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Monitoring of Insect-Hosts of Entomopathogenic
Nematodes in Bulgaria
Denis Gradinarov*, Nikola Atanasov**
*Sofia University, Dragan Tzankov 8, 1164 Sofia, Bulgaria;
**Plant Protection Institute, Panajot Volov, 2230 Kostinbrod, Bulgaria
The entomopathogenic nematodes of the families Steinernematidae and Heterorhabditidae are intensively investigated because of their potential
as biological control agents, but also because their specific biology. The cases of established naturally infected hosts are relatively rare. The aim of
the following work is to systematize the knowledge of insects – hosts of entomopatogenic nematodes (EPN), discovered in Bulgaria.
The insects from 6 genera and 7 families were found in Bulgaria as natural hosts of entomophatogenic nematodes (Table 1). They belong to the
orders Coleoptera, Hymenoptera and Diptera. Some of them are phytophagous another carnivores and the others are with mixed feeding.
Infected by S. bicornutum larvae or pupae of
Curculionidae, Carabidae (Fig. 4), and Asilidae (Fig.3)
were found in an riverside soil in the Zemen gorge (Fig.
2). This cases of invasion are of special interest. They
shows that EPN parasitized not only phytophagous
insects but also myxophagous and predators.
The species S. carpocapsae was isolated from a larva of Elateridae
in soil from Vitosha Mt. and from female ant (Formicidae) in a
riversides of Mesta. Infected with S. carpocapsae larvae of Cydia
pomonella L. were found also near town of Kjustendil (Vega et al.,
2000). The species H. bacteriophora was isolated from a larva and
a pupa of Drasterius bimaculatus Rossi (Elateridae).
Laboratory tests for parasitized of some economically important insects were performed. We used insects, gathered from an alfalfa
stand in experimental field near Sofia. These are imago of phytophagous Subcoccinella, Phytodecta and the beneficial species
Coccinella septempunctata L. A experimental invasion was with nematode cultures of the species H. bacteriophora and S. feltiae, which
were isolated from Bulgaria.
Even though the dosage of EPN was high, the results proved that these
nematodes have relatively low efficiency against the insects of the genera
Subcoccinella (Fig. 7) and Phytodecta. We determined via dissection that the
mortality rate is Coccinella septempunctata does not account on EPN.
Table 1. Detected natural host insects of the entomopathogenic nematodes in Bulgaria
Nematode Host insect Region Habitat
S. kraussei Bibio sp.
(Bibionidae) Vitosha Mts. beech and pine forest,
subalpine meadows
S. kraussei Curculionidae g.sp. Vitosha Mts. subalpine meadow
S. carpocapsae Cydia pomonella L.
(Tortricidae) Kjustendil apple garden
S. carpocapsae Limonius sp.
(Elateridae) Vitosha Mts. mezophilic meadow
S. carpocapsae Formica cinerea (Formicidae) Hadjidimovo swamp meadow
S. intermedium Cantharis sp. (Cantharidae) Sofia garden
S. bicornutum Curculionidae g.sp. Zemen gorge riverside meadow
S. bicornutum Harpalus sp. (Carabidae) Zemen gorge riverside meadow
S. bicornutum Asilidae g.sp. Zemen gorge riverside meadow
Steinernema sp. Bibio sp.
(Bibionidae) Vitosha Mts. pine forest
Steinernema sp. Asilidae g.sp. Osogovska Mts. subalpine meadow
Steinernema sp. “affine
group” Bibio sp.
(Bibionidae) Vitosha Mts. pine forest
H. bacteriophora Drasterius bimaculatus Rossi
(Elateridae) Kostinbrod strawberry fields
The species S.
intermedium is isolated
from pupae of Cantharidae
in town of Sofia (Fig.1).
On Vitosha Mts. (Fig.5) several times we had found infected
by EPN larvae of Bibionidae (Bibio sp.) (Fig.6). Almost in all
cases the invasion density was 1 – 3 nematodes per a
dipterian larva. The EPN appears to be one of the main
factors, which control the density of the bibionid flies in forest
habitats in Bulgaria.
The results of the experiment can be generalized in the following statements:
1.The species Subcoccinella and Phytodecta are vulnerable to invasion with the nematode H. bacteriophora;
2. The imago of Subcoccinella sp. is most effectively invaded by the species H. bacteriophora;
3. The species S. feltiae is more pathogenic to Phytodecta then H. bacteriophora;
4. The beneficial species Coccinella septempunctata is not affected from the species H. bacteriophora.
Fig.1. Pupa of Cantharis with nematodes
Fig.3. Larva of Asilidae
with nematodes
Fig.4. Antenna and urogomphus of Harpalus with nematodes
Fig.2. Zemen Gorge
Fig.5. Pine forest on Vithosha Mts. Fig.6. Infected bibionid larvae
Fig.7. Infected imago of Subcoccinella