Biodiversity of Adult Trichoptera and Water Quality Variables in Streams, Northern Thailand

AbstractThe diversity of adult Trichoptera was surveyed at Mae Tao and Mae Ku watersheds, northern Thailand during July 2011 to May 2012. The aim of the study was to determine the relationship between physicochemical parameters of water quality and adult Trichoptera for monitoring of water quality. A total of 9,475 adult Trichoptera representing 14 families and 126 species were collected. The correlation between the biodiversity of adult Trichoptera and water quality showed that the Ecnomus jojachin, Cheumatopsyche carmentis, C. chryseis, C. lucida, C. chrysothemis, C. dhanikari, Potamyia dryope, Leptocerus dirghachuka, L. trophonios, L. ganymedes, Oecetis scutulata, O. armadillo, O. raghava, O. asmada, O. tripunctata, Setodes flivialis, S. neptunus, S. endymion, S. okypete, Chimarra chiangmaiensis, Paduniella semarangensis, Lepidostoma doligung, Polyplectropus ahas, Psychomyia lak, Marilia sumatrana, Hydroptila thuna and Orthrotrichia typhoeus depended on some physicochemical factors including air temperature, pH, electrical conductivity, turbidity, sulfate, nitrate-nitrogen, orthrophosphate, ammonia-nitrogen and alkalinity in water

Transmission of pathogens by "Stomoxys flies (Diptera, Muscidae): a review

Les stomoxes sont des vecteurs mécaniques de pathogènes présents dans le sang et les tissus cutanés de leurs hôtes, spécialement le bétail, mais aussi parfois les humains. Pour le bétail, leurs effets directs sont principalement la perturbation des animaux, les lésions de la peau, la réduction de l'alimentation, le stress, la spoliation sanguine et un effet immunosuppressif global. Ils entrainent aussi le regroupement des animaux pour une protection mutuelle ; tout cela favorise le développement des parasites chez les hôtes et leur transmission. Leur effet indirect est la transmission mécanique de pathogènes. En cas de repas interrompu, les stomoxes peuvent reprendre leur repas de sang sur un autre hôte. En injectant de la salive avant l'absorption de sang, ils peuvent inoculer du sang infecté qui restait sur leurs pièces buccales. En plus de cette transmission immédiate, il a été observé que les stomoxes pouvaient conserver du sang dans leur jabot, qui offre un meilleur environnement pour les pathogènes. Ces derniers peuvent être régurgités lors du prochain repas de sang. Ainsi, une transmission retardée semble possible par les stomoxes. Un tel mécanisme a une conséquence épidémiologique considérable, puisqu'il permet une transmission de pathogènes entre les troupeaux. Les virus de l'anémie infectieuse équine, de la fièvre porcine africaine, des fièvres à West Nile ou de la Vallée du Rift, sont connus pour être transmis par des stomoxes ; d'autres sont suspectés. Des rickettsies (Anaplasma, Coxiella), d'autres bactéries et des parasites (Trypanosoma spp., Besnoitia spp.) sont aussi transmis par les stomoxes. Enfin, les stomoxes sont aussi des hôtes intermédiaires de l'helminthe Habronema microstoma et pourraient être impliqués dans la transmission de certaines espèces d'Onchocerca et de Dirofilaria. En étant cosmopolite, Stomoxys calcitrans pourrait avoir un impact plus important qu'initialement imaginé sur la transmission de pathogènes aux animaux et aux humains. (Résumé d'auteur

Behavioral responses to transfluthrin by Aedes aegypti, Anopheles minimus, Anopheles harrisoni, and Anopheles dirus (Diptera: Culicidae)

Airborne spatial repellency (SR) is characterized and distinguished from other chemical actions including contact locomotor excitation and toxicity. The use of volatile spatial repellents is a potential new intervention class for combatting mosquito-borne pathogen transmission; therefore, continuing investigations on the actions of these chemicals that modify mosquito host‐seeking behavior (i.e., bite prevention) is needed. The objective of this study is to characterize the key behavioral avoidance actions of transfluthrin (TFT) to advance spatial repellent development into practical products. Behavioral avoidance responses were observed for adult laboratory strains of Aedes aegypti, Anopheles minimus and An. dirus, and two field populations of An. harrisoni and Ae. aegypti, respectively. Established TFT sublethal (LC50 and LC75), lethal concentrations (LC99) and discriminating concentrations (DCs) were selected corresponding to each mosquito test species. Spatial repellency and contact excitation (‘irritancy’) responses on adult mosquitoes to TFT were assessed using an excito-repellency assay system. At LC50, TFT exhibited strong avoidance with An. minimus (60.1% escape) and An. dirus (80% escape) laboratory strains, showing between 12 and 16x greater escape response than Ae. aegypti (5% escape). Repellency responses for field collected Ae. aegypti and An. harrisoni were 54.9 and 47.1% escape, respectively. After adjusting the initial contact escape response (a measure of combined irritancy and repellency) to estimate only escape due to contact, the LC50 and LC99 showed moderate escape irritancy with laboratory Ae. aegypti (41.4% escape) and no contact activity against the field population. Adjustment showed only weak contact activity (16.1% escape) in laboratory An. minimus at LC50. Spatial repellency is the predominant mode of action of TFT among colonized and field mosquitoes used in this study. Established baseline (susceptible) dose-response curves assist in optimizing SR products for mosquito control and pathogen transmission prevention

Semi-field evaluation of human landing catches versus human double net trap for estimating human biting rate of Anopheles minimus and Anopheles harrisoni in Thailand

Background: Whilst the human landing catch (HLC) technique is considered the ‘gold standard’ for estimating human-biting rates, it is labor-intensive and fraught with potential risk of exposure to infectious mosquito bites. This study evaluated the feasibility and performance of an alternative method, the human double net trap (HDNT) relative to HLC for monitoring host-seeking malaria vectors of the Anopheles minimus complex in a semi-field system (SFS). Methods: HDNT and HLC were positioned in two rooms, 30 m apart at both ends of the SFS. Two human volunteers were rotated between both traps and collected released mosquitoes (n = 100) from 6:00 pm till 6:00 am. Differences in Anopheles mosquito densities among the trapping methods were compared using a generalized linear model based on a negative binomial distribution. Results: There were 82.80% (2,136/2,580) of recaptures of wild-caught and 94.50% (2,835/3,000) of laboratory-reared mosquitoes that were molecularly identified as An. harrisoni and An. minimus, respectively. Mean density of An. harrisoni was significantly lower in HNDT (15.50 per night, 95% CI [12.48–18.52]) relative to HLC (25.32 per night (95% CI [22.28–28.36]), p < 0.001). Similarly, the mean density of a laboratory strain of An. minimus recaptured in HDNT was significantly lower (37.87 per night, 95% CI [34.62–41.11]) relative to HLC (56.40 per night, 95% CI [55.37–57.43]), p < 0.001. Relative sampling efficiency analysis showed that HLC was the more efficient trap in collecting the An. minimus complex in the SFS. Conclusion: HDNT caught proportionately fewer An. minimus complex than HLC. HDNT was not sensitive nor significantly correlated with HLC, suggesting that it is not an alternative method to HLC

Evaluation of the Constituents of Vetiver Oil Against Anopheles minimus (Diptera: Culicidae), a Malaria Vector in Thailand

The development of resistance by mosquitoes to current synthetic compounds has resulted in reduced effectiveness of prevention and control methods worldwide. An alternative nonchemical based control tools are needed to be evaluated particularly plant-derived essential oils. Several components of vetiver oil have been documented as insect repellents. However, detailed knowledge of those components action against insect remains unknown. In this study, behavioral response of Anopheles minimus to four constituents of vetiver oil (valencene, terpinen-4-ol, isolongifolene, vetiverol) was evaluated by using the high-throughput screening assay system. Vetiverol and isolongifolene exhibited strong contact irritancy action at 1.0% (80.2% escaping) and 5.0% (81.7% escaping) concentration, respectively, while moderate action was found in both valencene and terpinen-4-ol at 5.0% (57.6% escaping). Only at 1.0% (0.7 spatial activity index [SAI]) and 5.0% (1.0 SAI) of valencene and 0.5% (0.7 SAI) of isolongifolene showed spatial repellency activity. High mortality (58.9–98.2%) was recorded in all concentration of vetiverol and isolongifolene. Meanwhile, valencene exhibited high mortality only at 5.0%, terpinen-4-ol showed very low toxic action (0–4.3%) in all concentration. These proved that valencene in vetiver oil is the promising constituent that can be developed as an alternative mosquito control mean in efforts to prevent disease transmission

Genetic Diversity and Gene Flow among Stable Fly Populations, Stomoxys calcitrans (L.) in Thailand

ABSTRACT Isozymes from five wild-caught Stomoxys calcitrans (L.) were compared using starch gel electrophoresis to estimate the rates of gene flow between and among S. calcitrans populations from five different geographic regions of Thailand. Among ten enzyme systems, 13 putative loci and 10 polymorphisms were detected. Limited genetic differentiation among the five populations was observed as indicated by the low F ST (0.078). The highest percentage of polymorphic loci was observed in eastern Trat province and northern Chiang Mai province (69.2%), whereas the lowest percent polymorphism was seen in south-central Saraburi province (23.1%). Gene flow between populations varied from 6.16 to 15.38 reproductive migrants per generation with no fixed genetic differences detected. Among the five population samples, no correlation was seen between genetic and geographical distances showing that sampled S. calcitrans fit closely in the same cluster taxa. The genetic and epidemiological ramifications of these findings are discussed

Scientific achievements and reflections after 20 years of vector biology and control research at the Pu Teuy mosquito field research station, Thailand

Additional vector control tools are needed to supplement current strategies to achieve malaria elimination and control of Aedes-borne diseases in many settings in Thailand and the Greater Mekong Sub-region. Within the next decade, the vector control community, Kasetsart University (KU), and the Ministry of Higher Education, Science, Research and Innovation must take full advantage of these tools that combine different active ingredients with different modes of action. Pu Teuy Mosquito Field Research Station (MFRS), Department of Entomology, Faculty of Agriculture, Kasetsart University (KU), Thailand was established in 2001 and has grown into a leading facility for performing high-quality vector biology and control studies and evaluation of public health insecticides that are operationally relevant. Several onsite mosquito research platforms have been established including experimental huts, a 40-m long semi-field screening enclosure, mosquito insectary, field-laboratory, and living quarters for students and researchers. Field research and assessments ranged from ‘basic’ investigations on mosquito biology, taxonomy and genetics to more ‘applied’ studies on responses of mosquitoes to insecticides including repellency, behavioural avoidance and toxicity. In the course of two decades, 51 peer-reviewed articles have been published, and 7 masters and 16 doctoral degrees in Entomology have been awarded to national and international students. Continued support of key national stakeholders will sustain MFRS as a Greater Mekong Subregion centre of excellence and a resource for both insecticide trials and entomological research