Alabama Vector Management Society

3 mosquitoes
 

Three Import-ant Mosquitoes to Know:

Aedes aegypti, Aedes albopictus and Ochlerotatus japonicus

          All mosquitoes look alike, right?  This may seem true if it’s dusk and you’re examining specimens which you’ve just slapped against your ankle.  However, if you ever take a really close look (maybe under a microscope or with a magnifying glass) you’ll see that mosquitoes can vary greatly.  In fact the usual way of telling one species from another is by examining the various bands, stripes, and spots that adorn their bodies.   Most people who work with mosquitoes acknowledge the importance of knowing which species are around you (or on you).  For instance, if you’re working in abatement then knowing whether the mosquito that’s biting your customer is a container-breeder versus a marsh-breeder could save you more than a few dollars on larvicide. 

         In Alabama there are about 60 different species of mosquitoes to contend with.  These range from the beneficial “cannibal mosquito” Toxorhynchites rutilus, which as a larva preys upon other mosquito larvae, to the infamous “Asian tiger mosquito” Aedes albopictus, a mosquito of major medical importance.  As common and ubiquitous as this menace is throughout Alabama, it’s a rather recent arrival to our state.  It was introduced to Texas in 1985 in a shipment of used automobile tires.  Since then it has spread throughout the Southeast.  It’s not the only import mosquito in Alabama, however.  Aedes aegypti, the “yellow-fever mosquito” was introduced from the Old world in the days of European colonization of North America.  It most likely arrived to our land as larvae in water cisterns aboard slave ships from Africa.  Another very recent immigrant mosquito is Ochlerotatus japonicus, the Japanese encephalitis mosquito.  In June of this year TVA medical entomologist, Kristy Gottfried, reported the arrival of this mosquito in northern Alabama.  It is native to the Orient and entered the US via New York. 

         So what else do these 3 species of imported mosquitoes have in common?  They are all vectors of deadly viruses (at least in some part of the world), they are all container-breeders, and they all look somewhat similar: black and white/silver mosquitoes each with striking dark and light stripes over much of their bodies.  Luckily these 3 mosquito species differ enough in body ornamentation to tell them apart.  The dorsal portion of the insect thorax is known as the scutum, and patterns on the scutum are often characteristic of a particular species.  The figures below illustrate the different patterns on the scutum of each of the 3 species discussed above, as well as Ochlerotatus triseriatus, a native container-breeding mosquito with comparable color patterns.

Aedes aegypti is generally described as having a pattern on its scutum in the shape of a lyre, or harp, a musical instrument used by the ancient Greeks (Figure 1).  This lyre-shaped pattern consists of 2 white stripes to either side of the midline which are partially surrounded by                                                                                                                                               Figure 1. A lyre

another wider white stripe (Figure 2A). 

                                  

                            Aedes aegypti                      Ochlerotatus japonicus

 

Figure 2.  Thoracic patterns of Aedes aegypti and Ochlerotatus japonicus

        

         Of the other 3 species discussed here, Ochlerotatus japonicus has markings which are most similar to those of Aedes aegypti.  Ochlerotatus japonicus, however, has a wide yellowish-white stripe down the middle of its scutum with 2 light stripes to either side (Figure 2B).  Like Aedes aegypti, these stripes are partially surrounded by another wider light-colored stripe.

         Aedes albopictus has a single broad white stripe down the middle of its scutum making this species stand out from the others (Figure 3A).  In contrast, Ochlerotatus triseriatus has pale silvery-white stripes along the lateral margins of its scutum with a broad dark stripe down the middle (Figure 3B). 

 

                                 

                      Aedes albopictus                         Ochlerotatus triseriatus

 

Figure 3.  Thoracic patterns of Aedes albopictus and Ochlerotatus triseriatus

 

While these mosquitoes seem to color-coordinate their attire, they don’t exactly match in every respect.  For example, Ochlerotatus triseriatus has solid black legs whereas the other 3 species have legs with black and white bands.  However, the real important difference between these mosquitoes (as far as we are concerned) is in the viruses they can transmit. 

 

 

Ochlerotatus japonicus is the major vector of Japanese Encephalitis virus in its native range, but a lot of concern has been expressed by health officials in the potential that it may have to transmit other viruses to humans, such as West Nile virus.  Ochlerotatus triseriatus is the primary vector of La Crosse Encephalitis virus in the Midwest.  Both Aedes albopictus and Aedes aegypti are vectors of viruses causing yellow fever and dengue in the tropics.  Each year cases of these diseases are diagnosed on U.S. soil, usually in travelers and immigrants.  In addition, Aedes albopictus has been shown to transmit more than 20 viruses, including West Nile virus, in laboratory experiments.

Knowing which mosquito foe you are fighting is important, so keep an eye out for these black and white biters and see if you can tell the difference between them.

 

Nathan Burkett

Auburn University

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2008 Alabama Vector Management Society
Last modified: 12/24/09