Life cycle of entomopathogenic nematodes (EPNs) /  by Ganpati Jagdale

 

Entomopathogenic nematode life cycle

  • EPNs complete most of their life cycle in insects with an exception of infective juveniles, the only free-living stage found in soil.
  • Infective juveniles of both Steinernema and Heterorhabditis locate a host and enter through its natural body openings such as mouth, anus or spiracles.
  • Infective juveniles of Heterorhabditis also enter through the intersegmental members of the host cuticle.
  • Infective juveniles then actively penetrate through the midgut wall or tracheae into the insect body cavity (hemocoel) containing insect blood (haemolymph).
  • Once in the body cavity, infective juvenile releases symbiotic bacteria from its intestine in the insect haemolymph.
  • Bacteria start multiplying in the nutrient-rich haemolymph and infective juveniles recover from their arrested state (dauer stage) and start feeding on multiplying bacteria and disintegrated host tissues.
  • Toxins produced by the developing nematodes and multiplying bacteria in the body cavity kill the insect host usually within 48 hours.
  • These bacteria also produce a plethora of metabolites, toxins and antibiotics with bactericidal, fungicidal and nematicidal properties, which ensures monoxenic conditions for nematode development and reproduction in insect cadaver.
  • Heterorhabditid and Steinernematid nematodes differ in their mode of reproduction. For example, in heterorhabditid nematodes, the first generation individuals are produced by self-fertile hermaphrodites (hermaphroditic) but subsequent generation individuals are produced by cross fertilization involving males and females (amphimictic). In Steinernematid nematodes with an exception of one species, all generations are produced by cross fertilization involving males and females (amphimictic).
  • Depending on availability of food resource, both heterorhabditid and steinernematid nematodes generally complete 2-3 generations within insect cadaver and emerge as infective juveniles to seek new hosts.
  • Generally, life cycle of entomopathogenic nematodes (from infective juvenile penetration to infective juvenile emergence) is completed within 12- 15 days at room temperature. The optimum temperature for growth and reproduction of nematodes is between 25 and 300C.

Species of the genus Heterorhabditis Poinar, 1976 /  by Ganpati Jagdale

Known species of Heterorhabditis Poinar, 1976 with a biocontrol potential- Identification based on morphological and molecular techniques

  1. Heterorhabditis amazonensis Andalo, Nguyen, & Moino, 2006
  2. H. argentinensis Stock, 1993
  3. H. atacamensis, Edgington, Buddie, Moore, France, Merino, & Hunt, 2011
  4. H. bacteriophora Poinar, 1976
  5. H. baujardi Phan, Subbotin, Nguyen & Moens, 2003
  6. H. brevicaudis Liu, 1994
  7. H. downesi Stock, Griffin & Burnell, 2002
  8. H. floridensis Nguyen, Gozel, Koppenhofer, & Adams, 2006
  9. H. georgiana Nguyen, Shapiro-Ilan, & Mbata, 2008
  10. Heterorhabditis gerrardi, Plichta, Joyce, Clarke, Waterfield, & Stock, 2009
  11. H. hambletoni (Pereira, 1937) Poinar, 1976
  12. H. hawaiiensis Gardner, Stock & Kaya, 1994
  13. H. heliothidis (Khan, Brooks & Hirschman, 1976) Poinar, Thomas & Hess, 1977
  14. H. hepialius Stock, Strong & Gardner, 1996
  15. H. hoptha (Turco, 1970), Poinar, 1979
  16. H. indica Poinar, Karunakar & David, 1992
  17. H. marelata Liu & Berry, 1996
  18. H. megidis Poinar, Jackson & Klein, 1988
  19. H. mexicana Nguyen, Shapiro-Ilan, Stuart, MCCoy, James & Adams, 2004
  20. H. poinari Kakulia & Mikaia, 1997
  21. H. safricana Malan, Nguyen, deWaal, & Tiedt, 2008
  22. Heterorhabditis sonorensis, Stock, Rivera-Orduno, & Flores-Lara, 2009
  23. H. taysearae Shamseldean, El-Sooud, Abd-Elgawad & Saleh, 1996
  24. H. zealandica Poinar, 1990

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Species of the genus Steinernema Travassos, 1927 /  by Ganpati Jagdale

Known species of Steinernema Travassos, 1927 with a biocontrol potential- Identification was based on morphological and molecular techniques

  1. Steinernema abbasi Elawad, Ahma & Reid, 1997
  2. S. aciari Qiu, Yan, Zhou, Nguyen & Pang, 2004
  3. S. affine (Bovien, 1937) Wouts, Mrácek, Gerdin & Bedding, 1982
  4. S. akhursti Qiu, Hu, Zhou, Mei, Nguyen, & Pang, 2005
  5. S. anatoliense Hazir, Stock & Keskin, 2003
  6. S. apuliae Triggiani, Mracek & Reid, 2004
  7. S. arenarium (Artyukhovsky, 1967) Wouts, Mrácek, Gerdin & Bedding, 1982
  8. S. ashiuense Phan, Takemoto & Futai, 2006
  9. S. asiaticum Shahina, Reid & Rowe, 2002
  10. S. australe, Edgington, Buddie, Tymo, Hunt, Nguyen, France, Merino, & Moore, 2009
  11. S. backanense Phan, Spiridonov, Subbotin & Moens, 2006
  12. S. balochiense Fayyaz, Khanum, Ali, Solangi, Gulsher & Javed, 2015
  13. S. beddingi Qiu, Hu, Zhou, Pang & Nguyen, 2005
  14. S. bicornutum Tallosi, Peters & Ehlers 1995
  15. S. brazilense, Nguyen, Ginarte, Leite, dos Santos, & Harakava, 2010
  16. S. carpocapsae (Weiser, 1955) Wouts, Mrácek, Gerdin & Bedding, 1982
  17. S. caudatum Xu, Wang & Li, 1991
  18. S. ceratophorum Jian, Reid & Hunt 1997
  19. S. cholashanense Nguyen, Puža & Mrácek, 2008
  20. S. citrae Stokwe, Malan, Nguyen, Knoetze, & Tiedt, 2011
  21. S. costaricense Uribe, Mora & Stock, 2007
  22. S. cubanum Mrá¡cek, Hernandez & Boemare, 1994
  23. S. cumgarense Phan, Spiridonov, Subbotin & Moens, 2006
  24. S. dharanaii , Kulkarni, Rizvi, Kumar, Paunikar& Mishra, 2012
  25. S. diaprepesi Nguyen, & Duncan, 2002
  26. S. eapokense Phan, Spiridonov, Subbotin & Moens, 2006
  27.  S. fabii Abate, Malan, Tiedt, Wingfield, Slippers, Hurley, 2016. 
  28. S. feltiae (Filipjev, 1934) Wouts, Mrácek, Gerdin & Bedding, 1982
  29. S. glaseri (Steiner, 1929) Wouts, Mracek, Gerdin & Bedding, 1982
  30. S. guangdongense Qiu, Fang, Zhou, Pang, & Nguyen, 2004
  31. S. hebeiense Chen, Li, Yan, Spiridonov & Moens, 2006
  32. S. hermaphroditum Stock, Griffin, & Chaerani, 2004
  33. S.  innovation Cimen, Lee, Hatting, Hazir, Stock 2015
  34. S. intermedium (Poinar, 1985) Mamiya, 1988
  35. S. jeffreyense Malan, Knoetze & Tiedt, 2016
  36. S. jollieti Spiridonov, Krasomil-Osterfeld & Moens, 2004
  37. S. karii Waturu, Hunt & Reid, 1997
  38. S. khoisanae Nguyen, Malan, & Gozel, 2006
  39. S. kraussei (Steiner, 1923) Travassos, 1927
  40. S. kushidai Mamiya, 1988
  41. S. leizhouense Nguyen, Qiu, Zhou, & Pang, 2006
  42. S. litorale Yoshida, 2004
  43. S. loci Phan, Nguyen & Moens, 2001
  44. S. longicaudum Shen & Wang, 1992
  45. S. monticolum Stock, Choo & Kaya, 1997
  46. S. neocurtillae Nguyen & Smart, 1992
  47. S. oregonense Liu & Berry, 1996
  48. S. pakistanense Shahina, Anis, Reid, Rowe & Maqbool, 2001
  49. S. papillatum  San-Blas, Portillo, Nermut, Puza, & Morales-Montero 2015
  50. S. phyllophagae Nguyen and Buss, 2011
  51. S. puertoricense Roman & Figueroa, 1994
  52. S. puntauvense Uribe, Mora & Stock, 2007
  53. S. rarum (Doucet, 1986) Mamiya, 1988
  54. S. riobrave Cabanillas, Poinar & Raulston, 1994
  55. S. ritteri de Doucet & Doucet, 1992
  56. S. robustispiculum Phan, Subbotin, Waeyenberge, & Moens, 2005
  57. S. sangi Phan, Nguyen & Moens, 2001
  58. S. sasonense Phan, Spiridonov, Subbotin & Moens, 2006
  59. S. scapterisci Nguyen & Smart, 1992
  60. S. scarabaei Stock & Koppenhöfer 2003
  61. S. serratum Liu, 1992
  62. S. siamkayai Stock, Somsook & Kaya, 1998
  63. S. sichuanense Mrácek, Nguyen, Tailliez, Boemare & Chen, 2006
  64. S. silvaticum Sturhan, Spiridonov & Mracek, 2005
  65. S. tami Luc, Nguyen, Reid & Spiridonov, 2000
  66. S. texanum Nguyen, Stuart, Andalo, Gozel, & Roger, 2007
  67. S. thanhi Phan, Nguyen & Moens, 2001
  68. S. thermophilum Ganguly & Singh, 2000
  69. S. websteri Cutler & Stock, 2003
  70. S. weiseri Mrácek, Sturhan & Reid, 2003
  71. S. xinbinense Ma, Chen, De Clercq, Waeyenberge, Han & Moens, 2012
  72. S. xueshanense, Mracek, Liu, & Nguyen, 2009
  73. S. yirgalemense Nguyen, Tesfamariam, Gozel, Gaugler, & Adams, 2005

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Entomopathogenic Nematode Facts /  by Ganpati Jagdale

Entomopathogenic nematodes (EPNs) of the two genera Steinernema Travassos, 1927 and Heterorhabditis Poinar, 1976 in the order Rhabdita kill most insects but they are harmless to some beneficial insects (e.g. honey bees), higher animals and environment. Third-stage juvenile is the only free-living stage in the life cycle of the nematode known as the infective juvenile or dauer juvenile that found in soil and can seek, infect and kill their insect hosts.

These infective juveniles are mutualistically associated with symbiotic bacteria (Xenorhabdus spp. or Photorhabdus spp.) in the family Enterobacteriaceae, which are capable of causing disease in insect pests and killing them.

Species of genus, Xenorhabdus are specifically assocaited with the members of the nematode genusSteinernema and Photorhabdus species are associated with the members of nematode genusHeterorhabditis.

In this mutualistic relationship, the nematode infective juveniles provides protection for bacterium outside the insect host (as bacterium is unable to survive in the outside environment i.e. soil or water) and a means of transmission to new hosts and in return bacteria provides nutrients required for the nematode development and reproduction.

Infective juveniles are adapted to remain in the soil environment without feeding until they find a suitable host.

They are also resistant to unfavorable environmental conditions such as desiccation, heat and freezing.

EPNs can infect soil dwelling stages of butterflies, moths, beetles, flies, crickets and grasshoppers.

Infective juveniles of different nematode species employ different foraging strategy to find and infect their insect hosts. For example, Heterorhabditis bacteriophora is a cruiser forager meaning that it actively finds out or hunts its prey, Steinernema carpocapsae is an ambusher forager that sits and wait for a pray to pass by and S. feltiae and S. rivobrave are intermediate foragers.

EPNs are now commercially produced using both in vivo (in living host) and in vitro (in artificial medium) techniques.

Since EPNs have a wide host range, they are currently used as potential biological control agents to manage insect pests of many field crops, greenhouse and nursery plants, horticultural crops, turfgrass, and in some instances insect pests of animals and humans.

EPNs also have a potential to use as biocontrol agents against plant-parasitic nematodes.

Commercially produced nematode infective juveniles can be stored for extended periods and easily applied in aqueous suspensions in the field using traditional sprayers.

Also, EPNs are compatible with several chemical fungicides, insecticides, nematicides and herbicides, and therefore, they can be easily included in IPM programs.

Under current pesticide regulations, the U.S. Environmental Protection Agency has exempted these biological control agents from registration.

Insect parasitic nematodes are our friends /  by Ganpati Jagdale

Nematodes are defined as thread-like microscopic, colorless, unsegmented round worms found in almost all habitats especially in soil and water. Nematodes may be free-living, predacious and parasitic. Nematodes that are considered our friends include entomopathogenic nematodes, insect-parasitic nematodes, slug-parasitic and free-living nematodes.

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