A Magyar Természettudományi Múzeum Évkönyve 53. (Budapest
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ANNALES HISTORICO-NATURALES MUSEI NATIONALIS HUNGARICI Tomus 53. PARS ZOOLOGICA 1961. On the Habits of Stilbum cyanurum cyanurum Forst. (Hymenoptera, Chrysididae) By L. MÓCZÁR, Budapest Summarizing the data of various authors, B e r 1 a n d (1938) lists that Stilbum cyanurum Forst, parasitizes Eumenes, Chalicodoma, Sceliphron and Megachile species. It was first bred, from Sceliphron nests, by Lichtenstein (1873), then by de Stefani (1888). The more comprehensive works, treating the nesting of Sceliphron destillatorum Illig. (B o t a r i - desz 1934, Mazek-Fialla 1936, Móczár 1946), also mention Stilbum cyanurum Forst, as a nest parasite. I observed the species, found rarely and sporadically only in Hungary, around the nests of Sceliphron destillatorium Illig., on the sides of the ravine below Mt. Csúcshegy of the Tihany Peninsula, several times in July 1938, 1942, 1943. In recent years, I noted it around the Sceliphron nests built in the cracks and rain-sheltered nooks of the same ravine at noontime on 24 and 30 July, at a temperature of 30—34° C ; the wasp was crawling repeatedly on the Sceliphron nests, feeling or flying around them. Another one was again flying up and down in front of the wall, in 31° C, at 13,30 on 22 July 1960. Therefore, on the basis of observations of many years standing, its presence in front of the face of the ravine of Tihany, and in the warm noontime hours at the end of July, may be taken for granted. I have discussed the ravine and the species nesting there elsewhere (M óczár 1960). On 30 July 1959, I succeeded to observe also the laying of the eggs of Stilbum in the place mentioned, and, as there is no data in this regard in litera ture, I hereby submit my findings. The wasp appeared in front of the wall at 12,19, flying onto a Sceliphron nest of but two cells built in a hollow. One of the cells was not yet finished, it still stood open, not even containing larval food. The Stilbum did not stay for long on this nest, but searching around for a while, left it and flew over to another Sceliphron nest consisting of two finished cells. During its flight, it gave voice to a buzz like that of a fly. After a short time of feeling about, it hovered above the center of one of the cells (already closed by its sheltering cover), then it repeatedly touched this place alternatingly by its mouth parts and the end of its abdomen. A single touch was of a short duration only, — the animal turned about quickly, placing the opposite end of its body at the point indicated. The causes and effects of its movements, made in the shadowy nook of the wall, could be ascertained only after jt flew away, in about 6 minutes. The place mentioned was namely much darker than its neighbour hood (Plate I, fig. 1), as the wasp had thoroughly moistened it during its licking. Also, there was a minute, funnel-like hollow, formed by the ovipositor of the parasite, in the middle of the dark patch. In spite of the fact that there extend backwards four hard chitinous teeth on the end of the Stilbum's abdomen, it is not likely that it should use these teeth for the enlarging and executing of the hole, because, in this case, the hollows ought to be at least 4 teeth wide. The teeth, as mentioned also by Bischoff (1927), are rather used for giving an adequate support to the ovipositor sunk into the cell. • The wasp had therefore first thoroughly moistened the hard, dry mud layer, then bore by its ovipositor a funnel-shaped hollow. As soon as it succeeded to sink a small depression into the wetted, soft mud, the parasite immediately moistened its bottom, boring thus always deeper into the hard cell-wall of Sceliphron until it reached the inside of the cell. The clayey wall of the Sceliphron nest at the inner end of the bored hole remained soft enough for the time required by the Stilbum to penetrate by its ovipositor the cocoon spun by the larve, and to place in it a parasite egg. When the wasp drew back its ovipositor, the soft mud closed again. After the departure of the Stilbum, there was visible a 1 mm wide hollow only, and I was unable to discover any hole, not even in its deepest portion. Some 9 mm away from this funnel, there was also a similar though more shallow one, — the probe shaft of probably another Stilbum. Having at a later time (September) uncovered the cell, the hole made by the ovipositor of the Stilbum on the original Sceliphron cocoon became visible (Plate I, fig. 2), then (16 May 1960) the much smaller cocoon spun by the Stilbum larve (Plate I, fig. 3) within the cocoon of the Sceliphron, as well as the developed Stilbum larve (Plate I, fig. 4). On 1 July 1960, as I again uncovered the cell, I found, in place of the Stilbum cocoon, an already colored but still curved imago, whose left wing was not entirely blown up yet. The animal reacted to the light by vivid move ments, and as soon as it left its broken cocoon, it run about with its usual viva city. The thickness of the cell-wall almost surpassed that of the wasp (Plate I, fig. 5), •— and then the reason for its extremely long ovipositor became at once clear. After the lapse of five days, also its left wing smoothed out, and the insect was running to and fro, with the nervous quivering of its antennae, characte ristical of the Chrysidid wasps (Plate 1, fig. 6). In spite of the food (sugar softened in water, that is, honey solution) given to it, the animal unfortunately perished after 13 days. References : 1. Borland, L. & Bernard, F. : Hyménoptères vespiformes, III. (in Faune de France, 34, 1938, pp. 145). — 2. B i s c h o f f, H. : Biologie der Hymenopteren (in Biologische Studienbücher, 1927, pp. 598). — 3. De S t e f a n i, T. : Note sulle Chrisididi di Sicilia (Le Naturaliste siciben, 7, 1888, p. 1 — 73). — 4. Lichtenstein, J. : Observations sur deux espèces de Chrysis (Bull. Soc. ent. France, 1873, p. 1 —15). — 5. M a z e k - F i a 11 a, K. : Angaben zur Lebensweise von Sceliphron destillatorium Hhg. am Neusidlersee, mit beson derer Berücksichtigung des Nestbaues (Zeitschr. wiss. Zool., 148, 1936, p. 298—308). — 6. M ó c z á r, L. : Megfigyelések a Tihanyi félsziget partszakadékain — Beobachtungen bei Ufer- absturzen der Halbinsel Tihany (Rovart. Közlem., 1, 1946, p. 35—46). — 7. M ó c z á r, L. : The Loess Wall of Tihany and the Nesting of Odynerus spiricornis Spin. (Hym. Eumenidae) (Ann. Hist.-nat. Mus. Nat. Hung., 52, 1960, p. 383—409). — 8. R o t a r i d e s, M. : Daten zur Biologie von Sceliphron destülatorium Illig. auf der Halbinsel Tihany (Arb. Ung. Biol. Forschungsinst., 7, 1934, p. 66 — 79). Explanation of Plate Plate I. Fig. 1 : The nest of Sceliphron destillatorium Illig., with point of penetration of Stilbum in dark center, due to moistening. Fig. 2 : Cocoon of Sceliphron destillatorium larve, with hole in it caused by Stilbum. Fig. 3 : Opened cocoon of Sceliphron destillatorium, below right with smaller cocoon of Stilbum within it. Fig. 4 : Developed larve of Stilbum cyanurum cyanurum Forst. Fig. 5 : Disrupted Sceliphron nest with hatched Stilbum. Fig. 6 : Stilbum cyanurum cyanurum Forst., reared from Sceliphron nest. (Author's original photographs). 30 Természettudományi Múzeum Évkönyve Plate I. .