicivorax. This adhesive material is also used as a cleansing or sterilizing factor for the nematode cuticle during host penetration. The fourth stage is the search-boring stage, characterized by spear thrusting and salivary secretions. The fifth stage is host immobilization. Here, the nematode's esophageal injections temporarily paralyze the host and cause temporary cardiac arrest. The immobilization of the host ensures cuticle penetration by reducing excess host activity that might dislodge the nematode. The last stage is cuticle penetration. The six stages occur in less than nine minutes (Shamseldean and Platzer 1989). (Shamseldean and Platzer, 1989)

Communication and Perception

Nematodes in general have papillae, setae and amphids as the main sense organs. Setae detect motion (mechanoreceptors), while amphids detect chemicals (chemoreceptors) (Barnes, 1987). (Barnes, 1987)

Food Habits

Romanomermis culicivorax reside in the hemocoel of larval mosquitoes (Jagdale and Gordon 1994). They feed only when in the parasitic stages and feed on haemolymph. These nematodes penetrate their hosts' cuticle by aid of a stylet along with glandular secretions (Shamseldean and Platzer 1989). (Jagdale and Gordon, 1994; Shamseldean and Platzer, 1989)

  • Animal Foods
  • body fluids

Predation

These parasites are probably not preyed on directly. Larval mortality is high as most of the parasites do not reach appropriate hosts.

Ecosystem Roles

Larval stages of Romanomermis culicivorax are parasitic on larval mosquitoes.

Species Used as Host

Economic Importance for Humans: Positive

Romanomermis culicivorax is the only nematode that has been proven an effective control for a wide range of mosquito species. It provides a rapid, control measure for mosquito pests and is best used for permanent control in areas where it can be established by inoculative release. This is notable in ponds in Florida, as well as in rice fields (Levy et al. 1979, Petersen and Chapman 1979, and Winner et al. 1978). R. culicivorax parasitize larval mosquitoes, including Aedes aegypti and Culex pipiens. (Levy, et al., 1979; Petersen and Chapman, 1979; Winner, et al., 1978)

Contributors

Renee Sherman Mulcrone (editor).

Jeanette Cruz (author), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

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Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

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agricultural

living in landscapes dominated by human agriculture.

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cosmopolitan

having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

freshwater

mainly lives in water that is not salty.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

marsh

marshes are wetland areas often dominated by grasses and reeds.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

parasite

an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

suburban

living in residential areas on the outskirts of large cities or towns.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

References

Barnes, R. 1987. Invertebrate Zoology. Orlando, Florida: Dryden Press.

Castwell-Chen, E., B. Westerdahl. 1998. "Romanomermis culicivorax" (On-line). Biology of Parasitism. Accessed October 07, 2004 at http://ucdnema.ucdavis.edu/imagemap/nemmap/Ent156html/E156rcB.

Hendry, L., A. Triantaphyllou, W. Hominick. 1986. Reproduction and Cytogenetics in Romanomermis culicivorax. Nematologica, 32: 98-105.

Jagdale, G., R. Gordon. 1994. Role of Catecholamines in the Reproduction of Romanomermis culicivorax. Journal of Nematology, 26: 40-45.

Levy, R., C. Rathburn, J. Petersen, D. Doggett, T. Miller. 1979. Aerial application of Romanomermis culicivorax (Mermithidae:Nematoda ) to control Anopheles and Culex mosquitoes in southwest Florida. Mosquito News, 39: 20-25.

Maggenti, A. 1997. Pp. 690-695 in McGraw-Hill Encyclopedia of Science and Technology, Vol. 11, 8th Edition.. R.R. Donnelley and Sons Company, The Lakeside Press..

Nickle, W. 1972. A contribution to our knowledge of the Mermithidae (Nematoda). Journal of Nematology, 4: 113-146.

Nickle, W. 1984. Chapter 22. Nematode Parasites of Mosquitoes. Pp. 801-804 in Nematode Parasites of Mosquitoes in Plant and Insect Nematodes. New York: Marcel Dekker, Inc..

Petersen, J., H. Chapman. 1979. Checklist of mosquito species tested against the nematode parasite Romanomermis culicivorax. Journal of Medical Entomology, 15: 468-471.

Shamseldean, M., E. Platzer. 1989. Romanomermis culicivorax: Penetration of Larval Mosquitoes. Journal of Invertebrate Pathology, 54: 191-199.

Winner, R., C. Steelman, P. Schilling. 1978. Effects of selected insecticides on Romanomermis culicivorax , a mermithid nematode parasite of mosquito larvae. Mosquito News, 33: 546-553.

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