The physiological susceptibility to insecticides and the behavioral responses of four wild-caught... more The physiological susceptibility to insecticides and the behavioral responses of four wild-caught populations of female Anopheles epiroticus to synthetic pyrethroids (deltamethrin, permethrin, and alpha-cypermethrin) were assessed. Test populations were collected from different localities along the eastern coast, Trat (TR), Songkhla (SK), and Surat Thani (ST) and one population from the western coast, Phang Nga (PN). Results showed that all four populations of An. epiroticus were susceptible to all three synthetic pyrethroids tested. Behavioral responses to test compounds were characterized for all four populations using an excito-repellency test system. TR displayed the strongest contact excitation ('irritancy') escape response (76.8% exposed to deltamethrin, 74.1% permethrin, and 78.4% alpha-cypermethrin), followed by the PN population (24.4% deltamethrin, 35% permethrin, and 34.4% for alpha-cypermethrin) by rapidly escaping test chambers after direct contact with surfaces treated with each active ingredient compared with match-paired untreated controls. Moderate non-contact repellency responses to all three compounds were observed in the TR population but were comparatively weaker than paired contact tests. Few mosquitoes from the SK and ST populations escaped from test chambers, regardless of insecticide tested or type of trial. We conclude that contact excitation was a major behavioral response in two populations of An. epiroticus, whereas two other populations showed virtually no escape response following exposure to the three pyrethroids. The explanation for these large unexpected differences in avoidance responses between pyrethroid-susceptible populations of the same species is unclear and warrants further investigation. Journal of Vector Ecology 39 (1): 32-43. 2014.
Isozyme frequencies were compared in seven field collections of Anopheles minimus complex using s... more Isozyme frequencies were compared in seven field collections of Anopheles minimus complex using starch gel electrophoresis. Mosquito collections were sampled from four districts in Kanchanaburi Province where malaria is endemic. From eight enzyme systems, nine loci and seven polymorphisms were detected, indicating limited genetic differentiation among the seven collections (FST = 0.061). The highest percent polymorphic loci were observed in Bong Ti Noi (BTN) Village (55.6%), whereas the least percent polymorphism was seen in Tha Kradan (TK) Village (22.2%). Comparing villages Pra Jedee (PJ) with Pu Teuy C (PTC) and Huai Khayeng (HK) with Pra Jedee (PJ), gene flow among collections varied from 3.72 to 62.25 reproductive migrants per generation. Among the seven collections, no correlation was seen between genetic and geographical distances (P > 0.05). Anopheles minimus (former species A) and Anopheles harrisoni (former species C) from Pu Teuy fit most closely in the same cluster, possibly indicating relatively recent divergence between taxa. The genetic and epidemiological ramifications of these findings are discussed.
Anopheles dirus females landing on humans inside experimental huts treated with residual applicat... more Anopheles dirus females landing on humans inside experimental huts treated with residual applications of DDT or deltamethrin were observed during the wet season in Pu Teuy Village, Kanchanaburi Province, western Thailand. Two identical experimental huts were constructed in the fashion of typical local rural Thai homes. Pretreatment (baseline) human-landing collections (HLC) in both huts showed an early evening peak of activity between 1900 and 2000 h with no signiÞcant difference in numbers of mosquitoes captured between huts over a period of 30 collection nights. During posttreatment HLC, female mosquitoes continued to show greater landing activity inside huts Þtted with insecticide-treated panels during the Þrst half of the evening compared with the second half. A greater number (proportion) of An. dirus females landed on humans in the hut treated with deltamethrin compared with DDT. Comparing pre-and posttreatment HLC, the DDT-treated hut showed a 79.4% decline in attempted blood feeding, whereas exposure to deltamethrin resulted in a 56.3% human-landing reduction. An odds ratio was performed to demonstrate the relative probability (risk) of mosquitoes entering and attempting to blood feed in the two treated huts compared with untreated control huts. Mosquitoes were 0.47 times less likely to land on humans inside a DDT-treated hut compared with the deltamethrin-treated hut. Although both chemicals exerted strong excitatory responses, DDT appears to have a more pronounced and signiÞcant (P 0.002) effect on behavior than deltamethrin, resulting in greater movement away from the insecticide source and thus potential reduction of blood-feeding activity.
Biting patterns of natural populations of Anopheles minimus s.l. females entering experimental hu... more Biting patterns of natural populations of Anopheles minimus s.l. females entering experimental huts treated with DDT and deltamethrin were carried out at Pu Teuy Village, Sai Yok District, Kanchanaburi Province, western Thailand. Two experimental huts, control and treatment, were constructed in the fashion of local Thai homes. Pre-spray biting activity of An. minimus females peaked at 19:00-22:00. Post-treatment exposure continued to show greater landing activity during the first half of the evening. An overall greater proportion of An. minimus females entered the hut treated with deltamethrin compared to DDT. The hut fitted with DDT-treated net panels showed a 71.5% decline in attempted blood feeding, whereas exposure to deltamethrin-treated panels resulted in a 42.8% human-landing reduction. DDT exhibited significantly more pronounced (P < 0.05) effects in overall reduction of biting activity than did deltamethrin. Journal of Vector Ecology 33 (2): 285-292. 2008.
In April 2001, a second suspected outbreak of dengue hemorrhagic fever in the easternmost region ... more In April 2001, a second suspected outbreak of dengue hemorrhagic fever in the easternmost region of Indonesia was investigated in Merauke, a town located in the southeastern corner of Papua, by the Indonesian Ministry of Health and the U.S. Naval Medical Research Unit No. 2. Principal case criteria of hemorrhagic disease provided for a study enrollment of 15 clinically acute
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Papers by Michael Bangs
From eight enzyme systems, nine loci and seven polymorphisms were detected, indicating limited genetic differentiation among the seven collections (FST = 0.061). The highest percent polymorphic loci were observed in Bong Ti Noi (BTN) Village (55.6%), whereas the least percent polymorphism was seen in Tha Kradan (TK) Village (22.2%). Comparing villages
Pra Jedee (PJ) with Pu Teuy C (PTC) and Huai Khayeng (HK) with Pra Jedee (PJ), gene flow among collections varied from 3.72 to 62.25 reproductive migrants per generation. Among the seven collections, no correlation was seen between genetic and geographical distances (P > 0.05). Anopheles minimus (former species A) and Anopheles harrisoni (former species C)
from Pu Teuy fit most closely in the same cluster, possibly indicating relatively recent divergence between taxa. The genetic and epidemiological ramifications of these findings are discussed.