Pesticide immunotoxicity on insects - Are agroecosystems at risk?

Elimination of certain honeybee venom activities by adipokinetic hormone

The primary aim of this study was to analyse the influence of honeybee venom on various aspects of Drosophila melanogaster physiology and to assess the efficacy of adipokinetic hormone (AKH) in mitigating venom toxicity. We examined the harmful effects of venom on the thoracic muscles and central nervous system of Drosophila, as well as the potential use of AKH to counteract these effects. The results demonstrated that envenomation altered AKH levels in the Drosophila CNS, promoted cell metabolism, as evidenced by an increase in citrate synthase activity in muscles, and improved relative cell viability in both organs incubated in vitro. Furthermore, venom treatment reduced the activity of two key antioxidative stress enzymes, superoxide dismutase and catalase, and modified the expression of six genes encoding immune system components (Keap1, Relish, Nox, Eiger, Gadd45, and Domeless) in both organs. The venom also disrupted muscle cell ultrastructure, specifically myofibrils, and increased the release of arginine kinase into the incubation medium. Notably, when administered alongside the venom, AKH influenced the majority of these changes. AKH was the most effective in minimising damage to the ultrastructure of muscle cells and preventing the release of arginine kinase from muscles to the medium; however, in other parameters, the effect was modest or minimal. Given that honeybee venom often affects humans, understanding its actions and potential ways to reduce or eliminate them is valuable and could lead to the development of pharmacologically important compounds that may have clinical relevance.

In Situ Electrochemical Reduction of Imidacloprid involving a Nitroso-Intermediate-Trapped DWCNT and Its Biomimetic Cellular Oxidative Stress-Related Mediated Oxidation of Thiols

Imidacloprid (IMP) is a widely used pesticide and insecticide known for its effectiveness in controlling pests and increasing crop yields. Exposure of the compound to water bodies has led to environmental pollution and adverse effects on human health. One major concern is the generation of oxidative-stress in the cellular system, which is often a result of IMP exposure. Although the exact mechanism of toxicity is not fully understood, it is believed that the nitroso-intermediate of IMP (IMP-NO) binds to acetylcholine receptors, disrupting neural function. Thiol pools in the blood serum act as antioxidants to mitigate the toxicity. This study presents an in situ electrochemical conversion of IMP into its key intermediate, IMP-NO, and its subsequent entrapment on a double-walled carbon nanotube-modified glassy carbon electrode (GCE/DWCNT@IMP-NO) as a surface confined redox-peak in a physiological solution. It was characterized by SEM, FTIR, Raman, SECM, and LC-MS techniques. The system exhibited excellent mediated oxidation of the thiol group, using cysteine as a model. The findings presented in this work correlate with observations related to cellular oxidative-stress and its thiol-assisted mitigation. Employing a Michaelis-Menten-type enzyme-substrate reaction mechanism and estimated the kinetic parameters. Chronoamperometric techniques were used to demonstrate the oxidative detection of thiol.

RNAi-mediated knockdown of HcCAT2 depresses the adaptive capacity of Hyphantria cunea larvae to cytisine and coumarin

The diversity of host plants is an important reason for the global spread of Hyphantria cunea. However, no studies have explored the role of the antioxidant defense system with catalase (CAT) as the core at the molecular level in the adaptation of the H. cunea to host plant secondary metabolites. Herein, the purpose is to explore how HcCAT2, highly expressed in cytisine- or coumarin-treated H. cunea larvae, mediates the adaptation of H. cunea to cytisine and coumarin, and to develop nucleic acid pesticides targeting HcCAT2. Findings revealed that H. cunea larvae treated with dsHcCAT2 alongside cytisine or coumarin exhibited significantly reduced body weight, survival rate, and expression levels of growth-related genes, energy metabolism genes, and oxidative damage regulatory genes compared to treated with cytisine or coumarin alone. HcCAT2 overexpression enhanced cell viability, lowered apoptosis rates, Ca2+ concentrations, ROS levels, and MPTP opening, and increased mitochondrial membrane potential in cytisine or coumarin-treated SF9 cells. Encapsulation of dsHcCAT2 in chitosan (CS) improved stability and gene silencing efficacy. CS-dsHcCAT2 treatment did not significantly affect SF9 cell, Lymantria dispar larvae, and Arma chinensis nymphs. However, H. cunea larvae treated with CS-dsHcCAT2 combined with cytisine or coumarin showed significantly reduced body weight and survival compared to those receiving secondary metabolites alone. Therefore, HcCAT2 is a critical antioxidant defense gene for adaptation of H. cunea larvae to cytisine and coumarin stress, with the ability of maintaining energy metabolism homeostasis and antioxidant defense level. The constructed CS-dsHcCAT2 can be developed as a synergistic agent for plant-derived pesticides.

Co-exposure to a honeybee pathogen and an insecticide: synergistic effects in a new solitary bee host but not in Apis mellifera

Pesticides and pathogens are major drivers of bee declines. However, their potential interactions are poorly understood, especially for non-Apis bees. This study assessed the combined effects of infestation by the honeybee pathogen Vairimorpha ceranae and chronic exposure to the insecticide flupyradifurone on Osmia bicornis and Apis mellifera. We investigated whether V. ceranae could reproduce in a new solitary bee host (O. bicornis) and assessed sublethal and lethal effects of the pathogen and the pesticide, alone and in combination. We also analysed the interactive effects of the combined exposure on V. ceranae proliferation and bee survival in the two bee species. Newly emerged bees were orally infected with 100 000 spores of V. ceranae and then exposed ad libitum to flupyradifurone at field-realistic concentrations. We showed, for the first time to our knowledge, that V. ceranae can replicate in the midgut of O. bicornis, causing histological damage, impaired phototactic response, reduced food consumption and decreased longevity. The pathogen-pesticide combination caused a synergistic effect in O. bicornis, leading to an abrupt survival decline. In A. mellifera, V. ceranae and flupyradifurone showed antagonistic survival effects, but the pesticide promoted pathogen proliferation. Our results warn against the potential effects of pathogen spillover and multiple stressor exposure on non-Apis bees.

Application and antagonistic mechanisms of atoxigenic Aspergillus strains for the management of fungal plant diseases

This review covers, for the first time, all methods based on the use of Aspergillus strains as biocontrol agents for the management of plant diseases caused by fungi and oomycetes. Atoxigenic Aspergillus strains have been screened in a variety of hosts, such as peanuts, maize kernels, and legumes, during the preharvest and postharvest stages. These strains have been screened against a wide range of pathogens, such as Fusarium, Phytophthora, and Pythium species, suggesting a broad applicability spectrum. The highest efficacies were generally observed when using non-toxigenic Aspergillus strains for the management of mycotoxin-producing Aspergillus strains. The modes of action included the synthesis of antifungal metabolites, such as kojic acid and volatile organic compounds (VOCs), secretion of hydrolytic enzymes, competition for space and nutrients, and induction of disease resistance. Aspergillus strains degraded Sclerotinia sclerotiorum sclerotia, showing high control efficacy against this pathogen. Collectively, although two Aspergillus strains have been commercialized for aflatoxin degradation, a new application of Aspergillus strains is emerging and needs to be optimized.