All the mosquito species found in the Cayman Islands
are described and recorded in other publications. The following notes on each
species are restricted to facts relating to their occurrence in the Cayman Islands.
Aedes aegypti
Ae. aegypti the yellow fever mosquito, was originally
present in all three islands in large numbers, being noted by the Oxford University
expedition in 1938 and by G. Giglioli in 1948. However, the DDT house-spraying
campaign of the early 1950s eliminated it entirely from Grand Cayman and no
traces were found when MRCU began operations in 1966, although high densities
were observed in Cayman Brac and Little Cayman at the time. Using the insecticide
temephos and with the assistance of the Pan American Health Organisation, MRCU
house spraying campaigns eliminated it from the latter two islands by 1971.
However, in 1973 it appeared again in Georgetown, Grand Cayman and another campaign
had to be mounted so it was not until 1974 that all three islands were completely
free of this mosquito and it was only by constant port disinsection and surveillance
(house surveys and ovitrapping) that reestablishment of the pest was subsequently
prevented. House-spraying is effective against Ae. aegypti as this mosquito
is completely domestic, being very rarely found away from occupied houses. It
breeds in container habitats, favouring clean, fresh water, and is adapted to
artificial containers. However, a few larvae were found in rock holes in Cayman
Brac, and a few were found on top of the bluff in cisterns used for watering
cattle. Aedes aegypti has not been found on any of the three islands
since May 1997.
Aedes albopictus was first recorded in Georgetown
in the early summer of 1997. Since then it has been collected sporadically from
a number of locations in Georgetown. It has not been observed else where in
Grand Cayman or on Little Cayman or Cayman Brac.
Larvae of this species were found in two fresh water
rock pools north of Pedro Village and have been recorded in CDC light traps
at Pedro and at North Side. However, it is not recorded in the New Jersey light
trap collections except possibly two specimens at the airport in November 1973.
It is not known from the Sister Islands.
This species was found in 1968 biting on the south
sound back road, Grand Cayman. It has not been recorded since and could have
been confused with Ae. scapularis as, like Ae. hemisurus, it is
a member of this complex. However, Arnell (1976) in his revision of the Scapularis
group regards the Cayman species as Ae. condolescens and adds a record
from Little Cayman collected by H. Peters in 1930.
In Cayman Brac, larvae found in freshwater buttonwood
and grass pools on the north coast were identified as Ae. hemisurus and
a few adult specimens were found biting and in light traps.
Ae. mediovittatus is a common mosquito in Cayman
Brac ad also occurs in Little Cayman but it is not found in Grand Cayman. It
is a tree hole and rock hole breeder and is one of the few species breeding
extensively on the Bluff in Cayman Brac. It can also be found in artificial
containers. The adult mosquito can be an annoying daytime biter especially in
shaded areas such as beneath the cliff face of the bluff.
Being active in the daytime, particularly late afternoon, it is not recorded
well in light traps. However, it is one of the three commonest species found
in Fay traps run during the day in Cayman Brac (the other two being Culex
bahamensis and wyeomyia vanduzeei). Cayman Brac light traps show
two peaks of abundance during the year, in June and October corresponding with
peaks of rainfall. Catches were higher in the late 1970s than in the 1980s corresponding
with periods of above and below average rainfall respectively.
This species is encountered regularly in Grand Cayman
but it is not abundant. The initial survey of the sister Islands failed to reveal
it at all, but it has since been recorded in small numbers in Cayman Brac. It
has been found breeding in red and white mangrove and grass and sedge pools
in Grand Cayman. Light traps show a bimodal seasonal distribution corresponding
with the early and late rainfall maxima.
In some years this mosquito is the main pest species
in Cayman Brac and it is also very common inn Little Cayman. It breeds in fresh
to brackish buttonwood and grass pools along the whole north coast of Cayman
Brac, favouring shaded locations, and shows definite dusk and dawn biting peaks.
In Grand Cayman it is one of the less common species but occurs in traps more
frequently the Ae. scapularis or Ae. sollicitans. It breed sin
black mangrove and the more saline rock holes and has recently been observed
in large numbers in the central red mangrove and buttonwood swamps of Grand
Cayman, south of Little Sound, where ground water is relatively fresh. It shows
a bimodal seasonal distribution very similar to Ae. scapularis.
Anopheles albimanus is widespread in all three islands
breeding in fresh and brackish water.The greatest numbers in Grand Cayman have
been found in buttonwood pools with a salinity of about 18 %.It also occurs
in fresh water grass pools, Typha swamps and shallow wells. It shows
a strong preference for un-shaded localities and is not found in deep wells.
In Grand Cayman it is present in low numbers through the dry season and does
not increase until July, the start of the rainy season. Numbers usually peak
in August and decline slowly through the latter, wetter part of the rains. From
1973 to 1979 numbers in trap catches declined rapidly and have remained at a
low plateau ever since. The mosquito readily bites man and animals and is an
efficient vector of malaria.
An. Atropos is the second most common Anopheline
in light traps in Grand Cayman but is not common in Cayman Brac. It favours
saline breeding sites such as the more permanent pools in mangrove areas. At
the beginning of the rains its numbers rise rapidly in line with those of An.
grabhami but after august its numbers drop to very low levels between November
and May.
This species has only been recorded from Grand Cayman
and is the least common Anopheline. Its seasonal distribution is similar to
An. Albimanus though it is slightly slower to build up in numbers in
the rains and slower to decline in the dry season.
Larvae are found in the less saline mangrove and
buttonwood swamps and also in grass pools, rock pools and well. Due to the difficulty
in distinguishing between the two species they have usually been grouped together
in both larval and adult collections. However, there is some evidence in Grand
Cayman that Cx. iolambdis favours deep shaded wells and Cx. atratus
more saline, open areas.In Cayman Brac the western end of the island on the
coastal platform produced the majority of these species, in fresh and brackish
environments but especially along the edges of red mangrove woodland.In light
trap catches in Cayman Brac Cx. iolambdis was more common than Cx.
atratus. In Grand Cayman traps , the two species together show peak numbers
in the last part of the rainy season, September to Decembers, but otherwise
occurred at an even level with no response either to the dry season or the first
rains.
Culex bahamensis is the most common mosquito in
Cayman Brac, and is also one of the main species found on Little Cayman, but
it is rarely found on Grand Cayman. Breeding in Cayman Brac is concentrated
in the west and south areas, mainly in Ironshore and tidal ponds. Brackish and
saline water is favoured but larvae can also be found in wells and other fresh
water sites. A strong seasonal variation in abundance is indicated by light
traps with a peak in July and August, coinciding with rain and high sea levels.
There is a sharp drop from August to low levels between January and August.
It was first found on Grand Cayman by Belkin and Gerberg in 1968 in coral rock
holes both at Boatswains Point and in the Newlands area. It has since been seen
in light trap catches from all regions of the island, but the highest numbers
have occurred in West Bay.
Several adults taken on the south side of Cayman
Brac in October 1971 by Nathan were thought to be this species, but the identification
remains tentative.
There is only a single record of this species, a
larva found among algal mats in a shallow, muddy, brackish-water depression
at the south west end of Cayman Brac.
A few larvae of this species have been found in natural
freshwater wells on the north coastal platform of Cayman Brac. Small numbers
of adults have been taken in light traps but it has not been recorded from the
other two islands.
One pupa was found in March 1970 in a buttonwood
pool at the north-west end of Cayman Brac where the salinity was about a quarter
that of sea water. The emerging adult was tentatively identified as Cx. janitor.
It was not found in a crab hole although it is a crab hole breeder in Jamaica.
This species was found in 1968 by Belkin and Gerberg
in coral rock holes at Old Man Bay, North Side Grand Cayman, but it has not
been seen since. It has previously been recorded from the Florida Keys.
This mosquito occurs in light trap catches in very
small numbers in Grand Cayman and Cayman Brac but has not been found on Little
Cayman. In Grand Cayman it has been found in rabbit baited traps and biting
has been experienced in black mangrove and buttonwood swamps. Its breeding sites
are not known but it has been found in crab holes in Jamaica and Florida. It
is synonymous with Cx. taeniopus
Four larvae were collected from a fresh water, rock-pavement
pool at Stake Bat, Cayman Brac. The pool was shallow and particularly shaded
by sedges growing at the edge. This species has not been taken in light traps
and has not been recorded from Grand Cayman or Little Cayman.
This species has only been found on Cayman Brac
where it is not common. It breeds in rock holes on the bluff but is also found
to a lesser extent in fresh water rock pools on the coastal platform. It shows
no marked seasonal trends.
Deinocerites cancer breeds only in the large burrows
of the land crab Cardisoma guanhumi in mangrove swamps. It is known to
bite man occasionally in the vicinity of the breeding sites. It is very common
throughout the Cayman Islands though in the Brac it only breeds at the west
end of the island. Its numbers reach a peak in May and June when the water level
in crab holes is high, but decline steadily in the second half of the year when
the mangrove swamps tend to be completely flooded.
Very low numbers of adult M. titllans occur
in light traps in Grand Cayman and Cayman Brac but there is no record from Little
Cayman. Immature stages have never been found
in any of the Cayman Islands. They are known from other areas to have a very
slow development attached to the roots of plants at the bottom of ponds. Respiration
is achieved by piercing the air cells in the roots with the tip of the siphon.
M. titillans is especially associated with the aquatic plant Pistia
stratiotes. It is the only species of mosquito in the Cayman Islands to
be more prevalent (in the adult stage) in the dry season than in the rains.
It must be largely dependent upon permanent pools, and the aquatic plants on
which it lays its eggs which are probably more easily available when water levels
are low in the dry season.
Until recently this species was recorded only from
Cayman Brac where it occurred in very small numbers in light trap collections.
In 1987 it was discovered biting in the central swamps of Grand Cayman south
of Little Sound. Larvae have not been observed, but the ground water in these
areas can be surprisingly fresh.
Ps. Johnstonii has only been recorded in Grand Cayman
where it appears to be very rare as it is hardly ever taken in light traps.
However, it has been found occasionally in the interior of East End biting in
enormous numbers and causing a considerable nuisance to cattle. This phenomenon
occurs within four days of extensive rain. It is clear that it must breed in
the multitude of fissures that pockmark the surface of the bluff dolostone.
Most of these must be well shaded by vegetation. East End is drier than the
western end of the island and the conditions producing Ps. Johnstonii
in huge numbers do not occur frequently.
This is the commonest Psorophora in Cayman
Brac and Little Cayman. In Cayman Brac it is a major pest species, breeding
all along the north coast and on the southwest coastal platform. It is basically
a freshwater, floodwater mosquito occurring in the same types of habitat as
Ps. Columbiae but is tolerant of more brackish conditions. It prefers
open, sunlit sites and in hot weather can complete its life cycle within three
or four days. Its seasonal distribution is the same as Ps. Columbiae
and like that species it has become much less numerous since 1980.
This is the smallest mosquito found in Cayman, occurring
in all three islands. Larvae have been found in fresh water rock pavement and
grass pools where vegetation or leaf litter give protection from predators.
Trap catches show seasonal peaks of abundance, one in July and the other in
December. This suggests that U. lowii favours conditions of falling water
levels following the main peaks of rain
