INTRODUCTION
The Culex/Anopheles Life Cycle is based upon physiological
and behavioral characteristics that are shared by species in four
different genera. All members of this group lay their eggs directly
on the water's surface or on very wet soil because their eggs
lack desiccation resistance. The larvae of the members in this
life cycle group are found in a variety of aquatic habitats ranging
from stagnant water-filled containers to relatively clean, quiet
littoral zones of ponds and marshes. They all have multiple generations
each season and typically show a marked increase in adult populations
as the season progresses. Mated females will overwinter in a sheltered
place, emerge in the spring and search for a blood-meal for the
production of eggs thereby repeating the cycle. There are a number
of mosquito species found in New England that fit into the Culex/Anopheles
Life Cycle category. These are listed below and belong to two
subfamilies spanning four genera.
Multivoltine Culicines
Culex restuans Culex pipiens
Culex territans Culex salinarius
Culiseta inornata
Uranotaenia sapphirina
Multivoltine Anophelines
Anopheles earlei Anopheles bradleyi
Anopheles punctipennis
Anopheles quadrimaculatus
REPRESENTATIVE SPECIES: CULEX TERRITANS
A closer look at Culex territans, a typical representative species of this group, will illustrate in finer detail the life cycle strategies common to the species in this category. While all other members of this group lay their eggs solely on the water's surface Cx. territans, according to various authors, can apparently also lay its eggs on wet soil relying on either rising water levels to float its eggs or runoff to carry its eggs to a suitable aquatic habitat. This is a mosquito whose larvae are usually found in the quiet littoral zones of aquatic habitats that are often overgrown with vegetation. Like all members of this category Cx. territans has multiple generations annually that begin with very small populations early in the season and build gradually as the season moves along. The greatest populations occur just prior to the first frost in the fall. The last emerging females will mate and subsequently search for a sheltered place in which to overwinter. Those mated females that survive the winter emerge in early spring and search out amphibian hosts, from which they acquire a blood meal for the production of eggs.
Culex territans is a widespread species both in the United States and worldwide. This species occurs throughout southern Canada and on the west coast of the United States reaching only as far south as central California. Additionally, it is found in suitable habitat east of the Rocky Mountains. In Europe it occurs north to Finland, east to all of European Russia and as far south as North Africa. Locally, Cx territans is widespread in New England and is typically found in rural, sylvan habitats that have good water quality.
The seasonal distribution of Culex territans starts with overwintering females that emerge from diapause in early spring. They are nocturnal feeders and feed for the most part on amphibian hosts, especially frogs rarely birds and mammals. The females, after acquiring a blood-meal, will produce eggs and subsequently search for a suitable oviposition site. Ovipostion, larval growth, pupation and emergence continue throughout the summer months resulting in widespread distribution of adults late in the season. The fall and winter distribution begins with a final brood of females that do not host seek, but instead seek out sources of carbohydrates that will enable them to overwinter. This cohort of females will mate and store sperm before they enter their winter diapause.
While Cx. territans is most often found in relatively clean aquatic habitats overgrown with vegetation, they are sometimes found in other less characteristic habitats as well. For this reason, Cx. territans can be found sharing its habitat with a fairly wide variety of associate species as listed below:
Associate Species
Aedes abserratus
Anopheles walkeri
Aedes aurifer
Anopheles quadrimaculatus
Aedes fitchii
Anopheles punctipennis
Culiseta morsitans
Uranotaenia sapphirina
Among the Culex species found in New England, Cx. territans
larvae are fairly easy to identify based on some specific morphological
characters. Culex territans larvae are characterized by
antennae that are constricted beyond the antennal tuft. The antennal
tuft is inserted on the outer one-third of the antenna whereas
the antennal tufts of all other Culex species are inserted
nearer the middle of the antennae. Additionally, the larvae usually
possess single upper head hairs (occasionally double), single
lower head hairs (rarely double) and comb scales in a large patch.
Adult Cx. territans females are characterized by a proboscis
and tarsi that are entirely dark and not striped. They also possess
white scales at the apex of the abdominal segments and not at
the base.
CONCLUSION
The above life cycle classification is a broad one that encompasses
a wide variety of New England mosquito species. The newly proposed
classification system presented at this symposium further divides
and simplifies the previously presented life cycle classification
system. The new classification system is a tool specifically designed
for use with northeastern mosquito species. This system will help
biologists and others sort out and thereby better understand this
complicated and oft confusing group of organisms.
ACKNOWLEDGEMENTS
This is New Jersey Agricultural Experiment Station Publication No. E-40400-05-97 supported by state funds and funds from the New Jersey State Mosquito Control Commission.