Introduction

Ambrosia beetles are an important group of forest insects that typically attack weakened or felled trees. Their name derives from the symbiotic fungus (ambrosia) they inoculate when they penetrate the xylem of their host. Megaplatypus mutatus (=Platypus mutatus) (Chapuis) (Platypodinae, Curculionidae) is an ambrosia beetle native to South America (Wood 1993) that only attacks standing, healthy living trees, digging deeply into the xylem and making large tunnels that are later colonized by the fungus they transport, Raffaelea santoroi (Guerrero) (Bascialli et al. 1996). These galleries subsequently weaken the tree’s stem, causing it to break under extreme stress and representing a serious problem in poplar, Populus deltoides Marshall (Salicaceae), commercial plantations (Alfaro et al. 2007; Achinelli et al. 2005). Furthermore, the dark staining of the tunnels caused by the decaying ambrosia mycelium reduces the quality of wood for export.

The attack is initiated when the male penetrates the bark and digs a tunnel a few centimetres deep. Then it builds a conical structure surrounding the entry hole using boring dust particles. From there it protrudes its abdomen and releases volatiles to attract the females (Santoro 1963; Gonzalez-Audino et al. 2005). A similar behaviour was reported for Platypus apicalis White and P. gracilis Broun in New Zealand (Milligan and Ytsma 1988). In the case of poplars, the black stain caused by the fungus decreases the commercial value of the timber. In the case of fruit trees, the wounds caused by this insect cause loss of water and nutrients, which can affect product yield and quality, and also increase the risk of attacks by microorganisms.

Megaplatypus mutatus was accidentally introduced to Italy in 1998 (EPPO/OEPP 2004, 2007). In 2000, it was detected in Populus canadensis (Mönch) in the Caserta province, in the Campania region. Attacks were also reported in Juglans regia (L.) and European hazelnut, Corylus avellana L. (Tremblay et al. 2000; Allegro and Della Beffa 2001); and later in Malus spp., Pyrus spp., Castanea spp., Prunus spp., Quercus spp. and Eucalyptus spp. (Carella and Spigno 2002). These reports do not indicate if the attacks had produced offspring or had been ineffective in these hosts.

The risk of dispersion and potential damage of M. mutatus to other regions of Europe (Alfaro et al. 2007) is of great concern to European regulatory authorities, who added it to the EPPO/OEPP Alert List in 2004. It was recommended as a quarantine pest in 2007 (Allegro and Griffo 2008; EPPO/OEPP 2004, 2007).

The population dynamics of M. mutatus suggests a bivoltine emergence in Argentina (Gatti et al. 2008b) and this pattern is also observed in Italy (H Funes et al. 2011). Although external temperature affects the duration of the various life stages (Santoro 1963), in central Argentina and southern Italy M. mutatus starts to fly in search of new host by the beginning of spring and by the end of summer. This species exhibits protandry (earlier emergence of males than females).

The development of pheromone-baited traps for surveillance and management programs of M. mutatus in infested poplar plantations is an important goal for both European and South American control efforts. Pheromone research of M. mutatus began in 2002 in Argentina with field experiments testing the attractiveness of pheromones of North American ambrosia beetles Gnathotricus sulcatus ((Scolytinae, (±)-Sulcatol and (−)-sulcatol) and Gnathotricus retusus ((+)-sulcatol) (Borden and McLean 1979) to M. mutatus populations (Alfaro et al. 2007). In 2003 these were evaluated by the Canadian forest service (Pacific Forestry Centre) in collaboration with the Istituto di Sperimentazione per la Pioppicoltura (Casale Monferrato, Italy) in the Caserta region of Italy (Alfaro et al. 2007). The field tests in Argentina and Italy indicated a low level, but consistent attraction of M. mutatus females to (±)-sulcatol.

Chemical analysis, electro-antennogram and olfactometer studies performed at the Centro de Investigaciones de Plagas e Insecticidas (CIPEIN) in Buenos Aires, Argentina, showed that male M. mutatus emit a sex pheromone composed mainly by (+)-sulcatol, its related ketone, sulcatone (Gonzalez Audino et al. 2005) and 3-pentanol (Gatti Liguori et al. 2008a). The CIPEIN recently showed the effectiveness of a two-component pheromone blend monitoring M. mutatus infestations in Argentina (Funes et al. 2009).

Although the presence of the galleries is an indication of the probable presence of M. Mutatus, it’s not easy to tell if a gallery is active or just an old empty gallery. Also, in some plant species, the cone of frass does not form on the bark so this sign of infestation cannot be evaluated and last, many galleries that do contain active larvae fail to produce emerging adults as their productivity is highly variable (ranging from 10 to 300 insects approximately (Santoro 1962). In this sense, pheromone traps are more reliable, more efficient, especially cost-efficient, mean of species detection.

The aim of this study was to conduct an operational test of a three-component M. mutatus pheromone blend, and survey the extension of the presence of M. mutatus in the province of Caserta, in the Italian Campania region.

Materials and methods

Selection of experimental fields

An initial visual survey of twenty-six plantations in the in the province of Caserta, searching for signs of infestation (Table 1) was performed in the first week of May 2007 with assistance of inspectors from the Phytosanitary service of region Campania, Italy. These consisted of 13 poplar plantations (P. canadensis (Mönch)), nine fruit tree plantations (three plantations of C. avellana L., three of J. regia L., two of Prunus avium L., one of Prunus persicum L.), and one Eucalyptus plantation. The level of infestation was characterized according to the presence of M. mutatus galleries. In order to monitor emergence of the first adults, emergence traps were installed on entry holes of active galleries, as described by Gatti Liguori et al. (2007). Based on this survey we selected for monitoring nine plantations in four areas of the Caserta province in which visible signs of active infestation were evident (Table 2).

Table 1 Plantations with probable infestation by M. mutatus in the Campania region of Italy
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Table 2 Poplar and fruit tree plantations surveyed for M. mutatus using pheromone traps in the Campania Region of Italy
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Pheromone traps

The traps were Mastrap A Version ® (Isagro S.R.L, Milan, Italy), with an effective surface of 630 cm2, baited with experimental slow release devices filled with (+)-sulcatol, sulcatone and 3-pentanol. The release devices were polyethylene bags with different effective surfaces in order to obtain different release rates. Optimal surfaces were evaluated in field and behavioural laboratory assays (Funes et al. 2009). The release rates of the different baits were quantified at 28 °C using a wind tunnel with a linear air velocity of 0.5 m/s. The selected surfaces released 10 ± 1, 7 ± 1 and 40 ± 2 mg per day for (+)-sulcatol, sulcatone and 3-pentanol respectively.

Traps were hung from the trees with ropes at 1.5–1.8 m above ground level. Baits were replaced before complete pheromone consumption every 15 days. The number of insects caught was surveyed twice a week between 22 May and 13 July, and once a week afterwards until the end of each trial.

Sexing: males have dark brown abdomen and females clear brown. The elytra of the females are less striated and have careens less salient than in males. Besides, the apical region of females has a gentle slope and at the apex the elytra are rounded.

Pheromones

Sulcatone (6-methyl-5-hepten-2-one) and 3-pentanol were analytical grade (Aldrich Co., Saint Louis, MO, USA); (+)-sulcatol ((+)-6-methyl-5-hepten-2-ol) 99 % was purchased from Pherotech, Vancouver, Canada.

Results

Degree of infestation in Caserta

We found signs of probable M. mutatus activity in ten of the 23 (43 %) plantations surveyed. In particular, seven of the 16 poplar plantations (53 %) were suspicious. All three plantations of C. avellana showed signs. We did not find possible infestations in Prunus, Juglans or in the single Eucalyptus plantation surveyed (Table 1). This work presents the first report of attack and successful development (full ontogeny) of the whole life cycle of M. mutatus in C. avellana (Fig. 1).

Fig. 1
figure 1

Damage in C. avellana. A arrows indicate sap exudation in 30 year-old productive C. avellana trees. B pellets of boring dust (frass). Bar = 1 cm

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Insect catch with pheromone traps

Adult M. mutatus were caught in all plantations in which traps were established confirming the presence of flying adults in the survey area (Table 3). In all, we caught 702 M. mutatus over the season, of which, 92 % were females. There were no insects caught in any of the control unbaited traps.

Table 3 Total number of M. mutatus, tabulated by sex, captured in infested plantations in the Campania region of Italy
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Temporal pattern of catches

Figure 2 shows the time pattern of insects caught in pheromone traps in poplar and hazelnut plantations of Campania region. The trapping season extends during the whole spring and summer with higher catches during summer. Catch level varied by location possibly reflecting population size, although this was not measured.

Fig. 2
figure 2

Temporal pattern of Megaplatypus mutatus catches in plantations in the Campania region (Italy), using pheromone traps. A Casanova poplar plantations, B Falciano del Massico poplar plantations, C Falciano del Massico hazelnut plantation, Presenzano and Teano poplar plantations

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Discussion

The emergence of M. mutatus from the parental gallery is followed by a dispersive flight searching for a host, in the case of males, or for a mating partner in the case of females.

Our trapping caught a large number of females (92 % of the catches) confirming that the chemical blend used behaves as a true sex pheromone and not as population aggregation pheromone. The role of the sex pheromone had been previously demonstrated in the behavioural bioassays (Gonzalez Audino et al. 2005). M. mutatus does not mass-attack the trees (Santoro 1963) and it is therefore unlikely to have developed aggregation semiochemicals.

The small number of male catches (8 %) could be due to the phenomenon described as local enhancement (Krebs et al. 1972). In this case, a recipient receives a message not intended for him and takes advantage of the information acquired. In this case, a male that quickly needs to find a host, interprets the sexual pheromone emitted by another conspecific as an indicator of the presence of a suitable host and directs its flight towards the sexual pheromone source. The dispersal and host-finding phase seems to be the most dangerous period in the life cycle of bark and ambrosia beetles (Atkins 1966; Byers 1995; Byers et al. 1998; Dahlsten 1982; Huber et al. 1999). For this reason, Zhang and Schlyter (2004) and Byers et al. (2000) suggested that natural selection would favour beetles that have evolved multiple mechanisms for quickly finding their host, and avoiding unsuitable hosts and non-host species. Local enhancement seems to be useful in finding the host and not to parasitize tunnels made by other males. However, testing these hypotheses is beyond the scope of this paper.

It is likely that the natural dispersion of M. mutatus towards other areas of the Italic peninsula, and eventually to other parts of Europe, is being delayed by the geography of the infested area, which is surrounded by highlands and mountains where suitable hosts are absent. At the time this study was performed, the southern detection limit was the town of Capua, and a natural dispersion of M. mutatus outside Caserta towards the more southern provinces of Napoli or Benevento, is likely. Further knowledge on the behaviour of M. mutatus in Italy and on the timber pathways in the region is needed to forecast potential movement to other areas.

Attacks on C. avellana indicate the potential of M. mutatus to switch hosts to non-related indigenous trees. This could have deep implications in the dispersion and population dynamics of M. mutatus in Italy and Europe, increasing the threat of potential economic damage, as this pest not only affects poplars destined for high quality timber, but also the yield of other products, such as hazelnuts, one of the most important crops in Italy, and other fruits species in the Mediterranean region. In South America, C. avellana has still not been identified as a host of M. mutatus although there are numerous commercial plantations of this crop.

This work has demonstrated the efficacy of the three-blend pheromone developed in Argentina against M. mutatus introduced to Europe, providing a tool to monitor future dispersal into other parts of the European continent. Our monitoring results provide a useful guide for the timing of chemical or mechanical control in Caserta.