Microplastic pollution in riverine ecosystems: threats posed on macroinvertebrates.

Microplastics (MPs) are pollutants of emerging concern that have been reported in terrestrial and aquatic ecosystems as well as in food items. The increasing production and use of plastic materials have led to a rise in MP pollution in aquatic ecosystems. This review aimed at providing an overview of the abundance and distribution of MPs in riverine ecosystems and the potential effects posed on macroinvertebrates. Microplastics in riverine ecosystems are reported in all regions, with less research in Africa, South America, and Oceania. The abundance and distribution of MPs in riverine ecosystems are mainly affected by population density, economic activities, seasons, and hydraulic regimes. Ingestion of MPs has also been reported in riverine macroinvertebrates and has been incorporated in caddisflies cases. Further, bivalves and chironomids have been reported as potential indicators of MPs in aquatic ecosystems due to their ability to ingest MPs relative to environmental concentration. Fiber and fragments are the most common types reported. Meanwhile, polyethylene, polypropylene, polystyrene, polyethylene terephthalate (polyester), polyamide, and polyvinyl chloride are the most common polymers. These MPs are from materials/polymers commonly used for packaging, shopping/carrier bags, fabrics/textiles, and construction. Ingestion of MPs by macroinvertebrates can physically harm and inhibit growth, reproduction, feeding, and moulting, thus threatening their survival. In addition, MP ingestion can trigger enzymatic changes and cause oxidative stress in the organisms. There is a need to regulate the production and use of plastic materials, as well as disposal of the wastes to reduce MP pollution in riverine ecosystems.

Functional groups of Afrotropical EPT (Ephemeroptera, Plecoptera and Trichoptera) as bioindicators of semi-urban pollution in the Tsitsa River Catchment, Eastern Cape, South Africa.

We examined the distribution patterns of Ephemeroptera, Plecoptera, and Trichoptera functional feeding groups (EPT FFGs) in five streams that drain semi-urban landscapes in the Tsitsa River catchment, Eastern Cape Province of South Africa. We undertook macroinvertebrate and physicochemical analysis over four seasons between 2016 and 2017 at eight sites in three land-use categories (Sites 1, 2 and 3), representing an increasing gradient of semi-urban pollution. Five EPT FFGs (shredders, grazers/scrapers, predators, collector-gatherers and collector-filterers) were fuzzy coded and analyzed using RLQ-R (environmental characteristics of samples), L (taxa distribution across samples) and Q (species traits) and fourth-corner analyses. Physicochemical variables, including phosphate-phosphorus, total inorganic nitrogen and temperature, were the most influential variables that significantly influenced the distribution patterns of EPT FFGs in the Tsitsa River. RLQ and the fourth-corner model revealed varying responses of FFGs to semi-urban pollution. Of the five FFGs, collectors were the most abundant EPT FFGs in the study area, exhibiting disparate responses to disturbances, with collector-gatherers associated with impacted sites and significantly associated with phosphate-phosphorus. On the other hand, collector-filterers decreased with increasing semi-urban disturbance and exhibited a significant negative association with phosphate-phosphorus, total inorganic nitrogen and temperature. Overall, this study provides further insights into the environmental factors that influence the distribution patterns of FFGs in Afrotropical streams and the potential use of FFGs as indicators of anthropogenic pollution in tropical streams and rivers.

Quantifying the Influence of Larval Density on Disease Transmission Indices in Culex quinquefasciatus, the Major African Vector of Filariasis.

Larval crowding is one of the abiotic factors affecting biological fitness in mosquitoes. This study aims at elucidating, quantitatively, the influence of more larval crowding on aspects of fitness in Culex quinquefasciatus mosquito. To this end, day-old larvae of the species were reared in 4 density regimens equivalent to 1 larva in 1.25, 2.5, 5, and 10 mL of distilled water. Developmental indices, adult fitness indices, and accumulation and utilisation of teneral reserves for metamorphosis were determined at these density regimens. The results revealed varying significant negative effects of larval density on all fitness indices measured for the species. The study also revealed high utilisation of teneral reserves for metamorphosis at high larval densities. The information generated will be useful in making informed-decisions in allocating scare resources for vector control, although field trials are advocated to establish these laboratory findings.

Effects of Varying Photoperiodic Regimens on Critical Biological Fitness Traits of Culex quinquefasciatus (Diptera: Culicidae) Mosquito Vector.

This study investigated the effects of varying photoperiodic conditions on critical life stages' parameters of Culex quinquefasciatus. To this end, first larval stage was reared under different constant photoperiodic regimens: 0, 6 (short), 12 (equal), 13 (prevailing condition), and 18 and 24 (long) hours of light (hL). Duration of development, survivorship, emergence successes, adult longevity, caloric indices (CIs), and utilisation of teneral reserves for metamorphosis at each regimen were monitored. Analyses revealed significant negative effects of increasing photoperiod on all entomological variables measured. Short photo-phases elicited faster development times, increased life stages' survivorship and number at emergence, adult longevity, and CI for all life stages while increasing teneral components for adult life traits. The information generated in this study is important in understanding the role played by photoperiod in disease transmission and for development of integrated vector control strategies based on environmental manipulation.