Introduction To Mosquitoes

• Biology and Identification of Mosquitoes (Aedes, Culex, Anopheles)

  • Life Cycle
    Feeding Habits

• Seasonal Abundance

  • Medical Importance
    Encephalitis

• Non-Chemical Control of Mosquitoes

  • Source Reduction
    Biological Controls

• Chemical Controls

  • Growth Regulators
    Larviciding
    Adulticiding
    Insect Repellents

• Summary
  

The purpose of this article is to provide you  with some reasonably detailed background information on mosquitoes and the reduction of its population. At the same time it cannot provide all the relevant information. I have tried to gear this article to the needs and the environment of a beach community.

Mosquitoes remain a major killer in other parts of the world, in the US they are more or less a nuisance with the exception of a few species that can carry disease. Mosquitoes serve a vital ecological function in that their larvae, pupae, and adults are important food sources for fish, birds, bats, frogs, and insects.

All mosquitoes require water to complete their life cycle. If we could control standing water, we could manage mosquitoes. While we can empty cans, fill a puddle, we cannot as easily manage salt marshes.

Biology and Identification of Mosquitoes

There are about 13 genera in the US. Most pest mosquitoes belong to one of three: Aedes, Culex, or Anopheles. Long Island and Fire Island has about 42 different species. Not all of them bite humans and only the females need the bloods protein to mature their eggs.

Aedes
Some Aedes mosquitoes are called "floodwater mosquitoes" because they lay their eggs singly on damp soil or vegetation in areas that are periodically wet. The eggs remain dormant until flooded and conditions are favorable. Salt marsh species breed in coastal marshes that are occasionally flooded by high tides. Many floodwater and salt marsh species can fly great distances of 5 to 20 miles subject to wind conditions. Aedes and Anopheles generally have a pointed tip at the end of the abdomen.

Aedes sollicitans is the most common salt-marsh mosquito on Fire Island. It lays it's eggs at the rack line, which is the inland waterline at the two monthly lunar high tides. The eggs are safe here from being washed out into deeper waters. After a drying phase the eggs hatch at the next lunar high tide. Biting will begin about a week to 12 days later. Sollicitans bite all day long.

Aedes vexans  (called the floodwater mosquito) is the other most common mosquito of the Aedes family.

Culex
These mosquitoes breed in quiet standing water of all types (from cans to pools). This species prefers polluted standing water with large amounts of organic material. Eggs are laid on the surface of the water in rafts of about 100 eggs. Culex mosquitoes have a blunt tip of the abdomen. Culex pippians, also called the common house mosquito, is quite prevalent on Fire Island.

Anopheles
Anopheles breed in permanent bodies of fresh water with an abundance of aquatic plants that provide protection from fish and other predators. Eggs supported by floats are laid singly on the waters surface.

Anopheles mosquitoes can be distinguished from Aedes and Culex mosquitoes in several ways: 1. Anopheles have patterned wings, 2. adult Anopheles females have palps that are almost as long as their proboscis, 3. Adults rest on surfaces with their head lower that the abdomen while Aedes and Culex species rest with the head and abdomen parallel to the surface (I thought this to be of interest next time you get stung) and 4. the Anopheles larvae float parallel to the surface of the water as opposed hanging down at an angle.

Life Cycle
There are four life stages: egg, larva, pupa, and adult. Except for the adult stage all are in the water.

The female lays her eggs on the water. Eggs laid in this way hatch in one to three days.

The larvae or wigglers that hatch must live in water to survive. They float at the surface breathing through an air tube and filtering food through their mouth brushes. When disturbed they dive to the bottom. This stage lasts from 4 to 5 days to several weeks depending on species and temperature. As the water temperature rises the process speeds up.

Larvae transform into pupae or tumblers. Pupae do not feed, but they are quite active as inside the adult mosquitoes develops. This stage lasts from two to three days. Winter is passed either as eggs or pupae.

Feeding Habits
Only female mosquitoes suck blood which is needed to lay eggs. Males feed on plant nectar.

Most mosquitoes, but not all feed after dark or early morning hours. Daylight hours are spent in dark damp places. Some species also feed in daylight hours and others day and night.

The blood sucking habit is what causes mosquitoes to become a vector for disease. If a female mosquito feeds for example on the blood of a malaria carrying person, the disease organisms survive and reproduce in the mosquitoes, ending up in her salivary glands. Next time she feeds on a new host, she inoculates her new host.

Seasonal Abundance
Mosquitoes may breed at any time from spring to the first frost. Populations are generally highest in summer and early fall. When rain is abundant, many species can lay eggs continuously and with ideal temperatures a cycle can be completed inside one week.

Medical Importance
Worldwide mosquito play an important role in diseases, like malaria. In the US they are more like a nuisance. Human mosquito transmitted diseases remain relatively rare and are generally limited to encephalitis among humans and dog heartworm among dogs.

Encephalitis
At least six types of mosquitoes transmitted encephalitis occur in the United States. One of them, the eastern equine encephalitis (EEE), occurs here in the eastern US. Encephalitis is caused by a virus affecting the nervous system and is considered serious because it often is fatal. Encephalitis is relatively rare, because it requires an enzootic cycle involving wild birds and mosquitoes in fresh water swamps. The vector involved is Culiseta melanura which rarely stings mammals, explaining the rare transmission to humans and equines. But recently I've heard suggestions that other vectors may be involved.

Non-Chemical Control of Mosquitoes

The decision which pest management techniques are most appropriate depends on a sampling of which mosquito species are present. This is best done by Vector Control on a regional basis. For the purpose of mosquito control in a beach community this discussion will limit itself to the strategies that may be effective on the local level.

Generally, source reduction - eliminating or altering the water in which mosquitoes breed - is the first choice for control. If this cannot be achieved effectively, then the second choice to consider would be biological control of the larvae with predators, bacterial insecticides, or growth regulators. Thirdly we may add education of residents since mosquitoes play an important food resource for many species.

Source Reduction
The fact that all mosquitoes require water to develop is the key to their control. No standing water means no mosquitoes. If we can reduce the breeding habitat we are a long way to winning the battle. These are some of the regional management tactics: ditching, ponding, draining, managing water levels. On the homeowner/community level: dispose of any container around the home containing standing water, fill in areas with standing water, ponding and the introduction of fish, clean roof gutters (watch for standing water), check children's toys, bird baths, plastic covers, etc.

Biological Controls

Mosquito-Eating Fish
Fish are the most important predator to larvae. Of course this control is only useful on a larger scale or on ponds created and managed by a home owner. Gambusa affinis, an inch-long freshwater fish that can tolerate contaminated waters eats hundreds of larvae an hour. The kilifish also eats larvae but is less tolerant of fetid waters.

Bacterial Insecticides
Products containing Bacillus thuringensis israelensis (B.t.i.) are available for treating bodies of water. This bacteria kills mosquito and black fly larvae. It is harmless to humans, other animals, fish, and predacious insects. It is only effective against larvae since it needs to be ingested. At the community level it is available so called Mosquito Dunks.
Suffolk County Vector Control is currently (1998) testing and using a product called Vectolex which is a different bacillus (Bacillus Sphaericus).

Natural Enemies
Mosquito larvae are an important food for aquatic organisms. Fish, insects, and spiders pray on them. Adult mosquitoes are fed upon by birds, bats, frogs, spiders, and insects ( one example is the dragon fly).

Chemical Control of Mosquitoes                            

Growth Regulators
Insect growth regulators do not kill the larvae, but prevent them from developing into adults. Application is difficult since only mature larvae are affected. Most growth regulators do not harm other non-target species. Suffolk County Vector Control uses the class of pesticides in the saltwater-marshes, applying them by helicopter at the appropriate time.

Larviciding
Petroleum oils and mineral oils can be applied to the water. The resulting oil film over the the surface suffocates the eggs, larvae, and pupae. Rain, wind, waves may break up the oil film and makes it less effective. Some oils are toxic to fish, plants or other organisms. This method is not permitted in NY

Adulticiding
Adulticiding is space spraying for adult mosquitoes with insecticides. It is considered the least effective method since it does not control the source. It can only provide temporary relief and non selectively kills all insects. Adulticiding is considered only effective where mosquitoes pose a health threat such as an EEE outbreak. Vector Control uses a product called Fyfanon ULV. The active ingredient is Malathion which the manufacturer claims has become safer over the years as purity has improved. Vector Control will apply Malathion only upon request of the community.

Insect repellents
Scientists have confirmed that mosquitoes are attracted by carbon monoxide as well as lactic acids. Also sweaty people, adults, men and larger people attract more mosquitoes.

Personal insect repellents containing DEET applied to clothing provide protection from bites. It may be toxic to children. See the EPA news release on DEET. The Journal of the American Academy of Dermatology indicated that children should never receive products with concentrations larger than 10% which may be superceded by the recent (4/98) EPA recommendation

Permethrin, another repellent is a contact insecticide, may only be used on clothing. Permethrin is a synthetic form of the African Chrysanthemum.

Citronella, the oil of a grass, can be quite effective albeit short lived.

A new plant-based repellent, called Bite Blocker, combines soybean oil with geranium and coconut oil. Canadian studies indicated close to 100% protection to certain species up to 3 hrs.

DEET, or any other chemical may be detrimental to your health. Witness the discussions on the state level whether DEET should be banned from New York.

Summary

Mosquito control and reduction can only be achieved using a multi-pronged approach. Not only need the State, County, and Town further regional projects, but also every home owner, resident, or even tenant needs to be vigilant in reducing potential sources of mosquito breeding spaces. Local communities are encouraged to implement educational programs to increase the publics awareness. Only when awareness is achieved at all levels will we reduce mosquito populations using the least toxic measures.

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Every effort has been made to provide correct, complete and up-to-date pest management information for New York State in this publication. Changes in pesticide regulations thus occur constantly, and human errors are still possible. These recommendations are not a substitute for pesticide labeling. None of the above has been verified by members of the Fair Harbor Community Association or employees of FairHarbor.com

READ THE LABEL CAREFULLY

BEFORE APPLYING ANY PESTICIDE

 

Can mosquitoes transmit AIDS?

The HIV virus that produces AIDS in humans does not develop in mosquitoes.  If HIV infected blood is taken up by a mosquito the virus is treated like food and digested along with the blood meal.  If the mosquito takes a partial blood meal from an HIV positive person and resumes feeding on a non-infected individual, insufficient particles are transferred to initiate a new infection.  If a fully engorged mosquito with HIV positive blood is squashed on the skin, there would be insufficient transfer of virus to produce infection.  The virus diseases that use insects as agents of transfer produce tremendously high levels of parasites in the blood.  The levels of HIV that circulate in human blood are so low that HIV antibody is used as the primary diagnosis for infection.  

Dr. Wayne J. Crans, MR&C, Rutgers University

 

Every effort has been made to provide correct, complete and up-to-date pest management information for New York State in this publication. Changes in pesticide regulations thus occur constantly, and human errors are still possible. These recommendations are not a substitute for pesticide labeling. Before using any product, chemical, or pesticide, read carefully, understand, and follow strictly any instructions on the product label. The above information has been obtained from sources believed to be reliable. Neither the Fair Harbor Community Association nor any employee of FairHarbor.com has verified the correctness of any information contained herein.