Mosquito Management: Ecology

Mosquito Ecology

{Female Culex pipiens getting a blood meal.}
Female Culex pipiens getting a blood meal.
Mosquitoes are a diverse group of insects belonging to the fly order, Diptera. There are over 2500 species of mosquitoes which can be found on every continent except Antarctica. While North America is home to about 200 species of mosquitoes, in Connecticut there are currently 49 known species which can be found in a variety of habitats. Of this number, approximately one-half are considered pests to humans or livestock and can transmit organisms causing disease.  (Identification Guide to the Mosquitoes of Connecticut)

Only the female mosquito bites because she requires a source of protein to produce her eggs. Once she has digested the blood she can lay over 250 eggs per brood and depending on the species, she can seek subsequent blood meals several times per season. She withdraws blood using specialized piercing and sucking mouthparts and is attracted to hosts by body heat, exhaled carbon dioxide and other complex physiological processes. Every human has their own unique body chemistry and may be more or less attractive to mosquitoes. Also, not all mosquitoes bite humans and, in fact, are fairly specific in their feeding preference. For example, some bite only birds or amphibians, such as toads, while others bite mammals, including humans. Males, in addition to females, feed on flower nectar and plant juices for energy.

{Female Culex pipiens laying an egg raft on the water surface.}
Female Culex pipiens laying an egg raft on the water surface.
Life Cycle of the Mosquito
{Mosquito Life Cycle}

The mosquito's life cycle includes egg, larva, pupa and adult stages. This type of development is referred to as "complete metamorphosis" by biologists and is similar to the development of butterflies. Mosquitoes, however, are aquatic, with most of their development occurring in or near water. Depending on the species, mosquito eggs are deposited either singly or clustered in egg “rafts” on the water surface, or individually on moist soil, the latter hatching when flooded by rain water or lunar tidal events. Eggs deposited on moist surfaces can withstand drying and can remain viable for several years. Certain species, such as Connecticut's saltmarsh mosquitoes, are very prolific breeders and can lay from 1,000 to 10,000 eggs per square foot on the moist mud found in a saltmarsh habitat. These moist depressions are usually found in the higher elevations of the saltmarsh which are dominated by salt hay grasses.
{larvae}
Mosquito larvae (“wriggler”) attached to the water surface showing the air siphon, abdomen, thorax and head.

Once the eggs hatch, mosquitoes develop through four larval stages (instars) as they feed and grow larger. They then progress to a non-feeding pupal stage and finally emerge as adults. The larvae and pupae breathe oxygen at the water's surface by means of specialized, snorkel-like air tubes. These air tubes are called "siphons" in the larvae and "trumpets" in the pupae. One species of mosquito obtains its oxygen by piercing the fleshy underwater roots and stems of aquatic plants, such as cattails, and actually breathing through the plant. Mosquito larvae actively feed by filtering bacteria and organic matter in the water. The development from egg to adult depends on the water temperature and can take as little as seven to 10 days in warmer weather or up to two months in cool, spring weather.

{Bucket with hundreds of larvae.}
Hundreds of larvae can be produced from a small area.
 
{pupae}
Mosquito pupae (“tumblers”) breathe through a modified air siphon and are very active in the water but do not feed.

Many mosquito species (genus Aedes, Ochlerotatus and Psorophora) in Connecticut deposit eggs in the fall which will not hatch until the following spring. With these mosquitoes, larval development usually begins in early March and egg deposition can extend into October, with adults most abundant from May through September. A few species (genus Culiseta and Coquillettidia) will overwinter in the larval stage, while adults of other species (genus Culex and Anopheles) will enter into buildings or sheltered areas and remain dormant until warmer weather arrives. (This is why adult mosquitoes are occasionally seen during a midwinter warm spell.) In Connecticut, some species of mosquitoes can produce up to 4 broods per year. Most have an average adult life span of about two weeks, excluding those which overwinter as an adult.

Mosquitoes can develop in a wide variety of aquatic habitats, with most species requiring a specific habitat. Stagnant water isolated from predators is ideal mosquito habitat. Examples of preferred mosquito habitats include saltmarshes, freshwater swamps, woodland pools, roadside ditches, catch basins and backyard habitats, such as clogged rain gutters, discarded tires or un-maintained bird baths. Some species, such as Culex pipiens remain close to their development sites and have a limited flight range of less than one-quarter mile. Other species, such as the common saltmarsh mosquito (Ochlerotatus sollicitans), can fly up to 40 miles from their saltmarsh habitats in search of an animal to feed on.

Mosquito Breeding Habitats

{Vernal pool}   {Standing water adjacent to dumster and trash.}
Mosquito eggs laid in the leaf litter of this vernal pool in the fall will hatch when the water warms up in the spring.   Stagnant, polluted water is an ideal spot for mosquitoes to lay egg rafts.
     
{Pile of tires.}   {Saltmarsh pothole}
Mosquito eggs laid on the inside walls of discarded tires will hatch when flooded with rain.   Saltmarsh mosquitoes lay their eggs on the exposed moist mud as this shallow pool or “pothole” dries down.