Mosquitoes of Teton County

There are more than three thousand species of mosquitoes described worldwide. Wyoming has more than 45 species, and Teton County hosts 39 species, although nine species are most problematic for humans.  Continuous surveillance and special control efforts are aimed at the nine most troublesome species in Teton County: Aedes vexans, Aedes cinereus, Ochlerotatus dorsalis, Ochlerotatus fitchii, Ochlerotatus increpitus, Ochlerotatus cataphylla, Ochlerotatus spencerii, Ochlerotatus sierrensis, Culiseta inornata, and Culex tarsalis.  In addition, there are many insects that are commonly mistaken for mosquitoes, but TCMA does not control for these look-alikes.  

Like most insects, the mosquitoes undergo complete metamorphosis with the life cycle consisting of egg, larva, pupa, and adult stages.

Adult females lay their eggs directly on the water’s surface or in areas that the female senses will flood from rainfall, stream overflow, snow melt, or irrigation. Mosquitoes can lay many batches of eggs and some species can produce hundreds of eggs in one batch. Eggs can remain dormant for years pending proper hatching conditions.

The eggs hatch and progress through four larval stages, known as instars.

Mosquitoes are unusual in that all four larval instars and the pupal stage are aquatic. Mosquitoes can be found in a variety of habitats during these stages, such as:  naturally flooded stream margins, flood-irrigated pasture and hayfields, fresh water swamps, temporary snow melt pools,  lakes and pits, ditches, tree holes, and artificial containers.

Mosquito larvae emerge from eggs and feed on a variety of organic and microbial substances. A few species are predatory and feed on other larvae and small aquatic organisms and have been used (unsuccessfully) to control other mosquito species in the past.  Larvae frequently can be seen at the water’s surface, breathing from an air-tube located at their posterior end. They only move to the bottom of the water to forage for food or if threatened.  The length of time for larval development largely depends on water temperature, available nutrients, and the species of mosquito in question. 

Fourth instar larvae molt to an inactive phase – the pupae. While the pupa is still motile for defensive purposes it does not feed. It breathes from two air tubes at the top of the head called trumpets.  During pupation, the immature mosquito pupa undergoes massive reorganization of its internal and external organs and their functions in preparation for adult emergence.

The adult, in an amazing display of metamorphosis, emerges from the pupal skin, rests briefly to dry and harden, then takes wing.  Adults typically live from a few days to a month depending on the species. However, there are some species whose eggs, larvae, or adults can over-winter for several months depending on weather conditions.

In order to complete development of the next batch of eggs, adult female mosquitoes seek a blood meal using a variety of complex sensory means to find their hosts.  They cue in on dark colors, odors, warm temperatures, carbon dioxide and moisture exhaled in the host’s breath.  Not all mosquitoes bite people; some blood-feed only on amphibians, birds, small mammals, or livestock, while others feed only on plant nectar.  After the female and male mate, the female mosquito flies off in search of a host to feed from. Once the blood meal is attained and digested the eggs will develop and the cycle will begin again.

For most, this  blood-feeding flying adult is the most familiar form of mosquito because of its association with disease and annoyance.  However more emphasis in mosquito control is placed on the mosquito larva.  In this stage, mosquitoes are concentrated in their aquatic breeding habitat and may be controlled in the most effective, economical, and environmentally-friendly way.