Mosquito and Diseases

Mosquitoes and Disease

Life Cycle in the Mosquito

Mosquitoes are insects with long slender bodies, narrow wings with a fringe of scales on the edge of the wing and along the veins, and long, thin legs. The females have firm mouthparts, usually well-adapted for piercing skin and sucking blood. The males cannot suck blood but both sexes feed on nectar of various plants. Mosquitoes are small insects with piercing-sucking mouthparts, and scales on their wings. Female mosquitoes suck blood but do not always need blood to lay the first batch of eggs.

Life Cycle of a Mosquito

The life cycle of a mosquito consists of four stages: egg, larva, pupa, and adult. The eggs may be laid singly or in rafts, deposited in water, on the sides of containers where water will soon cover, or on damp soil where they can hatch when flooded by rainwater or high tides. Common breeding sites for mosquitoes are drainage ditches, ponds, tin cans, old tires and tree holes. The eggs of some flood-water and salt-marsh mosquitoes may dry out for more than a year and still hatch when flooded. The eggs of most specie hatch in 2 to 3 days, and the larvae or "wigglers" feed in the water on organic matter. The larvae pass through 4 stages in about 7 to 10 days. The pupal stage lasts 2 to 3 days, and the adult emerges from the pupal skin at the water surface.

Mosquitoes can be an annoying, serious problem in man's domain. They interfere with work and spoil hours of leisure time. Their attacks on farm animals can cause loss of weight and decreased milk production. Some mosquitoes are capable of transmitting diseases such as malaria, yellow fever and dengue to man, encephalitis to man and horses, and heartworm to dogs.

Mosquito larvae

Regardless of the mosquito species, water is essential for breeding. Mosquito larvae are not adapted to life in moving waters. The larvae normally occur in quiet water. Since nearly half the total land area of Florida is subject to flooding, mosquitoes breed in large numbers throughout the state. Contrary to popular opinion, mosquitoes do not breed in the heavy undergrowth of weeds, bushes, or shrubs. Although these places provide excellent refuge for adults, they do not provide a suitable habitat for mosquito larvae.

The elongated eggs, about 1/40 inch long, are laid in batches of 50 to 200 and one female may lay several batches. In warm water, the eggs of most species hatch in two or three days. Some eggs require a drying period, remaining dormant for months, they hatch soon after water contacts them.

The larvae or "wigglers" feed on tiny bits of organic matter in the water. Many species breathe air through an elongated air tube which they extend through the water surface. Larvae change into comma-shaped pupae, often called tumblers, in about a week.

The pupae transform into adults in about two days. Male mosquitoes feed on nectar of flowers and do not bite. Female mosquitoes also feed on nectar; however, a blood meal is usually necessary to mature the eggs.

Mosquitoes show considerable variation in their preferred hosts. Some species feed on cattle, horses, or other domestic animals while others prefer man. A few species feed only on cold-blooded animals and some live entirely on nectar or plant juices. Some are active at night and others only during the daytime.

Mosquito Control

Mosquitoes and Stormwater Management

Illinois Natural History Survey

Microbial Larvicides in Mosquito Control

Mosquito identification

B. Debrunner-Vossbrinck, C. Vossbrinck, A. Zvilius, M. Vodkin, R. Novak

The primary vectors of St. Louis encephalitis virus are mosquitoes in the subgenus Culex. Adult females in this mosquito complex cannot be identified using "traditional" morphological techniques. We have developed an identification system using ribosomal DNA for species identification. A specific variable region of the mosquito's r-DNA is used to identify species and subspecies of the Culex complex. Using this method, a single mosquito leg is all that is needed for identification. This preserves the rest of the specimen for virus isolation, a voucher specimen, or any other required uses.

Biology of a predatory mosquito

H. Lee, E. Ontiveros, R. Novak

Mosquito larvae in the genus Toxorhynchites are predacious on other mosquito larvae. The adults in this genus feed on plant nectars and do not require a blood meal as do other mosquito species. The nutritional needs of Toxorhynchites larvae are therefore quite different than other mosquito species. The purpose of this investigation is to examine the influence of larval food (prey) on development and on the reproductive capabilities of adults. Results from this study will help to characterize this species and evaluate its use as a biological agent in artificial containers, such as used tires.

Mosquitoes and waste tires

R. Lampman, S. Hanson, R. Novak

Ten species of mosquitoes were collected in tires at a waste-tire site in Jasper County. The most abundant species, relative to the total number of larvae collected, were Culex pipiens and Cx. restuans. The most prevalent species were Aedes albopictus (70% of all tires) and Cx. pipiens (58% of all tires). Other species that were collected include Aedes atropalpus, Ae. triseriatus, Cx. salinarius, Cx. territans, Orthopodomyia spp., Anopheles punctipennis, and An. barberi. Since this used-tire site is adjacent to a tree-lined stream, investigations on the dispersal of Ae. albopictus are currently being studied.

Mosquito oviposition attractants

R. Lampman, R. Novak

The rapid dispersal and establishment of Aedes albopictus in Illinois, primarily in used tires, has serious public health implications. This species is a potential vector of numerous human and animal pathogens. This investigation focuses on monitoring gravid (egg bearing) adult females using oviposition attractants. Laboratory preference tests showed that these females preferred infusions of grass sod over pure water for oviposition. Olfactometer tests revealed that both males and nongravid females respond to volatiles from the sod infusion. This chemical ecology research may result in the development of effective tools for both mosquito surveillance and control.

Mosquito oviposition sites

R. Lampman, R. Novak

Many Culex species of mosquitoes prefer to oviposit in organically polluted or eutrophic aquatic sites. Oviposition traps and gravid traps mimic these natural oviposition sites through the use of crude infusion lures. Unfortunately, variability in number of mosquitoes per trap could represent either changes in actual density or microbial changes in the infusions. This investigation focuses on identifying methods that standardize the attractants by understanding biological activity. The major volatile components, bacteria species, and specific chemicals found in active infusions are currently being field tested.

Mosquitoes and storm drain tunnels

R. Lampman, S. Hanson, K. McClellan,
R. Novak

Drainage tunnels in Urbana and Champaign are being surveyed for the presence of overwintering mosquitoes. In the initial study, a 1.4 km drainage tunnel in Champaign was monitored monthly during 1994. The number of mosquitoes and their locations in the tunnel were recorded twice a month. This underground site and the data gained from this study will provide baseline data for a long-term study on the overwintering biology of Culex pipiens and Cx. restuans. Anecdotal evidence from city and utility personnel indicate that they frequently encounter large numbers of mosquitoes when servicing storm tunnels.

Mosquito feeding preferences

R. Lampman, R. Novak, N. Krasavin

A preliminary study was undertaken to determine whether a colony of Culex pipiens could be maintained on human blood as the sole source of protein for eggs. Mosquitoes that had been feeding for a year using quail as the primary blood source were allowed to feed only on human blood. Little is known about the proclivity of Culex pipiens to feed on mammals. However, a shift in feeding behavior from birds to mammals is a critical event in the successful transmission of St. Louis encephalitis virus.

Spore-forming bacteria in mosquito habitats

J. Siegel, R. Novak, J. Maddox

As part of a continuing project to identify mosquito pathogens in waste-tire dumps, water and soil samples were collected from tire dumps throughout Illinois. Spore-forming bacteria were cultured from the samples and identified by a variety of techniques including gas liquid chromatography. A catalog of species is being compiled that will provide important baseline information on potential food sources for mosquitoes.

Identification of microbial insecticides

J. Siegel, A. Smith, J. Maddox, R. Novak

Cellular fatty acid profiles have been created for microbial insecticides used in mosquito vector control. Additional work is being conducted to create similar profiles for microbial insecticides used in agriculture that also have some mosquito activity. These profiles are an essential tool for evaluating whether indigenous bacteria with mosquito activity can in fact be commercially produced. This technique will enable Survey researchers to quantify the persistence of commercial microbial insecticides in tires and in other areas where they are applied.

Protozoan pathogens of mosquitoes

J. Siegel, R. Novak

Research is being conducted on the protozoan pathogen Ascogregarina barretti. It is native to Illinois and infects the eastern treehole mosquito, Aedes triseriatus. We are interested in the impact that this pathogen may have on competition between Aedes triseriatus and the Asian tiger mosquito, Aedes albopictus. Our current emphasis is on growing suitable numbers of Ascogregarina barretti in order to infect mosquitoes in the laboratory.

Mosquito vector potential

J. Siegel, R. Novak

Historically, wing length has been an important predictor of blood-feeding success and longevity of female mosquitoes. A series of experiments to quantify nutritional and crowding factors that influence wing length is under way. This information will be used in turn to evaluate mosquitoes collected from waste-tire dumps. Researchers hope to compile an index so that tire dumps can be prioritized for cleanup.

Impact of tire removal on mosquitoes

J. Siegel, R. Novak

Preliminary surveys have been conducted to collect baseline data on the vector mosquito species present in a large tire dump prior to cleanup. Collections will then be made several times each summer to determine if the number of species declines or their percent abundance changes as the tire dump is shredded. We anticipate studying several dumps of varying size in the state in order to quantify the effect of cleanup.

A survey of mosquito larvae in urban areas

S. Hanson, R. Novak, R. Lampman, M. Vodkin, W. Ruesink

A method of surveying urban land-use zones for mosquito larvae and their habitats, especially used tires, was developed and tested. A preliminary survey was conducted in Champaign and Urbana during the summer of 1994. Habitats were classified as ground water, tree holes, tires, catch basins, or other artificial containers. A total of 3,620 larvae were collected of which 51% were Culex restuans, 26% were Orthopodomyia signifera, and 19% were Culex pipiens. The remaining 4% included Anopheles barberi, Aedes triseriatus, Culex salinarius, Culex territans, and Orthopodomyia alba.

Mosquito cold hardiness

S. Hanson, R. Novak

Currently, Aedes albopictus suffers considerable mortality in northern Illinois during the winter. However, is it possible that this mosquito could adapt to the severe Illinois winters. The objective of this investigation is to determine the ability of Ae. albopictus to adapt to repeated genetic selection for cold hardiness under laboratory conditions. The results of this study will help indicate whether Ae. albopictus can become better adapted to the northern Illinois climate, thus increasing both its distribution and numbers.

Hibernation of mosquito hybrids

S. Hanson, R. Novak

Culex pipiens pipiens and Culex pipiens quinquefasciatus both occur in Illinois. In many areas in southern Illinois, these subspecies occur in the same place and produce a large hybrid population. In the fall, shorter days cause adult female Culex pipiens pipiens to hibernate while Culex pipiens quinquefasciatus does not hibernate. However, it is unknown if the hybrids can hibernate. Determining the hibernation capabilities of these two types of mosquitoes may lead to possible control methods.

Winter survival of mosquito eggs

S. Hanson, R. Novak

The ability of Aedes albopictus eggs to survive the winter in Illinois and elsewhere in the United States is poorly understood. An ongoing investigation is comparing winter egg survival in tires in Chicago, Kankakee, Green Bay, Milwaukee, and Saginaw. The temperature of the eggs was monitored throughout the winter in order to determine critical limits for survival. During the winters of 1993-1994 and 1994-1995, the only eggs to survive were those located in Chicago, while 2% of the eggs survived the winter of 1993-1994 and 9% of the eggs survived the winter of 1994-1995.

Mosquito overwintering physiology

K. McClellan, R. Novak

Culex pipiens and Culex restuans mosquitoes overwinter as inseminated adult females. Successful overwintering depends on the development of reproductive diapause in response to short photoperiods, cessation of blood-feeding, hypertrophy of the fat body, and development of cold hardiness. Hypertrophy of the fat body and cold hardiness in these females result in changing lipid composition during an overwintering period. This project is investigating lipid composition changes during the winter and how these changes relate to mosquito survival.

The Asian tiger mosquito in Illinois

R. Novak

This is an ongoing study made up of two components: (1) direct surveillance at specific sites in Illinois, and (2) investigations based on direct requests from agencies, municipalities, and the public. Direct surveillance and monitoring movement of the Asian tiger mosquito has been ongoing in Chicago and in Cook, Kankakee, Peoria, Tazewell, Champaign, St. Clair, Madison, and Pulaski counties. These surveillance investigations provide current information on the spread of the Asian tiger mosquito in Illinois in order to develop health risk assessments of tire piles.

Studies of mosquito population dynamics

R. Novak, L. Szymczak, R. Cieslik, C. Etchison

The purpose of these investigations is to gather field information on mosquito distribution, density, and population dynamics. The mosquitoes of primary concern are the vectors species Culex pipiens and Cx. restuans (St. Louis encephalitis virus), Aedes triseriatus (La Crosse virus), and Ae. albopictus, which was recently introduced into the U.S. in used- tire casings and can transmit several local and exotic pathogens. These bionomic studies will include detailed temporal and spatial investigations of the egg, larvae, and adult stages and the pathogens they transmit.

St. Louis encephalitis virus surveillance

M. Vodkin, R. Novak, M. Koll, R. Cieslik (Chicago Department of Health), L. Szymczak (Chicago State University)

The weekly deposition of Culex mosquito egg rafts, the prevalence of St. Louis encephalitis (SLE) virus-specific antibodies in feral birds, and the prevalence of virus in mosquito pools were monitored in 1993. A total of 4,623 egg rafts were collected, representing a twofold increase from 1992. Virtually all of the early-summer egg rafts were Culex restuans. After mid-July, Culex pipiens eggs accounted for 20-70% of the total rafts collected. The prevalence for SLE viral antibodies (avian) and RNA (mosquitoes) were 0.2% and 0.02%, respectively. Both values were about 25-fold lower than during epidemic years. Surveillance will continue during 1995.

Detecting St. Louis encephalitis virus

M. Vodkin, J. Siegel, R. Novak, S. Nawrocki, Y. Randle (Harris County Mosquito Control District)

A reverse transcriptase-polymerase chain reaction assay (RT-PCR) was compared with two other commonly used methods, tissue culture assay (TC) and enzyme-linked immunoabsorbent assay (EIA), to detect St. Louis encephalitis virus. A large number of samples with a low viral prevalence was tested. Because of speed, accuracy, and cost, either the RT-PCR or the EIA can be used as the primary screen. As the sole assay, RT-PCR has an advantage over EIA because the amplified product contains sequence information that can confirm its identity.

Flood-induced stress on urban trees

J. Lloyd, F. Miller, P. Weicherding

Research to examine the immediate and long-term effects of the 1993 flood on urban trees was initiated in the fall of that year as a collaborative effort among scientists at the Illinois Natural History Survey, University of Illinois, Western Illinois University, and the University of Northern Iowa with cooperation from the U.S. Army Corps of Engineers and the city of Davenport, Iowa, and other flood-affected communities. Our foremost objective is to determine the "urban" tree species most susceptible to prolonged late-season flooding. Secondarily, we are interested in determining the cause of mortality (insects, disease, etc.) in years following the flood.

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