TABLE CONTENTS

Evolution of Mutualism, Phoresy, Parasitism and Amensalism in
Bursaphelenchus Nematodes
Kanzaki, N. (1), (2) & R.M. Giblin-Davis (1)
(1) Fort Lauderdale Research & Education Center, University of Florida/IFAS, 3205 College Avenue, Davie,
FL 33314 USA; (2) Forest Pathology Laboratory, Forestry and Forest Products Research Institute, 1
Matsunosato, Tsukuba 305-8687 Japan
The genus Bursaphelenchus encompasses fungal and plant-parasitic nematodes that are
mostly entomophilic. The relationships between Bursaphelenchus nematodes and their vector
(carrier) insects are mostly considered to be commensal (phoresy: nematodes use insects for
transport) or population mutualists (the plant-pathogenic nematodes kill more host plants to
serve as oviposition resources for their vectors, or fungivorus nematodes reduce fungal
enemy loads in the carriers’ habitat and gain mobility to nutritive breeding sites). Recent
advances in our understanding of the associations between Bursaphelenchus and their insect
hosts challenge current dogma. For example, some Bursaphelenchus species have an ‘insectparasitic
juvenile’ and/or ‘insect- parasitic adult’ stage classifying them as parasites. Some
species enter an insects’ tracheal system obstructing and swelling it in excessive infestations
that result in a reduction of the insect host’s longevity (amensalism). Thus, carrier (vector)
usage by Bursaphelenchus nematodes seems more divergent than originally expected. In the
present study, we coded insect usage by Bursaphelenchus species on molecular phylogenetic
trees to help infer the putative origins or patterns of ecological and symbiotic divergence. The
genus Bursaphelenchus was separated into three major clades. The first clade contains only
one species, the soil-dwelling bee associated B. abruptus, which is closer to a neighboring
clade, and may be more appropriate for inclusion in a new monospecific genus. The second
clade, which was not clearly resolved and comprises several subclades, contains many woodboring
Scolytidae- and Curculionidae-associated species. The third clade was well-defined
with high bootstrap support, but is the most variable in biology and morphology, including
species associating with wood-boring Scolytidae, Curculionidae, and Cerambycidae as well
as soil dwelling beetles (Nitidulidae) and bees (Halictidae). Both insect amensalistic and
parasitic relationships were observed in the second and third clades, but the nature of these
associations was different and presumed to have evolved independently within each of the
clades from commensal ancestors.
5 th International Congress of Nematology, 2008 10