Records of Atherix Ibis in Finland (Diptera, Athericidae) Juhani Itiimies, Kalevi Kuusela & Pekka Riiinii
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© Entomologica Fennica. 17.VIII. I990 Records of Atherix ibis in Finland (Diptera, Athericidae) juhani Itiimies, Kalevi Kuusela & Pekka Riiinii Wimies, J. , Kuusela, K. & Raina, P. 1990: Records of Atherix ibis in Finland (Diptera, Athericidae). - Entomol. Fennica I: 11 3- 117. Eight clusters of mummified females of Atherix ibis (Fabricius) were found on 6.IX. l 988 under a bridge over the Kouvanjoki River, PP: Pudasjarv i, northern Finland. Inspection of 120 bridges during the winter yielded 17 new finds. A distribution map complemented with records from museums indicates that the distribution in Finland is northern. Features of the clusters and characters of the larval stage are described and discussed. The larval development seems to last two years. Department ofZoology, University ofOu/u, SF-90570 Oulu, Finland A characteristic feature of the Ibis-fly (Atherix The distribution of Atherix ibis is palearctic, ibis (Fabri cius)) is the egg-laying behaviour of the extending from Japan through Siberia and the females, which become glued with their eggs in whole of Europe and up to the northern tundra large clu sters of up to several thousand flies (e.g. zone (Thomas 1978). The information on its oc Straffen 19 15 , Lindner 1925,Coyler 195 l).Straf currence in Finland is poor: one male was re fen ( 19 15) describes the phenomenon as fo llows: corded in Utsjoki in 1949 (Frey 1950) and some " In May- June the females can be fo und on larval finds were reported in a thesis (Kauppinen branches hanging over water. They lay their egg 1978) and stencilled student courses of the Uni masses at a certai n point, die and remain hanging versity of Oulu (edited by Tapani Valtonen and on the branch. More and more females become Kalevi Kuusela). Hackman ( 1985) reports that the glued to them, so that finall y a large crowd is left species li ves on river banks in Lapland. The pres suspended on the branch, which from some dis ent situation is summarized in this paper, for tance looks li ke a swarm of bees. The larv ae which the collections of Finnish entomological develop by first eating the remains of their moth museums have also been checked. In additi on ers and later drop into the water." In their Io ti c some aspects of its ecology are treated. environment the larvae are predacious. They suck the internal ti ssues from soft-bodied aquatic in vertebrates (e.g nymphs of the Ephemeroptera Records of female cluster and Plecoptera) (Thomas 1975, see also Hackman 1985). Pupation always occurs out of the water, on In autumn 1988 the author Raina found a con the adjacent river bank (Thomas 1976). spicuous occurrence of eight clusters underneath A. ibis is the only athericid species li vi ng in a timber bridge over a small rapid in the River Finland (Hackman 1980). Its re lative lbisia Kouvanjoki (PP: Pudasjarvi, Grid 27°E 73065: (formely Atherix) marginata Fabr. occurs in South 53 12. 6.9. 1988). Six of them were hanging on th e Sweden (Wahl gren 1907). These two species are downstream beam and two on the upstream beam easy to separate from each other even in the larv al of the bridge (Fig. 2). The biggest cone was I 0 em stage (see e.g. Brindle 196 1, Rozkosny & Spitzer high, with a di ameter of 7 em at its base. A small er 3 1965). cluster (7.5 em x 5.5 em = ca. 67 cm ) was taken 114 Itiimies eta/.: Atherix ibis in Finland • ENTOMOL. FENNICA Vol. 1 20 After our first find in Pudasjarvi, we (and some of our colleagues) inspected 11 9 bridges during the winter and spring of 1989. These yielded 17 new records, all made north of the Oulujo ki River (Fig. 1) . We also checked four bridges on highway 4 from Pithipudas northwards and 43 bridges in the area SE and E of the town of Kajaani, but without finding any signs of clusters of A. ibis. It seems probable that it does not occur in Central Finland or in Central and Southern Ostrobothnia, either, since it has not been listed in any of the numerous macroinvertebrate investiga tions made on rivers there. Judging from the present-day records, A. ibis seems to have a north ern di stribution in Fi nl and , but it occurs in Soviet Karelia, an area corresponding to the southern most latitudes of Finland. The occurrence on the River Livojoki (PP: Pudasjarvi, Sarajarvi, 730:5 1), about 2 km down stream from the mouth of the Kouvanjoki, was impressive in its abundance: the total number of females in the several tens of clusters of varying size was estimated (by eye) to be at least 50 000 100 km (Fig. 3). Interestingly, we could now see that a 30° cluster may be the product of a single or several females (Fig. 3). Fig. 1. The present-day records of Atherix ibis (Fabr.) The clusters of females were found on a vari in Finland. Open circle: the exact site not known (only ety of bridges. The smallest had a span of 5 m and name of parish); black circle: the newest records made a height of 2 m above the water, and the biggest by the authors and their co ll eagues (see Acknow ledgements). (rO =the main channels of the Oulujoki, had a span of 80 m and was 6.5 m high. The K = the city Kajaani , P =the parish of Pihtipudas). material of the bridges was wood or concrete, and sometimes the clusters were even hanging from iron nuts and washers. The masses were regularl y suspended above the midstream area of the river - none of them were hanging above the river to pieces and 613 almost undamaged females bani<. The clusters were always situated at the were counted: the density was thus nine per cubic downstream or upstream edges of the bridges centimetre and the biggest cluster must have (Fig. 3), never on similar places on girders in th e contained about 1500 flies. This number is still far central part of the bridge. At a few localities below the I 0 000 in one cluster reported by Lind (including Kouv anjoki) there was a preference for ner (1925), but we feel that his figure may have the downstream side. been overestimated, si nce the cone mentioned by him measured only 16 em x 10 em and , according to the density calcul ated by us, should not have Phenology contained more than 5000 females. Rozkosny & Spitzer ( 1965) have found an aggregation of more The pinned specimens (1 36 exx., including some than I 000 flies. Muttkowski ( 1929) mentions that Russian-Karelian samples) in Finnish museums the depositions of nearctic Atherix variegata were collected between 20.VI. and 9.VII. Flight (Walker) may often contai n "several thousand thus occurs arou nd and slightly after midsummer. dead fli es". The flying season seems to be short and well ENTOMOL. FENNICA Vol. I • Itiimies eta/.: Atherix ibis in Finland 115 Fig. 2. Two clu sters of Ath erix ibis fem ales (Diptera, Athericidae) on 6 .1 X.1988 under the bridge over the River Kouvanjoki (Pudas jarvi 730:53), northern Fin land. Fig. 3. A series of clusters of Atherix ibis females (Diptera, Athericidae) on 5.1.1989 under the frosty bridge over the River Livo joki (Pudasjarvi 730:51 ), northern Finland. synchronized, which accords with the swarming and rivers may be so local in nature that wide and egg-laying behaviour. A similarly briefflight variation occurs in the developmental cycles, giv period, lasting no more than ten days, has been ing the impression of a long flying season. Neveu reported by Vanhara (1975) in lbisia marginata in (1976) classifies A. ibis to an upstream species. C heckoslovakia. In Central Europe, the females of A. ibis gather for egg-laying in May- June (Straffen 1915). In Size of larvae mountain areas in South France, they have been found throughout the summer (Thomas 1974). For several years Atherix ibis larvae have been T he temperature conditions in mountain streams collected in A ugust from the River Oulankajoki 11 6 ltiimies et al.: Atherix ibis in Finland • ENTOMOL. FENNICA Vol. l N 80 0 Kouvanjoki (n=193) 60 • Oulankajoki (n=218) 40 Fig . 4. Th e length distribu tion of Atherix ibis larvae collected at th e end of August (1979, -83, -86) in 20 th e River Oul ankajoki (Kuu samo) and at th e beginning of January (1989) in th e River Kouvan NM-t iOIDI'- CDO>O,...NM-tiO ID I'-CD O> O N ~ ..-,....,.....,.... N N N joki (Pudasjarvi) , northern LENGTH, mm Finland. (Ks: Kuusamo, Kiutaki:i ngas, 736:60), during the thus represent a group of first time hibern ated zoological field courses of the University ofOulu. larv ae. Some samples also exist from the Oulu district (PP: Oulu, Sanginjoki, 720:44). In addition, we collected kicking-net sample from the River Comments Kouvanjoki (downstream from the bridge of our original find) on 5.I.l989. The above observatio ns are not enough to prove The total length of the larv ae was measured to two-year larval development. We can be sure, the nearest 0.5 mm. The Kuusamo materi al, which however, that sexual dimorphism is not involved, had been preserved in alcohol, incl uded some because the females are onl y sli ghtly (8-11 mm shrunken specimens, whose length were trans vs. 8-10 mm) bigger than the males (Thomas formed to correspond to those of relaxed larv ae 1974).