Intraspecific hybridization of Anopheles minimus (Diptera: Culicidae) species A and C in Thailand

Hybridization tests of laboratory-raised, isolines of Anopheles minimus, species A and C were conducted by induced copulation. The three isolines were established based on three morphological variants of wild-caught, fully engorged females and two distinct types of metaphase chromosomes. They were An. minimus species A: V form (X1,Y1), M form (X2,Y1); species C: P form (X3,Y2). The results of reciprocal and back crosses indicated that the two morphologically variant forms of species A were genetically compatible, providing viable progeny and completely synaptic salivary gland polytene chromosomes, whereas they were genetically incompatible with species C and/or the P form. Hybrid progeny was only obtained from both forms of species A females x species C males, but asynaptic salivary gland polytene chromosomes on 3L and partial development of ovarian follicles in females were seen. Back crosses of F1 hybrid males with parental species A females provided viable progeny, while back crosses of F1 hybrid females with parental species C males provided progeny of low viability and adult males with abnormal spermatozoa, suggesting the partial reproductive isolation of An. minimus species A and C.     

Need and demand for sedation or general anesthesia in dentistry: a national survey of the Canadian population

The aim of this study was to assess the need and demand for sedation or general anesthesia (GA) for dentistry in the Canadian adult population. A national telephone survey of 1101 Canadians found that 9.8% were somewhat afraid of dental treatment, with another 5.5% having a high level of fear. Fear or anxiety was the reason why 7.6% had ever missed, cancelled, or avoided a dental appointment. Of those with high fear, 49.2% had avoided a dental appointment at some point because of fear or anxiety as opposed to only 5.2% from the no or low fear group. Regarding demand, 12.4% were definitely interested in sedation or GA for their dentistry and 42.3% were interested depending on cost. Of those with high fear, 31.1% were definitely interested, with 54.1% interested depending on cost. In a hypothetical situation where endodontics was required because of a severe toothache, 12.7% reported high fear. This decreased to 5.4% if sedation or GA were available. For this procedure, 20.4% were definitely interested in sedation or GA, and another 46.1% were interested depending on cost. The prevalence of, and preference for, sedation or GA was assessed for specific dental procedures. The proportion of the population with a preference for sedation or GA was 7.2% for cleaning, 18% for fillings or crowns, 54.7% for endodontics, 68.2% for periodontal surgery, and 46.5% for extraction. For each procedure, the proportion expressing a preference for sedation or GA was significantly greater than the proportion having received treatment with sedation or GA (P < 0.001). In conclusion, this study demonstrates that there is significant need and demand for sedation and GA in the Canadian adult population.     

Behavioral responses to DDT and pyrethroids between Anopheles minimus species A and C, malaria vectors in Thailand

Behavioral responses of two field populations of Anopheles minimus complex species A and C for contact and non-contact actions of chemicals were compared during and after exposure to operational field concentrations of DDT (2 g/m2), deltamethrin (0.02 g/m2), and lambdacyhalothrin (0.03 g/m2) using an excito-repellency escape chamber. The two populations were collected from the Mae Sot District in Tak Province (species A) and the Tri Yok District in Kanchanaburi Province (species C) in western Thailand. Female mosquitoes of both populations rapidly escaped from chambers after direct contact with DDT, deltamethrin, and lambdacyhalothrin. The non-contact repellency response to DDT and the two synthetic pyrethroids was pronounced with An. minimus species A; however, non-contact repellency was relatively weak with An. minimus species C, but remained significantly greater than the paired controls (P < 0.05). We conclude that strong contact irritancy was present in both test populations, whereas non-contact repellency also played a significant role in the escape response of An. minimus species A.     

Larvicidal efficacy and biological stability of a botanical natural product,zedoary oil-impregnated sand granules,against <Emphasis Type="Italic">Aedes aegypti</Emphasis> (Diptera,Culicidae)

Chemical analysis on Curcuma zedoaria rhizome volatile oil, using gas chromatography-mass spectrometer techniques, demonstrated the presence of beta-tumerone (19.88%), 1,8-cineole (8.93%), and 7-zingiberene (7.84%) as major constituents. Larvicidal efficacy against Aedes aegypti mosquitoes of zedoary oil and its formulated preparation, zedoary oil-impregnated sand granules, were investigated and compared with that of Abate(R)sand (temephos). Zedoary oil exhibited pronounced potential against the fourth instar larvae of A. aegypti with an LC(50) and LC(99) of 33.45 and 83.39 ppm, respectively. Application of zedoary oil at a dosage yielding ten times that of LC(99) offered complete larval mortality (100% mortality) for a period of 3 days, and the larval mortality subsequently decreased to lower than 50% after application for more than 5 days. Zedoary oil-impregnated sand granules provided remarkably longer activity, with a larval mortality of 100% for a period of 9 days; and mortality below 50% was obtained in week 3 of application. The complete larval mortality that resulted from applying temephos at dosages of 0.1 and 1 ppm persisted for a period of 6 days and 4 weeks, respectively, and the larval mortality below 50% was reported on day 18 and week 11, respectively. Testing A. aegypti species against stored samples of zedoary oil-impregnated sand granules demonstrated that the product stored at 4 degrees C showed the longest larvicidal activity, followed by those kept at ambient temperature and 45 degrees C, yielding a complete larval mortality for 9, 8, and 6 days, respectively. Most samples of zedoary oil-impregnated sand granules stored at each temperature for 1 month showed slightly higher efficacy than those kept for 2 months. The larvicidal efficacy of samples stored at 4 degrees C seemed to be comparable to that of the fresh sample. The efficacy in killing A. aegypti larvae and good biological stability of zedoary oil-impregnated sand granules make this product promising as an alternative to essential oil in the development of new botanical natural larvicide for use in mosquito control programs.     

Irritant and repellent responses of Anopheles harrisoni and Anopheles minimus upon exposure to bifenthrin or deltamethrin using an excito-repellency system and a live host

Feeding responses of Anopheles harrisoni and An. minimus were evaluated following exposure to 2 pyrethroid insecticides, bifenthrin or deltamethrin, using an excito-repellency test system in the presence and absence of live host cues. The results demonstrated that contact irritancy was the primary action of bifenthrin or deltamethrin in both mosquito species. There was no noncontact repellency effect elicited by either insecticide. Anopheles minimus showed rapid escape response with high mortality rates following direct contact with deltamethrin in the absence of a host and delayed escape responses when a host was present. Similarly, exposure of An. minimus to bifenthrin also elicited a delayed escape response in the presence of a host but with lower mortality rates. In experiments using An. harrisoni, the presence or absence of a host had no significant effect on behavioral responses to either insecticide (P > 0.05). We conclude that deltamethrin elicited stronger irritant chemical effects than bifenthrin but that behavioral responses in vector populations are dampened in the presence of an available host. This information is useful for estimating probability of pathogen transmission when using irritant chemicals in proximity to a blood-meal source.     

Comparative assessment of the in vitro sensitivity of Brugia malayi infective larvae to albendazole, diethylcarbamazine and ivermectin alone and in combination

The antifilaricidal drugs ivermectin (IVM), diethylcarbamazine (DEC), and albendazole (ALB), used alone or in combinations against infective third-stage larvae (L3) of nocturnally subperiodic (NSP) Brugia malayi (Narathiwat strain), were tested in vitro for sensitivity, for 7 days. IVM alone reduced larval motility at concentrations of 10(-7), 10(-6), and 10(-5) M on day 3. DEC alone also had this effect at concentrations of 10(-6). 10(-5), and 10(-4) M on day 2. ALB alone did not have this effect throughout the experiment, at various concentrations. However, it had greater effect when used in combination with either DEC or IVM. The result also indicated that DEC or IVM, when used in combination with ALB at concentrations of 10(-6) M/10(-6) M, and 10(-5) M/10(-5) M was effectively better than each drug used alone at those concentrations. When both drug combinations were compared, ALB/DEC seemed to be more effective than ALB/IVM at a concentration of 10(-6) M/10(-6) M on day 3. Although IVM and DEC can reduce larval motility when used alone or in combination with ALB, they cannot kill these larvae in an in vitro cultivation, even at a high concentration (10(-5) M).     

Essential oils as potential adulticides against two populations of Aedes aegypti, the laboratory and natural field strains, in Chiang Mai province, northern Thailand

Essential oils derived from five plant species, celery (Apium graveolens), caraway (Carum carvi), zedoary (Curcuma zedoaria), long pepper (Piper longum), and Chinese star anise (Illicium verum), were subjected to investigation of adulticidal activity against mosquito vectors. Two populations of Aedes aegypti, the laboratory and natural field strains, collected in Chiang Mai province, northern Thailand were tested in pyrethroid-susceptibility bioassays. The results revealed that the natural field strain of A. aegypti was resistant to permethrin, with mortality rates ranging from 51 to 66%. A mild susceptibility, with mortality rates ranging from 82 to 88%, was observed in the natural field strain of A. aegypti exposed to lambdacyhalothrin, which suggested that this strain was tolerant and might be resistant to this insecticide. However, laboratory-reared A. aegypti exposed to discriminating dosages of permethrin and lambdacyhalothrin induced 100% mortality in all cases, thus indicating complete susceptibility of this strain to these insecticides. The adulticidal activity determined by topical application revealed that all five essential oils exerted a promising adulticidal efficacy against both laboratory and natural field strains of A. aegypti. Although the laboratory strain was slightly more susceptible to these essential oils than the natural field strain, no statistically significant difference was observed. Moreover, comparison of the adulticidal activity indicated that the performance of these essential oils against the two strains of A. aegypti was similar. The highest potential was established from caraway, followed by zedoary, celery, long pepper, and Chinese star anise, with an LC₅₀ in the laboratory strain of 5.44, 5.94, 5.96, 6.21, and 8.52 μg/mg female, respectively, and 5.54, 6.02, 6.14, 6.35, and 8.83 μg/mg female, respectively, in the field strain. These promising essential oils are, therefore, an alternative in developing and producing mosquito adulticides as an effective measure used in controlling and eradicating mosquito vectors.     

Effects of physiological conditioning on behavioral avoidance by using a single age group of Aedes aegypti exposed to deltamethrin and DDT

The behavioral and physiological responses of 6-d-old Aedes aegypti (L.) adult females exposed to deltamethrin and DDT were characterized using a free-choice excito-repellency test system. Excluding varying pretest age and carbohydrate availability as possible confounders, insecticide contact (measuring irritancy) and noncontact (measuring repellency) behavioral assays were conducted on two nonbloodfed groups, either unmated or mated (nulliparous), and two blood-fed groups, either parous or newly full-engorged mosquitoes. The degree of escape response to deltamethrin and DDT varied according to the physiological conditioning. Escape rates from contact and noncontact chambers with deltamethrin were more conspicuous in nonbloodfed groups compared with mosquitoes previously bloodfed. There were no significant differences in escape responses between unmated and nulliparous test populations. With DDT, a more pronounced escape response was observed in unmated compared with other physiological conditions. More moderate escape response was seen in nulliparous mosquitoes, and the least was observed in full bloodfed test individuals, regardless of test compound. Ae. aegypti, regardless of pretest conditioning, was completely susceptible to deltamethrin, whereas showing high resistance to DDT. Despite profound differences in resistance, there was no significant difference in avoidance response between chemicals and mosquito conditioning. Moreover, pre- and postbloodmeals were found to influence assay outcome and thus to have relevance on the interpretation of susceptibility and excito-repellency assays.     

Geographic distribution of stomoxyine flies (Diptera: Muscidae) and diurnal activity of Stomoxys calcitrans in Thailand

Stomoxyine flies (Stomoxys spp.) were collected in 10 localities of Thailand using the Vavoua traps. These localities represented four major ecological settings, as follows: small local dairy farms, large industrial dairy farms, a national park, and one elephant conservation area. Three species of stable flies were identified in the following proportions: Stomoxys calcitrans (91.5%), Stomoxys indicus (7.9%), and Stomoxys sitiens (0.6%). The number of flies collected differed significantly among collection sites (chi2 = 360.15, df=3, P < 0.05). The greatest number of stomoxyine flies was captured in dairy farms. Seasonal and daily activity of S. calcitrans was observed during a 1-yr period at two selected locations (Dairy Farming Promotion Organization of Thailand and Khao Kheow Open Zoo). S. calcitrans was more abundant during the rainy season (March-September), but was not associated with the total rainfall (r2 = 0.0002, P > 0.05). Peak of daily flight activity of males S. calcitrans was at 1000 and 1600 h, whereas females showed an increase of activity all along the day until 1600 h. A better understanding of stomoxyine fly behavior related to patterns of daily activity will facilitate and improve the efficiency of fly control measures in private and government sectors.