Tuesday, September 10, 2013

The Mosquito – World’s Deadliest Creature - Q & A

Dr Abe V Rotor  
Living with Nature - School on Blog
Paaralang Bayan sa Himpapawid (People's School-on-Air) with Ms Melly C Tenorio 
738 KHz DZRB AM Band, 8-9 evening class, Monday to Friday
Dengue mosquito (Aedes egypti)Photo taken by Mohammed Mahdi Karim 

Anopheles mosquito aims its needle sharp probosis to get through its host's clothing. Mosquitoes can live as long as 3 months, and two to three times longer under hibernation. 

Virtually no one escapes this cosmopolitan uncanny vampire, that hardly a day passes without sustaining a surreptitious bite from it.

The mosquito follows wherever man goes, and oftentimes is even ahead in the frontiers.  Its is there in the polar regions of Siberia, marshes of tropical America and Asia, at the Dead Sea basin, 1,300 feet below sea level, and on the Andes and Himalayas.

They come in armies or swarms but are not true colonies like those of the bees and ants.  Swarming is just an accident of enormous population buildup concentrated in a local breeding area.

The mosquito changed the course of history.  When irrigation canals built by the Babylonians joined the Tigris and Euphrates rivers, a vast swamp developed and became infested with malaria.  It was here Alexander the Great and his powerful army lost - to malaria.

The mosquito has successfully defended the wildlife bastions such as the Amazon, the jungles of India and Africa, and the forest islands of the Pacific.  The development of the tropics - the mosquito belt - was retarded for centuries, and mosquitoes almost prevented the building of the Panama and Suez Canals.

The mosquito occupies a vital link in the food chain, being a major food source for fish and amphibians.  Fishes feed upon its larvae, the wrigglers, while the adults are frog's favorite. Man's dependence on fish, - which are dependent on mosquitoes in turn - places him at the apex of the food pyramid.  There is only one guarantee that man continues to occupy this position - if he is willing to shed blood for it. Without blood, mosquito eggs fail to hatch and without a sip once in every 25 generations, its particular generation dies out, thus breaking the food chain and toppling the food pyramid.

In today's modern living, with technological breakthroughs in pests and disease control, human encounters with the once dreaded mosquito have been reduced mainly to physical annoyance and "pesky" problems. This is not however, entirely true as we shall see later.

Here are some questions commonly raised about the mosquito, and their scientific answers to update our acquaintance with our old enemy and friend.

Q.  Do mosquitoes bite only warm-blooded animals?
A.  In general yes, but there are also species of mosquitoes that bite turtles and snakes.

Q.  Do all mosquitoes bite?
A.  Only the female mosquito does.  The regular food of adult, male mosquitoes is plant sap and nectar.

Q.  How are mosquitoes able to locate their suitable hosts?
A.  They have chemoreceptors - a combination of smell and touch - located at the plumose antennae and hairy legs.  These are sensitive to heat waves and odor emitted by the hosts.

Q.  Do mosquitoes invade places far from their breeding grounds?
A.  Yes, although they seldom travel farther than 1000 feet from their birthplace.  Mass raids have been monitored to as far as 50 to 75 miles away, the swarm usually riding on air currents.

The British named their bombers and reconnaissance planes in World War II,  Mosquito, so with the Italians for their anti-tank rockets – a tribute to the superb agility of this pesky minutia. 

Q.  What is the needle of the mosquito made of?
A.  Actually it is a sheath bundle of modified mouthparts, the equivalent of teeth, lips and whiskers elongated to form a drill, siphon, probe and guide and rolled into a needle or proboscis.
Left: Anopheles and Culex wrigglers; Culex pupa. Note: oil film clogs the breathing apparatus of the wriggler  which causes asphyxiation. 
  Q.  How can this tiny needle penetrate tough skin and clothing?
A.  It works on the principle of jackhammer with high frequency.

Q.  What prevents blood from clotting in the body of the mosquito?
A.  The blood, before it is sucked, is first thinned by the mosquito's saliva, which contains an anti-coagulant substance.  It has also an anesthesia effect on the host.

Q.  Is this the reason why we do not feel a mosquito bite at once?
A.  Yes, and probably the location of the bite is away from a nerve.

Q.  Why do  mosquitoes make their presence known by buzzing near the ear?
A.  This is not true.  They simply whine and emit short wave buzzing which is picked up when passing near the ear.  (Wing beat is 600 per second, and the cymbal sound-producing membrane vibrates nearly 7000 cycles per second.).

Q.  How do you recognize disease-carrying species from one another?
A.  Anopheles, the malaria carrier has its head, body, and proboscis in straight line to each other but at an angle to the resting surface.  It has spotted colorings on the wings.  Its wrigglers lie parallel to the water surface.    

Culex, the carrier of viral encephalitis and filariasis holds its body parallel to the resting surface.  Its scaly proboscis is bent and uniform in color.  Its wrigglers are slender and long with breathing tubes covered with hair tufts.

Aedes, the carrier of yellow fever, dengue and encephalitis, holds body parallel to the resting surface with proboscis bent down, thorax silvery with white markings. Its wrigglers are short and stout with breathing tubes containing a pair of tufts. They hang from the water surface at 45 degrees angle.

      When you see a mosquito resting, or wrigglers hanging down from the surface of a pond, use the above reference.

Q. How serious is Dengue fever?  How can it be controlled?
A. The disease threatens two billion people in 100 countries.  In 1998 alone, 514 died of Dengue in the Philippines with one death for every 100 patients who were mostly children. Metro Manila had the highest incidence with more than six thousand cases. Since the disease is specifically transmitted by  Aedes egpypti, the key to the control of the disease is the extermination of the breeding places of the mosquito vector.

Q.  Do mosquitoes follow certain feeding hours?
A.  Yes.  For example, the Anopholes or malarial mosquito bites chiefly in the evening and early morning, while the Aedes bites during the day.

Q.  How fast do mosquitoes multiply?
A.  In a year's time there may be from 15 to 20 generations produced.   At the normal rate of 100 eggs laid per generation, a common mosquito could spawn 31 billion descendants in six generations.

Q.  What attracts mosquitoes?
A.  They are attracted by the regular breathing, color and texture of clothing, and odor.  Dr. A. Brown of  the University of Ontario reported that the rate of breathing is the principal factor in attracting mosquitoes.  He also found that only one-tenth landed on white clothing than on dark or black material.  The texture most avoided is luminescent satin.  A person who has not taken a bath gets more mosquito bites. Try it.

Q.  What is the best insecticide to make our homes "mosquito- proof?"
A.  When DDT was not yet banned, 200 milligrams of the powder could give effective proofing from 6 to 12 months.  Dieldrin at 50 milligrams gives a three-month proofing.   Carbamates, like Sevin, are preferred.  Even if they  have shorter residual effect, they are safer to health and the environment.  Eucalyptus trees in the surroundings repel mosquitoes.  Now and then smudge the area by burning dried leaves of Eucalyptus specially in the afternoon. 

Q.  Do mosquitoes develop resistance to chemicals?
A.  Yes, through biological specialization, survivors from previous sprayings tend to carry on a certain degree of resistance, which could be passed on to the next generation.  Chemical control should be judiciously practiced to cushion this phenomenon. Return to plant derivative insecticide like pyrethrum, rotenone, nicotine and derris is highly recommended.

Q.  How does a film of oil on water kill mosquito wrigglers?
A.  When they stick their tails out of the water to breath, the oil slick clogs the breathing tube, thus resulting to asphyxiation.

Q.  If it is impractical to drain the breeding ground of mosquitoes, how do we get rid of wrigglers and pupae?
A.  Keep the water free from organic matter and scum which are food of wrigglers.  Better still, put some fish, like kataba (Poecilia) and Gambusia, to feed on them.

Q.  Do mosquitoes fight each other?
A.  They seldom engage in combat, but there are species, which have preying habits.  These are Toxorphynchites nornatus, T. splendens, and T. brevipalpis which were introduced into Hawaii, Fiji, Australia and Southeast Asia to control pest mosquitoes.  Their wrigglers are larger and larvivorous, feeding on the smaller wrigglers of other mosquito species.

Next time a mosquito comes buzzing around your ears, take the message seriously because it is the world’s deadliest creature.  More people have died because of its bite than all who perished in all wars combined.

The British named their bombers and reconnaissance planes in World War II,Mosquito, so with the Italians for their anti-tank rockets – a tribute to the superb agility of this pesky minutia.


Mosquito repellant from bottle brush (Salix sp)
There is a way to get rid of mosquitoes without mosquito net and other paraphernalia. That is, to apply skin repellant. This simple extract preparation can be made - and used - at home. ~

Direct crude extract (ground fresh leaves) repels mosquitoes and flies. It also serves as fresh deodorant in the bathroom and kitchen.  

Dilute with tap water at 1:4, filter with ordinary cloth, and spray (atomizer) on garden plants and in dark corners. 

Another preparation is by dissolving the fresh extract with ethyl alcohol 1:2 ratio, air dry, and add Vaseline or Petroleum Jelly to the powder residue. This also serves as ointment for minor wounds 

The mosquito repellant that is advertised is made of synthetic compounds and there are reports that it is carcinogenic, affecting not only the skin but internal organs as well, since poison can be absorbed by the skin and goes into the blood stream which circulates throughout the body.

What then is a safer alternative?

Researchers from the University of Santo Tomas found out that the volatile oil of the weeping willow, also known as bottle brush (named after the form and shape of the leaves) is an effective mosquito repellant. The oil is extracted by dissolving the ground dried leaves with ethyl alcohol as solvent.

Results of the experiment showed that the extract is effective in repelling house mosquitoes (Culex pipens) with the same efficacy as the advertised commercial product. The result also validates the old practice of using weeping willow to ward mosquitoes by simply rubbing crushed fresh leaves on the skin. (Clemente R, Landan RP Luquinario MI and P Padua, UST 2002)

Poeciliids – Mosquito Fish
Dell H. Grecia, Columnist Women’ Journal

Raising poeciliids, or nature’s soldiers, in your backyard can help eradicate dengue- and malaria- causing mosquitoes.Aside from garden, you can also build a mini-pond in your backyard. Then you can fill the mini-pond with tilapia, catfish (hito), even carp and pangasius. The fishes are good predators of mosquito wrigglers. But there is another highly recommended fish, the kataba or poeciliid, a large family of small fishes known for being predatory as well as omnivorous.

Residents along esteros can live without window and door screens and mosquito nets due to the presence of this biological friend and nemesis of the kiti-kiti or mosquito wrigglers. 
The importance of insectivorous fish cannot be underestimated, says my friend, the biologist Dr. Abe V. Rotor. He mentions China, whose government mandated the raising of mosquito-eating fishes during the dengue outbreak in 1981. The Chinese raised fishes like the poeciliids (kataba or bubuntis), tilapia and catfish (hito) in canals, ponds, fields, and even household water containers. Indeed, the community project prospered and in no time the epidemic was contained.

Characteristics of the Kataba

The kataba fish is around three centimeters, form shout to tail tip. It is laterally compressed but stocky and fat-belied, hence its name bubuntis or kataba which means fat. Although brown or black in color, it exudes a dainty prism on its belly and sides- earning for it the name “rainbow fish”.

They are found almost everywhere as long as there is water- in fields, irrigation and drainage canals. For this reason, they are also called canal fish,” explains Abe.

If you see bubbling ripples in Manila’s esteros, you know the katabas are around- the fish can adapt to a wide range of environments, from canals to estuaries.
Imagine schools of poeciliids inhabiting the esteros, the tributaries of the Pasig River. They live around the bends, in coves, rock pools and in mudflats. When it rains, they go up stream. Poeciliids are found in Laguna Bay down Pasig River, reaching as far as the estuarine area. 

Biological Control
If there is a single program that warrants full attention, Abe stresses, it is the control of malaria and dengue, the most dreaded pandemic diseases which have killed coutless people in this country.

Deep concern has been demonstrated by governments. For example, in South Korea, a local fish Aphyocypris chinensis was found very effective in controlling mosquito vectors. Papua New Guinea and French Polynesia used Gambusia affinis and Aphanaus affinis in mosquito control. It was in Florida, Mississippi, Central America and Mexico where where Gambusia became popular, and soon this fish found its way to many countries.
But it is the poeciliids, according to Abe, which has adapted in this country, along with other insect-eating fish species which include liwalo, spotted gourami, tilapia, mudfish (dalag) and hito.

Poeciliids are also prey to many bigger fishes. Surprisingly, because of their number and rapid rate of reproduction, poeciliids have managed to maintain a stable populations even in open waters. Besides, the poeciliid prefers shallow areas and the edges of water where it is relatively safer.

Poeciliids swallow their food whole like a boa, except that their mouths are wide open. We call this luxury feeding. 

Poeciliids speak during the rainy season, Abe explains, reaching 81 percent in June, then declines in the cool months and toward summer. In January, only one out of two poeciliids are positive of insect prey, which means that they rely on plankton, like algae which are abundant in rivers and lakes at this time of the year. These facts were observed by Dr. Grace M. Cruz of the University of Santo Tomas in her 1998 dissertation.

Origin of Poeciliids
Abe adds that poeciliids were introduced into the country from Mexico by “accident”. It must have been during the Galleon Trade between Acapulco and Manila. But certainly the colonizers knew of the value of this fish and it was possible that it was purposely introduced for biological control.

Today, poeciliids are found in many countries. With little encouragement, the fish multiplies very fast. Instead of laying eggs, it gives birth to numerous young viviparous. And being non-seasonal and highly adaptable, population levels are safely established in a short time.

Abe describes the fish as having a barrel-shaped body, particularly in the case of the female which appears pregnant. Weight and length ratio shows that the female is more plump than the male of the same size.

The distinguishing mark of the male is the presence of gonopodium, which is the equivalent of a penis. Another is that the male’s dorsal fin is comparatively longer. The anal fin of the female originates beneath the dorsal fin, opposite the eleventh scale of the tail. The male’s anal fin, however, originates from beneath the anterior part of the dorsal fin opposite the eighth scale.

Practical way to clean jars and plastic containers
Abe, who makes basi wine (an Ilocano drink) and vinegar, uses poeciliids to clean the earthen jars used for aging the wine. He says: “After harvesting the wine after a year of aging, the most difficult part of the job begins: cleaning the jar. It has to be washed at least three times in one-week intervals, allowing the water to stand every washing. Its tedious work and the danger of breeding mosquitoes is inevitable.

“By culturing two to three pairs of poeciliids in the jar, you only need to change the water once. And it takes half the time to obtain a clean, odorless jar. The secret is that the poeciliids eat the wrigglers, algae and plankton, as well as other organic materials, converting them into stable organic residues. ~ 

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