BR. J. ENT. NA'I. HIST., 7: 1994 



SILENE ACAUUS (L.) JACQ. (CARYOPHYLLACEAE), 



THE LARVAL FOODPLANT OF DELIA PILIVENTRIS 



(POK.) (DIPTERA: ANTHOMYIIDAI ) 



K. P. Bland 



35 Charterhall Road, Edinburgh EH9 31 IS. 



The first British records of Delia piliventris (Pokorny, 1889) appear to be those 

 of Collin (1933). Under the name of ' Delia fasciventris Ringdahl M. S.', Collin reports 

 that '3 males and a possible female were taken by Dr Edwards at 2000 to 3000 feet 

 [i.e. 600-900 m] elevation in different localities in the Killin district (Perthshire)'. 

 This species has since been found very locally in several widely scattered montane 

 localities in western Scotland (Horsfield, 1984, 1988; D. Horsfield, pers. comm.). 

 Abroad the species has a circumpolar distribution; its headquarters is Scandinavia 

 but it extends via the Faroes to much of the arctic part of North America. It is also 

 well distributed in the Alps (Hennig, 1974). In spite of its widespread distribution 

 abroad, its larval habits do not appear to have been recorded. 



In July 1984 while collecting at 840 m on the south slopes of Sanna, in Kilpisjarvi, 

 Finland, I came across some dipterous larvae boring down the shoots of moss campion, 

 Silene acaulis (L.) Jacq. Although one of the larvae eventually pupated, it failed to 

 develop any further. 



On 2.viii. 1992 similar dipterous larvae were found at 500 m on the crags in 

 Corrie Fee (O. S. grid ref. N02474), Glen Doll, Angus (vice-county 90). Again they 

 were boring down the centre of the shoots of Silene acaulis. Each larva bored down 

 the centre of a shoot eating out the mesophyll from each leaf in turn until nearly 

 all the green leaves had been reduced to empty brown sheaths. It then emerged from 

 the shoot, crawled over the surface of the leaf cushion and bored down another shoot 

 often a centimetre or more away. Several shoots were consumed in this way before 

 the larva descended to the base of the cushion to pupate in the damp substrate. 

 If the larva fell through the cushion while moving from one shoot to another — a 

 difficult action in the wild but easily engineered in a rearing tube — it seemed unable 

 to find its way back up onto the cushion of growing shoots. This phenomenon indicates 

 that the larva is very dependent on the physical structure of its foodplant for its survival 

 and so may be restricted to Silene acaulis. This possible specificity to moss campion 

 is further supported by the close similarity of the known distributions of the fly and 

 of S. acaulis (Jones & Richards, 1962). Towards the end of August a single larva 

 burrowed into the damp tissues beneath the foodplant, successfully pupated and 

 became quiescent for the winter. In early May the puparium started to show imaginal 

 development within but the male imago died fully formed within the puparium 

 at the beginning of June. Dissection of the genitalia indicated the fly to be Delia 

 fasciventris Ringdahl, 1933 (based on illustrations in Ringdahl, 1959) or Delia 

 piliventris (Pokorny, 1889) (based on illustrations in Hennig, 1974). Hennig (1974) 

 gives fasciventris as a junior synonym of piliventris. 



On 16.viii.1992 at 600 m on Meall nan Tarmachan (O. S. grid ref. NN5940), near 

 Killin, Perthshire (vice-county 88) further dipterous larval signs were found on Silene 

 acaulis. Most of the larvae had abandoned the plants but a single larva was procured. 

 This larva pupated on 29.viii.1992. Again the larva burrowed down some 1 cm into 

 the damp substrate beneath the Silene acaulis before pupating. On 23.vi.1993 this 

 puparium poduced a female Delia piliventris. It is probable that this site is one of 

 Dr Edwards's original localities. 



