High prevalence and low diversity of chigger infestation in small mammals found in Bangkok Metropolitan parks.

Chiggers are recognized as vectors of scrub typhus disease caused by the bacteria, Orientia tsutsugamushi. The risk of disease exposure is mainly related to chigger bites when humans or animals roam into vector-infested habitats. In big cities, urban public parks could provide areas for the animal-human interface and zoonotic pathogen transmission. The ecology and epidemiology of urban scrub typhus are still poorly understood in Thailand. Small mammals were trapped and examined for chigger infestation in urban public parks across metropolitan Bangkok, Thailand. We found a high prevalence of infestation (76.8%) with surprisingly low diversity. Two chigger species, Leptotrombidium deliense and Ascoschoengastia indica, were identified using morphological characteristics and molecular confirmation. The generalized linear model identified host intrinsic variables (i.e. body mass index) with host density, habitat composition and open field as the extrinsic factors explaining the abundance of chigger infestation. The bacteria O. tsutsugamushi was not detected in chiggers (90 chigger-pooled samples) and animal host tissues (164 spleen samples). However, the existence of chigger vectors calls for the Bangkok Metropolitan Administration and public health authorities to develop a comprehensive scrub typhus monitoring and prevention strategy in the parks and nearby communities.

Geometric morphometrics to distinguish the cryptic species Anopheles minimus and An. harrisoni in malaria hot spot villages, western Thailand.

Anopheles minimus Theobald 1901 and An. harrisoni Harbach & Manguin 2007 belong to the same species complex. They are morphologically similar and can exist in sympatry but have blood host preferences. The most accurate method for their identification is based on molecular techniques. Here, we measure the level of interspecific discrimination by geometric morphometry. Sixty-seven An. minimus and 22 An. harrisoni specimens were selected based on their morphological integrity and confirmed by identification polymerase chain reaction of internal transcribed spacer 2. These samples were used as reference data allowing for a morphometric identification based on geometric shape. Despite size overlap between the two species, there was a significant shape divergence allowing for differentiation of An. minimus and An. harrisoni with 90% accuracy. An intraspecific study of An. minimus showed a summer period associated to the reducing of wing size, which did not influence the shape-based differentiation of An. harrisoni. Wing venation geometry can be used to distinguish between these cryptic species mainly based on shaped divergence. This study suggests that geometric morphometrics represent a convenient low-cost method to complement morphological identification, especially concerning damaged specimens, i.e., insects having accidentally lost the anatomical features allowing a reliable morphological identification.

Geometric morphometric analysis of the effect of temperature on wing size and shape in Aedes albopictus.

Wing geometry helps to identify mosquito species, even cryptic ones. On the other hand, temperature has a well-known effect on insect metric properties. Can such effects blur the taxonomic signal embedded in the wing? Two strains of Aedes albopictus (laboratory and field strain) were examined under three different rearing temperatures (26, 30 and 33 °C) using landmark- and outline-based morphometric approaches. The wings of each experimental line were compared with Aedes aegypti. Both approaches indicated similar associations between wing size and temperature. For the laboratory strain, the wing size significantly decreased as the temperature increased. For the field strain, the largest wings were observed at the intermediate temperature. The two morphometric approaches describing shape showed different sensibilities to temperature. For both strains and sexes, the landmark-based approach disclosed significant wing shape changes with temperature changes. The outline-based approach showed lesser effects, detecting significant changes only in laboratory females and in field males. Despite the size and shape changes induced by temperature, the two strains of Ae. albopictus were always distinguished from Ae. aegypti. The present study confirms the lability of size. However, it also suggests that, despite environmentally-induced variation, the architecture of the wing still provides a strong taxonomic signal.

Efficacies of five edible mushroom extracts as odor baits for resting boxes to attract mosquito vectors: A field study in Samut Songkhram Province, Thailand.

Effective trapping of adult mosquitoes in the wild can reduce the spread of deadly human pathogens, such as Plasmodium species causing malaria. The efficacy of this strategy depends on the capacity of the trap to attract and retain insects, and specific odorants such as octenol in mushrooms are strong attractants for mosquitoes. In this study, we assessed the efficiency of a resting box baited with five different extracts from local edible mushrooms, Pleurotus ostreatus, Thaeogyroporus porentosus, Volvariella volvacea, Pleurotus sajorcaju, and Lentinus edodes, for attracting mosquito vectors in Samut Songkhram Province, Thailand. Extracts were used in identical "resting box" at 50, 100, and 200 mg/mL per box. Compared to the unbaited resting box (control), only traps containing 200 mg/mL of L. edodes extract captured significantly more mosquitoes (16.00 ± 3.61 vs. 7.00 ± 1.00 per resting box per night, pandlt;0.05). Attraction efficacy did not increase progressively with tested amount for most extracts. These findings indicate that L. edodes extract can be used as an inexpensive, non-toxic, and locally sourced attractant to increase the efficacy of mosquito control.

Efficacies of five edible mushroom extracts as odor baits for resting boxes to attract mosquito vectors: A field study in Samut Songkhram Province, Thailand

@#Effective trapping of adult mosquitoes in the wild can reduce the spread of deadly human pathogens, such as Plasmodium species causing malaria. The efficacy of this strategy depends on the capacity of the trap to attract and retain insects, and specific odorants such as octenol in mushrooms are strong attractants for mosquitoes. In this study, we assessed the efficiency of a resting box baited with five different extracts from local edible mushrooms, Pleurotus ostreatus, Thaeogyroporus porentosus, Volvariella volvacea, Pleurotus sajorcaju, and Lentinus edodes, for attracting mosquito vectors in Samut Songkhram Province, Thailand. Extracts were used in identical “resting box” at 50, 100, and 200 mg/mL per box. Compared to the unbaited resting box (control), only traps containing 200 mg/mL of L. edodes extract captured significantly more mosquitoes (16.00 ± 3.61 vs. 7.00 ± 1.00 per resting box per night, p<0.05). Attraction efficacy did not increase progressively with tested amount for most extracts. These findings indicate that L. edodes extract can be used as an inexpensive, non-toxic, and locally sourced attractant to increase the efficacy of mosquito control.

Species diversity and distribution of mosquito vectors in coastal habitats of Samut Songkhram province, Thailand.

This study assessed species diversity and distribution of mosquito vectors in coastal habitats dividing it to three areas according to the distance from the sea. We also described a comprehensive analysis on factors associated with natural habitat preference of mosquito larvae in the Samut Songkhram province, Thailand. Adult and larval mosquito survey was conducted using black light traps and standard mosquito dipper during rainy season between October to November 2015. A total of 1,764 mosquitoes belonging to 3 genera with 5 species were captured. The most abundant species was Anopheles epiroticus accounting for 37.13% followed by Culex sitiens (34.92%), Cx. quinquefasciatus (27.66%), Aedes aegypti (0.23%) and Cx. gelidus (0.06%) respectively. Cx. sitiens and An. epiroticus larvae were collected from available breeding habitats. Highest density of mosquito larvae (603 larvae) was found at 2 kilometers distance from the sea whereas at 4 kilometers distance from the sea found the least of larvae numbers ( 331)s. Pearson correlation showed association the factors associated with breeding habitat preference of mosquito larvae. Cx. sitiens larvae were significantly higher in permanent, temporary water resources (p<0.01) and mangrove trees (p<0.05) than those of An. epiroticus. An. epiroticus larvae that significantly prefer water with green algae (p<0.05). These results provided important information with regards to mosquito vectors in coastal habitats of Samut Songkhram province, Thailand. It also provided information on species diversity, distribution and factors associated with breeding habitat, preference for surveillance and control to prevent the spread of mosquito-borne diseases to the population of the coastal communities. These findings fulfil knowledge of mosquito ecology and support mosquito control strategies that can be applied in coastal areas of Thailand in the future.