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206 D. P. Pes(
Background
Tephrltis dHscerata
Lw. (Diptera:
Tepbritidae)
Cystiphora sonchl
(Bremi) (Diptera:
Cecidomyiidae)
Both annual sow-thistles occur throughout Canada, but are more abundant in Ontario,
Quebec, and British Columbia than in other provinces (Frankton & Mulligan 1970). S.
lenerrimus is only reported from California (Shetler & Skog 1978).
No biological control of sow-thistles has been reported from other parts of the world. In
Canada, only one as yet unidentified Lepidoptera larva has been found feeding on the
flower heads or destroying seeds, and no monophagous insects have been reported
feeding on any other part of the perennial sow-thistle (M. Maw, 1982, personal communication).
Conners (1967) lists three disease organisms specialized on S. arvensis:
Marssonina sonchi Dearn. & Bisby, Seploria sonchi-arvensis Deam. & Bisby, and S.
sonchifolia Cke. However, these do not control their host. The survey in eastern Austria
and the Swiss Jura, and of the literature by Schroder (1974), and in Iran, Pakistan, and
Japan by Zwolfer (1973) on Sonchus spp. produced only six insect species which appeared
to be sufficiently host specific to warrant further study. Five of these are
endophytic in the flower heads and one is a leaf gall fly. Two of these, Tephriris dilDcerata
Loew and Cysliphora sonchi (Bremi) have been studied in detail and will be discussed
below. In addition, the moth Celypha rosaceana (Schlager) is reported from Sonchus
spp. and Taraxacum officinale Weber only and should be studied further (Bradley el al.
1979).
Ecology
The fly deposits clutches of six to seven eggs into flower buds and in the laboratory the
oviposition period may last up to ten weeks (Berube 1978a,1978b). The larvae transform
the flower bud into a gall in which they pupate when mature. The adult fly enters
diapause when exposed to a short day or cool temperatures or both and it overwinters as
an adult. There is one generation per year (Berube 1978a). T. dilacerata is widely distributed
in the palaearctic covering about three quarters of the range of S. arvensis (Berube
1978a).
Ecology
C. sonchi is recorded from Sweden (Sylven 1975) and Denmark in the north (Henriksen
1944) to Italy and Romania (Skuhrav6 el al. 1972) in the south, and from France (Kieffer
1899) in the west to the European part of the USSR in the east (Peschken, in press).
C. sonchi females lay their eggs on the underside of leaves. Galls are produced and
become about 5 mm in diameter when mature. The larvae pupate in the gall or in the
ground. The adults live up to 16 hours in the laboratory. Up to 721 galls were produced
on one perennial sow-thistle rosette by six females. There are three generations per year
in the field (Skuhrav6 & Skuhravy 1973).
The fly is host specific to Sone/lus spp. (Peschken in press).