[show abstract][hide abstract] ABSTRACT: A survey of adult anopheline mosquito diversities, collected from September 2009 to August 2010, was conducted in a malaria endemic area of western Thailand. Two anopheline species complexes, Dirus and Minimus, along with the Maculatus group were observed. Of several species documented from within each complex and group, four important malaria vectors were identified, including An. dirus, An. baimaii, An. minimus, and An. sawadwongporni. Information on biting activity and host preference for any single species within the Dirus complex has never been assessed. Using specific molecular identification assays, the trophic behavior and biting activity of each sibling species within the Dirus complex were observed and analyzed for the Kanchanaburi Province, Thailand.
Adult female mosquitoes were collected for two consecutive nights each month during a one year period. Three collection methods, human landing indoor (HLI), human landing outdoor (HLO), and cattle baited collections (CBC) were applied. Each team of collectors captured mosquitoes between 1800 and 0600 h.
From a total of 9,824 specimens, 656 belong to the Dirus complex (An. dirus 6.09% and An. baimaii 0.59%), 8,802 to the Minimus complex (An. minimus 4.95% and An. harrisoni 84.65%) and 366 to the Maculatus group (An. maculatus 2.43% and An. sawadwongporni 1.29%). Both An. dirus and An. baimaii demonstrated exophagic and zoophilic behaviors. Significantly greater numbers of An. dirus and An. baimaii were collected from cattle as compared to humans (P = 0.003 for An. dirus and P = 0.048 for An. baimaii).
Significantly greater numbers of An. dirus and An. baimaii were collected from cattle baited traps as compared to human landing collections (P < 0.05), demonstrating that both species show a strong zoophilic behavior. Knowledge of host-seeking behavior helps to define a species' capacity to acquire and transmit malaria and its contribution to the overall risk for disease transmission in the human population, as well as, assisting in the design and implementation of appropriate vector prevention and control strategies.
[show abstract][hide abstract] ABSTRACT: Host feeding patterns of Anopheles minimus in relation to ambient environmental conditions were observed during a 2-year period at Tum Sua Village, located in Mae Sot District, Tak Province, in western Thailand, where An. minimus is found in abundance and regarded as the most predominant malaria vector species. Detailed information on mosquito behavior is important for understanding the epidemiology of disease transmission and developing more effective and efficient vector control methods.
Adult mosquitoes were collected every 2 months for two consecutive nights from 1800 to 0600 hrs. Three collection methods were used; indoor human-landing collections (HLC), outdoor HLC, and outdoor cattle-bait collections (CBC).
A total of 7,663 female Anopheles mosquitoes were collected of which 5,392 were identified as members of 3 different species complexes, the most prevalent being Anopheles minimus complex (50.36%), followed by Anopheles maculatus complex (19.68%) and Anopheles dirus complex (0.33%). An. minimus s.s. comprised virtually all (> 99.8 percent) of Minimus Complex species captured. Blood feeding behavior of An. minimus was more pronounced during the second half of the evening, showing a slight preference to blood feed outdoors (~60%) versus inside structures. Significantly (P < 0.0001) more An. minimus were collected from human-baited methods compared with a tethered cow, indicating a more anthropophilic feeding behavior. Although a significant difference in total number of mosquitoes from the HLC was recorded between the first and second year, the mean biting frequency over the course of the evening hours remained similar.
The Human landing activity of An. minimus in Tum Sua Village showed a stronger preference/attraction for humans compared to a cow-baited collection method. This study supports the incrimination of An. minimus as the primary malaria vector in the area. A better understanding of mosquito behavior related to host preference, and the temporal and spatial blood feeding activity will help facilitate the design of vector control strategies and effectiveness of vector control management programs in Thailand.
[show abstract][hide abstract] ABSTRACT: Establishing baseline insecticide discriminating doses is crucial in accurately determining susceptibility status and changing temporal patterns of physiological response in mosquito populations. Pyrethroids are the predominant chemicals used for controlling adult Aedes aegypti and Ae. albopictus, both vectors of dengue viruses, in Thailand. Presently, only 2 pyrethroids, permethrin and lambda-cyhalothrin, have published diagnostic dose rates for monitoring Ae. aegypti. This study established the diagnostic lethal concentrations for 6 different pyrethroids available in Thailand for dengue vector control. United States Department of Agriculture insecticide-susceptible strain of Ae. aegypti was used to establish the baseline concentrations for subsequent susceptibility testing of field populations. Our findings showed lower discriminating concentrations for lambda-cyhalothrin and permethrin than those recommended by the World Health Organization (WHO), at 2.5- and 1.7-fold lower dosing, respectively. The susceptibility status of 3 different geographical populations of field-collected Ae. aegypti were tested using the standard WHO procedures. All 3 field strains demonstrated varying levels of physiological resistance to each compound. We conclude that establishing the baseline diagnostic concentration of an insecticide is of paramount importance in accurately determining the susceptibility status in field-collected mosquitoes. If possible, discriminating doses should be established for all insecticides and test assays run concurrently with a known susceptible strain for more accurate monitoring of resistance in mosquito populations in Thailand.
Journal of the American Mosquito Control Association 03/2012; 28(1):30-7. · 0.76 Impact Factor
[show abstract][hide abstract] ABSTRACT: Behavioral responses of female mosquitoes representing two species in the Minimus Complex exposed to an operational field dose of bifenthrin or DEET (N,N-diethyl-m-toluamide) were described using an excito-repellency test system. Two test populations of An. minimus, one from the field (Tak Province, western Thailand), the other from a long-established laboratory colony, and Anopheles harrisoni collected from Kanchanaburi Province, western Thailand, were used. Results showed that all test populations rapidly escaped after direct contact with surfaces treated with either bifenthrin or DEET compared to match-paired untreated controls. Greater escape response by exposed females to bifenthrin and DEET were observed in the An. minimus colony compared to the two field populations. Field-collected An. minimus demonstrated a more rapid escape response to DEET than to bifenthrin, whereas An. harrisoni showed a converse response. Although fewer females escaped from test chambers without direct contact with treated surfaces compared to contact tests, the spatial repellency response was significantly pronounced in all test populations compared to match-paired controls (P < 0.05). DEET was found to perform as both a contact stimulant and moderate spatial repellent.
Journal of Vector Ecology 12/2011; 36(2):321-31. · 1.23 Impact Factor
[show abstract][hide abstract] ABSTRACT: Excito-repellency responses of 3 test populations, representing 2 sibling species within the Minimus Complex, Anopheles minimus and An. harrisoni, were characterized for contact irritant and noncontact repellent actions of chemicals during and after exposure to alpha-cypermethrin at half the recommended field (0.010 g/m2), the recommended field (0.020 g/m2), and double the recommended field concentration (0.040 g/m2), using an excito-repellency escape chamber system. Two field populations of An. minimus and An. harrisoni collected from the malaria-endemic areas in Tak and Kanchanuburi provinces in western Thailand, respectively, were tested along with a laboratory population of An. minimus maintained since 1993. Females of all 3 test populations rapidly escaped after direct contact with treated surfaces for each concentration. In general, increased escape responses in the An. minimus test populations were proportionate to increased insecticide dosages. The greatest escape response for An. harrisoni was observed at the operational field concentration of alpha-cypermethrin. The noncontact repellency response to alpha-cypermethrin was comparatively weak for all 3 test populations, but significantly different from each paired contact test and respective noncontact controls. We conclude that strong contact irritancy is a major action of alpha-cypermethrin, whereas noncontact repellency plays no role in the escape responses of 2 species in the Minimus Complex in Thailand.
Journal of the American Mosquito Control Association 09/2011; 27(3):217-26. · 0.76 Impact Factor
[show abstract][hide abstract] ABSTRACT: Thirty-two Aedes aegypti populations collected throughout Thailand and five populations of Aedes albopictus from southern Thailand were subjected to standard WHO contact bioassays to assess susceptibility to three commonly used synthetic pyrethroids: permethrin, deltamethrin, and lambda-cyhalothrin. A wide degree of physiological response to permethrin was detected in Ae. aegypti, ranging from 56.5% survival (Lampang, northern Thailand) to only 4% (Kalasin in northeastern and Phuket in southern Thailand). All 32 populations of Ae. aegypti were found to have evidence of incipient resistance (62.5%) or levels of survival deemed resistant (37.5%) to permethrin. Four populations of Ae. albopictus were found with incipient resistance (97 - 80% mortality) and one with resistance (< 80%) to permethrin. The majority of Ae. aegypti populations (68.7%) was susceptible (> 98% mortality) to deltamethrin, with incipient resistance (observed 97-82% mortality) in other localities. In contrast, all populations of Ae. aegypti were completely susceptible (100% mortality) to the recommended operational dosage of lambda-cyhalothrin. All five populations of Ae. albopictus were found completely susceptible to both deltamethrin and lambda-cyhalothrin. Evidence of defined incipient or resistance to synthetic pyrethroids mandates appropriate response and countermeasures to mitigate further development and spread of resistance. In light of these findings, we conclude that routine and comprehensive susceptibility monitoring of dengue mosquito vectors to synthetic pyrethroids should be a required component of resistance management policies and disease control activities.
Journal of Vector Ecology 06/2011; 36(1):204-12. · 1.23 Impact Factor