Effects of imidacloprid on the survival and biomarker responses of Eristalis tenax larvae (Diptera: Syrphidae): a comparative study between indoor and outdoor exposures.

Imidacloprid is a widely used pesticide in agriculture. It is being found in aquatic ecosystems in agricultural regions. This study aimed to evaluate its effects on the survival rates, acetylcholinesterase (AChE) and catalase (CAT) responses of larval Eristalis tenax hoverflies. The larvae were exposed for 3, 7 and 14 days to increasing concentrations of imidacloprid (0, 0.1, 0.5 and 2 mg L-1) both indoors at a constant temperature of 20 °C and outdoors under varying environmental conditions. The results revealed that indoors and outdoors, the mortality of E. tenax significantly increased with increasing imidacloprid concentration and duration of exposure. Median lethal concentrations (LC50) varied from 0.03 to 0.17 mg L-1 depending on the duration and conditions of exposure. Indoors, AChE activity decreased in all the treatments for all three exposure durations, whereas outdoors the decrease was observed after the short (3-day) and long (14-day) exposure durations. AChE inhibition ranged from 6% to 62% (indoors) and 12% to 62% (outdoors). Variations in CAT activity were observed for both experimental setups, with a decrease outdoors in larvae exposed to 0.5 mg L-1 for 7 days and a gradual dose-dependent increase indoors for exposure lasting 3 and 7 days. This study sheds light on the potential ecological implications of imidacloprid contamination which may cause the decline of aquatic insect populations and pollination rates, leading to disruptions of the food chain and the overall decline of aquatic and terrestrial ecosystem health.

Climate-influenced vector-borne diseases in Africa: a call to empower the next generation of African researchers for sustainable solutions.

We look at the link between climate change and vector-borne diseases in low- and middle-income countries in Africa. The large endemicity and escalating threat of diseases such as malaria and arboviral diseases, intensified by climate change, disproportionately affects vulnerable communities globally. We highlight the urgency of prioritizing research and development, advocating for robust scientific inquiry to promote adaptation strategies, and the vital role that the next generation of African research leaders will play in addressing these challenges. Despite significant challenges such as funding shortages within countries, various pan-African-oriented funding bodies such as the African Academy of Sciences, the Africa Research Excellence Fund, the Wellcome Trust, the U.S. National Institutes of Health, and the Bill and Melinda Gates Foundation as well as initiatives such as the African Research Initiative for Scientific Excellence and the Pan-African Mosquito Control Association, have empowered (or are empowering) these researchers by supporting capacity building activities, including continental and global networking, skill development, mentoring, and African-led research. This article underscores the urgency of increased national investment in research, proposing the establishment of research government agencies to drive evidence-based interventions. Collaboration between governments and scientific communities, sustained by pan-African funding bodies, is crucial. Through these efforts, African nations are likely to enhance the resilience and adaptive capacity of their systems and communities by navigating these challenges effectively, fostering scientific excellence and implementing transformative solutions against climate-sensitive vector-borne diseases.

Local-Scale DNA Barcoding of Afrotropical Hoverflies (Diptera: Syrphidae): A Case Study of the Eastern Free State of South Africa.

The Afrotropical hoverflies remain an understudied group of hoverflies. One of the reasons for the lack of studies on this group resides in the difficulties to delimit the species using the available identification keys. DNA barcoding has been found useful in such cases of taxonomical uncertainty. Here, we present a molecular study of hoverfly species from the eastern Free State of South Africa using the mitochondrial cytochrome-c oxidase subunit I gene (COI). The identification of 78 specimens was achieved through three analytical approaches: genetic distances analysis, species delimitation models and phylogenetic reconstructions. In this study, 15 nominal species from nine genera were recorded. Of these species, five had not been previously reported to occur in South Africa, namely, Betasyrphus inflaticornis Bezzi, 1915, Mesembrius strigilatus Bezzi, 1912, Eristalinus tabanoides Jaennicke, 1876, Eristalinus vicarians Bezzi, 1915 and Eristalinus fuscicornis Karsch, 1887. Intra- and interspecific variations were found and were congruent between neighbour-joining and maximum likelihood analyses, except for the genus Allograpta Osten Sacken, 1875, where identification seemed problematic, with a relatively high (1.56%) intraspecific LogDet distance observed in Allograpta nasuta Macquart, 1842. Within the 78 specimens analysed, the assembled species by automatic partitioning (ASAP) estimated the presence of 14-17 species, while the Poisson tree processes based on the MPTP and SPTP models estimated 15 and 16 species. The three models showed similar results (10 species) for the Eristalinae subfamily, while for the Syrphinae subfamily, 5 and 6 species were suggested through MPTP and SPTP, respectively. Our results highlight the necessity of using different species delimitation models in DNA barcoding for species diagnoses.

Habitat components and population density drive plant litter consumption by Eudrilus eugeniae (Oligochaeta) under tropical conditions.

The ingestion of organic and mineral materials by earthworms is a prominent functional role that has profound consequences for the decomposition and stabilization of soil organic matter. To investigate the litter consumption of the African nightcrawler earthworm Eudrilus eugeniae under different tropical conditions, we used DNA barcoding to identify specimens of E. eugeniae collected from sites across the Adamawa region in Cameroon, and studied the influence of habitat suitability (soil properties), soil moisture, litter type, and population density on litter consumption. A total of four litter consumption experiments were carried out using soils collected from refuse disposal sites, agricultural lands, and savannahs dominated by the Mexican sunflower Tithonia diversifolia. The results revealed that litter consumption significantly increased in the refuse disposal and agricultural soils as opposed to the Mexican sunflower (T. diversifolia) soil, a cow dung enriched substrate, and a sterile soil horizon from the savannah (P < 0.05). The optimum moistures for litter consumption were between 24% and 50%. Litter type did not affect the consumption rate of the earthworms (P > 0.05). We observed a general positive density-dependent consumption with litter mass loss increasing with increasing density. Our results suggest that E. eugeniae has a strong direct effect on the decomposition of plant materials than expected from previous estimations, and that litter consumption rates are determined by several habitat components and population density.

Probabilistic health risk assessment of heavy metals at wastewater discharge points within the Vaal River Basin, South Africa.

Recently in South Africa, wastewater treatment plants (WWTP) have come under scrutiny because of increased reports of their ineffectiveness to treat wastewater adequately. This study focused on assessing potential health risks for humans exposed to concentrations of heavy metals in river systems that receive effluents from wastewater treatment plants in the Maluti-a-Phofung municipality. Untreated influents and treated effluents from two plants, one in the town of Phuthaditjhaba, the other in the town of Harrismith, were analysed for heavy metals. Water samples were also collected from the Elands and the Wilge Rivers, which receive effluents from the treatment plants in Phuthaditjhaba and Harrismith, respectively. All samples were analysed for heavy metals; Iron (Fe), Magnesium (Mg), Manganese (Mn), Zinc (Zn), Copper (Cu), Chromium (Cr), Nickel (Ni), Lead (Pb), Cobalt (Co), Arsenic (As), Cadmium (Cd) using Inductively Coupled Plasma Mass Spectrometry. The probabilistic human health risk was estimated using the Total Hazard quotient and Monte Carlo techniques. The results showed that there was no significant difference between treated and untreated wastewater (P > 0.05) in the concentration of heavy metals for both wastewater treatment plants using the student T-test. This indicated the inability of both treatment plants to remove metal contaminants adequately. Projections of non-cancer risk for metals in river water samples indicated a high potential for non-cancer risk for humans upon exposure via ingestion, with Arsenic being a significant contributor to overall risk. The results of this study underscore the need for improved wastewater treatment facilities in this region in order to ensure ecosystem integrity and public health safety.

Biochar alleviates the toxicity of imidacloprid and silver nanoparticles (AgNPs) to Enchytraeus albidus (Oligochaeta).

The present study investigated the use of biochar for the alleviation of the toxic effects of a nanosilver colloidal dispersion and a chloronicotinyl insecticide. The survival and reproduction of the potworm Enchytraeus albidus were assessed after exposure to imidacloprid and silver nanoparticles (AgNPs). E. albidus was exposed to 0, 25, 50, 100, 200, and 400 mg imidacloprid/kg and 0, 5, 25, 125, and 625 mg Ag/kg for 21 days in 10% biochar amended and non-biochar amended OECD artificial soil. In both exposure substrates, the effects of imidacloprid on survival were significant in the two highest treatments (p < 0.01). No biochar effect was observed as survival was statistically similar in both soils after exposure to imidacloprid. In the case of AgNPs, significant mortality was only observed in the highest AgNP treatments in both the amended and non-amended soils (p < 0.05). Nevertheless, statistically greater survival occurred in the biochar-amended treatment (p < 0.05). Reproduction results showed a more pronounced biochar effect with an EC50 = 22.27 mg imidacloprid/kg in the non-amended soil and a higher EC50 = 46.23 mg imidacloprid/kg in the biochar-amended soil. This indicated a 2-fold decrease in imidacloprid toxicity due to biochar amendment. A similar observation was made in the case of AgNPs where a reproduction EC50 = 166.70 mg Ag/kg soil in the non-amended soil increased to an EC50 > 625 mg Ag/kg soil (the highest AgNP treatment) in the amended soil. This indicated at least a 3.7-fold decrease in AgNPs toxicity due to biochar amendment. Although more studies may be needed to optimize the easing effects of biochar on the toxicity of these chemicals, the present results show that biochar could be useful for the alleviation of the toxic effects of imidacloprid and silver nanoparticles in the soil.

The enchytraeid reproduction test (ERT): A potentially quick and affordable tool for the assessment of metal contaminated soils in emerging economies.

The enchytraeid reproduction test (ERT) was used to assess the ecotoxicity of selected mine tailings and agricultural soils from South Africa. The mine tailings had higher cumulative metal concentrations than agricultural soils. The most contaminated mine tailings significantly reduced the survival of the oligochaete Enchytraeus doerjesi whose reproduction was suppressed in all mine waste substrates. Because it reliably singled out the most contaminated substrate and was found easy to perform, we suggest that the ERT could be a quick and affordable tool for assigning intervention values for soil remediation in emerging economies such as South Africa.

Combined effects of metal contamination and temperature on the potworm Enchytraeus doerjesi (Oligochaeta).

Cadmium (Cd) and zinc (Zn) toxicity in Enchytraeus doerjesi after 28-day exposure experiments was studied at 15, 20, and 25 °C. Cd lethal concentration (LC)(50) decreased with increasing temperature (293.01 mg kg(-1) at 15 °C, 261.62 mg kg(-1) at 20 °C, 231.79 mg kg(-1) at 25 °C). In contrast, Zn LC(50) increased with increasing temperature (420.21 mg kg(-1) at 15 °C and 518.42 mg kg(-1) at 20 °C). At 25 °C, a Zn LC50 could not be computed owing to the lack of sufficient adult mortality (LC(50) > 640 mg kg(-1)). The reproductive output at 20 and 25 °C was similar for each metal. Cd EC(50) for reproduction increased between 15 and 20 °C (from 23.93 to 35.11 mg kg(-1)) and decreased between 20 °C and 25 °C (to 16.84 mg/kg). Zn EC(50) increased dramatically from 15 °C (41.47 mg kg(-1)) to 20 °C (111.75 mg kg(-1)), and then slightly from 20 °C to 25 °C (112.17 mg kg(-1)). This indicated that metal-temperature effects on E. doerjesi may vary depending on the endpoint. The deleterious effects of Cd on the survival of E. doerjesi increased steadily with increasing temperature. With regard to reproduction, Cd toxicity could be exacerbated by extreme temperatures (15 and 25 °C) although conflicting pressures between high temperature and Cd toxicity may have prevented higher reproduction beyond 20 °C. The effects of Zn toxicity on survival decreased consistently with increasing temperature. The marginal increase in Zn EC(50) between 20 and 25 °C may explain the lack of a significant change in reproduction between the two temperatures. Energy redistribution between the below organism and higher organization endpoints in response to metal contamination may further explain these results.