Ingestion of Microplastic Fibres, But Not Microplastic Beads, Impacts Growth Rates in the Tropical House Cricket Gryllodes Sigillatus

The impact of microplastics on tissue-specific gene expression in the tropical house cricket, Gryllodes sigillatus

Microplastics are ubiquitous in our environment, resulting in animal exposure and consumption via food, water, and air. Animals that consume microplastics may suffer from physiological effects like immunotoxicity or mitochondrial dysfunction, but how specific tissues may differentially respond to plastic consumption is poorly understood, particularly in terrestrial insects. Here, we measured transcriptomic responses of tissues (midgut, hindgut, fat body and ovaries) to microplastic consumption in a generalist ground-dwelling insect, the tropical house cricket, Gryllodes sigillatus. Using this approach, we provide insights on how microplastics may impact specific organ systems. We generated a de novo transcriptome, a useful resource for further studies on this emerging model insect, that we then used to infer differential gene expression due to microplastic consumption in individual organs. Ingestion of microplastics elicited unique changes in gene expression depending on the tissue of focus, with notable differentially-expressed genes related to survival and stress pathways as well as those related to metabolism, immunity, and cancer.

Aquatic insects as mediator for microplastics pollution in a river ecosystem of Bangladesh

Microplastics (MPs) are emerging pollutants that threaten the aquatic ecosystem. Aquatic insects may play a crucial role in moving MPs into different trophic levels within and across the ecosystems. However, field-level evidence is still insufficient globally despite its tremendous ecological significance. Thus, for the first time in Bangladesh, MPs were explored in six species of aquatic insects along with water and sediment of the Daleshwari River. Digestion and density separation methods were used for the extraction of MPs. Microscopic inspection and Fourier transform spectroscopy (FT-IR) were done to identify and quantify MPs. The average concentration of MPs in sediment and water is 143.1 ± 28.52 of MPs/L and 30153.8 ± 2313.62 of MPs/kg, respectively. In aquatic species, the highest MPs found in D. rusticus (57.82 ± 14.98 MPs/g), followed by B. contaminate (38.53 ± 6.87 MPs/g), Ranatra sp. (34.05 ± 5.39 MPs/g), C. servilia (26.99 ± 7.88 MPs/g), D. annulatus (16.44 ± 6.95 MPs/g), and O. sabina (14.13 ± 4.52 MPs/g). A total of eight types of polymers have been identified. It was important to notice that the studied aquatic insects bear similar MPs (size, shape, and color) found in water and sediments from the river. It reveals the potential for the insects (accumulators of MPs) to be a driving factor for the transport of the MPs across different ecosystems. It has also been found that Aquatic insect's size, weight, feeding habitat, and host reserviour could be responsible for MPs ingestion. In addition, ecological risk assessment (Contamination Factor, Nemerrow Pollution Index, Pollution Load Index, Polymer Hazard Index) indicates different levels of risk for the pertaining river ecosystem.

Growth, development, and life history of a mass-reared edible insect, Gryllodes sigillatus (Orthoptera: Gryllidae)

Edible insects offer a viable alternative protein source to help meet the protein demands of a growing population. Optimizing insect mass-rearing for food and feed production depends on an understanding of insect life history. However, supporting data on growth, development, and reproduction from hatch to adulthood is often not available for many farmed insects, such as the decorated cricket (Gryllodes sigillatus Walk.). Here, we describe the life history of G. sigillatus from hatch to adulthood at 30 °C for traits relevant for mass-rearing and colony management. Female crickets first reached adulthood after 29 d and weighed 292.0 mg ± 74.09 mg, and male crickets first reached adulthood after 35 d and weighed 200.96 mg ± 34.51 mg. Crickets had 7 nymphal instars most characterizable by head width. Sex was identified by the development of ovipositors in females, and wings in both sexes. Crickets oviposited 56.74 ± 31.77 eggs every 48 h over 30 d and eggs hatched after 10.6 ± 0.5 d. This information provides the foundation to start and manage a cricket colony, to conduct research on life history and performance, and to facilitate practitioners to make informed decisions about rearing practices or identify arising issues. We highlight ways that a fundamental understanding of cricket biology can be informative for optimizing cricket growth, reducing variability in yield, and informing future precision farming practices.

Disruption of midgut homeostasis by microplastics in Spodoptera frugiperda: Insights into inflammatory and oxidative mechanisms

Microplastics have evolved as widespread contaminants in terrestrial and aquatic environments, raising significant environmental concerns due to their persistence and bioaccumulation. In this study, we investigated the toxicity of polyethylene microplastics (PE-MPs) on the agricultural insect, Spodoptera frugiperda. Maize leaves containing three sizes (0.5 μm, 5 μm, and 50 μm) of PE-MPs were fed to fall armyworm larvae for 12 days at concentrations of 1.25 g/ L, 5 g/L, and 20 g/L. The results showed that smaller size and higher concentration of microplastics led to increased toxicity. Furthermore, different sizes and maximum concentrations of PE-MPs were selected for subsequent experiments to observe changes in histological and enzymatic biomarkers, midgut microbiome, and metabolic responses. Following PE-MPs exposure, inflammation signs and oxidative stress were detected in the midgut. Significant changes were also observed in midgut microbiota and metabolomes, most related with oxidative stress, inflammatory disorders, and energy metabolism. These results provide evidence of midgut damage and alterations in the microbiota and metabolome of S. frugiperda because of PE-MPs exposure, highlighting the harm that microplastics can inflict on agricultural insects. Additionally, the study lays a theoretical foundation for future research on the transmission of microplastics through the food chain in agricultural ecosystems.

Microplastic contaminant adsorption by graphene oxide layer

The increasing prevalence of microplastics in water sources poses significant threats to both human health and environmental sustainability. Bisphenol A (BPA) and polyethylene terephthalate (PET), two hazardous microplastic contaminants, are known to cause endocrine disruption and other health risks. This study investigates the potential of graphene oxide (GO) as an efficient adsorbent for the removal of these contaminants through detailed molecular interaction analysis. The adsorption efficiencies of GO were quantitatively assessed, demonstrating strong binding affinities of ∆G = - 9.50 kcal/mol for BPA and ∆G = - 6.90 kcal/mol for PET. The adsorption process is primarily governed by π-π stacking interactions between the aromatic structure of the microplastics and the polycyclic surface of GO, with additional contributions from hydrogen bonding and van der Waals forces. Computational simulations revealed consistent binding across specific active sites on the GO surface, indicating minimal variation in adsorption performance. These findings highlight the potential of GO-based filtration systems for large-scale water treatment applications, offering a promising approach to mitigating microplastic contamination and ensuring safer water supplies. These findings highlight the potential of GO-based filtration systems for large-scale water treatment applications, offering a promising approach to mitigating microplastic contamination and ensuring safer water supplies. Future research should focus on optimizing GO-based filtration techniques and exploring their long-term environmental impact.

Impact of Polystyrene Micro- and Nanoplastics on the Biological Traits of the Japanese Carpenter Ant, Camponotus japonicus Mayr (Hymenoptera: Formicidae)

Insects, being among the most diverse and abundant organisms in terrestrial ecosystems, are inevitably exposed to ubiquitous micro- and nanoplastic contaminants. Although studies on the impact of these contaminants on terrestrial insects are gradually emerging, they remain limited in scope. In this study, we investigated the biological traits (including foraging behavior, food assumption, digging ability, body weight and survival) of the Japanese carpenter ant, Camponotus japonicus, in response to exposure to polystyrene micro- and nanoplastic (PS-M/NP) solutions containing three particle sizes (0.05, 1 and 50 μm) and four concentrations (0.1, 1, 10 and 50 mg/mL). The results showed that worker ants exhibited significant foraging preference and food consumption for non-contaminated solutions in multiple-choice experiments, indicating that worker ants C. japonicus can differentiate and avoid feeding on PS-M/NP-contaminated solutions. Meanwhile, PS-M/NPs significantly reduced the foraging ability of worker ants in multiple-choice and no-choice experiments, with the smallest particle size (0.05 μm) and highest concentration (50 mg/mL) of PS-M/NPs resulting in the longest pre-foraging period, the lowest percentage of licking and the amount of food consumption. In addition, the weight of sand removed by worker ants, the body weight and survival of worker ants showed a dramatic decline with a decrease in particle size, increase in concentration and prolonged in exposure time of PS-M/NP-contaminated solutions. The results of this study confirm that PS-M/NPs have an adverse effect on these worker ants in a particle size, concentration and exposure time-dependent manner, with small particle size, high concentration and longer exposure time being the key factors in decreasing the foraging behavior and biological traits of this insect.

Interaction of micro and nanoplastics (MNPs) with agricultural stored products and their pests

Micro and nanoplastics (MNPs) pose significant environmental concerns due to their potential implications for ecosystems and human health. While previous research has primarily focused on the environmental impacts (aquatic ecosystem, soil health) of MNPs, this review investigates their interactions with agricultural stored products, specifically their effects on stored product pests and grain quality. MNPs can infiltrate grains through various pathways, including atmospheric deposition, plastic residues from cultivation, and pest activity. These contaminants may influence pest feeding and behavioral patterns, reproductive cycles, and development. Simultaneously, MNPs have the potential to alter grain properties, including mineral content, protein composition, and starch synthesis, potentially compromising nutritional quality. Understanding these interactions is critical for developing strategies to mitigate the dual threats of MNP pollution and pest infestations to stored agricultural products.

Insecticide tolerance of the malaria vector Anopheles gambiae following larval exposure to microplastics and insecticide

Microplastic (MP) pollution poses a global threat to urban and rural environments and can have negative effects on a range of organisms. Mosquito larvae often breed in water contaminated with MPs, and given their important role as disease vectors, understanding the effects of larval exposure to MPs is critical for understanding the potential impact on their life history traits and subsequent methods for their control. Here, we have exposed first instar larvae of Anopheles gambiae s.s. to environmentally realistic concentrations of PET microplastics (1.0-7.5 μm) and a sub-lethal dose of insecticide mixed with microplastics, and quantified survival, development, and susceptibility of larvae over six generations. Adult mosquitoes from larvae exposed to these treatments were subsequently tested for insecticide resistance. Exposure to MPs decreased larval survival rates compared to the control; however, over six generations of exposure, survival rates significantly increased. Similarly, there was a higher survival rate of those larvae exposed to MPs mixed with insecticide compared to those exposed to just the insecticide, and survival increased further over the six generations. For the adult mosquito susceptibility tests, knockdown times (KDTs) indicated some level of insecticide tolerance when larvae had been previously exposed to MPs and insecticides. This is the first study demonstrating the selection of insecticide tolerance in adult mosquitoes after consecutive generations of larval exposures to varying concentrations of MPs. Therefore, field-scale studies are now urgently required to quantify whether larval insecticides are less effective at controlling mosquitoes in breeding sites commonly polluted with MPs.

Characterization of microplastics found in mosquito oviposition habitats

This study examined the presence and characteristics of microplastics (MPs) in water collected from potential mosquito oviposition habitats in Lubbock, TX. Water samples ranging from 10 to 1000 mL were collected from 36 suspected artificial and natural oviposition habitats, and sites were categorized as artificial containers, tires, or natural sites. Samples were filtered through a series of stainless-steel sieves and isopore membrane filters, and MPs were imaged and counted using a stereo microscope. MPs were classified by shape into fragments, fibers, films, spheres, and foams. Scanning Electron Microscopy (SEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA)were employed to characterize the size, morphology, and polymer type of MPs collected from a subset of oviposition habitats. Results suggest MPs are commonly found in artificial containers and tires, and at higher concentrations than natural sites. Furthermore, MPs found in all potential oviposition sites were predominantly fragments and fibers. SEM analysis revealed diverse morphologies and indicated potential microbial colonization on MP surfaces. Ultimately, this study provides insights into the distribution and characteristics of MPs in mosquito oviposition habitats, highlighting the potential impact of MP pollution and the potential effects on mosquito biology, and serves as a foundation for further research on the ecological implications of MPs in mosquito oviposition habitats.

Microplastic exposure reduced the defecation rate, altered digestive enzyme activities, and caused histological and ultracellular changes in the midgut tissues of the ground beetle (Blaps polychresta)

Concerns about microplastic (MP) pollution in terrestrial systems are increasing. It is believed that the overall amount of MPs in the terrestrial system could be 4-23 times higher than that in the ocean. Agricultural ecosystems are among the most polluted areas with MPs. Terrestrial organisms such as ground beetles, will be more vulnerable to MPs in various agricultural soil types because they are common in garden and agricultural areas. Therefore, this work aims to assess for the first time the potential adverse effects of chronic exposure for 30 days of ground beetles to a field-realistic concentration of 2 % (w/w) of three different irregularly shaped MPs polymers: Polystyrene (PS), polyethylene terephthalate (PET), and polyamide 6 (PA; i.e., nylon 6) on their health. The results showed no effect on beetle survival; nevertheless, there was a decrease in beetle defecation rate, particularly in beetles exposed to PS-MPs, and a change in the activity of midgut digestive enzymes. The effects on digestive enzymes (amylase, protease, lipase, and α-glucosidase) were polymer and enzyme specific. Furthermore, histological and cytological studies demonstrated the decomposition of the midgut peritrophic membrane, as well as abnormally shaped nuclei, vacuolation, disordered microvilli, necrosis of goblet and columnar cells, and necrosis of mitochondria in midgut cells. Given the importance of ground beetles as predators in most agricultural and garden settings, the reported adverse impacts of MPs on their health may impact their existence and ecological functions.

Plastic pollution in terrestrial ecosystems: Current knowledge on impacts of micro and nano fragments on invertebrates

The increasing accumulation of small plastic particles, in particular microplastics (>1 µm to 5 mm) and nanoplastics (< 1 µm), in the environment is a hot topic in our rapidly changing world. Recently, studies were initiated to better understand the behavior of micro- and nanoplastics (MNP) within complex matrices like soil, as well as their characterization, incorporation and potential toxicity to terrestrial biota. However, there remains significant knowledge gaps in our understanding of the wide-extent impacts of MNP on terrestrial invertebrates. We first summarized facts on global plastic pollution and the generation of MNP. Then, we focused on compiling the existing literature examining the consequences of MNP exposure in terrestrial invertebrates. The diversity of investigated biological endpoints (from molecular to individual levels) were compiled to get a better comprehension of the effects of MNP according to different factors such as the shape, the polymer type, the organism, the concentration and the exposure duration. The sublethal effects of MNP are acknowledged in the literature, yet no general conclusion was drawn as their impacts are highly dependent on their characteristic and experimental design. Finally, the synthesis highlighted some research gaps and remediation strategies, as well as a protocol to standardize ecotoxicological studies.

Co-exposure to polyethylene fiber and Salmonella enterica serovar Typhimurium alters microbiome and metabolome of in vitro chicken cecal mesocosms

Humans and animals encounter a summation of exposures during their lifetime (the exposome). In recent years, the scope of the exposome has begun to include microplastics. Microplastics (MPs) have increasingly been found in locations, including in animal gastrointestinal tracts, where there could be an interaction with Salmonella enterica serovar Typhimurium, one of the commonly isolated serovars from processed chicken. However, there is limited knowledge on how gut microbiomes are affected by microplastics and if an effect would be exacerbated by the presence of a pathogen. In this study, we aimed to determine if acute exposure to microplastics in vitro altered the gut microbiome membership and activity. The microbiota response to a 24 h co-exposure to Salmonella enterica serovar Typhimurium and/or low-density polyethylene (PE) microplastics in an in vitro broiler cecal model was determined using 16S rRNA amplicon sequencing (Illumina) and untargeted metabolomics. Community sequencing results indicated that PE fiber with and without S. Typhimurium yielded a lower Firmicutes/Bacteroides ratio compared with other treatment groups, which is associated with poor gut health, and overall had greater changes to the cecal microbial community composition. However, changes in the total metabolome were primarily driven by the presence of S. Typhimurium. Additionally, the co-exposure to PE fiber and S. Typhimurium caused greater cecal microbial community and metabolome changes than either exposure alone. Our results indicate that polymer shape is an important factor in effects resulting from exposure. It also demonstrates that microplastic-pathogen interactions cause metabolic alterations to the chicken cecal microbiome in an in vitro chicken cecal mesocosm.

IMPORTANCE

Researching the exposome, a summation of exposure to one's lifespan, will aid in determining the environmental factors that contribute to disease states. There is an emerging concern that microplastic-pathogen interactions in the gastrointestinal tract of broiler chickens may lead to an increase in Salmonella infection across flocks and eventually increased incidence of human salmonellosis cases. In this research article, we elucidated the effects of acute co-exposure to polyethylene microplastics and Salmonella enterica serovar Typhimurium on the ceca microbial community in vitro. Salmonella presence caused strong shifts in the cecal metabolome but not the microbiome. The inverse was true for polyethylene fiber. Polyethylene powder had almost no effect. The co-exposure had worse effects than either alone. This demonstrates that exposure effects to the gut microbial community are contaminant-specific. When combined, the interactions between exposures exacerbate changes to the gut environment, necessitating future experiments studying low-dose chronic exposure effects with in vivo model systems.

Exposure Pathways and Toxicity of Microplastics in Terrestrial Insects

The detrimental effects of plastics on aquatic organisms, including those of macroplastics, microplastics, and nanoplastics, have been well established. However, knowledge on the interaction between plastics and terrestrial insects is limited. To develop effective strategies for mitigating the impact of plastic pollution on terrestrial ecosystems, it is necessary to understand the toxicity effects and influencing factors of plastic ingestion by insects. An overview of current knowledge regarding plastic ingestion by terrestrial insects is provided in this Review, and the factors influencing this interaction are identified. The pathways through which insects interact with plastics, which can lead to plastic accumulation and microplastic transfer to higher trophic levels, are also discussed using an overview and a conceptual model. The diverse impacts of plastic exposure on insects are discussed, and the challenges in existing studies, such as a limited focus on certain plastic types, are identified. Further research on standardized methods for sampling and analysis is crucial for reliable research, and long-term monitoring is essential to assess plastic trends and ecological impacts in terrestrial ecosystems. The mechanisms underlying these effects need to be uncovered, and their potential long-term consequences for insect populations and ecosystems require evaluation.

Unravelling the microplastic menace: Different polymers additively increase bee vulnerability

Microplastics (MPs) are growing and ubiquitous environmental pollutants and represent one of the greatest contemporary challenges caused by human activities. Current research has predominantly examined the singular toxicological effects of individual polymers, neglecting the prevailing reality of organisms confronted with complex contaminant mixtures and potential synergistic effects. To fill this research gap, we investigated the lethal and sublethal effects of two common MPs, polystyrene (PS - 4.8-5.8 μm) and poly(methyl methacrylate) (PMMA - 1-40 μm), and their combination (MIX), on the pollinating insect Apis mellifera. For each treatment, we evaluated the oral toxicity of two ecologically relevant and one higher concentration (0.5, 5 and 50 mg/L) and analysed their effects on the immune system and worker survival. As immune activation can alter the cuticular hydrocarbon profile of honey bees, we used gas chromatography-mass spectrometry (GC-MS) to investigate whether MPs lead to changes in the chemical profile of foragers and behavioural assay to test whether such changes affect behavioural patterns of social recognition, undermining overall colony integrity. The results indicate an additive negative effect of PS and PMMA on bee survival and immune response, even at ecologically relevant concentrations. Furthermore, alterations in cuticle profiles were observed with both MPs at the highest and intermediate concentrations, with PMMA being mainly responsible. Both MPs exposure resulted in a reduction in the abundance of several cuticular compounds. Hive entry guards did not show increased inspection or aggressive behaviour towards exposed foragers, allowing them to enter the colony without being treated differently from uncontaminated foragers. These findings raise concerns not only for the health of individual bees, but also for the entire colony, which could be at risk if contaminated nestmates enter the colony undetected, allowing MPs to spread throughout the hive.

The digestive system of a cricket pulverizes polyethylene microplastics down to the nanoplastic scale

Microplastics (MPs; <5 mm) are a growing concern and a poorly understood threat to biota. We used a generalist insect (a cricket; Gryllodes sigillatus) to examine whether individuals would ingest and physically degrade MPs in their food. We fed crickets a range of concentrations (0, 2.5, 5, and 10% w/w) of fluorescent polyethylene MPs mixed into a standard diet and dissected the gut regions to isolate the MPs within. Comparing plastic content and fragment size within gut regions, we sought to identify whether and where crickets can fragment ingested MP particles. Given the digestive tract morphology of this species, we expected that the crickets would both ingest and egest the MPs. We also predicted that the MPs would be fragmented into smaller pieces during this digestive process. We found that G. sigillatus egested much smaller pieces than they ingested, and this fragmentation occurs early in the digestive process of this insect. We found this for both sexes as well as across the range of concentrations of MPs. The degree of plastic breakdown relative to plastic feeding time suggests that the ability to fragment MPs is intrinsic and not altered by how much time crickets have spent eating the plastics. The amount of plastics found in each region of the gut in relation to feeding time also suggests that this size and shape of PE microplastic does not cause any physical blockage in the gut. This lack of evidence for blockage is likely due to plastic breakdown. We found a ∼1000-fold reduction in plastic size occurs during passage through the digestive system, yielding particles very near nanoplastics (NPs; <1 μm), and likely smaller, that are then excreted back into the environment. These findings suggest that generalist insects can act as agents of plastic transformation in their environment if/when encountering MPs.

Quantifying microplastic ingestion, degradation and excretion in insects using fluorescent plastics

Plastic pollution is a growing threat to our natural environment. Plastic waste/pollution results from high emissions of both macro (>5 mm) and microplastics (MPs; <5 mm) as well as environmental fractioning of macroplastics into MPs. MPs have been shown to have a range of negative impacts on biota. Harmonized methods to accurately measure and count MPs from animal samples are limited, but what methods exist are not ideal for a controlled laboratory environment where plastic ingestion, degradation and elimination can be quantified and related to molecular, physiological and organismal traits. Here, we propose a complete method for isolating and quantifying fluorescent MPs by combining several previously reported approaches into one comprehensive workflow. We combine tissue dissection, organic material digestion, sample filtering and automated imaging techniques to show how fluorescently labelled MPs provided to insects (e.g. in their diet) in a laboratory setting can be isolated, identified and quantified. As a proof of concept, we fed crickets (Gryllodes sigillatus) a diet of 2.5% (w/w) fluorescently labelled plastics and isolated and quantified plastic particles within the gut and frass.

No Effect of Realistic Microplastic Exposure on Growth and Development of Wild-caught Culex (Diptera: Culicidae) Mosquitoes

Microplastic (MP) pollution is a threat to environments around the world and mosquitoes are particularly affected because of their high chance of encountering MP as larvae. Mosquitoes have been shown to readily consume microplastics and they have a significant impact on health in society, yet we have limited knowledge on the effects of MP exposure on fitness-related traits. Additionally, the data we do have come primarily from studies that have used unrealistically high microplastic concentrations, or unrealistic methods of exposure. Here we exposed wild-type first instar Culex pipiens and Culex tarsalis larvae to two 4.8-5.8 μm polystyrene microplastic concentrations (0 particles/ml, 200 particles/ml, 20,000 particles/ml) to evaluate the effect of MP exposure on body size, development, and growth rate. We found no effect of microplastics on any of the traits in either species. These results indicate microplastic exposures comparable to levels found in nature have minimal effects on these fitness-related traits. Future directions for this work include examining whether the effects of MP exposure are exacerbated when evaluated in combination with other common stressors, such as warming temperatures, pesticides, and food limitation.