prilagođeno pretraživanje po punom tekstu

ŠUMARSKI LIST 11-12/2012 str. 49     <-- 49 -->        PDF

The samples were put into Petri-dishes of 10 cm diameter. Dish bottoms were covered with tissue paper, which was humidified ca. every 3 days using faucet water. At least 5 pieces of peeled potatoes (ca. 0.5x1x1 cm) were distributed around the bark and on the top. They were moistened every 3rd day with water drops so that the potato’s surface was slightly moistened. When the potato-pieces began decaying due to microorganism growth, the frequency of the regular moistening was reduced. Histiostomatid mites are microorganism/bacteria feeders, and usually develop on the surface of these potatoes, which represent a growth medium for the enrichment of bacteria and other microorganisms from the original habitat (i.e. the bark and the beetle galleries). More or less constant climatic conditions were enabled by storing these Petri dishes inside larger plastic containers. Proper air circulation was also needed for this arrangement of the dishes. The cultures were kept at room temperature (about 21 °C).
The 10 m and the 20 m pieces of the trunk of T1 tree were only infested by the longhorn beetle A. reticulatus. The beetle’s larvae were numerous, and distributed under the bark about 4–6 cm from one another. No signs of scolytid beetle galleries were noted. The longhorn beetle was apparently the first coleopteran to colonise this tree. The larvae finally formed pupal-chambers in the xylem. The galleries of A. reticulatus contained representatives of different mite groups.
The 10 m and the 20 m pieces of the T2 tree were heavily infested by P. curvidens and P. spinidens. Young beetles already had emerged from the bark before it was brought into the climatic chambers. The typical galleries of these bark beetle species and the areas around them were crowded with representatives of different mite groups. In these samples one histiostomatid species was found.
From two of the samples taken from the T1 tree at a level of 20 m, the mite H. ulmi was easily reared. About 10 days after taking the bark sample from the trunk piece, first adults, males and females, were observed feeding on the potato-surfaces. It is not yet known where exactly these histiostomatids were developing, but presumably they lived inside the galle­ries of the beetle larvae. Histiostoma ulmi needs about two weeks to develop from a larva to an adult. Detailed studies about its life cycle do not yet exist. The mites prefer developing in areas which are not too wet, which means that only a very thin film of moisture was vi­sible, and they produce large numbers of deutonymphs in too dry conditions (on more or less dried out potato-pieces for example).
The mite was identified as belonging to the monophyletic Histiostoma-piceae group (Scheucher 1957; Wirth 2004). The drawings of Scheucher (1957) were used for identification of H. ulmi and light-microscopic slides with deutonymphs of H. piceae (collected on the original carrier and tree species in Germany) from the collection of J. Moser (USA) were used for morfological comparisons. This discovery documents for the first time the occurance of H. ulmi in silver fir and their possible phoretic association with A. reticulatus.
Emended diagnosis
Unaprjeđena dijagnoza
Deutonymph: The size of the deutonymphs was measured as an imaginary medial line beginning at the anterior outline of the proterosoma until the posterior end of the hysterosoma of mites, mounted on slides, in ventral view. Mean and range of three specimens 189 (185–193) µm. As in all species of the H. piceae-group, all dorsal setae (Figure 1C) are elongated and directed forwards. The median apodeme (st1), located directly posterior of the palposoma, does not touch the apodemes (bcx2), which run across between legs III; as is also the case in other H. piceae-group species (Fi­gure 1A). A notable character of H. ulmi and at least H. piceae is the median apodeme st1 forming a “wide collar" (Figure 1A) around the palposoma. This character was discovered in the slide-material of H. piceae/Moser-collection, no official types or paratypes, but collected from the original carrier and the original trees as described by Scheucher (1957) and in the slides of H. ulmi/Wirth (the character is barely visible in Scheucher’s drawings). The apodeme bcx2 of H. ulmi, H. piceae, H. trichophorum, H. crypturgi and H. vitzthumi is medially lineally running and laterally on both sides angled backwards (Figure 1A). Distinct (apomorphic) characters could not be found in the deutonymph of H. ulmi. Deutonymphs of H. ulmi and H. piceae look very similar to each other. Details about leg setation in deutonymphs are not visible in Scheucher’s drawings. In a comparison between H. ulmi deutonymphs from our cultures and H. piceae deutonymphs of the Moser-collection, the leg setation looks quite similar.
Adults: The size of adult males and females was measured as an imaginary median line beginning at the level of the stern­al apodemes a1 (the point where it touches the trochanters of legs I anteriorly) until the posterior end of the hysterosoma of mite specimens, mounted on slides, in ventral view.
Males: mean and range of three specimens 285 (253–264) µm. Females: mean and range of three specimens 355 (268–491) µm.
As in most histiostomatid species, males are smaller than females. Apodemes a2 in males (Figure 1E) that do not touch each other is a specific character of H. ulmi. The median endings of these apodemes are bulged posteriorly, a character not visible in Scheucher’s drawings.