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Abstract

Insect pathogenic nematodes of the families Steinermatidae and
Heterorhabditidae from 42 populations (four, genera and over nine species)
from Australasia, Europe and North America were found to be symbiotically
associated with bacteria of the genus Xenorhabdus.
A taxonomic study of Xenorhabdus showed that the bacterial symbionts
of the Heterorhabditidae were all X. Zuminescens and those of the Steinernematidae,
with one possible exception, were all X. nematophilus. Numerical
analysis of the taxonomic data indicated that the genus might be
heterogeneous.
Although the symbionts of most of the Steinernematidae (including
Steinernema kraussei which had previously been reported to be associated with a
Flavobacterium sp.) were classified within one species, the differences
between the bacteria associated with the various steinernematid species
were great enough to warrant the erection of four subspecies.
Results obtained with some tests used in the taxonomic study differed
from those previously reported. Amended descriptions of the genus Xenorhabdus
and its two species are proposed.
Each Xenorhabdus species was found to produce two forms of colony.
One form, designated the primary form, promoted significantly greater
nematode fecundity than did the secondary; it produced antimicrobial
substances whereas the secondary did not; and it was the form usually
found in the infective stage nematodes. The primary form was unstable
under many conditions, resulting in production of the secondary form which
in two subspecies was also unstable reverting to the primary form.
Attempts were made to elucidate the mechanism determining the change of
form.

Item Type:	Thesis - PhD
Authors/Creators:	Akhurst, RJ
Keywords:	Nematodes, Insects, Insect pests, Symbiosis
Copyright Holders:	The Author
Copyright Information:	Copyright 1982 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Thesis (Ph.D.) - University of Tasmania, [1983?]. Bibliography: l. 121-135
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