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POLLINATION OF STEVENIELLA SATYRIOIDES (ORCHIDACEAE) BY WASPS (HYMENOPTERA, VESPOIDEA) IN THE CRIMEA

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POLLINATION OF STEVENIELLA SATYRIOIDES (ORCHIDACEAE) BY WASPS (HYMENOPTERA, VESPOIDEA) IN THE CRIMEA
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  POLLINATION OF STEVENIELLA SATYRIOIDES  (ORCHIDACEAE) BY WASPS (HYMENOPTERA, VESPOIDEA) 1 IN THE CRIMEA Lindleyana 10(2): 109 – 114. 1995. V LADIMIR    V.    N AZAROV % Dr. Guenter Gerlach, Botanischer Garten, Menzinger Str. 65, 80638 München, Germany S TEVENIELLA SATYRIOIDES  (Stev.) Schltr. is currently the only species described in the genus. Its natural habitat covers Anatolia, Northern Iran, Caucasus and Crimea (Nevski, 1935; Baumann and Künke-le, 1988). In the Crimea this orchid is represented only in the mountainous parts of the peninsula. Here it grows in forests among thickets and in forest glades on primarily sothern facing grassy and mossy slopes (Vulyf, 1930). In the past S. satyrioides  grew in relatively large colonies in  places with a well-developed moss cover and high surface moisture (Vanykov, 1914). Only recently it was entered as a rare species in the Red Book of the Ukraine SSR (1980) and USSR (1988). The flower of Stevenialla satyrioides are simi- lar to that of Orchis . Steveniella , however, is dis-tinguished from Orchis  by the union of the sepals into a three-pronged hood, the characteristic “T” shape of the three-lobed lip covered at the base  by fine papillae and a short dichotomous spur (Senghas, 1973). Few flowers of this type are ca- pable of auto-pollination, and are only pollinated  by insects, and then only by those whose mor-109  1 I am grateful to Dr. Guenter Gerlach, Botanischer Garten,München, Germany who has made encouraging and construc-tive comments and the correction of the English translation. Field assistance was provided by my friend A.A. Alekseev,  Nikitskij Botanical Garden, Jalta (Crimea). Mrs. S. Werner, München, Germany, I thank for the translation of this article into English. e-mail: nazarov@gmx.net ABSTRACT:  Pollinators of the  Steveniella satyrioides  were studied in the Crimea. The nectarless orchid is pollinated by two species of wasps: Paravespula vulgaris  and Dolichovespula sylvestris . At the end of the flowering period pollinators had visited about 93% of all flowers in the population. S. satyrioides  attracts wasps with the help of reddish-brown papillae on the base of the lip, at the spur entrance; the wasps may take them as food. The inner cavity of the spur in S. satyrioides  may resemble a customary feeding site that is also reddish colored. Scratches from the mandibles were discovered on the inner surface of the spur in 78% of the examined flowers. The wasps press the hemipollinarium on the stigma with great force while attempting to tear off a section of the tissue. As a result, a significant portion of the massulae remain on the stigma. In Steveniella the number of ovules per ovary is distinctly geater than in Orchis and Dactylorhiza : this behavior of the wasps was reflected in the potential seed productivity of S. satyrioides .  phology corresponds to that of the flower (Dar-win, 1862). Furthermore, it is well known that the length of the pollinator’s proboscis must not be longer than the length of spur and the width of the facial parts of the head in the central area of the clypeus must correspond closely to the width of the spur-opening in the orchid (Nilsson, 1980, 1983, 1984; Fritz, 1990). The pollinators and pollination mechanism of S.   satyrioides had not been investigated. This lack of information induced us to conduct the present research, as it is beyond doubt that pollination data about any plant are relevant in organizing  projects to restore the species in areas where it has disappeared. The research was carried out in 1992 at two  points on the northern incline of the interior ridge of the Crimean mountains. The first sample group of plants was located in the vicinity of Skalistoye Bachchisaraisko district (A). The second sample group was situated in the central basin of the Cri-mean reserve (B). Sample group A was inspected regularly during the entire flowering season. In sample B the observations were made sporadi-cally. All insects seen visiting the orchid’s flowers were captured for subsequent identification. At the end of the flowering period the number of  MATERIAL AND METHODS   NAZAROV — POLLINATION OF STEVENIELLA 110 visited flowers was determined by changes caused  by pollinators in the flowers. The flowers were defined as visited when the hemipollinaria had  been removed or massulae had been deposited on the stigma. Ovules were counted following Nazarov (1989). The morphological measurement of the flowers and insect-pollinators was carried out by using the measuring scale of the MBC-9 binoc-ular microscope and sliding callipers down to an accuracy of 0.1 mm. RESULTS AND DISCUSSION  Plants of Steveniella satyrioides in samples groups A and B flowered from the end of April to the second/third week in May 1992. During this period they were visited by ten individual wasps, nine of them going to sample A. All were identified as workers of Paravespula vulgaris  L. Plants in sample B attracted only one specimen, a worker of Dolichovespula sylvestris  (Scop.). Two hemipollinaria of S. satyrioides were found in the center of the clypeus of one D. sylvestris and six P. vulgaris  wasps. Another individual of P. vulgaris  wasp had four hemipollinaria on its clypeus. The clypeus of both species of wasp is well suited to the distribution of pollen. Sparse and small hair on ist surface permit close contact of the viscidium with the chitin of the head (Fig. 1). The viscidium of S. satyrioides  in the studied samples adhered reliably to the pollinators. Intact hemipollinaria on the stigma of the flowers were not seen. Viscidia with caudicles remained on the  pollinators even after all the massulae of the hem-ipollinaria were removed by visits to many flow-ers. An investigation of the major parameters of the S. satyrioides  flower and the heads of the worker wasps revealed excellent morphological agree-ment between them. The width of the throat of the spur in S. satyrioides  in the samples studied averaged 3.2 mm (n=50). The width of the wasp heads measured through the center of the clypeus exceeded the width of the orchid’s spur-mouth. With P. vulgaris  it came to 3.9 mm (n=9) where-as with D. sylvestris  it was 3.4 mm (n=1) (Fig. 2 A). However, while visiting the flower the cen-ter of the clypeus of both wasp species was ex-actly opposite to the bursicula, which in S. satyr-ioides is located slightly higher than the edge of the spur (Fig. 3 B). The spur of S. satyrioides  reached, on avarage, 3.7 mm in length (n=50). The proboscis of both wasps hardly reached be-yond the border of the mandible. Therefore the length of the spur of S. satyrioides  is slightly greater than the distance from the center of the clypeus to the edges of mandible: the distance reached 2.9 mm in P. vulgaris  and 2.8 mm in D. sylvestris  (Fig. 2 B). A similar relationship be-tween the length of the spur and the mouth parts of the pollinator was repeatedly recorded in spe-cies of Dactylorhiza and Orchis . In these cases the insects had to press their head into the throat of the flower with great strength, which led to closer contact of the facial parts of the head with the viscidia (Nilsson, 1980, 1981a, 1983, 1984). It is known that wasps prefer visiting brownish-green colored flowers (Faegri and van der Pijl, 1982). This type of flower coloring is often en-countered within the Orchidaceae. For example, it is characteristic for the Epipactis species that are pollinated by solitary and social wasps (Dar- Fig. 1. Deposited hemipollinaria of Steveniella satyrioides  on the heads: A.   Paravespula vulgaris ; B.   Dolichovespula sylves-tris  (after various flower visits, most massulae removed).  Fig. 2. Comparison between: A.  Width of spur in flowers of Steveniella satyrioides and width of face (across the center of clypeus in ist pollen vectors);  B. Length of spur in flower of Steveniella satyrioides and distance from center of clypeus to top of mandible in pollen vector species. 111 win, 1862; Nilsson, 1978, 1981a; Judd, 1971). Within orchids pollinated by wasps, a different type of flower coloring also occurs, e.g. Hermi-nium monorchis  has the yellow-green flowers thatare, pollinated by primitive wasps of the genus Tetrastichus (Nilsson, 1979). Well documented is the role of the parasitic Ichneumonidae in the pol-lination of greenish flowers of Listera ovata . The  NAZAROV — POLLINATION OF STEVENIELLA  Fig. 3. Floral morphology in Steveniella satyrioides . A:  Flower and ovary, front (left) and lateral (right) view; B: Column and spur (lip and part of spur removed), front view; C:  Hemipollinaria, front (above) and lateral (below) view. Abbreviations: anther ( a ), anther-pockets with one removed hemipollinarium ( ap ), bursicula (  b ), caudicule ( c ), labellum ( l ), massulae ( m ), ovary ( o ), stigma ( s ), spur ( sp ), papillae (  p ), viscidia ( v ). 112  NAZAROV — POLLINATION OF STEVENIELLA   NAZAROV — POLLINATION OF STEVENIELLA 113 wasps are guided to the orchid flowers by their fragrance (Nilsson, 1981b). The orchid species mentioned above reward their pollinators with nectar. They produce nectar in open nectaries that are easily accessible for wasps with a short pro- boscis. Non-nectar producing species are uncommon among orchids pollinated by wasps. These or-chids attract wasps to their flowers by deceit. It is known that several Australian species of Ca-ladenia , for example, are pollinated by Thynninae  males as   a result of pseudo-copulation (Stouta - mire, 1983). In other species of the Caladenia  and Diuris  a   "false prey"-syndrome has been de - scribed: when the Scoliidae  wasps produce sting - ing movements   at the    part of the lip that resem -  bles the insects, they take it as prey (van der Pijl, 1966). In these cases investigators may easily confuse the stinging movements with copulative movements. The spurs of Steveniella satyrioides  do not con-tain free nectar. However, worker Paravespula   vulgaris  and Dolichovespula sylvestris  wasps ac-tively visit the flowers. At the end of the flow-ering period, 93 % of all flowers had been visited  by pollinators in population A; 69% of the flow-ers bore fruits. Such high percentages of visits and pollination are not characteristic for non-nec-tar producing orchids. In non-nectar producing species that attract pollinators to their flowers by mimicking “reward giving” plants, the percent-age of fruit set is almost half (Dafni, Ivri, 1981a,  b). The observations have shown that the wasps are interested not only in the spur but also in the special lip of S. satyrioides . After landing on the orchid flower, the workers of P. vulgaris  wasps generally first inspect the papillae at the base of the lip. Only after a few seconds do they plunge their mandibles into the spur. Direct sighting makes it reasonable to assume that in doing so the wasp is attempting to tear off a section of the tissue. An inspection of the inner surface of the spur of 60 pollinated flowers showed that in 78 % of the flowers were there scratches made by the wasp’s mandibles. The morphology of the spurs are adapted to the wasps' behavior. The pro-file of the spurs repeats exactly the profile of the lower parts of the wasps' heads with expanded mandibles (Fig. 3 B).  P. vulgaris  and D. sylvestris , like other speci-mens of Vespidae , are predatory insects. The food given to the larvae of these wasps consists chiefly of pulped animal food (Tobias, 1978). The flow-ering period of S. satyrioides  starts at the begin-ning of the establishment of the wasp colony when the workers were actively preparing food for their larvae. The general model of flower coloring in S.   sa-tyrioides  is excellently suited    to flowers visited  by wasps. In its coloring it has yellowish-green and reddish-brown tones. The peripheral part of the perianth including the distal part of the lip creates an olive   or yellowish-green    background. The reddish-brown center clearly stands out against this. It forms the upper part of    the column and    the base of the lip.   The reddish-brown flower is strongly   colored on   the part of    the   lip covered with flattened papillae (Fig. 3 A). The worker wasps probably take the reddish-brown centre of the S. satyrioides flower to be a piece of animal food. Apart from the similarity in coloring, the imitation could be reinforced by the flat papillae at the base of the lip. Above all they imitate the texture of a fleshy substratum. The inner cavity of the spur, also coloured in a reddish tone, pos-sibly resembles a customary feeding site of other wasps. The morphology of the S. satyrioides  flower is also well adapted to the “aggressive” behavior of the pollinating wasps. The sepals of its flower are united to form a rigid hood, and it is joined from  behind to the upper part of the column. A rela-tively tight but heavy lip is directed almost ver-tically downward which considerably reduces the force of the shoulder of the lever. At the same time the “T”-shaped form of the lip and the small  broadening at the end of its central lobe probably create favorable conditions on the lip for retaining the wasps while they attempt to eat in the spur (Fig. 3 A). “Aggressive” behaviour of the worker Vespidae  wasps on the flowers of S. satyrioides  is also re-flected in the basic reproductive characteristics of this orchid. In the species of Dactylorhiza  and Orchis  that are pollinated by such powerful pol-linators as Bombus  and Psithyrus  (Nilsson, 1980, 1983, 1984), one often finds as many massulae remaining on the hemipollinaria (on a pollinator) as have been deposited on stigmas. Such a phe-nomenon is not typical for S. satyrioides . Its mas-sulae are positioned on the stigma of the pollen-
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