LIGHT AND SCANNING ELECTRON MICROSCOPIC STUDIES OF THE DEVELOPMENTAL STAGES OF RHABDITIS SP. (NEMATODA: RHABDITIDAE) NATURALLY INFECTING THE EARTHWORM "ALLOLOBOPHORA CALIGINOSA" (ANNELIDA: CLITELLATA) IN EGYPT

The earthworms are one of the most familiar invertebrate animals, which have environmental, clinical and economic beneficial importance. It is of very high importance to identify and study precisely the parasites that inhibit the earthworms. The present work aims to stud the incidence of Rhabditis sp. parasitic infection of earthworms, with special reference to its life cycle and morphological characterization by light and scanning electron microscopy. In the present study, two hundreds of earthworms were collected from March 2014 to February 2015 from four different cities of Assuit Governorate. The study revealed that 52 out of 200 earthworms were infected with nematodes Rhabditis sp. with total infection prevalence (26%). The presence of infected earthworms at four different cities Abnub (7/32, 21.8 %), Abu-Teg (12/45, 26.7 %), Assiut (24/80, 30 %) and El-Fath (9/43, 20.9 %) was found. Eighty-five of nematodes Rhabditis sp. were collected from 52 infected earthworms. The percentage of nematode of males was 47.1% (40/85) and that of females was 52.9 % (45/85). The life cycle of Rhabditis sp. naturally infecting the earthworm, Allolobophora caliginosa was described as the following: (a) the ovum: is thick-walled, smooth, elongated and measured 64.6 ´ 28.6 µm; (b) the larval stages: the length of first stage larvae is 0.75-0.80 mm (average = 0.77 mm), while the length of the second stage larvae is 0.85-0.92 mm (average = 0.89), which is naturally infected earthworms and encapsulated as multiple capsule or brown bodies, the length of the third stage larvae is 0.95-1.2 mm (average = 1.07 mm), which will develop only when the earthworm dies and then complete their life cycle in soil and invaded by bacteria, the length of the fourth stage larvae is 1.4-1.6 mm (average = 1.5 mm); (c) the adults: from 7-10 days, the fourth stage of larvae develops into an adult. Scanning electron micrographs showed that the male body is small, cylindrical in shape, body length is 1.75-1.85 mm (average = 1.80 mm) and the width is 0.21-0.19 mm (average = 0.20). The length of gravid female is 2.0-2.8 mm (average = 2.4 mm) and the maximum width is 0.37-0.40 mm (average = 0.39 mm). Adult female of Rhabditis sp. started laying eggs after 10-15 days. Histological examinations revealed that the cysts or brown bodies occupied the coelomic cavity of earthworms. These cysts contain juveniles of nematode Rhabditis sp.