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Cheilosia caerulescens

 
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stuart
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Joined: 11 May 2005
Posts: 737
Location: Peterborough, UK

PostPosted: Thu Sep 18, 2008 9:04 am    Post subject: Cheilosia caerulescens Reply with quote

Cheilosia caerulescens (Meigen, 1822)

Identification ease/difficulty: 3

Status:
  • Unknown (newly added to the British list)

Sources of information:
  • Keyed out by van Veen (2004) p58.
  • Collins & Halstead (2008) (Dipterists Digest, 15: 23-26) illustrate the distinctive facial profile and suggest an additional couplet for Stubbs & Falk (2002) where it will probably run to the "pagana group"


Last edited by stuart on Thu Sep 18, 2008 9:39 am; edited 2 times in total
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stuart
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Joined: 11 May 2005
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Location: Peterborough, UK

PostPosted: Thu Sep 18, 2008 9:32 am    Post subject: Cheilosia caerulescens Reply with quote

Cheilosia caerulescens (Meigen, 1822)

Added to the British List by Collins, G.A. & Halstead, A.J., 2008. Cheilosia caerulescens (Meigen, 1822) (Diptera, Syrphidae) new to Britain. Dipterists Digest (New Series) 15(1): 23-26.

Identification: Keyed out by van Veen 2004. It will most readily run to the "pagana group" in Stubbs & Falk (2002) but it is quite a striking hoverfly and it should be immediately obvious that it is not one of the species included there. The wing has a pronounced, dark central cloud and the face profile is strongly produced (profile illustrated in the reference quoted above and additions to the couplets in Stubbs & Falk are suggested).

Biology: Larvae mine the leaves of houseleeks, mainly Sempervivum tectorum but also more rarely in S. montanum and S. arachnoideum. It has also been claimed to occur in other species of Rosaceae and Asteraceae. The egg is inserted between the leaves into the heart of the rosette of the plant. Older larvae can completely empty a leaf within a day before moving onto another one. Small rosettes can be killed completely and the fly is considered as a pest by gardeners! The larva pupates in the soil below the plant. In Europe, the species is bivoltine with larvae commonest in June and again in August/September and with adults flying in May and July.

Distribution: The host plants are alpine in their natural habitat, but have been cultivated for a very long time, growing on roofs and walls and often planted in rock gardens and, more recently, as patio plants. The hoverfly has spread north and west across Europe and its arrival in Britain has been expected. For example, it was first found in the Netherlands in 1986, but by 2005 it was reported to be widespread and common in urban gardens in Leiden.

An adult female was found by Graham Collins in his garden in South Croydon (Surrey) in May 2006 but was not immediately identified. In 2008 Andrew Halstead noticed that houseleeks in his garden near Woking, Surrey were in poor condition and found that the leaves were being attacked by a hoverfly larvae. Some were sent to the Central Science Lab and 4 male and a female reared. These were identified by Nigel Wyatt at the Natural History Museum. A check on plants at the RHS garden in Wisley, Surrey in June this year also showed that some of these were mined. Given the experience in Belgium and Holland, we can expect this species to spread rapidly and become widespread in gardens.
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stuart
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Joined: 11 May 2005
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Location: Peterborough, UK

PostPosted: Thu Sep 18, 2008 5:49 pm    Post subject: Identification Reply with quote

Here is the couplet from Collins & Halstead (2008) which suggests an ammendment to Stubbs & Falk's (2002) key to the "Pagana group" (p119) to take account of this species:

1 Scutellum without distinct black marginal bristles AND face with erect hairs ....... [latifrons]

- Scutellum with at least some black marginal bristles. Face bare at sides ....... 1a

1a Wing with distinct dark central cloud, membrane around cross-veins and at base of vein R4+5 strongly infuscated, veins here almost black. Face strongly projecting; length from apex of knob to eye margin about twice length of third antennal segment ....... caerulescens (Meigen, 1822)

- Wing with little or no trace of a cloud, membrane not infuscated, veins in central area pale yellowish to light brown. Face not strongly projecting; length from apex of knob to eye margin about equal to, or considerably less than, the length of third antennal segment ....... 2


Profile of the head from Collins & Halstead (2008)


Profile of head and wing from van Veen (2004)

There are photographs taken by Han Endt on the web here and here.
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