Prevention and protection

Season for biting mosquitoes

Fig. 35 Mosquitoes are mostly troublesome when they are numerous. This happens when the pupae of the forest mosquitoes hatch in June.

Mosquitoes have been kept away from humans and animals using smoke from fires. The ancient Egyptians and Romans rubbed themselves with highly odorous plants. At the beginning of this century, numerous mosquito balms of plants like clove, cinnamon, lavender, camphor, etc. were developed. The best was citronella oil, which is extracted from a tropical ryegrass. It is still used, in citronella candles, but the effect is weak and brief. During World War II the search for effective mosquito repellents intensified. To this day, the effects of more than 30,000 different repellents have been tested, and only few were found to be effective.

Effective oil-based mosquito repellents. Repellents containing DEET (N,N-diethyl-m-toluamide) and / or dimethyl phthalate were among the best. When used carefully, they can maintain the repellent effect for several hours after application. Instead of using the repellents directly on the skin, clothing can be treated with the repellent. In Danish pharmacies, it is not possible to buy repellents with DEET, however, there are other types of repellents with almost the same effect. For example the Autan repellent is also recommended if you need protection in the tropics.

The modus operandi of mosquito repellents. As mentioned, the mosquito primarily finds its blood host by searching for the warm, moist air that is radiated from the skin. The mosquito has some small hairs on its palps, and these senses moisture in the air. There are many indications that effective mosquito repellents can clog the fine pores of the sensory hairs and prevent the moist air from entering. Therefore, the repellents do not give out an odor that mosquitoes do not like. Furthermore, it is not to be expected that the repellents keep mosquitoes at a distance. The mosquitoes are not confused until they are about to land.

Pot decorated with mosquitoes from the 13th century

Fig. 34. Around the year 1200, a potter from New Mexico decorated a bowl with this swarm of mosquitoes. (Rodeck)

Vitamin B. It is sometimes claimed that taking large quantities vitamin B is mosquito repellent. The effect of vitamin B is a result of parts of the vitamin being excreted through the skin. People, who eat large amounts of vitamin b, often smell of yeast or bread. In controlled studies, including studies done at the Danish National Pest Infestation Laboratory, has failed to show any effect on mosquitoes.

Smoke from Pyrethrin-based coils or sticks, or from tablets that are electrically heated, can keep mosquitoes away from the room or from the terrace. They must be placed so that you sit in the smoke or the smoke is between you and the mosquitoes.

Sound – A flying female mosquito, beat her wings about 320 times per second. This gives a sound with a frequency of 320 Hertz. It is the sound you hear when a mosquito is approaching. The male mosquitoes have good auditory organs on the bushy palps, and they find the females by listening. A trap, which sends out sounds with a frequency of 3-400 wing beatings per second, can catch male mosquitoes. These traps are used for research, but they have no practical significance, since it is the female mosquito that bites. The female mosquito’s auditory sense is not well developed, and it has never been proven to be useful. Nevertheless, new devices that claim keep the mosquitoes away using sound are regularly introduced. They send out tones which are not very loud but have a high frequency of about 15000-20000 Hertz. The frequency is so high, that the human ear can barely hear the sound. There is no reasonable explanation as to why the female mosquitoes should react to this sound. Consequently, there is nothing to suggest that the devices work. There are users of these devices who think that they work. (The World wants to be deceived).

Lights – especially from the ultraviolet part of the spectrum – are appealing to many insects. Several types of insect traps lure the insects with ultraviolet light and capture animals in traps or kill them with electricity. The ultraviolet light attracts mosquitoes, but the traps are not suitable for use outdoors. First, they attract more mosquitoes than they catch, and secondly, they kill many peaceful moths and other insects that fly at night.

Nets. Tulle or other suitable fabrics can be used to cover windows and doors. This is a reasonable way to prevent mosquitoes from entering the house or the caravan.

If too many mosquitoes enter the house, they can be killed with one of the pyrethrin insect repellents for flying insects.

Aedes mosquitoes - Bedbugs, Bites, Stings and Itches - Page 64

Aedes mosquitoes

Blackflies - Bedbugs, Bites, Stings and Itches - Page 64

Blackflies

Midges - Bedbugs, Bites, Stings and Itches - Page 64

Midges

Fig. 36. Of the three Diptera species which attacks humans, mosquitoes the largest. Black flies and midges are the smallest. Here, they are shown in natural size.

Transmission of disease

The mosquito probiscis

Fig. 33. The proboscis of a mosquito consists of many parts which collectively form a pair of thin tubes that are injected into the skin. (Herm)

As mentioned, there are malaria mosquitoes in Denmark; however, the malaria has died out. Malaria parasites are not present in Denmark. Therefore, it is not dangerous to be bitten by mosquitoes in Denmark. They are not suspected of transmitting serious diseases.

It has been discussed whether mosquitoes can transmit infectious jaundice or AIDS to humans. They are virus diseases which can be transmitted from person to person by contaminated syringes. It is an obvious conclusion that a mosquito, a small flying needle must be able to do the same. Such transmission does probably not happen with these diseases, because the mosquito sucks and spits through two separate pipes. The blood it has sucked from a jaundice or AIDS patient is therefore not spit into the next victim. The risk that a random infectious agent is still on the thin proboscis when the mosquito has finished digesting and is ready to bite again is so small that it is highly unlikely. However, scientists still research the mosquito’s ability to transmit the virus to humans. If a virus is to be transmitted from mosquitoes to humans, it must be able to multiply both in humans and in mosquitoes. Furthermore, it must be able to get into the mosquitoes’ hypopharynxt, so that it can be spit into humans.

Control

In Denmark, mosquitoes are not of importance as related to public health, and eradication campaigns have been abandoned. The campaigns were carried out in the 1960s and 70s, where puddles and ditches were sprayed with diesel oil in an attempt to suffocate the larvae, and large meadows were treated with insecticide. A more reasonable approach is to eliminate the accumulations of water in which mosquitoes lay their eggs, and where the larvae develop. Today, however, people are more reluctant about draining too much water in the landscape as this result in destroying other organisms’ habitats. Very reasonably – you have to protect yourself from the mosquitoes.

Mosquito bites

Aedes mosquito and blood

Fig. 3. First mosquitoes: I read in “Bites, Sting and Itches” that mosquitoes do not do not prefer the blood of some people to other’s, but are only attracted to the heat and humidity. Other mosquitoes: Well yes, but there are also male mosquitoes do not suck blood, and I can see from our antennas that we are males. First mosquitoes: What a stupid book. (Drawing from Don Martin MAD)

Most mosquitoes can lay a few eggs even if they do not get to a single drop of blood. They simply tap into their food reserves or produce some eggs at the expense of the flying muscles. In order to exploit its possibilities to lay eggs to the full, the female mosquito will attempt to have some blood meals.

The mosquito proboscis consisting of 7 different piercing and cutting parts, and the system is very flexible so that it can search for capillaries under the skin. The mosquito sucks through the labrum, which together with the hypopharynxt form a tube. The hollow hypopharynxt is drilled into the skin with the other mouth parts, and the mosquito uses it to spit into the wound.

How the mosquito finds its prey. Initially, the carbon dioxide we exhale is what makes mosquitoes aware of a potential blood donor nearby. The carbon dioxide only increases the mosquito’s search activity, and is not directly appealing to them. Previously, certain body odor, (lactic acid, etc.) were thought to attractive to mosquitoes. However, this cannot be confirmed. Recent studies show that the heat and humidity radiated from the skin might lead the mosquitoes to us.

Mosquito appeal. When some people are more appealing to mosquitoes than others, it is partly because there is a difference in how much heat and humidity, we radiate. In studies of various peoples’ mosquito appeal, it has been proven that the individual differences are not as significant as it is perceived. Part of the explanation may be of a psychological nature. Some people feel aggrieved when mosquitoes are nearby, and they feel as if all the neighborhood mosquitoes only want their blood. However, the difference probably also lies in the fact that people have different reactions to the bites.

Mosquitoes

Mosquito, Aedes vexans

Fig. 30. Mosquitoes, the species Aedes vexans (PEUS)

Aedes mosquito - Bedbugs, Bites, Stings and Itches - Page 57

Aedes mosquito

Mosquitoes, of the family Culicidae, are slim, elegant, 5-6 mm long, grayish midge-like flies. There are also some peaceful midges, which are similar to the mosquito in appearance, for example the non-biting midges or chironomids, which are often seen in large swarms over lakes and bays. Mosquitoes are characterized by the long, thin, flexible proboscis on the front of the head, as well as by the fine scales that cover most of the body.

The mosquitoes have long sensory palps. Male mosquitoes have bushy palps, while female mosquitoes have shorter hair on their palps. Only female mosquitoes bite. In Denmark, there are 30 different biting species of mosquitoes, which may bite people when the opportunity presents itself.

Mosquitoes and flies

Mosquitoes and flies make up the insect order, which is called dipterans (Diptera). They have, in contrast to most other insects, only one pair of wings. The second pair of wings is small, knobbed structures modified from the hind wings. These are called halteres and are help the insect balance during flight.

The larvae are legless maggots that live in water or damp places. About 60,000 different kinds of mosquitoes and flies are known.