Heterorhabditidae - Diagnostic Characters

Family Heterorhabditidae Poinar, 1976
Diagnostic characters:(Rhabditida. Rhabditoidea.) Obligate parasites of wide range of insects.
Adults: Stylet absent. Head truncate or slightly rounded, having six distinct lips which may be fused at base; each lip with a single labial papilla; two additional papillae at the base of each submedian lip; lateral lip with a single cephalic papilla and a circular amphidial opening. Cheilorhabdions present as a refractile ring in anterior part of stoma. Posterior part of stoma collapsed , with reduced pro-, meso, and metarhabdions. Base of stoma surrounded by oesophagous. Oesophagous with wide and cylindrical procorpus, followed by narrow isthmus, and then expanding into distinct basal bulb with reduced valve plates. Nerve ring distinct, surrounding isthmus in females and basal bulb in males. Excretory pore always located posterior to nerve ring in all the stages.
Females: Hermaphrodites with sperms in proximal portion of ovotestes and functional vulva. Amphimictic females with didelphic amphidelphic reflexed gonad. The reflexed portion long, extending past the vulval opening. Sperms in proximal part of oviduct. Vulva functional only for mating, but otherwise non-functional due to ovoviviparous nature. Mated females often with a mucoidal substance ( mating plug ) around the vulva. Tail pointed with postanal or anal swelling. Rectal glands present.
Males: Testis single and reflexed. Spicules paired and separate, nearly straight. Gubernaculum present. Bursa present, open, peloderan or weekly leptoderan, supported by nine pairs of genital papillae.
Infective juveniles: Third stage juvenile often inside the second stage cuticle. Body tapers more in the posterior region to a long acutely pointed tail. Head with armature on the dorsal side ( hook or spine ) sometimes opposed by small subventral spine. Mouth and anus closed. Oesophagous narrow with a weak basal bulb having weakly developed valve plates. Cuticle with paired longitudinal double lines, while second stage ensheathing cuticle with numerous longitudinal ridges. Excretory pore posterior to nerve ring. IJs develop into hermaphrodites.
Family Heterorhabditidae
(emended): Rhabditoidea, Rhabditida. Obligate insect parasites. Infective juveniles carrying symbiotic bacteria. Both hermaphroditic and amphimictic females present.
Hermaphroditic females(FIG.SEM): After entry into an insect host, infective juveniles developing into hermaphroditic females. Head truncate to slightly rounded, six conical lips well developed, separate, each with a terminal papilla; one or two small raised structures sometimes visible at the base of each lip; amphidial opening small. Stoma wide but shallow; cheilorhabdions present, forming a ring, in lateral view resembling two refractile elongate structures.Other parts of the stoma fused to form a collapsed posterior portion. Posterior part of stoma covered by esophagus. Esophagus without metacorpus; isthmus slender; basal bulb swollen; valve in basal bulb reduced. Nerve ring at middle of isthmus. Excretory pore usually posterior to end of esophagus. Vulva slight anterior to mid-body (V%=43-48), slit-like, surrounded by elliptical rings; ovotestis amphidelphic, reflexed. Oviparous, later becoming ovoviviparous. Tail pointed, longer than anal body width, postanal swelling usually present.
Amphimictic females: Similar to, but usually smaller than, hermaphroditic female; labial papillae prominent. Reproductive system amphidelphic. Vulva not functional for egg deposition, but functional for mating.
Males: Testis one, reflexed. Spicules paired, separate, slightly curved ventrally. Spicule head short, offset from lamina by a constriction. Gubernaculum usually about half as long as spicule length. Bursa peloderan with nine pairs of genital papillae.
Infective juveniles: Third-stage infective juvenile usually with sheath (cuticle of second-stage juvenile). Sheath with anterior tessellate pattern and longitudinal ridges; IJ cuticle striated with one smooth band marginated by two ridges in lateral fields. Head with prominent dorsal tooth . Mouth and anus closed. Stoma appearing as a closed chamber with parallel walls. Esophagus and intestine reduced. Excretory pore posterior to nerve ring. Symbiotic bacterial cells found in intestine. Tail pointed.

Type and only genus: Heterorhabditis Poinar, 1976
Compendium and Key to the species
A compendium of valid 8 species of Heterorhabditis has been prepared on the basis of morphometric characters of infective juveniles ( Table 4 ) and first generation males ( Table 5 ). Hominick et al., (1997) provided a key to the species of Heterorhabditis wherein they used the character "presence or absence of rostrum in spicules" which may not be easily seen by novice taxonomists. Therefore, following key to the species of Heterorhabditis is proposed with some modifications.

Heterorhabditis zealandicaPoinar, 1990
Females: Hermaphroditic females (first generation) with cuticle smooth, lateral lines not observed. In small females lip region with pronounced labial papillae projecting. In large females lip with wide shoulders surrounding stoma. Labial papillae large, resemble flaps that may have a function in foot gathering. Cheilostome as long as wide with thick non- sclerotized walls. Protostome-telostome initially as wide as cheilostom, taping posteriorly, in larger females expanding, becoming wider and shorter, funnel shaped. Oesophagus short in relation to total length narrowing at of nerve ring. Basal bulb pyriform, large as compared to other stages but small in relation to body size, valve distinct. Cardia present. Excretory pore at level of basal bulb. Genital tract paired, reflexed. Uterus and spermatheca located ventrally between vulva and reflex, ovaries located dorsally beyond reflex. Vulva lips protruding. Rectum and anus distinct. Body slightly widening near anus. Tail tapering rapidly over anterior half, especially in large thick females, more slowly over posterior half. Small females usually with slight swelling in posterior half of tails which tend to disappear in larger animals when tail swells, tail tip usually rounded.
Amphimictic females(second generation females> are identical to small first generation females and, differ from large first generation females as follows: typical protruding labial papillae never develop into elaborate flaps; wide shoulders of lip region and wide open, funnel shaped protostome-telostome of large first generation female absent, usually no eggs are laid; no sperm observed; vulva occasionally excreting mucous never observed in first generation females. Males: As it is assumed that the males do not feed their morphometrics may be of importance. Cuticle smooth, no lateral lines. Lip region and stoma as in pre-adult female. Esophagus more than half body width wide narrowing distinctly at level of nerve ring, basal bulb pyriform with distinct valve. Cardia large. Excretory pore located posterior to level of base of oesophagus. Testis transparent, reflexed, fills body width posteriorly and approximately half body width anteriorly. Spicules slender, paired. Gubernaculum small, single. Tail tapering as in pre-adult male. Tail tip with clear digitate blunt terminus. Bursa enveloping tail, supported by nine pairs of papillae, three preanal, six postanal.
Measurements (n=15): L: 914 (848-1044) micrometers (um); greatest width: 41 (36-45) um; length of esophagus: 118 (110-128) um; length of basal bulb of oesophagus: 23.7 (22-26) um width of basal bulb: 17.5 (16-19) um; body width at level of base of esophagus: 32 (30-34) um; distance from anterior end to excretory pore: 139 (130-150) um; testis length: 656 (562-780) um; spicule length: 51 (48-5-5) um; gubernaculum length: 22.2 (19-25) um; body width at level of anus: 20.7 (18-24) um; length of tail: 35 (30-41) um.
Infective juveniles: As the free-living, infective juveniles do not feed and their internal developments proceeds very slowly, without further growth, the body length and other morphometrics vary little and may be of diagnostic importance. Body slender, tapering regularly from base of esophagus to anterior end and from anal area to tail terminus. Cuticle with large number of longitudinal lines starting short distance behind the head and terminating on tail. Transverse annulation present between lip region and level of excretory pore. Lip region smooth , not set off. Cheilostome narrow rounded in face view, asymmetrically running between thick lips of cephalic region. Protostome-telostome a wider tube of sclerotised, indistinct triangles anteriorly and with continuous cylindrical lining posteriorly. Cephalic region with six papillae, six lips and two amphid. Esophagus long and narrow, with triradiate lumen, 1/3 to 1/4 body width wide, narrowest at level of nerve ring, terminating in valved bulb. Nerve ring distinct, cardia present. Excretory pore and hemizonid obscure. Wide lumen of anterior end of intestine containing bacteria, rest of intestine inactive. Intestine wall dark with globules. Genital primordium obscure. Sphinter muscle between rectum and intestine distinct. Rectum thick walled. Anus distinct. Tail conical with very narrow pointed terminus. Phasmids and deirids not observed.
Measurements (n = 25): L = 685 um (570-740); width = 27 um (22-30); distance of the: rhabdions from the anterior end = 7.6 um (3.5-6.0); rhabdion length = 11.0 um (9.0-12-5); distance of nerve ring from anterior end = 100 um (90-107); distance of hemizonid and excretory pore from anterior end = 112 um (94-123); esophagus length = 140 um ( 135-147); tail length = 102 um (87-119).
DIAGNOSIS Heterorhabditis zealandica is characterized by body length (685 um), E% (108)and c ratio (6.6) of infective juveniles. Spicule long (51 um) and body width of male are also good identifying characters of this nematode species.
Heterorhabditis spp.
Key to the species of Heterorhabditis
(Based on infective juveniles and males)
1. Infective juveniles with average L > 700 ?m; males with long mucron
extending beyond the bursal membrane --------------------------------------- H. megidis
- Infective juveniles with average L < 700 ?m; males without long mucro, not extending
beyond the bursal membrane ------------------------------------------------ --- 2
2. Infective juveniles' average tail length < 80?m ( 68-80 )------------------- H. brevicauda
- Infective juveniles' average tail length > 80 ?m ( 82-119) -------------------3
3. Average testis reflexion > 145 ?m( 147- 174 )--------------------------------------4
- Average testis reflexion < 145?m ( 79 - 132 ) --------------------------------------5
4. Males'average L = 998?m (864-1130); excretory pore < 150 ?m ( range 71-146 ); IJs
mean ratio c < 6.5 ( 5.8-6.4 ) -------------------------------------------H. hawaiiensis
- Males' average L= 1445?m; excretory pore > 150?m ( range 145-172 ); IJs mean ratio
c > 6.5 ( 6.7- 8.1) --------------------------------------------------------H. argentinenesis
5. IJs mean ratio c < 5.5 (4.5-5.6); IJ's average ES<120?m---------------- H. indica
- IJs mean ratio c > 5.5( 5.5-7.0); IJ's average ES>120?m ---------------------------------6
6. IJs mean ratio c=6.0; mean ratio e >1.0 (0.89-1.1)------------------------- H. marelatus
- IJs mean ratio c > 6.0; mean ratio e >1.0( 1.03-1.3 ) ---------------------------------------7
7. IJs average L=588?m( 512-670);oesophagous<130?m( 100-139);Males testis
reflexion <100?m (59-87); spicule length < 45?m (36-44)------------H. bacteriophora
- IJs average L=685?m (570-740); oesophagous >130?m ( 135-147);Males' testis
reflexion > 100?m ( 88-173 ); spicule length > 45?m (46-52)---------------- H. zealandica