Fly Day Friday: The Good Mosquito

Believe it or not, there is a mosquito species I look forward to seeing every year. You may think I'm crazy, but hear me out. There are at least three reasons to love elephant mosquitoes in the genus Toxorhynchites. They are pretty, beneficial in the larval stage, and do not bite as adults.

A male Elephant Mosquito

Elephant mosquitoes are also known as giant treehole mosquitoes, so you can sense a theme here. They are indeed large for mosquitoes, averaging about seven millimeters in body length. That does not include the mouthparts and antennae. Their long legs make them appear larger still. Why the name "elephant mosquito?" It may be a reference to the long, upcurved palps of the males, which suggest elephant tusks.

Notice the tusk-like palps (part of the mouthparts), and bushy antennae on this male.

There is no denying the beauty of our single North American species, Toxorhynchites rutilus. They are iridescent blue and purple, with silver and gold highlights, and white tips on the hind legs. It seems that no one photo captures all the colors all at once. Despite their brilliance, they are surprisingly cryptic in the dimming light of dusk, when they are most active (though they are considered day-fliers).

As their other name indicates, elephant mosquitoes breed mostly in water-filled treeholes. The larval stage, at least in later instars, is predatory on other aquatic insects, including....wait for it....the larvae of other mosquitoes. Yes, you heard that correctly, they are a natural biological control of the mosquito species that pose a threat to human health. The larvae are reddish in color, with a short anal siphon (bearing the spiracle that permits intake of air at the water surface), and a broad, black head with strong mandibles. There are four larval instars, an instar being the interval between molts.

The female Elephant Mosquito has straight palps, and simple bristle-like antennae.

The adult elephant mosquito has a distinctive proboscis, bent strongly downward near the middle of its length. Instead of using their beaks to draw blood from other animals, elephant mosquitoes of both sexes feed only on flower nectar. As flower visitors, they are also pollinators of wildflowers. Some other species in the genus may also feed on fruit juices, and honeydew (the sugary liquid waste of aphids, scale insects, and various planthoppers).

The female again, showing that long,sharply-curved proboscis.

Here in northeast Kansas, on the Missouri border, I have found Toxorhynchites rutilus only in late autumn, and only on the flowers of White Snakeroot. I have only seen them in our yard, in fact, but I am not usually exploring elsewhere as sunset approaches. The species ranges from the eastern half of Texas and Oklahoma diagonally northeast to southern Pennsylvania, Connecticut, and Delaware.

Can you tell which sex this one is?

There are roughly eighty species of Toxorhynchites, occuring mostly in tropical regions around the globe. Due to their unique appetite for other mosquitoes, they have been employed as biological controls for container-breeding mosquitoes in Japan, southeast Asia, the Caribbean, and in some cities in the United States.

Are you a new fan of elephant mosquitoes yet? If not, please see the resources and links below for additional information on the biology of these remarkable flies. Mosquitoes, like most insects, and people, defy neat categorizing as "bad" or "good." Entomology is a great place to learn lessons like that.

So handsome!

Sources: Alomar, Abdullah A. and Barry W. Alto. 2022. "Elephant Mosquito Toxorhynchites rutilus Coquillett, 1896 (Insecta: Diptera: Culicidae)," Ask IFAS EENY-787/IN1380. University of Florida.
Coin, Patrick, et al. 2004. "Species Toxorhynchites rutilus - Elephant Mosquito," Bugguide.net
Donald, Claire L., Padet Siriyasatien, and Alain Kohl. 2020. "Toxorhynchites Species: A Review of Current Knowledge," Insects 11(11): 747.
McAlister, Erica. 2017. The Secret Life of Flies. Buffalo: Firefly Books. 248 pp.
Ricciuti, Ed. 2019. "Meet the Mosquito With a Big Appetite - for Other Mosquitoes," Entomology Today.

The Zika Virus

The Zika virus, transmitted by mosquitoes, has captured headlines recently and set off something of a panic. This is technically not a "new" virus, as it was first discovered in the course of researching yellow fever in Africa in 1947. A rhesus monkey, caged near the Zika Forest in Uganda, contracted a fever of unknown origin, later (1952) determined to be caused by what we now call the Zika virus.

Aedes aegypti, one vector of Zika virus

The first human case occurred in Nigeria in 1954. It has remained rare and largely innocuous throughout its distribution in Africa and southeast Asia, until 2007 when an epidemic erupted on Yap Island in Micronesia. Subsequent epidemics in the Polynesia, Easter Island, the Cook Islands, and New Caledonia increased concern, but nothing like events in the last two months.

Two concerns have cropped up that have infectious disease specialists alarmed: Zika has jumped the Pacific Ocean and is now found in many countries in South America, Central America, and a few Caribbean nations. It has therefore been classified as a pandemic; there is also evidence the virus may be linked to birth defects, specifically microcephaly. There is also the possibility that the virus can, rarely, trigger Guillain-Barré Syndrome, a type of autoimmune disease.

What we know for certain is that the virus is not contagious. It cannot be spread from one person to another through casual contact. It is transmitted by mosquitoes in the genus Aedes, and possibly by sexual intercourse. Most people who contract the virus exhibit symptoms typical of the flu, and recover quickly.

Cases of the Zika virus in the U.S. are known from Florida, Illinois, Texas, and Hawaii. All victims had returned from travel overseas to countries known to harbor Zika.

This chain of events prompted the Centers for Disease Control to issue a Level 2 Travel Alert for pregnant women on January 15, 2016. Recommendations are that pregnant women avoid traveling to countries where the Zika virus is known to exist. This includes Puerto Rico.

An explosion of 3,500 microcephaly cases in Brazil between October, 2015 and January, 2016 is certainly cause for alarm; and it is at least suspicious that this coincides with the recent infiltration of Zika from the Old World.

Whether mosquito populations in the Gulf Coast states of the U.S. will become carriers of Zika is open to speculation, but considering the other illnesses vectored by mosquitoes, it is always an excellent idea to practice preventive measures such as wearing pants, long sleeves, and hats when outdoors. Repellents with DEET as the active ingredient can be applied per instructions (follow them to the letter). Emptying reservoirs and containers that trap rainwater is also crucial, as these are breeding grounds for mosquitoes.

Sources: Etymologia: Zika virus. Emerg Infect Dis [Internet]. 2014 Jun [date cited]. http://dx.doi.org/10.3201/eid2006.ET2006
"Zika Virus," Wikipedia

Mosquitoes

It’s “Fly Day Friday,” and while not everyone thinks of mosquitoes as flies, that is exactly what they are. Mosquitoes make up the family Culicidae. The majority are aquatic in the egg, larva, and pupa stage of their life cycle. They do not require a great deal of water, or time, to complete their development, and this makes them very difficult to control.

Female Culiseta incidens, the "Cool Weather Mosquito"

The adult female insect, in most species, needs a meal of blood in order to nourish her eggs. Human beings are not usually the host of choice, but we will do in a pinch. Mosquitoes are often cited as the most dangerous of all animals because of their efficiency in delivering disease pathogens to human populations. West Nile Virus may make headlines, but other dangerous mosquito-borne illnesses fly under the radar. Our pets and livestock are also at risk.

The Mosquito Life Cycle

Many mosquitoes breed in treeholes
Female mosquitoes deposit eggs in “rafts,” or singly, on the surface of still water. Larvae, called “wrigglers,” emerge from the eggs and begin their aquatic lives. They breathe through a spiracle at the end of an elongated tube called a “siphon,” at the tip of the abdomen. Most species are filter-feeders that use their mouthparts to strain food particles and/or microorganisms from the water. A few species are predators of other mosquito larvae.

Larvae grow by molting, shedding their flexible yet constraining exoskeleton periodically. Eventually, they molt into the pupa stage, known as a “tumbler.” The pupa is not inert, but quite active, able to dive when danger threatens by thrashing its abdomen. Tumblers breathe through paired siphons (“trumpets”) on its “shoulders.”

Mosquito Life Cycle, © Eric R. Eaton

The adult mosquito pops out of the top of the pupa, and sits on the water surface while its new, winged body hardens and pigments become evident. Adult mosquitoes are covered in scales that may serve to attract mates, but also allow the insects to skip off spider webs, shedding scales instead of becoming entangled.

Mosquito Diversity
There are 176 species of mosquitoes currently recognized in North America. This includes species introduced from other parts of the world through commerce. A new species, Anopheles grabhamii, was described from the Florida Keys in 2002, so there is certainly potential for future additions to our mosquito fauna through several avenues. Only female mosquitoes bite, and not all species bite mammals. Many feed only on birds, a few on amphibians. Some species don’t bite at all.

Male Culex mosquito

Male Mosquitoes
Male mosquitoes are often easily identified by their plumose (feathery) antennae, which they use in part to find females of the same species. They also frequently have enlarged, brush-like palps, paired appendages that are part of their mouthparts. The palps might be mistaken for antennae themselves. Both male and female mosquitoes fuel their flight muscles with flower nectar which they sip through that needle-like proboscis.

Asian Tiger Mosquito

Asian Tiger Mosquito
One prominent example of an exotic species is the Asian Tiger Mosquito, Aedes albopictus. It was first documented in Texas in 1985. One year later it turned up in Florida, among tires imported from overseas for re-treading. This is probably how it spread, as this is one of the “container-breeding” mosquitoes that needs little water to complete its life cycle. Rainwater collects in discarded tires exposed to the elements, and mosquitoes in general are adept at finding such resources. The Asian Tiger Mosquito is now found over much of the eastern U.S. An outbreak in Los Angeles, California in 2001 was traced to a shipment of “lucky bamboo” from China. The insects were eradicated, but subsequent introductions may not have been so successfully suppressed.

Mosquito vs. Mosquito
Aedes albopictus has largely replaced the Yellow Fever Mosquito, Aedes aegypti here in the U.S. Larvae of the Asian Tiger Mosquito compete better for food, and parasites brought with the Asian Tiger Mosquito have had an adverse impact on A. aegypti. Sterility of offspring from interspecific matings has also affected the Yellow Fever mosquito disproportionally. Today, Aedes aegypti is limited to the southeast U.S., a few isolated areas in New York state, and Arizona.

Yellow Fever Mosquito

Disease Transmission
The success of the Asian Tiger Mosquito is ironically somewhat helpful to us. While A. albopictus is known to be able to transmit over thirty viruses, it is not a very efficient vector. Western and Eastern Equine Encephalitis, St. Louis Encephalitis, LaCrosse Encephalitis, and dengue fever are all serious diseases potentially vectored by the Asian Tiger Mosquito.

Malaria is, thankfully, not currently a problem in North America. This was not always the case. Anopheles quadrimaculatus was the vector of this disease in the U.S. and Canada. Malaria affected most of the United States by 1850. One century later, thanks to improvements in sanitation that reduced breeding spots for mosquitoes, and the widespread use of DDT and other potent pesticides, the disease was largely eradicated.

Female Anopheles mosquito

West Nile Virus is transmitted almost exclusively by mosquitoes in the genus Culex. Birds and horses suffer much more frequently from this disease than people; and there is a vaccination available for equines. The elderly, and those people with compromised immune systems, are most at risk.

Dog Heartworm is also a mosquito-borne disease that occasionally afflicts cats as well. The illness itself is caused by a roundworm that is transmitted by at least sixteen species of mosquito. Risk for Dog Heartworm is greatest along the southern Atlantic and Gulf coasts, and the Mississippi River Valley (Nayar & Rutledge-Connelly, 2012).

The "Gallinipper," Psorophora ciliata, a real giant whose larvae eat other mosquito larvae

Mosquito Control and Prevention
You can do a great deal to reduce your risk of exposure to mosquitoes and the diseases they may carry. Consider taking the following measures and precautions:

• Eliminate standing water on your property by cleaning gutters regularly, storing toys, flowerpots, and other potential rainwater collectors indoors, and draining water wherever else it accumulates.
• Apply insect repellents with DEET as the active ingredient, paying careful attention to the directions on the product.
• Comply with local city and county vector control regulations.
• Maintain swimming pools properly
• Change the water in the birdbath frequently, remembering mosquitoes can complete their life cycle in about a week.
• Sleep under mosquito netting when traveling overseas to locations where malaria, dengue, and yellow fever are still problematic.
• Get your pet checked for, and immunized against, Dog Heartworm.

Mosquitoes have their own pests: this one has mites (red spots)

What good are mosquitoes?
When asked this question, I am sometimes tempted to answer “Ask a Plasmodium (the malaria parasite).” We are naturally anthropocentric in our view of other organisms, especially when we see no direct benefit to us. We do know that mosquito-borne diseases have driven our own evolution. Sickle-cell Disease was an evolutionary response to malaria, the misshapen blood cells being inhospitable to the malaria parasite. What else do we owe to mosquitoes, positive or negative? We have much yet to learn, no doubt. Meanwhile, mosquitoes are a fundamental building block in the food chain, responsible for supporting the enormous diversity of fish, birds, bats, and predatory insects found around the globe. We also don’t know what we might lose with the microbes dependent on mosquitoes for transportation from host to host. The next medical breakthrough might come from studying one of those organisms. Lastly, mosquitoes can be important pollinators of flowers. Both male and female mosquitoes visit blossoms for nectar. Still want to wipe them off the face of the Earth?

Yellow Fever Mosquito sipping nectar

Sources: “Asian Tiger Mosquitoes,” Greater Los Angeles County Vector Control District, 2012.
Rios, Leslie, and James E. Maruniak. 2004. “Asian Tiger Mosquito (EENY-319),” Featured Creatures. University of Florida.
Nayar, Jai K., and C. Roxanne Rutledge-Connelly. 2012. “Mosquito-borne Dog Heartworm Disease,” EDIS. University of Florida.
”Mosquito-borne Diseases,” American Mosquito Control Association, 2011.