Dixa laeta, (Loew, 1849) (Loew, 1849)

Håland, Øyvind, 2017, Dixella laeta (Loew, 1849) (Diptera, Dixidae) new to Norway, and some characters possibly useful in creating species groups, Norwegian Journal of Entomology 64, pp. 10-18 : 11-16

D. laeta

Proposed synonyms: Dixella fuscifrons Edwards, 1928 = D. laeta Loew, 1849 [ Peus, 1934]; Dixella mediterranea Martini, 1929 = D. laeta Loew, 1849 [ Peus, 1936]; Dixella lateralis Nielsen, 1937 = D. laeta Loew, 1849 [ Rozkošný, 1990]

Wagner et al. (1992) described D. fuscifrons from Greece as a species separate from D. laeta , thus not accepting the synonymy of Peus (1934).

At the end of the description of Dixa mediterranea Martini (1929) writes (p. 39): “ Von F.W. Edwards aus Corsica beschrieben. Ich erhielt das stuck, ein ♂, nach dem vorstehende Beschreibung und Abbildung sind, durch seine Liebenswürdigkeit.“ It thus seems that the species of Edwards and that of Martini are from the same collection, and thus probably conspecific. Why they are given different names by the two authors is probably a misunderstanding between them.

Part of Nielsen’s (1937) figure of D. lateralis is reproduced here (figure 8) to show the whole hypopygium, as none of the preparations in the author’s collection were quite suitable to figure.

The gonostylus (dististylus) ( Figure 1A ) has a longitudinal lamella (lobe) on the outer side of the middle part. The distal end of the gonostylus has two somewhat crooked spines, that bend quite near the end. The apical lobe ( Figure 1B ) seems to be identical to that of dyari , with one spine at the end. The basal lobe ( Figure 1C ) is somewhat more square than in dyari . The cercus ( Figure 1D ) has five to six distinct spines, one at the end a bit shorter than the others, all placed at a low but distinct “foot”. The distal end of the 10 th sternite ( Figure 6A ) is roundish in outline, with two areas with long stiff and bent setae on each side of the middle point.

When comparing the figures published of D. laeta with the present specimens, one can notice at least one difference, namely the lack of the basal lobe on the gonocoxite in the published figure of mediterranea and it is hardly seen in the drawing of fuscifrons . This is probably just an omission as this lobe may be easily hidden by other parts of the hypopygium.

It can be seen from Table 1 that the character of M 1 being of the same length as Mst is not very good to separate it from other species, since several specimens of both D. obscura and D. hyperborea may show the same ratio. The hypopygia of these two species are clearly different, however, and in addition, the wing veins of D. obscura are also differing, so much that Enderlein (1936) created the new genus Dixina for this species, a genus that has not been recognized later on.

The lateral patch of the scutum is connected by a dark patch consisting of many small patches. D. dyari

This species is very similar to D. laeta in its hypopygial characters, but differs in the structure of the “knee” on the gonostylus (dististyle) being much more robust in dyari ( Figure 2A ), being a clearly distinct part of the gonostylus, but like in laeta it is naked, i.e. without the pubescens that covers most of the hypopygium. The two spines at the distal end of the gonostylus are a bit thicker than in laeta , straight almost to the end. In one specimen there are three spines. The basal lobe ( Figure 2B ) seems to be more rounded than in laeta . The shape of the cercus ( Figure 2C ) is a bit different, with four or five spines, and with a variable “foot” size. The distal part of the 10 th sternite ( Figure 6B ) is very similar to the one in D. laeta , but seems to be a bit more square in outline.

On the thorax there is not a connecting dark area between the lateral and middle stripe.

Dixella laeta Loew :

Adults were found 9-25. July in Buskerud BV in just two different ponds at almost the same height. One pond is small, without a name, surrounded by Sphagnum spp , situated close to the eastern end of lake Ossjøen in Hol municipality at 970 m a.s.l. 60.3822579 N 8.2535357 E. Other species of Dixella found in the same pond are D. dyari , D. naevia and D. aestivalis .

The other habitat is a much greater pond, also surrounded by Sphagnum but much of the lakesides are also stony or with willows. This lake , Solheimstultjørni , is in Jønndalen in Nore og Uvdal municipality, at 975 m a.s.l. 60.3035629 N 8.3515717 E. Other species of Dixella found here are Dixella dyari , D. obscura and D. aestivalis .

Figures

FIGURE 1. Dixella laeta Loew, 1849. A. Distal part of gonocoxite with gonostylus and apical lobe, lateral view; B. Detail of the distal end of the apical lobe; C. Basal lobe; D. Cercus.

FIGURE 2. Dixella dyari Garrett, 1825. A. Distal part of gonocoxite with gonostylus and apical lobe; B. Basal lobe; C. Cercus.

FIGURE 6. Distal end of 10th sternite of (A) D. laeta, (B) D. dyari, (C) D. obscura, and (D) D. autumnalis.