Illinois Natural History Survey - University of Illinois

INHS Reports November-December 1998

Mosquito Marauders

Mosquitoes have effectively used man's transportation system to invade new habitats either man-made or natural. An example of a worldwide expansion of a mosquito is the yellow fever mosquito, Aedes aegypti. This mosquito was moved from its African home to the New World in sailing ships and into Asia via the dhow trade primarily into port cities along the Indian Ocean coast. This species spread into the United States from the Gulf Coast as far north as southern Illinois via river and ground transportation. The control of the yellow fever mosquito was critical for the U.S. to build and maintain the Panama Canal. In Illinois Aedes aegypti is still collected in and around Cairo and has been imported into Chicago almost every summer. Luckily this species is not adapted to freezing weather and has not been established in Illinois. Today, the rapid worldwide movement of man, animals, and domestic goods coupled with increasing urbanization into natural areas amplifies the risks of invasion of mosquitoes and mosquito-borne diseases.

The invasion and rapid establishment of the Asian tiger mosquito, Aedes albopictus, highlighted the ever-increasing vulnerability of the United States to unwanted pests. Eggs of this mosquito were carried unknowingly in used tires from Japan to the port of Houston, Texas, and within two summer seasons spread north into Illinois. The immediate concern of both federal and state public health agencies focused on this mosquito's superior ability to transmit both exotic and local microbes that affect the health of man and animals. The Asian tiger mosquito can transmit 26 viruses that cause disease in man as well as the worm responsible for dog heartworm, a major problem in every county in Illinois for canines. This mosquito is a continuing challenge to agencies mandated to protect the public from nuisance and public health mosquito pests. The Asian tiger mosquito differs in both its ecology and behavior from other Illinois species because the immature stages prefer artificial containers (e.g., tires, cans, birdbaths, tree holes) and the adult is active during the day. It is definitely a mosquito adapted to exploit man-made habitats and its global dispersal is intimately linked with domestic goods, especially used tires.

The Asian tiger mosquito, Aedes albopictus.

The Asian tiger mosquito was not the only new mosquito in recent years to invade and expand in numbers in Illinois. Used tires were also used by the rockpool mosquito, Aedes atropalpus, another container-inhabiting mosquito to expand throughout the state. Recently, Culiseta impatiens was found for the first time in Illinois. Fortunately both of these species have not been associated with the transmission of pathogens affecting man or animals.

Natural catastrophes can also play an important role in expanding the distribution of mosquitoes. During the flood of 1993, Culex tarsalis, the primary transmitter of western equine and St. Louis encephalitis viruses in the western U.S., was collected in large numbers along the Mississippi and Illinois rivers. Before this natural event, this species was rarely found, and then only in very small isolated pockets. The expansion and establishment of this species could change the transmission cycle of St. Louis encephalitis virus in Illinois as well as provide for the emergence of western equine encephalitis east of the Mississippi River.

Mosquitoes, because of their blood-feeding behavior, are generally considered by both the lay population and scientific community as threats to either our public health or quality of life. However, the ecological roles that mosquitoes play both in aquatic and terrestrial environments are an important challenge for the Illinois Natural History Survey's Medical Entomology Program. This is especially important when a new species invades and becomes established in Illinois. Numerous questions need to be answered, such as Is this new species replacing a native, and if so how does this affect the intricacies and subtleties of the habitat? Mosquitoes in their aquatic stages, for example, help break down plant detritus and are sources of food for a variety of aquatic animals. In the adult stages mosquitoes help in pollination and are sources of food for a number of predators, and since mosquitoes transmit numerous pathogens that affect wild animals they could play a significant role in the process of natural regulation.

The invasion of exotic mosquitoes from foreign lands as well as the expansion of North American species into Illinois establishes the scientific need to address both the public health and ecological questions associated with this large insect group. Whenever a new species becomes established the natural history of the area will change. It is critical to understand and perhaps forecast whether the invader is beneficial or destructive. The basic biology of the invasive species must be evaluated in the context of its habitat or ecosystem before steps are taken toward managing populations or eradicating them. Invasive mosquito species must be evaluated in regards to their threat to public health and to domestic animals and wildlife, as well as short- and long-term ecological considerations.

Robert Novak, Center for Economic Entomology

Charlie Warwick, editor