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BIO-ETHOLOGY OF ANISANDRUS DISPAR F. AND ITS POSSIBLE INVOLVEMENT IN DIEBACK (MORIA) DISEASES OF HAZELNUT (CORYLUS AVELLANA L.) PLANTS IN CENTRAL ITALY

2005; International Society for Horticultural Science; Issue: 686 Linguagem: Inglês

10.17660/actahortic.2005.686.60

2406-6168

D. Bucini, G.M. Balestra, C. Pucci, B. Paparatti, Stefano Speranza, C. Proietti Zolla, L. Varvaro,

Powdery Mildew Fungal Diseases

Hazelnut is one of the most important orchards in central Italy (Viterbo province). More than eighty phytophagous insect pests adversely affect hazelnut orchards, but only a few of these, such as Anisandrus dispar F. (Coleoptera, Scolytidae), induce severe damage. A bacterial disease (called moria) constitutes one of the main phytopathological problems of hazelnut plants in central Italy. Two years ago, the Lazio Regional Government and local hazelnut cooperatives supported a research into the bio-ethology of A. dispar and its possible association with moria disease on hazelnut plants in Viterbo. In 2003 and 2004 two experimental hazelnut areas were selected in the Capranica and Caprarola districts (Viterbo), where eighteen chemio-chromotrophic traps were installed to study the dynamic population of A. dispar and to catch live Scolytidae females. Representative samples of live A. dispar females were used to isolate and identify the bacterial populations present both outside and inside the insects. After two years 5,726 A. dispar females had been caught. Of more than 1,400 live A. dispar females, 10% were submitted to microbiological analyses by morphological, physiological, biochemical and molecular techniques. The populations of the main bacteria (by outside and inside) associated with the phytophagous were identified as Erwinia billingae, Brenneria quercina, Pantoea cedenensis and Pseudomonas spp. Studies are currently in progress to: i) clarify the biological cycle of A. dispar; ii) identify the role (direct and/or indirect) of the insect respect to the epidemiology of moria disease; iii) carry on pathogenicity tests on bacterial isolates to prove their involvement in bacteriosis; iv) develop specific primers to identify the presence of these bacteria when associated with the insect and with asymptomatic hazelnut plants; v) verify the influence of environmental parameters on the biology of both the insect and the disease. INTRODUCTION Hazelnut (Corylus avellana L.) orchards are the most common orchards in the Cimini Hills (Viterbo province). They are important not only for the local, but also for the national economy. In the Lazio region, of a total of more than 23,300 ha dedicated to the production of stone fruits, more than 16,400 ha produce hazelnut (Carbone et al., 2004). More than 80 phytophagous can infest hazelnut plants (Pollini, 1998) but only a few of them, such as Coleoptera Scolytidae Anisandrus dispar F. are able to cause severe damage and loss (Viggiani, 1984), as they prefer to attack twigs and young hazelnut stems (∅ 1-3 cm) (Pollini, 1998). A. dispar is present in the paleoartic region and infests many fruit plants (apple, pear, apricot, plum, peach, walnut, and hazelnut) and broad-leaved wood plants such as chestnut, oak, beech, elm, poplar, etc. This ambrosia beetle establishes a complex symbiosis with a fungus (Ambrosiella hartigii B.) that allows larvae to develop in wood tissues, which are notoriously poor in nutritious substances (Pollini, 1998). In the adult stage, the females, which are the only ones able to fly, make small Proc. VIth Intl. Congress on Hazelnut Eds.: J. Tous, M. Rovira & A. Romero Acta Hort. 686, ISHS 2005 436 cortical perforations that sometimes provoke rugosity and bark deformations. They subsequently bore new prolification galleries (horizontal semicircular galleries from which they vertically depart) (Natali et al., 1994). The females then lay about fifty eggs, in piles, at the end of the vertical galleries. Larvae are born after a few days and exclusively nourish on the mycelium of the symbiont fungus, which is transported by the females and grows inside the galleries. The last larvae instar is reached within a period of 30-40 days, they turn into a chrysalis. This stage lasts an average of 15 days. The new adults stay inside the galleries until the following spring (Pollini, 1998). Scolytidae can cause direct damage to branches and sometimes even the death of young hazelnut plants. It also seems to be involved in spreading a serious bacterial disease called “moria” (Balestra et al., 2003). Hazelnut plants attacked by this disease initially show a light green/yellow colouring. Within a few days, one or more whole branches show evident signs of dieback. The yellow leaves then remain attached to twigs and branches for the whole vegetative season and then finally the hazelnut plants die. Since 2002, a Lazio Regional project on different aspects related to this disease, was financed in collaboration with the hazelnut cooperatives of Viterbo province (Fig. 1). It has examined a possible link between A. dispar populations and the spread and infection processes associated with moria disease in the hazelnut orchards of central Italy. The aims of the present research include trying to clarify the bio-ethology of this Scolytidae and studying which bacterial populations are carried (internally and externally) by the A. dispar that are normally present on hazelnut plants and in neighbouring forests. MATERIALS AND METHODS During 2003 and 2004 samples of Scolytidae A. dispar were collected from two hazelnut orchards (“a” and “b”) located close to Lake Vico in the Caprarola district (Viterbo, Italy) whose plants showed typical symptoms of moria (Fig. 1). The sampling process involved the use of “Rebell Red” chemio-chromotropic traps. These were specifically selected for the capture of A. dispar females and characteristically contained ethylic alcohol with toluol 1% diluted in water at 50% and no soluble glue (Temocid by Kollant). The traps were installed 12 and 19 March 2003. They were monitored on a weekly basis as part of a process that is still ongoing. The traps were taken into the lab once a week, where the insects caught were counted and collected. During the 2004 hazelnut season, samples were carried taken at two hazelnut experimental areas: “a” near Lake Vico and “c”, in Caprarola and the Capranica (VT) district, respectively (Fig. 1). In that specific season, Mastrap L (ISAGRO) traps were modified and used. These traps are normally used to catch the insect Traumatocampa pityocampa (Den. & Schiff) which attacks pine trees. The traps were installed not only in healthy and diseased hazelnut areas (“a”, “c”) but, were also considering the polyphagy of the insect set up in the “forest“ (characterized by oaks, walnut, chestnut, beech, maple, elm and ash trees) very close to hazelnut area “a” (Fig. 1). Samples were also taken on a weekly basis in 2004. During 2003 the manual capture of insects was carried out in stressed hazelnut plants within hazelnut area “a”, coinciding with the different biological phases (larvae, pupae and female adults) of the pest. From May 1 until 30 June, numerous isolations of the bacterial cells present, were collected from these insects (both externally and internally). Sampling for the 2004 hazelnut season started on March 15 and was still in progress when this article was written. In the current season, given the large number of A. dispar collected, groups of 10 insects were worked together each time and these were selected from the different areas (“a”, “c”, and “forest”). In both years, each insect was washed (in 1 ml of sterile distilled water, SDW) for 2 hrs at 28°C, using an orbital shaker at 100 rpm. Later, 0.1 ml of each suspension was plated on Petri dishes containing nutrient agar supplemented by 5% of sucrose (NAS). The Petri dishes were subsequently placed in an incubator at 28±1°C for 48-72 hrs and