Part 2: Nematocera and Aschiza not dealt with by Falk (1991) - JNCC

temporary water bodies are known to be used, a lowering of
the water table could render these sites unsuitable in the
longer term. Pollution such as agricultural runoff, sewage
and industrial effluent as well as a gradual loss of salinity
following sea wall construction are also hazards.
Management and conservation Avoid any drainage of
sites and encourage a range of conditions, including pools
or ditches amongst the vegetation types described above.
Use rotational ditch or pond management where necessary
and maintain seasonal fluctuations in water level.
Maintenance of a range of salinities through a continual
input of seawater into coastal marsh is also necessary.
Published sources Austen (1895); Burke (1946); Chandler
(1998d); Edwards (1939); Kidd & Brindle (1959); Marshall
(1938); Morgan (1988); Nye (1955); Palsson (1992); Piffard
(1895); Service (1969); Snow et al. (1998).
OCHLEROTATUS FLAVESCENS
A mosquito LOWER RISK (Near Threatened)
Order DIPTERA
Family CULICIDAE
Ochlerotatus flavescens (Müller, 1764)
Identification Keyed by Snow (1990) as Aedes flavescens.
Distribution Scattered localities on the east coast of
England, predominantly for the Thames Estuary: Isle of
Sheppey (1922), Maidstone (1928) and Lydd (1989), East
Kent; Isle of Grain (1981, 1985, 1986), West Kent; several
records from Essex, including Barking (pre 1955), Vange
Marshes and the Blackwater Estuary (1987) in South Essex,
Walton-on-the-Naze (1928), Colne Estuary and Tollesbury
Wick Marshes (1987) in North Essex; also Barton-on-
Humber, Lincolnshire (1963). An inland record from an old
railway cutting at Great Cransley, Northamptonshire (1979)
(Osborn 1980) requires further investigation. A site in
Somerset is also indicated by Snow et al. (1998) but without
further details.
Habitat Coastal marshes, both freshwater and brackish (up
to 50% seawater). Larval sites include ditches, marshy areas
and small temporary pools (winter flooding is required),
mainly amongst growth of Festuca rubra and Juncus
gerardii. Schoenus nigricans was also cited by Cranston et
al. (1987) for Kent, but this is in error because the plant is
not known from this county. Larval sites are always open,
sunlit and unshaded.
Ecology This species is predominantly univoltine in this
country, although a second egg hatch may occur in summer.
Eggs are laid in mud or in plant debris in situations which
normally remain dry until flooded by late autumn or winter
rains. Eggs immersed in autumn or winter do not hatch until
February or March, whereas eggs laid in June will hatch in
the summer if subjected to intermittent immersion, a
proportion hatching on each soaking. Adults recorded from
May to August, peaking in late May and early June.
Females are recorded as biting man but seem to prefer
domestic animals such as cattle, horses and sheep.
Status A very restricted species with only nine certain post
1960 sites. Several of its sites are situated upon the
threatened Thames Marshes and some of its former
localities may now be degraded beyond suitability following
sea wall construction and agricultural reclamation.
However, it is also clear that O. flavescens has increased its
abundance on the Isle of Grain, whilst O. caspius which was
formerly common is now rare, possibly through competition
within the larval site. O. flavescens was also found in
abundance at the Lincolnshire site. Status revised from RDB
2 in Shirt 1987 and Falk 1991, where it was included as
Aedes flavescens. It is a widespread Holarctic species.
Threat Habitat loss through coastal development, including
the construction of sea walls and improvement of coastal
marsh for agriculture. Fluctuating water levels are an
important feature of sites, and an alteration to the water
table could lead to a great reduction in the frequency of
suitable breeding sites within an area. Whilst a range of
salinities seem to be tolerated by the larva, it is strongly
evident that some degree of sea water input is required, even
if only intermittently, and this feature is being lost from
numerous coastal marshes following sea wall construction.
Pollution such as agricultural runoff, sewage and industrial
effluent could also render sites unsuitable.
Management and conservation Avoid any drainage of
sites and attempt to maintain any natural seasonal
fluctuation of water levels; also maintain a range of
salinities in pools and ditches through a continued input of
sea water into coastal marsh, even if this is only seasonal.
Use rotational ditch or pond management where necessary
to maintain a variety of aquatic situations, including those
prone to flooding in winter months but dry in summer.
Published sources Cranston et al. (1987); Edwards (1939);
Marshall (1938); Mattingly (1950); Nye (1945); Osborn
(1980); Service & Smith (1972); Shute (1933); Snow et al.
(1998).
OCHLEROTATUS LEUCOMELAS
A mosquito
DATA DEFICIENT
Order DIPTERA
Family CULICIDAE
Ochlerotatus leucomelas (Meigen, 1804)
Identification Keyed by Snow (1990) as Aedes leucomelas.
Distribution Only known from a single male from
Widmerpool, Nottinghamshire in May 1919 (Marshall
1938) and an old record for Dartford, Kent in foreign
literature which is unauthenticated.
Habitat On the continent, larvae have been recorded from
unshaded and partly shaded fresh and brackish water, in
pools and ditches, in coastal and inland districts.
Ecology Larvae probably develop in small pools or ditches,
development often continuing in winter, at times below ice.
There is probably only one generation per year. There is no
information concerning adult feeding.
Status A very poorly known species in Britain, which is
uncommon in north-west Europe generally although
occurring widely across the continent. The site is not
apparently outstanding biologically and this species may
prove to be more widespread but undetected by the low
levels of recording both past and present. It is, however,
considered doubtfully indigenous by mosquito workers.
Currently there is inadequate information to assess the risk
of extinction. Status revised from RDB 1 (Shirt 1987) and
RDB K (Falk 1991), where it was included as Aedes
leucomelas.
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