@article {50885, title = {Subalpine forest near Bonneval/Arc (Savoie) since 2007: recovery of a Sciophila population (Diptera, Mycetophilidae) diminished by hard winters and strictly related to Phellinus tremulae, a rare parasite of aspens}, journal = {Bulletin de la Societe Zoologique de France}, volume = {135}, year = {2010}, month = {2012}, pages = {237-263}, abstract = {

Observations performed over many years, concerning aspens of a subalpine forest growing in Haute-Maurienne (Savoie), provide clear evidence of a \"climacic\" balance between a population of a Mycetophilid fly, Sciophila bonnevalensis n. sp. and the fungus Phellinus tremulae, a strict parasite of aspen trees above 1800 m. We have recently outlined the disastrous effects of the very low temperatures that occurred during the 2004-2005 winter. attaining -28[degree]C. Very few Sciophila larvae survived to the following summer. At the same time, the protective webs of others were partly destroyed. being reduced to white dots dispersed on the carpophores of Phellinus. Consequently, we thought that an almost irreversible situation had been attained. However, despite a second hard winter (-23[degree]C), the population of Sciophila was again observed to be slowly growing during July 2006. Moreover, the 2006-2007 winter (-17.5[degree]C) was not strongly destructive and consequently we observed a relatively strong increase of the Sciophila population in July 2007: protective webs were eight times as numerous as in July 2005. Nevertheless, this increase in larval activity may have been slightly slowed in 2007 as a consequence of a brief period of frost and snow at the beginning of July. This was strong enough to induce death of Yponomeuta padella larvae everywhere, the nymphosis of which is known to locally hinder Sciophila larval growth. We believe that our climatic and biological observations, patiently built up during many years, could provide a starting point for a more complete study (we give also new results for 2008 and some details for 2011). Such a study concerns only a local geographical and ecological subject, but it could be compared with well-known strong global disturbances observed by eminent specialists. In fact, in these limited, subalpine mountain conditions, it could be possible to take into account some parameters that are relatively easy to evaluate on yearly basis. Thus, we observed that local warming strongly favours the growth of aspen, which can climb along rocky slopes and among frontal moraines of the Arc glacier. After some years, this can consequently enhance Phellinus growth, as described in this work. On the other hand, we still lack knowledge about the effects of wind and snow: are these determinant or minor factors? As detailed here, it is clear that very low winter temperatures affect Phellinus growth and induce Sciophila larval mortality. Such parameters can be easily studied, evaluated, and, in combination, could constitute an appropriate model to investigate local climatic disturbances and perhaps even serve as a reference for comparisons with similar studies undertaken elsewhere, in other biotopes

}, author = {Bouchard, Jacques and Bouchard-Madrelle, Christiane} } @article {28732, title = {Effets redoutables d{\textquoteright}un grand froid hivernal sur la relation du diptere mycetophilide Sciophila sp. et du polypore Phellinus tremulae, en haute maurienne}, journal = {Bulletin de la Societe Zoologique de France}, volume = {131}, year = {2006}, pages = {227-247}, abstract = {This work provides an improved interpretation of our previous observations concerning ecology of Sciophila sp., a Mycetophilid (Diptera) living as a [much less than] symbiont [much greater than] on Phellinus tremulae which is a specific parasite of Populus tremula in subalpine forest islands. In a recent paper (2005), we have shown that Phellinus tremulae is strictly eaten by larvae of Sciophila sp. and that the Mycetophilid contributes to the dispersion of this species in aspen islets. It seems that the ecology of this insect has not been previously described. This relationship has been observed since 1978-1979 at Bonneval/Arc (Isere), as well as at other places in the Alps. It has been concluded that the relation between P. tremulae and Sciophila is mutually beneficial: Sciophila larvae are slowly digging superficial furrows in the hymenium and nibble spores of the Polypores, which, in return, find a benefit when flying Sciophila transport spores from place to place and show a great degree of specificity for their breeding habits. However, in summer 2005, we have been disappointed by the fact that Phellinus and Sciophila have strongly suffered among aspens of Bonneval. Some Polypores are seriously dried. Moreover, many larvae of Sciophila have been killed. Webs which usually protect these animals are reduced to debris scattered on hymenium of Polypores. In fact, very few larvae are remain alive. It seems interesting to determine what sort of factors may induce such a degradation. In an attempt to get some information, meteorological events could were studied in the vicinity of Bonneval (Bessans). Maximal-temperature mean in June-July was 21.4[degree]C for 2005, compared to 19.5[degree]C for the previous 10 years. This difference cannot be responsible of the observed mortality. In 2005, pluviometry was normal and storms have not been particularly violent. From 2004 October to 2005 Marsh, snowfalls were relatively limited: 332cm versus 400-450cm on average for previous 10 years. Moreover, maximum thickness was around 120-160cm against 200-230cm during previous years. This last point is striking. We note that minimal winter temperatures have been unusual; for example, -16.7[degree]C have been observed during February 2005, against -9.9[degree] for the same month of 10 previous years and even -8.8[degree]C for 20 previous years. The weather was also very cold during 4 months corresponding to winter period. A temperature of -35[degree]C has sometimes been recorded depending on exposition. It now appears that death of most Sciophila larvae may be the result of an excessive cold allied to low snow thickness: frost killed larvae. We have to note that in the past, 1979, 1991 and 1995, we observed some similar facts: Phellinus tremulae individuals and Sciophila larval-webs have been partly affected. These were exceptions, clearly depending on their location in the forest and their positioning along trunks. Moreover, in the western part of the forest, during the summer of 2005, just before metamorphosis, larvae of a cherry-tree moth (Hyponomeutidea: Yponomeuta padella L.), were climbing on trunks of Populus, covering Polypores and Sciophila larvae with dense webs. Although cyclic, such an invasion is quite unusual, ordinarily limited to the host-plant or its neighbouring bushes or rocks, but in 2005, aspens were also dressed with a sort of grey shroud. It is clear that such webs contribute to Phellinus and Sciophila degeneration. It should be noted that Yponomeutidea lay their eggs on low branches of the host Aria nivea, which is abundant around Bonneval: snow is always high enough to protect them during very cold winters. But this situation is only secondary, restricted to a small lower part of the forest island. In fact, the P. tremulae population, associated with Sciophila, is slowly climbing among masses of fallen rocks of sub-alpine zone. Aria nivea cannot follow such trees, which are able to survive in spite of drastic ecological conditions. However, we suggest that partial destruction of Phellinus and Sciophila could induce lasting disruptions in the model association described, as long as meteorological disturbances may persist from year to year.}, author = {Bouchard, Jacques and Bouchard-Madrelle, Christiane} } @article {23834, title = {Relation stable, "symbiotique", entre un diptere Sciophilide et son hote subalpin, le polypore Phellinus tremulae (Bond.), parasite de Populus tremula (L.). Stable "symbiotic" relationship between a sciophilid fly and its subalpine host, the polypore Phel}, journal = {Bulletin de la Societe Zoologique de France}, volume = {130}, number = {3}, year = {2005}, note = {Using Smart Source Parsing}, pages = {235-261}, abstract = {

Among Diptera, Mycetophilidae are often observed on mushrooms, but Polyporus are not really attractive hosts. However, we have studied an alpine species which grows on a fungus, Phellinus tremulae, a parasite of the Poplar, Populus tremula. This fungus is infrequent in France, but has been recorded by a Mycologist, P. HEINEMANN (Bruxelles) from Haute-Maurienne-Savoie near Bonneval-sur-Arc (1979; registered samples in Jardin botanique national de Belgique, August 1978). With him, we saw that larvae of a mycetophilid (tribe Sciophilini) of the genus Sciophila devour Phellinus tremulae, even though its hymenium is relatively hard. Some preliminary observations were published in 1994 (J. BOUCHARD), but it was clear that a study needed to be carried out on a longer period, because of the gradual evolution of the woodland. In the study area, a valley oriented West-East, Poplars grow among fallen rocks in the upper border of the subalpine forest, between 1820 and 1900 m. They form a woodland of 18-20 ha which has been climbing eastwards between the rocks for about twenty years. The Mycetophilid Sciophila sp. is limited to this woodland area: Phellinus tremulae is evidently absent on Poplars below Bonneval. The question arose as to whether this complex relation between three partners can be defined and we tried to determine some controlling factors. Young Poplars, 20-25 years old, are not infested by the fungus, and Phellinus cannot be observed on the western border of this woodland, exposed to rather strong winds blowing during sunny days. Carpophores are not found on Poplars growing on wet soils and particularly near the torrent, where these trees take advantage of the best conditions for growth. On the contrary, carpophores appear on the lower parts of old trees living elsewhere, the bark of which is grooved, frequently injured, or if a branch has been broken. The spores of Phellinus tremulae are extremely small (2-3 [mu]m) and smooth. A priori, anemophily seems to be the mode of dispersal of the fungus. However, this pathway is far from the only one. After studying Sciophila for more than twenty years, it is clear to us that this animal is always related to Phellinus tremulae growing just above Bonneval-Tralenta. Such a correlation has also been observed by HEINEMANN in two other parts of our Alps (pers. comm.) and we found an other example along a high valley situated in the Queyras, a southern region of the Alps, once more at the top of the subalpine forest (1950-2000 m). The larvae of the four successive instars eat the spores and the hymenium of the carpophore, where they stay for months under a solid web secreted by the salivary glands. This web constitues a good protection against small predators; small birds generally stay near the border of the forest, eating in bushes or among grassland and we have neither seen nor heard Certhiides, the only true corticols able to eat such small preys along trunks. Possessing strong mouthparts and powerful cephalic muscles, as determined from histological sections, but with a lengthy digestion, the larvae slowly dig a superficial furrow in the fungus, leaving a wet slimy trail. They are able to restore their web rapidly, in a few minutes, if it is destroyed. The gut of the larva is always stuffed with spores and debris of hymenium, but the waste is eliminated at the end of the last larval instar. Adult Sciophila walk and can sometimes jump, but cannot fly vigorously : strong winds, which frequently blow in summer, send it away from the western border of the woodland and induce a concentration of these animals in protected areas. Direct microscopic observation of imago allows the location of spores on the body and especially along veins of the wings. Histological sections made using the trichromic method (Regaud-Masson), show many spores forming clumps in the folds of the integument or trapped between bristles of the margin of abdominal segments. They are often embedded in sticky liquids, easily stained with aniline-blue and apparently produced by the fungus and certainly harves ed on wounded trunks. The results suggest that the male and female imagoes are richly supplied with numerous and diverse sensillae. Abundant on the antennae, they are prominent on the long and complex palps, where thousands of batteries of short chemoreceptor sensillae can be seen at high magnification. Long and short bristles exist elsewhere, such as on the legs. Antennae and palps are able to detect the specific odors produced by the wounded Poplars and those of the fungus (perceptible to humans). While feeding, Sciophila favours the dispersal of spores and is the real infestive agent in newly-injured trees. After a study of the various small animals wandering on the carpophores, such a dispersal does not seem to be favoured by other species such as Collembola, mites and tiny Insects. Having studied this complex relationship for more than twenty years, we found that it tends towards a climacic equilibrium, strictly limited to the upper part of subalpine forests. However, it is clear that near Bonneval the woodland tends to slowly invade screes, proliferating between rocks and climbing towards the foot of the cliff. We regard this as a consequence of increasing temperatures. Now, it is time to study the health of the young Poplars which are not yet attacked by Phellinus tremulae and thus devoid of Sciophila. In Savoie or Queyras, such poplar islets seem to be glacial relicts. Mycologists have observed Phellinus tremulae parasitizing Populus tremula in both Palearctic and Nearctic cold countries (Scandinavia, Russia, Canada...). It is to be hoped that other workers will investigate the chemical processes of the inter-relationship that we have observed : it could serve as a model study which could provide insights concerning what is probably a symbiosis between Sciophila and Phellinus, which are clearly interdependent. The complex evolutinary interactions between these three organisms is certainly worth of further study.

}, keywords = {Diptera, Insecta, Mycetophilidae : Nematocera}, author = {Bouchard, Jacques and Bouchard-Madrelle, Christiane} }