Wednesday 27 April 2016

Pine Die-back in Crete, Greece

Pinus brutia
Last Saturday (16/04/2016) amateur botanist Steve Lenton and I visited the heavily wooded area around Kato Symi (Crete, Greece). We were immediately alarmed by the state of the pine trees (Pinus brutia) in the area and I decided to investigate the cause or causes.

Thaumatopoea pityocampa caterpillar

The first suspect was the Pine Processionary  Moth, Thaumatopoea pityocampa due to the high number of nests which were visible. These cause massive defoliation of pine trees.

Closer examination of the trunks showed white, fluffy extrusions which looked similar to Pine Beetle pitch tubes.

Marchalina hellenica

The true culprit however was nearby in prodigious numbers: The Giant Pine Scale, Marchalina hellenica.

Honeydew (600x)

These produce the white fluff that is packed full of nourishing honeydew.

Apis melifera
 This honeydew is an important food source for the Honey Bee, Apis melifera, from which seems to “originate all the pine honey in Greece” [Portrait of an Insect: Marchalina hellenica]. There were a lot of bee hives in the area and it is not unknown for beekeepers to deliberately introduce this pest (even if ultimately it is like killing the goose that laid the golden egg).

Meanwhile, at the base of the tree the Pine moth caterpillars were not having it all their own way as they were being trapped in sticky threads that appeared to be emanating from the ground.

My guess (and it is only a guess) is that this is some sort of fungal mycelium.If so, what is it and does it have any connection to either the caterpillars or the scale insects? There is still a lot of investigation to be done on plant/fungi relationships and I wonder if the tree could be ‘calling up’ a fungus as a defence mechanism or if the fungus is attacking an already weakened tree.

 The following photos show the threads at different levels of magnification and I welcome feedback from mycologists and entomologists on this fascinating (if destructive) set of interactions.



 Steve Daniels, Crete, Greece, April 19th 2016.

I originally posted this on Facebook (Naturalsits Group) and LinkedIn (Ecology & Evolutionary Biology). As comments are coming in from both groups as well as Steve Lenton's Facebook Group (Cretan Flora) I have decided to publish it here complete with comments from all sides in order to keep the conversation in one place. SD 27th April 2016. 


  1. Via LinkedIn: (Ruark Cleary) Pine trees typically need to be already stressed before succumbing to (or attracting) such a host of parasitoids. Drought history, soil moisture levels, and maybe even soil pH and composition, would be some of the things I would check.

  2. Via LinkedIn:(Sylvia Rains Dennis) Thank you for your observations and photos. I'm wondering about survival and growth for seedling/sapling life stages of the native trees, as well as the cohort of native plants (herbaceous and shrubs) that might normally be present.

  3. Via LinkedIn:Thanks for your comments. Ruark: I hope that this this is already being done by the Mediterranean Agronomic Institute of Chania who, I believe, have a responsibility for Crete Forests and I have invited them to join the discussion. Sylvia: As far as I could tell it was only the pines that were affected but I have passed your question to Steve Lenton who knows the plant life of the area far better than I.

  4. Via Facebook (Steve Lenton Message from Salvatore Pasta.)
    I am trying to have a more qualified opinion from some Sicilian plant pathologists. Waiting for their answer I made a rapid research on Marchalina and I suggest the following sites to know something more:
    By the way, as Marchalina is native to East Mediterranean, I do not expect that this species alone is able to make such severe (and almost sudden) damages. On the other hand, a friend of Laf who lives near the damaged forests of Kato Simi observed the dying pines and noticed there the huge presence of caterpillars, so I think (and also Laf does) that it as more probable that different co-occurring factors exasperated the effect of insect scales, or even that these ones do not play any role at all in recent pine death events. On this purpose, I would check more thoroughly for demographic explosions of pine processionary caterpillars (Thaumetopoea pithyocampa), which are know to induce severe and widespread damages to pines forest all over the Mediterranean area, especially when intense and long-lasting drought stress co-occurs. This is my opinion, but I will come back to you as soon as I have some more infos from my friends/colleagues.
    As concerns any direct effect of Marchalina on other plant species living under the canopy of pine trees, I think it is highly improbable, while indirect effect are certain, because a wide and sudden damage to tree layer canopy could induce a sharp change in several environmental patterns typical to pine forests (e.g. yearly and summer solar radiation, yearly and summer air and soil temperature, etc.).
    Moreover, as all Mediterranean pine species seedlings and saplings are typically light-demanding, I would not expect a very huge damage in the medium- or long-time on native pine populations."

  5. Via LinkedIn: Sylvia Rains Dennis Sorry for any confusion: my intention was to learn more about the natural vegetation and thereby any innate resilience factors for the pine ecosystem. So, I had wondered if there are other stressors, such as lack of infiltration or percolation through soils, consequent soil structure / nutrient availability / seedbank concerns, impacts to mutualistic associations, or even aboveground conditions that might coincide with such an impact to the pines. Their regeneration would presumably rely on seedlings and saplings re-establishing within a native plant community well-adapted to shifts in precipitation, temperature, etc. Some of these issues have since been raised. I did not mean that Marchalina was impacting other species, but that the plant community dynamics seem stressed overall (remembering examples seen elsewhere, even among shade intolerant pines).

  6. Via Facebook (Steve Lenton Message from Salvatore Pasta.)
    Here is the translation (and summary) of the first infos provided by my friend Giuseppe Campo (Regional Forest Department of Sicily):
    I am looking for further and more detailed infos. As concerns the phytosanitary problems induced by Marchalina in Italy, up to now it has been recorded only on the volcanic islands of Ischia ad Procida (S Tyrrhenian).
    Most of the severe pine forest decline or death events are caused by parasites and phytophagous insects which exploit plant weakness or stress, although this is not the rule. Among insects, the most noxious are Scolytidae smile emoticon bark beetles) such as Tomiscus destruens, more rarely T. minor, Orthomiscus erosus, Ips sexdentatus, Hylurgus liniperda, Crypturgus numidicus, Pityogenes calcaratus etc.) sometimes the Curculionidae smile emoticon snout beetle) like Pissodes notatus.
    Among mushrooms the most noxious are Heterobasidion annosum and Armillaria mellea
    Very often drought (water+heat) or soil stress factors or anthropogenic disturbance (e.g. fires), may enhance sudden death events.
    The pine caterpillar normally does not cause the death of the plants but may weaken them, so that subsequently they are more exposed to bark beetles.
    No connection or synergic action of Marchalina and Thaumetopoea has been recorded as far as I know. I suspect that strong drought stress could have favoured Scolytidae and mushrooms.
    As far as I know Marchalina has been found occasionally on the plants growing under pine canopy (e.g. Acanthus mollis) but apparently only due to falling after windy days and not feeding or living on such plants
    Thaumetopoea is strictly linked to Pinus species
    He will tell me if, when, how and how much specimens should be collected to understand more about the problem
    To next update,


    If you think it's a good idea, please publish all my message to share with all the 'Cretan' community. Cheers, Salvo

  7. Via LinkedIn:(Sascha Rieger) Does the rising salinity of ground water factor into this?

  8. Via LinkedIn: Sascha, the altitude is about 850m. Would rising salinity of ground water be applicable at this altitude?

  9. So the sitation at present is that we have three prime suspects: Pine Processionary Moth, Thaumatopoea pityocampa; Giant Pine Scale, Marchalina hellenica; and/or Soil Impoverishment.
    All of these require further investigation along with any other contributing factors as well as the defence mechanisms that the trees themselves are using to try to protect themselves.
    From here we can predict the oucome if the situation is left unchecked and if necessary try to find a course of remedial action to
    a) protect the existing trees
    b) prevent the spread to neighbouring trees
    c) prevent recurrence
    d) stop further outbreaks elsewhere

    Your further comments and observations would be welcome.

  10. Via Facebook (Cretan Flora): Fotis Samaritakis Everything started many years ago when human decided to create scratches on the trees in order to attract bees to get the pine tree honey..the trees became vulnerable to diseases and gave the opportunity to a special insect to create that white sticky powder on them.. the authorities are still looking for a solution. At least this is what happened at the pine trees of Aradaina and Agios ioannis in Sfakia


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