Comparative field efficacy of newly developed formulations of larvicides against Aedes aegypti (L.) (Diptera: Culicidae).

Aedes aegypti (L.) is known as vector of dengue and chikungunya fever. Larvicides are used to control this vector. We evaluated the efficacy of newly developed formulations of larvicides to control Ae. aegypti under field conditions for 24 weeks post single application. Mosdop P and Mosdop TB containing diflubenzuron (2% and 40 mg/tablet, respectively) as the active ingredient, were applied at a dosage of 0.1 mg a.i./1 and Mosquit TB10, Mosquit TB100 and Temecal containing temephos (1%, 10% and 1%, respectively) as the active ingredient were applied at a dosage of 1 mg active ingredent (a.i.) to 200 liter water storage jars. Two water regimens were used in the jars: in one regimen the jar was kept full of water all the time and in the other regimen a full jar had half the volume removed and refilled weekly. The larvicidal efficacy was reported as the level of inhibition of emergence (IE%) calculated based on the pupal skins in the jars versus the original number of larvae added. Mosdop P, Mosdop TB, Mosquit TB10, Mosquit TB100 and Temecal showed complete larvicidal efficacy (100% IE) in the constantly full jars for 16, 17, 14, 20 and 13 weeks posttreatment, respectively; in the jars where half the volum of water was replaced weekly, the larvicides had complete larvicidal efficacy (100% IE) for 19, 20, 17, 24 and 15 weeks post-treatment, respectively. The five larvicide regimens evaluated in this study are effective for controlling Ae. aegypti larvae.

Insecticide resistance in bedbugs in Thailand and laboratory evaluation of insecticides for the control of Cimex hemipterus and Cimex lectularius (Hemiptera: Cimicidae).

Bedbugs are found in many countries around the world, and in some regions they are resistant to numerous insecticides. This study surveyed bedbugs in Thailand and determined their resistance to insecticides. The surveys were carried out in six provinces that attract large numbers of foreign tourists: Bangkok, Chonburi, Chiang Mai, Ubon Ratchathani, Phuket, and Krabi. Bedbugs were collected from hotels and colonized in the laboratory to evaluate their resistance to insecticides. Cimex hemipterus (F.) was found in some hotels in Bangkok, Chonburi, Phuket, and Krabi, whereas Cimex lectularius L. was found only in hotels in Chiang Mai. No bedbugs were found in Ubon Ratchathani. The colonized bedbugs showed resistance to groups of insecticides, including organochlorines (dichlorodiphenyl trichloroethane, dieldrin), carbamates (bendiocarb, propoxur), organophosphates (malathion, fenitrothion), and pyrethroids (cyfluthrin, deltamethrin, permethrin, lambda-cyhalothrin, etofenprox) in tests using World Health Organization insecticide-impregnated papers. The new insecticides imidacloprid (neonicotinoid group), chlorfenapyr (pyrrole group), and fipronil (phenylpyrazole group) were effective against the bedbugs; however, organophosphate (diazinon), carbamates (fenobucarb, propoxur), and pyrethroids (bifenthrin, cypermethrin, esfenvalerate, etofenprox) were ineffective. Aerosols containing various pyrethroid insecticides with two to four different active ingredients were effective against the bedbugs. The results obtained from this study suggested that both species of bedbugs in Thailand have developed marked resistance to various groups of insecticides, especially those in the pyrethroid group, which are the most common insecticides used for pest control. Therefore, an integrated pest management should be implemented for managing bedbugs in Thailand.

Temporal and spatial distribution, sex ratio and fecundity of the eye fly siphunculina funicola (Diptera: Chloropidae) at aggregation sites during diurnal and nocturnal periods.

The present study was aimed to determine the distribution and abundance of the eye fly Siphunculina funicola (de Meijere) in Thailand and to investigate the sex ratio and fecundity of eye flies from aggregation sites collected during the day-time and night-time. The flies were collected from several provinces in central Thailand and Phuket in the south. Observations were regarding the relative abundance of eye flies in different regions and seasons. During 2007 and 2008, large populations of eye flies were noted at resting sites in central Thailand with both day and night collections. Males flies outnumbered female flies. Smaller populations were seen in Chumphon and Surat Thani Provinces with increasing numbers in Krabi and Phuket Provinces in the south. The gravid rate was nil in the few females collected in Chomphon and Surat Thani but were 3.9% and 36.3% in Krabi and Phuket, respectively. The gravid rates were higher during the dry season or during dry spells than during wet and rainy periods, suggesting egg retention by the females when oviposition sites (presumably soil) were dry. Numerous day and night collections were made in Chon Buri Province. In most collections males predominated but there was no differences in the numbers of flies collected during the two time periods. There was a slightly greater percentage of females (still lower than males) during the night collections. During the dry and hot season, due to lack of optimum oviposition sites because of dryness, the eggs were retained in the females. A series of day time collections at the end of April 2008 and in February-March 2009 had higher numbers of gravid females. Day time collections in May 2008 (start of the rainy season) showed a moderate number of gravid females, but the gravid rates were low during the rainy season, indicating higher oviposition activity by females.

The eye fly Siphunculina funicola (Diptera: Chloropidae) as a carrier of pathogenic bacteria in Thailand.

The oriental eye fly Siphunculina funicola (1.0-1.6 mm) is extremely annoying to humans and domestic animals, feeding on mucous membranes, secretions, wounds, eyes, and other moist surfaces of the host body. In many rural areas of Thailand heavy populations of this fly prevail where they aggregate on a variety of hanging substrates, such as strings, nest trailings, electrical lines, decorations, ropes, cob webs, clothes hangers, automobile radio antennae and other items in open shade close to their hosts. Both males and females feed voraciously on wounds and moist skin. With this type of persistent feeding, the eye flies are suspected to carry and transfer germs to their hosts. In the present study, bacteria were isolated from S. funicola captured from wounds, host seeking flies and from their resting sites. Some enriched and bacterial culture media were more suitable for isolation than others. A diverse group of bacteria (64 species), both gram-posi-tive and gram-negative, most in risk category 2, were identified. Bacterial colony counts from Trypic soy broth ranged from 10 to > 3.0 x 10(3) cfu/ml. The most common bacteria isolated were Acinetobacter, Aeromonas, Bacillus, Corynebacterium, Enterobacter, Enterococcus, Escherichia, Kocuria, Pantoea, Pseudomonas, Staphylococcus and others. These bacteria may cause disease conditions in humans and animals. This is the first time bacteria from S. funicola have been reported.

Identification of blood meal of field caught Aedes aegypti (L.) by multiplex PCR.

Laboratory bred female Aedes aegypti (L.) was used to determine sensitivity of multiplex PCR for detecting human blood meal. Human blood DNA was detected in live fully fed mosquitoes until 3 days after blood feeding, and for 4 weeks when stored at -20 degrees C. Among 890 field caught female mosquito samples examined for vertebrate DNA by multiplex PCR, results were positive for human, pig, dog, cow and mixture of 2 host DNA at 86.1, 3.4, 2.1, 1.0 and 3.6%, respectively, while 3.9% of the samples were negative. Blood feeding pattern must be considered when mosquito control strategies become employed.

Laboratory and field evaluation of spinosad, a biorational natural product, against larvae of Culex mosquitoes.

Spinosad, a fermentation product from the naturally occurring soil actinomycete bacterium Saccharopolyspora spinosa, has been reported to have a high level of activity against phytophagous insects and insects impacting human and animal health. It has low mammalian toxicity and a favorable environmental profile, including low persistence and no toxicity to fish and wildlife at mosquito larvicidal rates. In order to determine the activity and efficacy of spinosad against larvae of Culex mosquitoes, technical powder and liquid formulations of spinosad were tested against mosquito larvae under laboratory and field conditions. In the laboratory, spinosad powder was highly active against 2nd and 4th instars of Culex quinquefasciatus after 24 h of exposure. The extent of mortality increased slightly after 48 h of exposure. Second instars were slightly more susceptible than 4th instars. The liquid formulation showed somewhat higher activity (about 2x) than the technical powder material at both the LCs50 and LC90 levels. In field microcosm tests against natural populations of mosquitoes, the liquid formulation yielded excellent control of immature Culex spp. for 21 days at concentrations of 0.05 mg (AI)/liter and 35 days at 0.1 to 0.5 mg (AI)/liter in outdoor tubs. This formulation also yielded excellent control of natural Culex mosquitoes for 14 days or longer at 0.025 to 0.1 mg (AI)/liter in outdoor ponds. From our data, it appears that spinosad as a new mode of action has a good potential for controlling mosquito larvae.

Field evaluation in Thailand of spinosad, a larvicide derived from Saccharopolyspora spinosa (Actinomycetales) against Aedes aegypti (L.) larvae.

Two formulations of spinosad, direct application tablet (DT) and 0.5% granules (GR), at 3 dosages (0.25, 0.5 and 1.0 mg/l) in 200-liter earthen jars were evaluated against the larvae of Aedes aegypti. Two water regimens were used in the jars: jar full all the time and a full jar in which half the volume of the water was removed and replaced at each assessment interval. All treatments and controls were replicated 4 times and challenged with cohorts of 25 third-instar larvae of Ae. aegypti at weekly intervals during the study. The number of pupal skins (indicating successful emergence of adults) in the treated and control regimens were counted 7 days post-addition and they were used to calculate inhibition of emergence (% IE) based on the original number of larvae used. The DT formulation at the highest concentration (1.0 mg/l) yielded 79-100% IE for 34 days in the full jars, efficacy declining beyond this period. However, the longevity of this dosage was much longer with 90-100% IE for 62 days post-treatment in the water exchange regimen. The target and manufacturer-recommended concentration of 0.5 mg/l of DT gave good control (92-100% IE) for 20 days, declining below 92% IE thereafter in full jars. This dose also yielded good control with IE of 97-100% for 27 days in the water exchange regimen. The 0.5% GR formulation at all 3 dosages showed higher efficacy and greater longevity in the jars than the DT. In the full jars, all 3 dosages produced IE of 76-100% for 55 days post-treatment. In the water exchange regimen, the efficacy and longevity were increased by about one week, up to 62 days post-treatment. It is clear that the DT formulation can be used effectively against Ae. aegypti larvae at a target dose of 0.5 mg/l in 200-liter jars. This dose can be increased to 1.0 mg/l if slightly longer residual activity is desired. In containers where water is consumed and more water added, the longevity of efficacy will be longer for the DT than in jars which remain full all the time. GR (0.5%) gave longer control than DT. GR (0.5%) floated on the surface and produced scum and an oily film, features not desirable in stored water.

Field evaluation of repellents and insecticidal aerosol compositions for repelling and control of Siphunculina funicola (Diptera: Chloropidae) on aggregation sites in Thailand.

The oriental eye fly Siphunculina funicola, a small member (1.5-1.6 mm) of the family Chloropidae, is extremely annoying to humans and domestic animals, feeding on mucous membranes, secretions, and other moist surfaces of their hosts. In central Thailand heavy populations were detected during 2006-2007 in some rural, agricultural, and periurban areas of the region. They were noted to exhibit strong synanthropy and aggregation behavior, congregating on thin (1-5 mm diam) substrates hanging in or near human habitations and animal shelters and other structures open on one or more sides. We initiated studies on the repelling and control of this eye fly at their aggregation sites, the most vulnerable targets near or in human habitations. Four formulations of repellents consisting of Everside, 3 fatty acids (with 8, 9, and 10 carbons), permethrin, and the acids C8910 plus permethrin in Everside were diluted 1:3 in tap water and sprayed on to the aggregation sites. Prior to treatment all sites including controls were disturbed to dislodge eye flies, and then the blank sites were sprayed with the aqueous suspension of the repellents. Additionally, we evaluated 3 commercially available household insecticidal aerosol formulations by treating eye flies and their resting sites (without dislodging the flies) with puffs of the aerosols. Two treatments with permethrin alone and permethrin plus acids in Nakhorn Ratchasima Province caused a complete absence of flies from the sites up to 23 h. After treatment with the repellents, the repelled flies and others were found to congregate on untreated favorable sites close to the treated ones. The repellents tested against eye flies in Chonburi Province at 2 locations caused almost complete absence of this insect on aggregation sites up to 120 h. Three household insecticide aerosols applied to aggregation sites with resting and hovering eye flies produced high to complete mortality and reduction of eye flies for 48 h or possibly longer in the treated sites. This is the first time that procedures for the evaluation of repellents and insecticides against eye flies have been tested and developed. The use of commonly available insecticide aerosol products could provide a good source of materials for the elimination of eye flies from their domestic and peridomestic aggregation sites.

Control of aggregated populations of the eye fly Siphunculina funicola (diptera: chloropidae) using pyrethroid aerosols.

Three commercially available insecticide aerosol compositions containing cyphenothrin, imiprothrin, cypermethrin, d-tetramethrin and permethrin, in various combinations and concentrations were evaluated for control of the oriental eye flies Siphunculina funicola (de Meijere) from their aggregation substrates in two villages in the Chon Buri Province, Thailand. Each aerosol produced almost complete kill of eye flies on most of the treated substrates. Time to reoccupation of each treated substrate was determined at 24, 48 and 72 hours post-treatment. All 3 aerosol preparations killed eye flies on most of the treated substrates and kept most of the substrates free of eye flies for at least 48-72 hours. The effectiveness and longevity of the aerosols varied depending on the type and location of the substrate. Smooth, hairy and polished substrates did not intercept sufficient insecticide; therefore providing low residual activity compared to porous and coated surfaces. Aerosols applied to substrates located at higher levels gave good initial kill, but reoccupation of these substrates by flies occurred relatively quickly (within 24-48 hours) following treatment. Attempts should be made to discharge aerosol flumes closer than 1 m from the aggregation substrates.

Pestiferous nature, resting sites, aggregation, and host-seeking behavior of the eye fly Siphunculina funicola (Diptera: Chloropidae) in Thailand.

Species of eye flies and eye gnats (Diptera: Chloropidae) are severe and persistent pests of man, domestic and wild animals, and potential vectors of pathogens. The species prevailing in the Oriental region belong to the genus Siphunculina, while those in the Neotropic and Nearctic regions belong to Liohippelates and Hippelates. These are small insects of 1-2 mm that feed on wounds, lacerations, scratches, and mucous membranes of man and higher animals. One species, Siphunculina funicola, commonly known as the Oriental eye fly, is considered the most anthropophilic in the genus, with potential involvement in the spread and mechanical transmission of infectious agents to humans and animals. Very little is known about the biology, prevalence, host-seeking, and aggregation behavior of this species in South and Southeast Asia. We initiated studies on biological aspects of this potential vector and human pest in central Thailand. The most significant findings of our study were the aggregation behaviors of S. funicola, that both sexes attack hosts, and that males outnumbered females attacking humans, dogs, and other domestic animals. They feed on wounds, scabs, lacerations, eyes, and mucous membranes. They hover around and feed on hosts during the daylight hours when host-seeking activities are more pronounced at temperatures above 25-27 degrees C under calm conditions. We noted that large masses of males and females aggregated on a variety of hanging objects such as strings, trailings, electrical lines, decorations, ropes, twines, abandoned cob webs, clothes hangers, and other hanging substrates in open shade of structures and dwellings. This behavior of eye flies brings them closer to human and animal hosts. In these aggregations, both males and females were present, with mating pairs frequently noted. In the aggregations, about 37% of the females had fully developed eggs in the rainy season, but only <1-3.6% were gravid in the hot and dry season. The average number of eggs per female was generally 42 to 44.

Simulated field evaluation of the efficacy of two formulations of diflubenzuron, a chitin synthesis inhibitor against larvae of Aedes aegypti (L.) (Diptera: Culicidae) in water-storage containers.

Tablet (40 mg a.i./tablet) and granular (2% a.i.) formulations of diflubenzuron, a chitin synthesis inhibitor, insect growth regulator, were evaluated for larvicidal efficacy against the larvae of Aedes aegypti (L.) in water-storage containers under field conditions in Thailand. Each formulation was applied to 200-1 clay jars at 5 different dosages (0.02, 0.05, 0.1, 0.5 and 1 mg/l a.i.). The jars were covered with solid celocrete sheets and placed in the shade under a roof. Another experiment was also carried out using 3 different dosages (0.1, 0.5 and 1 mg/l) where half the water in each treated jar and the control was removed and refilled weekly. Each treatment was replicated four times. The treatments were challenged by adding 25 3rd instar larvae/jar weekly. Assessments were made of each treatment through emergence inhibition (%EI) by removing and counting pupal skins one week after larval addition. Using these assessment techniques, a high degree of larvicidal efficacy (96-100%EI) was achieved with 4 dosages (0.05, 0.1, 0.5 and 1 mg/l) of both (tablet and granular) formulations for a period of 23 weeks post-treatment. The efficacy of the lowest dosage (0.02 mg/l) of tablet and granular formulations lasted for 21 and 22 weeks post-treatment, respectively. Under the conditions of water removal and weekly refilling, a high degree of larvicidal efficacy (96-100%El) at the 3 dosages was obtained with the tablet formulation 18 to 21 weeks post-treatment, whereas the efficacy of the granular formulation persisted 15 to 23 weeks post-treatment depending on the dosage. This study clearly demonstrates a high level of residual activity with both formulations of diflubenzuron against larvae of Ae. aegypti in water-storage containers. Considering environmental factors and water-use conditions, it is likely that dosages of 0.05 to 0.1 mg a.i./l are effective dosages providing long-lasting control for 3 to 4 months in the field.

Field evaluation of novaluron, a chitin synthesis inhibitor larvicide, against mosquito larvae in polluted water in urban areas of Bangkok, Thailand.

Novaluron, an insect growth regulator, a benzoylphenyl urea insecticide, was evaluated in the field against the larvae of polluted-water mosquitoes. The study was carried out in highly polluted sites infested with populations of mosquito larvae, mostly Culex quinquefasciatus Say, in low-income communities in urban areas of Bangkok, Thailand. An EC10 formulation was premixed in water and applied by pressurized spray tank to plots ranging from 180 to 1,000 m2 at the rate of 0.1 ml EC 10/m2 (equal to 10 mg a.i./m2) of the breeding sites. Assessments were made by sampling mosquito larvae and pupae to determine the trends of immature populations before treatment and weekly after treatment. Reduction of the populations in percents were then computed by comparing counts of immature mosquitoes (larvae and pupae) to the pretreatment counts at each particular site. It was found that the immature populations of mosquitoes in the treated areas were dramatically suppressed and remained at extremely low levels for 3-7 weeks after the treatment depending on the prevailing conditions of each experimental site. No negative impact on fishes or aquatic plants in the treated areas were detected during the study period and three months after the experiment was discontinued. Novaluron is an effective agent to control immature populations of polluted-water mosquitoes, especially Cx. quinquefasciatus in habitats in urban areas. This IGR larvicide may play an important role in vector control programs in terms of effectiveness, environmental friendliness and strategies for insecticide-resistance management in vector mosquitoes.

Repellent activity of essential oils against cockroaches (Dictyoptera: Blattidae, Blattellidae, and Blaberidae) in Thailand.

Seven commercial essential oils extracted from the plant species Boesenbergia rotunda (L.) Mansf., Citrus hystrix DC., Curcuma longa L., Litsea cubeba (Lour.) Pers., Piper nigrum L., Psidium guajava L. and Zingiber officinale Roscoe, and naphthalene as a control, were evaluated for repellent activity against the three cockroach species Periplaneta americana (L.), Blattella germanica (L.) and Neostylopyga rhombifolia (Stoll) under laboratory conditions. The essential oil derived from Citrus hystrix showed the best repellency over other candidate essential oils and naphthalene. The essential oil of Citrus hystrix exhibited complete repellency (100%) against P. americana and B. germanica, and also showed the highest repellency (among the essential oils tested) of about 87.5% against N. rhombifolia under laboratory conditions. In the field, Citrus hystrix essential oil formulated as a 20% active ingredient in ethanol and some additives provided satisfactory repellency of up to 86% reduction in cockroaches, mostly P. americana and N. rhombifolia with a residual effect lasting a week after treatment. Citrus hystrix essential oil has good potential for being used as a cockroach repellent. Further improvements in efficacy and residual activity may be realized with appropriate formulations.

Field evaluation of deet, Repel Care, and three plant based essential oil repellents against mosquitoes, black flies (Diptera: Simuliidae) and land leeches (Arhynchobdellida: Haemadipsidae) in Thailand.

Diethyl methyl benzamide, or deet, a commercial plant-based repellent (Repel Care), and essential ils from 3 species of plants (finger root rhizomes, guava leaves, and turmeric rhizomes), steam distillated and formulated as insect repellents, were evaluated in the field on human volunteers against hematophagous mosquitoes, black flies, and land leeches in Thailand. Field trials were conducted against wild mosquitoes in Bang Bua Thong District, Nonthaburi Province, and in the Thap Lan National Park Headquarters, Nadee District, Pranchinburi Province; anthroophilic black flies (Diptera: Simuliidae) at the Forestry Fire Control Station in Doi Inthanon National Park, Chomthong district, Chiang Mai Province; and land leeches (Arhynchobdellida: Haemadipsidae) in the Khao Yai National Park, Pak Chong District, Nakhon Ratchasima Province. The 3 experimental plant-based essential oil formulations as well as Repel Care and deet provided complete protection from mosquito landing and biting for up to 9 h (duration of the experiment). Similar results were obtained with the 5 products against black flies, providing 100% protection for 9 h but 96-82% protection after 10 and 11 h posttreatment. The 5 repellent products also provided 100% protection against land leeches for at least 8 h. Thi is the 1st report of repellency of plant-based repellents against black flies and land leeches in Thailand. The identification and availability of inexpensive sources of plant-based oils, i.e., finger root rhizomes, guava leaves, and turmeric rhizomes providing long-lasting repellency against blood-sucking organisms are promising leads into commercial production of relatively safe and effective repellents.

Ovipositional and ovicidal effects of the microbial agent Bacillus thuringiensis israelensis on Culex quinquefasciatus say (Diptera: Culicidae).

The magnitude of oviposition as well as the size, shape and the number of eggs per of egg rafts egg raft were determined after gravid Culex quinquefasciatus Say oviposited on water treated with water dispersible granules (WDG) of Bacillus thuringiensis ssp. israelensis (Bti) and on untreated water. The mean number of eggs/raft was lower in the treated than in the untreated water. Bti concentrations from 0.5 to 2.0mg/L affected the shape of egg rafts and number of eggs in each raft. As the concentration of Bti increased from 0.5 to 2.0 mg/L the shape of egg rafts became more irregular with fewer eggs in each raft. Exposure to Bti at 2- and 26-h reduced the hatching rates, and fewer eggs hatched at 26-h of exposure to Bti. As the concentration of Bti WDG increased from 0.5 to 2.0 mg/L, the hatching rate decreased. Eggs exposed for 2-h to 2.0mg/ L Bti had a hatch of 30% after 24 h, the rate increasing to 57% after 72 h. In contrast, in 26-h exposed eggs to 2.0 mg/L Bti, the hatching rate after 24 h was only 12% and this rate increased to 39% after 72 h. In larvae from eggs exposed for 2 h, the survival rate was 40% at 2.0 mg/L Bti and 87% in untreated controls. In contrast, the survival rates of larvae from 26-h exposed eggs was 91% in controls while it was 30% at 2.0 mg/L Bti. As the concentration of Bti increased from 0.5 to 2.0 mg/ 1 the survival rates of larvae decreased. The combined effects of reductions of egg rafts, low number of eggs per egg raft, and reduced hatching and survival rates could have significant cumulative effects on the yield of adult mosquitoes, and this could result in a greater control potential of this microbial agent.

Susceptibility of the adult eye gnat Liohippelates collusor (Diptera: Chloropidae) to neonicotinoids and spinosad insecticides.

Imidacloprid, thiamethoxam (first and second generation neonicotinoid insecticides), and spinosad (a naturally derived biorational insecticide) were evaluated in the laboratory against adult eye gnats, Liohippelates collusor (Townsend), using two modes of exposure. Ingestion experiments revealed that toxicity was the highest for thiamethoxam (Platinum soluble concentrate) followed by technical thiamethoxam, imidacloprid (Admire 2 flowable concentrate), and spinosad (Success* soluble concentrate). When incorporated into 5% sucrose solutions, eye gnat mortality was significantly increased compared to the same concentrations of aqueous insecticide solutions. Contact toxicity experiments revealed that thiamethoxam formulation (Platinum) was the most toxic, followed by technical thiamethoxam, imidacloprid, and spinosad. Increasing the duration of exposure time from 15 min to 30 min significantly increased adult eye gnat mortality, but no further mortality occurred by extending exposure from 30 min to 60 min. Our results suggest that Platinum has good ingestion and contact activity against adult eye gnats. Admire and Success have appreciable ingestion toxicity but low contact activity against adult eye gnats.

Double infection of heteroserotypes of dengue viruses in field populations of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) and serological features of dengue viruses found in patients in southern Thailand.

In order to understand more about the epidemiology of DHF, a study of the type of dengue viruses and vectors under natural conditions was carried out. Mosquito vectors in the field and the serum of DHF patients in southern Thailand were examined. The two mosquito species are abundant and DHF incidence remains high in this region. Dengue viruses were examined in field-caught mosquitoes by RT-PCR technique. The mosquitoes were caught in 4 provinces: Krabi, Phuket, Phang-Nga and Surat Thani during the late dry season until the early rainy season in 2005. Three dengue serotypes (DEN-2, DEN-3, DEN-4) were detected in Ae. aegypti males and females, and 2 (DEN-2, DEN-3) were detected in Ae. albopictus females. Double infection with 2 serotypes of dengue viruses (DEN-2 and DEN-3) were detected in Ae. aegypti males and females and Ae. albopictus females. DEN-2 and DEN-1 were the most prevalent serotypes found in the serum of the patients in this area, followed by DEN-4 and DEN-3. The prevalence of the predominant dengue serotype varied from province to province. Detection of viruses in adult male mosquitoes reveals the role of transovarial transmission of dengue viruses in field populations of DHF vectors and elucidates circulation of dengue viruses in vectors in the natural environment of endemic areas. The incidence of multiple serotypes of dengue virus in Ae. aegypti and Ae. albopictus in the same area points toward a high risk for an epidemic of DHF. These findings provide greater understanding of the relationship among mosquito vectors, virus transmission and DHF epidemiology in endemic areas.

Repellency of essential oils extracted from plants in Thailand against four mosquito vectors (Diptera: Culicidae) and oviposition deterrent effects against Aedes aegypti (Diptera: Culicidae).

In this study we evaluated and reported repellent effects of essential oils from Thai plants against 4 mosquito vectors: Aedes aegypti, Ae. albopictus, Anopheles. dirus and Culex quinquefasciatus under laboratory conditions using human volunteers. The essential oils were extracted from 18 plant species, belonging to 11 families, and the oils were then prepared as 10% solution in absolute ethanol with additives. Two chemical repellents, deet and IR3535, were also prepared in the same formulation as the essential oil repellents and tested for repellency as controls. The essential oils were also evaluated for oviposition deterrent effects against Ae. aegypti under laboratory conditions. The results show night-biting mosquitoes (An. dirus and Cx. quinquefasciatus) and Ae. albopictus were more sensitive to all the essential oils (repellency 4.5 - 8 hours) than was Ae. aegypti (repellency 0.3 - 2.8 hours), whereas deet and IR3535 provided excellent repellency against all four mosquito species (repellency 6.7- 8 hours). All essential oils exhibited oviposition deterrent activity against Ae. aegypti with various degrees of repellency ranging from 16.6 to 94.7%, whereas deet and IR3535 had no repellency. The present study demonstrates the potential for using essential oils as mosquito repellents and oviposition deterrents. These findings may lead to new and more effective strategies for protection from and control of mosquitoes.

Toxicity and effects of microbial mosquito larvicides and larvicidal oil on the development and fecundity of the tadpole shrimp Triops newberryi (Packard) (Notostraca: Triopsidae).

Tadpole shrimp (TPS), Triops newberryi (Packard) (Notostraca: Triopsidae), is a predatory agent for immature mosquitoes breeding in aquatic habitats. This biological control agent could be used with other larvicides in mosquito control programs. In order to elucidate compatibility of the TPS and commonly used mosquito larvicides, studies were initiated to investigate effects of Bacillus thuringiensis ssp. israelensis (B.t.i.) de Barjac, Bacillus sphaericus Neide and Golden Bear-1111 larvicidal oil on growth, longevity, and fecundity of TPS in laboratory and field. The exposure of TPS to high dosages of B.t.i. and B. sphaericus in the laboratory or in the field did not have significant adverse effects on growth, longevity, and fecundity. These results indicate that TPS are compatible with microbial larvicides and can be used jointly in practical mosquito control programs. The larvicidal oil GB-1111, on the other hand, caused almost 100% mortality within 48 h after treatment in the laboratory even at the low dosage of 0.38 gallons/ac. The impact of oil in the field was less severe, as significant adverse impact on population density was noted at 1 gallon/ac when water temperatures were warmer, or 2 gallons/ac when water temperatures were cooler. Almost 100% mortality within 48 h was noted at 2 gallons/ac when water temperatures were warmer or at 4 gallons/ac when the water temperatures were cooler. These results indicate incompatibility between this larvicidal oil and TPS at the higher rates of the label range, and joint use of TPS and larvicidal oil at dosages of 1-2 gallons/ac or greater, depending on water temperatures, should be avoided.