Showing papers in "Journal of The American Mosquito Control Association in 1998"

Simplification of adult mosquito bioassays through use of time-mortality determinations in glass bottles

Abstract: A simple method is described for treating 250-ml glass Wheaton bottles with insecticide, and using them as test chambers for detecting insecticide resistance in mosquito and sandfly populations. The methods for treating bottles, obtaining baseline data, and applying this technique to insects from the field are described. Sample data are presented from tests run on different vector species using a variety of insecticides. Time-mortality data from the bottle bioassay are presented alongside results from biochemical detection methods applied to the same mosquito population. The potential role, advantages, and limitations of the time-mortality bottle method are discussed.

Introduction and establishment of Aedes (Stegomyia) albopictus skuse (Diptera: Culicidae) in Albania

Abstract: In August-October 1979, infestations of the mosquito Aedes albopictus were discovered at a number of widely separated sites in Albania. Used tires were the principal larval habitat. The species was probably introduced from China in the mid-1970s. The initial infestation was probably at a rubber factory adjacent to the port of Durres (Durazzo), from where the mosquito was shipped in tires to recapping plants in other parts of the country. This is the first recorded infestation of Ae. albopictus outside Oriental and Australasian regions.

Ovicidal Activity of Neem Products (Azadirachtin) Against Culex Tarsalis and Culex Quinquefasciatus (Diptera: Culicidae)

Abstract: Bioactive compounds contained in the seed kernel and other parts of the neem tree (Azadirachta indica A. Juss) have been found to show insecticidal activities and other effects in many species of insects. These activities include antifeedancy, growth regulation, fecundity suppression, male sterility, oviposition repellency, changes in biological fitness such as loss of flying ability, immunodepression, enzyme inhibition, splitting of biological rhythms, and so forth. We investigated the ovicidal effects of various formulations of azadrirachtin (AZ) against the mosquitoes Culex tarsalis Coquillett and Culex quinquefasciatus Say. The formulations tested were wettable powder Azad WP10, emulsifiable concentrate Azad EC4.5, and technically pure AZ. The ovicidal activity of the test neem products was influenced by concentration of AZ, age of the egg rafts, and age of the neem preparations. Other factors such as formulation and mosquito species were also involved in the degree of ovicidal activity. When the egg rafts were deposited directly in fresh neem suspension and left there for 4 h before transfer to untreated water, 1 ppm of AZ produced almost 100% mortality in eggs. When egg rafts aged for 0, 4, 8, 12, and 24 h were exposed to 10 ppm neem suspensions for 36 h, the ovicidal activity was only attained in the egg rafts deposited directly (0 h old) in the neem suspension, not in those with ages of 4-24 h. On aging, depending on the formulations and mosquito species, the neem suspensions at 1 ppm completely lost ovicidal activity within 7-20 days. The egg rafts of Cx. quinquefasciatus were more susceptible to the test neem products than those of Cx. tarsalis. The formulated neem products were more persistent and effective than the technical AZ. The wettable powder (WP) formulation was slightly more persistent and effective than the emulsifiable concentrate (EC). The ovicidal activity of the neem products against mosquitoes from the current research clearly demonstrated the potential of neem products as possible ovicides against Culex mosquitoes.

Aedes albopictus and the world trade in used tires, 1988-1995: the shape of things to come?

Abstract: In the decade since used tires were identified as the mode of introduction of Aedes albopictus to the United States, similar infestations have been reported from 10 other countries in the Americas and 2 in Europe. Millions of used tires are still being traded throughout the world and although a few governments have implemented inspection procedures to prevent further introductions, these are unlikely to be effective. Further introductions of mosquitoes of potential public health significance are inevitable.

Evolution of malaria in Africa for the past 40 years : Impact of climatic and human factors

Abstract: Different malarial situations in Africa within the past 40 years are discussed in order to evaluate the impact of climatic and human factors on the disease. North of the equator, more droughts and lower rainfall have been recorded since 1972; and in eastern and southern Africa, there have been alternating dry and wet periods in relation to El Nino. Since 1955, the increase in human population from 125 to 450 million has resulted in both expansion of land cultivation and urbanization. In stable malaria areas of West and Central Africa and on the Madagascar coasts, the endemic situation has not changed since 1955. However, in unstable malaria areas such as the highlands and Sahel significant changes have occurred. In Madagascar, cessation of malaria control programs resulted in the deadly epidemic of 1987-88. The same situation was observed in Swaziland in 1984-85. In Uganda, malaria incidence has increased more than 30 times in the highlands (1,500-1,800 m), but its altitudinal limit has not overcome that of the beginning of the century. Cultivation of valley bottoms and extension of settlements are in large part responsible for this increase, along with abnormally heavy rainfall that favored the severe epidemic of 1994. A similar increase in malaria was observed in neighboring highlands of Rwanda and Burundi, and epidemics have been recorded in Ethiopia since 1958. In contrast, in the Sahel (Niayes region, Senegal), stricken by droughts since 1972, endemic malaria decreased drastically after the disappearance of the main vector, Anopheles funestus, due to the destruction of its larval sites by cultivation. Even during the very wet year of 1995. An funestus did not reinvade the region and malaria did not increase. The same situation was observed in the Sahelian zone of Niger. Therefore, the temperature increase of 0.5 degree C during the last 2 decades cannot be incriminated as a major cause for these malaria changes, which are mainly due to the combination of climatic, human, and operational factors.

Pharmacokinetics, formulation, and safety of insect repellent N,N-diethyl-3-methylbenzamide (deet): a review.

Abstract: This review is intended to provide the reader with an overview of the all-purpose topical insect repellent N,N-diethyl-3-methylbenzamide (deet), with emphasis on its pharmacokinetics, formulation, and safety aspects. N,N-diethyl-3-methylbenzamide is effective against a variety of mosquitoes, flies, fleas, and ticks, and its protection efficacy depends on factors such as type of formulation, application pattern, physical activity of the user, environment, and species and feeding behavior of the insects. It offers an inexpensive and practical means of preventing the attack of biting insects and, more importantly, the transmission of vector-borne diseases. In both humans and animals, deet skin penetration and biodistribution are rapid and extensive, and metabolism and elimination appear to be complete. As evidenced by over 4 decades of human experience and rigorous animal testing, deet is generally safe for topical use if applied as recommended, although it has occasionally been related to side effects such as toxic encephalopathy, seizure, acute manic psychosis, cardiovascular toxicity, and dermatitis, along with a few cases of death due to extensive skin absorption. N,N-diethyl-3-methylbenzamide may compete in metabolism with and alter the biodistribution properties of other compounds to which a subject is simultaneously exposed, resulting in an added risk of side effects. The appropriate use of formulation techniques and new formulation excipients not only offers a way to extend the duration of protection, but also reduces deet skin penetration. In addition to extended repellency, minimal skin penetration of deet should be an important consideration in the evaluation of a deet formulation during new product development.

A critical review of ultralow-volume aerosols of insecticide applied with vehicle-mounted generators for adult mosquito control.

Abstract: This review of ultralow-volume (ULV) ground aerosols for adult mosquito control includes discussion on application volume, aerosol generators, droplet size, meteorology, swath, dispersal speed, assay methods, insecticide efficacy, and nontarget effects. It summarizes the efficacy of ULV insecticidal aerosols against many important pest and disease-bearing species of mosquitoes in a wide range of locations and habitats in the United States and in some countries of Asia and the Americas. Fourteen conclusions were drawn from the review. 1) ULV ground aerosol applications of insecticide are as efficacious against adult mosquitoes as high- or low-volume aerosols. 2) ULV aerosols with an optimum droplet size spectrum can be produced by several types of nozzles including vortex, pneumatic, and rotary. Droplet size of a particular insecticide formulation is dependent primarily on nozzle air pressure or rotation speed and secondarily on insecticide flow rate. 3) Label flow rates of insecticide for ULV aerosol application can be delivered accurately during routine operations with speed-correlated metering systems within a calibrated speed range, usually not exceeding 20 mph. 4) The most economical and convenient method of droplet size determination for ULV aerosols of insecticide is the waved-slide technique. 5) The efficacy of ULV ground aerosols against adult mosquitoes is related to droplet size because it governs air transport and impingement. The optimum droplet size for mosquito adulticiding is 8-15 microns volume median diameter (VMD) on the basis of laboratory wind-tunnel tests and field research with caged mosquitoes. 6) In general, ULV aerosols should be applied following sunset when mosquitoes are active and meteorological conditions are favorable for achieving maximum levels of control. Application can be made during daytime hours when conditions permit, but rates may have to be increased. The critical meteorological factors are wind velocity and direction, temperature, and atmospheric stability and turbulence. 7) Maximum effective swaths are obtained with aerosols in the optimum VMD range during favorable meteorological conditions in open to moderately open terrain. The insecticide dosage must be increased in proportion to increased swath to maintain the same level of mosquito control. 8) Dispersal speed within a range of 2.5-20 mph is not a factor affecting efficacy if insecticide rate and optimum droplet size are maintained. 9) The results of caged mosquito assays are comparable with reductions in free-flying natural populations. 10) The field efficacies of mosquito adulticides applied as ULV ground aerosols are predictable from the results of laboratory wind-tunnel tests. 11) Results of field tests in open to moderately open terrain during favorable meteorological conditions indicated that ULV insecticidal aerosol application rates producing 90% or more control of Anopheles, Culex, and Psorophora spp. are below or approximately equal to maximum United States Environmental Protection Agency label rates. Against some Aedes spp., some pyrethroid insecticides must be synergized to produce 90% control at label rates. 12) Results of field tests in residential areas with moderate to dense vegetation and in citrus groves or other densely wooded areas showed that insecticide rates of ULV ground aerosols must be increased 2-3-fold to obtain 90% or more control of adult mosquitoes. However, the maximum rates on some insecticide labels would have to be increased to allow higher application rates. 13) Applications of ULV ground aerosols of insecticide in accordance with label directions following sunset do not pose a serious threat to humans, nontarget beneficial animals, or automotive paints. 14) Some aerosol generators operated at high RPM levels exceed the OSHA 8-h hearing hazard criteria of 90 dBA and may require hearing protectors for operators.

Field evaluation of colored light-emitting diodes as attractants for woodland mosquitoes and other diptera in north central Florida

Abstract: The attraction of mosquitoes to transmitted light from colored super-bright light-emitting diodes (LEDs) (100-nm bandwidth) was evaluated by comparison of capture numbers with and without carbon dioxide-baited (200 ml/min) Centers for Disease Control (CDC) traps. Traps with either colored LEDs or control lights were arranged in Latin square designs at 2 north central Florida woodland locations and checked daily during July and August 1996. When data were analyzed by species, a significant difference in attractivity of lights was found in some species. Aedes atlanticus, Aedes dupreei, Aedes infirmatus, Anopheles crucians s.l., Culiseta melanura, Culex nigripalpus, Psorophora columbiae, and Uranotaenia sapphirina showed significant color preferences. These results will have potential for use by ecologists, epidemiologists, and mosquito control personnel for improving collection efficiency of certain species of mosquitoes.

Mosquito (Aedes taeniorhynchus) resistance to methoprene in an isolated habitat.

Abstract: Salt-marsh mosquitoes (Aedes taeniorhynchus), collected on 2 barrier islands in Lee County, Florida, that had been treated from 1989 to 1994 with 150-day methoprene briquets, were bioassayed with technical s-methoprene in the laboratory. Susceptibility of the indigenous Captiva strain (median lethal concentration [LC50] estimate, 6.71 ppb) collected from Captiva Island was 14.9-fold lower than the naive Flamingo strain (LC50 estimate, 0.45 ppb) from Everglades National Park. The Lover's Key strain (LC50 estimate, 6.66 ppb) was 14.8-fold less susceptible than the naive strain. Determinations of the susceptibility of nearby foci of the mainland mosquitoes exposed in the past several years to methoprene have not been completed, but probit analysis of laboratory exposures revealed that the only mainland strain tested (Burnt Store) was no less susceptible (1.06-fold) than the naive Flamingo strain. These findings support the theory that the observed resistance might be restricted to the barrier islands. The known resistance foci (generated with briquet formulations) are located west of the mainland where there is minimal likelihood of inflow of genome from the mainland. On the other hand, the mainland mosquitoes, which were exposed to liquid formulations of methoprene from 1987 to 1994, are believed to have substantial gene flow between exposed and nonexposed populations and thus a reduced likelihood of selection for resistance.

A comparison of surveillance systems for the dengue vector Aedes aegypti in Port of Spain, Trinidad.

Abstract: When the currently used larval surveillance system (visual inspection) for the dengue vector Aedes aegypti was compared with the surveillance for the presence of eggs by ovitrapping in Port of Spain, Trinidad, it was found that the latter (39.1%) was significantly more sensitive than the visual inspection system (10.1%). At the same time, the presence of the nuisance mosquito Culex quinquefasciatus was detected in 38.4% of the households. Both Ae. aegypti and Cx. quinquefasciatus showed preference for ovipositional attractants in ovitraps: hay infusion > yeast suspension > plain tap water. Although all the socioeconomic and geographic areas produced both mosquito species in 1996, upper middle class (UMC) areas (8.6-43.4%) produced more Ae. aegypti than did lower middle class (LMC) areas (7.8-38.8%), which produced more than working class (WC) areas (3.9-29.9%). For Cx. quinquefasciatus, the order of production was reversed with WC areas (50.1%) > LMC areas (30.0%) > UMC areas (26.0%). Change in vector surveillance strategies incorporating some ovitrapping and stratified sampling are recommended for Caribbean countries.

Impact of treatments with Bacillus sphaericus on Anopheles populations and the transmission of malaria in Maroua, a large city in a savannah region of Cameroon.

Abstract: Simultaneously with a control of breeding sites primarily for Culex quinquefasciatus and secondarily for anophelines with Bacillus sphaericus in the town of Maroua (120,000 inhabitants) in North Cameroon, a survey of anopheline populations and of transmission rates of malaria was performed. Monthly night catches in 8 districts of the town emphasized the relation between the biting rate by Anopheles in the districts and two main factors. One factor was the distance of a district from the breeding sites, i.e., natural flooded areas along the periphery of the town or artificial breeding sites (ditches, puddles) filled with rain water during the rainy season and with water from the water network throughout the year. The second factor was the density of the habitation that reduced dispersal of female mosquitoes from the breeding sites and the risk for inhabitants to be injected because of scattered bites. The treatment with B. sphaericus was followed by a delay (2 months) in the beginning of the transmission period and a decrease in the incidence of malaria cases studied in a health facility of the town. It thus seems to be possible to reduce malaria transmission by applying B. sphaericus to the breeding sites, but this requires a good knowledge of the location and dynamics of breeding sites and an improved formulation of the pesticide.

Effect of marsh design on the abundance of mosquitoes in experimental constructed wetlands in southern california

Abstract: The species composition and abundance of larval mosquitoes were studied in the vegetated regions of 2 types of experimental constructed wetlands: one-phase marshes, which have continuous vegetation throughout the marsh, and 3-phase marshes, which have 2 vegetated regions separated by a region of comparatively deeper open water. Larvae of Culex spp. were significantly more abundant in one-phase marshes than in 3-phase marshes. Larval populations in one-phase marshes also contained proportionately more older larval instars (stages III and IV) than did populations in 3-phase marshes. Mortality rates of larvae increased during the summer and were higher in 3-phase marshes than in one-phase marshes during the initial 6 wk of the study. Differences in mortality rates between marsh types were related to predator abundance during the first 6 wk of the study and thereafter were not strongly associated with predator populations. An infusion of decaying bulrush (Schoenoplectus californicus) stimulated oviposition by gravid Culex stigmatosoma more than by gravid Culex quinquefasciatus and Culex tarsalis. Culex erythrothorax was the most abundant host-seeking species collected in CO2-baited traps; however, larvae were rarely collected during routine dip sampling and egg rafts were never collected in oviposition studies.

Effect of female size on fecundity and survivorship of Aedes aegypti fed only human blood versus human blood plus sugar.

Abstract: We determined whether size, an indirect measure of teneral energy reserves, modifies the fitness advantage (sigma survival x egg production/female/day) conferred to female Aedes aegypti (L.) maintained on human blood over cohorts fed human blood plus sugar. Different sized females were obtained by rearing them at different larval densities and with different amounts of food per larva. Each female in 4 treatment groups of 23 mosquitoes each was maintained in a separate cage. A 10% sucrose solution was provided ad libitum to mosquitoes in the sugar-plus-blood treatments and water to the blood only groups. Eggs deposited and survival were monitored daily for each mosquito until all had died. Within a size category, survival of mosquitoes in different treatments was not different and mosquitoes fed only human blood laid more eggs than those fed blood plus sugar. The numbers of eggs laid by small mosquitoes fed human blood alone and large mosquitoes fed human blood plus sugar were not different. Mosquitoes fed only human blood had higher net replacement and intrinsic rates of growth than similar sized mosquitoes fed blood plus sugar. Female Ae. aegypti fed only human blood, regardless of the variation in size that we studied and thus energy reserves at emergence, had a fitness advantage over those fed a diet that included sugar.

The acetylcholinesterase gene Ace: a diagnostic marker for the Pipiens and Quinquefasciatus forms of the Culex pipiens complex.

Abstract: The taxonomy of the Culex pipiens complex remains a controversial issue in mosquito systematics. Based on morphologic characters, 2 allopatric taxa are recognized, namely Cx. pipiens (including the form "molestus") in temperate areas and Cx. quinquefasciatus in tropical areas. Here we report on variability at the nucleotide level of an acetylcholinesterase gene in several strains and natural populations of this species complex. Few polymorphisms were found in coding regions within a subspecies but many polymorphisms were observed between subspecies in noncoding regions. We describe a method based on a restriction enzyme polymorphism in polymerase chain reaction-amplified DNA, in which the presence or absence of one restriction site discriminates Cx. pipiens, Cx. quinquefasciatus, and their hybrids. This technique reliably discriminates mosquitoes from more than 30 worldwide strains or populations. Polymerase chain reaction amplification of specific alleles may also be a useful tool for characterizing specific alleles of each sibling taxon.

Natural habitats of Aedes Aegypti in the Caribbean--a review.

Abstract: Natural breeding habitats of Aedes aegypti in the Caribbean region were reviewed by conducting larval surveys in Trinidad. Puerto Rico, and the U.S. Virgin Islands and referring to records from the Mosquitoes of Middle America project. Twelve types of natural habitats were recorded: rock holes (9.7%), calabashes (2.4%), tree holes (19.5%), leaf axils (4.8%), bamboo joints (14.9%), papaya stumps (7.3%), coconut shells (4.8%), bromeliads (7.3%), ground pools (14.9%), coral rock holes (9.7%), crab holes (2.4%), and conch shells (7.3%), of which the coconut shell and calabash habitats were new to the Caribbean. The countries having the highest prevalence of natural habitats were Trinidad. Puerto Rico, and Jamaica, with 9 types (22.0%), 7 types (17.0%), and 6 types (14.6%), respectively. The distribution of natural habitats of Ae. aegypti in the Caribbean region is discussed in relation to vector control measures.

Toxicity of a phenyl pyrazole insecticide, fipronil, to mosquito and chironomid midge larvae in the laboratory.

Abstract: Toxicity of a phenyl pyrazole insecticide, fipronil, to 4th-instar larvae of 6 species of colonized mosquitoes (Aedes aegypti, Ae. albopictus, Ae. taeniorhynchus, Anopheles quadrimaculatus, Culex nigripalpus, and Cx. quinquefasciatus) and 2 species of field-collected chironomid midges (Chironomus crassicaudatus and Glyptotendipes paripes) was evaluated in the laboratory. All mosquito species were highly susceptible with 48-h median lethal concentration (LC50) values ranging from 0.00043 ppm (Ae. taeniorhynchus and An. quadrimaculatus) to 0.023 ppm (Ae. albopictus). Chironomus crassicaudatus and G. paripes also were extremely susceptible (48-h LC50 of both species: 0.00042 ppm) to fipronil. Larval mortality checks of Ae. taeniorhynchus, Cx. nigripalpus, and G. paripes at 24 h and again at 48 h posttreatment revealed delayed activity of this compound against these species. First-instar larvae of Ae. albopictus and Cx. quinquefasciatus were significantly (P < 0.01) more susceptible to fipronil than the 4th-instar larvae of these mosquito species.

Field trials of biolarvicide Bacillus thuringiensis var. israelensis strain 164 and the larvivorous fish Aplocheilus blocki against Anopheles stephensi for malaria control in Goa, India.

Abstract: Severe outbreaks of malaria occurred in the coastal villages of the Candolim Primary Health Centre (PHC) of Goa, India, in 1993 and 1994. These outbreaks were associated with accelerated construction activity with an influx of migrant laborers. The weekly application of Bacillus thuringiensis var. israelensis (B.t.i.) strain 164 at 1 g/m2 and introduction of the indigenous larvivorous fish Aplocheilus blocki in major breeding habitats of Anopheles stephensi replaced ongoing DDT spraying and pyrethrum fogging in June 1994. The objective of this study was to evaluate the effects of B.t.i. and larvivorous fish on An. stephensi and subsequent transmission of malaria in the Candolim PHC, Goa, India. In 1995 the populations of an. stephensi in larger habitats (habitats with immatures: t = 5.19, P = 0.0017; immature density: t = 3.57, P = 0.007) and smaller habitats (habitats with immature: t = 3.86, P = 0.005; immature density: t = 4.93, P = 0.002) and malaria incidence declined substantially (malaria cases: chi 2 = 712, P < 0.001; slide positivity rate: chi 2 = 10.36, P < 0.001; annual parasite index; chi 2 = 15.1, P < 0.001), whereas the incidence of malaria continued to increase in other nearby towns.

Evaluation of butanone, carbon dioxide, and 1-octen-3-OL as attractants for mosquitoes associated with north central Florida bay and cypress swamps.

Abstract: Field studies were conducted to determine the responses of mosquitoes found in north central Florida bay and cypress swamps to carbon dioxide (CO2), light, butanone, and 1-octen-3-ol (octenol), alone and CO2 in combination with each of the others. The response of these mosquito species to 5 CO2 release rates (2, 20, 100, 200, and 2,000 ml/min) of CO2 was also determined. The use of CO2 resulted in a response in all the species studied; the pattern of response to increasing CO2 levels varied from species to species. In general, collection size increased as CO2 release rate increased; however, 5 species (Aedes dupreei, Anopheles perplexens, Culiseta melanura, Culex erraticus and Mansonia titillans) deviated from this pattern. Collection size of Ae. dupreei, Cs. melanura, and Cx. erraticus decreased at the 2,000 ml/min release rate. Collection size of An. perplexens and Ma. titillans remained constant at each CO2 level to which these species responded. In the CO2 and light studies, the general pattern for collection size was: CO2 + light > CO2 alone > light alone. The combination CO2 + octenol (2.2 mg/h) resulted in a synergistic response (i.e., greater than the combined response obtained by CO2 and octenol alone) for all species except Cs. melanura, Culex nigripalpus, and Culex restuans. Only 2 species (Aedes atlanticus and Aedes canadensis) responded to octenol in relatively large numbers (i.e., response to octenol alone > or = 5% of that obtained by using CO2 alone at the 200 ml/min release rate). Octenol at the release rate tested repelled Cs. melanura. The butanone + CO2 bait combination increased the responses compared to CO2 alone of Aedes infirmatus, Culex salinarius, Coquillettidia perturbans, and Psorophora ferox, but decreased the response of Cs. melanura.

Acute toxicity of selected pesticides to the Pacific blue-eye, Pseudomugil signifer (Pisces).

Abstract: Because the larvivorous fish Pseudomugil signifer is native to southeastern Queensland and is abundant in shallow estuarine habitats, intertidal marshes, wetland habitats, and freshwater streams, it was chosen as an indicator species for toxicologic studies with pesticides. Acute toxicity studies with 2 organophosphorus pesticides (pirimiphos-methyl and temephos) and 3 alternate compounds under evaluation for registration in Australia (Bacillus thuringiensis var. israelensis, s-methoprene, and pyriproxyfen), were tested in 96-h laboratory trials. Pirimiphos-methyl was the most toxic compound, with a median lethal concentration (LC50) of 0.091 ppm (0.3 times the estimated field concentration [EFC] for a 15-cm-deep pool). Temephos had an LC50 value of 0.594 ppm (9.9 times the EFC). Bacillus thuringiensis var. israelensis and pyriproxyfen produced LC50 values of 6.1 x 10(11) International Toxic Units (477 times the EFC) and 0.854 ppm (106 times the EFC), respectively. s-Methoprene was the least toxic compound, with no mortality recorded at 500 times the EFC.

Genetic polymorphism of morphological and biochemical characters in a Natal, Brazil, population of Lutzomyia longipalpis (Diptera: Psychodidae).

Abstract: The phlebotomine sand fly, Lutzomyia longipalpis, is the vector of visceral leishmaniasis in the New World. Variability in its tergal spot morphology has led to conflicting interpretations of the species status of the various forms. An L. longipalpis field population from eastern Brazil was found with three co-occurring morphological variations--1-spot, 2-spot, and an intermediate form. Genetic profiles were established for each form. Fifteen isoenzyme loci provided the data matrix for comparison of genetic variation among the forms. Spot patterns and isoenzyme frequencies fit Hardy-Weinberg expectations, and no significant differences in isoenzyme frequencies were associated with morphological phenotype. The spot phenotype appears to be a polymorphic character not related to genetic isolation or differentiation at the species level.

An experimental study on the detection of fructose in Aedes aegypti

Abstract: Male and female Aedes aegypti fed a 10% sucrose solution and/or blood were tested to determine the duration of fructose detection in their bodies and the volume of sugar solution they ingested. The limit of detection of fructose by the cold anthrone test was investigated in a series of experiments. Results were applied to the interpretation of sugar feeding by Ae. aegypti collected inside houses in Puerto Rico during times of low (cool season) and high (hot season) dengue transmission in 1996. We conclude that, under our experimental conditions, the cold anthrone test can detect a 10% sucrose solution in male and female Ae. aegypti up to approximately 4 days after ingestion, even the smallest volumes of 10% sucrose solution ingested by experimental mosquitoes are detectable, the test is sensitive enough to detect 0.6 microgram of fructose, and the cutoff point for defining positive fructose values in field-collected females should be based on blood-engorged specimens. We confirmed that female Ae. aegypti collected from natural resting sites inside houses in Puerto Rico seldom, compared to males, contain detectable amounts of fructose.

Effect of skin abrasions on the efficacy of the repellent deet against Aedes aegypti.

Abstract: Abrasion of repellent-treated human skin affected the efficacy of a sustained-release insect repellent containing N,N-diethyl-3-methylbenzamide (deet) against bites of Aedes aegypti. Skin treated with repellent when abraded up to 30 times showed significantly lower protection than unabraded skin against mosquito bites for 10 h. The mean value of the kinetic coefficient of friction during skin abrasion by clothing (battle dress uniform fabric) for repellent-treated skin (0.159 +/- 0.003) was significantly higher than untreated skin (0.122 +/- 0.005). Repellent-treated skin appeared stickier than the untreated skin. An increase in the number of skin abrasions by clothing resulted in a reduced duration of protection against mosquito bites.

Evaluation of lambdacyhalothrin-impregnated bednets in a malaria endemic area of India. Part 1. Implementation and acceptability of the trial.

Abstract: In malaria endemic forested villages in Orissa State, India, a 3-year comparison of nylon nets treated with lambdacyhalothrin at 25 mg/m 2 , untreated nets, and no nets was carried out. Treated nets retained high insecticidal efficacy for more than 7 months. Nets washed after 3 months of use gave 98% kill in a bioassay with a 3-min exposure. Based on these bioassays during the first year, nets were later reimpregnated at 6-monthly intervals with participation of the users. Compliance with the use of nets was good. Eighty-eight percent of nets were usable even after 3 years. The main benefits perceived by treated net users were reductions in malaria, mosquito bites, head louse infestations, and other nuisance insects. The trial was well accepted by the community. Issues related to social marketing and promotion of nets are discussed.

Colonization of Anopheles pseudopunctipennis from Mexico

Abstract: Two colonies of Anopheles pseudopunctipennis, Tapachula and Abasolo strains, were established under laboratory conditions with a thermoperiod (29 degrees C during the day; 24 degrees C during the night) and artificial dusk. To stimulate mating, a light beam from a flashlight was shone on the cage shortly after lights off. This procedure was repeated for the first 6 mosquito generations (parental to F6) and thereafter light stimulation was unnecessary for mating. The Tapachula colony has been maintained for 24 generations in 24 months, with insemination rates in females > 80% since the F3, and a monthly production of 30,000 pupae since the F7. Using the same procedure, the Abasolo colony from northeastern Mexico has been maintained for 13 generations in 14 months, with insemination rates of 26-52%.

Evaluation of lambdacyhalothrin-impregnated bednets in a malaria endemic area of India. Part 2. Impact on malaria vectors.

Abstract: In malaria endemic villages of the Indian State of Orissa, the impact of bednets treated with lambdacyhalothrin at 25 mg/m 2 on malaria vectors was assessed during a 3-year intervention trial beginning in May 1990. The main malaria vector was Anopheles culicifacies with a small contribution from Anopheles fluviatilis. The impregnated bednets caused a significant reduction in vector density as assessed by morning indoor resting catches, man-biting rate, light trapping, the proportion of females engorged with human blood, and the parity rate as compared with villages with untreated or no nets. No statistically significant difference was observed in these parameters between the villages with untreated nets or no nets. The trial demonstrated that the lambdacyhalothrin-treated nets were highly effective against the malaria vectors.

The use of microsatellites to study gene flow in natural populations of Anopheles malaria vectors in Africa: potential and pitfalls.

Abstract: The potential of microsatellites as population genetic markers in the malarial vectors Anopheles gambiae and Anopheles arabiensis was assessed using 4 loci. Substantial genetic divergence was found not only between these species but also between the Mopti and Forest chromosomal forms of An. gambiae, demonstrating that microsatellites do have the power to detect barriers to gene flow in these mosquitoes. However, application and interpretation of microsatellites was not necessarily straightforward. Despite the use of semiautomated fluorescent technology that enabled fragment sizes to be determined precisely, some difficulty was encountered in allele classification. Sequence analysis revealed insertions/deletions and base changes in the flanking regions of the microsatellite as the probable cause of this problem. The implications of this and other potential pitfalls in the use of microsatellites to study vector populations are discussed.

Bacterial density and survey of cultivable heterotrophs in the surface water of a freshwater marsh habitat of Anopheles quadrimaculatus larvae (Diptera: Culicidae).

Abstract: We examined surface water samples collected in September and October 1994 from a freshwater marsh habitat containing larval Anopheles quadrimaculatus mosquitoes. Bacterial densities in direct microscopic counts ranged from 9.7 x 10(5) to 1.3 x 10(7) cells/ml. Densities of cultivable bacteria on trypticase soy agar medium ranged from 1.0 to 1.5 x 10(5) cells/ml. The majority of 888 isolates were gram-positive rods (41%) followed by gram-negative rods (28%). Analysis of the cellular fatty acid profiles of 824 isolates using gas chromatography and Microbial Identification Systems TSBA (Rev. 3.60) library software grouped the bacteria into Bacillus spp. (35%), other gram-positive bacteria (16%), pseudomonads (15%), other gram-negative bacteria including mainly Enterobacteriaceae and Vibrionaceae (21%), and profiles not recognized (13%). Among 33 genera within these groups, the most common were Bacillus, Pseudomonas, Aeromonas, and Arthrobacter.

Laboratory and field evaluation of efficacy of VectoBac 12AS against Culex sitiens (Diptera: Culicidae) larvae.

Abstract: Laboratory bioassay studies of the efficacy of VectoBac 12AS (active ingredient: 1,200 International Toxic Units [ITU]/mg Bacillus thuringiensis var. israelensis) against field-collected late 3rd/early 4th-instar larvae of Culex sitiens indicated excellent control potential. A 95% lethal concentration (LC95) value of 1.381 x 10(7) ITU was calculated, which equated to a dosage of 0.011 liters/ha. This dosage represented 1.8% of the recommended lowest dosage rate for the product. A field trial of VectoBac 12AS against late 3rd/early 4th-instar field specimens of Cx. sitiens in floating mesh cylinders was then conducted in salt-marsh pools near Coomera Marina, southeast Queensland, Australia. At a rate of 0.5 liters/ha, 100% mortality of Cx. sitiens larvae was recorded at 24 h posttreatment.

Evaluation of lambdacyhalothrin-impregnated bednets in a malaria endemic area of India. Part 3. Effects on malaria incidence and clinical measures.

Abstract: In Indian villages with high malaria endemicity use of nylon bednets treated at 25 mg/m2 at 6-month intervals for 3 years caused significant reductions in malaria incidence, slide positivity rate, slide falciparum rate, annual parasite index, and parasite rate in the entire population, as well as reductions in rates of splenomegaly and anemia in children. In villages with untreated nets, considerable reduction also occurred in these parameters except for the rate of splenomegaly. In the village without nets, a relatively small drop occurred in the parasite rate and anemia but no change occurred in malaria incidence, and an increase occurred in the rate of splenomegaly. The trial thus showed the efficacy of impregnated bednets against malaria in the forested hills of Orissa State where the existing control strategy based on indoor residual spraying of DDT has remained incapable of interrupting malaria transmission.

A diagnostic polymerase chain reaction assay for species A and D of the Anopheles Dirus (Diptera: Culicidae) species complex based on ribosomal DNA second internal transcribed spacer sequence.

Abstract: A polymerase chain reaction assay based on differences in the internal transcribed spacer regions of ribosomal DNA was developed for distinguishing 2 members of the Anopheles dirus sibling species complex. This assay distinguished An. dirus species A from species D by producing diagnostic bands, 374 base pairs (bp) in length for species A and 663 bp in length for species D. Both laboratory colonies and field collections from Hainan and Yunnan provinces of China were identified with 100% accuracy.