Romanomermis culicivorax

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.

• Biogeographic Regions
• nearctic nearctic
  • native native
• palearctic palearctic
  • introduced introduced
• oriental oriental
  • introduced introduced
• ethiopian ethiopian
  • introduced introduced
• neotropical neotropical
  • introduced introduced
• australian australian
  • introduced introduced

• Other Geographic Terms
• cosmopolitan cosmopolitan

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 .

• Habitat Regions
• temperate temperate
• tropical tropical
• freshwater freshwater

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

• Wetlands
• marsh marsh
• swamp swamp

• Other Habitat Features
• urban urban
• suburban suburban
• agricultural agricultural
• riparian riparian

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).

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger
• sexes shaped differently

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).

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).

• Key Reproductive Features
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• fertilization fertilization
  • internal internal
• oviparous oviparous

• Parental Investment
• pre-fertilization
  • provisioning
• pre-hatching/birth
  • provisioning

Lifespan/Longevity

The entire life cycle may take 3-6 weeks, depending on water temperature.

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).

• Key Behaviors
• parasite parasite
• motile motile
• sedentary sedentary

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).

• Communication Channels
• tactile tactile
• chemical chemical

• Other Communication Modes
• pheromones pheromones

• Perception Channels
• tactile tactile
• chemical chemical

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).

• Primary Diet
• carnivore carnivore
  • eats body fluids

• 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.

• Ecosystem Impact
• parasite parasite

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 .

Additional Links

Encyclopedia of Life

Contributors

Renee Sherman Mulcrone (editor).

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

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.