Mediation of deet repellency in mosquitoes (Diptera: Culicidae) by species, age, and parity

Laboratory bioassays assessed differences in the protection time provided by the repellent deet (N,N-diethyl-3-methylbenzamide) against 5-d-old nulliparous and 10-, 15-, and 20-d-old nulliparous and parous female Aedes aegypti (L.), Anopheles albimanus (Weidemann), and Anopheles quadrimaculatus Say sensu lato. Mean protection time was shortest against An. albimanus (1.6 h) and An. quadrimaculatus (1.5 h) and longest against Ae. aegypti (6.5 h), but was not significantly influenced by mosquito age or parity. Mean percentage of biting at repellent failure time was highest in An. albimanus (14.2%), followed by An. quadrimaculatus (7.0%) and Ae. aegypti (2.9%), was higher in parous females (10.8%) than in nulliparous females (5.9%), and was highest overall (35%) in 20-d-old parous An. albimanus. Interaction between mosquito species and parity and between parity and age factors, respectively, resulted from a significant decrease in percentage of biting by parous An. quadrimaculatus compared with other females, and a significant increase in biting by 20-d-old parous females compared with other females. The main finding of this study is that repellent protection time is unaffected by parity; this is important because parous mosquitoes are the primary target of personal-protection measures in disease-endemic areas. When repellent failure did occur, there was a higher risk of bite by old, parous An. albimanus than for any other species, age, or parity grouping of females.

Failure to predict abundance of saltmarsh mosquitoes Aedes sollicitans and A. taeniorhynchus (Diptera: Culicidae) by using variables of tide and weather

Weather and tide variables were used to develop regression models with light trap counts of Aedes sollicitans (Walker) and Aedes taeniorhynchus (Wiedemann) from 1984 to 1995. Rains, tides, and temperatures, both during and preceding the sample period, all showed significant correlations with trap counts. These multiple regression models forecasted general population levels during 1996 and 1997, but not the size of the peaks. Therefore, weather alone can predict general trends but cannot be used to accurately predict population levels of Ae. sollicitans and Ae. taenio-rhynchus.

Development of an indicator to evaluate the impact, on a community-based Aedes aegypti control intervention, of improved cleaning of water-storage containers by householders

Householders in a community-based programme to control dengue in El Progreso, Honduras, are being encouraged to improve the cleaning of the water-storage containers in which many of the vectors thrive. The objective of the present study was to develop an indicator of the change occurring in human behaviour. Traditional Aedes aegypti larval indices do not differentiate between containers in which all the immature stages are present and those which hold only first- and second-instar larvae. However, it is not essential to prevent all larval development to limit transmission of pathogens by the adults; if the Ae. aegypti in the containers only manage to develop to young larvae before the containers are cleaned, then control of the vector in these containers will be effective. In field trials, sampling of third- and fourth-instar larvae in washbasins by taking five dips (quick immersions to a standard depth) with a hand-held net was found to be sufficient for estimating the true population size of that same cohort. This sampling method was then included in a large-scale survey of households, conducted for programme monitoring. An index was then developed as a summary measure of the degree of infestation of a washbasin by Ae. aegypti. This index was the sum of four variables assessed in the survey: presence of any immature stages (larvae and/or pupae); presence of pupae; detection of third-fourth-instar larvae in a five-dip sample; and a log-transformation of the number of larvae recovered. Based on this new index, the 884 washbasins encountered in the survey were classified as infestation-free (76.2%), or with low-(6.7%), medium-(14.9%) or high-level (2.2%) infestation. Application of the same procedure to 240 drums encountered in the survey showed that 66.3% were infestation-free and 9.2%, 17.1% and 7.4% had low-, medium- and high-level infestations, respectively. Compared with the traditional indices, this new index should be more sensitive to changes in human behaviour resulting from a control programme exposure than a simple, dichotomous variable (i.e. positive/negative for presence of immature stages). The use of such an index could make the control programme more efficient, allowing the greatest efforts to be targeted at households that have medium-high levels of infestation.

[Epidemiologic significance of Aedes albopictus breeding places in bromeliads]

A breeding place of immature stages of Aedes albopictus in bromeliads is described. The epidemiological role of bromeliaceae as natural or artificial containers, is discussed. The ability of the mosquito to expand its habitat calls for attention especially as regards its adaptability as an invading species.

Estimation of predation by the larvae of Toxorhynchites splendens on the aquatic stages of Aedes aegypti

Predation by instars of Toxorhynchites splendens on aquatic stages of Aedes aegypti was studied by estimating functional response parameters such as attack rate (a') and handling time (Th) in the laboratory. The predator displayed typical type-II functional response, similar to that of most insect predators when presented with increasing densities of any given size class of prey. Second instar predator attacked prey significantly at higher rate than the other instars. Small prey were attacked at higher rate than the predation on larger prey. Except second instar predator, other instars showed significant reduction in a' with increase in Th. Foraging surface area did not influence the predation rate. Predation was high at high water temperature and this was more prominent in the second instar predator. However, prey handling time was independent of the water temperature. Modeling of the predation of mixed age populations of prey and the predator through this short-term functional response experiment is discussed.

Effect of size and geographic origin of Aedes aegypti on oral infection with dengue-2 virus

Differences in larval habitats cause variation in the size of Aedes aegypti (L.) adults. We suspected that such size variation was related to the ease with which the mosquitoes could be infected with dengue virus. Using a rearing procedure that produced three distinct size classes of mosquitoes, we determined the percentage of mosquitoes that developed disseminated dengue-2 infection following oral feeding with a suspension containing 3.3 x 10(7) plaque-forming units/ml. Mosquitoes were reared from eggs deposited by females captured in either of two villages in Chachoengsao Province or in Bangkok, Thailand. More of the larger mosquitoes (10.7%) were infected than the medium (5.6%) or small (5.7%) mosquitoes. Mosquitoes from Bangkok were less easily infected (5.0%) than mosquitoes from either of the two villages (8.5% and 10.7%). These results suggest that quantitative risk assessment of dengue transmission may be very difficult unless inoculation rate is measured directly. Also, control procedures that reduce density of larvae in individual containers may exacerbate dengue transmission by creating larger mosquitoes that are more easily infected.

Effect of heavy metals on Aedes aegypti (Diptera: Culicidae) larvae

Studies were conducted to determine the biological effects of heavy metals on the development of Aedes aegypti. Embryos immersed in 32 ppm Cu or 5 ppm Cd did not hatch. The arrest of hatching was in part reversible by removal of the heavy metals. The mortality rate of third-instar larvae exposed to heavy metals for 24 h was metal and dose dependent; the 50% lethal concentration (LC50) endpoints were 3.1, 16.5, and 33 ppm for Hg, Cd, and Cu, respectively. Interestingly, a proportion of Aedes aegypti third-instar larvae exposed to either Cu or Cd for 24 h failed to produce a dissectable peritrophic matrix. This failure to produce a dissectable peritrophic matrix also was metal and dose dependent. These results are discussed in the context of Aedes aegypti as a model system for investigating the molecular biological effects of heavy metals in aquatic insects.

Monitoring the abundance of Aedes (Ochlerotatus) albifasciatus (Macquart 1838) (Diptera: Culicidae) to the south of Mar Chiquita Lake, central Argentina, with the aid of remote sensing

Surges in the size of adult populations of the flood-water mosquito Aedes albifasciatus can produce important economical losses because of the way this species irritates livestock. Although this species is also the main vector of west equine encephalitis in Argentina, little is known about the factors affecting its population dynamics, as it is difficult to obtain data on its abundance over a large area. However, the results of intensive study of the mosquito in a few sites might reasonably be extrapolated to a regional scale by the use of remotely sensed data. The adult, larval and pupal stages of Ae. albifasciatus were sampled at five field sites to the south of Mar Chiquita Lake, either once a month (during the dry, cold season) or once a fortnight (during the warm, rainy season), between August 1992 and April 1993. The measured abundance of adults or pre-adults and a meteorological coefficient useful for the estimation of larval abundance each showed significant correlation with various statistics derived from normalized-difference, vegetation indices (NDVI) calculated from satellite (NOAA-AVHRR) imagery. A linear discriminant analysis, using data on NDVI, rainfall and temperature, accurately identified periods with and without pre-adults. The satellite imagery was also useful in the estimation of larval abundance and consequently could be used to predict adult abundance 7 days in advance. Even though the satellite data employed have poor spatial resolution, their high temporal resolution makes them very useful in studies of the population dynamics of mosquitoes in general, at least once the relevant variables and their relationships with mosquito breeding and survival have been identified.

Differential accumulation and tissue distribution of mosquito hexamerins during metamorphosis

The pupal hexamerins were characterized for two mosquitoes representative of the culicine and anopheline families, Aedes aegypti and Anopheles gambiae. Like higher Diptera, both mosquito species express two types of hexamerins, Hex-1 and Hex-2, whose subunits are distinguished by different levels of methionine and aromatic amino acids. In A. aegypti there are two heterohexamers, AaHex-1 and AaHex-2. In A. gambiae there are two homohexamers, AgHex-1.1 and AgHex-1.2, and one heterohexamer, AgHex-2. These hexamerins are rich in aromatic residues, with 18-23% Phe + Tyr for Hex-1 subunits and 13-17% Phe + Tyr for Hex-2 subunits. In addition, both mosquito species synthesize methionine-rich Hex-1 subunits: Aedes AaHex-1 gamma (8% met) and Anopheles AgHex-1.1 (3.9% met). Aedes Hex-1 and Hex-2 proteins exhibit different, stage-specific tissue distributions: AaHex-2 is the primary hexamerin of late larval hemolymph whereas AaHex-1 is the most important non-hemolymph protein of early pupae. Although both proteins are stored in the pupal fat body, peak AaHex-1 levels are 2-fold higher. Both pupal protein levels decline rapidly between 25 and 36 h after pupation. Furthermore, AaHex-1 not only reaches peak values in female Aedes pupae later than in males, but the methionine-rich AaHex-1 gamma subunit level is specifically higher in females. These observations suggest different roles for Hex-1 and Hex-2 during mosquito development.

[Breeding places of Aedes scapularis (Diptera: Culicidae) in artificial containers]

Breeding places of Aedes scapularis were found in the Ilha Comprida and Pariquera-Açu counties of S. Paulo State, Brazil. They included several types of artificial water container. As 270 (250 larvae and 20 pupae) immature forms were collected, the hypothesis is raised that behavioral change is occurring as a secondary adaptation, as a consequence of the anthropic environment. This tends toward a reduction in ground breeding places and, at the same time, to an increase in the number of artificial containers. So the synanthropic tendence of thus mosquito may be favored by or even be a result of the man-made environment. Reference is made to the epidemiological consequences of this phenomenon for encephalitis transmission specifically for the Southeastern region of Brazil.

Transamination of 3-hydroxykynurenine to produce xanthurenic acid: a major branch pathway of tryptophan metabolism in the mosquito, Aedes aegypti, during larval development

An electrochemically active compound was detected in the larvae of Aedes aegypti mosquitoes and progressive accumulation of this compound was observed during larval development. The compound was purified from mosquito larvae using various chromatographic techniques and spectral analysis of the purified compound resulted in its identification as xanthurenic acid. Production of xanthurenic acid results from the transamination of 3-hydroxykynuorenine, and analysis of the biochemical pathway in xanthurenic acid production revealed the presence of a particular transaminase that has a much higher specific activity to 3-hydroxykynurenine than to kynurenine in the mosquito larvae. Concentration of xanthurenic acid is closely related to the level of this transaminase activity. Results suggest that this particular transaminase plays an important role in regulating the level of 3-hydroxykynurenine in the mosquito, A. aegypti during larval development.

Description of the pupa of Aedes pseudotaeniatus (Giles) (Diptera: Culicidae)

The pupal stage of Aedes pseudotaeniatus (Giles) is described for the first time. Collections of this species were made in the Himalayan Kingdom of Nepal. Group E of subgenus Finlaya is discussed.

A fitness advantage for Aedes aegypti and the viruses it transmits when females feed only on human blood

Literature on arthropod-borne diseases has traditionally supported the notion that mosquito vectors maintain a feeding duality that includes vertebrate blood meals for egg development and sugar meals from plants for the synthesis of flight and survival energy reserves. Aedes aegypti was found to deviate from that feeding pattern by obtaining a reproductive advantage when feeding only on human blood. Female mosquitoes fed human blood alone had a greater net replacement rate and intrinsic rate of growth during all phases of their reproductive life than conspecifics fed human blood plus sucrose. Feeding frequently on human hosts during each gonotrophic cycle is necessary to avoid death due to starvation and increases exponentially the spread of Ae. aegypti-borne disease. Our results help explain why Ae. aegypti is such an unusually efficient vector of human disease; frequent biting of humans results in a high reproductive rate for vectors as well as the viruses they transmit.

Effects of developmental asynchrony between Aedes triseriatus (Diptera:Culicidae) and its predator Toxorhynchites rutilus (Diptera:Culicidae)

Newly hatched Toxorhynchites rutilus (Coquillet) were added to experimental populations of Aedes triseriatus (Say) at varying days after prey hatch to test the hypothesis that a developmental asynchrony of Ae. triseriatus and Tx. rutilus leads to escape from predation by Ae. triseriatus in small water bodies. Presence of Tx. rutilus significantly affected prey survivorship. Regression of survivorship [log10 (x + 1) transformed] versus days head start for prey yielded a small, but significant positive slope, indicating that survivorship increased slightly with an increasing number of days head start. For females, mean weight at emergence was not significantly affected by treatments; however, median days to emergence differed significantly between the treatments, with females taking significantly longer to emerge with Tx. rutilus absent than when the predator was present. For males, neither mean mass nor median days to emergence was significantly affected by treatments. Treatments had no significant effect on the frequency of deaths or on mean weight of Tx. rutilus. Thus, a developmental asynchrony between Tx. rutilus and Ae. Triseriatus appears to have no effects on the predator, but does have a weak effect on prey performance at high hatch densities.

[A description of Aedes aegypti colonization in the region of São José do Rio Preto, São Paulo]

The aim of this study is to describe the colonization by the Aedes aegypti in the region. A survey carried out in 1985 detected the species in São José do Rio Preto. The mosquito has spread and reached the 30 countries of the region till 1988. In the district and rural areas, the first vector focus was found out in 1987 in one of the 29 districts and rural areas, having spread to the others till 1991. The foci have been mainly identified through larval researches in locations with a great concentration of containers, and the greatest occurrence of larvae of Aedes aegypti has been in tires, the most frequent means of spread. The foci have been mainly identified between November and April, periods of greater incidence of rains. The delimits of foci showed that the containers which were mostly infested by the mosquito in homes have been tires and vases of plants. The most important consequence of the presence of Aedes aegypti has been the occurrence of dengue epidemics.

Analysis of LaCrosse virus S mRNA 5' termini in infected mosquito cells and Aedes triseriatus mosquitoes

Nucleotide sequences were determined for the 5' termini of La Crosse virus (LAC) S segment mRNA from persistently infected mosquito cell cultures (C6/36 from Aedes albopictus) and embryos (Aedes triseriatus). LAC primes transcription of its mRNA with "scavenged" 5' caps and adjacent oligonucleotides from host mRNAs, and these non-virus-encoded 5'-terminal extensions are heterogeneous in infected mammalian cells. The nature of mosquito host-derived primers has not been previously investigated. During early C6/36 cell infection, LAC mRNA 5'-terminal sequences were heterogeneous, but variability decreased as infection persisted. One predominant sequence, 5' CCACTCGCCACT (sequence 1), was observed throughout C6/36 cell infection but was more prevalent after 15 days postinfection. This LAC mRNA 5'-terminal sequence comprised 81% of the scavenged host oligonucleotides from vertically infected A. triseriatus eggs during embryogenesis. As these embryos progressed in the dormant overwintering stage (diapause), the predominant scavenged sequence became 5' AGGAAAAGATGGT (sequence 2), and sequence 1 became less prevalent. As the eggs emerged from diapause, the LAC mRNA 5' termini were more variable; 33% had sequence 1, and the remainder were heterogeneous. In post-diapausing eggs, 100% of viral mRNAs had sequence 1 at their 5' termini. Molecular analyses thus revealed continuous but selective LAC cap scavenging during persistent C6/36 cell infection and during embryogenesis and diapause in A. triseriatus eggs. The variety of host-derived sequences was limited in both biosynthetically active (embryonating) and dormant (diapausing) eggs.

Larval competition in Aedes triseriatus (Diptera: Culicidae): effects of density on size, growth, sex ratio, and survival

We assessed the effect of increased larval density on selected life table attributes of larval Aedes triseriatus. Larvae were reared at densities of 0.125, 0.250, and 0.375 larvae/cm3 of water. The parameters we evaluated included duration of each developmental instar, percent survival to adult emergence, sex ratio, and size of early and late emerging adults. The amount of time spent in the first and second instar was not affected by density, but crowding lengthened duration of later instars significantly. Males emerged earlier than females at all densities, and there was no difference in the ratio of males to females due to crowding. Crowding did increase the overall developmental time of both sexes and produced significantly smaller adults of both sexes. Densities of 0.375 larvae/cm3 resulted in a significant increase in mortality. Results suggest that the effects of crowding in container habitats should be allowed for in the construction of time-specific life tables where duration of larval instars is used in the calculations. The importance of smaller body size as a result of crowding in container habitats is discussed in terms of vector competence of Ae. triseriatus in the transmission of LaCrosse encephalitis virus.

Factors favoring houseplant container infestation with Aedes aegypti larvae in Marília, São Paulo, Brazil

Since reinvasion of São Paulo State by the Aedes aegypti (L.) mosquito in 1985, flower pots and vases have been important larval habitats despite educational messages focusing on their control. The objectives of this study were to characterize flower pots and vases as larval habitats with respect to the quantities present and infested, the types of plants involved, and the specific locations of the mosquito larvae; to explore local names for houseplants; and to examine factors affecting acceptance of control measures. The results showed an average of more than four potential plant-related larval habitats per premises, of which only 0.4% were occupied by the vector. Plant-related containers represented 31% of all the containers with Aedes aegypti larvae. Although a sample of 126 respondents was able to list 105 different houseplant names, 49% of the positive plants were of two types: ferns and the ornamental plant Dieffenbachia avoena. The public's apparent unwillingness to accept recommended anti-aegypti control measures involving houseplants seems related to the relative rarity of aegypti larvae in the very common houseplant containers, the control program's poor credibility as a source of information about plants, and a perception that the recommended control measures are harmful to plants. An intervention currently being planned for dengue control will use educational material that refers specifically to those plants whose containers are most commonly found to harbor aegypti larvae; it will also utilize information sources such as botanists with greater credibility regarding plants; and it will set out alternative plant care recommendations that are more likely to appeal as beneficial to the plants and that will stand a better chance of being accepted.

Methoprene affects the rotation of the male terminalia of Aedes aegypti mosquitoes

The rotation of the male terminalia of Aedes aegypti mosquitoes was investigated with chemical surgical, and mechanical methods. Neither decapitation nor ventral nerve cord transection affected the postemergence rotation, but methoprene administered to 4th-instar larvae and early instar pupae slowed rotation significantly and, in the case of pupal treatment, also interfered with successful insemination. Methoprene appeared to interfere with the developmental maturation of the cross muscles located between the 7th and 8th abdominal segment and postemergence nervous or humoral signals did not appear to affect this rotation.

Pupal survey: an epidemiologically significant surveillance method for Aedes aegypti: an example using data from Trinidad

This report documents the results of a country-wide pupal survey of Aedes aegypti (L.) conducted in Trinidad. The survey was designed to identify the important Ae. aegypti-producing containers, importance being a function of a container's abundance and its productivity. Results are summarized on a country-wide basis and by county: urban versus rural comparisons are also made. Numerically, the most common water-filled containers positive for the larvae or pupae of Ae. aegypti (foci) were outdoor drums, water storage tanks and buckets, laundry tubs, discarded tires, and small miscellaneous containers such as drink bottles and cans. The island-wide average number of foci per hectare was 287 and ranged between 65 and 499. The average standing crop per container of Ae. aegypti pupae was 9.5 and ranged 12-fold, the most and least productive being the flower pot (> 30) and the small indoor vase (< 3), respectively. In terms of production by type of container, four of the 11 types, outdoor drums, tubs, buckets, and small containers, accounted for > 90% of all Ae. aegypti pupae: the remaining seven types were responsible for < 10%. If targeted source reduction programs were directed by how important various container types were in the production of Ae. aegypti, environmental sanitation efforts designed to actually eliminate the ubiquitous small receptacle and tires would reduce mosquito densities by 43%; the provision of an adequate water supply system precluding the need for water storage in drums and buckets would have the potential to eliminate an additional 38%. Combined, these two measures have the potential to reduce the sources responsible for > 80% of Ae. aegypti production in the country. In our survey, the traditional Stegomyia indices used to document the density of Ae. aegypti and predict the threat of dengue transmission, the House, Container, and Breteau indices, were seen to have virtually no correspondence with the actual number of pupae per hectare or per person. We conclude that pupal survey is more appropriate for assessing risk and directing control operations.

[Detection of Aedes aegypti and Aedes albopictus, in an urban zone of the municipality of Catanduva, SP, after control of a Dengue epidemic]

After the realization of control research that had in view the transmission of dengue virus, we started to monitor two kinds of entomological vigilance, Breteau Index and ovitrap. We intended to evaluate the necessary time elapsed before Aedes sp mosquitoes were again detected at the urban area of Catanduva s town (SP). The ovitraps showed positiveness for the Aedes aegypti two months after the control research, while the Breteau Index became positive only at the fourth month after the end of the referred research.

Lipophorin levels in the yellow fever mosquito, Aedes aegypti, and the effect of feeding

High density lipophorin (HDLp) is the major lipid transport vehicle in insect hemolymph. Using an indirect ELISA, levels of HDLp were measured in the yellow fever mosquito, Aedes aegypti. The level of lipophorin, when normalized to the total weight of the insect, was similar in the different developmental stages. Starvation (access to water only) of adult females did not affect the level of HDLp nor its density when compared to sugar-fed females. On the other hand, blood feeding (of normally sugar-fed females) resulted in a three-fold increase of the HDLp level at 40 h after feeding. This increase was accompanied by a slight but significant increase in the density of HDLp at 24 h after feeding. Ingestion of a lipid-free protein meal or a lipid-supplemented protein meal induced changes in HDLp level and density that were comparable to those induced by ingestion of a blood meal. Ingestion of a blood meal, following starvation (access to water only) from the moment of adult emergence, did not induce an increase in HDLp level. The results presented indicate that, in contrast to other insect species, A. aegypti responds to an increased need for lipid transport in the hemolymph by increasing the amount of HDLp. Arch. Insect Biochem.

[1st isolation of Aedes (Ochlerotatus) sticticus (Diptera, Culicidae) in the Po-Venetian valley]

Aedes sticticus is recorded for the first time in northern Italy. The species was collected in some relict woods mainly at sea level in the Po-Venetian valley (Northern-Italy). Larval growth took place in residual puddles originated by rain or river floods. The most abundant adult emergence was observed in April or May. Minor earlier or later adult emergencies were observed depending from egg submersion and temperature. Data on larval chetotaxy are presented.

[A new culicid in Italy: Aedes (Ochlerotatus) annulipes (Diptera, Culicidae)]

The first italian record of Aedes annulipes is described. The species was collected in various sites of the eastern Po-Venetian valley (North-eastern Italy), from sea level up to 190 m a.s.l. The larval breeding sites were seasonal fresh water marshes within woods. Preimaginal development took place from February to May. Ae. annulipes was univoltine with a possible second minor generation. The females were strongly anthropophilic. Main morphological data are provided and compared with those of the close species Ae. cantans. The adaptation to environments south of Alps and even at sea level by a northern palearctic element such as Ae. annulipes is presumably achieved by the exploitation of sufficiently cold biotopes available for larval breeding during the winter-spring period.

The biology and predatory potential of notonectid bug, Enithares indica (Fabr) against mosquito larvae

The biology of a notonectid bug Enithares indica against immatures of Anopheline, Culicine and Aedine mosquitos was studied in the laboratory. The life cycle of the bug consists of the egg and five nymphal stages and takes about 64 +/- 1.54 days for completion. All stages of E. indica have good predatory potential. It can be used as a biological control agent in an integrated disease vector control program.

Disposable containers as larval habitats for Aedes aegypti in a city with regular refuse collection: a study in Marília, São Paulo State, Brazil

In Marília, Brazil, refuse is collected at least every other day, yet non-useful, non-returnable containers such as cans, plastic bottles and tires account for almost half of the container habitats found positive for the Aedes aegypti mosquito. A study was therefore conducted to investigate why these containers exist despite regular refuse collection and a high level of awareness of dengue prevention, and how the control program could most effectively respond. Differing community perceptions as to what constitutes refuse were found to lead people to store a variety of containers in their yard. Other dimensions of the problem include the presence of informal refuse collectors in search of saleable materials, and dumping of refuse in vacant lots and along roads. An intervention based on these data will involve the informal refuse collectors in implementation of a community-based recycling project.

Microdroplet application of mosquitocidal Bacillus thuringiensis using ultra-low-volume generator for the control of mosquitos

In an effort to develop a more effective technique in dispersing a microbial control agent, Bacillus thuringiensis (Bt), a truck-mounted ultra low volume (ULV) generator (Scorpion) was used to disperse B. thuringiensis israelensis (Bti) and Bti with malathion. Complete larval and adult mortalities for all tested mosquito species within the first 70-80 feet from the ULV generator were achieved. Beyond that distance less than 50% mortality was achieved as insufficient sprayed particles reached the area. A minimum of 10(3) Bti colony forming units per ml is required to cause 100% larval mortality. The sprayed Bti larvicidal toxins were persistent in the test water 7 days post ULV. The effectiveness of B. thuringiensis jegathesan (Btj), a new mosquitocidal Bt serotype was also evaluated. Similar mortality results as Bti were achieved except that the Btj toxins underwent degradation in the test water, since less than 50% less in larval mortality was observed in 7 days post ULV samples. This ULV method has the potential to disperse Bt and malathion effectively for a simultaneous control of mosquito adults and larvae.

Critical examination of Aedes aegypti indices: correlations with abundance

The following immature stage indices for Aedes (Stegomyia) aegypti surveillance were evaluated in four north Queensland, Australia towns with respect to their relationship to immature and adult female densities: Breteau, House, Container, Larval Density, Stegomyia (and modifications thereof), and a newly created Adult Productivity Index. Spearman's correlations of indices that considered larval or immature (larvae and pupae) numbers had a better relationship with immature abundance but this was not necessarily the case against adult abundance. To examine the robustness of the indices, data from 758 premises in Townsville, Charters Towers, Ravenswood, and Mingela were pooled and 30 random subsamples, each consisting of 50 premises were taken. After each subsample was taken, the premises selected were reintroduced into the original data bank of 758 premises, and therefore, were available for further selection, i.e., sampling with replacement. Indices were calculated for each of the 30 subsamples and the coefficients of variation of each index were estimated from these. The Breteau, Adult Productivity, House, and Adult density indices proved to have the smallest coefficients compared with index size. No alternate index was regarded as being superior to the Breteau, including the Adult Productivity Index measuring both container type frequency and immature density. For this reason and in view of the labor intensiveness of estimating immature indices that incorporate productivity, it is recommended that new and cost-effective methods of adult surveillance be pursued.

Distention and sugar feeding induce autogenous egg development by the Asian tiger mosquito (Diptera:Culicidae)

Mechanisms initiating autogenous egg development were studied using a selected strain of Asian tiger mosquito, Aedes albopictus (Skuse), that required a sugar meal to develop eggs autogenously. Caloric intake and the abdominal distention produced by ingesting sucrose solutions were interrelated in their effects on autogeny. Distention of the abdomen with 2 microliters of saline, with no caloric intake, induced autogenous egg maturation in 66% of the females. Abdominal distention produced by 2 microliters of saline did not induce egg development if the ventral nerve cord was transected. However, eggs were produced when females ingested 200 micrograms of sucrose in 2 microliters of water following ventral nerve cord transection. A meal containing at least 100 micrograms of sucrose was required for egg development if abdominal distention was < 1 microliter. Mating influenced autogeny in only 10% of the population. Neither distention, caloric intake nor mating affected the number of eggs that matured.

Involvement of peroxidase in chorion hardening in Aedes aegypti

Peroxidase activity is detectable in Aedes aegypti ovaries, containing developing eggs, at 24 h following blood feeding, and peak peroxidase activity is reached at 36-48 h after the blood-meal. Peroxidase is associated with the chorion layer in mature eggs and the majority of the enzyme is released from the chorion layer by treating the isolated chorion fraction with SDS/urea. Analysis of the SDS/urea solubilized chorion proteins using SDS-PAGE with tropolone/H2O2 or dopa staining verified the presence of both peroxidase and phenol oxidase in the released chorion proteins. The molecular weight of chorion peroxidase is about 61,000 Da as determined by SDS-PAGE analysis. Incubation of the solubilized chorion proteins with tyrosine and H2O2 produces dityrosine, and hyrolysis of hardened egg chorion results in the detection of dityrosine and trityrosine in the chorion hydrolysate. Data suggest that chorion peroxidase is involved in the hardening of the mosquito egg chorion by catalyzing the formation of ditryrosine through tyrosine residues on structural proteins. The overall hardening of the A. aegypti egg chorion includes both peroxidase-mediated chorion protein crosslinking through dityrosine formation and phenol oxidase-catalyzed chorion melanization.

Simulating development and survival of Aedes vexans (Diptera: Culicidae) preimaginal stages under field conditions

Ecology and population dynamics of Aedes vexans (Meigen), were studied for 3 yr in southern Switzerland. Demographic data were compiled into single and multicohort stage-frequency lifetables that indicated variability in individual developmental times and losses caused by mortality. The structure of life table matrices suggested an analysis using a timevarying distributed delay model with attrition. Field data then were used to construct and validate a simulation model that input the number of 1st instars and output the number of emerging adults. The delay was the time required to complete development and attrition corresponded to mortality. Under optimal food supply, temperature was the most important driving variable. The model was parameterized with data obtained from laboratory experiments and evaluated with field data. Development and survival of preimaginal Ae. vexans were simulated reasonably well under 2 different pool habitats. Addition of a hydrology component to the model would enhance control operations by predicting hatch rates in the field.

Classification of immature stage habitats of Culicidae (Diptera) collected in Córdoba, Argentina

In order to classify mosquito immature stage habitats, samples were taken in 42 localities of Córdoba Province, Argentina, representing the phytogeographic regions of Chaco, Espinal and Pampa. Immature stage habitats were described and classified according to the following criteria: natural or artificial; size; location related to light and neighboring houses; vegetation; water; permanence, movement, turbidity and pH. Four groups of species were associated based on the habitat similarity by means of cluster analysis: Aedes albifasciatus, Culex saltanensis, Cx. mollis, Cx. brethesi, Psorophora ciliata, Anopheles albitarsis, and Uranotaenia lowii (Group A); Cx. acharistus, Cx. quinquefasciatus, Cx. bidens, Cx. dolosus, Cx. maxi and Cx. apicinus (Group B); Cx. coronator, Cx. chidesteri, Mansonia titillans and Ps. ferox (Group C); Ae. fluviatilis and Ae. milleri (Group D). The principal component analysis (ordination method) pointed out that the different types of habitats, their nature (natural or artificial), plant species, water movement and depth are the main characters explaining the observed variation among the mosquito species. The distribution of mosquito species by phytogeographic region did not affect the species groups, since species belonging to different groups were collected in the same region.

A North American model to contain the spread of Aedes albopictus through tire legislation

The introduction, spread, and establishment of the Asian tiger mosquito, Aedes albopictus, in the United States has been facilitated by used or waste tires. This species has not only caused considerable concern among public health officials but also highlighted that the growing accumulations of used tires are a serious solid waste problem and a challenge to the recycling industry. This paper illustrates how the State of Illinois addressed the public health and solid waste problems associated with waste tires, mosquitoes and mosquito-borne pathogens. The goal of the State was to develop and implement through legislative process the Illinois Waste Tire Act. The purpose of the Waste Tire Act is: 1) to ensure that used and waste tires are collected for disposal and recycling, 2) to provide for the abatement of used and waste tire dumps and associated threats to public health, 3) to encourage the development of used and waste tire processing facilities and technologies, including energy recovery, and 4) to provide for research on vectors associated with used and waste tires, and the diseases they spread. The discussion will include key statutes from the Act and the model used to coordinate the effort of five different governmental agencies. An up-to-date presentation of vector-related research, mandated by the Act, ranging from applied investigations on mosquito control to more basic studies investigations on virus identification using molecular technology will be discussed. Finally a discussion of problems that have been encountered along with solutions dealing with legislative language, multidisciplined agency efforts and interactions with the general public are presented.

History and updating on the spread of Aedes albopictus in Italy

The present distribution in Italy of Aedes albopictus, the Asian mosquito recently introduced, is described. Until now this mosquito species has been established in 8 regions of our country: Liguria, Veneto, Lazio, Lombardia, Emilia-Romagna, Toscana, Piemonte and recently Sardegna. The established populations have been able to overcome the winter season. These populations, certainly imported from temperate areas, have reconfirmed the great adaptation of the species, reaching the high latitude of 46 degrees North of the Padova area in Northern Italy. The origin of the infestation in Veneto region was shown to be strictly related to the importation of used tires and demonstrated at least for one load of tires from USA. The internal trading of tires from Veneto is the source of infestation of the other Italian regions, with the exception of Liguria and Lazio. Since the introduction and the establishment of Ae. albopictus in Italy represent a new problem of public health, a centre for the surveillance and control of this species has been set up at the Department of Parasitology, Istituto Superiore di Sanità, Roma.

Understanding productivity, a key to Aedes aegypti surveillance

The objective of this work was to define criteria that could be applied to achieve faster, more economical, and accurate assessment of vector populations for control of dengue viruses. During 1989-1990, 1,349 premises were surveyed in Townsville, Charters Towers and Mingela/Ravenswood, Queensland, Australia. In each locality, 1.9-8.4% of premises contained three or more containers with Aedes aegypti immature forms and were designated as key premises. Comparison of surveys in Townsville from 1989 to 1990 indicated that positive premises (i.e., those with at least one container with Ae. aegypti present) were 3.22 times more likely to remain positive than negative houses to become positive the following year. The Ae. aegypti population in Townsville was seen to be totally associated with garden receptacles, discarded household items, and trash but one well and one rainwater tank were responsible for 28% of all immature forms recorded in the 1,349 premises inspected. These breeding sites of high productivity were designated as key containers. At Charters Towers, Mingela, and Ravenswood, rainwater tanks were seen as the most important key container because although they constituted 13-29% of positive containers, they supported 60-63% of the immature forms. This study demonstrates that there is a certain degree of stability with regard to positive premises and that some of these, or some container types, contribute disproportionately to the Ae. aegypti population. Control programs could be made more efficient if efforts were concentrated on these sites of key vector productivity.

Global distribution and continuing spread of Aedes albopictus

Aedes albopictus ranks second only to Ae. aegypti in importance to man as a vector of dengue and dengue haemorrhagic fever (DHF) which viruses place at risk a potential population of 2 billion people living in tropical and sub-tropical regions. Due to its predilection for breeding in a plethora of habitat within urban and suburban environs as well as peri-rural areas it is spreading rapidly where suitable breeding is available. It exhibits strain differences ranging from the cold-hardy to tropic loving, yet despite limited flight range, it has spread beyond the Orient to China, the Pacific, the Indian Ocean islands, the Americas, parts of continental Africa and into southern Europe. This has been done principally by means of transport of eggs in used tyres via rapid air and sea transport. Egg positive used tyres, when shipped, and later rehydrated by rainfall, produce adult mosquitoes within a few days rapidly infesting new areas. Although dengue and other vector-borne arboviral diseases have not been in Europe in epidemic form for many decades, travelers do not infrequently return from dengue endemic areas with dengue and other similar infections. Aedes albopictus is a potential vector of a number of arboviruses and can transmit them in a vertical or transvenereal manner in nature, thereby providing a means for their maintenance and transmission. Where Ae. albopictus newly occurs, the affected populace immediately are aware of a new daytime, nuisance biting mosquito and complaints addressed to local mosquito control authorities increase significantly. The biological characteristics of the mosquito make its spread within Europe highly probable. The paper offers several avenues to be pursued to reduce the global spread of Ae. albopictus, when examined within the context of Europe and the wider world community.

The role of Aedes albopictus as an arbovirus vector

The recent rapid spread of Aedes albopictus to many areas previously free of such infestations, including Albania and Italy, has heightened concern among public health and vector control officials. Ae. albopictus is a proven or potential vector of several arboviruses, including some that are, or have been, actively transmitted in southern Europe. These virus/vector relationships are reviewed with a view toward assessing the risk posed by the current presence of Ae. albopictus in the region.

The Premise Condition Index: a tool for streamlining surveys of Aedes aegypti

Premise inspections and treatment of the larval habitats of container-breeding Aedes aegypti are extremely labor intensive. Since this means of control is the only one available in relation to dengue fever, this report presents an effective approach for streamlining premise surveys in north Queensland, Australia. From a survey of 877 premises in Townsville, Charters Towers, and Mingela/Ravenswood in 1990, occupier and premise variables were collected to examine any relationships with the presence of Ae. aegypti. Statistical modeling of these parameters using multiple and simple Poisson regression indicated that for both adjusted and unadjusted models respectively, the degree of shade and tidiness of the yard had strong correlations with both the proportion of positive premises and the numbers of infested containers therein. Condition of the house was also a significant variable in the unadjusted model. On this basis, the Premise Condition Index is proposed as a rapid assessment tool that can increase efficiency of detecting positive premises and containers by 270-370%. Although habitat selection by Aedes varies throughout the world, this approach could be used as a model for control of vectors of both dengue and yellow fever.

Aedes albopictus: a potential problem in the United Kingdom

The United Kingdom is within the geographical area in which Aedes albopictus could survive. A large number of used car tyres are imported and a number of introduced cases of dengue fever occur annually. The health authorities should be aware of the possibility of dengue transmission.

Nutritional reserves in autogenous and anautogenous populations of Culex pipiens and Aedes caspius (Diptera: Culicidae)

Proteins, carbohydrates, and lipids were compared in larval, pupal, and adult stages of autogenous and anautogenous populations of Culex pipiens and Aedes caspius. All developmental stages of autogenous mosquitoes accumulated significantly more proteins and carbohydrates than did anautogenous sibligns. For lipids, the same pattern was observed with the exception that adult females of both autogenous and anautogenous Ae. caspius had comparable quantities (170-176 micrograms/mg). In general, mosquito larvae contained the highest quantities of the nutrients which then started to decrease in pupae and adults. In addition, autogenous Ae. caspius accumulated more carbohydrates and lipids but less proteins than did Cx. pipiens. The results suggest that autogeny is associated with an inherent ability of autogenous mosquitoes to store more nutritional reserves than anautogenous counterparts. Those reserves are the precursors for oogenesis to produce the first egg clutch in autogenous femles.

Hirsutellin A, a toxic protein produced in vitro by Hirsutella thompsonii

A toxic protein, hirsutellin A, has been purified from the mite fungal pathogen, Hirsutella thompsonii, using ammonium sulphate precipitation, ion exchange chromatography and gel filtration on Bio-Gel P-10. The protein has been characterized as a monomer with a molecular mass of 15 kDa and an isoelectric point of 10.5. The amino acid composition and the N-terminal sequence of hirsutellin A (34 amino acids) have been determined. From these results, the toxin appears to be distinct from other known proteins. It is not glycosylated, and does not show proteolytic activity. The toxin is also antigenic, thermostable and not inactivated by treatments with proteolytic enzymes. Toxicity bioassays showed that injection of larvae of the waxmoth, Galleria mellonella, with hirsutellin A at low dosages [1 microgr toxin (g body wt)-1] caused a high mortality rate. Hirsutellin A was also toxic per os to neonatal larvae of the mosquito Aedes aegypti.

Duration of larval and pupal development stages of Aedes albopictus in natural and artificial containers

Aedes albopictus were reared in different containers: a tree hole, a bamboo stump and an auto tire. The total times from egg hatching to adult emergence were of 19.6, 27.3 and 37.5 days, respectively, according to the container. The first, second and third-instar larvae presented growth periods with highly similar durations. The fourth-instar larvae was longer than the others stages. The pupation time was longer than the fourth-instar larvae growth period. The temperature of the breeding sites studied, which was of 18 degrees C to 22 degrees C on average, was also taken into consideration. The mortality of the immature stages was analysed and compared as between the experimental groups; it was lower in the natural containers than in the discarded tire. The average wing length of adult females emerging from tree hole was significantly larger (p < 0.05) than that of those emerging from the tire.

Effect of some new insect growth regulators on metamorphosis & reproduction of Aedes aegypti

Fourth instar larvae and pupae of Ae. aegypti were treated with four most active insect growth regulators from a new series of mixed alkyl and aryl diethers based on geraniol. Considerable reduction in fecundity and fertility of adults was obtained. Treatment of pupae or pharate adults did not affect adult emergence. Topical treatment of adult females caused great reduction in fertility and fecundity in older as compared to younger females. In addition to the effects on reproduction, adult survival was also reduced in the treated younger females.

Ovariolar 'basal body' development and physiological age of the mosquito Aedes aegypti

Dissection of the ovaries of the mosquito Aedes aegypti (Diptera: Culicidae) revealed, in each ovariole, a group of seven to nine specialized epithelial cells in a region of the calyx wall that is enclosed by the end of the ovariolar sheath. This group of cells is termed the basal body. During ovulation, the mature oocyte passes from the ovariole into the calyx lumen through the basal body. Subsequently, granulation occurs in the basal body cells. The granular basal bodies differ from all previously described ovarian structures. In multiparous females the size and optical density of the granular basal bodies increase after each ovulation. Examination of the granular basal bodies in intact ovaries, stained with neutral red, provides an easy method for distinguishing parous from nulliparous females, and has potential as a new method of age grading.