Plant parasitic nematodes belonging to the family Hoplolaimidae Filipjev, 1934 have global distribution in agricultural soils and uncultivated lands. Over 400 species have described so far of which 10-12 species are profuse in their distribution in different parts of the world like America, Africa, Asia and Australia. The majority of the hoplolaimid species are found in soil closely associated with plant roots in a wide assortment of habitats. Species of the genus Helicotylenchus Steiner, 1945 comprise one of the most common and consistent components of hoplolaimid population attacking agricultural crops under diverse climatic and edaphic conditions. Under the present taxonomic studies of the family Hoplolaimidae, up-to-date lists (1995) of the total number of species, belonging to eleven genera viz., Helicotylenchus Steiner, 1945; Hoplolaimus Daday, 1905; Rotylenehus Filipjev, 1936; scutellenchus Andrassy, 1958; Aorolaimus Sher, 1963; Aphasmatylenchus Sher, 1965; Antarctylus Sher, 1973; Pararotylenchus Baldwin & Bell, 1981; Rotylenehulus Linford & Oliveira, 1940; Acontylus Meagher, 1968 and Senegalonema Germani, Luc & Baldwin, 1984, have been provided. Rotylenchoides valdeclarus, Williams, 1983 and Rotylenchoides whiteheadi Ganguly & Khan, 1987 have been shifted under genus Helicotylenchus as H. valdeclarus (Williams, 1983) n. combination and H. whiteheadi (Ganguly & Khan, 1987) n. combination. A diagnostic compendium of the genus Helicotylenchus prepared for the diagnosis of Helicotylenchus species, with pertinent morphometric data derived from the original descriptions or subsequent redescriptions, have been provided for nominal species of Helicotylenchus in tabular form to facilitate the identification of species. The tabular key is based on 16 diagnostic characters and illustrations of female anterior and posterior regions of the 196 valid species.
Under the present studies of Hoplolaimid nematodes of Pakistan many extensive surveys (1989-1995) of different regions were carried out and about 800 soil and root samples were collected from cereals, vegetables, fruit, herbaceous plants and other crops of economic importance. The analysis of these samples has revealed a large number of nematode species belonging to the family Hoplolaimidae. Among these, nine new species and eleven known species have been described and redescribed respectively. The new species include: Helicotylenchus discocephalus Firoza & Maqbool, 1993; H. microtylus Firoza & Maqbool, 1993; H. meloni Firoza & Maqbool, 1994; H. striatus Firoza & Maqbool, 1994; H. arcuatus n.sp., H. lemoni n.sp., Hoplolaimus tabacum Firoza, Nasira & Maqbool, 1990; Rotylenchus capsicumi Firoza & Maqbool, 1991 and R. goldeni Firoza & Maqbool, 1993. The 11 known species Le., Helicotylenchus abunaamai Siddiqi, 1972; H. arachisi Mulk & Jairajpuri, 1974; H. falcatus Eroshenko & Nguen Vu Thanh, 1981; H. oscephlus Anderson, 1979; H. platyurus Perry, Darling & Thorne, 1959; H. seshadrii Singh & Khera, 1979; H. willmottae Siddiqi, 1972; Hoplolaimus aegypti Shafiee & Koura, 1969; Rotylenchus dalhousiensis Sultan & Jairajpuri, 1979; R. himprus (Sultan, 198u) Fortuner, 1981 and R. jagatpurensis Sultan, 1984 have been redescribed and illustrated as first records in Pakistan.
In addition to these, twelve nematode species of this group which were reported earlier, have been redescribed giving morphometric data and illustrations for the first time in Pakistan which include: Helicotylenchus conicephahus Siddiqi, 1972; H. crenacauda Sher, 1966; H.digonicus Perry, Darling & Thorne, 1959 ; H.dihystera (Cobb, 1893) Sher, 1961; H. egyptiensis Tarjan, 1964; H. erythrinae (Zimmermman, 1904) Golden, 1956; H. indicus Siddiqi, 1963; H. microdorus Prasad, Khan & Chawla, 1965; H. pseudorobustus (Steiner, 1914) Golden, 1956; Hoplolaimus tylenchiformis Daday, 1905; Rotylenchus buxophilus Golden, 1956 and Rotylenchulus parvus (Williams, 1960) Sher, 1961. Moreover, some of the important hoplolaimid species of common occurrence viz., Helicotylenchus dihystera(Cobb, 1893) Sher, 1961, Hoplolaimus indicus Sher, 1963 and H. columbus Sher, 1963 have also been redescribed with the help of SEM. About 120 new host records of some of the hoplolaimid species have also been given. Numerical threshold for the infection and control experiment using plant extracts on H. dihystera have also been carried out. H. dihystera has been found pathogenic to brinjal, tomato and wheat with an inoculation of 1,000 nematodes per 250 g soil per plant while datura leaf extract gave maximum mortality (80%) of this species as compared to calotropis (70%) and neem (40.6%) respectively.