When possible, specimens used to identify species of Steinernema should be reared in vivo (Galleriamellonella or another appropriate host), and adults of the first generation should be dissected from the cadavers. Infective juveniles collected for a week after their frst emergence from cadavers usually meet the criteria of the original descriptions but the body lengths of those collected after that period tend to be significantly shorter. All data may be obtained from either live or fixed specimens. Species of Steinernema can be identified with the following key. But, while using a key, one should keep in mind that keys are only used to narrow decision, the identity should be verified by comparing its morphometrics, morphological characters with the data from original descriptions. Ratios and abbreviations used in the following key are: D% = EP/ES x 100 (EP = distance from anterior end to excretory pore; ES = esophagus length); E% = EP/T x 100 (EP = distance from anterior end to excretory pore; T = tail length); IJ = infective juvenile; SW = spicule length divided by anal body width.
Key to species of the genus Steinernema
1- Infective juvenile (IJ) with a double horn-like
structure on labial region .......................... 2
IJ without a double horn-like
structure on labial region ..................................................3
2- Body length of IJ 769 (648-873) um, spicule length 65
(53-70) um, SW=2.22
(2.18-2.26) .........................................................................................
S.
bicornutum
Body length of IJ 706 (691-800) um, spicule
length 71 (54-90) um SW=1.4
(1.0-2.0) ..........................................................................................S.
ceratophorum
3- Body length IJ >800 um ...............................................................................................4
Body length of IJ <800 um .........................................................................................13
4- Average length of IJ greater than 1,000 um ...................................................................
5
Average length of IJ less than 1,000
um .........................................................................9
5- Tail of IJ 67-88 um..................................................................
................................... 6
Tail of IJ >90 um ..........................................................................................................
8
6- D% about 93 (88-102), spicule length 84 (81-91) um, spicule
tip ball-shaped
...........................................................................................................
S. arenarium
D% about 70, spicule length about 77
um, spicule tip not ball-shaped .............................7
7- EP about 82 (76-89) um, E% about 94 (87-100), c about
12.6.........................S. caudatum
EP about 102 (87-110) um, E% about 131
(122-138), c about 14.7......................
S. glaseri
EP about 106 (101-114) um, E% about
160, c about 19.2............................. S.
cubanum
8- E% averaging 101 (88-108); in male D% about 77.…….............…....…
S.
puertoricense
E% averaging 85 (range not known); in
male D% about 62............…… S. longicaudum
9- In IJ, EP extremely short, 18 (14-22) um, E%=23; in
male, D% averaging 19 (13-25)
.............................................................................................................S.
neocurtillae
In IJ, EP=53 um or more, E% about 69-110;
in male, D%>50.. ..................................10
10- Male tail with mucron ..............................................................................................11
Male tail without mucron
................................................................ .........................
12
11- Spicule head as long as wide, spicule length 49 (42-53)
um, body
length averaging 951 (797-1102)
um ......................................................... S.
kraussei
Spicule head 1.5-2.0 times
as long as wide, spicule length 70 (65-77) um, body
length averaging 849 (736-950)
um ...........................................S.
feltiae (=bibionis)
12- Body length averaging 980 (820-1110) um; spicule length
71 (65-73) um
............................................................................................................
S.
oregonense
Body length averaging 932
(876-982) um; spicule length 83 (73) um
.......................................................................................................................S.
karrii
13- Average length of IJ >600 (622-693) um .................................................................
14
Average length of IJ <600
(510-589) um ................................................................17
14- IJ tail length 77 (71-95), E%=76 (63-86), c=9.3 (7.6-11.1);
in male D%=55 (49- 61)
.............................................................................................................S.
monticolum
IJ tail length averaging
62 (maximum 74), E%>94, c>10; in male D%>60................. 15
15- Spine-like structure inside IJ tail tip; mucron present,
small.............................. S. affine
No spine-like structure
inside IJ tail tip; mucron absent 16
16- Spicule length about 93 (80-106) um; E% about 96 (89-108)
............. S. intermedium
Spicule length about 67
(63-75) um; E% about 105 (93-111)…..............….S.
riobrave
17- Average body length of IJ about 510 um or less.......................................................
18
Average body length of IJ much
longer........................................................................
21
18- Average body length 446 (398-495) um, tail length 36 (31-41)
um
…………………………………………………...............…..…….……S.
siamkayai
Average body length about 510 um or
more, tail length 50 um……...................……….19
19- First generation male without mucron; spicule length
69 (58-75) um, SW=1.56
(1.44-1.57); in IJ, E% averaging
88................................................................. S.
ritteri
First generation male with mucron;
spicule length 47 (42-52) um, SW = 0.94
(0.91-1.05); in IJ, E% averaging
72 .................................................................S.
rarum
20- Male tail without mucron ..........................................................................................21
Male tail with mucron ...............................................................................................22
21- Body length of IJ averaging 589 (424-662) um, spicule length/
spicule width about 3.9
(3.6-4.3)……………….................……..............................……….…….S.
kushidai
Body length of IJ averaging 541 (496-579)
um, spicule length/spicule width about 5.1
(4.7-5.8) ………………………….............................………………….…S.
abbasi
22- Spicule length 83 (72-92) um, spicule shaft prominent,
SW ratio averaging 2.52
(2.04-2.80),
female with large, double-flapped epiptygma..................S.
scapterisci
Spicule shorter, female
without epiptygma ..............................................................23
23- Body length about 558 um, spicule length 66 (58-77)
um, spicule shaft very short ,
SW ratio averaging 1.72
(1.40-2.00)………………....………….…S. carpocapsae
Body length 530 um, spicule
length 77(71-84) um, spicule shaft long, SW ratio
averaging 2.0 ………………………………………………………………S.
tami
To
identify species of Steinernema and Heterorhabditis, the
following should be considered:
a) IJ morphometrics
usually are insufficient for species identification, and male and female
characteristics must be used.
b) IJ produced
on artificial media (laboratory reared or commercial products) are shorter
(rarely longer) than those produced in vivo, and usually
do not meet the criteria of the original description. Males and females
collected 4 or 5 days after the host dies, and IJ collected for one week
after they first appear from cadavers, usually meet original species descriptions.