Glutathione S-transferase in the insect Apis mellifera macedonica kinetic characteristics and effect of stress on the expression of GST isoenzymes in the adult worker bee

Bioinsecticide spinosad poses multiple harmful effects on foragers of Apis mellifera

There are multifactorial causes for the recent decline in bee populations, which has resulted in compromised pollination and reduced biodiversity. Bees are considered one of the most important non-target insects affected by insecticides used in crop production. In the present study, we investigated the effects of acute oral exposure to spinosad on the survival, food consumption, flight behavior, respiration rate, activity of detoxification enzymes, total antioxidant capacity (TAC), brain morphology, and hemocyte count of Apis mellifera foragers. We tested six different concentrations of spinosad for the first two analyses, followed by LC₅₀ (7.7 mg L^-1) for other assays. Spinosad ingestion decreased survival and food consumption. Exposure to spinosad LC₅₀ reduced flight capacity, respiration rate, and superoxide dismutase activity. Furthermore, this concentration increased glutathione S-transferase activity and the TAC of the brain. Notably, exposure to LC₅₀ damaged mushroom bodies, reduced the total hemocyte count and granulocyte number, and increased the number of prohemocytes. These findings imply that the neurotoxin spinosad affects various crucial functions and tissues important for bee performance and that the toxic effects are complex and detrimental to individual homeostasis.

Biomarkers of oxidative stress in the post-embryonic characterization of the neotropical annual killifish

Annual killifish are among the most remarkable extremophile species with the shortest vertebrate life span. Few studies have reported on the oxidative balance throughout their life cycle and its association to the natural aging process of these neotropical animals in a natural environment. We standardized and analyzed physiological markers related to the redox balance of the annual killifish (Cynopoecilus fulgens) throughout the post-embryonic life cycle (enzyme activity of Superoxide Dismutase, Catalase, Glutathione Peroxidase, and Glutathione S-transferase, as well as the determination of the levels of Lipoperoxidation, Carbonylated Proteins, and Total Proteins). We tested the influence of environmental variables on these biomarkers. Individuals were collected, including juveniles, adults, and seniles, in three sampling units around the Parque Nacional da Lagoa do Peixe, located in the Coastal Plain of Rio Grande do Sul. We observed that males and females used different physiological strategies of their redox balance during their life cycle, and their oxidative balance was influenced by their reproductive period and environmental variables (water temperature, abundance of predators, abundance of another sympatric annual killifish species, and abundance of C. fulgens). The population of each temporary pond presented different physiological responses to the adaptation of their life cycle, and there was an influence of environmental component as a modulator of this cycle. Our study offers reference values that will be useful for comparison in future research with short-lived organisms.

Review on Sublethal Effects of Environmental Contaminants in Honey Bees (Apis mellifera), Knowledge Gaps and Future Perspectives

Honey bees and the pollination services they provide are fundamental for agriculture and biodiversity. Agrochemical products and other classes of contaminants, such as trace elements and polycyclic aromatic hydrocarbons, contribute to the general decline of bees' populations. For this reason, effects, and particularly sublethal effects of contaminants need to be investigated. We conducted a review of the existing literature regarding the type of effects evaluated in Apis mellifera, collecting information about regions, methodological approaches, the type of contaminants, and honey bees' life stages. Europe and North America are the regions in which A. mellifera biological responses were mostly studied and the most investigated compounds are insecticides. A. mellifera was studied more in the laboratory than in field conditions. Through the observation of the different responses examined, we found that there were several knowledge gaps that should be addressed, particularly within enzymatic and molecular responses, such as those regarding the immune system and genotoxicity. The importance of developing an integrated approach that combines responses at different levels, from molecular to organism and population, needs to be highlighted in order to evaluate the impact of anthropogenic contamination on this pollinator species.

Salinity stress from the perspective of the energy-redox axis: Lessons from a marine intertidal flatworm

In the context of global change, there is an urgent need for researchers in conservation physiology to understand the physiological mechanisms leading to the acquisition of stress acclimation phenotypes. Intertidal organisms continuously cope with drastic changes in their environmental conditions, making them outstanding models for the study of physiological acclimation. As the implementation of such processes usually comes at a high bioenergetic cost, a mitochondrial/oxidative stress approach emerges as the most relevant approach when seeking to analyze whole-animal responses. Here we use the intertidal flatworm Macrostomum lignano to analyze the bioenergetics of salinity acclimation and its consequences in terms of reactive oxygen/nitrogen species formation and physiological response to counteract redox imbalance. Measures of water fluxes and body volume suggest that M. lignano is a hyper-/iso-regulator. Higher salinities were revealed to be the most energetically expensive conditions, with an increase in mitochondrial density accompanied by increased respiration rates. Such modifications came at the price of enhanced superoxide anion production, likely associated with a high caspase 3 upregulation. These animals nevertheless managed to live at high levels of environmental salinity through the upregulation of several mitochondrial antioxidant enzymes such as superoxide dismutase. Contrarily, animals at low salinities decreased their respiration rates, reduced their activity and increased nitric oxide formation, suggesting a certain degree of metabolic arrest. A contradictory increase in dichlorofluorescein fluorescence and an upregulation of gluthathione-S-transferase pi 1 (GSTP1) expression were observed in these individuals. If animals at low salinity are indeed facing metabolic depression, the return to seawater may result in an oxidative burst. We hypothesize that this increase in GSTP1 could be a “preparation for oxidative stress”, i.e. a mechanism to counteract the production of free radicals upon returning to seawater. The results of the present study shed new light on how tolerant organisms carry out subcellular adaptations to withstand environmental change.

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High salinity induces O₂·- formation while hypo-salinity increases DCF fluorescence.

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Hypersalinity is accompanied by upregulation of antioxidant enzymes such as SOD.

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Hyposalinity causes animals to go into a certain degree of metabolic arrest.

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Low salinity also causes GST-pi upregulation as a preparation for reoxygenation.

Detoxification mechanisms of honey bees (Apis mellifera) resulting in tolerance of dietary nicotine

Insecticides are thought to be among the major factors contributing to current declines in bee populations. However, detoxification mechanisms in healthy, unstressed honey bees are poorly characterised. Alkaloids are naturally encountered in pollen and nectar, and we used nicotine as a model compound to identify the mechanisms involved in detoxification processes in honey bees. Nicotine and neonicotinoids have similar modes of action in insects. Our metabolomic and proteomic analyses show active detoxification of nicotine in bees, associated with increased energetic investment and also antioxidant and heat shock responses. The increased energetic investment is significant in view of the interactions of pesticides with diseases such as Nosema spp which cause energetic stress and possible malnutrition. Understanding how healthy honey bees process dietary toxins under unstressed conditions will help clarify how pesticides, alone or in synergy with other stress factors, lead to declines in bee vitality.

Modulation of Anopheles stephensi gene expression by nitroquine, an antimalarial drug against Plasmodium yoelii infection in the mosquito

Background

Antimalarial drugs may impact mosquito’s defense against Plasmodium parasites. Our previous study showed nitroquine significantly reduced infection of Anopheles stephensi by Plasmodium yoelii, but the underlying mechanism remains unclear. In order to understand how transmission capacity of An. stephensi was affected by nitroquine, we explored the transcriptome of adult females after different treatments, examined changes in gene expression profiles, and identified transcripts affected by the drug and parasite.

Methodology/Principal Findings

We extended massively parallel sequencing and data analysis (including gene discovery, expression profiling, and function prediction) to An. stephensi before and after Plasmodium infection with or without nitroquine treatment. Using numbers of reads assembled into specific contigs to calculate relative abundances (RAs), we categorized the assembled contigs into four groups according to the differences in RA values infection induced, infection suppressed, drug induced, and drug suppressed. We found both nitroquine in the blood meal and Plasmodium infection altered transcription of mosquito genes implicated in diverse processes, including pathogen recognition, signal transduction, prophenoloxidase activation, cytoskeleton assembling, cell adhesion, and oxidative stress. The differential gene expression may have promoted certain defense responses of An. stephensi against the parasite and decreased its infectivity.

Conclusions/Significance

Our study indicated that nitroquine may regulate several immune mechanisms at the level of gene transcription in the mosquito against Plasmodium infection. This highlights the need for better understanding of antimalarial drug’s impact on parasite survival and transmission. In addition, our data largely enriched the existing sequence information of An. stephensi, an epidemiologically important vector species.

Comparative proteomics reveal characteristics of life-history transitions in a social insect

Background

Honey bee (Apis mellifera) workers are characterized by complex social behavior. Their life-history is dominated by a period of within-nest activity followed by a phase of long-distance flights and foraging. General insights into insect metabolism imply that foraging onset is associated with fundamental metabolic changes, and theory on social evolution suggests metabolic adaptations that are advantageous for the colony as a whole.

Results

Here we address the life-history characteristics of workers with LC-MS/MS based relative quantification of major proteins. Our approach includes: i. Calculation of a false positive rate for the identifications, ii. Support of relative protein quantification results obtained from spectral count by non-parametric statistics, and iii. Correction for Type 1 error inflation using a bootstrap iteration analysis. Our data are consistent with the use of glucose as the main fuel for honey bee flight. Moreover, the data delivers information on the expression of ATPsynthases/ATPases, and provide new insights into nurse- and forager-specific patterns of protection against oxidative stress.

Conclusion

The results show the suitability of this approach to investigate fundamental biochemical changes in an insect, and provide new evidence for metabolic specializations that occur during the social ontogeny of worker honey bees.