Lao PDR, a landlocked country in the lower Mekong River basin of Southeast Asia, has been considered a global biodiversity hotspot with a high level of biological endemism. In recent years, urban development and industrialization have affected the water quality of freshwater ecosystems in Lao PDR. However, the assessment of water quality in the country is primarily focused on a physicochemical method, while the application of a multimetric index (MMI) approach using benthic macroinvertebrates for biomonitoring in rivers and streams has not been established. MMI, based on benthic macroinvertebrates, is a biomonitoring tool that considers the effects of multiple anthropogenic impacts on benthic macroinvertebrate metrics associated with their biological attributes (e.g., taxa richness, composition, pollution tolerance, habits, and functional feeding) and aggregates individual metrics into a single value for assessing the water quality and health conditions of aquatic ecosystems. Here, we developed an MMI based on macroinvertebrate communities collected during 2016–2018 from 10 localities of streams and wadeable rivers in Lao PDR. Of the 54 potential metrics tested, 35 candidate macroinvertebrate metrics representing richness, composition, trophic structure, habit, and tolerance to pollution were selected, while 19 metrics were excluded. Of the 35-candidate metrics, a total of 11 core metrics (Total taxa, EPT taxa, Ephemeroptera taxa, %Diptera, %Plecoptera, %Tolerant, Beck’s biotic index, %Intolerant, Filterers taxa, %Sprawlers, and %Burrowers) were finally selected for the development of MMI based on their sensitivity, redundancy, and easy-to-apply tool for the biomonitoring program. These metrics can be used to distinguish the reference (seven sites) from stressed conditions (seven sites). In addition, the final MMI scores classified 40 sampling sites into four classes of water quality, including excellent (25%), good (10%), fair (60%), and poor (5%), which the conventional physicochemical method could not clearly distinguish. The Lao MMI developed in this study is an effective tool for evaluating the water conditions of sites affected by human activities, particularly agricultural areas, and, thus, is appropriate for use in future studies for assessing the ecological conditions of rivers and streams in the Mekong region.

Six new species of Caenis from Thailand are described herein: Caenis ludovicin. sp., Caenis nasutan. sp., Caenis longiforcipatan. sp., Caenis karenaen. sp.,Caenis obtusostilatan. sp. and Caenis acutostilatan. sp., as well as the larvae of Caenis picea Kimmins, 1947 and Caenis ulmerianaMalzacher, 2013, which were so far only known as males. Furthermore, a new species of the genus Kalimaenis, Kalimaenis proceran. sp., is described. Also described from the same area are two new genera of the subfamily Caeninae: Elatosaran. gen. (Type species Elatosara phanomensisn. sp.) most probably belongs to the tribe Clypeocaenini; Thainisn. gen. (Type species Thainis kalimaenoidesn. sp.), is classified within the tribe Caenini. The phylogeny of the new genera is discussed. A larval key to the Caeninae from Thailand is provided and the key to the male Caenis of the Oriental region (Malzacher 2015) is replenished.

The tribe Caenoculini Sun & McCafferty, 2008 is revised, now including the genera Caenoculis Soldán, 1986, and Tigrocercus Malzacher, 2006. Improved diagnoses of these two genera are given. Caenoculis dangi Soldán, 1986 is transferred to the genus Tigrocercus and Tigrocercus nastassjae Malzacher, 2013 to the genus Caenoculis. Caenoculis acutalis Zhou, Sun & Mccafferty, 2003 is regarded as representative of a separate genus Brachoculis n. gen. A diagnosis of the new genus is given. Relationships within the Brachycercinae are discussed. Der Tribus Caenoculini Sun & McCafferty, 2008 wird revidiert. Er umfasst nun die Gattungen Caenoculis Soldán, 1986 und Tigrocercus Malzacher, 2006. Von beiden Gattungen werden verbesserte Diagnosen erstellt. Caenoculis dangi Soldán, 1986 wird in die Gattung Tigrocercus und Tigrocercus nastassjae Malzacher, 2013 in die Gattung Caenoculis transferiert. Caenoculis acutalis Zhou, Sun & Mccafferty, 2003 wird als eigene Gattung, Brachoculis n. gen., betrachtet, für die eine Diagnose erstellt wird. Die Verwandschaftsverhältnisse innerhalb der Brachycercinae werden diskutiert.

Shallow water sponges settled on a raft along the Pong River (Lower Mekong Basin, Thailand) were investigated to highlight the taxonomic richness, composition, relative abundance and lifestyle of sponge-dwelling aquatic Insecta. The three-dimensional biogenic structures of the model sponges hosted 4 orders of Insecta, belonging to 10 families and 19 genera/species, able to strictly coexist at the level of the sponges in aquiferous canals and/or at the body surface, and/or dwelling in the extracellular matrix. On the basis of the identified 379 larvae and pupae, Trichoptera and Diptera were found to be the dominant inhabitants of Corvospongilla siamensis (Demospongiae: Spongillida), endemic to Southeast Asia. In the focused lotic ecosystem, dominated by soft bottoms, sponges play a functional role. Insecta use sponges as a substratum, nursery ground, food source, and shelter microhabitat, protecting them from predation and environmental aggression. Moreover, their feeding behavior indicates the insects’ adaptive traits to recycle sponge siliceous spicules as a source of exogenous material to strengthen the larval–pupal cases and the digestive system. The results of the Thai sponge model contribute to the inventory of global engineering species richness, ecosystem types, and biogeographic diversity, thus raising awareness for freshwater biodiversity conservation. In this regard, the present data, along with the worldwide inventory, focus on sponges as (a) key habitat-forming species for aquatic insect assemblages, (b) ecosystem engineers in river/lake/wetland ecosystems, providing water purification, the processing of organic matter, recycling of nutrients, and freshwater–terrestrial coupling, and (c) promising candidates in restoration projects of tropical freshwater ecosystems by bioremediation.

Rapid bioassessment for water quality has not been established in Loa PDR. This study provides baseline information on the composition and distribution of benthic macroinvertebrate diversity and Trichoptera adults in two streams and three wadeable rivers for future rapid bioassessment in Lao PDR. Benthic macroinvertebrates were collected at each site in 20 sweeps using a D-Frame net (450 µm mesh size) in April 2017, 2018, and November 2017. Adults of Trichoptera were collected using an ultraviolet light trap. A total of 4,539 benthic macroinvertebrates belonging to 176 taxa, 84 families, 15 orders, and 3 phyla were found. Ephemeroptera and Trichoptera were the two orders with the most taxa richness and abundance. A total of 160 species in 16 families of Trichoptera adults were found. Leptoceridae and Hydropsychidae were diverse and abundant family. Agricultural activities had altered water to high electrical conductivity, high total dissolved solids and increased nutrient input even though almost all sampling sites were classified by the National Water Quality Standard as good water quality. Total taxa richness of benthic macroinvertebrates decreased with increasing disturbance. In contrast, high electrical conductivity and total dissolved solids at Nam Hinboun, a preserved area with no human disturbance exhibited the natural characteristics of a karst river. Canonical Correspondence Analysis revealed that physical variables, especially water velocity and water depth, determined benthic macroinvertebrate assemblages rather than chemical variables. The composition and distribution of Trichoptera larvae were determined by their species-specific ecological requirements. Benthic macroinvertebrate assemblages could respond to physico-chemical variables of streams better than the EPT taxa or Trichoptera taxa (both larvae and adults) and using macroinvertebrate assemblages to detect change in streams is promising.