Pegomya terminalis

Michelsen, Verner, 2008, The Palaearctic species of the Pegomya terminalis species group (Diptera: Anthomyiidae), with descriptions of two new species, Zootaxa 1781, pp. 31-46 : 32

The Pegomya terminalis species group

Griffiths (1983) defined a Pegomya terminalis superspecies in which he identified 5 Nearctic and 1 Holarctic species. The monophyly of this species group was strongly supported by a peculiar elongation of the distal part of the phallus (e.g., Fig. 21 ). However, the Pegomya terminalis species group as defined in the present paper even includes a species, P. granadensis Ackland , without the elongation of the distal phallus ( Fig. 13 ). The argument for grouping P. granadensis together with P. terminalis and allied species is the obvious agreement in a number of apomorphic traits in the female abdomen and oviscapt (see Figs. 14, 15 and 22, 23 ): length of tergite V tends to exceed combined length of tergites III and IV; fully extended oviscapt with very long “intersegmental” membranes and 1.5–2.0x as long as remaining abdomen, portion distal to segment VI increasingly depressed; segment VI short, but abundantly setose at hind margins of weakly sclerotized tergite and sternite; segments VII and VIII very long, with numerous fine to very reduced setulae at hind margins; epiproct more or less reduced, with 0–3 apical setulae; hypoproct small, with scattered setulae and no cuticular pubescence; cerci depressed, only bearing short setulae and sensilla, towards apex forming a cutting edge (less evident in P. granadensis ).

The Pegomya terminalis species group is presently known by five species endemic to the Nearctic ( Griffiths 1983): P. g l a b r a (Stein, 1920), P. d i s t i c h a Griffiths, 1983, P. flaviventris Griffiths, 1983 , P. aldrichi Griffiths, 1983 and P. cedrica Huckett, 1939 . A further species recorded from Canada as ‘ P. terminalis (Rondani) ’ by Griffiths (1983, 1997) appears to be new. From the West Palaearctic subregion are presently known five species, of which four are largely Mediterranean: P. terminalis ( Rondani, 1866) ranging from Spain and Morocco to Uzbekistan, P. granadensis Ackland, 1977 from Spain and Morocco, P. s k u l e i sp. nov. from Greece, and an undescribed species known by a single female from Turkey (aff. P. granadensis ). The fifth species, P. glabroides sp. nov., has a northern and montane distribution in Europe. Finally, the P. terminalis group is represented by an undescribed species in South Africa (D.M. Ackland in litt.).

Very little is known about the biology of the Pegomya terminalis species group except for the brief but significant note by Huckett (1941: 61) that two females of P. glabra from Washington state had emerged from horsetail ( Equisetum sp.). On that background it may be inferred that all members of the P. terminalis species group have larvae that feed in stems of horsetails. The unusual association with horsetails is supported by the peculiar structure of the oviscapt having sharp-edged cerci in combination with the smooth and slender eggs. Both suggest that the females are capable of inserting their eggs through the tough, siliceous tissues of their host plants. It remains to be discovered whether the larvae live inside the aerial stems or the underground rhizomes. The distribution of the species of the P. terminalis species group in the West Palaearctic subregion is either northern and montane or Mediterranean, which suggests that only a few of the species of Equisetum occurring in the subregion are exploited as host plants, such as the southern E. ramosissimum (branched horsetail) and the boreal and montane E. variegatum (variegated horsetail).

Few phytophagous insects are specialized feeders on Equisetum , notably the larvae of some sawflies and weevils. Among Diptera , such association is known only for three species of Liriomyza Mik (Agromyzidae) .

Figures

FIGURES 16 – 21. Pegomya terminalis, male. 16, 17. Sternite V, ventral and lateral views. 18, 19. Hypopygium, caudal and lateral views. 20. Pre- and postgonites, lateral view. 21. Phallus and phallapodeme in lateral view, ejaculatory apodeme in oblique ventral view. Same scale.

FIGURES 8 – 13. Pegomya granadensis, male. 8, 9. Sternite V, ventral and lateral views. 10, 11. Hypopygium, caudal and lateral views. 12. Pre- and postgonites, lateral view. 13. Phallus, lateral view. Same scale.

FIGURES 14, 15. Pegomya granadensis, female. 14. Oviscapt, flat mounted. 15. Distal part of same.

FIGURES 22, 23. Pegomya terminalis, female. 22. Oviscapt, flat mounted. 23. Distal part of same.