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We investigated the interactions of tadpole shrimp, a mosquito biological control agent, with the juvenile hormone analog methoprene and a monomolecular surface film. In laboratory assays, the tadpole shrimp (TPS) Triops newberryi (Packard) was able to tolerate high concentrations of methoprene without negative impacts on its growth, longevity, and fecundity when exposed to 1 to 10 mg/liter, or 90-900 fold, of the IE(90) levels against a laboratory colony of Culex quinquefasciatus Say. The same held true in field trials when the habitats were treated with Altosid(®) Liquid Larvicide (Altosid(®) LL, 5% methoprene) at 0.3-1.2 liters/ha. or 1-4 fold of the label rates for mosquito control. However, some significant impacts on the TPS occurred when they were exposed to Agnique(®) Monomolecular Film (Agnique(®) MMF) at the label rates for mosquito control ranging from 1.89-9.45 liters/ha. under laboratory and field conditions. To avoid the negative impact of Agnique MMF on tadpole shrimp, it appears that 1.89 liters/ha. would be the maximum rate when Agnique MMF is used to control mosquitoes in the habitats where the TPS is employed as a biological control agent, or prevailing in the aquatic habitats with potential for suppressing mosquito larval populations., (© 2014 The Society for Vector Ecology.)

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.

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.

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 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Aqueous extracts of nine medicinal plants were bioassayed against larvae of Culex quinquefasciatus Say and Aedes aegypt (L.). Among these plants, the long pepper, Piper retrofractum Vahl (Piperaceae), showed the highest level of activity against mosquito larvae. To gain more information on larvicidal activity of P. retrofractum, fresh fruits of this plant were extracted in water and the extracts made into powder and bioassayed against 3rd and 4th instar larvae of Cx. quinquefasciatus and Ae. aegypti in the laboratory. Extracts of unripe (001/3) and ripe (002/3 and 001/4) fruits showed different levels of activity against Cx. quinquefasciatus larvae. Extracts 001/3 and 002/3 were equi-toxic to a Bacillus sphaericus resistant and susceptible strains, both from Thailand. The ripe fruit extract 002/3 was somewhat more active against Ae. aegypti than Cx. quinquefasciatus. Another ripe fruit extract (001/4) was much more toxic to both mosquito species. Diluted solutions of the solid extract (002/3) in distilled water lost their larvicidal activity upon aging. Loss of activity at 25 degrees C was greater than that stored at 4 degrees C, and greater in water than in acetone solution.

Two microbial mosquito larvicides, Bacillus thuringiensis ssp. israelensis (Bti) and Bacillus sphaericus (Bsph), have been shown to be highly effective in controlling mosquito larvae and have been used in larvicidal programs for many years. In exploring other modes of action of these agents, we studied the ovipositional response of Bsph susceptible and resistant Culex quinquefasciatus to aqueous suspensions of Bti and Bsph water dispersible granules (WDG). We quantified the level of mortality of adult mosquitoes caused by exposure to Bti and Bsph suspensions during oviposition. Significantly lower numbers of egg rafts were laid and collected from the treatments than the control regimen. There was an inverse relationship between Bacillus product concentrations and oviposition. As the concentration of Bti or Bsph increased from 0.0 to 2.0 mg/L, treated waters received progressively fewer egg rafts. In addition to the negative effects of Bacillus on oviposition, both male and female adult mosquitoes suffered high mortality on landing and imbibing on Bti and Bsph suspensions, the extent of mortality directly proportional to concentration. These two microbial agents used solely as mosquito larvicides thus have the additional benefits of reducing mosquito oviposition and killing adult mosquitoes, especially gravid females that come in contact with the treated water either for oviposition or drinking. Reducing the number of gravid females may also result in reduced transmission rates of pathogens. The combined effects of reduced oviposition and adult mortality could result in higher control potential of these microbial agents.

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.

Two long-term experiments were carried out on the release profile and efficacy of temephos 1% GR (sand granules) against Aedes aegypti larvae in water-storage containers. In the first experiment, the efficacy of temephos 1% GR enclosed and tied in a muslin cloth and placed in water at the bottom of 200 L earthen water-storage jars was studied by exposing the packets for four to nine wk in one set ofjars and then transferring them sequentially to new sets ofjars four times successively. Temephos released slowly from the granules, the magnitude of release being adequate in the initial period of two to three wk after treatment. Following this period, the efficacy of the granules increased substantially where 92-100% inhibition of emergence even at the lowest dosage of 1 g/100 L (0.05 mg/L AI) was obtained for about another five mo or longer. On removal of the packets from a given set of jars, the released residues remaining in the jars and water lasted a maximum of one to six wk post-removal depending on the magnitude of prior release into the jars. This experiment provided clear evidence that temephos is released slowly over a long period of time in water-storage jars. In the second experiment, we compared the efficacy of temephos 1% GR at 1 and 10 g (0.05 and 0.5 mg/L AI) per 200-L water in jars painted and unpainted on the inside. The efficacy in the painted jars, although high, was consistently lower than that in the unpainted jars, where 99-100% control of larvae was achieved at both rates for a minimum of five mo after treatment. On the basis of this experimental evidence, it is desirable to study the efficacy of lower dosages of temephos than those currently used in Ae. aegypti control programs. The use of controlled release formulations or sachets that are retrievable during cleaning and washing will be more practical and desirable. Both of these interventions will make the program more cost effective.

Bacillus sphaericus (Bsph) Neide has been recognized as an effective mosquito larvicide since its discovery 20 years ago. Various strains of this agent, such as 2362, 2297, 1593, and C3-41, have been developed, formulated, and field-evaluated against mosquito larvae in different countries. Their high efficacy in controlling mosquitoes breeding in various habitats, especially those in polluted water, has been documented. However, resistance to Bsph has been reported in Culex pipiens complex in both laboratory colonies and natural populations. During our field trials on Bsph water-dispersible granules (WDG) against natural populations of Cx. quinquefasciatus Say in a low-income community, Nonthaburi Province, Thailand, control failure occurred within 4 months after 5 treatments using VectoLex WDG at the dosages of 50-200 mg/m2. The suspected Bsph-resistant Cx. quinquefasciatus mosquitoes were collected and colonized in the laboratory, from which the late stage larvae of generations F14 through F17 were used in bioassays to elucidate the resistance profile. A high level of Bsph resistance was documented in this colony as compared with the susceptible mosquitoes from the same area in Thailand or from California, USA. The resistance ratios (RR) at LC50, depending on reference colonies, were 21,100-28,100-fold against Bsph WDG or greater than 125,000-200,000-fold against Bsph technical-grade material. These Bsph-resistant mosquitoes, however, were completely susceptible to Bacillus thuringiensis var. israelensis, (Bti) preparations, LC50 ranging from 0.017 ppm for technical material with 7000 ITU/mg to 0.052 ppm for water-dispersible granules with 3000 ITU/mg. The RR to mixtures of Bsph + Bti in this highly Bsph-resistant mosquitoes increased steadily upon the increase of Bsph ratios in the mixtures from 50, 75, 90, 95 to 99%. The resistance levels to the mixtures with various ratios of Bsph and Bti, however, were substantially lower than that in Bsph alone, suggesting addition of Bti to Bsph substantially enhanced the mosquitocidal activity (synergism) against these highly Bsph-resistant Cx. quinquefasciatus. Moderate tolerance to low levels of resistance to Bsph/Bti recombinant (RR 7.29-12.75 at LC50 and 5.15-13.40 at LC90) was also noted in this Bsph-resistant population.

Field trials on the initial and long-term efficacy of a new formulation of temephos granules (1% on zeolite) applied at 1 ppm active ingredient (AI) were conducted in water-storage containers against Aedes aegypti in 3 villages in the Kanchanaburi Province in Thailand. A total of 316 water-storage containers of various types and sizes were included in the study. In the initial survey, we found that some containers were positive for larval Ae. aegypti, whereas others were devoid of larvae before the initiation of treatments. The containers all were numbered with paint and divided into 4 groups: with larvae and treated, without larvae and treated, with larvae untreated, and without larvae and untreated. Assessment of larval abundance was made 48 h after treatment and monthly thereafter for 5 months. Containers with larvae and that were treated exhibited almost complete absence of larval Ae. aegypti for 2 months, but a small proportion became positive after 3 months. Most of these positive containers were devoid of zeolite granules, which are visible in the containers. The number of positive containers increased in months 4 and 5, despite the fact that residues of temephos granules were present in some of the larvae-positive containers. The containers initially without larvae and treated with temephos essentially were devoid of larvae for 2 months. After 3, 4, and 5 months, about 6-23% of the containers became positive despite the fact that some had visible amounts of temephos granules. In the 2 control groups initially with and without larvae, sustained and consistent production of larvae occurred. Even in the group initially without a larval population, the containers became positive for larvae 1 month after the start of the experiment and the positivity rate increased as the trial progressed. From these studies, the conclusion can be made that a single application of temephos zeolite granules at 1 ppm AI can provide highly satisfactory control of larval Ae. aegypti in water-storage containers for at least 3 months in the field under normal water-use practices.

In the laboratory, three microbial mosquito larvicidal products consisting of Bacillus thuringiensis ssp. israelensis de Barjac (Bti), Bacillus sphaericus (Neide) (Bsph) (strain 2362), and the University of California Riverside (UCR) recombinant (producing toxins of both Bacillus sphaericus and Bacillus thuringiensis ssp. israelensis) were bioassayed against larvae of Culex quinequefasciatus Say (susceptible and resistant to Bsph 2362), and Aedes aegypti (L.). Bti proved highly effective against Cx. Quinequefasciatus susceptible and resistant strains, with LC50 values of 0.009 and 0.011 ppm and LC90 values of 0.057 and 0.026 ppm for Bsph-susceptible and -resistant strains, respectively. Bti was also highly active against Ae. eagypti with LC50 and LC90 values of 0.014 and 0.055 ppm, respectively. The UCR recombinant was equally active against both Bsph-susceptible and -resistant strains of Cx. Quinquefasciatus; LC50 values were 0.005 and 0.009 and LC90 values were 0.030 and 0.043 ppm, respectively. Bti and the UCR recombinant essentially showed similar activity against Bsph-susceptible and -resistant strains. UCR recombinant showed high toxicity against Ae. eagypti with LC50 and LC90 values of 0.023 and 0.064 ppm, respectively. Bsph was highly active against susceptible strain of Cx. quinequefasciatus with LC50 and LC9o values of 0.006 and 0.024 ppm, respectively. Bsph exhibited little toxicity against Ae. eagypti larvae and also no toxicity to Bsph resistance. In the field, we evaluated four experimental corn grit formulations of Bti (VBC 60021), Bsph (VBC 60022), UCR recombinants VBC 60023 (7.89%), and VBC 60024 (1.87%) in simulated field (microcosms) against Bsph-susceptible Culex mosquitoes. Bti and low-concentrate UCR recombinant showed similar initial activity as well as persistence. Both materials provided high-to-moderate level of control for 2-7 d posttreatment at low treatment rates. At low dosages, residual activity of Bti and UCR recombinant lasted for <7 d. Bsph and high-concentrate UCR recombinant (VBC 60023), however, were more effective against natural populations of Cullex and achieved longer control (7-21 d) than the other two materials.

In Thailand, water-storage jars, barrels, drums, pails, and tanks constitute vast developmental sites for Aedes aegypti in urban, semiurban, and rural areas. Earthen water jars, cement jars, and concrete tanks constitute the greatest proportion of artificial containers where Ae. aegypti breed. This species is a major vector of the causal agents of dengue and dengue hemorrhagic fever, and vector control by larviciding is one of the main approaches to disease control. At present, temephos sand granules (SG) (1%) are used in large-scale community-based larviciding programs. Because of the use of this larvicide over the past 30 years, the likelihood exists that Ae. aegypti already has become resistant to this larvicide. To develop more options for control and make them available for use, we evaluated VectoBac tablets (Bacillus thuringiensis var. israelensis [Bti] 5%) and a new formulation of zeolite granules (ZG) of temephos (1%) and compared these formulations for efficacy with temephos SG (1%) in water-storage jars. In these tests, we used 48 identical glazed earthen water-storage jars (200-liter capacity) and developed quantitative sampling procedures for larvae, pupae, and pupal skins. Pupal skins were the easiest to count and this technique was used for the 1st time for assessing emergence of adults in water-storage containers. Three water regimens were used: full jars, half-full jars, and full jars emptied half way and refilled weekly. The 3 formulations with 3 regimens of water were assessed over a period of 6 months. VectoBac tablets at the dosage of 1 tablet or 0.37 g per 50 liters of water provided excellent control for about 112 days in full water jars. In the other 2 water regimens, VectoBac gave excellent control for 90 days. The 2 temephos formulations at the operational rate of 5 g per 50 liters of water were equal in efficacy, yielding almost 100% control for more than 6 months. Unlike temephos SG, the temephos ZG had no objectionable odor. Both the temephos ZG and Bti tablets increased clarity of the water, a feature desired by the users. Lack of odor and depression of turbidity are important attributes of Bti tablets and temephos ZG.

Significant numbers of the Asian tiger mosquito, Aedes albopictus, were detected on the west coast of the USA in mid-June 2001, in containerized oceanic shipments of "lucky bamboo" (Dracaena spp.) originating from South China. Wholesale nurseries in California importing large quantities of lucky bamboo became the focal points of infestation. Greater Los Angeles County Vector Control District immediately implemented an adulticiding protocol at the Los Angeles/Long Beach Harbors, followed by larviciding soon after the shipment was delivered to the wholesale nursery. Intensive surveys are currently being conducted above ground and in the underground storm drain systems using battery-operated CDC/CO2-baited light traps and ovitraps, both enhanced with an attractant (water rinse of tiger shrimps), to determine extent of infestation and perhaps establishment of Ae. albopictus locally.

Novaluron, a new chitin synthesis inhibitor type of insect growth regulator, was evaluated in the laboratory and field against larvae of the mosquito Aedes aegypti (L.). In the laboratory, the technical material showed a high level of activity against 2nd and 4th instar larvae. The inhibition of emergence (IE) was 100% at concentrations of 0.25 to 1.0 microg/L. Second instars were slightly more susceptible than fourth instars. At the high concentration (1 ppb), most of the mortality occurred in the larvae, but at sublethal concentrations (for larvae) mortality also occurred in pupae and adults (incomplete eclosion). An EC10 (emulsifiable concentrate containing 10% active ingredient) formulation of novaluron was evaluated against Ae. aegypti in water-storage containers in the field in Thailand. Two tests at high (0.05 to 1 mg/L) and low (1 to 20 microg/L) concentrations were carried out in clay jars (200 L) and plastic pails (75 L). At high concentrations in clayjars, we obtained 86-96% inhibition of emergence (IE) for about 190 d, but the mortality declined at low concentrations after 190 d. At much lower concentrations, in jars and plastic pails in the second experiment, the IE was 80-100% for 2 mo. The highest concentrations of this series (10 microg/L in jars and 20 microg/L in pails) were active for 75 and 68 d respectively, losing efficacy by 82 d post-treatment. In the experiment using low concentrations, all treatments in jars and plastic pails failed to provide adequate control 90 d after treatment. These studies show that novaluron, even as EC10, has exceptional long-term activity against Ae. aegypti in water-storage containers, with higher concentrations yielding greater long-term control than low concentrations.

Limited laboratory and field studies have indicated that the insect growth regulator (IGR) novaluron exhibits good activity against larvae of pest species in the orders Coleoptera, Hemiptera (suborder Heteroptera), and Lepidoptera by both ingestion and contact. We completed laboratory and field studies to evaluate activity and efficacy of novaluron against Culex mosquitoes. In laboratory studies, novaluron was highly active against Cx. quinquefasciatus, as indicated by low levels of inhibition of emergency (IE), at the 50% level, IE50 (0.159 ppb for 2nd-stage larvae and 0.118 ppb for 4th-stage larvae) and IE90, at the 90% level, (0.604 ppb for 2nd-stage larvae and 0.595 ppb for 4th-stage larvae). In outdoor microcosm and mesocosm studies against natural populations, novaluron yielded excellent control of immature Culex mosquitoes for up to 14 days at 1.25, 2.5, and 5 ppb in microcosms, and for up to 7 days at the dosages of 1, 5, and 10 mg/m2 in mesocosms. Based on qualitative observations, novaluron seemed to have a favorable margin of safety for nontarget aquatic invertebrates cohabiting with mosquito larvae. Further large-scale field studies are warranted to evaluate initial efficacy and longevity of novaluron against various mosquito species, as well as its safety for nontarget biota.

Several strains of Bacillus sphaericus (Neide) (Bsph), a spore-forming bacterium that produces potent mosquitocidal toxins, have been widely used against mosquito larvae globally. In some locations in the field and in the laboratory, moderate to high levels of resistance in Culex pipiens complex mosquito larvae to Bsph have been reported. Practical strategies for dealing with the resistance problem and more importantly to delay or possibly prevent development of resistance to Bsph in the first place are urgently needed. From published reports, we deduced that Bsph-resistant mosquito larvae are completely susceptible to Bacillus thuringiensis ssp. isreaelensis (Bti) and that there is no appearance of cross-resistance to Bti. On the basis of this information, we hypothesized that Bti offers a good potential for the management of resistance to Bsph, especially when it comes to delaying or preventing emergence of resistance. We conducted laboratory studies to see whether rotation of Bsph and Bti or mixture of both delays or prevents resistance development in Bsph-susceptible California Cx. quinquefasciatus. Development of resistance using Bsph alone increased after F15 and fluctuated slightly on further selections. Rotation of Bsph and Bti resulted in much higher level and rapid emergence of resistance to Bsph. However, selection with mixtures of Bti and Bsph for 36 generations showed no emergence of resistance. On the basis of this information, we believe mixtures have a good potential in delaying or preventing Bsph resistance.

Underground storm drain systems in urban areas of Orange County include thousands of miles of gutters and underground pipelines, plus hundreds of thousands of catch basins and manhole chambers, all of which drain runoff water from residential, business and commercial establishments as well as highways and streets. These systems serve as major developmental and resting sites for anthropophilic and zoophilic mosquitoes. Investigations on spatial and temporal distribution of mosquitoes in these systems were conducted during November 1999 to October 2001. Immature mosquitoes were sampled by dipper or dipping net and adult mosquitoes by non-attractive CDC traps in manhole chambers, catch basins and a large drain. Culex quinquefasciatus Say prevailed at all 15 structures of the study in 4 cities of Orange County as the predominant species (> 99.9%). Larvae and pupae were present from April to October, peaking from May to September. The population density of adults was the lowest in February with 2 peaks of abundance occurring from May to July and from September to October. Manhole chambers and catch basins harbored more mosquitoes than did the large drain. Minimum and maximum temperatures during a 24 h sampling period was an important factor influencing adult mosquito activity and catches; more mosquitoes were caught in traps when it was warmer, especially when the minimum temperatures were higher. The proportion of females to males in general increased during winter and early spring an ddeclined during summer. The proportion of gravid females to empty females was higher during the winter than in summer. Other dipteran taxa such as psychodid moth flies and chironomid midges exhibited somewhat similar seasonal patterns as did mosquito populations. Average water temperature was relatively stable throughout the year, and water quality in underground drain systems was characterized by low dissolved oxygen, coupled with above normal electrical conductivity and salinity levels that were more pronounced during the summer. The episodes of measurable rains that occurred during the winter months (February and March) reduced mosquito population density (both larvae and adults) and altered water quality in the underground drain systems.

In recent years, highly potent mosquitocidal strains of the microbial agent Bacillus sphaericus (Bsph) have been isolated and developed for the control of mosquito larvae around the world. Laboratory selection experiments with the most active strains and their use in large-scale operational mosquito control programs resulted in the emergence of resistance in larvae of the Culex pipiens complex. This generated great concern among vector control agencies around the world, who feared reduced efficacy of this highly active larvicidal agent. To address this issue, the current studies were started to find practical strategies for controlling resistant mosquitoes and more importantly to develop resistance management strategies that would prevent or delay development of resistance. We initiated field studies in 3 low-income communities in Nonthaburi Province, Thailand. In 1 of the communities, larvae of Culex quinquefasciatus that were highly resistant (>125,000-fold) to Bsph strain 2362 were successfully controlled with applications of Bacillus thuringiensis var. israelensis (Bti) alone or in combination with Bsph. To prevent or delay resistance to Bsph, 2 other sites were selected, 1 treated with Bsph 2362 alone and the other treated with a mixture of Bsph 2362 and Bti. Mosquitoes treated with Bsph 2362 alone showed some resistance by the 9th treatment and almost complete failure of control occurred by the 17th treatment. After 9 treatments with the mixture over a 9-month period at another site, no noticeable change in susceptibility to Bsph was detected. During this period, the site treated with Bsph alone required 19 treatments, whereas the site treated with mixtures took only 9 treatments because of slower resurgence of larvae at the site treated with the mixture than at the site treated with Bsph alone. This is the 1st field evidence for delay or prevention of resistance to microbial agents in larval Cx. quinquefasciatus by using mixtures of Bti and Bsph. Further studies on the use of mixtures for the management of field resistance are warranted.

Isolated incidences of Aedes albopictus in the continental U.S. were reported as early as 1946 and the first incidence in California was reported in 1972. These introductions were referred to as "isolated incidences" because very few immatures were observed in used tires shipped from Southeast Asia. The first major discovery of a large population and subsequent establishment of Ae. albopictus in the U.S. was reported in 1986 from Houston, TX, in a shipment of used tires from Japan. In early June 2001, infestations of this species associated with containerized oceanic shipments of "lucky bamboo" (Dracaena spp.) packaged in standing water were introduced into southern California from mainland south China. Focal points of infestation are currently at the wholesale nurseries in southern as well as northern California. A control protocol for adulticiding and larviciding has been implemented by the Greater Los Angeles County Vector Control District. Surveys are presently being conducted by local vector control agencies in southern and northern California to determine the extent of infestation. Potential forAe. albopictus establishment is discussed.

Tadpole shrimp (TPS), Triops newberryi (Packard), has been reported to have a potential as a biocontrol agent for larval mosquitoes breeding in intermittently flooded habitats. To develop and promote this predator for controlling mosquitoes, a date garden devoid of preexisting TPS populations was chosen in the Coachella Valley, southern California in 2000 to receive introductions of TPS eggs and mature TPS. Mosquito control by TPS was assessed in the plots one year after their introductions. In a selected block on this ranch, 2 rows were stocked with TPS eggs, where soil containing approximately 2,000 eggs was spread over the surface of dry ground in each row before flooding. Another 2 rows were used for mature TPS introduction, where about 400 mature TPS were released into standing water in each row 1 day after flooding. After a single egg or mature TPS introduction, active TPS in water and viable eggs in dry surface soil were noted in increasing numbers during the 3-4 subsequent irrigations. Disking before irrigation, which turned the eggs over and mixed them into the soil column, reduced TPS egg populations at the soil surface and subsequent active TPS populations in standing water after irrigation. After one or two irrigations, viable eggs and active shrimp were found in centers adjacent to the introduced plots in the stocked rows. Ample evidence is presented to show that TPS populations were established after a single introduction of eggs or mature TPS. TPS eggs and/or newly hatched TPS were also carried into the neighboring rows across the borders by the overflowing irrigation water, and TPS populations became established there too, as active TPS were noted after each irrigation in the adjacent unstocked rows. Considering the ease and economical storage, transportation and handling, dessication--resistant eggs have advantages over mature TPS for field introductions. Mosquito control by TPS was assessed in rows with and without TPS in July 2001, one year after TPS introductions. Production of Psorophora columbiae Dyar and Knab and TPS populations were determined 4-5 days after each of 2 irrigations, when there was no or little vegetation inside the rows. As compared with the row without TPS, the presence of relatively high numbers of TPS reduced Ps. columbiae by 73 to 99% as based on the average numbers of larvae, pupae and exuviae per dip in the rows with versus without TPS.

The tadpole shrimp (TPS), Triops newberryi (Packard) (Notostraca: Triopsidae) is a potential biological control agent for immature mosquitoes breeding in ephemeral habitats. The occurrence of TPS eggs in soil and their hatch were investigated in 11 flood-irrigated date gardens in the Coachella Valley of southern California in 1999. Each garden was sampled several times after the rows were recently irrigated. All these date gardens harbored from very few to a large number of eggs in the soil. Overall, the average density of total eggs on ranches with clay loam soil was significantly higher than that on ranches with silt loam soil. The average densities of total eggs were significantly lower on the ranches that were disked compared to those on the ranches that were undisked before sampling. Two types of eggs were found and designated as "fresh" (yellowish to brownish) and "old" (blackish) eggs. This is the first time that these dimorphic eggs have been reported. The density of fresh eggs was lower than that of old eggs in most soil samples. The date gardens with high egg densities were sampled for determination of vertical occurrence, where soil was sampled up to 38.5 cm deep. Fresh eggs were recovered from soil in depths up to 25.6 cm, but the densities progressively declined with depth. The old eggs, however, were recovered from all soil depths studied, and there was no obvious relationship between soil depth and their density. This pattern of vertical occurrence of TPS eggs is the result of frequent disking for weed control and fruit harvest. Hatch of TPS eggs in surface soil samples ranged from 0 to 7.2 per 100 g dried soil. Hatch of viable eggs had an inverse relationship with soil depth. No TPS hatched out from the soil samples taken deeper than 15.4 cm. Fresh and old eggs distinguished by color were subjected to hatching tests. Fresh eggs exhibited high hatch, with hatching rates of 35.5-45.0% and 40.2-60.3% for the 1st and 1st plus the 2nd hydrations respectively. The old eggs, however, did not hatch at all. These findings provide quantitative information with regard to occurrence of natural TPS populations in flood irrigated agricultural fields, which could serve as a potential regulatory force of immature mosquito populations sharing ephemeral habitats with TPS.

Bacillus sphaericus (B.spi) strain 2362 has been recognized as a promising mosquito larvicide, and various preparations of this strain have been tested and used in mosquito control programs worldwide. This control agent has advantages of high efficacy, specificity, persistence, and environmental safety. However, resistance in Culex pipiens complex mosquitoes to Bsph has occurred in both laboratory and field populations, necessitating development of resistance management strategies. Studies were initiated aiming at reversing previously established Bsph resistance in a laboratory colony of Culex quinque fasciatus Say by selections with Bti alone, Bti and Bsph in rotation, or mixture. Partial restoration of susceptibility to Bsph was achieved by selection of resistant colony for 10 generations with Bti alone at LC80). After this colony was switched back to Bsph selection for 20 generations, resistance to Bsph partially increased to a stable level. Selections of Basph-resistant colonies with Bti and Bsph in rotation or mixture resulted in steady decline of resistance over 30 generations, with rapid decline in resistance noted in the initial 10-15 generations. It is interesting to note that selections with Bti and Bsph in rotation increased susceptibility to Bti in Bsph-resistant colony. It is promising that selection with Bti alone, Bsph and Bti in rotation, or mixture have a potential for developing practical strategies to overcome acquired resistance to Bsph in Cx. quinquefasciatus populations.