TABLE CONTENTS

SESSION FORTY-ONE – BIOLOGICAL CONTROL AND ECOLOGY OF
NEMATODE ANTAGONISTS
CONVENORS: BRIAN KERRY & GREGORY NOEL
Top-down Control of Nematodes in Natural Ecosystems
Brinkman, E.P. & W.H. Van der Putten
Netherlands Institute of Ecology (NIOO-KNAW), Centre for Terrestrial Ecology, P.O. Box 40, 6666 ZG
Heteren, The Netherlands
Plant-feeding nematodes play a role in structuring the plant community composition in
natural ecosystems. However, little is known on factors that regulate nematode abundance in
nature. I will discuss results of a series of studies on factors that regulate the plant-feeding
nematodes of the dune grass Ammophila arenaria. This grass is attacked by ectoparasitic,
migratory endo- and sedentary endoparasitic nematodes. Each of these nematode species is
regulated by several mechanisms, including bottom-up, horizontal and top-down control. For
example, the sedentary endoparasite Heterodera arenaria is bottom-up controlled by the host
plant A. arenaria. The presence of other endoparasitic nematodes regulated the timing of root
attack by Meloidogyne maritima, whereas arbuscular mycorrhizal fungi (AMF) controlled
numbers of Pratylenchus penetrans. Addition of microorganisms decreased the numbers of
the ectoparasite Tylenchorhynchus ventralis. All in all, these combinations of control
mechanisms resulted into a complicated protection of A. arenaria against plant-feeding
nematodes.
I will also discuss nematode control in other natural systems. In a study on mid-succession
grassland species, inoculation of soil microorganisms reduced the numbers of plant-feeding
and plant-associated nematodes. Interestingly, the nematodes influenced aboveground
interactions between plants, aphids and aphid parasitoids. Nematode addition reduced aphid
offspring production independent of microorganism inoculation. Aphid populations were
lowest in microcosms with combined nematode and microorganism inoculations. In contrast,
parasitoid mortality and the proportion of males were significantly lower in microcosms with
combined nematode and microorganism inoculations.
In another study on mid-succession grassland species, addition of nematodes reduced the
biomass of grasses and increased the biomass of non-legume forbs. Addition of
microorganisms and earthworms did not significantly affect numbers of plant-feeding
nematodes. However, earthworm addition increased the tolerance of grasses to nematodes.
We conclude that nematode control in nature depends on a variety of top-down, horizontal
and bottom-up controls.
5 th International Congress of Nematology, 2008 150