Steinernema affine

(Bovien, 1937) Wouts, Mracek, Gerdin & Bedding, 1982

DESCRIPTION

Females: Cuticle smooth, head rounded not offset from rest of body, six lips united at base but distinct at tips. Each lip bearing a single labial papilla forming an inner circle of six papillae. A second outer circle was observed with four cephalic papillae. Amphids present. Stoma as in other steinernematids. Cheilorhabdions a thick sclerotized ring represented by two thick dots in lateral view. Below this is a second, smaller sclerotized ring representing the prorhabdions. The last part of stoma partially collapsed forming a funnel-shaped structure. Esophagus muscular with cylindrical procorpus followed by a slightly swollen nonvalvated metacorpus. Below this is the isthmus followed by a basal bulb containing a reduced valve lined with refractive ridges. Nerve ring is located near center of the isthmus. Lateral fields and phasmids inconspicuous. Gonads amphidelphic, reflexed Vulvar lips protruding. Tail usually with a terminal knob at base, while the second generation females possess a straight tail which often ends in a fine mucron.
  1.  Males : Anterior region similar to females except nerve ring usually resting on anterior portion of basal bulb. Testis single, reflexed. Spicules variable in shape (FIG.SEM), moderatelly curved and colorless. Spicule head somewhat longer than wide. Shaft short. Blade smoothly curved to both end. Velum present. In ventral view, gubernaculum tapering smoothly anteriorly to a ventrally curved end. Cuneus long, needle-shaped, pointed posteriorly (Fig. SEM). Twenty three genital papillae present with eleven pairs and a single ventral preanal one. Five pairs subventral, anterior to cloaca, three pairs in the region of spicule and gubernaculum ,two pairs ventral subterminal, one pair poscloacal, subdorsal.

Measurements (n=10): Length=1800 micrometers (um), width=118 um (95-164), stoma length=4.2 um (3.2-6.4), stoma width=5.1 um (3.2-6.4), anterior end to excretory pore=94 um (82-114), to nerve ring=105 um (89-117), esophagus length=153 um (136-174), testis reflexion=715 um (485-926), tail=51 um (45-56), width at cloaca=60 um (53-72), spicule length=70 um (67-86), spicule width=14 um (11-19), gubernaculum length=46 um (37-56), gubernaculum width=9.6 um (8-10). D%=61 (60-66), GS (gubernaculum/spicule)=0.66.

Infective juveniles : This stage is a third stage juvenile that is often still enclosed in the second stage cuticle. The mouth and anus are closed and intestine collapsed. Cells of Xenorhabdus spp. are contained in a modified vesicle in the anterior portion of the intestinal lumen. All mature infective juveniles with a minute spine in the tip of their tail.

 Measurements (n = 15): Length= 693 (608-880); width= 30 um (28-34); distance from head to excretory pore = 62 um (51-69); to nerve ring = 95 um (88-104); esophagus length = 126 um (115-134); tail length = 66 um (64-74); anal body width=17 um (16-19); a=23 (21-28); b = 5.5 (5.1-6.0); c = 10.5 (9.5-11.5); D = 0.49 (0.43-0.53); E = 0.94 (0.74-1.08).

 Diagnosis and relationships

Bovien (1937) provided only two quantitative characters of S. affine and these were the length (1.0-1.62 mm) and width (59-100 um) of the males (no designation regarding whether these were the first or second generation). Additional descriptive remarks were restricted to qualitative characters which separated S. affine from S.feltiae. As Bovien (1937) pointed out, S. affine could be separated from S.feltiae : 1) color of the spicules, grey or colorless in S. affine but orange-brown inS. feltiae; 2) the slope of the spicules (shorter capitulum and more curved calomus in S. afine); 3) shorter average size of infective stages (693 um for S. affine and 825 um for S. feltiae) although there is some overlap in ranges and 4) the presence of spine in the tip of the tail of the infective stages of S. affine (absent in S. feltiae). Bovien (I 937) also stated that the gubemaculum of S. affine was more evenly curved without a proximal knob or hook, however in the present investigation, knobbed and hooked gubernacula were observed. The size of the infective stage, presence of a spine in the infective stage tail, color and shape of the spicules, and presence of a minute cuticular male tail spine separate S. affine from the previously described S. glaseri, S. carpocapsae, S. intermedium, N. anomalae and S. rarum . The presence of a spine in the tail tip of the infectives is unusual in neoaplectanids. In S. affine, this structure appears only in the fully mature infectives and is very minute. It is now apparent that the form that Poinar (1979) redescribed as N. bibionis was in actuality S. affine since the isolations made in Denmark obviously comprised both species and the description fits N. affinis as redescribed by Poinar, 1988. It is interesting to note that the bacterial symbiont of S. affine is similar to the Xenorhabdus symbiont of S. feltiae.

 Type materials : Bovien (1937) designated no types for N. affinis. Through the courtesy of Dr. K. Lindhardt, Poinar was able to examine Bovien's original slides of N. affinis and N. bibionis. Bovien designated preserved material of N. affinis as " Neoaplectana bibio II " and of N. bibionis as " Neoaplectana bibio I ". Unfortunately the slides were mostly broken and the nematodes had dried, so it was impossible to obtain any meaningful quantitative data from these specimens. However, Poinar had designated a lectotype slide containing males of N. affinis and two paralectorypes, one with males and one with females. These, as well as topotypes of both sexes from the subsequent collection of Poinar and Lindhardt (I 97 1) are deposited in the Nematology Collection at the University of California, Davis, California, USA.

REFERENCES

Bovien, P. 1937. Some type of association between nematodes and insects. Videnk. Meddr
Naturh. Foren. 101: 1-114.

Poinar, G. O. 1988. Redescription of Neoaplectana affinis Bovien (Rhabditida: Steinernematidae).
Revue de Nematology 11:143-147.

This document was constructed and is maintained by KHUONG B. NGUYEN
Entomology & Nematology Department
University of Florida