Delia cardui

Michelsen, Verner, 2007, Two new European species of Delia Robineau-Desvoidy (Diptera: Anthomyiidae) with a bipartite male sternite III, Zootaxa 1469, pp. 51-57 : 52

The Delia cardui species group

The two new species described below have a ventro-basal thickening on mid tarsomere 2 in the male sex ( Fig. 1 ), a derived character used by Hennig (1974a) to define a Delia cardui species group. The following species described from the western Palaearctic region (see Hennig 1974a, b, c) share this character: D. brunnescens (Zetterstedt) , D. cardui (Meigen) , D. crinita Hennig , D. criniventris (Zetterstedt) , D. floricola (Robineau-Desvoidy) , D. nuda (Strobl) , D. penicillaris (Rondani) , D. penicillosa Hennig , D. persica Hennig , D. pilitibia (Stein) and D. pseudofugax (Strobl) . A few species in this list are further recorded from Japan: D. brunnescens (Suwa 1999) , China: D. cardui , D. penicillaris and D. penicillosa (Wei et al. 1999) and North America: D. cardui and D. nuda (Griffiths 1991a) . Species apparently endemic to East Asia are D. bipartita Suwa ( Japan, China) and D. penicilella Fan ( China) , while D. polaris Griffiths is a Nearctic species.

In addition to the tarsal character of the Delia cardui species group, both new species have strikingly short, posteriorly excavated male tergites III–IV separated from each other and from tergites II and V by relatively wide areas of flexible inter-segmental cuticle ( Fig. 2 , x). The exposed male abdominal intersegments are characteristic of nearly all species of the Delia cardui species group, but are also present in some obviously closely related species with simple male mid tarsi, D. alatavensis Hennig , D. carduiformis (Schnabl) and D. piliventris (Pokorny) . The condition allows an upward flexure of the caudal part of the abdomen and resulting exposure of the variously specialized sternites III–IV (see Hennig 1974a for further details and a suggestion on its functional significance).

Unfortunately, as pointed out by Hennig (1974a) and Griffiths (1991a), the male tarsal character is somewhat unstable and liable to secondary reduction. The same applies to the modifications of the male tergites III–IV as described above. Firstly this character complex is barely apparent in D. pilitibia of the Delia cardui species group, and secondly the same character complex is seen in a moderated version in some more distantly related species, e.g., D. echinata (Séguy) .

Griffiths (1991a) abandoned the male mid tarsal character as the only criterion for inclusion in his ‘ Delia cardui superspecies’ by adding two species ( D. alatavensis , D. piliventris ) without this character. Unfortunately, the integrity of the resulting superspecies against his ‘ Delia pruinosa superspecies’ and ‘ Delia fallax superspecies’ is rather ambiguous and needs some adjustment. I suggest the following diagnosis for the Delia cardui species group: male mid tarsomere 2 with a ventral swelling and/or male abdominal tergites III and IV distinctly shorter than tergite V, posteriorly excavated and separated by widely exposed intersegmental cuticle. By this diagnosis the limits of the Delia cardui species group are slightly expanded to further include the Holarctic D. carduiformis , a species that Griffiths (1991a) referred to his ‘ Delia pruinosa superspecies.’

Available biological data suggest that the phytophagous larvae of the Delia cardui species group all feed on leaves, shoots or floral parts of species of Caryophyllaceae . However, as pointed out by Griffiths (1991a), a larval association with that plant family is characteristic of a more inclusive species group within Delia denoted by Griffiths as the ‘ Delia cardui subsection’. Morphologically, this subsection is characterized by more or less pronounced modifications in shape and/or vestiture of the male abdominal segments III–IV.

Figures

FIGURES 1 – 3. Delia rimiventris, male. 1. Right mid tarsus. Arrow points at basal thickening of tarsomere 2. 2. Tergites I – VI, dorsal. 3. Tergites I – VI, left lateral. Different scales for 1 and 2 – 3.