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The performances of the human-baited double net trap (HDNT) and the human-baited host decoy trap (HDT) methods were compared against the outdoor human landing catch (OHLC) method in Thailand and Vietnam. Two study sites were selected in each country: a rural village and a nearby forest setting. The three outdoor trap methods were rotated nightly between three set trapping positions, in a pre-assigned Latin square design. Volunteers were rotated following the trap rotation to avoid bias. The greatest number of adult mosquitoes was collected from the forest sites in both countries, showing Anopheles minimus (s.s.) Theobald (96.54%) and Anopheles dirus (s.s.) Peyton & Harrison (25.71%) as the primary malaria vectors in Thailand and Vietnam, respectively. At the Thai forest site, OHLC collected significantly more anopheline mosquitoes per trap night than HDNT and HDT, with mean ± standard error values of 14.17 ± 4.42, 4.83 ± 1.56, and 4.44 ± 1.45, respectively, whilst HDNT and HDT were significantly less productive at 0.34 times and 0.31 times, respectively, than OHLC in capturing anopheline mosquitoes. However, there were no significant differences among the three methods of trapping malaria vectors for the village site. At the Vietnamese forest site, HDNT achieved the highest performance in collecting Anopheline mosquitoes at 1.54 times compared to OHLC, but there was no significant difference between the two traps. The results suggested HDNT could be a possible alternative trap to OHLC in this area. Although HDT was less efficient at attracting Anopheline mosquitoes, it was highly efficient at trapping culicine mosquitoes., (© The Author(s) 2022. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Excito-repellency activity of plant extracts have been increasingly studied as mosquito repellents. In this study, the crude extract of Andrographis paniculata was evaluated for its noncontact repellency, contact excitation (irritancy + repellency), and knockdown/toxicity response against five colonized mosquitoes; Aedes aegypti (L.), Aedes albopictus (Skuse), Anopheles dirus Peyton & Harrison, Anopheles epiroticus Linton & Harbach, and Culex quinquefasciatus Say (Diptera: Culicidae) using an excito-repellency assay system under laboratory-controlled conditions. The escape responses were observed at four different concentrations (0.5-5.0% w/v) with A. paniculata showing strong spatial repellency against Ae. albopictus (96.7% escape) and Ae. aegypti (71.7% escape) at the 2.5% and 0.5% concentrations, respectively. At 0.5% and 5.0% concentrations, the greatest repellency was seen for An. dirus (48.2% escape) and Cx. quinquefasciatus (59.7% escape), respectively. Comparatively, low repellency action was observed against An. epiroticus (1.6-15.0% escape). Escape in contact assays (before adjustment) was generally less pronounced compared to noncontact spatial repellency, with Ae. albopictus showing highest percent escape (71.4% escape) in the contact assay at 1.0% concentration. After adjusting for spatial repellency, escape due to contact irritancy alone was either not present or an insignificant contribution to the overall avoidance response for all species. No knockdown or mortality at 24-h postexposure was observed in any trials. These findings indicate that the A. paniculata crude extract is more active against day-biting mosquitoes; however, this may be a reflection of the time of testing. This study demonstrates compelling evidence that A. paniculata extract performs primarily as a spatial repellent. Further investigations exploring the use A. paniculata as a potential active ingredient in repellent products are needed., (© The Author(s) 2019. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Aedes aegypti (L.), the primary vector of dengue and dengue hemorrhagic fever, breeds and rests predominately inside human dwellings. With no current vaccine available, vector control remains the mainstay for dengue management and novel approaches continue to be needed to reduce virus transmission. This requires a full understanding of Ae. aegypti ecology to design effective strategies. One novel approach is the use of contact irritants at target resting sites inside homes to make the surface unacceptable and cause vectors to escape before biting. The objective of the current study was to observe indoor resting behavior patterns of female Ae. aegypti within experimental huts in response to two fabrics under consideration for insecticide treatment: cotton and polyester. Results indicate that fabric type, coverage ratio of dark to light fabric and placement configuration (vertical vs. horizontal) all influenced the resting pattern of mosquito cohorts. Findings from this study will guide evaluations of a push-pull strategy designed to exploit contact irritant behaviors and drive Ae. aegypti out of homes prefeeding.

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 significant 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 fitted with insecticide-treated panels during the first 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 approximately 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 significant (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.

Chemicals can protect humans from the bites of hemophagous arthropods through three different primary actions: irritancy (excitation), repellency, or toxicity, actions that can be evaluated using a laboratory-based assay system. In this study, the deterrent and toxic actions of three synthetic pyrethroids and DDT were characterized on six field strains of Aedes aegypti from Thailand under laboratory-controlled conditions using the high throughput screening system. All six strains showed significant contact irritant responses to the three synthetic pyrethroids, but significantly weaker irritant responses to DDT. Marked repellency responses were seen in all six Ae. aegypti test strains exposed to DDT, whereas the synthetic pyrethroids resulted in greater toxicity than DDT under similar test conditions. Although significantly different in actions, irritancy and repellency may reflect and be influenced by the background insecticide susceptibility status of a particular mosquito population. Results from this study can be used to guide decision making regarding more effective Ae. aegypti adult control in Thailand.

This study quantified both contact irritancy and noncontact repellency behavioral responses of three strains of Aedes aegypti (L.) (one long-term colony and two F1-F2 generation field-caught strains) to field application rates of DDT (2 g/m2) and alpha-cypermethrin (ACyp) (0.025 g/m2) by using an excito-repellency test chamber. The colony The colony strain (USDA) was completely susceptible to DDT and ACyp. One field strain was collected from Chiang Mai (CM) Province, northern Thailand, and was characterized as tolerant (reduced susceptibility) to DDT and completely susceptible to ACyp. The second field strain, collected from Kanchanaburi (KAN) Province, western Thailand, was highly resistant to DDT but fully susceptible to ACyp. All three strains exhibited marked irritancy to contact with ACyp, with more pronounced escape responses occurring in the two field strains. With DDT, the KAN strain demonstrated the lowest escape response during both contact and noncontact trials, whereas a greater response was seen in trials conducted with CM and USDA strains. With exposure to ACyp, repellency was less profound than irritancy but still resulted in a significant escape response compared with paired controls without insecticide (P < 0.05). DDT elicited both irritancy and repellency responses but comparably greater spatial repellency than ACyp. Findings indicate ACyp functions primarily as a strong contact irritant, whereas DDT functions as a relatively strong noncontact repellent in the strains tested. The higher the degree of physiological resistance to DDT, the greater the apparent suppression of both behavioral avoidance responses. Most importantly, observations using susceptible, tolerant, and resistant Ae. aegypti strains show that behavioral responses that can interrupt human-vector contact still occur regardless of degree of physiological susceptibility to compounds tested.

Adult mosquitoes were collected from 3 areas in northern Thailand with different availabilities of rice fields for larval habitats by using blacklight, truck, and pig-baited traps. Culex tritaeniorhynchus Giles and Culex gelidus Theobald were dominant in all samples. Significant study-area differences were found in light and truck trap collections for Cx. tritaeniorhynchus and Cx. gelidus, but not for Culex vishnui Theobald + Culex pseudovishnui Colless. In pig-baited sample area differences were significant only for Cx. gelidus. Adults of Culex fuscocephala Theobald were relatively rare, comprising only 0.6-7.9% of the total mosquitoes collected. When compared with the results from previous studies in the Chiangmai area, we conclude that Cx. fuscocephala has become a minor species and that changes in the mosquito fauna have occurred in northern Thailand.

In 1991-1993, the density (numbers per 10 dips) and abundance (density x flooded area) of mosquitoes were studied in 3 areas of northern Thailand with different environmental conditions. Culex tritaeniorhynchus Giles, Cx. vishnui Theobald, and Cx. gelidus Theobald were predominant among the 8 Culex species collected. Abundance of these 3 species varied significantly among the 3 areas. Type of habitat classified according to agricultural practices in rainy and dry season significantly influenced larval abundance of Cx. tritaeniorhynchus and Cx. vishnui. Seasonal variation in larval abundance was significant only in Cx. vishnui. The response of the 3 vector mosquitoes to environmental heterogeneity is discussed.