Speciation dynamics in the noctuid moth Plusia chrysitis L. (Lepidoptera, Noctuidae) By Josef H. Reichholf Zoologische Staatssammlung München Abstract Plasia chrysitis L. is a widespread noctuid moth in temperate Europe. A form, in which both metallic bands across the forewing are connected (= forma juncta), extends across temperate Asia to the east. The taxonomic Status of this form is quite uncertain. Some authors include it into the taxon P. chrysitis as a (seasonal) form. Others treat it as a valid species Plusia. tutti (Kostrowicki) despite the extraordinary high degree of Variation in the genitalia. Both "forms" occur together in Central Europe, but 'juncta' is much more abundant in southeastern Bavaria than expec-ted. Light-trap captures in the Lower Bavarian valley of the river Inn, which were made in the period from 1969 to 1982, show aclearcut seasonal Separation and revealed a very low degree of intermediary forms (1.2 per cent). The form 'juncta' flies earlier in season with a first maximum in early June and a second one in early August. P. chrysitis attains its first peak in early July or towards the end of June and a second one in late August or early September. There is, therefore, a sufficient Separation in time of season (allochronic occurrence) to keep the gene pools of both taxa separated. The form 'juncta' may represent or include at least a valid species, which was described by Kostro-wicki as Plusia tutti. Since there is some degree of intermediary forms the hypothesis is discussed that P. chrysitis is a western and P. tutti an eastern population. The latter may be spreading towards the west. The Separation of both taxa is perhaps not complete yet. They may be still in the process of speciation. 1. Introduction Plusia chrysitis L. is a common noctuid moth in the palearctic region. The ränge extends from the British Isles and the Iberian Peninsula through Central Europe and the southern parts of Northern Eu-rope to Japan and the Far East. Within this very extensive ränge one would expect a number of geogra-phically well defined populations in the taxonomic rank of subspecies. But Kostrowicki (1961) sho-wed, that the whole complex is probably composed of two sibling species, which can be largely separa-ted according to the metallic bands on the forewings. The nominate form is Plusia chrysitis L. . The me-tallic bands are well separated and mostly without a connection in between (fig. l).The other species Plusia tutti (Kostrowicki) shows a broad connection of both metallic bands, and this type has been cal-led forma juncta. This taxon predominates in Eastern Europe. In the Asian part of the ränge it is the Single form existing. But in the west it is replaced by the other species Plusia chrysitis. The conclusion of Kostrowicki (1961) was based on differences in the genitalia, which coincided to some degree (but not completely) with the presence or absence of the connection between the metallic bands. Lempke (1965) examined specimens from Dutch collections. At first he agreed with Kostrowicki (1 96 1 ), but in a second paper (Lempke 1966) he doubted whether the morphological features are conclu-sive enough to keep both species valid. There was too much Variation in the form of the valves, a result which is quite surprising, because the structure of the genitalia normally is specific enough to separate very similar moth species. This amount of Variation led Lempke (1966) to the conclusion, that the two 75
BioStor
