In holometabolous insects, life‐history characteristics can vary in response to diet. The main aim of this contribution was to examine which diet best promotes larval development and survival of the aquatic saprophagous hoverfly Eristalis tenax L. (Diptera: Syrphidae). This study was motivated by a need to optimize techniques for rearing these insects in captivity. We studied how adding yeast to several rearing media based on animal droppings or decaying plant material affected development and survival in captive larvae, and whether these effects could be optimized depending on the amount of yeast and the rearing medium. In addition, premature exit of larvae was examined in two medium volumes to investigate differences in pupation. Larvae in yeast supplemented rabbit growth medium pupated and emerged faster than those in horse and antelope growth media. A high number of adult females emerged when compared to males, and both seemed to have a shorter developmental period in yeast supplemented growth media. Pupal survival was significantly greater in a mixture of droppings and plant organic matter, and a high medium volume of 140 ml (p < 0.05). Between 10% and 17% of larvae prematurely exited the aquatic medium in high (140) and low (70 ml) medium volumes, respectively. These results provide additional information that may be crucial for the successful mass rearing of E. tenax in captivity, and suggest that apart from the addition of yeast, growth medium quality and volume may be limiting factors for the production of large colonies of adults.

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 degrees 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.

Extended use of glyphosate poses the problem of its accumulation into soil and further on crops. The objective of this study was to evaluate the effects of different doses of soil glyphosate on growth parameters and chlorophyll content of maize Zea mays L. and bean Phaseolus vulgaris L. plants. An experiment was arranged in randomized complete blocks design with ten replications. Glyphosate solutions were applied to the soil in six concentrations, two subdoses of 0.1 and 0.2 g, the recommended dose of 0.4 g and three overdoses of 0.6, 0.8 and 1.0 g kg-¹ of soil. An uncontaminated soil control was used. At 21, 28, 35 and 42 days after sowing (DAS), evaluations of plant height, number of leaves, stem diameter, leaf surface and plant injury were conducted. At 42 DAS, nodulation (in bean), root length, chlorophyll and dry matter yield were assessed. Already at the recommended dose and beyond, glyphosate caused significant damage to growth characteristics, nodulation and chlorophyll content in both plants. Some similar effects of the product were observed on the both plants at each time period. Therefore, there was an evidence that soil glyphosate already at the recommended dose had an inhibitory and even a phytocide effects on non-target plants.

With an obsolete livestock sector, Gabon relies on its huge hydrographic network rich in fish to supply its populations with animal proteins. This study aimed to conduct metal analyses in four fish species (Oreochromis niloticus, Clarias gariepinus, Chrysichthys nigrodigitatus, Polydactylus quadrifilis) frequently consumed by human populations in the Moyen-Ogooué and Haut-Ogooué Provinces of Gabon and infer the potential human health risks for those populations who rely on these freshwater produces as a source of proteins. Fish were sampled from Ezanga, Oguemoué, Onangué, Nguenè (Moyen-Ogooué) and Grand Poubara (Haut-Ogooué) Lakes during the high flow period (HF) and low flow period (LF) from 2021 to 2022, and analysed for seven heavy metals (HMs) using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) techniques. Throughout the flow periods, and regardless of the lake and fish species, Fe was found to have the highest concentration, followed by Al > Mn > Hg > Pb> As> Cd. The relatively high concentration of Hg was recorded in the muscle tissues of C. gariepinus (6.65 mg. kg⁻¹) sampled during the LF period at Grand Poubara. The concentrations of Hg found in the muscle of all fish species also exceeded the maximum acceptable limits set by the American Environmental Protection Agency. The concentrations of Fe in C. gariepinus (Grand Poubara, LF) and O. niloticus (Onangué, LF), and those of Al in O. niloticus (Nguenè, HF), P. quadrifilis (Onangué, HF) and C. nigrodigitatus (Oguemoué, LF) were amongst the highest concentrations ever reported on the African continent. Health risk assessments indicated a heightened risk of cancer for local populations consuming the fish species from all the lakes investigated. There is a need to implement an increased surveillance programme at national level in order to raise awareness and improve the management of fishery resources while preserving the environment and the health of local populations that rely upon these resources for their subsistence.

Since the establishment of a free economic zone and a simultaneous increase in the population of the QwaQwa region, aquatic systems of the area were expected to undergo an increase in metal contamination. The aims of this study were to assess the quality of sediments from the Metsi-Matsho, Namahadi and Elands Rivers of the QwaQwa region, and to investigate their impact on the survival and reproduction of the collembolan Folsomia candida. Due to the lack of freshwater sediment quality guidelines in South Africa, metal contents of the sediments were analysed and critically interpreted using the national action list for the screening of dredged sediment proposed for marine disposal, and international sediment quality guidelines (SQGs). In the laboratory, F. candida was exposed to 0, 50, 75 and 100% of the sediment samples for 28 days at 20 °C. Sediments were variably contaminated with Cr, with the Namahadi River middle site having the highest concentration (569 mg.kg⁻¹, dry weight) followed by the lower site on the Elands River (529 mg.kg⁻¹, dry weight), both above the recommended prohibition level of 500 mg Cr.kg⁻¹. According to the consensus-based SQGs, only the concentrations of Cr and Ni (upper reach of Metsi-Matsho River) were higher than probable effect concentration, denoting that harmful effects of those metals are likely to occur. Of the two endpoints assessed, reproduction was the most sensitive with the upper reach of the Metsi-Matsho River (half maximal effective concentration, EC₅₀ = 24% sediment) being the most deleterious site to the reproduction of F. candida. Ecotoxicological bioassays using F. candida could be suitable complements to chemical analysis in the assessment of the ecological risks of freshwater sediments as this collembolan species is sensitive to sediments with variable ranges of metal contamination.