Heterorhabditis gerrardi
Summary - A
new entomopathogenic nematode species from Australia, Heterorhabditis gerrardi n. sp. (Nematoda: Heterorhabditidae) is
described. Morphological and molecular studies together with
cross-hybridization tests indicated that this nematode represents a new
undescribed species, closely related to members in the 'indica-group'. However,
the new species can be distinguished from other species in this genus by a
combination of several qualitative and quantitative morphological traits. Key diagnostic
features include: body size and excretory pore position of the third-stage
infective juveniles; male bursa with a reduction of bursal rays, usually
affecting the terminal set of papillae, with symmetrical or asymmetrical loss
of one or two pairs; vulva of hermaphrodites more anteriorly located than in
other species in the indica-group (V% average: 43), with non-protruding or
slightly protruding lips, and longer tail length (average: 106 mum). The new
species can be further characterized by molecular traits of sequence data from
the internal transcribed spacer (ITS) region of ribosomal DNA. Additionally,
the bacterial symbiont of this new species, Photorhabdus asymbiotica Kingscliff
strain, was phenotypically characterized and compared with other P. asymbiotica
strains. The Kingscliff strain revealed many characters not present in other
strains of this species. We hypothesize that the newly found traits may
contribute to the maintenance of this mutualistic association of the bacterium
with its nematode host.