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Florida is not only home for
abundant mosquitoes, but also for minute biting insects known
locally as "sandflies" (elsewhere as "no-see-ums"or "punkies"),
although the more correct name is biting midges. They are
especially troublesome in coastal areas, where most of Florida's
population lives. Biting midges are particularly abundant in the
vicinity of mangrove swamps or salt marshes.
What Are Biting Midges?
These insects are all extremely small, less than 1/8" long. They
belong to the insect order Diptera (two-winged flies), family
Ceratopogonidae, genus Culicoides. Florida has 47 species in
this genus, but only seven are significant human pests. The four
most important, in order of their pest status, are Culicoides
furens, C. mississippiensis, C. hollensis and C. barbosai; these
are coastal in distribution. Several species are associated with
dairy cattle, horses and farming operations.
Appearance, Life Cycle, and
Breeding Sites
Adult biting midges are gray in color with distinct wing
patterns. When biting, or at rest, the wings are folded,
scissor-like over the abdomen. The eyes on each side of the head
are black and the biting mouthparts protrude forwards and
downwards. Eggs are minute, cigar, or sausage shaped and black
in color. The eggs of C. furens take about 3 days to hatch at 80
°F. Those of C. barbosai, C. mississippiensis, and C. hollensis,
take 5 days to hatch at 80°F.
Some species occur primarily in
wet mud in and around mangrove swamps and salt-marshes. Some
larvae occur in the wet, but not submerged, mud around farm
operations. The eggs, which cannot survive drying, are laid on
wet mud in the breeding places, that is, the habitats where the
juvenile stages (larvae) are found. The larvae develop through 4
stages (instars) and are creamy-white in color and eel-like.
They are predaceous, feeding on other small organisms. Full
grown larvae are 1/8 to 1/4" long. The total time spent in the
larval stage depends on temperature and the season. When mature,
the larvae change to pupae and remain in this stage for about
2-3 days.
Biting Habits
Only the female midge bites and takes blood. When biting, the
midge uses small cutting teeth on the elongated mandibles in its
proboscis to make a small cut in the skin. At the same time, a
chemical in the saliva is injected to prevent blood clotting.
Capillaries severed by the cut bleed and form a tiny pool of
blood, which is then sucked up. Feeding takes approximately 2-5
minutes. The greatest biting activity in both species is around
dawn and dusk. Some biting may continue through the night, but
rarely during the day, unless the sky is heavily overcast and
the winds are calm.
Reproduction
Female midges take blood to provide a source of protein for egg
production. However, female C. furens and C. mississippiensis
may also be autogenous, which means that some individuals are
able to develop eggs immediately after they emerge from the
pupal stage, without first taking blood. When blood has been
taken, it is digested and the protein extracted to form eggs in
the female midge's two ovaries. The number of eggs produced
depends on the size of the female and how much blood she takes.
Culicoides furens females will produce between 50 and 110 eggs
per blood meal and C. mississippiensis from 25 to 50.
Seasonal Abundance
Culicoides furens is primarily a warm weather species that
begins to appear in large numbers as soon as the spring warming
trend begins. Biting females are abundant throughout the summer,
with numbers decreasing as temperatures drop during the fall and
winter months. Depending on local conditions, C. furens may
continue to be a pest in south Florida even during the winter.
Culicoides mississippiensis has two major population peaks, one
from February through April, the other from late September
through December. Populations of this species are lowest during
the summer.
Human Disease Transmission
Both C. furens and C. barbosai , especially the former, are
vectors of Mansonella ozzardi, a human nematode parasite. This
worm, which rarely produces symptoms of disease in infected
persons, is native to South America and is found also in several
islands in the West Indies. The worms live primarily in the
blood, but its juvenile forms (microfilariae) are found also in
the skin. Female midges ingest the microfilariae when they take
blood and then transmit the parasite to uninfected persons.
Veterinary Importance
- Blue Tongue - sheep and
cattle
- Primary vector
Culicoides sonorensis
- Losses ca. 120 million
U.S., 3 billion world-wide
- Mortality: 5-50% in
sheep and cattle <5%
- One human case
documented lab worker on blue tongue
- Onchoceriasis (River
Blindness) - horses
- Sweet itch or summer
dermatisis - horses
- Nematodes - most
nonpathogenic
- Leucocytozoon parasites -
poultry in SE Asia and Africa
In Sarasota, C. insignis is a
problem inland associated with cattle pastures and other rural
habitats. Water choked ditches with water hyacinth are a problem
in late summer to early fall. Nine species of Culicoides were
aspirated from horses in Florida during a study of equine
Culicoides hypersensitivity (CHS). Approximately 90% of the 2933
midges were C. insignis.
Control and Personal
Protection
Control of adult biting midges with insecticide sprays is
mediocre at best and temporary in nature due to the continual
emergence of these flies. The larval habitats are so extensive
that control of the larvae is not possible. Mosquito control
districts in Florida are not funded to provide control of biting
midges.
On the east coast of Florida,
large areas of swamp in several counties have been impounded
(surrounded by dikes and kept flooded with water), an
environmental method, that involves changing the breeding
habitat of the midges. Females no longer lay their eggs and
larvae no longer develop in the flooded mud. Impounding is an
effective control method both for salt-marsh mosquitoes and
biting midges.
Recommendations for Bite
Prevention
- Avoid outdoor activity
during peak biting times.
- If outdoor activity cannot
be avoided during biting times, apply repellents labeled for
biting midges according to the label.
- Increase air movement in
screened porches by using high velocity fans.
- Screens can be treated with
barrier sprays or portable foggers according to the label
for temporary reductions in small backyard situations.
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