International Congress BIOLOGICAL PRODUCTS - Gruppo di ...

27
ECO-TOXICITY OF THE ENTOMOPATHOGENIC BACTERIUM-NEMATODE SYMBIOTIC
COMPLEX TOWARD NON-TARGET ORGANISMS
M. Ricci, M. Colli, R. Barcarotti and A. Ragni
BioTecnologie BT srl Pantalla di Todi 06050 Perugia Italy
Tel: ++39 – 075 - 895091 Fax: ++39 – 075 – 888 776 E-mail: mricci.bt@parco3a.org
Introduction
In agriculture, the use of bio-control agents is growing; this is due, in particular, to their ability to avoid pest’s
resistance and to their friendly environmental impact.
A mini-review of the entomopathogenic bacterium-nematode symbiotic complex toward non-target organisms is
presented; bibliographic data and original data coming from research are shown. In particular it is mentioned a
work which first demonstrated specificity of the entomopathogenic bacterium-nematode symbiotic complex
toward target organisms (insects).
The present work concerns three sections related to the eco-toxicity of entomopatogenic nematodes: a) Short
review; b) Demonstration of entomopathogenic nematodes host specificity; c) Laboratory results toward nontarget
hosts: Earthwoms, Scorpions and Millipeds.
a) Short review
Poinar (1990) reported that although Steinernematids and Heterorhabditids are considered entomopathogenic
nematodes because all natural infections have involved insects, they do have the ability to enter and kill noninsect
invertebrates, at least in the laboratory (Wayne et al., 1987). Steps of their infection process are normally
completed in most insects but various obstacles to their completion occur with many non-insect invertebrates
(Wayne et al., 1987). The effect of these nematodes on vertebrates is of a great concern. Off all the vertebrates
(among the following classes: Pisces, Reptilia, Amphibia, Aves and Mammalia) thus far challenged with
infective stage of Steinernematids and Heterorhabditids, only young tadpoles of frogs and toads were vulnerable.
But the reason was given to the fact that when penetrating into the host the nematodes were carrying foreign
bacteria.
b) Demonstration of entomopathogenic nematodes host specificity ( Ricci et al., 1994)
Introduction
Entomopathogenic nematode infective juveniles (IJs) locate and parasitise potential hosts. The success of this
process depends with suitability of the host. Ricci et al. (1994) and Lewis et al. (1996), demonstrated that a
nematode's subsequent degree of attraction to CO2, stimulated by contact with the cuticle of an arthropod,
should signify that the exposed IJs recognize it as a potential host. The level of stimulation caused to S.
carpocapsae, a nematode that forages primarily by ambushing passing hosts, by 12 potential hosts (3
Lepidoptera, 4 Coleoptera, 1 Orthoptera, 1 Blattodea, 1 Diptera and 2 non-insect arthropods) was compared. To
determine whether arthropods that stimulate a high level of attraction of IJs are suitable hosts, three parameters
were tested: nematode induced mortality, nematode invasion rate and reproductive potential.
Materials and methods
Behavioral Recognition Assay: nematodes were exposed for a certain time to the cuticle of different insects or
non-insects or inert materials, then exposed to chemical volatile cues emitted by the insects Galleria mellonella
in an apparatus called Agar Plate Arena (see Figure 1). After a certain time the nematodes that accumulated in
the proximity of the cue emissions, were collected and counted.
Nematode Infectivity Assay: host mortality was recorded after 2 days in Petri dishes at the concentrations of 200
and 500 nematodes per host.
Nematode Invasion Assay: Nematodes that penetrated the host during the Infectivity assay were counted.
Reproductive Potential Assay: pre-weighed hosts were exposed to 500 IJs. After 2 days the cadavers were
transferred on a nematode collecting trap. Every 2 days, the emerged IJs were collected until the exploitation of
all the host tissues was completed.
PDF creato con FinePrint pdfFactory versione dimostrativa http://www.secom.re.it/fineprint
128