Mosquitoes Are Here – Part 1

I hear “I wish it would quit raining” all the time, now I know you don’t really mean it or your memory is short and you don’t remember the 2011 drought conditions or our lake 24 feet low.  That being said, I realize the water in many areas is crazy.  It makes doing daily chores hard, for instance our cattle pens like many others haven’t been dry in months.  Along with all of those problems, it is time to gear up for a major mosquito crop all summer.  For the past month or so I have been throwing a baseball in the evenings with my son and some repellents aren’t good enough and we have to go inside.  While we would hope that environmental conditions would help with limiting insect populations, the reality is that insects are very adapted to Texas conditions.  One of the most adapted is the mosquito. This is the first of a two part series for controlling mosquitoes around the home.

Mosquitoes are the most prominent of the numerous species of blood-sucking arthropods that annoy man and other warm blooded animals.  Great swarms may be produced even in small quantities of water.  They breed in all sorts of still water, fresh and salt, foul or potable; water in tin cans, car tires, hoof prints, tree holes, water deposits in leaf cups, water impoundments and salt marshes. 

Mosquitoes are the sole vectors of the pathogens that cause malaria, yellow fever and dengue.  All three of these diseases have been in Texas at one time or another but are still considered relatively rare.  However, the viruses that result in encephalitis may be of more immediate concern.  At least three types of encephalitis virus have been found in Texas; St.  Louis encephalitis (SLE), Western equine encephalitis (WEE), Eastern equine encephalitis (EEE), as well as West Nile Virus (WNV).  Pets can also be impacted by mosquitoes which can transmit canine heart-worm from infected dogs to healthy dogs by several species of mosquitoes.

There are about 2,500 described species of mosquitoes in the world; about 150 occur in temperate North America.  Mosquitoes found in Texas include the Vexans mosquito, Saltmarsh mosquito, Yellow fever mosquito, Floodwater mosquito, Common malaria mosquito and Southern House mosquito.

A mosquito passes through four stages in its life cycle.  The stages are the egg, larva, pupa and adult.  Mosquitoes that deposit eggs in rafts and some that deposit eggs singly need standing water.  Floodwater species require water present as moisture in the soil surface.  Some floodwater species will oviposit into depressions subject to inundation or in fairly dry situations where pools will be formed later by rains or tidal action.  The eggs of some floodwater species will hatch after being dry as long as two years.

Food for both the larvae and adults must be present near larval sites.  Larvae or “wigglers” ingest some dissolved substances, but depend for their sustenance principally on particulate matter, ranging from bacteria to clearly visible pieces, collected by vibrating the labial brushes on their mouthparts.  Particulate matter may be floating in the surface film, suspended throughout the water or clinging to submerged surfaces, or it may be in the form of other animals that can be as large as the larvae themselves.  The adult female needs a blood meal in order to lay eggs.  The males do not feed on blood but both females and males will feed on flowers as a source of nectar and plant juices.

The larvae molt four times, the last molt resulting in the pupa.  Under optimum conditions, the larval stage of some mosquitoes may only take a week.  The pupa or “tumbler” does not feed, but is nevertheless very active.  It breathes by means of a pair of “trumpets” thrust through the surface of the water, but can let go and dart through the water with a tumbling motion to seed shelter.  After a few moments, it returns to the surface with little effort and re-establishes contact with the air.

Active females generally live 2 or more weeks in natural sites, except that hibernating species may remain dormant for several months.

Moisture, warmth and carbon dioxide are the three primary components of attraction of mosquitoes to hosts.  In general, dark colors are more attractive than light colors.

The flight range of mosquitoes varies with the species, time of year, wind direction and also with the distance mosquitoes must fly from their sources to where there are warm blooded animals upon which to feed.  Record flights include 28 miles downwind in the lower San Joaquin Valley of California, and 110 miles along the coast in North Carolina.  Mosquitoes can disperse in all directions when wind speed is below 4 miles per hour.  Above 4 miles per hour, dispersal is downwind.  In general, most species in Texas stay within 0.5 miles of their breeding site, although one species is a strong flier and can easily cover one to five miles.

Do not encourage the gathering of birds on your property since they are the source of encephalitis viruses.  The Culex species responsible for transmitting SLE and WEE encephalitis viruses normally feed on birds and only occasionally on humans.  These viruses are transmitted to human when humans, infected birds and the virus-carrying mosquitoes are in close proximity to each other.

Eliminate all low areas that allow water to collect and stagnate.  If total elimination is not possible then the areas need to be treated with available “over the counter” larvicides.  When used properly the products will halt mosquito development before adults can emerge.  The most convenient products are “dunks” or “toss-its” which contain Bacillus thuringiensis var.  israelensis (Bti).  Bti is an environmentally friendly, natural, non-polluting, bacterially produced chemical.  Large bodies of water, such as ponds, generally contain fish and minnows that keep the mosquitoes in check.  Introducing fish and minnows into ponds or landscape pools is a good way to control mosquitoes.

Reduce or alter landscape watering so that no runoff is produced.  This not only saves you money but helps eliminate major breeding sites as there is no runoff to collect and stagnate in drainage ways.  Do not allow water to stand in potted plant saucers, pet bowls, wading pools or other water holding containers for more than three days.  Changing the water every three days will eliminate these breeding sites.  Tightly cover or treat rain barrels.

Do not allow water to collect in rain gutters.  Clearing these of leaves and debris that tend to hold the water preventing it from discharging will eliminate gutters as a breeding site.