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Silva Lusitana

versão impressa ISSN 0870-6352

Silva Lus. vol.19 n.Especial Lisboa  2011

 

Association Scolytus intricatusBursaphelenchus eremus on Oak in Italy

 

Leonardo Marianelli *, Lorenzo Marziali *, Beatrice Carletti *, Fabrizio Pennacchio *, Alba Cotroneo ** and Pio Federico Roversi *

* C.R.A. – Consiglio per la Ricerca e la Sperimentazione in Agricultura. Centro di Ricerca per l'Agrobiologia e la Pedologia, Via di Lanciola 12/a, Cascine del Riccio – 50125 FIRENZE

** Servizio fitossanitário del Piemonte. Environment Park Palazzina A2, Via Livorno 60 – 10144 TORINO

 

Abstract

Recent zoological research carried out in several regions of northern and central Italy has revealed a remarkable occurrence of Nematodes inside the tissues of trunks and branches of various oak species, i.e., Quercus cerris, Q. robur and Q. suber. Taxonomic studies of samples collected from the natural Parks of Ticino Valley, Stupinigi, Groane and Sesia (Lombardia and Piemonte regions) and from Montefalcone and Maremma areas (Tuscany) have always led to detection of the presence of Bursaphelenchus eremus Rühm (Goodey) which had so far only been recorded from Germany, the Czech Republic and Georgia. Plenty of individuals of the nematode were always found inside the samples and a high reproduction rate of that species was confirmed in the laboratory. The nematode was seen to be massively transported by the scolytid insect Scolytus intricatus Ratz. so that where high population levels of that bark beetle are present, the nematode/beetle association can become very harmful to the host oaks.

Key words: Scolitus intricatus; Bursaphelenchus eremus; nematode/beetle association

 

Associação Scolytus intricatusBursaplelenchus eremus em Carvalhos em Itália

Sumário

Pesquisas recentes efetuadas em várias localidades do Norte e Centro de Itália detetaram populações de nemátodes no interior dos troncos e ramos de várias espécies de carvalhos, tais como Quercus cerris, Q. robur e Q. suber. A análise de amostras recolhidas dos Parques naturais do Vale de Ticino, Stupinigi, Groane e Sesia (região da Lombardia e Piemonte) e das áreas de Montefalcone e Maremma (Toscânia) permitiram detetar a presença sistemática de Bursaphelenchus eremus Rühm (Goodey). Anteriormente apenas tinha sido detetado na Alemanha, Répública Checa e Georgia. Vários exemplares deste nemátode foram detetados nas diferentes amostras recolhidas, tendo-se observado uma elevada taxa de reprodução desta espécie quando mantida em laboratório. Constatou-se que o nemátode é transportado pelo inseto escolitídeo Scolytus intricatus Ratz., pelo que a ocorrência de níveis populacionais elevados deste inseto e do nemátode associado pode contribuir para o declínio dos carvalhos hospedeiros.

Palavras-chave: Scolitus intricatus; Bursaphelenchus eremus; associação nemátode/inseto

 

Introduction

Forest decline is one of the most serious phytopathological problems in the new millennium, considering the size of the geographical area affected, the number of woody species involved and the impact on the health of forest ecosystems (MANION and LACHANCE, 1992). Quercus is the plant genus most seriusly damaged by this phenomenon, both in central and western European countries as well as in many Mediterranean areas, including Italy (RAGAZZI et al., 2000). The decline phenomenon is characterised by a complex symptomatology and is worsened by the concomitant or contributing action of various weakness parasites which increase the pathological status of already declining trees, leading to death (ANSELMI et al., 2004).

Recent zoological research initiatives, carried out in several regions of Northern and Central Italy in broadleaf woods displaying symptoms of decline, have revealed a remarkable occurrence of nematodes inside the tissues of trunks and branches of various oak species, i.e., Quercus cerris L., Q. robur L. and Q. suber L. This work reports on the occurrence, in sampled areas located in Central and Northern Italy, of Bursaphelenchus eremus Rühm (Goodey). It is a forest nematode inhabiting broad-leaved trees belonging chiefly to the families Fagaceae, Salicaceae and Ulmaceae (RYSS et al., 2005). B. eremus was often found in association with the bark beetle Scolytus intricatus Ratzeburg (Figure 1). Dauer juveniles were also recovered from collected bark beetles.

 

Figure 1 - Adult of Scolytus intricatus Ratzeburg

 

Materials and methods

Studies were conducted in the natural Parks of Ticino Valley, Stupinigi, Groane and Sesia (Lombardy and Piemonte Regions) on Quercus robur and in Montefalcone and Maremma areas (Tuscany) on Q. cerris and Q. suber, between May 2004 and May 2006 (CARLETTI et al., 2005; CARLETTI et al., 2007).

Samples were taken from either stored logs and felled trees (as part of logging operations) or fully grown damaged trees. In the forest, disks were sawed at different positions along the length of the trunks, as well as logs with bark. All the woody samples showed signs of insect activity and the presence of fungal growth.

In the laboratory, the bark was removed to reveal insect gallery systems and to collect emerging insects to be observed and identified. Sawdust from several parts of the disks and logs was produced with a drill. Nematodes were extracted from the wood by the Baermann funnel technique over 48 h at 24°C. When possible, a proportion of the juveniles was inoculated with a strain of non-sporulating Botritis cinerea 5% (v/v) grown on glycerol-supplemented malt extract agar and incubated at 24-26°C. Five multiple-specimen isolated cultures were successfully established.

Insects isolated from the broad-leaved trees and identified as S. intricatus were dissected in Petri dishes with water to collect the emerged dauer juveniles, always packed beneath the elytra and/or wings.

Photomicrographs were taken with an inverse Nikon microscope (Figures 2-3).

 

Figure 2 - Dauer juveniles of B. eremus packed beneath the elytra of S. intricatus

 

Figure 3 - Dauer juvenile of B. eremus on a wing of S. intricatus

 

Results and conclusions

Plenty of individuals of B. eremus were recovered from damaged and recently dead oak trees. The dauer juveniles of the nematode are specialised dispersal juveniles resistant to adverse conditions; they were seen to be transported massively by the scolytid S. intricatus, resulting as its vector insect.

The pathogenicity of B. eremus has not been investigated but a high reproduction rate of this species was confirmed in the laboratory.

The nematode appears to have a very large distribution and high population densities whenever there are high population levels of the bark beetle.

Futher investigations are necessary to determine the exact role of the presence of this nematode/beetle association and its importance to the decline of oak forests.

 

References

ANSELMI, N., CELLERINO, G.P., FRANCESCINI, A., GRANATA, G., LUISI, N., MARRAS, F., MAZZAGLIA, A., MUTTO ACCORDI, S., RAGAZZI, A., 2004. Geographical distribution of fungal endophytes of Quercus sp. in Italy. In Ragazzi A., Moricca S. & Dellavalle I.: Endophytism in forest trees pp. 75-89.         [ Links ]

CARLETTI, B., FAGGI, M., PENNACCHIO, F., 2005. On the presence of Bursaphelenchus eremus (Rühm) Goodey (Nematoda: Parasitaphelenchidae) on turkey oak in Italy. Redia LXXXVII(2004): 77-80.         [ Links ]

CARLETTI, B., AMBROGIONI, L., IRDANI, T., BRANDSTETTER, M., PULERI, F., SURICO, F., PENNACCHIO, F., ROVERSI, P.F., 2007. Morphometrics and molecular identification of some Italian populations of Bursaphelenchus eremus Rühm (Goodey) associated with Quercus spp. Redia, XC: pp. 3-21.         [ Links ]

MANION, P.D., LACHANCE, D., 1992. Forest Decline Concepts. APS Press, St. Paul, MN.         [ Links ]

RAGAZZI, A., MORICCA, S., DELLAVALLE, I., TURCO, E., 2000. Italian expansion of oak decline. In: Ragazzi, A. & Dellavalle, I. (eds.), Decline of Oak Species in Italy. Problems and Perspectives. Accademia Italiana Scienze Forestali, Italy, pp. 39-75.         [ Links ]

RYSS, A., VIEIRA, P., MOTA, M., KULINICH, O., 2005. A synopsis of the genus Bursaphelenchus Fuchs, 1937 (Aphelenchida: Parasitaphelenchidae) with keys to species. Nematology 7(3): 393-458.         [ Links ]

 

Acknowledgements

The authors wish to thank Dr. Laura Ambrogioni for her suggestions and constructive comments and Mr. Flaviano Surico and Mr. Federico Puleri for their technical assistance.