Marchalina hellenica is spreading in Greece: addition to the EPPO Alert List
The attention of the EPPO Secretariat was drawn by a Greek non-governmental organization involved in forest protection ‘Philodassiki Enossi Athinon’ to the uncontrolled spread of Marchalina hellenica on pine trees in Greece. So far, this scale insect originating from the Mediterranean region has been considered a useful species as it produces honeydew which then constitutes a significant source of food for honey bees. In recent years, M. hellenica was voluntarily introduced into new areas of Greece to enhance the production of honey. At the same time, outbreaks of M. hellenica were reported from various parts of Greece together with a severe decline of pine forests. This raised a strong debate in Greece about the exact role of M. hellenica in pine tree decline and mortality, and whether its deliberate release in pine forests should be continued or not. Although scientific data is lacking, the observations which are currently being made in Greece advocate for precautionary measures and it seems advisable not to introduce this insect into other parts of the EPPO region.
Marchalina hellenica (Homoptera: Margarodidae)
Why: Between 1996 and 2000, Greek beekeepers were encouraged to artificially introduce a scale Marchalina hellenica in pine forests to increase their production of honey (it is estimated that 60% of honey produced in Greece is made from pine). The honeydew produced by the scale is used as a significant source of food by honey bees. At the same time, severe decline and significant tree mortality were observed in infested pine forests. A strong debate is currently taking place in Greece about the exact role of M. hellenica. Very different opinions are expressed, as for some the insect only causes cosmetic damage and for others it is the primary cause of pine mortality. It is also argued that M. hellenica could be a factor among many others involved in the decline of pine forests (e.g. ozone and soil pollution, drought, urban development and reduction of growth space for trees). But despite the lack of scientific information on the exact impact of M. hellenica on pine forests, the EPPO Secretariat added M. hellenica to the Alert List to draw countries’ attention to the possible risks of moving this pest to new areas where it may escape control.
EPPO region: Italy (only in the island of Ischia, Campania), Greece (spreading on the mainland and several islands including Crete, Rhodos), Turkey (at least in the Aegean region, data is lacking for other regions). In Italy it was officially reported on the island of Ischia (Campania) in 1984 but it is suspected that it was introduced in the 1960s. M. hellenica is thought to originate from the eastern Mediterranean region.
On which plants: Pinus species: especially P. brutia, P. halepensis and to a smaller extent, P. sylvestris, P. nigra, P. pinea. After artificial infestations studied at Mount Helmos in Greece, M. hellenica was also able to develop and establish on Abies cephalonica.
Damage: M. hellenica is a sap-feeding insect. It produces large amounts of honeydew on which sooty moulds develop. It prefers the lower part of the tree and mainly nests on the main trunk, but infestations can be also observed on branches and even exposed roots. Large populations cause branch dieback, gradual desiccation eventually followed by tree death. So far, pine mortality is mainly observed in Southern Greece and Crete. In Italy, on the island of Ischia, M. hellenica was found damaging Pinus trees on the coast and in urban environments (streets and parks). In Turkey, a study was done to assess the impact of M. hellenica on P. brutia growing in the forests near Muğla (Aegean region). It showed that infestations could present a significant negative impact on trees (e.g. with up to 3.4% loss of volume increment in tree stands). But no tree mortality was mentioned in this study.
M. hellenica can be found in bark crevices, covered by white waxy secretions. The insect has 1 generation per year (although in some cases 2 generations have been observed). It is considered that M. hellenica mainly reproduces through parthenogenesis, as males are rarely found. Females are apterous and lay approximately 200-300 yellow, oval-shaped eggs covered by waxy secretions (in April, in Greece). 1st instar larvae (antennae with 6 segments) hatch approximately 20 days after egg-laying. They are light yellow, ellipsoid in shape and they start feeding and secreting a waxy cotton-like substance (from May to October). 2nd instar larvae (antennae with 9 segments) with an ellipsoidal shape are found from October to March. Each larval instar lasts approximately 6 months and the insect overwinters as 2nd instar larvae. Bright yellow adult females (antennae with 11 segments) covered by waxy secretions are then observed (body is approximately 7-11 mm long and 3-5 mm large). Male have rarely been found in Greece. The immature male stages have spindle-shaped, yellowish bodies (5.3 mm long, 3.6 mm large) and adults are winged (wingspan of approximately 11 mm).
Dissemination: M. hellenica has a low mobility, females are apterous and winged males are rarely observed. Results of genetic studies done on different Greek populations of the insect were also consistent with a very low mobility of this species. Artificial and intentional infestations done by man have obviously been very efficient in disseminating M. hellenica into new areas in Greece, where its populations reached high levels.
Pathway: Pinus plants for planting, cut branches.
Possible risks: Although scientific data is lacking about the impact of M. hellenica on Pinus forests, there is indication that large populations of the pest are damaging trees. In urban environments, insects producing large amounts of honeydew are always considered as a nuisance. Pines are widely present in the EPPO region, in forests but also in parks and gardens. Treatments against M. hellenica are being studied but most of them are difficult to apply in natural environment. The possible action of natural enemies, such as Neoleucopis kartliana (Diptera: Chamaemyiidae) or Chartocerus sp. (Hymenoptera: Signiphoridae) is being studied. In Italy, phytosanitary measures have been put in place to contain the pest within the island of Ischia (e.g. movements of host plants from the island of Ischia are prohibited, new outbreaks must be reported, pruning material should be destroyed). Although the risk presented by M. hellenica to Pinus trees is still being debated, it is advisable to avoid the introduction of M. hellenica into new areas.
EPPO RS 2006/130
Panel review date - Entry date 2006-06
Personal communication with Mr Melas, Philodassiki, Athens, 2006-02.
Personal communication with Dr P. Milonas, Benaki Phytopathological Institute, Kifisia, Greece, 2006-06.
Anonymous (2005) Linee guida per interventi urgenti nelle pinete dell’isola d’Ischia, finalizzati al contenimento delle infestazioni in atto di coleotteri corticicoli (Tomicus destruens ed Orthotomicus erosus) e di omotteri fitomizi (Marchalina hellenica). Servizio Fitosanitario Regionale Campania. http://www.sito.regione.campania.it/AGRICOLTURA/difesa/linee-guida-pinete.htm
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Petrakis P, Roussis V, Vayias C (2006) Scientists are testing what could prove the definitive way to save pine trees from a slow and certain death. Ekathimerini. (on-line version of a Greek newspaper - 2006-16-03) http://www.ekathimerini.com/4dcgi/news/content.asp?aid=67533
Yeşil A, Gürkan B, Saraçoğlu Ö, Zengin H (2005) Effect of the pest Marchalina hellenica Gennadius (Homopera, Margarodidae) on the growth parameters of Pinus brutia Ten. in Muğla region (Turkey). Polish Journal of Ecology 53(3), 451-458.