Collembola are Among the Most Pesticide-Sensitive Soil Fauna Groups: A Meta-Analysis

Ecotoxicological evaluation of an aqueous phytoextract of Melia azedarach L

Melia azedarach L. is a Meliaceae that has shown important insecticidal activities. However, few researchers have extensively studied the toxicology of aqueous extracts of M. azedarach (MAE). Therefore, the main objective of this study was to characterize the phyto-eco-toxicological profile of MAE. First, a botanical and phytochemical characterization of MAE was performed using a histological, and metabolomic multi-analytical approach. Second, the toxicological effects on pollinating insects (Apis mellifera ligustica) and soil collembola (Folsomia candida) were evaluated. In addition, acute toxicity was evaluated in zebrafish (Danio rerio) to assess effects on aquatic fauna, and toxicity was determined in human neuroblastoma (SH-SY5Y) and fibroblast (FB-21) cell models. Finally, phytotoxic effects on germination of Cucumis sativus L., Brassica rapa L. and Sorghum vulgare L. were considered. Metabolomic analyses revealed the presence of not only limonoids but also numerous alkaloids, flavonoids and terpenoids in MAE. Histological analyses allowed us to better localize the areas of leaf deposition of the identified secondary metabolites. Regarding the ecotoxicological data, no significant toxicity was observed in bees and collembola at all doses tested. In contrast, severe cardiac abnormalities were observed in zebrafish embryos at concentrations as low as 25 μg/mL. In addition, MAE showed toxicity at 1.6 μg/mL and 6.25 μg/mL in FB-21 and SH-SY5Y cells, respectively. Finally, MAE inhibited seed germination with inhibitory concentrations starting from 5.50 μg/mL in B. rapa, 20 μg/mL in S. vulgare, and 31 μg/mL in C. sativus. Although M. azedarach extracts are considered valuable natural insecticides, their ecological impact cannot be underestimated. Even the use of an environmentally friendly solvent (an aqueous solution), for the first time, is not without side effects. Therefore, the data collected in this study show the importance of evaluating the dosages, modes of administration and production methods of M. azedarach phytoextracts in agricultural settings.

A global meta-analysis reveals a consistent reduction of soil fauna abundance and richness as a consequence of land use conversion

Land use conversion of natural to production systems is one of the most important threats to belowground communities and to the key ecosystem processes in which they are involved. Available literature shows positive, negative, and neutral effects of land use changes on soil fauna communities; and these varying effects may be due to different characteristics of natural and production systems and soil organisms. We hypothesize that land conversion from high to low plant biomass, diversity, and structural complexity systems may have the most negative impacts on soil fauna. Here, we performed the first meta-analysis evaluating the overall effects of land use conversion on soil invertebrate communities and the influence of factors related to characteristics of natural and production systems, of soil fauna communities and methods. We compiled a dataset of 260 publications that yielded 1732 observations for soil fauna abundance and 459 for richness. Both abundance and richness showed a global decline as a consequence of natural land conversion to production systems. These negative effects were stronger, in general, when the conversion occurred in tropical and subtropical sites, and when natural systems were replaced by croplands, pastures and grazing systems. The effects of land use conversion also depended on soil property changes. In addition, the abundance of most taxa and richness of Acari and Collembola were strongly reduced by land use changes while Annelida were not affected. The highest reduction in abundance was recorded in omnivores and predators, whereas detritivores showed a reduction in richness. Our meta-analysis shows consistent evidence of soil biodiversity decline due to different land use changes and the partial dependence of those effects on the magnitude of changes in vegetation. These findings stress the need to continue developing production modes that effectively preserve soil biodiversity and ecosystem processes, without hampering food production.

Combined toxicity of abamectin and carbendazim on enzymatic and transcriptional levels in the soil-earthworm microcosm

To reveal the toxicological mechanisms of pesticide mixtures on soil organisms, this study concentrated on evaluating enzymatic activity and gene expression changes in the earthworm Eisenia fetida (Savigny 1826). Despite being frequently exposed to multiple pesticides, including the common combination of abamectin (ABA) and carbendazim (CAR), environmental organisms have primarily been studied for the effects of individual pesticides. Acute toxicity results exhibited that the combination of ABA and CAR caused a synergistic impact on E. fetida. The levels of MDA, ROS, T-SOD, and caspase3 demonstrated a significant increase across most individual and combined groups, indicating the induction of oxidative stress and cell death. Additionally, the expression of three genes (hsp70, gst, and crt) exhibited a significant decrease following exposure to individual pesticides and their combinations, pointing toward cellular damage and impaired detoxification function. In contrast, a noteworthy increase in ann expression was observed after exposure to both individual pesticides and their mixtures, suggesting the stimulation of reproductive capacity in E. fetida. The present findings contributed to a more comprehensive understanding of the potential toxicity mechanisms of the ABA and CAR mixture, specifically on oxidative stress, cell death, detoxification dysfunction, and reproductive capacity in earthworms. Collectively, these data offered valuable toxicological insights into the combined effects of pesticides on soil organisms, enhancing our understanding of the underlying risks associated with the coexistence of different pesticides in natural soil environments.

Using dietary exposure to determine sub-lethal effects from imidacloprid in two springtail (Collembola) species

Standard toxicity tests expose springtails (Collembola) through soil, while dietary exposure tests with animals visible on a surface are less commonly applied. We refined a method for dietary chemical exposure for two widely distributed and abundant Collembola species: Folsomia quadrioculata and Hypogastrura viatica as existing methods were sub-optimal. Newly hatched Collembola were offered bark with a natural layer of Cyanobacteria that was either moistened with a solution of the neonicotinoid insecticide imidacloprid using a micropipette or soaked in the solution overnight. The first method was superior in producing a measured concentration close to the nominal (0.21 and 0.13 mg/kg dry bark, respectively), and resulting in sub-lethal effects as expected. The adult body size was reduced by 8% for both species, but egg production only in H. viatica. Contrastingly, soaked bark resulted in a measured concentration of 8 mg/kg dry bark, causing high mortality and no egg production in either species. Next, we identified the sub-lethal concentration-range by moistening the bark to expose H. viatica to 0, 0.01, 0.04, 0.13, 0.43 and 1.2 mg imidacloprid/kg dry bark. Only the highest concentration affected survival, causing a mortality of 77%. Imidacloprid reduced moulting rate and the body size at first reproduction. The age at first reproduction appeared delayed as some replicates did not reproduce within the experiment duration. The method of moistened bark for dietary exposure proved optimal to continuously study life history traits, such as growth and reproductive outcomes, which are important to understand effects on key events crucial for population viability and growth.

Locomotion behavior testing as a complementary tool in Collembola avoidance assays with neurotoxic insecticides

This study aimed (1) to assess the ability of collembolans Folsomia candida to avoid soils contaminated with three seed dressing insecticides imidacloprid, clothianidin, and fipronil; (2) to assess the effects of the insecticides on collembolans' locomotion behavior; (3) to check if changes in the locomotion behavior would explain the avoidance/preference responses; and (4) to evaluate the possibility to use locomotion behavior as toxicity biomarker of the tested insecticides. Avoidance and locomotion behavior assays with collembolans F. candida were performed with commercial seed dressing formulations of three insecticides (imidacloprid, clothianidin, and fipronil). Results showed no avoidance behavior at any concentration, while a "preference" was observed with increasing concentrations of the three tested insecticides. Significant reductions in the locomotion of exposed collembolans were observed at ≥ 1 mg kg-1 for imidacloprid (18-38%) and fipronil (29-58%) and ≥ 4 mg kg-1 for clothianidin (10-47%). At the higher insecticide concentrations, the collembolans had their trajectories restricted to smaller areas, with a tendency for circular movements. Our results confirm that the "preference" for contaminated soils with neurotoxic substances is likely due to locomotion inhibition impairing the ability of organisms to escape. This effect highlights that only avoidance assays may be not sufficient to assure the safety of some substances and confirm the potential of locomotion behavior as a sensitive toxicity biomarker for neurotoxic insecticides.

Paraquat is toxic to the soil-dwelling arthropod, Folsomia candida (Collembola: Isotomidae), and has potential effects on its Wolbachia endosymbiont

The springtail, Folsomia candida, is a soil arthropod commonly used to evaluate environmental toxins. Conflicting data on the toxicity of the herbicide paraquat prompted re-evaluation of its effects on F. candida survival and reproduction. Paraquat has an LC₅₀ of about 80 μM when tested in the absence of charcoal; charcoal, often used in test arenas to facilitate visualization of the white Collembola, has a protective effect. Survivors of paraquat treatment fail to resume molting and oviposition, suggesting an irreversible effect on the Wolbachia symbiont that restores diploidy during parthenogenetic reproduction of this species.

Nano-based smart formulations: A potential solution to the hazardous effects of pesticide on the environment

Inefficient usage, overdose, and post-application losses of conventional pesticides have resulted in severe ecological and environmental issues, such as pesticide resistance, environmental contamination, and soil degradation. Advances in nano-based smart formulations are promising novel methods to decrease the hazardous impacts of pesticide on the environment. In light of the lack of a systematic and critical summary of these aspects, this work has been structured to critically assess the roles and specific mechanisms of smart nanoformulations (NFs) in mitigating the adverse impacts of pesticide on the environment, along with an evaluation of their final environmental fate, safety, and application prospects. Our study provides a novel perspective for a better understanding of the potential functions of smart NFs in reducing environmental pollution. Additionally, this study offers meaningful information for the safe and effective use of these nanoproducts in field applications in the near future.