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Life cycle of Rhabditis sp.

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Life cycles differ depending upon the species of nematode. life cycle is summarized in( Fig.1). The
nematode parasite (Rhabditis sp.) infected earthworms (Allolobophora caliginosa) (Fig.2,A), but only in its larval stage(Second
stage), encapsulated in the body wall or in the coelom were mostly active
juveniles  or infective stage, whereas
others were able to encapsulated and  incorporated
into “brown bodies ” in the earthworm coelom (Fig.2,B),and this
encapsulation process is an effective defense reaction(Fig.2,C). Rhabditis
larvae found in earthworm (Fig.2,D)develop only when the earthworm dies and
complete the life cycle in soil. Dead earthworm were completely decomposed,
with only a faint outline remaining. When “brown bodies” that
represents spherical masses of host cells surrounding parasites and containing
living nematodes were placed on nutrient agar, only a few nematodes escaped,
and cultures were rarely established. no sign of inflammation in the  earthworm was noted. All of the 585 specimens
of (Allolobophora caliginosa) which were collected contained 151 of Rhabditis
sp.

 Larvae begin feeding on the
bacteria in soil that the tissues losses from 5 days  to weeks days. of Mostly died after lay the
eggs .Fourth stage larvae of Rhabditis sp. Appeare in two shapes females
more than males (from week to 10 days ). Adult Rhabditis sp. lay eggs
after 10 -15 days. Once formed, first and second stages the infective Rhabditis
sp.  will continue their development, on
fresh box cultivated  with bacteria.
These nematodes will continue their life cycle by finding the earthworm and penetrate
the earthworm’s pores and cocoons’  host.
Infective larvae of Rhabditis sp.  were able to persist in the soil
with lack of food up to 4 weeks, thus increasing their chance to meet a host. In the
earthworm’s host developed to third stage in life cycle.

Description of Rhabditis sp. ( Based on 10 males and 10 females )

Light microscopically study:

stage larvae of Rhabditis sp., (Fig.4,L)
were collected from the anterior of the coelom of living earthworm
host(Fig.2,D). Adult Rhabditis sp., male(Fig.4,A)and female (Fig.4, E) were
collected from a culture as free living 
nematode ,151 out 585 Allolobophora caliginosa were infected and
prevalence of infection was 25.81% , males 52 out 151 and prevalence of
infection was 34.43% and females 99 out 151 and prevalence of infection was 65.56%.
The excretory pore is below the level of the esophageal bulb ,the esophagus
ends in valvulate, sub-spherical bulb which is separated from esophageal body
by small constriction ,the posterior part of tail is elongated, smooth and form
a thin needle-like projection (Fig. 3).

Scanning Electron Microscopically study:

Male
:

          SEM micrographs show that the  males (Fig.4,B) Body cylindrical and color
are creamy white ,small and cylindrical in shape, Cuticle thick(Fig.4,J)  is 4 – 6 µm (av.=5) µm, bearing a pattern of
tiny dots arranged transversely and longitudinally rows. the body length is 1750 -1850µm (av.=1800)
and the width is 210-190µm (av.200).  The
esophagus is cylindrical and the length (including bulb) is 290-270 µm (av. =280).  The alae are well expanded near the posterior
end of body .Two lateral cuticle alae extending along body, interiorly  initiating slightly in front of nerve ring
level and posterioly reaching to cloacae. 
The alae reached 30-50µm in width and 100-150 µm in length.  the distance of excretory pore from the
anterior end is 540-650 µm(av.=595) . Nerve ring is 300 – 380 µm (av.=340). Filiform
tail conical-elongate (Fig.4,D)  extends 302-279
µm (av.=291)beyond postcloacal papillae and no specula is present . There are
three pairs of genital papillae, not all included in caudal alae.  The first pair of papillae is preanal and
formed by small sessile papillae. The second one is the first of the post anal
pairs and situated near the posterior border of caudal alae.  The second postanal pair is formed by a large
pedunculated papillae and situated immediately below foregoing pair.

Female:

          The female (Fig.4,F) is larger than
male, the length of gravid females is 2800-2000 µm (av.=2400) and the maximum
width is 370-400 µm (av.= 385). The mouth is surrounded with six lips(Fig.4,C).The length of esophagus
(including bulb) is 450-350 µm (av.=400) with a 81– 140 µm wide posterior bulb.
 Nerve ring and excretory pore lie 340 –
398 µm (av.=369) and 510 – 600 µm (av.=555) respectively from anterior
extremity.  vulva lies anterior 145 – 80 µm
(av.=112.5). The valval opening is transversely oval shaped and possesses
double walled anterior and posterior cuticular lips . A narrow cuticular
transverse groove possessing anterior and posterior cuticular folds is present
at a short distance behind the vulva. In live worm the vagina was seen as a
straight muscular measuring 141 µm long. The uterus occupied most of the body .The
ovaries are situated at the posterior half of body .The vagina is extending
inwards to one-third of body diameter, with thicker walls at proximal portion .
The uterus contains large number of a thick walled, smooth and elongated eggs (Fig.4,K)  , the egg measured 64.6 x28.6 µm. The tail(Fig.4,I)  is filiform tail, 480- 420 µm (av.=450)  in length. The cuticle surface of the body is
regularly transversely striated, each is 0.025 mm wide .Mouth opening is
triangular .  The mouth is surrounded
with six lips(Fig.4,G)
 .The 6lips possess 3 oral papillae. On
each side of the body, the lateral alae is represented by two longitudinal and
parallel ridges separated by a smooth cuticular band . About 10-12 longitndinal
ridges start from cervical region and run posteriorly to end slightly anterior
to the bursa in the male or behind the level of the vulva in the female .      

 Figure 1. Developmental
stages in the life cycle of Rhabditis sp. infected earthworms
(Allolobophora caliginosa).

Table1: Measurements of (in µ m) of males (n = 10) and females (n = 10) of Rhabditis sp.

Characters

Males

Females

Host

Allolobophora caliginosa

Allolobophora caliginosa

Locality

Assiut

Assiut

numbers

10

10

Habitat(adult)

Free
living in adult form

Free
living in adult form

Habitat(larva)

The coelom
of earthworm

The coelom
of earthworm

Length

1800

2400

Width.

200

385

Cuticle thick

4-6

4-6

Cuticle tiny dots

2.5- 2.8 x3.3-3.7

2.5- 2.8 x3.3-3.7

Esops-length

400

280

Bulb

30

50

Excretory pore.

595

612

Vulva

112.5

Lips

6

6

Nerve ring

340

369

lateral alae

present

present

Tail

291

450

Ovum

64.6
x28.6 µ

 

Figure2.
A; Earthworm “Allolobophora caliginosa”
with
“brown body”(arrows) and (circle)  B;  Rhabditis
sp. In capsule or “brown body” in the earthworm “Allolobophora caliginosa”,C; A
section in the earthworm showing cyst (circle)
(H& E X 100) and ,D; section in the earthworm
showing Rhabditis sp. Larvae
(circles)
(H& E X 100).

 

 .                                                                                           
 

 

Figure
3. Rate
of natural infection with nematodes “Rhabditis sp.” In the Assiut  earthworms, “Allolobophora caliginosa”.        

Figure 4. Developmental
stage in the life cycle of Rhabditis SP.A;
Morphological
characters of male ,B;  adult male of
Rhabditis SP by SEM,C; anterior region of male
,D; Lateral view of male tail by SEM,E; Morphological characters of female ,F; adult
female of Rhabditis SP by SEM,G; anterior
region of female ,H; anterior region of female
showing 6 lips ,I; Lateral view of female tail by SEM,J; Cuticle
structure by SEM,K; ovum by SEM ,L; and M; Juvenile
nematodes .

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