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BIOLOGY, DISEASE RELATIONSHIPS, AND CONTROL OF Aedes albopictus

Jose G. Estrada-Franco, Ph.D. Department of Entomology University of Maryland College Park,'Maryland, U.S.A. and George B. Craig, Jr., Ph.D. Vector Biology Laboratory Department of Biological Sciences University of Notre Dame Notre Dame, Indiana, U.S.A.

Technical Paper No. 42

PAN AMERICAN HEALTH ORGANIZATION Pan American Sanitary Bureau, Regional Office of the WORLD HEALTH ORGANIZATION 525 Twenty-third Street, N.W. Washington, D.C. 20037 PAJrIO Library Cataloguing in Publication Data

Estrada-Franco, Jos6 G. Biology, disease relationships, and control olAcdes albopictus Jose G. Estrada-Franco, Ph.D., and George B. Craig, Jr., Ph.D. Washington, D.C. PAITO, (C)1995 v, 49 p. (Technical Paper 42)

ISBN 92 75 13042

I. Title IT. (Series) Til. Craig, George B. 1. AEDES 2. ARBOVIRUS INFECTIONS 3. MOSQUITO CONTROL-methods NI-M 0X525

ISBN 92 75 13042

The Pan American Health Organization welcomes requests for permission reproduce translate its publications, in part in full. Applicalions and inquiries should be addressed the Publications Program, Pan American Health Organization, Washington, D.C., which will be glad provide the latest information any changes made to the text, plans for editions, and reprints and translations already available.

(C) Pan American Health Organization 1995

Publications of the Pan American Health Organisation enjoy copyright protection in accordance with the provisions of Protocol of the Universal Copyright Convention. All rights reserved. The designations employed and the presentation of the material in this publication do impiv (he expression of any opinion whatsoever the pan of the Secretariat of the Pan American Health Organ- ization concerning the legal of any country, territory, city, of its authorities, concerning the delimitation of its frontiers boundaries. The mention of spccilic companies of certain manufacturers' products does imply that they endorsed recommended by the Pan American Health Organization in preference others of similar that mentioned. Errors and omissions exccpicd, the of proprietary products distinguished by initial capital tellers. CONTENTS

Page PREFACE INTRODUCTION PIIYLOGENETIC RELATIONSHIPS AND GEOGRAPHICAL DISTRIBUTION BIOLOGY 2 Eggs...... 5 Egg Diapausc, Photoperiod, and Adaptations 6 Egg Cold Hardiness 7 Egg Morphology 8 Larvae 8 Larval Seasonal Prevalence 10 Larval Morphology 10 Larval Habitat...... 10 Larval Pathogens and Predators 16 Pupae 18 Adults 18 Longevity...... 18 Mating Characteristics 19 Oviposition 20 Host Preference 22 Biting Behavior...... 22 Plight Range 23 Resting Behavior...... 23 Adult Morphology 23 Competition Studies 23 DISEASE RELATIONSHIPS 27 General Information Arboviral Diseases 28 Arbovirus Field Isolations in the Americas 28 Eastern Equine Encephalitis (EEE) 28 Potosi (POT)...... 30 Tcnsaw (TEN) and Keystone (KEY)...... 30 Laboratory Vector Competence Studies of Some Important Arboviruses from the Americas 31 Dengue (DEN)...... 31 Yellow Fever (YF) 31 Venezuelan Equine Encephalitis (VEE)...... 32 La Crosse (LAC) 32 Mayaro (MAY) and Oropouche (ORO)...... 33 Arboviruses Common in Areas Outside the Amcricas 34 Japanese Encephalitis (JE)...... 34 Sindbis (SIN)...... 34 Chikungunya (CHIK) 34 Ross River (RR) 34 Transovarial Transmission 35 Other Arboviral Studies 35 Protozoan and Filarial Diseases 35 Filarial Worms 35 Avian Malarias 35 DISSEMINATION AND CONTROL 35 Mode of Dissemination and Origin...... 35 Control 37 Chemical Control 37 Biological Control...... 38 Environmental Control 39 Health Education...... 39 Legal Measures 39 Integrated Control 40 CONCLUSIONS 40 ACKNOWLEDGMENTS 41 REFERENCES...... 41 PREFACE

The first version of this document, titled "Ecology, Biology, and Control of Aedes albopictus (Skuse)," was prepared in January 1987 to provide scientific and technical background for the "Plan of Action onArdes albopictus in the Ameri- cas." It discussed at the 99th Meeting of the Executive Committee of the Pan American Health Organization (PAHO), held in Washington, D.C., in June 1987 (PAHO Document CE99/15, 1987). The document produced by the Communic- able Diseases Program under the coordination of Dr. F. J. Lopez-Antunano and joint effort of Dr. Jose G. Estrada-Franco, PAHO Temporary Adviser; Dr. George B. Craig, Biology Department, University of Notre Dame; and Drs. Fran- cisco Pinhciro, Bruce Knudsen, and Michael Nelson of PAHO/WHO. Since the 1987 version produced, three excellent reviews the biology, genetics, and disease relationships of Aedes albopictus have appeared, in addition to plethora of scientific articles the species (Hawley, 1988; Rai, 1991; Mitchell, 1991). This second version is presented in order to include important information about this mosquito species that has been brought to light during the past five years by series of studies and research projects conducted primarily in the United States of America. The findings of these studies provide insight into what could be- of the important arthropod vectors of human diseases and in the American Region. This document is published in the hope that it will be of value to health agencies in the Americas that concerned with vector surveillance and control. INTRODUCTION The intent of this document is to bring together the in- formation available to date the biology, disease relation- Until the early 1980s Aedes alhopicius assumed to ships, and control ofAc. albopicliis. The Asian information, solely inhabit certain islands of the Indian Ocean, various summarized in 1987 document, is supplemented by the countries in the oriental region of Asia, and the Hawaiian findings of studies conducted mainly in the United States, Islands in the Pacific Ocean (Huang, 1972). In the mid- with emphasis data generated in the 1990s. 1980s, however, this picture underwent sudden and alarming shift. In August 1985 Ae. alhopictus mosquitoes discov- PHYLOGENETIC RELATIONSHIPS AND ered breeding in lire dumps in Harris County, in and around GEOGRAPHICAL DISTRIBUTION Houston, Texas. The Houston Ae. (ilbopictus population represented the first established infestation in the reported Aedes albopicliis first described by Skuse in 1894 Western for Disease Control and Pre- Hemisphere (Centers from specimens collected in the city of Calcutta the In- vention 1986a; Monath, 1986; and [CDC], Sprengcr dian subcontinent (Barraud, 1928). Phylogcnetically, the To Ac. has been Wuithiranyagool, 1986). date, albopictus species has been placed in the order Diptcra, suborder Ne- from other states in the United States of America reported 22 matocera, family Culicidae, genus Ac'dc's, subgenus Stego- it has moved the northernmost thus far northward, point myia. group sculcllaris, and subgroup albopictus (Iluang, at 42 being Chicago, located about latitude (D. Gubler, pcrs. 1972; Rai ct al., 1982). comm., 1993). The southward movement of Ae. alhopictus It is believed that Ac. ulboplctiis originated in the tropical in the United States has reached the city of Brownsville, forest of Southeast Asia. where many closely related spe- Texas, located at 2554.3' latitude (Womack, 1993). cies known to coexist (Smith, 1956). This is also Elsewhere in the Americas, Ac. albopictu', first considered to be the place where classical dengue had its ported in Brazil in June 1986 in the states of Espirito Santo. origin. Another medically important Stegomyia, Aedes Minas Gerais, Rio de Janeiro, and Sao Paulo (Forattini, gypli, is thought to have been introduced into Asia from 1986; Parigot, 1986). By April 1994 the species had been Africa (Mattingly, 1957). These two species the most reported in three stales-Maranhao (San Luis de Mar- important vectors of dengue in Southeast Asia (Smith. anhao) and Bahia and Parana (several locations)-for to- 1956; Pant et al., 1973; Chan, 1985). In Asia, Ac. ulbo- tal of 673 infested municipalities (J. C. Mangabeira da piclus far north Bcijing, China, at 40 latitude Suva, pcrs. comm., 1994). The extent of Brazil's Ae. al- (World Health Organization fWHOJ, 1980). It is also dis- bopiclns infestation prompted panel of experts, meeting tributed in the Korean peninsula and in Japan to northern at PAHO Headquarters in 1986, to hypothesize that the spe- Honshu, Japan's main island, reaching the city of Sendai cies first introduced into the country years ago at 36 N (Kamimura, 1968; Hong ct al., 1971). Beijing and (PAHO, 1987; CDC, )986b). Chicago, Illinois (at about 42 north latitude in the United Furthermore, the third and fourth countries with estab- States), the northernmost reported distribution points of lished infestations have recently been identified: the Do- Ac. albopictus in the Palcarctic and Nearclic regions, minican Republic, where the mosquitoes have been found respectively. mainly in parkland of the capital city of Santo In Southeast Asia the species has extended its range to Domingo (C. Pena, National Malaria Program, pers. comm., the coastal cities of Irian Jaya, the Solomon and Santa Cruz June 1993), and Mexico, with infestations in towns along the Islands, and Papua New Guinea; it has also been found in U.S.-Mexico border in the slates of Coahuila and Tamauli- Brisbane and Darwin, Australia, where the infestations pas (C. Castancda-Barron, Tamaulipas State Health Services, promptly eradicated (Elliot, 1980; D. Gubler, pers. pers. comm., 1992; C. Moore, pers. comm., 1993). The spe- comm., 1993), and recently in New Zealand (Kay ct al., cies has also been reported in continental Africa and Europe 1990; Craig, 1993). It has been reported in the Mariana, (Savage et al., 1992; Sabatani et al., 1990). Caroline, and Hawaiian Islands, Palau, the Asian continent, The potential threat posed by the presence in the Ajner- and westward to several islands in the Indian Ocean such icas of this exotic and efficient vector species of dengue Madagascar, Mauritius, Reunion, the Seychelles, and the and possibly yellow fever and other arboviruscs has gen- Chagos Archipelago (Surtees, 1966; I-ambrccht and Van erated great among the countries (PAHO, 1987). Somcren, 1971; Ho el a)., 1972). In addition, the species has recently been found in Europe (Albania and Italy) and buildings. By contrast, in urbanized sections of the in mainland Africa (coastal South Africa and various vil- city, Ae. aegypti appears to remain the dominant species lages in Nigeria) (Sabatani et al., 1990; Savage et al., 1992; (New Orleans Mosquito Control Board [NOMCBj/ 1987). Craig, 1993; references in Hanson and Craig, 1994). The tendency of Ac. albopiclus to inhabit natural containers Also. noted above, Aedes albopicliis has recently colo- (tree holes and bromcliads) in places where vegetation is nized portions of four countries of the Americas. It has been abundant has also been observed in several other of found in midwestern and southern states in the United Stales. the United States and Brazil (O'Mcura et al., 1992; Gomes three towns in northern Mexico along the border with Texas, et al., 1992). As in Asia, American Ae. albopiclus have states in Braxil, and parts of the city of Santo Domingo shown much greater propensity for using natural contain- in the Dominican Republic (Moore et al., 1988; Mangabeira than have Ae, aegypli. da SUva, pers. comm., 1994; Moore, pers. comm., 1994). The species is known to all continents except Australia and Antarctica. Map summarizes the worldwide BIOLOGY distribution of Ac. albopicliis. Maps 2 and illustrate its distribution in three countries of the Americas. In the United States, the duration of the larva-to-adult In terms of altitude, Aedes alhopictus has been found up phase of the life cycle of Ae. albopiclus in tires esti- to 1,800 meters in the mountains of Thailand (Scankm and mated by comparing the population density of early instar Esah. 1965). Pant and co-workers (1973) reported the pres- larvae with that of emerging aduits. Studies conducted dur- of Ac. alhopiclus in Thai village located at 1,700 ing the spring of 1989 in New Orleans (average ambient meters. Both studies noted finding the species at every al- temperature of about 26 C) with field populations of Ae. titude surveyed, from level to the highest. Ho el al. albopictus established that the average time period between (1972) reported maximum altitudes for Ac', albopictus of 24 peak abundance of first instar larvae and peak abun- to ISO meters in West Pakistan, Sri Lanka, Taiwan, and dance of emerging adults about 10 days (NOMCB, Malaya, but this study appears to underestimate the 1989). Under natural conditions in Viet Nam, eggs ot'AAedes aegypti overlap in the urban environment Krishnamoorthy (1982) determined that at tempera- (Harrison ct al., 1972; Azzizar, 1980; Chan, 1985), Ac. al- ture (26 C to 30 C) development from egg to adult of hopictus is commonly found in suburban and rural female Ae, albopictus ranged from 11 to 12.4 days, whereas where open, vegetated spaces prevalent (Ho et al., males reached the adult stage in 10 to 11.4 days. The op- 1972; Pant et al., 1973; Chan, 1985). It is generally timal water temperature for Ac', alhopictus development has cepted that Ae. albopictus originally sylvan species, been reported to be 25 C. At this temperature the egg in- breeding and feeding in forest fringes, which began to adapt cubation period is two days (Sheng and Wu, 1953; Ho et to the domestic environment throughout several parts of its al., 1972). geographical range (Bonnet and Worchester, 1946; La In addition to temperature, food supply also affects the Casse and Yamaguti, 1950; Surtccs, 1970; Miyagi et a!., size and development time of the Ae. albopiclus larvae. 1983). In the United States, studies based ovitrap col- Larvae placed in contaminated water with high organic lections carried out in New Orleans, Louisiana, in 1987 tent found to develop rapidly, while starvation and showed that Ae. albopictus the most abundant species in suburban environments. These habitats characterized by open with plentiful vegetation, surrounded by 'Address: 6601 Lakcshore Drive, New Orleans, LA7012A.

<;?-' ^H by county andPledrasNegras, Coatiuila, Matamoros.Tamaulipas, Data from: Dr. Chester Moore, Division of Vector-Borne Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado; C. Castanedo-Barron, Tamaulipas State Health Services, and S. Ibanez-Bernal. Map 2. Aedes alhopicfus-infestcd areas in the United States of America and northern Mexico, as of December 1994

-ESPl'RITO

Saude, Saude, Brazil,

Map 3. Aedes albopictus-'mfested areas in Brazil, by state, April 1994 overcrowding retarded development and increased mortal- fore they exposed to dry conditions. Gubler (i970a) ity under laboratory and field conditions (Mod, 1979). In found that Ac. allwpictus eggs highly resistant to dry general, the duration of the larval stage extended by conditions if they kept in humid conditions for four decreasing the food supply and shortened by increasing it. days before being exposed to drought. The study At 0.035 mg tbod/larva/ml, the development time corded maximum egg longevity of 243 days at 25 C and from egg hatching to adult 6.1 days. while at 0.004 relative humidity of 70%-75%. In another laboratory rog/larva/ml, the duration 32.4 days (Chan, 1971). periment Hien (1975b) showed that eggs kept wet cotton Variables known to affect the life cycle of any mosquito wool for four days and then exposed to 25-26 C air at 60%- species include food, photoperiod, relative humidity, and 70% relative humidity highly resistant to dryness. After temperature. Significant information how these factors two months under these conditions of exposure, 94.7% of affect each developmental stage is summarized below. the eggs with conditioned embryos produced larvae. Maxi- mal resistance to desiccation has been observed when eggs exposed to humidity for at least 24 hours, whereas Eggs partial total mortality has been recorded when eggs less than 16 hours old dried (references in Hawley. 1988). Mosquito eggs (including those of Aedes spp.) not A density-dependent factor that appears to play im- fertilized until the moment before they actually laid. portant role in the survival of Ae. alhopictus eggs is pre- Sperm stored in the spermatheca enters each fully developed dation. Gubler (1971a) found that the egg mortality of egg (oocyte) it passes the opening of the spermathecal natural population of Ae. alhopictus from Calcutta, India, duct its way out. Once the eggs have been laid, kary- greater than 50% during the first 24 hours, primarily ogamy and development of the embryos proceeds. result of predation by ants. A study conducted in New Embryonic development may be defined the develop- Orleans, Louisiana, in 1989 examined the survivorship of mental changes taking place in the egg between fertilization Ae. albopictus eggs in tires (NOMCB. 1989). Eggs for and hatching (Christophers, 1960). The length of the period these experiments obtained from field sources, kept of embryonic development depends mainly the temper- under insectary conditions for five to days to favor ature and relative humidity to which the eggs exposed. embryonation and viability, and then returned to the Laboratory observations have shown that Asian strains study Ovislrips placed in "dry" conditions of Ae. albopiclus eggs embryonated in periods of two to (tires with holes to prevent flooding) and "wet" conditions four days at tempenitures between 24 C and 27 C (ref- (tires filled up with water). The study found that survivor- in Hawlcy, 1988). Ideal conditions for embryogen- ship of the field-collected eggs under both sets of conditions esis of Ac. albopictus eggs from the Americas appear to be between 10% and 30% after 24 hours. Thus, the rate exposure under natural and laboratory conditions to tem- of egg loss between 70% and 90% and quite similar perature of 21 C, relative humidity of 70%-80%, and in both "wet" and ^dry" conditions. It presumed that photoperiod of 16L:8D hours for six to days egg loss caused mainly by predation by other arthro- (NOMCB, 1989; Edgerly el al., 1993; Hanson and Craig, pods, such arachnids, psocids, orlhopterans, isopods, and 1994). Once embryogenesis has been completed, the eggs others. The initial loss of eggs occurred when the stay unsubmerged and almost completely dry for long number of intact eggs (to differentiate from collapsed periods without loss of viability. damaged eggs) per ovistrip approximately 50 and the Egg survival may depend combination of density- eggs in clumps. The rate of egg loss became negli- dependent and density-independent selective pressures. gible when the number of intact eggs diminished to Events that may promote egg loss include desiccation, pre- about per ovistrip. Thus, the data indicated that egg loss dation, and freezing. Egg survival also may be affected by is related to egg density. Egg survival in Ac. alhopk'lus certain female parental factors such unembryonated eggs appears to depend small numbers of eggs that avoid that collapse eggs that fall off because they not prop- predation by being widely spaced. erly attached to substrate. We will focus such factors Like all Aedes of the suhgenus Sffgomyiu. Ae. albopictus desiccation, predation, and freezing, since to the best of females lay their eggs singly and spread them around the knowledge studies have dealt with the female pa- container at varying distances from the water surface. Each rental effects Ae. albopiclus egg survival. egg is attached at the water's edge in the meniscus in Ac. albopictus eggs survive desiccation in wide variety the wet just above the surface. Amerasinghe and AI- of indoor and outdoor artificial containers (flower pots, agoda (1984) observed that female Ae. alhopictus follow earthenware jars, tin cans, coconut shells, tree holes, bam- set pattern when they oviposit bamboo traps. About 75% boo stumps, etc.) and hatch the containers fill of their eggs deposited within 16 of the water up with water (Fcng, 1937; Ho et al., 1972). The number face, vertically and obliquely, with wide spacing left be- of Ae. albopictus eggs that survive low humidity appears tween singly laid eggs- Oviposition extends to 53 to depend upon the development stage of the embryos be- above the water level. Eggs of Ae. albopicius hatch when they exposed to The phenomenon of diapause is considered to be specific stimulus. After embryonic development has been hormonally mediated, resulting in state of low metabolic completed, hatching within minutes of flooding, activity imposed by specific stimulus. For Ae. alhopictus and larval growth and development proceed immedi- strains from temperate areas, the stimulus appears to be ately. As batch of Ae. albopictus eggs begins to hatch, related mainly to photoperiod and temperature, and it is the time between the emergence of the first and the last adaptive in nature (Hawley, 1988; Focks et al., 1994). In larvae range from few minutes to several dozen days this the word "adaptive" genetically deter- depending mainly water temperature and food avail- mined characteristic that enhances the ability of organ- ability. A widespread phenomenon within the genus Aedes, ism to cope with its environment; adaptation is process including Ae. alhopictus, is that eggs may hatch read- whereby population is altered in such way to be better ily in response to the stimulus of inundation, while others suited to its environment (Ricklefs> 1979; Futuyma, 1986). may remain dormant for varying periods despite being sub- Overall, shorter days (<13.5 hours) trigger egg diapause, merged (Edgerly et al., 1993). This phenomenon is known with low temperatures enhancing the photopcriodic installment hatching (Gillel, 1971), and is in Ae. sponse. I-onger days tend to favor continuous nondiapause alhopiclus when batch of eggs undergoes hatching growth and development. followed by several additional small hatchings (Gublcr, Other environmental variables such latitude (geo- 1971b; Hien, l975c; Hanson and Craig, 1994). graphical origin of the strains) and elevation also play Another parameter that is important for the hatching of role in the induction of diapause in Ae. albopicius. Geo- Ae. albopicius eggs is the amount of oxygen dissolved in graphical variation in the "critical photoperiod" (Cpp-the the water. Low oxygen levels, usually associated with high photoperiod at which 50% of the individuals in the levels of microbial activity and nutrients in the water, in- quito population produce diapause eggs) has been reported hatching (Hien, l975c; Imai and Maeda, 1976; Ed- among strains ofAe. albopictus from the United States and gerly et al., 1993). After egg flooding, microorganisms col- Japan and is known to vary clinally with latitude (Pumpuni, onize the egg surfaces, resulting in decrease in dissolved 1989; Pumpuni et al., 1992). Some modeling studies also oxygen owing to increase in metabolic microbial activ- indicate that higher elevations associated with in- ity; this, in turn, stimulates egg hatching (Edgerly ct al., creased Cpp in Ae. albopictus (Focks et al., 1994). Strains 1993). Thus, larval feeding microorganisms to be ofAc. albopictus from tlie tropics and subtropics do not dem- basic mechanism that may inhibit egg hatching. As onstrate sensitivity to photoperiod. Also, Ac. ulhopictus eggs sult of this observation, studies have focused larval graz- from tropical have not demonstrated overwintering ing activity possible explanation of interspecific and pabilities. For tropical Ae. alhopictus, survival to de- intraspecific egg hatch inhibition among At.', albopicius and pend erratic rather than delayed hatching. Ae. albopictus congeneric species (Edgerly et al., 1993). This research is is considered to display facultative diapause.2 Mori et al. discussed further in the section competitive interactions. (1981) demonstrated that pupal and adult Ae. albopictus The effects of egg freezing in Ae. albopictus, together the stages that sensitive to photoperiod. with diapause, discussed in the following section. The photoperiodic response ofAe. albopicius from tem- perate appears to have favored the rapid northerly spread of the species in the central and eastern United Egg Diupuuse, Photoperiod, and Adaptations States, where it has colonized vast territory in just few years. Ae. albopicius moved northward from latitude of In temperate regions of the world, particularly the Aedes 30 N in Houston. Texas, to 42 N in Chicago, Illinois, aUMpictus-infested of North America and the north- within three years. This observation also reinforced early ernmost points of its distribution in Asia (Japan and China), conclusions that Ae. albopictus from North America have the species overwinters in the egg state (Ishii ct al., 1954; temperate origin in Asia (Hawley et al., 1987). The north- Wang, 1962; Wang. 1966; Imai and Maeda, 1976; Mori and distribution of Ae. alhopictus in the United States is Wada, 1978; Mori et al., 1981). Survival of the northern clearly limited by cold tolerance. Nawrocki and Hawley Ae. tilhopictus depends all most of the eggs entering (1987) have concluded that the -5 C January isotherm is state of hatching-suppression sufficient to outlast winter. This is genetically determined property known diapause. The diapause slate is characterized by reduced morphogen- Diapause in this is defined period during which growth esis, increased resistance to environmental extremes, and al- development of Ihc insect is spontaneously suspended. In species with tered reduced behavioral activity. All known of egg obligatory diapau;>e, only single generation per year is found (univol- diapause in the Culicidae correspond to suppression of tine species). Some Audi's species present this phenomenon and southern latitudes. species with facultative diap.iu.se, such to stimuli formed first instar larvae sponse hatching by fully albopiclu'i, multiple generations possible during ihc (mul- within the egg; state of suspended embryonic development li\olline species). This type of diapause usually midnorlhcrn and has been demonstrated. midsouthcrn latitudes (approximately 35-65). good predictor of the northernmost distribution of the et al., 1991). A recent publication by Hawley rein- species in the United States. forced the assumption that the Brazilian populations may By contrast, the southward movement of Ae. albopictus share temperate ancestor with the U.S. popula- has been relatively slow, leading scientists to hypothesize tions (Hawley, 1991). that the temperate origin and associated photopcriodic sponse of the U.S. populations would prevent their colo- nization of the Neotropics. For instance, for Ae. albopictus populations to remain active in southern Texas and Florida Egg Cold Hardiness during significant portions of the year, they will require lowering of the day length threshold total elimination of The ability of insect to survive suboptimal tempera- the photoperiodic response, because in these regions day tures is known "cold hardiness" (Hanson, 1991). Cold hardiness role in life of lengths for most of the year less than 13.5 hours. How- plays important the cycle several rapid selection for both of these features has been insects inasmuch it affects factors such adaptation to noticed in Ae. alhopictus populations along the southern seasonal changes, long-term population fluctuations, and edge of its Florida distribution, suggesting rapid adaptation the geographical distribution and colonization trends of in- to shorter photoperiods (O'Meara et al., 1993). A theoret- vading species, ical explanation for this phenomenon could resemble the It is well accepted that there (wo different types of following scenario: A temperate-zone population trans- cold-hardy insects: freeze avoiding and freeze tolerant. ported to location (southern of Texas Freeze-avoiding insects produce antifreezes such low- Florida) would experience combination of short day molecular-wcight carbohydrates, polyols, and thermal lengths and favorable temperatures for egg and larval de- hysteresis proteins, and may also discard ice-nucleating velopment for part of the year. During these periods, substances to decrease their supercooling points (SCP). The photoperiodic Ae. ulbopiclu', genotypes would multiply, SCP of insect is the temperature at which it freezes. while photopcriodic genotypes would remain diapausing Freezc-tolcrant insects survive by producing ice-nucleating eggs. Thus, the transformation of photoperiodic popula- agents that increase their SCP by inducing ice formation. tion into nonphotoperiodic requires mutation, but Low-molecular-weight sugars and polyols to merely change in gene frequency. both freezc-avoiding and freeze-tolerant insects. Glyccrol In the laboratory, selection of nonphotoperiodic Ae. al- to be the most frequently encountered substance of bopiclus from originally photoperiodic population has this type (Somme, 1982). It appears that the most been accomplished within generations. In natural stimulus for cold hardiness is low temperature (0-5 C) populations of Ae. alhopictus from southern Texas and (Baust and Lee, 1981; Horwalh and Duman, 1983; Kukal Florida, the ability to diapausc has been lost three- el al., 1989). Other environmental factors associated with year period (Craig, 1993). This indicates that the selection this phenomenon photoperiodic diapause (Lee and Den- for loss of photosensitivity is phenomenon of southern linger, 1985), desiccation (Patterson and Duman, 1978), latitudes, Ae. alhopictus' invasion of the southern United diet (Knight and Bale, 1986), thcrmoperiod (Horwath and States (i.e., peninsular Florida) began slowly in comparison Duman, 1986), and anoxia hypoxia (Somme, 1966). to its northern and eastern expansion. The genes had to Cold-hardiness studies have focused eggs of several change via natural selection. Now the species has lost its orders of the class Insecta, particularly those of the order ability to diapause, and the southern populations of Texas Diptera. All insect eggs studied to dale freeze avoiding. and Florida analogous to their tropical ancestors and Egg cold hardiness studies have been carried out in several different from their temperate antecedents of the 1980s. It species of the genus Aedes, including Ac. albopictus is clear that the species is already in position to invade (Hatchett, 1946; Hawley et al., 1987; Copeland and Craig, any of Neotropical America, and the process may al- 1990; Hanson, 1991). ready have begun (i.e., northern Mexico and the Dominican Hawley et al. (1987) found that eggs of Ae. ulbopiclus Republic). from northern Asia and the United States cold Finally, also in regard to the photoperiodic response, tolerant than eggs from tropical sites. In this study eggs strain from Cariacica City, Brazil, showed sensitivity to subjected to -10 C for 24 hours, treatment that any photoperiod. Based this observation, Hawley and killed all Aedes aegypti and tropical Ae. albopictus, U.S. co-workers (1987) hypothesized that all strains from the strains, however, showed hatch rate of 80%-90%. Eggs United States might have origin in northern Asia placed outdoors in South Bend, Indiana, in mid-October (probably Japan), while those introduced into Brazil had 1986 showed survival rate of 100% in mid-February different origin (likely tropical one). However, recent 1987. These studies clearly demonstrated that the species studies based allozyme analysis indicated that the U.S. overwinters in the northern United States and that cold and Brazilian populations appear to share origin, climation and diapause increase the cold hardiness of tem- with the evidence pointing to northern Japan (Kambhampati perate Ae. albopictus strains (Hawley et al.. 1989). Laboratory studies based genetic between temperate and tropical strains of Ac. albopiclus showed that hybrid eggs with temperate female parent 36% cold hardy than those with tropical female parent (Han- son, 1991). The male parent docs influence the trait but appears to play lesser role. The results suggest that the mode of inheritance of cold hardiness "is under maternal influence by either cytoplasmic sex-linked factors'' (Hanson, 1991). A set of experiments carried out in East St. Louis, Illi- nois. which designed to insert genes to reduce the overwintering ability of Ae. albopictus field strains, pro- duced decrease in cold hardiness and diapause incidence in the populations (Hanson, 1991). In the studies, males from tropical strain of Ae. alhopictus with distinctive isozyme marker released. Subsequent egg samples from the release site showed high (24%) frequency of the genetic marker accompanied by reduced cold hardiness of the field populations. These experiments may open the way for genetic control of Ae. albopictus in the colder parts of its range. All in all, cold acclimation and diapause enhance the cold hardiness of only temperate strains of Ac', alhopictus.

Egg Morphology

The eggs of Ae. albopiclus cigar-shaped, like those of Ac', aegypli, and devoid of floats. Egg morphology, based scanning electron microscopy observations, is fol- lows: Eggs average of 609.8 |j,m (+/- 5.9) in length and 192.9 (im (+/- 2.4) in width (Linley, 1989). They have "large, central outer chorionic tubercles smoothly rounded, with surrounding cell fields almost invariably de- void of small tubercles, leaving distinct clear around each large tubercle," shown in Figure (Linley, 1989). For purposes of comparing the structure of the eggs of the two species of subgenus Stegomyia in the Amcricas, electron micrograph of Ae. aegypti egg shows the outer chorionic tubercles surrounded by fairly narrow, feature- less ring (Figure 2). Ae. albopictus eggs blunt at the anterior end and tapering in the posterior region. The ventral margin is crescendo than the dorsal margin and has conspicuous micropylar collar that is moderately prominent, compared with the very prominent found in Ae. aegypti (Linley, 1989). This characteristic visibly dif- ferentiates the two species.

Larvae

Under natural conditions Ae. albopictus larvae de- Figure 1. Electron micrograph of entire egg of velop in water with low turbidity and at pl-1 ranging from Aedes Scale: bar 100 (Photo by 5.2 to 7.6, with optimal pH between 6.8 and 7-6 in Asia albopictus. (JLM. (Ho et al., 1972). Water containing amino acids, ammonia, Dr. John Linley, Florida Medical Entomology and, in general, high organic nitrogen content appears to Laboratory, University of Florida at Vcro Beach.) be the ideal habitat lor Ae. albopictus (Laird, 1959). To the effects of pH fourth instarAf. albopiclus lar- vae, laboratory studies conducted with colonized strains in New Orleans. Larvae tested to determine their tolerance to various pH levels. The results showed that pH equal to acid than 2.0, equal to alkaline than 12.0, is fatal to mature larvae after four-hour exposure (NOMCB, 1987), The studies also reconfirmed the observation that the species is able to survive in water containing relatively high concentrations of strong electro- lytes. Measurements in the natural larval habitats of the strains in the New Orleans study showed pH ranges of 6.33-8.35 for tires and 6.43-8.23 for tree holes. Larvae have been known to survive ranges of dissolved oxygen of 3-6 ppm in variety of habitats (Ho et al., 1972). Much lower survival ranges have been observed in the tree holes of New Orleans (sugarberry and red maples), which had range of 0.6-2.7 ppm. Also, the larvae have been found alive at values low 1.3 ppm of dissolved oxygen in tire yards in New Orleans (NOMCB, 1987). Adaptability to varied habitats enables the species to breed successfully in wide variety of water-retaining tainers. It also appears that Ae. ulhopicfus larvae tolerant of water with high organic content than Ae. aegypli larvae, although the latter species has been reported from highly organic water conditions such found in tree holes, septic tanks, soak away pits, and the like. lAirval size and the duration of larval development influenced by temperature, food supply, crowding, and Under laboratory conditions, Hien (1975a) demonstrated that temperature affects the duration of larval development. At 30 C development look 6 days, while at 25 C and 20 C, it took 9 and 13 days, respectively. Laboratory studies of the Brazilian strains have shown larval developmental period ranging from 4 to 9 days at temperature of 25 C (Xavicr et Singapore (Ho cl Habitat al., 1971), Bangladesh (Azzizar, 1980). Japan (Toma ct al., Larval 1982; Sota ct al., 1992), and the United States (NOMCB, is container breeder. It breeds in both 1987; NOMCB, 1988) have shown thai the species is abun- Ae. albopictus natural and artificial Ae. has been dant during the rainy It is important to point out receptacles. albopictus found in such natural habitats tree holes, bam- that since Ae. albopictus1 range extends from the tropics to breeding boo holes and coconut shells, axils the temperate zone, seasonal peaks will differ with stumps, plant (bromc- and rock Its artificial habitats In representative of the tropics such the city of liads), ground pools, pools. include rubber tires, tin cans, drums, earthenware contain- Singapore, Ac. alhopiclus presents three well-defined larval ers, bottles, flower pots, cisterns, and buckets. population peaks: December, April-May, and August- In the continental United States, infestations of Ae. al- September. The population peaks of the larvae precede those bopiclus have been found in used tire stockpiles, salvage of the adults by almost exactly two months (Ho et al., 1971). yards, illegal dumps, the premises of tire dealers working In temperate regions, such northern Japan, larvae of Ae. with trucks and large equipment, and tire retreaders. Sur- albopiclus present from late March through mid-Septem- veillance conducted in residential of the United States ber. High larval population peaks have been observed in has also reported infestations in tin cans, bird baths, July-August and October, shortly after the rainfall peaks clogged rain gutters, water bowls for pets, buckets, plastic (Toma et al., 1982; Sola et al., 1992). High larval mortality and metal containers holding rainwater, and cemetery has been observed to in the winter (Makiya, 1973; flower pots (Moore et al., 198S; O'Meara and Gettman, Mori and Wada, 197S; Mod ct al., 1981). 1991). Natural containers such tree holes and tank bro- In Okinawajima Island in (lie Japanese subtropics, large mcliads appear to be among the preferred habitats of Ae. peak in the larval population observed from June to albopictus larvae in suburban settings of the United States mid-July, and the population became very low during No- and Brazil (NOMCB, 1987; O'Meara et al.. 1993; Gomes vember through March. Larvae collected every month ct al., 1992). Recent reports from the Dominican Republic of the year (Toma et al., 1982). have determined that tree holes, rock holes, and fast-food Studies in the United States conducted in New Orleans containers the main larval breeding places. Tree holes in tire yards and tree hole habitats during the of of Celtis luevigala, species of sugarbcrry, of the 1987 indicated that the abundance of Ae. albopictus larvae main breeding habitats of the species in New Orleans, Lou- peaked in June (almost simultaneously with rainfall peaks) isiana (NOMCB, 1987). Examples of larval breeding places and decreased gradually through August (NOMCB, 1987). for Ae. albopiclus from the United States presented in Conversely, maximum larval production in Ircc holes in Figures 4 to 14. of the Paraiba Valley, Sao Paulo, Brazil, docs not Preferred natural larval habitats in various countries of coincide with rainfall ef a]., appear to peaks (Gomes 1992). Asia bamboo stumps, coconut shells, rock holes, and The larval observed in the months highest production ground pools (La Cassc and Yamaguti, 1950; Hong et al., of March and which to the fall in April, correspond 1971; Harrison et al., 1972; Ho el al., 1972; Huang, 1972; the Southern Hemisphere. Rozeboom and Bridges, 1972; Miyagi et al., 1983). In counlries of Southeast Asia other major breeding habitats include earthenware, tin cans, ant traps/ rubber tires, bowls, Larval Morphology and drums. Ant traps (he most indoor habitat in places such Singapore, Dacca, and urban of Ma- Microscopic examination is necessary to identify Ae. al- laysia (Ho ct al., 1972; Azzizar, 1980; Chan, 1985). bopictus larvae and differentiate them from other Aedcs Landscape lank bromeliads have been studied breed- species, especially Andes aegypii larvae. The most signifi- ing places for Ae. albopictus in number of locations in cant differences between Ae. uegypli and Ae. albopiclus, central and southern Florida in the United States (O'Meara which sometimes share the habitat, the following: ct al., 1993). In the northern latitudes of Florida, immature On the mesolhorax and mctathorax.Ac. albopictus has pleu- Ae. albopictus have been recovered from Aeclimea disti- ral hair groups that lack the long spines found in Ae. aegypli. chantha, cold-hardy tank bromeliad, which grows in tral in of N In Ae. albopictus there two branches in seta 7-C the Florida the city Gainesvillc (2940' latitude). head, while Ae. aegypti has only The ventral brush of Before Ae. albopiclus became established in the area, the Ae. albopiclus has four pairs of hairs, whereas Ae. aegypii's brush has five pairs. Ae. alhopictus comb scales have bare ^inall ceramic jars fillixl with pjaced under the leys ol sates apical spine and of small spinules basally each in houses without refrigerator;,.

10 Figure 3. Drawing illustrating the most important differences between Aedes albopictus and Aedes aegypti larval stages. (Drawing provided by Dr. George O'Meara, Medical Entomology Laboratory, University of Florida at Vero Beach.)

bromeliad the dominant microhabital for Wyeomyia pyramidalis, and Aechmea fasciatus. In these microhabitats spp. It appears that Ae. alhopiclus is the main species Ae. albopictus collected from fewer than 10% of the in Aechmea distichantha, replacing other culicids. The spe- plants sampled, while \^/yeomyia spp. found in nearly cies has been found in than 70% of all bromeliads 90% of the bromeliads sampled. Thus, the main culicids at sampled in the Gainesville studies. This observation ap- this site Wyeomyia spp. (O'Meara et al., 1993). pears to have been influenced by the fact that many other In countries of tropical Asia, the breeding preferences of species of tank bromeliads killed severely damaged Ae. albopiclus in plant axils include leaves of Pundanus by hard freeze. Two months after the freeze and for and banana trees and leaves of Colocusis esculenta (taro) period of than 15 months, Ae. albopictus the only (Kurihara, 1984). species recovered from the cold-hardy tank bromeliad. A study conducted by Laird (1959) in several of Thus, because of the cold winter, and in the absence of the city of Singapore described of the characteristics 'Wyeomyia, Ac. ulbopictus is the dominant species (O'Meara of the larval microhabitat ofAe. albopictus where the larvae et al.. 1993). had optimum development. In relation to the aquatic flora Farther south of Gainesville in Vero Beach, Florida and fauna, the water of the larval habitat classified (2740' latitude), Ae. albopictus larvae have been found in p mesosaprobic. p mesosaprobic waters supported other bromeliads such Neorcgalia spectabilis, BUlbergia rich and diverse flora and fauna consisting of several spe-

ll Figure 4. Aedes albopictus-mfested tires, Houston, Texas, U.S.A., March 1986. (Photo by Dr. C. G. Moore, Division of Vector-Borne Infectious Diseases [DVBID], CDC.)

Figure 5. Placement of a CDC ovitrap for Ac. albopictus surveillance (Photo by Dr. C. G. Moore, DVBID, CDC.) Figure 6. Tree hole containing water and Ae. alhopictus larvae, New Orleans, Louisiana, U.S.A. (Photo by Dr. J. E. Freier, DVB1D, CDC.)

Figure 7. Bottle with water and Ac. albopictus larvae. (Photo by Dr. C. G. Moore, DVBID, CDC.) Figure 8. Discarded refrigerator door, with water and leaf litter infested with Ae. albopictus larvae. New Orleans, Louisiana, U.S.A. (Photo by Dr. J. E. Freier, DVBID, CDC.)

Figure 9. Checking for adult Ac. atbopictus at used tire retread facility, Atlanta, Georgia, U.S.A. (Photo by Dr. C. G. Moore, DVBID, CDC). Figure 10. Aedes albopictus larvae in discarded toilet bowl tilled with water. (Photo by Dr. C. G. Moore, DVBID, CDC.)

Figure 11. Aedes albopictus larvae in plastic sheet with water and leaf litter. Note adjacent tire casing also containing water. New Orleans, Louisiana, U.S.A. (Photo by Dr. J. G. Freier, DVBID, CDC.) The fungus Coelomomyces slegomyiae found several Ae. albopiclus larvae in Singapore. The second in- star larvae showed the heaviest infections, concentrated in the head capsule, thorax, and anal papillae (Laird, 1959). High infection rates in experimental trials with Coelomo- myces slegomyiae chapmani have demonstrated the po- tential of the fungus to biological control agent for Ae. alhopicfu'i well other Culieidae (Lien and Lin, 1990). The infection process of Ae. alhopiclus larvae by another fungus, Tolypocliiumm cylyndrosporum, has also been described. The pathogcnesis of the fungal invasion of the exoskeleton and the digestive apparatus of the larvae has been studied to extent, but the potential of this fungus biological control agent for the species is not yet clear (Ravallcc et aL, 1989). A gregarine protozoan parasite, Lankvsteriu culicis (= Ascogregarina iaiwanensis Hen & Levine, 1980) is known to develop trophozoites in the cells lining the larval midgut ofAeiley albopiclus (Huang, 1972). Recent studies conducted in Illinois (Munstermann and Wesson, 1990) have demonstrated the presence of Asc. taiwanensis in strains of Ac. albopictus from North America. Field-collected specimens showed infection rates of 67% to 95% at tour sampling sites; subsequent isolations of the parasite from field-collected Ae. albopictus hosts to show path- ogenicity in the larvae and pupae of laboratory strains of Ac. alhopictus. In general, although the gregarine protozoan has little effect its natural host, it does appear to have marked deleterious effect indigenous mosquitoes of North America such Ae. aegypti and Ae. alropalpus (see the discussion parasitism in the section competition stud- Figure 12. Miscellaneous container habitats for ies). Also, the study reports strain variation in suscep- mosquitoes, infested with Ae. alboplctus larvae. tibility to infection among the different North American Ae. (Photo by Dr. C. G. Moore, DVBID, CDC.) alhopictus populations. This study is the first to find this gregarine protozoan in culicid larvae in North America. Some workers have reported experimental infections of Ae. albopictus larvae with the nematode Komanomermis cics of diatoms, desmids, microcmstaceans, phytoflagellates culicivot-ax (Petersen and Chapman, 1979; Blackmore, (Eiiglenaccac), ciliates. and different many rotifers, cyclo- 1992). So far, parasitism of Ae: albopiclus by mermithid poids, ostracods, and All of the dccapods. above provided ncmatodes has not been reported in any natural populations ideal conditions for of Ac. development albopictus because of the species. The laboratory studies mentioned above of the abundance of food and the low relatively concentra- have shown intermediate infection rates in North American tion of deleterious substances. The mesosaprobic habitat strains of Ae. albopiclus. Mermithids known to infect less well suited for Ac. alhopiclus development; larval mosquitoes by penetrating the cuticle and subse- theless, substantial densities of Ae. alhopiclus larvae quently maturing in the hcmocoel of the host. found. That water contained free-living green algae, blue- Laird (1959) also found variety of other pathogens, grecn algae (Oscillatorio), flagellates, phytoflagellatcs (Eu- such the ciliates Tetraliymena pyriformh and Epislylis gle-na), Paramecium, vorticellas. and rotifers. The lacuslrLs, the alga Oscillaiona hrevis, and the bacterium tacean fauna abundant in cyclopoids and cladoccrans. Sphae-roiilus dichotomus. In regard to predators, Marten (1984) observed cope- pod predator, Mesocyclops leuckarii pilosa, feeding upon Larval Pathogens and Predators first instar larvae of Ae. albopictus. The copcpod pable of eliminating them entirely. A drawback to the Several pathogens and predators oiAe. albopiclus larvae of this predator is that it appears to be in Ae. albo- have been described in the literature. piclus habitats. Further research conducted by the in-

16 Figure 13. Discarded tires potential Ae. albopictus breeding site. (Photo by Dr. C. G. Moore, DVBID, CDC.)

Figure 14. Inspection of tire casings from Asia for Ae. albopictus larvae. (Photo by R. E. Schoeppncr, San Mateo Mosquito Abatement District, Burlingame, California, U.S.A.) vcstigator has demonstrated Ihc successful of other spe- portant epidcmiologic information, because greater longev- cies of larvivorous copcpods in controlling Ac. albopiclus ity increases the probability of transmitting diseases. One larvae in tire piles. In period of S-10 weeks the crusta- of the most important questions concerning Ac. tillmpictus Macrocyclops albidus (Jurine), species with broad is whether adult females of this species capable of living distribution in the Amcricas, able to completely elim- long enough to become infected and subsequently transmit inate larvae in tire piles found in and around New Orleans infectious agents. Studies of male survival may also be im- (Marten, 1989a; 1989b; 1990a; 1990b). Marten also dis- portant, especially in the application of certain genetic the of mixtures of several species of cyclopoid trol In addition, survival data may be useful in copcpods to control species otSlegomyia and other culicids the assessment and administration of vector control of medical importance and these copepods' potential effect operations. larval aquatic habitats. The mixtures of Macrocyclops The bulk of the data longevity ofAe. albopiclus adults atbidus and Mesocyclops rultneri, both collected in natural (survival studies) from laboratory research (reported habitats in New Orleans, proved to he effective in Hawley. 1988). Few studies have attempted to estimate Macrocyclops by itself. An advantage of this approach longevity otAe. albopiclus adults in the field. Thus far, two the increase in survival rates of both species in the mixture, studies have been carried out with North American strains. compared to the survival rate when single species Some of these laboratory and field studies described below. introduced (Marten, 1990b). Environmental factors stimulate responses thai greatly Finally, various Toxorynchiles mosquito species modify the behavior and biology of the adult mosquito. known to prey Ae. albopiclus larvae. One of these pred- Temperature and relative humidity among the factors ators that has been found breeding successfully with Ae. that play vital role in adult survival. Gao et al. (1984) alhopiclus larvae in Asia is Toxorynchiles splendens (Siir- reported that during eight years of observations of caged tccs, 1966). II appears that Toxorynchites spp. may be Ae. albopictus (kept at temperature conditions of 25 +/- effective in controlling Ae. albopiclus larvae. Two species C and relative humidity of 80 +/- 5%). the maximum of To-wrynchites, introduced (amboinensis) and the longevity of the adult females 30-40 days. The other indigenous (rulilus septenirionalis}, have been study demonstrated that the upper thermal survival limit sively produced in insectaries, and control trials being 40 C (LT;(, 0.9 hour) and the lower limit carried out in of New Orleans to test their efficacy in -5 C (LTso 0.85 hour). the field (Freier, pcrs. comm., 1993). Hylton (1969) showed that longevity of the adult Ae. albopiclus female reached about 84 days at temperature Pupae of 22.2 C and relative humidity of 80%. Ae. albopiclus tolerant of low temperatures (15.5 C) and higli and low humidities, whereas Under ideal conditions, Ae. albopiclus remains in the pu- high temperatures (32.2 C) de- creased survival, of pa! stage for about two days (Sheng and Wu, 1951; Surtces, independent the relative humidity. It appears that the ability of Ac. to 1966; Hicn, 1975a), and. in other Aedes species, Ae. albopiclus survive various temperatures and humidities albopiclus males emerge before females. Livingslonc and may have favored its distri- bution in climatic Krishnamoorthy (1982) showed that the pupal development conditions that range from temperate to tropical. It has been period 32-36 hours tor males, while females reached suggested thatAc. alhopictus body fluids at low the adult stage in 49-52 hours. The experiment sug- humidities, thereby preventing (issue desiccation, through control gested that pupal development of females requires mini- spiracular another moisture dark period of 12 hours. regulating mechanism (Hylton, 1967). longevity in the is also Hicn (1975a) studied the ctfcci of water temperature laboratory affected by feeding. Gublcr and Bhaltacharya maintained pupal development. The results showed that pupal devel- (1971) mosquitoes at temperature of 26 C and relative of opment lasted two days at 30 C, three days at 25 C, and humidity 50%- 60%, and demonstrated that blood-nourished Ac. five days at 20 C. Ae. albopiclus pupae survive desiccation albopictus females lived from 38 to 112 for up to two days at 26 C and relative humidity of 87%. days. A maximum of 117 days found Hien Pupal mortality about 1% under field conditions by (1976a). (Ho et al., 1972). By contrast, mosquitoes that fed with water and kept at temperatures of 25-26 C and 6()%-70% relative humidity began to die after three days. The majority of Adults starving Ac. albopiclus did not live longer than five to days (Hicn, 1976a). Under natural conditions female Longevity would normally find suitable host before this time interval elapsed. Studies of longevity (survival) in different populations of There two general approaches for measuring the rate vector mosquitoes (particularly females) often provide im- of survival in insects: indirect methods based physio-

18 logical age within population and direct estimates by Mark-release-recapture methods used to directly esti- mark-rclease-rccapture experiments (Service, 1976). mate survival usually involve marking known number of Indirect methods to female survival based individuals with various dyes, releasing them into the wild, chiefly tracheation of the ovaries and ovariolar dilata- and then trying to recapture them by different A tions (Polovodova, 1949; Detinova, 1962). Analysis of the regression line is then constructed by plotting the values of trachcaiion of the ovariolcs yields the parity rate, i.e.. the the logm(recaptures + 1) against the number of days post- proportion of the population that has oviposited. Therefore, release. Next. the slope of the regression is calculated in the mosquito population be separated into two groups: simple way to obtain the probability of daily survival, p older group with oviposition cycle (parous) (Walker et al., 1987). The antilog of the regression coeffi- and younger group with oviposition cycle (nulHpa- cient yields the daily survival rate. Aside from being of rous). The greater the proportion of parous females, the chief importance in survival studies, direct methods, such older the population. Parity rates determined by dis- mark-recapture analysis, also used for the following secting the ovaries of unfed recently fed females and purposes: to estimate adult densities; to dispersal; examining them for the presence absence of clumped to determine the timing of reproductive events; to evaluate coiled iracheoles. It' the tracheoles coiled, the female is the extent to which individual vector returns to the nulliparous; if they not coiled, the female is parous. species for its blood source; and to identity resting places, Parity rates important for comparing the age of popu- especially outdoors and during the of minimum lations of different species in different after in- density. secticide treatment. Most important, if the oviposition cycle In Singapore the oldest females collected in houses and the gonadotrophic cycle is known, both the daily survival human baits had undergone three gonotrophic cycles, rate (proportion surviving through day) and the average suggesting period greater than 11 days, while in Cal- age of the population be estimated mathematically. The cutta dissections of wild females showed only two daily survival rate /; is estimated by extracting from the ovipositions, indicating shorter life-span than in proportion of parous females the root equal to the number Singapore (Ho ct ai- 1972; Gubler and Bhattacharya, of day?, in the oviposition cycle. The formula is follows: 1971). Some other studies have reported collection of p ==-\/proportion ol' parons females, where the ovipo- marked Ae. ulbopictus females at periods greater than 20 sition cycle in days. The ovariolar dilatation method deter- days postrelease (Bonnet and Worchestcr. 1946; Rosen et mines the number of times that female mosquito has al., 1976; Niebylski, 1992). oviposited by examining dilatations in the basal part of the Mark-reieasc-recapture studies conducted with North follicular tube (pedicel), small duct that connects each American Ae. alhopiclus strains in the eastern part of the ovariole in the ovary to the lateral oviduct (calix). Each city of New Orleans during the rainy of 1987 oviposition produces dilatation; thus, the number of di- showed overall average probability of daily survival of latations found in the follicular tubes of ovary indicates 0.77 for both males and females (NOMCB, 1987). Thus, the number of times the mosquito has oviposited. The the life expectancy value for the population about four ber of ovipositions indicates the physiological age of the days. More recent research, also from North America, mosquito, which, when multiplied by the estimated number carried out in tire yard in Potosi, Missouri, during 1989- of days in the oviposition cycle, yields estimate of the 1991 and showed higher survival rates for Ae. albopictus chronological age. females than those reported in other studies. In this research Estimates of adult longevity of Ae. ulbopictus based the p value for females 0.89, which corresponds to 8.6 ovariolar dilatations and tracheation of the ovaries have (or about 9) days life expectancy in this population (Nie- been carried out in several laboratory studies. Hawley bylski, 1992). In this particular study, single female (1988) discusses their shortcomings, pointing out that age observed to survive 24 days. The survival rate p of the adult may be underestimated when the estimate is based males 0.77, which is comparable to the values reported riolar dilatations. For instance, studies have shown by other researchers. An average 8-day survival ofA

19 enon, form of competition for mates, is known satyr- Hien (1976b) observed that Ae. albopictus females ism, and it has been noticed in laboratory experiments and ready to lake blood meals several times during single in the field, particularly with maleAe. aihopictus. Further- gonolrophic cycle, that is, the second and third days more, it is known that injections of matrone, the Ae. ai- after the first meal. Gubler and Bhattacharya (1971) also hopictus male accessory gland pheromonc. renders the fe- observed that Ae. albopictus females took blood for male Ae. aegypti refractory to subsequent inseminations ond time in single gonotrophic cycle. Multiple feeding (Mi and Rozeboom, 1973; Nasci et al., 1989; Craig, 1993). during gonotrophic cycle could be important On the other hand, matrone from male Ae. aegypti has ponent in the epidemiology of vector-borne diseases (Bur- effect female Ae. albopictus. It is believed that the pro- kot et al., 1988). This behavior could increase the ability ficiency of the Ac. albopictus males in mating with other ofAf. alhopiclus to acquire and deliver infections from and species could be involved in the dramatic displacement to different hosts, thereby spreading pathogens to larger trends of Ae. aegypli by the Ae. albopicliif populations in susceptible human population. Information regarding Ae. the southern United States (Nasci et al., 1989). albopiclus feeding patterns is sketchy; however, it is known Natural mating behavior of Ae. albopicluf reported that the species has wide host range compared with other in Calcutta study (Gubler and Bhattacharya, 1972). It Slegomyia species. Thus, there is real possibility that Ae. found that male Ae. alhopiclus swarmed around the feet alhopiclus may pick up pathogens in ?.oonotic cycle and and ankles of human observer. Female Ae. albopictus carry them to humans in the domestic environment. rived later and mated they approached the host to Knowledge of the interval between successive oviposi- feed. Mating took place in flight and usually occurred tions (the duration of the gonotrophic cycle) allows within to three feet of the ground. Most of the matings version of the physiological age into longevity lasted from 5 to 15 seconds. A majority of the copulating for the population and also the study of population dynam- females that captured nulliparous, and most ics. In general, Ac. aihopictus laboratory experiments inseminated in the vicinity of the host. The study also to agree with field studies, pointing to average duration reported swarming of males at the bases of trees and of five days for the first and second gonotrophic cycles. For metal baskets, leading to copulation and insemination instance, Mori and Wada (1977) demonstrated that under nat- of females. It has been reported that copulation is suf- ural conditions, with average field temperature of 25 C, ficient to fertilize batch of eggs and that females the period from emergence to the first blood meal of Ac. not inseminated until they 30 to 36 hours old (Ho ct albopictus about two days and the duration of gono- al., 1972). lrophic cycle five days. These results in accord with laboratory experiments. Using Detinova's method, the studies showed that Ae. albopiclus females ready Oviposition to feed again within 24 hours after oviposition. Under laboratory conditions, Del Rosario (1963) found The speed of egg production, like that of other physio- that the first blood meal taken two days after logical processes of insects, is critically dependent gence, and the gonotrophic cycle found to last three to vironmental factors such temperature. four days before oviposition at temperature of 24--29 C The underlying mechanism that triggers oviposilion in and 80%-93% relative humidity. Gubler and Bhattacharya Ae. albopictus has been studied to extent in strains (1971) also observed that the first blood meal of Ae. al- from India and from Lake Charles, Louisiana, in the United bopictus females took place two days after emergence, with States (Lcahy and Craig- 1965; Klowden and Chambers, gonotrophic cycle lasting three to five days after blood 1992; Klowden, 1993). Experimental studies have indicated meal at temperature of 25-26 C and relative humidity of that male accessory gland components of Ac. alhopiclus 50%-60%. Hien (1976b) showed that the gonotrophic cycle play role in inducing egg deposition in the females (Leahy after blood meal lasted three to three-and-a-half days and Craig, 1965; Klowden, 1993). It appears that the ovi- at temperature of 25-26 C and relative humidity of position stimulant for females is not related to the mechan- 60%-70%. ics of mating but rather to stimulant substances produced The number of eggs laid by Ac. albopictus depends by the male accessory gland. Likewise, abdominal disten- the physiological age of the mosquito, the body weight after tion resulting from blood meal to provide second emergence, and, particularly, the size of the blood meal stimulus that initiates ovarian development (Klowden, (Hien, 1976a). In general, it appears that there is linear 1993). correlation between blood meal size and number of eggs Although it is generally accepted that Ae. alhopiclus fe- oviposited. Hien (1976a) observed that, average, Ae. al' males begin to feed two days after emergence (Del Rosario, bopictus females lay eggs after blood meat of al least 0.7 1963; Gubler and Bhattacharya, 1971; Hawley, 1988), mg. For females taking from 0.8 mg to 2.5 mg of blood. Ae. alhopiclus have been observed to take their first blood the average number of eggs produced in the first gono- meal during their first day postemergence (Hien. 1976b). trophic cycle 72 per female (Hien, 1976a). The study

20 also demonstrated that the number of eggs produced in- vided by the researchers. Based data from this research, creased with the size of the blood meal taken by the female it hypothesized that food accumulated in (85 more eggs at 2.0 mg of blood). extended larval life cycle, compared to that of Ae. A study conducted by Klowden and Chambers (1992) gypli, may favor stores of lipids and proteins that enhance showed that Ae. albopictus females possess the ability to the expression of autogeny in Ae. albopiclus. These obser- utilize extremely small blood meals to develop their eggs, vations part of studies assessing the reproductive and in contrast to other species ofSfegomyia (i.e., Ae. aegyp{i). metabolic differences between North American strains of Values low 0.1 |xl of blood enough to trigger Ae. albopiclus and Ae. aegypll. egg development in Ac', albopiclus strains from Lake With strains from Mauritius and Madagascar, Bat-Miriam Charles, Louisiana. The average number of eggs oviposited and Craig (J966) demonstrated that adults that fed 18 per female. In contrast, the other North American only sugar and raisins produced few eggs. The strain Slegomyici, Ae. uegypli, unable to develop any eggs from Mauritius able to present autogeny for 12 gen- unless the blood meal volume than (xl. Gublcr erations. Cui (1982) observed that larvae collected in and Bhatlacharya (1971) found that the number of Guangzhou City and reared in the laboratory displayed eggs in the first gonotrophic cycle 63.4 per female. togeny. The aulogeny index reported for the Guangzhou Similar results obtained in two other studies: Udaka strain varied from 1.96 to 2.96. while in the Mauritius strain (1959) reported 62 eggs per female feeding sugar and it 2.7 eggs per female. blood, and Soekiman et al. (1984) observed average of Oviposition activity and horizontal and vertical ecologi- 57.5 eggs per female after single blood feeding. cal stratification have been studied by Gubler (197 Ib). He Based measurements of parity rates for Ac. albopicius, determined from series of 18 ovitrap collections that most Hawlcy (1988) determined that the number of egg batches of the eggs laid al ground level, but de- laid bv female wild mosquito in its life-span is in the posited at height of 15 meters, in the tops of trees in range of 0.2 to 2.1. The average number of ovipositions Calcutta, India. In Paradeniya, Sri Lanka, Amerasinghe and inferable from these data is approximately Alagoda (1984) made similar observations; Ae. alhopictus The number of eggs laid also depends the physiolog- females laid about 52% of their eggs at ground level, and ical age of the female, and the number progressively de- there decrease in oviposilion with increasing height age increases (Gublcr and Bhattacharya. 1971; above ground. Only 33% of the eggs laid at 3.5 meters Hien, .1976a). Generally speaking, the first gonotrophic cy- and just 16% of the eggs laid at 7 meters. The results cle produces the highest number of eggs, with gradual suggest that Ae. albopictus females, although preferring decrease in subsequent cycles. On average, Ae. albopiclus horizontal range stratification for oviposition, able to females the laboratory found to produce 283-344 migrate and oviposit in the treclops. eggs per mosquito during their life cycle (Gubler and Bhat- Oviposition sites affected by habitat type, light, tem- tacharya, 1971; Hien. 1976a). perature, and humidity, well by such subtle influences Autogcny has been observed in laboratory strains of Ac. characteristics of the water (biolic and abiotic) and albopictus (Bat-Miriam and Craig, 1966; Cui, 1982; Klow- the oviposition surface (Bently et al.. 1976; Amerasinghe den and Chambers, 1992). Autogeny in this is defined and Alagoda, 1984). Ho ct al. (1972) reported that, under egg maturation without exogenous of protein. laboratory conditions, female Ae. albopictus preferred to namely, the blood meal. Conversely, species requiring in- oviposit in habitats with rough gray surface and low gestion of proteinaceous foodstuffs for egg development is flectivity rather than smooth black surface with high known anautogenous species (Roubaud, 1929). It has reflectivity. Yap (1975) observed that ovitraps coaled with been suggested that autogenous mosquitoes accumulate red and black preferred ovitraps of other colors. considerably during their larval life than do In their natural habitat, Ae. alhopiclus usually lay eggs in anaulogenous This situation may be related to the water reservoirs containing decaying vegetable matter somewhat longer larval developmental periods in autoge- (Hien, 1976a). strains. Autogeny in mosquitoes is not controlled The quality of larval food appears to affect the adult's solely by larval nutritional conditions but also by genetic oviposition capacity. This effect observed in Ac. al- components (Twohy and Rozcboom, 1957). Autogeny hopiclus females reared with banana powder in the larval therefore has ecological significance, since it allows the stage: egg laying particularly weak except al constant mosquito to lay eggs in the absence of host for temperature (Ho ct al., 1972). feeding, thus ensuring the continuity of the species. In nature, it observed that Ae. alhopictus females In Ae. allwpictus strains from Lake Charles. Louisiana, seldom laid all of their mature eggs in single oviposition. autogenous behavior expressed in adult females main- Instead, they appeared to from place to place, at each tained sugar diet (Klowden and Chambers, 1992). In site leaving behind few eggs. The female probably lays sample of 100 individuals, 5% displayed autogeny. No all mature eggs during the of several ovipositions, data the number of eggs oviposited per female pro- periodically interrupting her egg laying to fly to another

21 container. This strategy is considered species survival findings of other researchers (Tempclis ct al., 1970) and mechanism (Rozcboom el al., 1973). adds to the potential of the species to become involved in Laboratory observations assessing the influence of blood the cnzootic/endcmic transmission cycles of indigenous in oviposition have been carried out in New Or- boviroses and other vector-borne diseases. Ac. albopictus leans, Louisiana. The results showed that mosquitoes feed- breeds in surrounding the human environment and has ing rodent species laid significantly eggs than demonstrated highly anthropophilic behavior; thus, the spe- those feeding avian, rabbit, human hosts (NOMCB, cies participate in the sylvan zoonotic cycle and carry 1989). diseases to

Host Preference Biting Behavior

Aedes alhopictus females feed wide range of On average, Ae. albopictif, females take their first blood mals well birds. Host-feeding patterns for wild Ac. meal two days after emergence (Del Rosario. 1963; Hien, albopictus populations in the New World showed that the 1976a). Adult females vigorous daytime biters (al- species is opportunistic feeder that appears to be pri- though they sometimes bite at night) and typically bite out- marily attracted to mammals rather than other types of hosts doors (Feng, 1938; Sheng and Wu, 1951; Surtccs, 1966; (Savage ct a]., 1993). Savage and co-workers conducted Ho et al., 1972; Pant ct al., 1973; J. Frcicr, unpublished studies in the of 1989 and 1990 in large tire information). The diurnal biting cycle of Ac. albopiclus ap- dump located in Potosi, Missouri. Their sample consisted pears to be generally bimodal, with period in early Ac', of 172 alhopictus females, which tested by morning and the other in evening (Gubler, I971b; Ho el of the precipitin test and direct ELISA. The results showed al., 1973; Basic and Santos-Basio, 1974). that 64% of the mosquitoes had fed mammals and 16.9% Did studies conducted during the of 1987 birds. This study identified nine mammalian taxa Ae. albopictus strains from New Orleans, Louisiana, showed hosts: rabbits, deer, and dogs (the three most common), this bimodal cycle of biting activity. The first biting cycle followed in decreasing order by humans, squirrels, opos- occurred between 6:00 and 10:00 and the second be- sums, myomorphs (except Raltus), bovincs, and tween 4:00 and 10:00 p.m. Statistical analysis suggested Four avian taxa also identified asAe. albopiclus blood positive correlation between biting activity and relative hu- hosts: passcritbrms, columbiforms, ciconiit'orms, and quail. midity (r 0.33, p 0.005). The study observed biting Various blood meals from unidentified mammalian activity throughout the 24-hour period, decreasing but not and avian hosts. disappearing during the night-time hours (NOMCB, 1987). In extension of the Missouri studies to four In Calcutta, Gubler (I971b) observed thai the diurnal states (Florida, Illinois, Louisiana, and Indiana), Niebylski tivity of Ae. albopiclus females presented primary peak (1992) and Niebylski et al. (I994a) found two between 6:00 and 8:00 and secondary peak between malian laxa (rats and cats), well turtles, preferred 4:00 and 6:00 p.m. In Singapore, well-defined biting activ- hosts, in addition to the nine mammalian taxa named above. ity of female Ae. alhopictus found, with morning The variation in blood hosts between sites and within sites peak just after sunrise at 7:30 and evening peak could be governed by the relative abundance of specific around sunset from 5:30 to 6:30 p.m. The prominent vertebrates at the time of sampling. ning peak may be important factor contributing to dis- In Thailand and the Hawaiian Islands, Ae. alhopictus fe- transmission, since in certain tropical human out- males collected in sylvan environment fed humans, door activity increases in late afternoon (Ho ct al., 1973). horses, pigs, buffalo, bovine species, dogs, chickens, and In the Philippines, Basio and Santos-Basio (1974) ob- boobies (Tempclis et al., 1970; Sullivan cl al., 1971). In the served minor biting peak between 9:00 and 10:00 Hawaiian Islands, 93% of the females fed mammals and and major peak between 4:00 and 5:00 p.m. The biting 7% birds. cycle similar in four different geographical Under laboratory conditions, Ae. alhopictus feeds hu- Although biting activity of females occurred predomi- mans, rabbits, mice, chickens, rats, and guinea pigs (Del nantly at ground level, it observed high 9 meters Rosario, 1963; Ho cl al., 1972). Ae. albopiclus females in above the ground during the peak biting time in Calcutta breeding cages have also been reported to teed snakes (Gubler, I971b). Population studies of Ae. albopiclus and frogs (Miyagi, 1972). conducted by Mogi and Yamanura (1981) indicate tlialAe. According to Ho et al. (1972), Ae. albopictus prefers to albopiclus attraction to humans depends host factors feed humans, but host availability appears to play fun- such sex, age, race, and clothing, well mosquito damental role in the average behavior of the mosquito pop- responsiveness influenced by circadian rhythm, micro- ulations. The confirmation in the U.S. studies that Ae. ai- climatic conditions, and undetermined factors related to the hopictus is opportunistic blood feeder supports the individual host. Thus, females attack humans under the

22 guidance of carbon dioxide, moisture, organic chemicals, the adults appeared in mosquito nets, kitchens, drawing ;ind visual factors including movement. The study rooms, pig sties, among weeds in the field (Surtees, found that the range of attraction of Ae. iilbopiclus to 1966; Ho et al., 1972). human is circle with radius of about 4-5 meters (an In the United States resting Ac. iilbopiclus have been of 50-80 m2). The host-seeking pattern of Ae. albo- found in forest fringes where both canopy and understory piclus appears to follow two phases: initial random flight present (Nicbylski. 1992). and directional flight after encountering stimuli from host. This assertion is supported by the observation that Ac. alhopklus distribute vertically within the range where stim- Adult Morphology uli from human being the ground detectable. Seasonal abundance of adults varies according to the Adults of the genus Aedcs be differentiated from geographical Therefore, seasonal biting activity is in- other Culicidac because their abdomen is pointed. The main fluenced mainly by temperature and rainfall. characteristic that distinguishes Ac*, tilbopicliis from Ac. In Ncvf Orleans, adult mosquito abundance peaks gypti is the conspicuous lyre-shaped silver pattern the days after the beginning of rainfall. Larval mosquito pop- scutum of Ae. acgypli, compared with the distinct longitu- ulations reach their peak densities in tree holes and tires dinal sil\ line of Ae. aibopictus. If the scales from the during the month of June. Adults found between the thorax inadvertently rubbed off during collection if months of May and August. Most adult activity disappears other handling problems occur, there is another character in late September following the onset of diapause that distinguish these species. Tlic clypcus, structure (NOMCB, 1987; NOMCB, 1988). located the head between the palpi, is covered with In the tropics, tor example, in the city of Singapore, there white scales in the Ae, aegypti female and black scales in three adult population peaks: in March, in June-July, the Ac. albopictus female. A pictorial key provided by Dr. and in November-December. Thus, female feeding activity G. O'Meara and another trom the Supcrintcndcncia de is highest during those three periods. The population peaks Campanhas de Saudc Publica (SUCAM, 1989) in Brazil closely follow those of rainfall (Ho ct al., 1971). (Figures 15 and 16) show differences in greater detail for On the subtropical island of Okinawa, Toma et al. (1982) the adult stages of both species. In addition, Walter Reed found females feeding throughout the year, with peaks in Biosystematics Unit plate illustrates the external morphol- feeding activity occurring from April to June and from Au- ogy of adult Ae. albopictus (Figure 17). gust to November. In temperate of Japan, adult peaks from late March to mid-September. La Cassc and Yamaguti (1950), in Honshu, Japan, observed that biting Competition Studies rates of Ae. alhopiclus peaked during the last two weeks of August. Arclcs albopictus utilizes the kind of artificial ter containers that the principal of Ac. acgypti, Flight Range and several studies report that Ac. albopictus and Ae. aegypii may share the habitat (Gilotra el al., 1967; Bonnet and Worchester (1946) determined during mark- Chan, K. L., ct al., 1971; Ho et al., 1972; Azzizar, 1980; rclease-recapture studies with Ac. albopictu.f thai the Sprenger and Wuithiranyagool, 1986; Nasci el a)., 1989; imum recapture distance 134 meters. Thus, it is ap- O'Meara el al., 1993). Because of this association, it has parent that Ac. albopictui has short flight range, rarely been hypothesized that in parts of Southeast Asia reaching 500 meters (Stojanovich and Scott, 1965). This Ae. aegypti has completely replaced the indigenous Ac', al- observation has been confirmed by recent dispersal studies Iwpiclus in urban (Pant et al., 1973). Conversely, ob- conducted with North American Ac. albopictus strains from servations the spread of Ae. albopictus in the southern Potosi. Missouri (Nicbylski, 1992; Nicbylski el al., coastal slates of the United States indicate that the expan- 1994b). Using mark-release-rccaplure trials, the maximum sion appears to be occurring al the expense of Ac. aefypti. dispersal distance estimated for females 525 meters, The introduction of Ac. albopictus has been accompanied whereas the maximum dispersal distance for males by drastic and rapid decline of Ae. aegypti populations 225 meters. It also noted that than 90% of the (Nasci et a)., 1989; O'Meara et al., 1993). Ac. albopictus specimens from the study dispersed Historically, laboratory studies of larval competition less than 100 meters. ducted with different Asian strains of Ac. ulbopictiis and Ac. aegypti showed Acdes ac^ypti better able to compete Resting Behavior than Ae. albopictus (Macdonald, 1956; Gilotra et al., 1967; Moore and Fisher, 1969; Sucharit et al., 1978). Information Aedfs alhopiclw, adults have been found resting outdoors obtained by these researchers suggested that Ac. albopiclus in clearings and rubber plantations in Malaysia. In China, would not become established in locales inhabited by Ae.

23 Aedes albopictus

I \ 7T W / I fr- ^ \_i_ Clypeus __/ Figure 15. Differences in the clypcus of At', albopictus and^ Ae. aegypti. The female Ae. albopictus clypeus is covered only with dark scales, while Ae. aegypti shows white scales. (Drawings provided by Dr. George O'Meara, Medical Entomology Laboratory, University of Florida at Vero Beach.)

because aegypli of competitive displacement competitive containers and by 30% in natural habitats, while thai ofAe. exclusion.'1 albopiclus increased (Rozcboom and Bridges, 1972). The phenomenon of competitive displacement involving In North America, Ae. albopiclus has been found Ac. ulhopiclus and other species has also been suggested ciated with Ae. Iriserialus in tires and tree holes (NOMCB, other by scientists. For instance, in cage experiments Gub- 1987; Livdahl and Willey, 1991; O'Meara et al.. 1993). ler (l970b) demonstrated induced sterility when males of Laboratory larval competition studies between the two spe- Ae. alhopkliis cross-inseminated females of Ae. polyne- cies using tree hole and tire fluid suggest that they could sieiisis. Gublcr (1970c) suggested competitive displace- coexist in tree holes, but that Ae. Iriserialus would become ment principle by showing experimentally that at ratio of locally extinct in lire habitats (Livdahl and Willey, 1991). 10 Ae. albopictus males to Ae. polynesiensis male, cage The mechanism proposed by the researchers lo explain this colony of Ar. polynesiensis completely eradicated. result is that "resources exist within tires that be used Likewise, Ac. albopiclus is reported to have displaced Ae. effectively by Ac. albopiclus than Ae. Iriseriams, and guiimensis from of Guam and the Mariana Islands. that tree hole fluid contains that each species Ae. guumeiisis is indigenous to Guam. bul Ae. albopiclus is ploits differentially." In general, these laboratory-based known to have been introduced in 1944. One study hypoth- sumptions have been supported by field studies conducted esized that (in part due to competition) the population density in Florida which showed "progressive increase in the of Ae. guamensis decreased by much 95% in artificial frequency of artificial containers with Ac. albopiclus and concomitant decrease in those with Ae. Iriserialus" (O'Meara el al., 1993). competitive exclusion principle, (iiiusc's hypothesis, [h Hie prin- The apparent of Ae. albopictus competitor ciple Unit species 1m ing identical ecological requirements to be corroborated by observations the relative exist indefinitely. abundance of the other New World Stegomyia, Ae. aegypti,

24

Figure 17. Adult morphology ofAc. albopictus. A, dorsal aspect of the male; B, lateral aspect of the male abdomen; C, lateral aspect of the female head; D, lateral aspect of the male thorax; E, anterior surface of the male legs. (Drawings provided by Walter Reed Biosystematics Unit, Smithsonian Institution, Washington, D.C.) in various southern cities of the United Stales in the 1980s, hatch of Ae. triserialus and Ae. aegypti, combined with and the subsequent dramatic decrease in Ac. aegypti pop- their propensity to hatch into occupied habitats, may pro- ulation;; following the introduction of Ae. albopictus. Field vide the species with significant advantage they observations of artificial habitats, including tires, in Texas, counter resident populations." Edgerly and co-workers Alabama, and Florida appear to reconfirm the phenomenon (1993) concluded that the "competitive ability of Ae. al- (Sprengcr and Wuithiranyagool, 1986; Hobbes et al., 1991; bopictus larvae may help to explain why Ae. albopictus has O'Meara et al., 1993). achieved rapid dominance in domestic container habitats Another hypothetical mechanism suggested for compet- previously occupied by Ae. triseriatus and Ae. aegypti in itive replacement otAe. aegypti by Ae. albopictus in North the southern United States.'' America is parasitism. For instance, the intestinal gregarine Further studies focusing adult mating behavior have protozoan Ascogregarina taiwanen'iis, which parasitizes Ac. examined mating interference (interspecific matings) to try albopictus larvae, appears to have to the New World to explain the observed differences between Ae. ullwpicfus along with Ac. albopictus (Munstermann and Wesson, and Ae. aegypti. Interspecific matings between Ae. alho- 1990). After spores ingested by the larvae, the sporo- pictus males and Ae. aegypti females have been demon- zoites penetrate and grow in the midgut cells, then emerge strated in both field and laboratory experiments (Nasci et and go to the Malphigian tubes where their life cycle is al., 1989). Ae. aegypli females inseminated by Ae. albo- completed by sexual fusion of the gametes, cyst production, pictus males contained clumps of few dead sperm in their and spore excretion by the emerged adults. Ae. alhopictus spermatheca, which implies refractoriness to further mating tolerates its parasite well; very heavy infections produce by the female. In turn, the observations suggest mating in- maximum larval mortality rate of 10%-20%. Experiments terference at high Ae. albupiclus densities, which may be carried out by G. Craig at the University of Notre Dame important factor in determining the distribution of the have demonstrated cross-infections of Asc. taiwanensis in two Stegomyia in North America. The problem with this Ae. aegypti. However, in that species the infection settles likely explanation is that the experiments have not been in the midgut and does not complete its sexual cycle. More replicated either in cages in the field by other researchers. important, heavy infections of Asc. taiwanensis have been Additional approaches have been pursued to try to shown to produce high larval mortality in Ae. aegypti. plain the decline ofAe. aegypti and the role Ae. allmpiclus Thus, it has been suggested that At', albopiclus' parasite has played in that decline in North America, hut conclu- gives it major competitive edge in the field, which in turn sive general explanation has not yet emerged. More field may help to explain the decrease in Ae. aegypti populations. studies needed to the true impact of Ae. albo- Edgcrly ct al. (1993) studied the inhibitory effects of lar- pictus Ae. aegypti populations- In general, researchers the hatch rate of conspecific and congeneric eggs agree that not enough evidence is available to prove potential population regulatory mechanism. Their labo- whether the decline ofAe. aegypli and Ae. triseriatus has ratory experiments assessed the egg hatch rates of Ae. al- been caused by Ae. alhopictus. In all likelihood, combi- hopictus in response to increases in the larval density of nation of several factors (including larval competition) may two possible competitors, Ac. aegypti and Ae. friserialus. be contributing to the decline of Ae. aegypti and other The rationale behind the research approach is that after egg Aedes in North America. flooding, "microorganisms colonize the egg surfaces and Regarding the Asian situation, in which Ae. aegypti ap- the subsequent decline in dissolved oxygen due to micro- pears to have displaced Ae. albopictus, lidgerly et ai. bial respiration triggers hatch." Therefore, larval feeding (1993), in agreement with Hawley (1988), consider that microorganisms could be simple mechanism for hatch "habitat changes have dramatic effects the outcome inhibition. "Foraging larvae of other Aedes species may of biological invasions; rampant urbanization in Southeast impose interspecific, well intraspecific, hatch inhibi- Asia apparently stimulated increase in abundance in Ae. tion." Rggs of each species exposed to varying aegypti introduced from Africa, at the expense of native binations of larval species and density for 24 hours and Ae. ailwpictus.'' their respective hatch rates then assessed. Of the three Despite several likely explanations, both phenomena- species, Aedes albopictus eggs showed the lowest level of the Asian and North American competitive Aedes replace- inhibition when exposed to high larval densities. In addi- ments-still constitute ecological enigma. tion, al the lowest larval density, Ae. albopictus imposed the most intense interspecific hatch inhibition. It hy- pothesized that the observed differential hatch responses the result of differences in larval feeding rates, respiration DISEASE RELATIONSHIPS rates, and oxygen thresholds required for hatch, well differential changes in larval grazing behavior with in- The potential public health importance cifAe. alhopictus creased density. The conclusions of the study suggest that is indicated by its ability to transmit various arboviruses, the relative of "Ae. albopictus in inhibiting egg filarial worms, and protozoa. Both field and laboratory stud-

27 ies indicate that this species is susceptible to infection with [WEEJ, Venezuelan equine encephalitis [VEE], and Mayaro and able to transmit pathogens of medical im- [MAY] viruses); the family Flaviviridae, genus Fliivivirus portance. However, it is important to note that thus far Ae. (St. Louis encephalitis [SLE], yellow fever, and dengue vi- aibopiclus has not been implicated in the transmission of ruses); and the family Bunyaviridac, genus Biinyavinif (La diseases of public health importance in the Amcricas. Gen- Crossc encephalitis [LAC], trivittatus \TVr\. and James- eral information arboviral diseases and overview of town Canyon []C] viruses). Table summarizes the key of the important of these diseases, well vector competence information available for Ae. albopiclits their potential relationship to Ac. alboplctus, presented in studies carried out primarily with strains from the Amer- below. icas. It also includes relevant information from stud- ies conducted with strains from Hawaii Asia that pre- dated the discovery of Ae. albopiclus in the New World. General Information on Arboviral Diseases Aedes albopiclus has been shown to be susceptible to in- fection with at least 26 different arboviruses and able to Arthropod-borne viruses (arboviruses) consist of group transmit at least 24 of them. Information natural and of animal viruses that able to reproduce in arlhropod experimental infections of Ae. albopiclus and its potential and be transmitted to vertebrate host. According to the to transmit these viruses to humans and other vertebrates is World Health Organization (1985), "arboviruses viruses discussed below. that maintained in nature principally, to important extent, through biological transmission bchveen susceptible Arbovirus Field Isolations in the Americas vertebrate hosts by hematophagous arthropods through transovarial and venereal transmission in arthro- possibly Four arboviruses have been isolated from Ae. albopiclus the viruses multiply and produce viraemia in the pods; collected at various locations in the continental United in the tissues of arthropods, and passed tebrates, multiply States. These Potosi (POT) virus from mosquitoes col- to vertebrates by the bites of arthropods after period lected in central Missouri in 1989, Tensaw (TEN) virus of extrinsic incubation." Vertical and venereal (transovarial) from Texas in 1991, Keystone (KEY) virus from central transmission in arthropods may basic long-term Florida in 1991, and EEE virus from central Florida in maintenance mechanisms for arboviruses. 1991. The role ofAe. ulbopicius in the natural transmission DeFoliart et al. consider vertical transmission to (1987) cycles of these four viruses remains obscure. Of the four be survival mechanism developed by the virus to resist isolations, probably the most disturbing is that of EEE adverse climatic conditions that may affect its arthropod virus (Mitchell et a]., 1992). host. Vertical transmission involves "the direct transfer of infection from parent organism to his. her, its off- spring." In contrast, horizontal biological transmission in- Eastern Equine Encephalitis (EEE) volves ingcstion of the virus in the blood of vircmic tebrate, multiplication of the virus in the midgut of Ihc This RNA virus, belonging to the genus Alphavirus of mosquito, dissemination of the virus to the hemocoel, in- the family Togaviridac, forms part of complex of enccph- fection of the salivary glands, and transmission of the virus alitidcs transmitted by mosquito species (Acha and Szyfres, to susceptible vertebrate host by bite (Turell, 1988). The 1987). In North America the virus is maintained in fresh- virus also be transmitted cither horizontally by arthro- water swamp habitats in cnzoolic cycle principally in- pods infected vertically, mechanically by arthropods that volving Culiseta melanuru and variety of bird species obtain partial blood meal from infected host and then (Scott and Weaver, 1989). Various species of mosquitoes continue their feeding susceptible (i.e., arthropods believed to be bridge vectors between this maintenance contaminated flying syringes). cycle and susceptible mammalian hosts. In North America, Sliroycr (1986) and Mitchell (1991) reviewed the vector these vectors include Coquillettidia pcrlurhans and Aede'i competence of Ae. albopictus, including North and South sollicitan'i. in the tropical countries of the Amcricas, the American strains, to arbovirus infections. The term "vector vectors appear to be Culcx nigripalpiis, Culcx laeniopus, competence'' used herein corresponds to the definition and Aedes taemorhynchus (Calisher et al., 1981). cited by Mitchcll (1983): "the combined effect of all of the EEE is but disease of humans in physiological and ecological factors of vector, host, patho- the Americas with overall case-fatality rate among clin- gen, and environment that determine the vector status of ical of between 50% and 80% (Shopc, 1985a). The given arthropod population." laboratory studies have dem- disease in humans has sudden onset and is manifested by onstrated that Ar. alhopiclus is competent vector of most high fever, cephalalgia, conjunctivitis, nausea, vomiting, of the American encephalitis viruses. These include and lethargy, progressing rapidly to delirium and bers of the family Togaviridac, genus Alphavirus (eastern Neurologic signs include neck stiffness, convulsions, equine encephalitis [EEE], western equine encephalitis spasms of the muscles of the extremities, and altered

28 Hexes. A biphasic is in children, with fever, lated in Argentina, Canada, Colombia, Cuba, Guatemala, vomiting, and headaches for two days, followed first Guyana, Haiti, Mexico, Panama, Peru, the United States, by apparent recovery and then by rapidly fatal and Venezuela (Acha and Szyfres, 1987). cephalitis. Sequelae and in the Although FEE disease in humans, it young. About 60% of the survivors show mental retardation primarily affects domestic mammals and exotic birds. Nu- (Shope, 1985a; Acha and Szyfrcs. 1987). Sporadic human epizootics have been reported among horses, with of REE have been reported from Brazil, the Domin- high mortality rates. Such outbreaks may may not be ican Republic, Jamaica, and Trinidad and Tobago. (WHO. accompanied by clinical in the human population. Ex- 1985). Elsewhere in the Americas, the virus has been iso- otic birds that be affected by EEE include pheasants,

Table 1. Susceptibility of Ac. iilbopictus to oral infection with arboviruses, ability to transmit them by bite, and status in nature. Infected Oral Oral in Virus in feel. trans. References Chikungunya'"1' No Tcsh al., 1976; TurcllTuroll al.,ill., 19921) Dengue 1,2,3,4"" Yes Roscn al.,ill., 1985; Milchcll al.. 1987 EEF.- Yes Mitchcll al., 1992; Turcll al., 1994 Jamestown Canyon'' No Grimslad al., 1989 JE- Yes Roscn al., 1978 Keystone1' Yes Milchcll al.. 1992 La Crosse1' No Sircit and Grimslad, 1990 Mayaro1' No Smith and Prancy, 1991 Nodamnra'' No Tesh. 1980 Oropouctn^ No Smith and Franci, 1991 Oningo'' No Kay al., 1982; Tomori and Aitken, cited in Shroyer, 1986 Polosi" Yes Francy ct al., 1990a Ril'l Valley lever" No Turcll al.. 1988 Ross River''' No Mitchcll and Guhlcr, 1987; Milchcll al., 1987 Sinilbis" No Dohm and Turcll, unpublished data, 1993 San Angelo'' No Tcsh. 1980 SLE" No Milarrmra al., 1940, cited in Shroyer, 1986; Hardy al.. 1980 Tensaw* Yes Mitchcll al., 1992 Triviiiatus1' No Grimslad al., )989 West Nile" No Akiiler al., 1982 WEE" No Kramcr al., unpublished information, cilcd in Milchcll. 1991; Simmons al.. died in Shroyer, 1986 VEE IAB" No Tnrcll al.. 1992a Yellow fcvel"" No Mitchcll al., 1987; Miller and Ballinger. 1988

Studies conducted with Ac. uibopictus strains Irom Hawaii and/or Asia. Studies conducted with {ilbopH'tna strains from United Slates and/or Brazil. EEE equine encephalitis virus JK Japanese encephalitis virus SI.E Sl. I-ouis encephalitis \irus WEE Western equine encephalitis virus, VEP. Venezuelan equine encephalitis Swim': taken from Shroyer (1986). Milchell (1991). and updaled information published o! Juh 1993. Special emphasis is given studies carried with strains from Americas.

29 quails, peking ducks, emus, and partridges. In out- Studies of vertebrate susceptibility to POT virus breaks in the United States attack rates of up to 50% have carried out with suckling mice, hamsters, rabbits, and pi- been recorded, producing serious economic losses (WHO, geons. This virus is pathogenic for suckling mice. 85% 1985). (n 59) became symptomatic after intracercbral inoculation Fourteen strains of EEE virus isolated from Ac'. of POT virus (Niebylski, 1992). The range of symptoms albopictus collected during the of 1991 in tire detected in mice included loss of coordination, tremor and dump in Polk County, Florida (Mitchell et al., 1992). This prostration, and limb paralysis- Overall mortality 62%, the first reported isolation of arbovirus of known with average survival time of 8.8 days. Hamsters and public health importance from wild-caught Ae. albopictus rabbits developed low levels of viremia (2.0 login median in the United States. In June 1992, after active participation tissue culture infective doses fTCID^]/ml to 4.3 logic by the local Mosquito Abatement District and destruction TCID,(i/ml of whole blood) with sign of illness. Neither and removal of the tire dump, several research agencies viremia signs of illness detected in pigeons In- failed to EEE virus fromAAnopheles crucians collected in ined), transovarial transmission may still play role in the Baldwin County, Alabama (Coleman, 1969). The virus pro- long-term maintenance of this virus in nature. To date, the duces clinical disease and death in suckling and adult mice public health significance of the EEE field isolations from but not in rabbits, guinea pigs, hamsters. Antibodies have Ae. albopicius remains unclear. However, because of the been detected in dogs, raccoons, cattle, and humans (Cham- high sensitivity of this species to EEE viral infection, its berlain et al.. 1969). The importance of TEN virus opportunistic feeding behavior, and its continued expansion public health threat remains unknown (Coleman, 1969). within the Americas, the natural transmission cycles of EEE KEY virus recovered from pool ofA<:'. albopicius virus may be modified by the inclusion ofAe. albopictus. collected during the Florida studies that recovered EEE virus from this species. The virus belongs to the fam- ily Bunyaviridae, genus Runyavirus, and has been isolated from cotton rats (Sigmodon hispidus) in Georgia and Flor- Potosi (POT) ida (Sudia et al., 197 la). Aedes allunlicus and/or tormentor appears to be the principal vector, although KEY virus has Ten strains of POT, newly recognized virus, been isolated from nine other mosquito species. Antibodies covered from Ac. albopicius collected in the of have been detected in rice rats, cottontail rabbits, gray 1989 in the United States (Francy et al., 1990a). The iso- squirrels, raccoons, white-tailed deer, sika deer, horses, and lates determined to belong to the family Bunyaviridae, humans (Sudia et al., 1971a; Watts et al., 1982). genus Bunyavirns, and the Bunyamwera serogroup. These Although the impact of TEN and KEY viruses human isolations made from pools ofA

30 arthropods vectors, may be transmitted to humans by Ac. 1985). Naturally infected Ac. albopicliis collected in albopictus result of the aggressive feeding o( this spe- Asia by Rudnick and Chan (1965). cies humans well other mammalian hosts.'' Various studies have found Ae. albopictus to be associ- ated with epidemics of dengue fever (Chan. Y. C., et al., 1971; Jumali et al., 1979; Fan et al.. 1989). However, be- Laboratory Vector Competence Studies of Some Ae. albopictus often overlaps in distribution with Ae. Important Arboviruses from the Americas aegypti, another known vector of DEN viruses, it is ol'len difficult to determine the relative contribution of the two species to disease transmission. During massive dengue ep- Dengue (DEN) idemics in the Seychelles Islands and in Guandong, China, where Ae. aegypti absent, Ae. albopictus incrimi- DEN viruses consist of antigenic subgroup of four nated the principal vector (Mctsclaar et al., 1980; Oiu el closely related, but antigcnically distinct, viruses designated al., 1981). Thus, experimental and natural association of the DEN-1, -2, -3, and -4. which belong to the genus Flavivi- four DEN viruses with Ac. albopiclus has been documented rus, family Flaviviridac (Westaway et al., 1985). in several instances. The classical form of dengue is characterized by acute In the Americas, geographical strains of Ac. albopiclus febrile illness with headache and joint and muscle pains from Brazil (Cariacica City) and the United States (Hous- (WHO, 1986a). Epidemics of dengue annually affect mil- ton) competent laboratory vectors of all four DBN lions oF people in tropical of the world. Dengue hem- rotypes (Mitchcll. 1991). In addition, both North and South orrhagic fever/dengue shock syndrome (DHF/DSS) is American strains of Ae. albopictus transmit all four form primarily in children, although it affect DEN serotypes vertically (Mitchell and Miller, 1990; Bosio adults well. It is caused by the DEN virus clas- ct al., 1992). Thus, Ae. albopiclus may impor- sical dengue. However, DHF/DSS may have immuno- tant maintenance vector of DEN viruses in endemic areas, pathologic basis, and the case-fatality rate is 5% to 10% and endemic foci may be initiated by importation of (WHO. 1986a). DHF is major of morbidity and vertically infected eggs (Gubler, 1987; Shroyer, 1990). mortality among children in many countries of Southeast Asia, and recently its importance has increased in the Americas (Halstead, 1980; Monath, 1986; Kouri ct al., Yellow Fever (YF) 1989; I'AHO. 1992). In the Americas, dengue worsened public health YF virus is member of the genus Flavivirus, family Fla- problem during the 1980s. Between 1980 and 1990 viviridae- This viral disease is endemic in tropical regions of than million dengue reported to PAHO. The both the Americas and Africa. In the Americas, the endemic majority of these caused by serotypes 1, 2, and for Yl'' include the Amazon and Orinoco-Magdalena 4, will few imported related to DEN-3. During basins in Bolivia, Brazil, Colombia, Ecuador, French Guiana, those years, increase in of DHF/DSS observed Peru, and Venezuela (Acha and Szyfrcs, 1987). The disease in various countries of the continent. Thus far, the most may range from subclinical to fatal. Depending the important outbreak of DHF/DSS in Cuba in 1981, verity, the signs and symptoms of yellow fever include fe- when than 300,000 dengue cases, 10,312 DHF/DSS ver, headache, nausea, epistaxis, albummuria, and body cases, and 158 deaths recorded (Kouri et al,, 1989). pain. In cases, the disease is characterized by oli- A second major outbreak occurred in Venezuela from Oc- guria, jaundice, and hcmorrhagic manitcslations that in- tober 19S9 to January 1990, with 5,990 and 70 deaths clude epistaxis, black vomitus, mclena. and uterine (PAHO, 1992). Other countries in the Americas that have hemorrhage (WHO, 1985). reported DHF Aruba, Brazil, Colombia, the Dominican Dingcr et al, (1929) reported that Ae. albopictus females Republic, El Salvador, French Guiana, Honduras, Mexico, transmitted YF virus to monkeys in laboratory experiments. Nicaragua, Puerto Rico, Saint I.ucia, Surinamc, and the Vir- However, infection and transmission rates not gin Islands (Institut Pasteur dc Guyane, 1991; PAHO, determined. 1992). Monath (1986) suggested that, because of the ecological The ability of Ae. albopictus to transmit DEN virus adaptability of Ac. albopictus, this species could bridge the first shown in studies involving human volunteers early gap between the jungle and urban YF viral transmission 192fi (Siler et al., 1926). More recently, Ae. ulbopiftus cycles. This scenario would favor the spread of YF in vil- shown to be able to transmit all four DEN serotypes lages and towns, particularly in endemic of South both horizontally (Gubler and Roscn, 1976) and vertically America. Ae. alhopiclus could fill ecological niche anal- (Roscn et al., 1983). The species also found to be ogous to that of Ae. simpsoni, major bridging and epi- susceptible to oral infection with all four DEN serotypes demic vector of YF in East Africa. These assumptions have than Ae. aegypli (Jumali et ai., 1979; Rosen ct al., been reinforced by experimental studies indicating that both

31 Texas the U.S. (Houston) and Brazilian (Cariacica, Espfrito Santo strains (24%) than for U.S. strains from Indiana strain from State) strains of Ac. ulbopictus susceptible lo oral in- (5%) (Beaman and Turcll, 1991); however, VEE virus fection with YF virus (Mitchcll el al., 1987; Miller and New Orleans (Gcntilly), Louisiana, transmitted The Ballingcr, 1988; Miller el al., 1989). However, the North most efficiently (45%) (Turcll and Bcaman, 1992). strain American strains significantly efficient vectors transmission rate observed for the New Orleans Pso- than their southern counterparts. comparable to higher than those reported for rophora confimis (33%) and Aedes soUicilam (38%), two of the natural vectors of epizootic VEE (Sudia el al., 1971b; Venezuelan Equine Encephalitis (VEE) Turcll et al., 1992a). Turcll and co-workers (1992a) spec- ulate that the observed differences in strain susceptibility VEE virus is member of the genus Alplwvirus, family may be the result of either founder effect separate ef- Togaviridae. Based the kinetics of the hcmagglutination- introductions in the of origin of the strains. The al- inhibition test, Young and Johnson (1969) first established ficient transmission of VEE virus by of the As. classification for VEE virus consisting of complex hopiclus strains presently found in the Americas suggests of group divided into four subtypes (I-IV). Subsequently, six that the presence of this species has increased the risk antigenically related virus subtypes numbered through VI transmission of VEE. defined (Walton and Grayson, 1989; Calishcr, 1994). Also recognized the varieties IAB, 1C, ID, III, and IF within subtype I, well the varieties II1A, IIIB, and La Crosse (LAC) IIIC. for total of eight different variants (Calisher, 1994). Among the five antigenic variants of subtype I, two (IAB LAC virus is member of the genus Runyavirus of the and 1C) virulent to horses and responsible for family Bunyaviridae and belongs to the California epidemics/epizootics, while the other members of the VEE group. Isolation of LAC virus has been reported only from complex generally considered cnzootic viruses (Cal- North America, and LAC is endemic throughout large por- with LAC ishcr, 1994). The VEE complex is native to the Americas tions of the midwestcrn United Stales. Infection and is endemic in Central America and northern South virus encephalitis, particularly in children and America well Mexico, Trinidad and Tobago, and the adolescents under 15 years of age. The endemic in- state of Florida in the United States (WHO, 1985). cludes Minnesota, Wisconsin, Illinois. Indiana, Ohio, West VEE in humans is usually respiratory illness with fe- Virginia, and New York. Although fewer than 100 ver, headache, and muscle pain similar to self-limiting usually reported each year, it is likely that many infections influenza-like febrile illness. However, infections with LAC virus incorrectly diagnosed of mild, develop into serious encephalitis (Shope, 1985a; Acha undift'crcntiated fever of unknown origin. Infection with and Szyfrcs, 1987). In most cases, the onset of the disease LAC virus may result in illness with high fever, with is accompanied by malaise, chills, ccphalalgia, and, fre- without generalized convulsions. Vomiting, focal seizures, quently, vomiting, and diarrhea. The illness may paralysis, abnormal reflexes, and mental manifestations resolve after three to five days unless encephalitis (Shope, 1985b), and neurological sequelae Peripheral neurological symptoms, such flaccid spastic persist for years after the acute illness. The case-fatality rate paralysis and alterations in reflexes similar to the neurolog- is less than 0.5%. ical symptoms of other arbovirus encephalitides, typical Various species of mammals, especially rodents, of VEE encephalitis (Acha and Szyfres, 1987). Encephalitis ceptible to infections by LAC virus, but it is believed that is frequent in children than in adults. Mortality rates these infections generally asymptomatic (Acha and low but may reach 3.6% in with deficient medical Szytres, 1987). The tree hole mosquito Aedes Iriserialiis is services (Shope, )985a). Sequelae, including behavioral considered to be the principal vector of LAC virus to both changes and learning defects, also Horses may de- amplifying rodent hosts and humans. The main vertebrate velop rapid fulminating illness with sudden death hosts of LAC appear to be the eastern chipmunk (Tamius encephalitic syndrome. During the period 1967-1971. stnalus), gray squirrel {Sciurus caroUnensis), and red fox 100,000 equine deaths due to VEE, well hundreds of (Viilpes ftilva) (Calishcr, 1994). thousands of human infections, reported from Central The introduction ofAe. alhopictus into cnzootic for America and the United States (WHO, 1985). LAC has led to various studies of the vector potential of Experimental studies indicate that both North and South this species for LAC virus (Tcsh and Gubler, 1975; Grim- American strains of Ae. alhopiclus competent vectors stad et al., 1989; Strcit and Grimstad, 1990; Cully et al., of VEE virus (Bcaman and Turell, 1991; Turcll and Bca- 1991; Cully ct al., 1992). Ac. alhopicliis is highly suscep- man, 1992). However, susceptibility to infection and rates tible to oral infection with LAC virus, nearly all (1,633 of transmission varied significantly among the five strains >99%) of 1,637 Ae. alhopicltis contained LAC virus tested. Transmission rates higher for South American when tested 14 days after ingcstion of blood-LAC virus

32 suspension containing virus tilers simulating doses that Mayaro (MAY) and Oropouche (ORO) would be encountered in nature (3.5-4.5 logs). These stud- ies included 27 strains of Ac. albopiclun, 14 from locations MAY virus is member of the genus Alphaviru^, family within the continental United States, 5 from Brazil. and the Togaviridae. Its activity has been documented only in the rest from temperate Asia, tropical Asia, and Hawaii (Streit Amcricas, where it has been isolated in Bolivia, Brazil, and Grimstad, 1990). Moreover, 97% of the 1,637 Panama, Suriname, Trinidad, and the United States (Pin- head-positive for the virus, suggesting dissemination of heiro and LcDuc, 1989). In endemic areas, such the Am- LAC virus beyond midgut barriers and throughout the he- regions of Bolivia and Brazil, 10%-15% of residents mocoel. All 43 Ac'. Iriscriatus fed the blood-virus have antibodies to MAY virus (Pinheiro and LcDuc, 1989). suspension also had disseminated LAC virus infections The onset of the illness is abrupt, with fever, headache, (Streit and Grimstad, 1990). Other experiments conducted epigastric pain, backache, arthralgia, photophobia, dizzi- with LAC-viremic eastern chipmunks (T. siriatus) suggest ness, and chills (Pinheiro et al.. 1981; Pinheiro and LcDuc. that the infection threshold otAe. albopictus is lower than 1989). Humans appear to be accidental hosts that become that of Ae. triserialus (Streit, pers. 1993). More infected in forest where MAY virus circulates among than 30% of fully engorged Ae. alhopicluf, became infected, wild vertebrates and mosquitoes. MAY virus has been compa-'ed to less than 109& of similarly exposed Ac', iriser- isolated from several species of mosquitoes, especially iatus. after feeding chipmunk with LAC virus titer Haemagogiis spp., although it has also been recovered from of 3,600 viral plaque-forming units (PFU)/ml blood (84 Culex, Sahethes, and Aedes spp. hour postinfection). In transmission experiments conducted A strain of Ac', albopictus from Sao Paulo, Brazil, after 14 days of extrinsic incubation, 43% of Ac', albopictus competent laboratory vector for MAY virus, with infection transmitted virus to suckling mice (Streit and Grimstad, rates of 9%-85% and transmission rates of 45%-50% 1990). Ae. albopictus infected either orally transovarially (Smith and Francy, 1991). transmitted LAC virus to susceptible eastern chipmunks It concluded that "with large Ae. albopictus popu- (Cully cl al., 1992). As with other arboviruses, there lations and extensive MAY virus amplification, this species significant variation in transmission rates (18%-75%) could secondary vector during outbreaks and among the various Ae. albopictus strains tested. Brazilian perhaps bridging vector for MAY virus between the and tropical Asian strains tended to transmit LAC virus forest habitats and settled areas" (Smith and Francy. efficiently than did North American and temperate 1991). The danger that Ae. alhopiclus will become in- Asian strains (Streit and Grimstad, 1990). volved in the transmission cycle of this virus is increased Ae. albopictus also transmit LAC virus transovarially by the recently reported infestations of Ac. albopictus in (Streit and Grimsfad, 1990; Cully ct al., 1992). Minimum the state of Maranhao, which is contiguous with the state filial i'.ifeclion rates range between 1% (Teresa Brazilian of Para, where past outbreaks of MAY have been reported strain) and 4.5% (Oahu strain). In recent study, filial in- (Pinheiro et al., 1981). fection rates ranged from 3%-22% (average 10%) for prog- OHO is member of the Simbu serogroup of the genus eny of individual LAC virus-infected females (Streit and Runyavirus, family Bunyaviridae (Karabatsos, 1985). In- Grimslad, 1990). Streit (1994) found that transovarial trans- fection with ORO virus has been recognized major mission of LAC increased rapidly with selection. After of human febrile illness in the Amazonian region of three generations, he established LAC-disseminated line Brazil. Between the years 1962 and 1980, several outbreaks which continued 90%-r positive for 10 generations. In occurred in Para State which affected at least 165,000 per- other line he established, transovarial transmission in various urban centers (Pinheiro et al., 1982). Al- tinued for 10 generations among mosquitoes that though deaths have been attributed to infection with ceived blood (i.e., completely autogenous). This ORO virus, many patients became severely ill and required ability opens remarkable possibilities for the maintenance prolonged convalescence (Shope, 1985b). The disease is of reservoir. In economically depressed in East manifested by sudden onset of fever, chills, and malaise St. Louis, Illinois, 50% of wild-caught Ac. albopiclus had and is marked by myalgia, dizziness, headache, photopho- fed urban rats. Antibodies to LAC found in rats bia, and sometimes mild epigastric pain, nausea, and and opossums. Streit (1994) suggests the possibility of vomiting. u'ban cycle for LAC. Studies carried out with Ae. ulbopictus strain from The fact that Ae. albopictus becomes infected and trans- Sao Paulo, Brazil, suggest that this species may not be mits LAC virus at rates similar to those of the natural vector competent vector of ORO virus (Smith and Francy, 1991). (Ae. triseriatus), along with its establishment in where Infection rates 2%-12%, and mosquito of this LAC virus is endemic and its general feeding behavior, in- strain transmitted the virus by bite. This is not surprising, dicates that Ac. allwpicius may become involved in the nat- since Culicoides paraensis is considered the natural vector ural LAC virus cycle and secondary vector in (Pinheiro et al., 1982). However, although the risk thatAe. where LAC virus is active. albopicfus will become involved in ORO virus transmission

33 appears low based the results of Smith and Francy mosquitoes and birds, with various Acdes spp- acting (1991), other strains of Ac', albopictus might be effi- bridge vectors that infect humans. cient vectors of the virus. Laboratory studies indicate thai Ae. ulbopicliis is at least efficient vector of SIN virus is Cx. pipiens, known vector (D. Dohm and M. Turell, unpublished data). SIN Arboviruses Common in Areas Outside the virus has not yet been recovered from wild specimens of Americas Ae. albopicius.

Ae. albopicius is competent vector of several viruses not endemic to the Americas. These include Japanese Chikungunya (CHIK.) cephalitis (JE), chikungunya (CHIK), Ross River (RR), Sindbis (SIN), and West Nile (WN) viruses. In addition, CHIK virus is also member of the genus Alphavirus. Ac. albopictus transmit JE virus (ransovarially, raising family Togaviridae. and dengue-like disease in hu- the possibility that JE virus could be introduced into the This disease has abrupt onset, with high fever, Americas via infected eggs. Information JE, SIN, CHIK. myalgia, and sudden intense pain in joints and RR viruses is summarized below. (Shope, 1985a). Outbreaks of chikungunya fever have been recognized in Angola, Congo, Nigeria, Senegal, and Zim- babwe in Africa and in Cambodia, India, Malaysia, the Japanese Encephalitis (JE) Philippines, and Thailand in Asia (Karabatsos, 1985); these outbreaks affected tens of thousands of people. JE virus is member of the West Nile antigenic complex Ae. albopicius adults highly susceptible to infection of the genus Flavivirus, family Flaviviridae. Monath (1985) with CHIK virus in laboratory experiments and also considers the disease it to be the most important of capable of transmitting the virus by bite (Mangiafico, 1971; the arboviral encephalitides in terms of morbidity and Yamanishi et al., 1983; Turell et al., 1992a). High infection tality. Epidemics of JE seasonally in temperate and transmission rates for Ae. albupictus (100% and 69%, of Asia and in the northern part of tropical Southeast Asia. respectively) readily testify to the importance of this Illness may be manifested febrile headache syndrome, quito potential vector of CHIK virus (Mangiafico, aseptic meningitis, encephalitis. When neurological dis- 1971). Furthermore, Turell and colleagues (1992b) dem- orders appear, they usually accompanied by fever, onstrated high infection rates (range, 72%-97%) in eight chills, anorexia, nausea, vomiting, dizziness, and drowsi- Ae. albopictus strains from different of Asia, Brazil, Case-fatality rates during epidemics range from 20% and the United States after the mosquitoes fed vircmic to 50%, but these high rates reflect recognition of only the rhesus monkey. Disscminalion rates (36%-80%) observed most in the experiments higher than those found in Ae. In the laboratory, Ae. albopictus is susceptible to infec- aegypti, the natural vector of CHIK virus in Southeast Asia. tion with JE virus and is able to transmit virus vertically to Transmission rates not calculated. The virus has not its F, progeny after cither intrathoracic inoculation in- yet been recovered from wild specimens ofAe. allwpicius. gestion of virus-sucrosc-crythrocytc mixture (Rosen et al., 1978). As adults, at least five of the infected F, female Ac'. Ross River albopictus transmitted JE virus to chicks which they fed. (RR) Moreover, Huang (1982) reported that strains of the is member of the and the JE virus isolated from field-collected Ac', albopictus RR virus genus Alphavirus larvae from Fukien, China. etiologic agent of epidemic polyarthritis (EPA) (Shope, 1985a; MitcheH and Gublcr, 1987). Individuals affected by the disease complain of pain, swelling, and limitation of Sindbis (SIN) movement in the joints of the hands and ankles. Patients may develop maculopapular rash the trunk and S]N virus is member of the western equine encephalitis tremities. Other symptoms include throat, enlarged complex of the genus Alphavirus, family Togaviridae, and lymph nodes, and tender palms and soles (Shope, 1985a). dengue-like disease in humans. Clinical symptoms Until the late 1970s, reports of epidemics of EPA in- include fever, rash. headache, general malaise, and arthral- itially received only from Australia, the Solomon Islands, gia (Niklasson, 1989). Although fatal have been and New Guinea. In 1979 major outbreak of EPA reported, arthralgia may be enough to require hos- curred in the Western Pacific region, affecting than pitalization and may persist for up to three years. SIN 50,000 individuals in Fiji, the Samoan Islands, the Cook in Europe, Africa, Asia, and Australia- Various Culex Islands, and parts of Melanesia (see references in Mitchell spp. have been implicated potential vectors, and the nat- and Gubler, 1987). Antibodies for the virus have been ural transmission cycle is believed to be between Culex found in domestic animals such dogs, sheep, pigs,

34 horses, and cattle. Antibodies also have been found in wild Protozoan and Filarial Diseases mammals such kangaroos, wallabies, and rodents (Shope, 1985a). The most important vectors of RR virus Filarial Worms appear to be Culex annulirostris, Aedes vigilax, and Aedes polynesiensis (Kay et al., 1982). Field-collected specimens ot'ADirofilaria immitis, the causative for RR virus (Mitchell and Gubler, 1987; Mitchell et al., agent of dog heartworm in Japan and the United States 1987). Variation in vector competence among the geograph- (Mori and Wada, 1977; Scoles and Craig, 1993). Ae. al- ical strains also detected in the trials. Infection rates hopictus populations from the United States have marked approached 100% following ingestion of high-titer blood genetic variability in terms of susceptibility to Dirofilaria meals from golden Syrian hamsters (6.3 log;,, PFU/ml-7.1 immiiis. Work carried out in North Carolina found that Ae. logio PFU/ml). Strains from Sri Lanka and Singapore dem- albopictus entirely refractory to infection with D. im- onstrated less susceptibility to infection (53%-80%). Trans- mitis (Apperson et al., 1989). However, recent work mission rates also high in the Houston and Hawaii conducted at the University of Notre Dame showed that strains (52% and 77%, respectively) by day 14. Both strains 40% of Ae. albopictus population from New Orleans able to transmit RR virus to suckling mice by day 7 developed infectious L3 larvae: the results for other U.S. postinfcction. When larvae from the second oviposition of populations intermediate (Scoles and Craig, 1993). infected female parent tested, they failed to show Several laboratory experiments also have demonstrated that proof of vertical transmission. Ross River virus has not yet Ae. albopicius be infected with D. immitis (Galliard and been recovered from field-collected Ae. albopiclu.'s. Ngu, 1938; Stojanovich and Scott, 1965; Konishi. 1989). However, Ae. albopictus is not vector of human fila- riasis caused by Hrugia Wuchereria spp. (Sasa, 1976). Transovarial Transmission The larval tail to develop in the thoracic muscles. Roscn et al. (1976) justified their release of Ac. albopictus In addition to high susceptibility to oral infection, Ae. small Pacific atoll attempt to replace vector of albopictus is able to transmit viruses to its prog- filariasis (Ae. poiynesiensis) with nonvector. Unfortu- eny tran?.ovarially. Strains of Ae. albopictus from Hawaii nately, Ac. albopicius failed to persist the atoll. Asia known to be able to transmit vertically 15 boviruse?;: DEN-1, DEN-2, DEN-3, DEN-4, Banzi, Bus- Avion Malarias suquara, Ilheus, Kokobera, Kuirjin, JE, SLE, and Uganda S viruses in the family Flaviviridae; and KEY, LAC, and San Avian malarias have been experimentally transmitted by Angelo viruses in the family Bunyaviridae (Tesh, 1980; Ae. aihopictus. The species became infected with and trans- Shroyer, 1986). Stabilized infections of San Angelo virus mitted Plasmodium lophurae beginning 12 days after feed- in Ae. albopicius, and very efficient vertical trans- ing infected duck (Laird, 1941). Likewise, Ae. al- mission takes place for up to 38 consecutive generations Iwpictus is susceptible to infection with Pla^modium (Tesh and Shroycr, 1980; Shroyer, 1986). In the laboratory, gallinaceum; female mosquitoes developed sporozoites in Ae. albopicius strains from the Americas have vertically the salivary glands and gut 15 days after infectious blood transmitled DEN-1, DEN-4, YF, POT, and LAC viruses meal (Russell and Menon, 1942). These mosquitoes also (Mitchell, 1991; Streit and Grimstad, 1990). transmitted P. gallinaceum to normal fowls. The ability of Ae. albopictus to harbor P. gallmaceum has made this quito useful model for malaria studies ct al- Other Arboviral Studies (Hu 1989).

Shroyer (1986) lists arbovimses that able to DISSEMINATION AND CONTROL replicate in Ae. albopicius specimens following intrathora- cic inoculation- However, there is information whether Ae. albopicius be orally infected with these Mode of Dissemination and Origin arbovin'ses and subsequently transmit them by bite. These viruses include the phleboviruses Arumowat, Bujaru, Chi- Since the discovery of Ac. alhopicfus in the Ainericas in libre, Tcoaraci, Itaporanga, Karimabad (Tesh, 1975), and 1985 and its rapid spread to than 300 counties in 23 Rift Valley virus (Turell et al., 1988), and the rhabdoviruses states of the continental United States and 673 municipal- Chandipura, Gray Lodge, Joinjakaka, Piry, Sigma, and ities in 7 states in Brazil (C. Moore, pcrs. comm., Septem- vesicuh.r stomatitis (Rosen, 1980). ber 1994; J. Mangabeira da Silva, pers. comm., April 1994),

35 questions have arisen to how the mosquito intro- pictus to shorter photoperiods (O'Meara et al., 1993). duced in the first place and how it is spread to Moreover, since 1986, in many in Louisiana Ae. al- The spread of Ac. albopicfus is widely believed to be bopictus has shown that it spread from tire piles into associated with the massive movement of used tires around tree holes (NOMCB, 1987). the world (Rai, 1991). There is compelling evidence that The appearance of the species in the Dominican Republic used tires imported in containers from Asia and holding raises several iniiinswered questions. The infestation may larvae and of Ac. albopictus responsible for its in- be strain of temperate origin (from either Asia conti- troduction into the United States (Monath, 1986; Craven el nental America) that originally had photoperiodic al., 1988; Francy et al., 1990b). After the Houston experi- sponse but progressively lost it result of genetic selec- ence, in which tires found to be the main breeding tion for nonphoroperiodic trait. Another possible scenario of Ac. albopictus (Sprenger and Wuithiranyagool. is that this infestation is independent of others in the Amer- 1986), surveys carried out in other states have focused icas. having been brought inadvertently in shipping cargos tire yards. that originated in tropical Asia. Current research will The recent infestations of Ac. aihopictus reported in doubtedly these questions in the future. towns along the northern border of Mexico in the states of Brazil's infestation appears to be linked to the interna- Coahuila and Tamaulipas may also be due in part to the tional seaport of Victoria in the state of Espfrito Santo movement of used (ires and other artificial containers. It is (PAHO, 1987). Since used tires from the United States important to note that the officially reported figures the regularly unloaded in this area, it is possible that secondary number of used tires exported from the United States to dispersion of Ac. albopiclus may have been responsible for Mexico have been increasing steadily since the 1980s. Fur- its introduction into Brazil. It thus appears that all the infes- thermore, Mexico is the principal customer for U.S. used tations reported from the Americas classic examples of tires in the Western Hemisphere, having bought 173,708 the role played by increased travel and between units in 1991 alone (U.S. Department of Commerce, Bureau countries in the proliferation of non-native species. of the Census, National Trade Data Bank, CN TRADEX Studies North American and Brazilian strains of Ac. A4012200000-Used pneumatic tires of rubber). In addi- albopictus have shown that populations from both tion, it is well known that many trucks transport scrap tires cicctrophoretically similar to Ae. albopictus populations from infested of the United States throughout Mexico, from temperate of northern Asia (Kambhampati et al., which clearly favors the spread of the infestation. Thus. it 1991). is uncertain whether the Mexican infestations restricted In the United States, studies carried out to determine the to those bordering the state of Texas whether the degree of differentiation among mosquitoes collected at species has already become well established in the country. several sites in the city and among populations from In the four countries in the Americas known to harbor different cities showed levels of genetic variation in the the species-Brazil, the Dominican Republic, Mexico, and Houston and New Orleans populations. These results sug- the United States-Ac. albopictus has been reported breed- gested large and independent introductions oiAe.dcs to both ing in tires, well in artificial and natural water-filled cities and support the idea that Houston and New Orleans containers. Regarding the issue of used tire exports. (Black et al., 1987) the first sites of introduction in O'Meara and co-workers (1993) pointed out that "there is the United States. major threat of exporting Ac. allwplctus from the United Overall, enzyme electrophoretic observations carried out States to countries that currently free of this mosquito. by Drs. W. Hawley and L. Munstcrmann with Southeast Used tires being shipped from Florida and other Gulf Asian populations of At', albopiclus show extreme genetic Coast states, without adequate inspections for mosquitoes. differentiation, in marked contrast to the relative homoge- to destinations in the Caribbean region and Central and neity of North American populations. "This appears to in- South America." Introduction of Ae. albopictus to addi- dicate that gene flow in the introduced populations of the tional countries in the Americas would appear to be im- Americas is much higher than that found among indigenous minent may have already occurred owing to such factors populations'' (Hawley, pcrs. comm., 1991). Other molec- the rapid expansion of and traffic by land, air, ular studies appear to reinforce the notion of high levels of and Moreover, since adequate entomological surveil- gene flow in the species. For instance, variation in mtDNA lance and vector control activities lacking in most of analyzed in 17 populations of Ac. allwpictus using 18, the countries of the Americas, the spread is likely to 4, 5, and 6 bp cutting restriction enzymes (Kambhampati continue. and Rai, 1991), The results revealed low level of restric- In the state of Florida, three other specific factors besides tion fragment length polymorphism in the Ac. alhopictus the movement of containers appear to be contributing to the populations, compared with other insect species. Only three spread of the species. These factors the widespread populations found to carry novel mtDNA haplotypcs. availability of suitable aquatic habitats, the decline of Ac. An analysis of individual mosquitoes revealed that these aegypli populations, and the rapid adaptation of Ac. albo- populations included individuals carrying both the ancestral

36 and the novel mtDNA haplotypcs, suggesting that the di- portable thermal tog generator. With treatment of vergence of the populations is incomplete. The study entire 11.5-km'1 island Singapore, good control cluded that the recent range expansion of the species and achieved for 10 days; however, the population recovered gene flow facilitated by human activities could explain the rapidly during the third week. With two treatments spaced low level of polymorphism. Rai (1986 and 1991) reviewed week apart, prolonged control achieved (a 92% studies the genetics of Ac. allwpictus. reduction for up to eight weeks). In general, it is believed that populations that highly As already stated, in Singapore, chemical control is used variable, i.e., genetically plastic, better able to avoid only during outbreaks of dengue hemorrhagic lever. During control and to develop resistance. Partial resis- such epidemic in 1973, special attention given to tance lo organophosphates, specifically malathion, has 400 construction sites where vector breeding places and arisen inAe. alhopictus populations from Houston and New harborages profuse. To kill the adult mosquitoes, all Orleans (NOMCB, 1987; Khoo et al, 1988; Robert and the construction sites fogged with hioresmethrin Olson, 1989). Various levels of resistance to organophos- mixed with equal parts of piperonyl butoxide synergist; phates have been observed in several populations in the the containers treated with 1% temephos sand gran- United States, while Brazilian strains from Kspirito Santo ules 1% malathion emulsion to kill the immature stages. Slate (Cariacica City) have been found to be highly The DHF continued, however, continuous daily ceptible to the insecticides studied (Wesson, 1990). treatment implemented at these sites. This approach resulted in significant drop in DHF incidence (WHO, 1986b). Control In Louisiana, ultra-low-volume (ULV) application of the synthetic pyrethroid bioresmethrin reduced the adult Ae. It is difficult to control eradicate Ae. alhopictus ulbopictus population by 60%, but the reduction lasted for than Ae. because Ac. alhopiclus is found farther aegypti only about three days (Anderson, New Orleans Mosquito from human habitation and in wider range of habitats. Control District, pers. comm., 1986). In New Orleans, for- Population suppression may be economical only in mulations of permethrin sandcorc granules containing 1.5% human communities. Clearly, the best approach for active ingredient tested to control larvae in experi- controlling Ae. athopiclus and other Stegomyia species is mental plots containing tire piles. The pesticide applied to limit the availability of larval habitats. Massive educa- using manually operated sprayers. The approximate tional programs encouraging citizens to take actions to pre- weight per treated tire 8 g. A single application pro- vent mosquito breeding around and in their homes play duced larval control of nearly 100% during period of cential role in control efforts. 121 days (NOMCB, 1987) and greater than 80% for nearly Prior to the U.S. infestation, very few studies evalu- 300 days (NOMCB, 1988). A similar experiment, also ations dealt with the control ofAe. allwpictus. In fact, this ried out in tire piles New Orleans, conducted to species rarely, if ever, the primary target of control the effects of combination of corncob fenoxicarb- program. More often, it considered secondary in im- impregnated material (\% active ingredient) and granular portance to Ae. aegypti. To date. the most extensive effort formulations of Bti (Bacillus thuringicnsis Israelensix) to control Ae. aegypti and Ae. alhopictus has been carried (200 ITUs). The weight of granules received in each out in Singapore. This integrated program, begun in 1968, tire 5.8 g. Mortality of larvae in the treated tires includes environmental management, health education, le- ceeded 80% al 60 days, but tell to 9% at 81 days (NOMCB, gal measures, and community participation; chemical 1987). trol is reserved solely for outbreaks of dengue hemorrhagic During the of 1989 aerial ULV malathion treat- fever (WHO, 1986b). ments conducted in two urban of New Orleans. The twin-engine aircraft equipped with two self- Chemical Control contained Micronair spray pod systems utilizing rotary at- omisers. Aerial treatment rates 3 oz/acre, at treat- House-to-house control campaigns, directed specifically ment altitude of 120-200 feet and flight speed of 150 at Ar. aegypti, appear to be less effective against Ae. al- mph, resulting in swath width of 500 feet; this treatment bopicius, whose control requires coverage of larger areas, succeeded in suppressing the population of Stegomyia including the forest. For instance, island the Gulf mosquitoes for days (NOMCB, 1989), of Thailand, temephos applications and malathion fogging Jardina (1990) reported the eradication of Ac. albopictus effectively suppressed the Ae. aegypti population but did from Indianapolis in Marion County, Indiana, through not significantly reduce the Ae. alhopiclus population combination of chemical treatment and reduction (Gould et al., 1970). (removal of tires and trash from yards). The classical treat- Dowling (1955) reported control ot'Ae. allwpictus using ment of malathion and granular Abate replaced with 15% dieldrin applied at 88 ml per ha with SwingFog(R) syncrgized rcsmethrin and granular Bti. In September 1987.

37 adulticiding performed around infested tire retread- control QiAedes albopictus in rural areas....'' On the other ing company and surrounding roads using ULV fogging hand, Ncwkirk (1947) believed that T. splendens would unit mounted truck. Synergized resmethrin used cupy minor role in the elimination of mosquitoes: "Its at rate of 130 ml/min during five consecutive days. The long life and few offspring, when compared to Aedes al- operation conducted twice day at the optimal spray- hopicJus..., and its low survival rate tend to nullify the ing times of mid-morning and early evening. In addition, importance of (T.) splendens in biological control." An at- portable ULV unit used in inaccessible Simul- tempt to reduce the breeding of Ae. albopictus by intro- taneously, larvicidc operations with Bti carried out in ducing small numbers of T. inornaius in Hawaii in the 3,500 tires six times during period of 45 days. Surveil- 1920s failed when this predator died out (Gerberg, 1985). lance operations conducted in 1988 and 1989 failed to de- The technology developed for the rearing and field tect any Ae. allwpictus in the trials of T. brevipalpis and T. rutilus for the control of Ac*. Other studies ofAf. ulbopictus populations from around aegypli in the Amcricas (Gerberg, 1985) may be utilized Houston, Texas, demonstrated the adulticidal effects of with better results against Ae. albupictus, since both methrin, which produced 96% mortality at concentrations the latter species and these predators breed readily in nat- of 1.5 ng/feroale (48 hours posttreatmcnt at 21 C) (Khoo ural containers away from homes, while the breeding sites et al., 1988). Another pyrethroid showing moderately toxic of Ae. uegypli domestic. effects Ae. ulhopiclus strains from Malaysia is cyfluthrin In laboratory tests with the parasitic mermithid nematode (Responsar) (Vythilingam et al., 1992). Both wettable and Romanomermis culicivorax, Ae. albopictus rated "3" emulsifiable concentrates of cyfluthrin sprayed plywood susceptibility scale of to 5, indicating that the host (10 nig [aij/rar) produced about 60% mortality after 20 days showed moderate physiological resistance (Finney-Crawlcy, of exposure. 1985). Studies carried out with U.S. strains of Ae. albopictus Roberts et al. (1983) report two observations of labora- have shown considerable variation in the response of tory infection ofAe. ulbopictus with viruses: densonucleo- ious geographical populations to organophosphate insecti- sis virus, which only retarded growth at low temperatures cides (Khoo ct al., 1988; Robert and Olson, 1989; Wesson, (16 C), and Nodamura virus, small RNA virus that in- 1990; Sweeney, 1993). According to Wesson (1990), there fects vertebrates. This virus caused death in Ae. albopictus two possible for the variation in insecticide when inoculated into the thorax but little mortality when ceptibility among the U.S. strains: the U.S. populations may ingested by adults immersed larvae. have originated from number of different Asian with In the laboratory, susceptibility of Ae. albopictus to the distinct insecticide exposure conditions, selection for in- bacterium Bacillus ihuringlensis israe-lensis found secticide resistance may have taken place in the United to be lower than that of Ae. aegypti from Enugu, Nigeria, States since Ac', alhopictus became established. Wesson the- and Djakarta, Indonesia, but higher than that of Ac. aegypti orizes that the observed differences may be the result of from Bora Bora (de Barjac and Coz, 1979). both factors. Some selection for insecticide tolerance to Infection with three species of grcgarine protozoans of malathion is believed to have taken place in populations the genus Ascogregarina observed in Ae. alhopiclus in from Texas and Louisiana. Taiwan (Lien and Levinc, 1980). Beicr and Craig (1985) Brown (1986) and Neng et al. (1993) report that Ae. al- state, "Although many workers have suggested the poten- bopictus is resistant the organochlorincs DDT and HCH tial of gregarines control agents, these parasites appear in China, India, Japan, Malaysia, Southeast Asia, and the to be relatively harmless to their natural mosquito hosts." Philippines and resistant to the organophosphate malathion Various species of the pathogenic fungus Coelomomyces in Singapore and Viel Nam, fenthion in Malaysia, and fen- found parasitizing A*?, ulbopictus larvae from bamboo itrothion in Madagascar. stumps and tree holes in Taiwan between 1955 and 1967 (Laird, 1967). Two species of this fungus (predominantly C. stegomyiue) that parasitized Ae. albopictus in Singapore Biological Control collected and introduced into three atolls of the To- kelau Islands, New Zealand, in 1958. After two years the With the exception of the trials carried out with cyclo- fungi had significantly reduced the population of Ae. poid copepods (Marten, I990a, 1990b), there have been few pofynesiensis, and by 1963 there fourfold increase in field trials of predators, parasites, pathogens of Ae. al- parasitized larvae (Laird, 1967). bopictus. Reports have been limited mostly to findings of Finally, the of copepods (Mesocyclops), discussed field infections and species associations. earlier larval predators, has been demonstrated in field The predatory mosquito larva Toxorhynchites splendens trials in New Orleans (Marten el al., 1989a; Marten, I990a, found to be frequently associated with Ae. ulbopictus 1990b). Several species of cyclopoid copepods that in Singapore, and Chan (l968a) concluded that "... T. naturally in New Orleans, such Mucrocyclops alhidus, splendens probably be most effectively utilized for the Mesocyclops longisetus, and Mesocyclops aspericornis,

38 have been shown to be highly effective for controlling first In Singapore, where Ae. albopictu'i populations instar larvae of Ac', albopictus in discarded tires. The most found to have three peaks during the year, fluctuating in effective of the three appears to be Macrocyclops albidus, step with rainfall, the best control aimed at which, at density of 72 per tire, killed average of 45 preventing the population peaks by destroying the major larvae in 24-hour period. Treatment of tires with this breeding during the period immediately prior to pepod lias provided control for period of two years (Mar- those peaks (WHO, 1986b). ten, 1990b). Survival of this species is excellent when it is The most effective form of environmental control is to introduced into tires around wooded modify completely and permanently the where Another species that has shown promise in controlling quito production Slums, which the Ac. alhopiclus first instar larvae is Mesocyclops longisetus. sponsible for most Aedes breeding in Singapore, have been This species appears to be highly effective in tires situated virtually eliminated by government housing program. By in the open and exposed to hot conditions. Nine- 1984, than 75% of the total population housed teen specimens eliminate 40 larvae per day. The dis- in government-constructed apartment buildings. However, advantage of Mesocycfops longiselus is tliat tlie species this effort did not solve the problem of infestations in large does not survive the winter season, and it is sensitive houses with compounds, because although Ae. aegypfi in- to freezing temperatures than Macrocyclops (Marten, dices in such houses low, Ae. cilbopiclus house infes- 1990b). tation almost 100%. This the because these Another approach that has been recently introduced in- premises usually had suitable Ae. albopictus breeding hab- volves treating tire piles with mixtures of copcpods and Bti. itats, such tin cans, tree holes, and leaf axils of plants Such treatment has been found to provide control for about (WHO, 1986b). year. Bti at concentrations of 1,200 ITU/ml mixed with Macroi-yclopv alhidiis had detectable toxic effect the Health Education cyclopoid, but killed both late instars and instars ef- fectively (Marten et al., 1993). Public health education is aimed particularly at the neigh- borhoods where Aedes indices highest. To motivate peo- ple to eliminate and mosquito-borne diseases, Environmental Control prevent number of public campaigns be imple- mented. These may involve the holding of seminars, work- Environmental management involves the elimination shops, and exhibitions; the distribution of pamphlets and reduction of vector breeding Commonly known posters; the preparation of feature articles for newspapers reduction, it appears to be the single most effective and magazines; the presentation of talk shows and the method Aedes vector control thus far available. The of slogans the radio, television, and in schools; the derlying^principle of reduction consists of the elim- of film strips; and the personal message of the vector ination of breeding in order to disrupt the immature control officer working door-to-door. In Singapore, it life cycle of the mosquito. This objective be imple- concluded that "there is doubt that continuous routine mented by such simple burying destroying health education contributed immensely to the unwanted water-bearing receptacles. Particular attention prevention and control of Aedes breeding in premises" should be given to reducing standing water in and around (WHO, 1986b). seaports, bus terminals, train stations, and airports, well in containers such discarded tires, which favorite breeding sites of the Acdcs species. Additional actions that Legal Measures be taken include upending large containers such jars, drums, and water tanks that kept in the open and The legal component of Aedes control has two aspects: ering water-holding containers with tight-fitting lids. People laws that permit the health inspector to enter each building be encouraged to change the water weekly in containers and examine all potential breeding sources, and legislation around their homes, such water jars, flower vases, and that makes it illegal to have breeding places the prem- ornamental jars, and to scrub and thoroughly rinse these ises. In Singapore, the Destruction of Disease-Bearing In- containers lo dislodge Aedes eggs before refilling with sects Act permits the control officer to orders and ter. Achieving permanent mosquito control in natural offenders who maintain conditions condu- tainers such tank bromeliads is difficult, but homeowners cive to breeding harboring mosquitoes. For private may consider limiting the numbers of these plants that they homcowner, order is served when breeding has been place in their yards. In such Florida it is confirmed. mended that tank bromeliads be flushed out twice week To lessen the likelihood that Ae. ulbopiclus will with garden hose equipped with appropriate nozzle from the United States to other countries of the Americas, (O'Meara and Gettman, 1991). the Centers for Disease Control and Prevention has pro-

39 posed discussion of the following four options: (a) de- gypli has been known to enter into the cycle of velop and implement regulations to require disinsection of EEE. all used tires exported from the United States; (b) formulate Ae. albopictus has the potential to enter into the La guidelines for by PAHO countries to require fumigation Crosse virus cycle, while Ae. aegypti has chance of of used tires shipped from the United States; (c) maintain doing because it cannot survive the winter cold. constant surveillance in port and at destinations of Ac. albopiclus feed wide variety of hosts, while imported used tires in each receiving country; and (d) pro- Ae. aegypti outside Africa is highly domestic and is vide assistance by CDC through PAHO to countries wish- likely to in contact with feral ing to design surveillance and control plans (CDC, 1993). The information about Ae. alhopictus presented in this document portrays very complex species. Its ability to Integrated Control harbor indigenous arboviruses has been demonstrated in the United States, and wealth of experimental data have No single control method is sufficient to lower inforced the evidence of its potential role in vectoring hu- quito levels for long period of time. Instead, it is and animal arboviral diseases. Complicating the pic- sary to combine the various methods of the vector control ture is the catholic feeding behavior of the species, which arsenal in the most effective, most economical, and safest has been reported feeding not only small and large possible way. In Singapore, system of routine vector mals, including humans, but also birds, snakes, and tur- veillance, continuous year-round reduction, health tles. Ae. albopiclus enter into sylvan zoonotic cycles education, and fogging of premises in where and bring such viruses to man; that is why it is danger- than 5% of the houses infested implemented in Moreover, unlike swamp and marsh mosquitoes, Ae. 1974. This system effective in achieving year-round albopiclus breeds close to human habitations. control of the vectors Ae. aegypli and Ac. albopictus, and A very disturbing development is isolation of the eastern also successful in preventing two epidemics that swept equine encephalitis (EEE) virus from Ae. albopictus through other parts of the region (WHO, 1986b). quitoes collected at the Polk County Tire Dump in Florida. EEE and often fatal disease in humans. It is also important disease of domestic animals and has killed CONCLUSIONS significant number of animals belonging to endan- gered species, such the whooping Houston (Texas) and Brazilian strains of Ae. albopictus Some health officials and members of the scientific have shown susceptibility to experimental oral infection with munity have suggested that Ae. albopictus is less impor- the four dengue serotypes (Mitchell and Miller, 1990). IfAe. tant vector of dengue virus than Ae. aegypti. Experience in albopictus spreads into Central America and the Caribbean, Asia the past 30 years supports this contention in that, it could add complexity to the scenario of dengue in with only few exceptions, the major epidemics of dengue the Americas. Ae. albopictus breeds in urban, rural, and for- and dengue hcmorrhagic fever have been transmitted by Ac. ested in water retained by artificial containers and aegypti. Nevertheless, the threat of Ae. albopictus in the natural vegetation. It is exophilic and prefers to breed out- Americas should not be underestimated. Craig (1993) side human dwellings, which makes it potentially danger- points out the differences that exist between the two Sfe- maintenance vector. gomyia species in the Ajnericas and describes them Seven years after its in the Americas. Ae. al- follows: discovery bopiclus continues to expand its range into geograph- Ac. albopictus has far greater geographical range than ical In 1986, 11 states in the United Slates Ae. aegypli because of its cold tolerance. ported to be infested; by 1991, 11 additional states Ae. albopiclus has inaccessible habitat because it known to have significant populations of Ae. albopiclus. breeds in plants, and therefore it is far harder to control. Similarly, in Brazil infestation reported in 89 munici- The species have different habitats, with Ae. aegypti palities in 1986; by April 1994, 676 municipalities and found in the inner city and Ac. albopiclus in suburban three states-Maranhao, Parana, and Bahia-had been and rural added to the list of infested areas, indicating well-estab- Ae. albopiclus has already achieved far greater popula- lished breeding population in the country. In addition, the tions in the United States than Ae. aegypti, which has expansion is not restricted to the Americas. In the last few been major biting pest in that country; for years, the species has spread rapidly to many communities ample, in New Orleans, 80% of the mosquito complaints in northern Italy. currently about Ae. alhopictus. There still many unanswered questions about Ac. al- Ae. albopictus harbor the range of arboviruscs bopictus and its relationship to human diseases. For in- and is efficient vector for of them; Ae. stance, association of Ac. albopictus with arboviral dis-

40 outbreaks has been reported in the Americas. The read the drafts, made valuable comments, and suggested Ministry of Health of Brazil did not find any evidence changes to improve the document. For providing data. sociating/le. albopictus with the dengue outbreaks reported drawings, and photographs indebted to Dr. Chester during the past five years, but detailed studies need Moore, Division of Vector-Borne Infectious Diseases, Cen- to be carried out during such events, especially since ter for Infectious Diseases, Centers for Disease Control and eral of the recent dengue epidemics took place in Brazilian Prevention, Fort Collins. Colorado; Dr. John R. Linley, states wliereAc. ulbopictus is known to be present. Clearly, Florida Medical Entomology Laboratory, Institute of Food such studies help to resolve many of the enigmas which and Agricultural Sciences, University of Florida at Vero surround this species in natural settings. Beach; Dr. Ralph Harbach, Walter Reed Biosystematics Ae. alhopictus is highly adaptable species. Its evolu- Unit, Smithsonian Institution, Washington, D.C.; and Mr. tionary plasticity is demonstrated by its ability to develop Arthur Botelho dc Barros, Superintendencia de Campanhas insecticide resistance after only lew generations of labo- de Saude Publica (SUCAM), Brazil. Part of the research ratory selection. Insecticide selection studies of Ae. albo- reported bv G. B, C. supported by NIH Research Grant piclus strains from the United States indicated unusually No. 02753. high tolerance to malathion, resulting in resistance ratio of 21 after just six generations (Wesson, 1990). Control efforts in infested may be compromised if Ac. alho- pictus develops resistance trait. REFERENCES Enzyme electrophoretic studies appear to indicate that gene flow in the introduced populations of the Americas is ACHA, P., and B. Sy-ytres. 1987. 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Fagerstonc, K. A.; Ramey, C. A.; Keith, J. 1995. ABSTRACT. Mongoose management to protect endangered species in Hawaii. In: The Wildlife Society 2d Annual Conference Abstracts; 12-17 September 1995; Portland, OR. Bethcsda, MD; The Wildlife Society: 41-42.

FAGERSTONE, KATHLEEN A., C. A. RAMEY, AND J. KEITH. Mongoose management to protect endangered species in Hawaii. USDA APHIS Denver Wildlife Research Center, Denver, CO 80225-0266 USA.

Mongooses (Herpesles auropunctatus) were introduced into Hawaii in 1883 to control introduced rats and now occur on all main islands except Kauai. Whereas mongooses have not limited rat populations, they have limited the productivity of many ground nesting avian species. They have also restricted the recovery of at least 8 species of endangered Hawaiian birds by consuming both their eggs and young. The Denver Wildlife Research Center (DWRC) began investigations in Hawaii in 1984 to develop a management tool for mongoose control. Studies of mongoose biology and toxicology revealed an extreme susceptibility to the anticoagulant diphacinone. Using DWRC data, Bell Laboratories, Inc. obtained a state registration in 1991 for use of diphacinone to control mongoose in bird nesting areas.