Insect nematodes

By KHUONG B. NGUYEN

ORDER OXYURIDA Weinland, 1858

ORDER TYLENCHIDA (Filipjev, 1934) Thorne, 1949

 Diagnosis: Cuticle annulated. Amphid on labial region. Stoma with a protrusible, hollow stylet bearing three knobs posteriorly. Esophagus with procorpus, metacorpus, isthmus and glandular portion. Dorsal-esophageal gland opening near stylet knobs or in median bulb. Female gonads single or double; when single, post vulval sac not very well developed. Males mostly with bursa. Nematodes in this order live in soil or in different parts of plants. Most of them are parasites or associates of plants, and some of them are parasites or associtaes of insects.

The following families were reported to contain insect parasitic nematodes: (in the order of more important first):

Family Allantonematidae

Sphaerulariidae

Phaenopsitylenchidae

           Iotonchidae  

                       Parasitylenchidae

           Fergusobiidae 

 Family Allantonematidae (Pereira, 1931) Chitwood & Chitwood, 1937

Diagnosis: Sphaerularioidea. Nematodes in this family have very short free-living life, females penetrate the host after mating. Females: Free-living stage: Stylet strong, length 15 μm or less. Esophageal glands elongated, lobe-like. Gonad one. Postvulval sac short or absent. Uterus elongate often containing minute sperms. Tail conoid with bluntly pointed terminus. Parasitic stage: body obese, round, oval, spindle-shaped, or elongated sac-like. Body cavity mostly filled with reproductive organs.

Males: Not parasitic and having a short life in the environment. Morphologically similar to free-living females but esophageal glands not enlarged. Esophagus may be degenerate. Testis outstretched. Spicules arcuate, pointed, usually less than 25 μm long. Gubernaculum rarely absent. Tail conoid with or without bursa.

There are 2 subfamilies: Allantonematinae and Contortylenchinae.

 Subfamily Allantonematinae Pereira, 1931: Parasitic female body round, oval, sac-like, never dorsally curved. Vulva indistinct.

Type genus: Allantonema Leuckart, 1884

 
Key to genera: (Modified after Siddiqi, 1986 and Remillet & Laumond 1991)

      1.     Free-living females without stylet ................................................................. Bradynema zur Strassen, 1892

            Free-living females with stylet ................................................................................................................................. 2

     2.    Males without stylet; esophagus degenerate ....................................................................................................... 3

            Males with stylet; esophagus normal or partially degenerate ....................................................................... 4

     3.    Free-living forms generally with clavate tails; parasitic female small, round to oval,

            with one or two eggs in uterus; parasites of thrips ......................................... Thripinema Siddiqi, 1986

            Free-living forms without clavate tails; parasitic female large, generally

              tuboid, with a number of eggs or juveniles in uterus; not parasites of thrips.

            ............................................................................................................................................... Howardula Cobb, 1921

     4.    Parasitic female round, oval, or bean-shaped; labial region of free-living forms

                        offset............................................................................................................ Allantonema Leuckart, 1884               

   Parasitic female elongate, sausage-shaped; labial region of free-living forms

               not offset ................................................................................................................................................................... .5

     5.                In free-living female, excretory pore at anterior margin of nerve ring or more

             anterior ........................................................................ Metaparasitylenchus Wachek, 1955 (Nickle, 1967)

            In free-living female, excretory pore posterior to nerve ring ....................................................................... 6

     6.    Bursa absent .............................................................................................................. Protylenchus Wachek, 1955

            Bursa present .................................................................................................................................................................. 7

     7.                Body surface of parasitic female wavy, with constrictions and swellings

            .................................................................................................. Sulphuretylenchus Rühm, 1956 (Nickle, 1967)

            Body surface of parasitic female neither wavy nor with constrictions and swellings

             ........................................................................................................................................................................................... 8

     8.    In free-living females, excretory pore about 105-125 μm from anterior end; stylet

            with distinct knobs....................................................................................... Parasitylenchoides Wachek, 1955

            In free-living females, excretory pore at less than 100 μm from anterior end.........................................9

     9.    Stylet of free-living forms distinctly knobbed; parasites of staphilinid beetles    

            ...............................................................................................Proparasitylenchus Wachek, 1955 (Nickle, 1967)

            Stylet of free-living forms without distinct knobs but with basal thickenings,

             parasites of bark beetles.............................................................................. Neoparasitylenchus Nickle, 1967

 
Subfamily Contortylenchinae Ruhm, 1956

Parasitic female body dorsally curved, vulva distinct in a depression.

Type genus: Contortylenchus Ruhm, 1956

Key to genera (Modified after Remillet & Laumond, 1991)

 
     1.    Stylet with basal knobs or thickenings; parasites of Coleoptera................................................................... 2

            Stylet without basal knobs or thickenings; parasites of Siphonaptera

            ................................................................................................... Spilotylenchus Launay, Deunff, and Bain, 1983

     2.    Parasitic female length < 0.8 mm long; body length/body width < 8;

            parasites of Scolytidae .................................................................................................. Bovienema Nickle, 1963

            Parasitic female > 0.8 mm long; body length/body width > 10.............................................................. 3

     3.    Parasitic female strongly dorsally curved; parasites of Scolytidae

             .................................................................................................................................. Contortylenchus Rühm, 1956

            Parasitic female slightly dorsally curved or straight; parasites of Cerambycidae

            ......................................................................................................................................... Aphelenchulus Cobb, 1920

 
Family Sphaerulariidae (Skarbilovich, 1947) Lubbock, 1861.

Diagnosis: Sphaerularioidea. Nematodes in this family have very short free-living life, females penetrate the host after mating. Females: Free-living stage: Stylet length11-19 μm well developed, conus with distinct lumen, stylet base tripartite or knobbed.Esophagus with glands not elongate. Vulva indistinct. Post vulval sac present or absent. Uterus very long with sperms in fertilized females. Ovary immature. Tail cylindroid with rounded tip. Parasitic stage: Found in the host haemocoel. Uterus large, everted usually hypertrophies into a sac containing oviduct, ovary, eggs and juveniles. Males: Not found in host. Similar to females. Testis outstretched, or reflect. Spicules cephalated. Bursa present, except absent in Tripius.

Type genus: Sphaerularia Dufour, 1837.

 Key to genera of Sphaerulariidae (Modified after Remillet & Laumond, 1991)

 
          1-       Parasitic female with uterus hypertrophied but not everted

                    .................................................................................................................................... Scatonema Bovien, 1932

                     Parasitic female with uterus partially or totally everted...................................................................... 2

          2.       Parasitic female with partially everted uterus not larger than body; male without

                    bursa ........................................................................................................................ Tripius Chitwood, 1935

                    Parasitic female with completely everted uterus much larger than body; male with

                    bursa ...................................................................................................................................................................... 3

 
             3.        Stylet knobbed; everted uterus surface smooth; bursa distinct, completely

            enveloping tail; parasites of bark beetles and hymenopterous parasitoids

                        ................................................................................................................ Sphaerulariopsis Wachek, 1955

                        Stylet not knobbed; everted uterus surface with numerous large rounded  elevations; bursa 

                       indistinct; parasites of bumblebee queens and their  hymenopterous parasitoids

                       ......................................................................................................................... Sphaerularia Dufour,1837

 Subfamily Deladinae Siddiqi, 1986

            Mycetophagous present. Parasitic female long and large. Type  genus : Deladenus Thorne, 1941 (Syn. Beddingia Blinova & Korenchenko, 1986.

 

Genus Deladenus  Thorne, 1941

Diagnosis: Mycetophagous females: Lateral field with 10 -15 incisures and reduced to 7-9 at vulva (observed with silver deposition). Four lips, each with a single papilla. Stylet 8-12 μm long, lumen narrow, basal knobs well developed. Esophagus with fusiform corpus. Isthmus narrow joining with intestine immediately posterior to nerve ring. Dorsal esophageal gland opening close to stylet base, subventral gland opening near mid-corpus. Excretory pore prominent. Hemizonid present. Vulva with protuberant lips, close to anus. Gonad single without post vulval sac. Males: similar to mycetophagous female. Bursa striated enveloping tail tip. Spicules and gubernaculum present, tylenchoid type. Spicule length variable 13-28 μm. Males associated with these mycetophagous females have large amoeboid spermatozoa (10-12 μm in diameter).

Infective females: Lateral field with 8-13 incisures, 3-5 on tail. Stylet very different from mycetophagous female, length variable 14-31 μm: lumen wide, laking of conspicuous knobs, not taper anteriorly but dorsally extended further than ventrally. Esophagus with cylindrical corpus, slightly constricted near stylet base. Isthmus short, broad. Vulva close to anus, barely protruding. Gonad single with a small post vulval sac. Males: associated with infective females have very small spermatozoa (1 -2 μm in diameter) consisting  mainly of nucleus. Mature parasitic females: Very large, 3-25 mm long 0.1- 0.5 mm wide, usually greenish in color. Esophagus and glands degenerate. Reproductive tube filled with eggs and juveniles. Position of vulva just discernible. Tail rounded or tapering.

Type species: Deladenus wilsoni Bedding, 1968

This nematode was first found as parasite of woodwasp Sirex noctilo (F).

             Genus Phaenopsitylenchus Blinova & Korenchenko, 1986.

This genus resembles Beddingia except, in Beddingia, free-living form may have several successive generations and the types of males; in Phaenopsitylenchus there is only one generation of parthenogenic female in the free-living form and one type of fungus-feeding males.

Type species: Phaenopsitylenchus laricis Blinova & Korenchenko, 1986.

 Family Iotonchidae Goodey, 1953 (Skarbilovich, 1959). Parasitic females found only in Paraiotonchium

Diagnosis: (Modified after Siddiqi, 1986)(Siddiqi placed this family in his new superfamily Iotonchoidea, 1986, Maggenti placed it in the super family Sphaerularioidea, 1991). Two types of females occur in host=s body cavity: a primary heterosexual female curving ventrally and spirally and a secondary parthenogenic female with larger body. Free-living form: Female stylet more than 18 μm long, usually without knobs but thickening present. Excretory pore at the level of,  or posterior to, nerve ring.

Ovary small. Post vulval sac absent. Tail elongate or conoid. Males: stylet and esophagus degenerate, stylet sometimes absent. Spicules strong, L-shaped or straight anteriorly and curved posteriorly. Bursa present or absent.

Type subfamily Iotonchinae Gooddey, 1963

 Genus Paraiotonchium Slobodyaniuk, 1975

Diagnosis: Iotonchinae. There are two types of female, heterosexual and parthenogenetic. Heterosexual females: Young females: impregnated in the environment with body straight or slightly curved ventrally. This is the infective form. Stylet well developed without knobs but usually slightly thickened. Esophageal glands lobe-like with three cells extending posteriorly beyond mid-body overlapping intestine dorsally. Esophageal glands openings prominent. Vulva in posterior fourth of body. Gonad prodelphic with large cylindrical uterus, ovary usually with three cells and terminal cap cell. Anus small, obscure. Tail tapering gradually to a point. Parasitic females: much larger than young female. Body strongly curved ventrally, forming C or O shape. Head truncate or rounded. Somatic muscle with prominent nuclei. Stylet as in young female. Esophagus degenerate. Intestine large, dark in color, nuclei of intestinal cells prominent, larger than those of muscles and gonad. Gonad prodelphic outstretched, extending beyond mid-body but never to base of esophagus. Germinal zone 3-4 oocytes wide. Tail curved ventrally sometimes spicate. Males: Posterior end of body well curved dorsally. Head continuous with body. Stylet shorter than that of female, very thin, no knobs or thickenings observed. Esophagus partially degenerate. Gonad monorchid outstretched, extending beyond mid-body, with two rows of cells. Spicules with anterior part almost straight, posterior part curved. Gubernaculum absent. Tail tapering to a point. Parthenogenic females: Cigar-shaped or long and swollen. Somatic muscles and intestine cells with prominent nuclei as in parasitic female. Stylet very thin without knobs. Gonad prodelphic wider and longer than that in heterosexual form. In most individual, ovary extending into head region, becoming reflexed. Germinal zone of ovary large 9-10 oocytes wide. Many eggs in uterus. Tail subcylindrical or tapering with or without mucron.  

 
Family Parasitylenchidae Siddiqi, 1986

Diagnosis: (Modified after Siddiqi, 1986). Sphaerularioidea. Two or three types of adult in host body cavity: primary heterosexual generation, secondary heterosexual and/or parthenogenic generation. Primary heterosexual female not spiral-shaped when relaxed. Female stylet generally under 18 μm long, distinctly knobbed. Orifice of dorsal gland close to or farther behind stylet base. Excretory pore usually anterior to nerve ring. Vulva less than two body widths from anus; no ventral body pore near vulva. Vagina poorly muscular. Post vulval uterine sac absent. Female tail short, conoid. Male may occur in host=s body cavity (Parasitylenchus). Spicules slender, ventrally curved, about 20 μm long or less (27-30 μm long in Parasitylenchus macrobursatus). Bursa enveloping tail, absent in Heterotylenchus. Gubernaculum present or absent.

Type subfamily Parasitylenchinae Siddiqi, 1986

 Subfamily Parasitylenchinae Siddiqi, 1986

Diagnosis: Pasitylenchidae.There are 2 free-living forms, males and females in the environment, and three forms, primary females, secondary female and male in host=s body cavity. Primary heterosexual female sausage or spindle-shaped, produces secondary heterosexual forms which copulate in body cavity of insects and produce male and female juveniles. These juveniles leave the host for further development to adults, copulation in the environment.

Type and only genus: Parasitylenchus Micoletzky, 1922

      Parasite of Coleoptera and Diptera.

 Subfamily Heterotylenchinae Siddiqi, 1986

Diagnosis: Parasitylenchidae.There are two free-living forms, males and females in the environment, and two forms, primary heterosexual females which produce only female juveniles that develop to parthenogenetic females, in insect body cavity. Parthenogenetic females produces male and female juveniles which exit the host for further development to adults and copulation occurs in the environment.

Type genus: Heterotylenchus Bovien, 1937 

Parasite of Coleoptera and Diptera.

 Key to genera of Heterotylenchinae (Modified after Remillet & Laumond, 1991)

 

1-         Parasitic females dorsally curved..................................................................................................... 2

            Parasitic females not dorsally curved............................................................................................... 3

2-         Both parasitic heterosexual and parthenogenetic females dorsally curved, parasites of  Siphonaptera     

            .................................................................................................Psyllotylenchus Poinar & Nelson, 1973

                        Only parthenogenic females dorsally curved, parasites of Siphonaptera

            .............................................................................Incurvinema Deunff, Launay & Beaucournu, 1985

3-         Cephalic region and papillae in parasitic females prominent; male with six pairs of  caudal papillae                                                        .......................................................................................................Paregletylenchus Slobodyanyuk, 1984

            Cephalic region and papillae in parasitic females not prominent; male without caudal  papillae .....  4

4-         Parasitic heterosexual female with elongate body; male without gubernaculum; parasites of Diptera           

            ....................................................................................................................Heterotylenchus Bovien, 1937

            Parasitic heterosexual female with sausage-shaped body; male with gubernaculum;

            parasites of Coleoptera    .............................................................Wachekitylenchus Slobodyanyuk, 1986

 

Subfamily Heteromorphotylenchinae Siddiqi, 1986

Diagnosis: Parasitylenchidae. Primary parasitic female in insect haemocoel produces only female juveniles which develop to 4th stage juveniles before leaving the the insect host. These Juveniles undergo the last molt and become parthenogenetic females which live on their food reserve, do not feed, and produce a small number of eggs.  These eggs develop into males and females, which mate. Fertilized females invade larvae, pupae or nymphs of the insect host. 

Type and only genus: Heteromorphotylenchus Remillet & Waerebeke, 1978

Parasite of Coleoptera.

 
Family Fergusobiidae Goodey, 1963 (Siddiqi & Goodey, 1964)

Nematodes in this family are unique, parastize both a plant and an insect. Adult males and females parasitized flower buds, leaf buds and stem tips of various Eucalyptus and Syzigium spp. in Australia and India. They cause galls to form in flower buds. The fertilized female invades and becomes parasitic in the haemocoel of females larvae of agromyzid flies of the genus Fergusonina.

 
Diagnosis: Sphaerularioidea. All forms partially obese. Stylet with knobs. Anterior part of esophagus swollen, cylindrical containing a large valve. Isthmus short, narrow, surrounded by the nerve ring. Posterior bulb glandular, slightly overlapping intestine dorsally. Female with one gonad, without post vulval sac. Male with bursa, spicules strong, gubernaculum absent. Tail of both sexes short, conoid.

Type and only genus: Fergusobia Currie 1937.

 Suborder Aphelenchina Geraert, 1966

Diagnosis: Nematoda. Stylet without knobs but sometimes with thickenings. Dorsal esophagal gland duct emptying into esophageal lumen within the large median bulb, anterior to the valve plates. Gonad one. Bursa sometimes with ribs, sometimes short enveloping only the tip of the tail, often absent. Spicules usually rose-thorn-shaped. Nematodes in this order are either living free in soil, predaceous on other nematodes, mycophagous, parasitic in leaves, roots, stems, and bulbs or are insect associates or parasites.

 

Family Entaphelenchidae Nickle, 1970. Nematodes in this family are either endo- or ectoparasites of insects.

Diagnosis: Aphelenchida. Usually with three adult forms, including vermiform male and female, and a swollen endoparasitic female. Two adult forms also present with ectoparasitic nematodes. Stylet with or without basal flanges. Esophagus with large median bulb and overlapping glands. Male usually without bursa. Spicules rose-thorn-shaped. Gubernaculum absent.

Type subfamily Entaphelenchinae Nickle, 1970

Subfamily Entaphelenchinae Nickle, 1970

Diagnosis: Entaphelenchidae. Nematodes with at least three adult forms. Stylet short, less than 25 μm. Endoparasites of insects.

Type genus: Entaphelenchus Wachek, 1955

Diagnosis: Entaphelenchinae. Three adult forms. Small vermiform males and females 0.5-1.0 mm long not found in insect body cavity. Labial region offset. Stylet 17-22 μm long, without basal knobs. Excretory pore posterior to median bulb. Ovary with few cells, post vulval sac short. Tail conoid with rounded tip. Spicule paired, rostrum prominent. Tail conoid with rounded tip. Bursa and gubernaculum absent. Parasitic form large 1.3-2.5 μm, found in insect body cavity. Perivaginal glands well developed, filling the body in this region. Body usually convoluted. Tail with spike-like tip.

Type species: Entaphelenchus oxyteli Wachek, 1955


Genus Peraphelenchus Wachek, 1955

Diagnosis: Entaphelenchinae. Three adult forms, all found in insect body cavity. Stylet 17-18 μm with wide lumen, without knobs. Procorpus cylindrical, lumen wide. Median bulb absent. Basal bulb with valve. Esophageal glands as a long lobe. Female ventrally curved. Ovary with fee cells, post vulval sac present. Tail short, conical. Male scorkscrew-shaped. Spicules with prominent rostrum. Tail bluntly rounded with two pairs of postanal caudal papillae. Parasitic female with larger body, ovary short.

Type species: Peraphelenchus necrophori Wachek, 1955

 Genus Praecocilenchus Poinar, 1969

Diagnosis: Entaphelenchinae. Three adult forms found in insect body cavity. Female and male found in uterus of adult parasitic females. Labial region not offset. Stylet 8-10 μm with wide lumen, without basal knobs. Female very small, less than 0.4 mm long. Esophageal gland long, extending to midbody. Ovary short, post vulval sac short. Tail conical. Male small 0.4-0.5 mm long spicule paired, rose-thorn-shaped with prominent rostrum. Tail curved. Bursa and gubernaculum absent. Parasitic female body large 0.9-2.3 mm long and swollen, C-shaped, curved ventrally. Uterus containing sexually mature males and females, post vulval sac absent. Stylet short with wide lumen. Vulval lip protruding. Tail bluntly rounded.

Type species: Praecocilenchus rhaphidophorus Poinar, 1969

Genus Roveaphelenchus Nickle, 1970

Diagnosis: Entaphelenchinae. Three adult forms found in insect body cavity. Stylet slender without basal knobs. Esophageal glands short. Female: Ovary one, usually with one large juvenile in uterus, post vulval sac absent. Tail cylindrical, ending in four mucronate point. Male: when relaxed, tail well coiled. Testis reflexed. Spicules with prominent rostrum. Tail bluntly rounded. Caudal papillae not seen. Bursa and gubernaculum absent. Parasitic female: body swollen, ovary convoluted, extending to neck region. Uterus containing pre-adult stage juvenile. Tail short, digitate.

Type species: Roveaphelenchus jonesi Nickle, 1970

 Subfamily Acugutturinae Hunt, 1980

Diagnosis: Entaphelenchidae. Nematodes with two adult forms. Stylet very long, 50 to more than 100 μm. Ectoparasites of insects.

 Genus Acugutturus Hunt, 1980

Diagnosis: Acugutturinae. Body 0.6-0.9 mm long with a single lateral line. Head rounded, offset by, constriction. Stylet long 50-60  μm, slender with conus three times longer than shaft, basal knobs absent. Procorpus long, reflexed. Female gonad one without post vulval sac. Tail conical. Spicules rose-thorn-shaped with prominent rostrum. Tail without bursa, two pairs of caudal papillae present. Ectoparasite of American cockroach.

Type species: Acugutturus parasiticus Hunt, 1980

 Genus Noctuidonema Remillet & Silvain, 1988

Diagnosis: Acugutturinae. Body 0.5-0.8 mm, females swollen, club-shaped. Stylet very long (over 100 μm) with small basal thickenings. Procorpus long and reflexed. Excretory pore very anterior. Gonad one, outstretched. Tail very short. Spicule large, 90 μm long with long ventral arm. Gubernaculum absent.There are two pairs of genital papillae, one preanal and one caudal. A small terminal bursa present. Ectoparasite of noctuid moths.

Type species: Noctuidonema guyanense Remillet & Silvain, 1988

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Thorne, G.1949. On the classification of the Tylenchida, new order (Nematoda, Phasmidia. Proceedings of the Helminthological Society of Washington 16:37-73.

 Wachek, F. 1955. Die entoparasitischen Tylenchiden. Parasitol. Schriftenr. 3:1-119.

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Update on April 12 2010