Clitostethus arcuatus (Rossi, 1794)

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POLYPHAGA Emery, 1886

CUCUJOIDEA Latreille, 1802

COCCINELLIDAE Latreille, 1807

COCCIDULINAE Mulsant, 1846

Clitostethus Weise, 1885

Clitostethus is a small genus of tiny ladybirds with four species in the U.S.A. and at least two species in Europe. C. dispar  Siccard, 1929 occurs in Western Europe but not in the U.K.  while C. arcuatus (Rossi, 1794), thought to be native to Israel, is a widespread Palaearctic species distributed from Portugal to the east of Russia, Sardinia, the Middle East and Africa, but further north it becomes scarce; it is absent from Scandinavia and the Baltic countries but it does occur in the UK. Introduced into California as a biological control agent, it is now widespread in the U.S.A. and also occurs in Canada. It is a specialist whitefly predator used in many countries as a biological control agent of the ash whitefly Siphoninus phillyreae. In Europe S. phillyreae can cause stress to fruit trees leading to premature leaf drop, wilting and the production of smaller fruit, and outbreaks occur when their natural enemies have been destroyed by agricultural practices or pesticides. Beyond this Clitostethus has been recorded feeding upon a wide range of whitefly as well as aphids and the eggs of Tetranychus urticae - the Two-spotted Spider Mite, a cosmopolitan agricultural pest with a very wide range of hosts. Since the 19th century C. arcuatus has been considered a rare species in the UK; Hyman and Parsons (1992) summarized the pre 1970 records from Surrey, Berkshire, Oxfordshire, East Suffolk, Leicestershire and Rutland, and from 1970 onwards from Oxfordshire and East Suffolk only. Since that publication there have been more modern records scattered through England north to Yorkshire and west to Worcestershire, and these may represent a modern expansion of the range. Locally we have a single record; on 29/6/2008 a specimen was found in a Watford garden by pulling apart dry and decayed grass cuttings over a sheet, this may have been feeding on whitefly on an adjacent Viburnam tinus, a host already associated with the species. An association with ivy has been noted since Fowler (1889) and often repeated, but U.K. records show a diverse range of host plants. Adults have been found overwintering on holly and dispersing in April to whitefly-infested plants. This may also be the basis for the association with ivy; simply used for shelter. In the U.K. Clitostethus has been recorded feeding on the whitefly Aleyrodes lonicerae Walker on Welsh Poppy Mecanopsis cambrica (L.) and Honeysuckle Lonicera periclymenum (L.), on A. proletella (L.) on wild cabbage and on whitefly on Greater Celandine Chelidonium majus (L.) That the species is small and cryptic might explain the widely distributed but small number of modern records but if the range is increasing, as seems likely, it may become more conspicuous in the future. In the U.K. adults have been recorded from February to October.

Clitostethus arcuatus 1

Clitostethus arcuatus 1

© Lech Borowiec

Clitostethus arcuatus 2

Clitostethus arcuatus 2

© U.Schmidt

This tiny coccinellid, around 1.5mm in length, is distinctive and easily identified by the horseshoe-shaped pale mark on the elytra. There is generally another transverse pale mark further towards the apex but otherwise the colour is variable; head generally dark with pale anterior margin, pronotum pale with a variable dark central mark and the elytral ground colour varies from pale to dark brown. Appendages pale. The entire upper surface has dense, fine silvery pubescence. Head finely and sparsely punctured. Eyes large and coarsely faceted.  Antennae about as long as the head width, yellow but generally darker towards the apex. Pronotum transverse, very finely and sparsely punctured. Lateral and basal margins finely bordered, hind angles slightly obtuse. Elytra sinuate and finely bordered laterally, punctation stronger than on head and pronotum.