Biology subjects

MacMillan, H. A.

Publications and source records attributed to MacMillan, H. A..

At least 19 recordsLinked to original sources

bioRxiv2026

Defecation in preparation for ecdysis drives microplastic clearance in cricket nymphs

Plastic pollution is widespread in both terrestrial and marine environments, creating significant ecological concerns. Animals that occupy lower trophic levels, like many small insects, can ingest and retain plastics for extended periods before eliminating them. Ecdysis, or moulting, occurs in arthropods during development and facilitates growth, but its role in microplastic (MP) clearance, and whether it is impacted by plastics, are largely unexplored. We used the cricket Gryllodes sigillatus to examine how moulting influences MP clearance in a hemimetabolous species known to ingest and tolerate MPs throughout development. We tested two competing hypotheses of how moulting influences plastic clearance: (1) that moulting of the gut lining removes MPs, or (2) that cessation of feeding and purging frass before ecdysis occurs removes MPs. In doing so we also provide new evidence that cricket nymphs exhibit a cyclical (cosinor) pattern of frass production associated with ecdysis. MPs were eliminated from the crickets gut before ecdysis, driven by the cessation of feeding and cyclical frass production that clears the gut in preparation for ecdysis. We also observed that the timing of ecdysis and overall frass production remained unaffected by continuous MP ingestion, whereas switching between MP and non-MP diets caused modest changes in frass timing within an instar. Crickets are known to biofragment MPs into NPs, which, with gut-clearing, likely allows them to deposit plastic-laden frass rapidly and reduces the likelihood of upward trophic transfer by reducing plastic retention.

physiology↗

bioRxiv2025

Ecological stoichiometry and life history theory, not the identity of genomic variants, predict rapid adaptation

SignificanceForecasting how populations adapt to changing environments is a central challenge in evolutionary biology. We tested the predictability of rapid adaptation by tracking both phenotypic and genomic trajectories of evolution in replicate outdoor populations of Drosophila melanogaster and comparing these data to predictions derived from life history theory, ecological stoichiometry, and genomic data. We found that life history theory and ecological stoichiometry forecasted the direction of phenotypic evolution, even with temporal changes in the direction of evolution. In contrast, genomic predictors were largely unable to forecast the SNPs or genes underlying adaptation. These results demonstrate the utility of ecological frameworks to provide general, but robust, forecasts of adaptation in complex environments. Determining the scale and scope of the predictability of evolution is fundamental to understanding biological processes and to managing biodiversity. Ecological frameworks, including life history theory and ecological stoichiometry, offer testable predictions about the direction of adaptation and trade-offs between traits in response to environmental change. Similarly, well-characterized molecular pathways, genotype-phenotype linkages, and prior evolutionary genomic studies could be predictive of the genomic architecture underlying adaptation. We tested whether ecological frameworks and evolutionary genomic data can be used to forecast rapid adaptation in replicated outdoor populations of Drosophila melanogaster evolving in response to natural seasonal fluctuations from summer to late fall. Life history theory predicted the observed pattern of adaptive tracking: in summer, reproductive output increased and stress tolerance decreased, while in fall, this direction reversed, with evolution of increased stress tolerance at the expense of reproduction. Stoichiometric phenotypic evolution was also predictable, with phosphorus and magnesium content, both linked to growth rate, and alkali metal, associated with maintaining homeostasis in response to thermal stress, showing rapid and parallel evolution indicative of adaptation. Temporal genomic data revealed a complex genomic architecture of temporal adaptation and the SNPs and genes involved in adaptation were largely unpredictable. These results demonstrate that ecological frameworks, more than genomic data, have utility in forecasting adaptation in complex and variable environments.

evolutionary biology↗

bioRxiv2025

Temperature outweighs diet in shaping developmental performance in two cricket species via growth delays and physiological limits

Understanding how chronic environmental stressors shape animal development is essential for predicting ecological responses and optimizing rearing systems. This perspective complements the use of short-term tolerance assays, which overlook the cumulative effects of sustained stress. Temperature and nutrition affect key life-history traits such as growth, development rate, and survival, which are closely tied to reproductive success and fitness. While both factors have been widely studied, their relative impacts arent clearly defined. We investigated how constant temperature (26- 41{degrees}C) and dietary protein-to-carbohydrate (P:C) ratio (0.15-2.18) influence development in two cricket species, Acheta domesticus and Gryllodes sigillatus. Growth trajectories were modelled using a unified-logistic equation to estimate asymptotic mass and relative growth rate. This approach captures the growth trajectory in a simplified and interpretable way, enabling comparisons across treatments. Asymptotic mass was combined with developmental rate and survival to calculate a composite metric of developmental performance. Developmental performance peaked at 35{degrees}C but fell at thermal extremes due to delayed development (in cold) or reduced mass and survival (in heat). Diet had more modest effects. Performance was stable across most P:C ratios, declining only at extreme imbalances. Notably, the performance cost of the most unbalanced diets was comparable to a 4-5{degrees}C shift from thermal optimum. Our results demonstrate that temperature, more than diet, drives variation in developmental performance during ad libitum feeding. This integrative framework provides a robust approach to quantify environmental sensitivity, define performance limits, and guide us toward the mechanisms underlying those limits and/or performance trade-offs. Summary statementTemperature more strongly influences growth trajectories and developmental performance than diet, due to delayed development and reduced survival at thermal extremes.

physiology↗

bioRxiv2025

Farmed cricket performance remains stable over five generations of rearing on a waste-based diet

Farmed insects like crickets offer a sustainable protein source to feed the growing global population. A benefit of cricket farming is the potential to use waste diets instead of unsustainable, expensive feeds. Brewers spent grain is a nutritionally valuable organic waste product that has been used to rear crickets in single generation studies. However, the long-term effects of spent grain-based feeds are unclear, which makes incorporation into commercial feed risky for producers. We reared a farmed cricket (Gryllodes sigillatus) for five generations on a high inclusion (75%) spent grain diet. Crickets reared on spent grain were 18.5% smaller at adulthood than control crickets reared on farm feed, resulting in decreased yield (mass of crickets harvested), but were able to reproduce and had high survival rates. Cricket performance remained stable over five generations, indicating that spent grain contains adequate nutrition to support long-term cricket production. We also reared crickets on a gradual inclusion spent grain diet that increased from 15-75% spent grain over five generations. While this "weaning" approach did not improve cricket performance on high-inclusion spent grain diets, crickets on low inclusion diets (15-30%) displayed nearly a 30% increase in survival and yield compared to those fed the control. Therefore, inclusion of low amounts of spent grain in cricket feed may not only be beneficial from an environmental and feed cost perspective, but also from a production yield perspective. Our findings are the first to show that spent grain is a suitable feed ingredient for long-term rearing of farmed crickets.

ecology↗

bioRxiv2024

Sex-dependent latent chilling injury changes estimates of thermal tolerance in a model insect

Thermal tolerance limits are closely associated with insect distribution. Thermal injury sets limits to mobility or survival after removal from the stress, and these limits are frequently integrated into models describing or predicting climate suitability for species of interest. Cold stress severity, sex, and prior thermal acclimation status can all influence lower thermal limits. There is a growing understanding of chilling injuries initially manifest, but we poorly understand repair or further injury that may happen after rewarming. We exposed male and female Drosophila melanogaster to an acute or chronic cold stress before assessing their mobility over a 24 h period. Females progressively worsened under both conditions, but male mobility neither worsened nor improved. Female mobility declined slower in flies recovering at cooler temperatures, and cold acclimation significantly mitigated latent injury in females following the same degree of initial injury, regardless of recovery temperature. We conclude that latent chilling injury can be sex-specific, occurs independently from mechanisms driving tissue damage in the cold, is temperature-dependent, and is mitigated by prior thermal acclimation. We argue that latent chilling injury and the factors that influence it should be more carefully considered in estimating tolerance limits.

physiology↗

bioRxiv2024

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

Insects provide a potential source of sustainable, alternative protein that can help meet the protein demands of a growing population. Efficient farming of insects to meet this demand depends on an understanding of insect life history. Yet, detailed information and expertise about a single species are not always available for practitioners to make informed decisions about rearing practices or identify arising issues. The cricket (Gryllodes sigillatus) is commonly farmed for human consumption or animal feed, but few studies have characterized the life history of this species throughout ontogeny. Here, we describe the growth and development of G. sigillatus from hatch to adulthood and quantify reproductive traits relevant to mass-rearing and colony management, including egg development. This information provides foundation to start and manage a cricket colony and to conduct research on growth and performance. 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.

zoology↗

bioRxiv2024

Brewery Waste as a Sustainable Protein Source for the Banded Cricket (Gryllodes sigillatus)

Crickets, like other edible insects, can convert organic by-products of the food and agricultural industries into high-value protein. Waste products high in protein like brewers spent grain and brewers spent yeast are particularly attractive replacements for unsustainable protein sources in cricket feed like fishmeal or soy. Such replacement will only be advantageous, however, if feeding on these waste products does not impact, or only minimally impacts, cricket survival, growth, and body composition. In this study, a farmed cricket species, Gryllodes sigillatus, was reared in isolation on experimental diets in which fishmeal was wholly or partially replaced with either brewers spent grain or brewers spent yeast. Cricket survival, development and macromolecular composition were not different across diets. However, wholly replacing fishmeal with brewers spent yeast or brewers spent grain reduced cricket adult body mass by approximately 16%. To extend these findings toward a farm environment, a second cohort of crickets were reared communally on diets in which fishmeal, and fishmeal and soy (a secondary protein source), were replaced by brewers spent grain. We found that in a communal environment, crickets reared on both diets performed equally as well as the control. Therefore, brewing waste products are promising candidates for use as a primary protein source in the feed of G. sigillatus. In addition to contributing towards the goals of a circular bioeconomy through the repurposing of waste, the use of brewing waste in cricket feed may have a positive impact of the cricket farming industry as a cost-effective and sustainable alternative to traditional feed. Conflict of InterestThe authors have an ongoing research agreement with Aspire Food Group and Entomo Farms, who produce crickets as food and feed. Funding StatementThis research was funded by Discovery Grants awarded by the Natural Sciences and Engineering Research Council of Canada (NSERC) to H.A.M. (RGPIN-2018-05322) and S.M.B. (RGPIN-2017-06263). Additional support was provided by an NSERC Alliance Grant (568647-21) and a Deep Space Food Challenge grant (22IUCCAR22) from the Canadian Space Agency awarded to both H.A.M. and S.M.B. Equipment used in this study was purchased with support to H.A.M. from the Canadian Foundation for Innovation (project number 37721).

physiology↗

bioRxiv2024

Larger diet particle sizes cause crickets to grow faster with no effect on final body size

Artificial diets are costly to produce, so diet efficiency is critically important to the success of mass rearing insects. One way to improve feed efficiency is through dietary particle size optimization. We used a commercially reared species, Gryllodes sigillatus, to test whether individual crickets reared from hatch to adulthood on diets of different particle sizes would grow differently. Crickets fed a diet [≥]0.5 mm grew heavier during the first three weeks but weighed the same after six weeks regardless of diet size. We then provided crickets with a choice of particle size throughout development to test for dietary size preference. Given a choice, crickets consumed the most food from the 1.0-1.4 mm diet. Crickets also preferentially select ingredients from mixed diets, so to test whether grinding a conventional diet to a finer particle size could influence performance traits, we ran a large-scale group rearing experiment and found no effect of further grinding on colony mass gain or development time. Pelleting diet is another method for eliminating self-selection of ingredients, and so we tested whether pelleting finely ground conventional cricket feed would result in any substantial changes to the developmental life history of individual crickets. Crickets fed a 2 mm pelleted diet grew larger body size but were not significantly heavier. Overall, our results demonstrate that particle size optimization can be leveraged to enhance cricket life history traits important to mass production, as growth was accelerated on larger particle size diets and crickets preferred to eat larger-sized diets. Researchers focusing on physical properties of insect diets should carefully consider the timing of growth and development through which diet particle size may influence feed efficiency.

ecology↗

bioRxiv2024

Glial voltage-gated K+ channels modulate the neural abiotic stress tolerance of Drosophila melanogaster

Severe abiotic stress causes insects to lose nervous function and enter a state of paralytic coma. Central to this loss of function is a spreading depolarization (SD), where a characteristic collapse of ion gradients depolarizes neuronal and glial membranes and rapidly shuts down the CNS. Despite representing a critical limit to CNS function, the stress threshold that elicits SD can be altered by the process of acclimation, though the mechanisms underlying this response remain largely unknown. Here, we made electrophysiological measurements of SD and investigated the role of K+ channels in acclimation of the CNS stress response of Drosophila melanogaster. First, we demonstrate that improved cold tolerance in the CNS elicited by cold acclimation was abolished by pharmacological blockade of K+ channels with voltage-gated K+ channels representing most of this effect. Next, we used the UAS/Gal4 model system to screen for candidate genes encoding glial voltage-gated K+ channels and found that knockdown of sei- and Shaw-encoded channels mimicked the effect of K+ blockade in cold-acclimated flies. Furthermore we show that the knockdown of glial sei-encoded channels also impair tolerance to anoxia and heat stress. These findings suggest that voltage-gated K+ channels, especially those encoded by sei, are integral to the CNS stress- and acclimation-response and we posit that this is elicited through mechanisms involving glial spatial buffering and barrier function. Establishing such causal links between tissue-specific expression of candidate genes and SD mechanisms will inevitably aid our understanding of insect ecophysiology and SD-related neuropathologies. New and NoteworthyUsing thermal acclimation and pharmacology, we demonstrate that voltage-gated K+ channels are involved in setting the threshold for cold-induced spreading depolarization (SD) in the Drosophila melanogaster CNS. Glial knockdown of channels encoded by sei and Shaw reduced the resistance to cold-induced SD, highlighting their importance in acclimation of the CNS. Glia-specific sei-knockdown also reduced tolerance to anoxia and heat. We posit that sei-channels are involved the CNS stress- and acclimation-responses through glial spatial buffering mechanisms.

neuroscience↗

bioRxiv2024

Farmed crickets raised with dermestids suffer from reduced and delayed growth, but not enough to explain reports of dramatic yield loss

The mass production of crickets for food and feed is an expanding North American industry. Facilities that mass rear insects are at risk of pest infestations because the optimal environmental conditions for rearing beneficial species may also support the development of pest species. Here, we present the first recorded results detailing the interactions between dermestids and farmed crickets. Cricket farms have reported extremely low harvest yield during heavy dermestid infestations, but the exact reasons for this low yield are unknown. Many dermestid larvae are covered in dense, detachable, barbed setae called hastisetae, which are used by the larvae as an active trapping system against arthropod predators. We designed a series of experiments to test the hypotheses that dermestids (Dermestes ater DeGeer) may be directly impacting cricket (Gryllodes sigillatus Walker) yield through the physical effects of hastisetae ingestion and/or indirectly impacting cricket yield through competition for fishmeal, a primary source of protein in conventional cricket feed. Our predictions that cricket life history and survival would be negatively affected by dermestids were largely refuted. Females fed infested diets grew less mass, but not smaller body size, compared to females fed uninfested diets. We also found that while crickets experienced delayed growth early in life after living with dermestids, they were able to tolerate living with, and consuming, dermestid larvae. We discuss how these findings have led to new hypotheses concerning how dermestid infestations drive reductions in cricket farm yield.

ecology↗

bioRxiv2024

Thermal acclimation of spreading depolarization in the CNS of Drosophila melanogaster

During exposure to extreme stress, the CNS of mammals and insects fails through a phenomenon known as spreading depolarization (SD). SD is characterized by an abrupt disruption of ion gradients across neural and glial membranes that spreads through the CNS, silencing neural activity. In humans, SD is associated with neuropathological conditions like migraine and stroke. In insects, it is coincident with critical thermal limits for activity and can be conveniently monitored by observing the transperineurial potential (TPP). We used the TPP to explore the temperature-dependence and plasticity of SD thresholds and SD-induced changes to the TPP in fruit flies (Drosophila melanogaster) acclimated to different temperatures. Specifically, we characterized the effects of thermal acclimation on the TPP characteristics of cold-induced SD, after which we induced SD via anoxia at different temperatures in both acclimation groups to examine the interactive effects of temperature and acclimation status. Lastly, we investigated these effects on the rate of SD propagation across the fruit fly CNS. Cold acclimation enhanced resistance to both cold- and anoxic SD and our TPP measurements revealed independent and interactive effects of temperature and acclimation on the TPP and SD propagation. This suggests thermodynamic processes and physiological mechanisms interact to modulate the threshold for activity through SD and its electrophysiological phenomenology. These findings are discussed in relation to conceptual models for SD and established mechanisms for variation in the thermal threshold for SD.

physiology↗

bioRxiv2024

Dietary potassium and cold acclimation additively increase cold tolerance in Drosophila melanogaster

In the cold, chill susceptible insects lose the ability to regulate ionic and osmotic gradients. This leads to hemolymph hyperkalemia that drives a debilitating loss of cell membrane polarization, triggering cell death pathways and causing organismal injury. Biotic and abiotic factors can modulate insect cold tolerance by impacting the ability to mitigate or prevent this cascade of events. In the present study, we test the combined and isolated effects of dietary manipulations and thermal acclimation on cold tolerance in fruit flies. Specifically, we acclimated adult Drosophila melanogaster to 15 or 25{degrees}C and fed them either a K+-loaded diet or a control diet. We then tested the ability of these flies to recover from and survive a cold exposure, as well as their capacity to protect transmembrane K+ gradients, and intracellular Na+ concentration. As predicted, cold-exposed flies experienced hemolymph hyperkalemia and cold-acclimated flies had improved cold tolerance due to an improved maintenance of the hemolymph K+ concentration at low temperature. Feeding on a high-K+ diet improved cold tolerance additively, but paradoxically reduced the ability to maintain extracellular K+ concentrations. Cold-acclimation and K+-feeding additively increased the intracellular K+ concentration, aiding in maintenance of the transmembrane K+ gradient during cold exposure despite cold-induced hemolymph hyperkalemia. There was no effect of acclimation of diet on intracellular Na+ concentration. These findings suggest intracellular K+ loading and reduced muscle membrane K+ sensitivity as mechanisms through which cold-acclimated and K+-fed flies are able to tolerate hemolymph hyperkalemia. Highlights- Insect cold tolerance varies in relation to ionoregulatory capacity - Cold acclimation improves cold tolerance and K+ handling during cold exposure - A high K+ diet also improves cold tolerance, but reduces the K+-handling capacity - We highlight a novel mechanism for preventing K+ gradient disruption

physiology↗

bioRxiv2024

Applying nutritional ecology to optimize diets of crickets raised for food and feed

Increasing yield is a primary goal of mass insect rearing for food and feed, and diet shapes insect life history traits important to yield, such as survival, development time, and body size at adulthood. Little is known about how developmental macronutrient intake impacts survival, growth, and adult body size of mass reared insects. Here, we applied the nutritional geometry framework and reared individual tropical house crickets (Gryllodes sigillatus) from hatch to adulthood on a wide range of protein:carbohydrate diets. We measured weekly food consumption, survival, development time to adulthood, and adult body size and mass, and calculated a yield metric to extrapolate our individual-level results and predict how diet influences yield at the mass rearing level. Yield was maximized on a 3P:1C diet, as crickets fed this diet were most likely to develop into adults and grew maximum mass and body size. When provided with a choice between diets, crickets selected a relatively balanced 1.05P:1C diet throughout development, but males consumed 17% more protein than females. Our results represent a crucial first step towards determining the optimal standard feed formulation required to maximize cricket farming yield.

ecology↗

bioRxiv2024

The freeze-avoiding mountain pine beetle (Dendroctonus ponderosae) survives prolonged exposure to stressful cold by mitigating ionoregulatory collapse

Insect performance is intrinsically linked to environmental temperature, and surviving through winter represents a key challenge for temperate, alpine, and polar species. To overwinter, insects have adapted a wide range of strategies to become truly cold hardy. However, while the physiological mechanisms underlying the ability to avoid or tolerate freezing have been well-studied, little attention has been given to the challenge of maintaining ion homeostasis at frigid temperatures in these species, despite this being a central issue for insects susceptible to mild chilling. Here we investigate how prolonged exposure to temperatures just above the supercooling point affects ion balance in freeze-avoiding larvae of the mountain pine beetle (Dendroctonus ponderosae) in autumn, mid-winter, and spring, and relate it to organismal recovery times and survival outcomes. We found that hemolymph ion balance was gradually disrupted during the first day of exposure, characterized by hyperkalemia and hyponatremia, after which a plateau was reached and maintained for the rest of the seven day experiment. The degree of ionoregulatory collapse experienced by larvae correlated strongly with recovery times, which followed a similar asymptotical progression. Mortality increased slightly during the most severe cold exposures, where hemolymph K+ concentration was highest, and a logistic relationship was found between survival and hyperkalemia. Thus, the cold tolerance of the freeze-avoiding larvae of D. ponderosae appears limited by the ability to prevent ionoregulatory collapse in a manner similar to less tolerant chill-susceptible insects, albeit at much lower temperatures. Furthermore, we posit that a prerequisite for the evolution of insect freeze avoidance is a convergent or ancestral ability to maintain ion homeostasis during exposure to extreme cold stress.

physiology↗

bioRxiv2023

Effects of a high cholesterol diet on Drosophila chill tolerance are highly context-dependent

Chill susceptible insects are thought to be injured through different mechanisms depending on the duration and severity of chilling. While chronic chilling causes "indirect" injury through disruption of metabolic and ion homeostasis, acute chilling is suspected to cause "direct" injury, in part through phase transitions of cell membrane lipids. Dietary supplementation of cholesterol can reduce acute chilling injury in Drosophila melanogaster, but the generality of this effect and the mechanisms underlying it remain unclear. To better understand how and why cholesterol has this effect, we assessed how a high cholesterol diet and thermal acclimation independently and interactively impact several measures of chill tolerance in both male and female flies. Cholesterol supplementation positively affected tolerance to acute chilling in warm-acclimated flies (as reported previously). Conversely, feeding on the high-cholesterol diet negatively affected tolerance to chronic chilling in both cold and warm acclimated flies, as well as tolerance to acute chilling in cold acclimated flies. Cholesterol had no effect on the ability of flies to remain active in the cold or recover movement after a cold stress. Our findings support the idea that dietary cholesterol reduces mechanical injury to membranes caused by direct chilling injury, and that acute and chronic chilling are associated with distinct mechanisms of injury. Feeding on a high-cholesterol diet may interfere with mechanisms involved in cold acclimation, leaving cholesterol augmented flies more susceptible to chilling injury under some conditions. HighlightsO_LICholesterol improves cold shock tolerance of warm-acclimated flies C_LIO_LICold acclimation and chronic cold instead lead to negative effects of cholesterol on chill tolerance C_LIO_LICholesterol did not affect the ability of flies to remain active in the cold C_LIO_LIBoth sexes were similarly affected by a high cholesterol diet C_LI

physiology↗

bioRxiv2023

Tropical butterflies lose central nervous system function in the cold from a spreading depolarization event

Insects are ectotherms and their physiological functions are therefore directly influenced by the environmental temperature. By extension, their ability to tolerate thermal extremes is directly linked to their thermal niche and distribution. Understanding the physiological mechanisms that limit insect thermal tolerance is therefore crucial for our ability to predict biogeography and range shifts. Recent studies on fruit flies and locusts suggest that the loss of coordinated movements at the critical thermal minimum is due to a loss of central nervous system function via a spreading depolarization. We hypothesized that a similar mechanism limits nervous function in other insect taxa. Here, we use electrophysiology to investigate whether the same spreading depolarization event occurs in the brain of butterflies exposed to stressful cold. Supporting our hypothesis, we find that exposure to stressful cold induced spreading depolarization in all species tested. This reinforces the idea that loss of central nervous function by a spreading depolarization is a common mechanism underlying the critical thermal minimum in insects. Furthermore, our results highlight how central nervous system performance is finely tuned to match species environments. Further research into the physiological mechanisms underlying the spreading depolarization event is likely to elucidate key mechanisms determining insect ecology.

physiology↗

bioRxiv2023

The digestive system of a cricket pulverizes polyethylene microplastics

Microplastics (MPs; <5 mm) are a growing concern and a poorly understood threat to biota. Despite a recent spike in research on MPs, most of this work has focused on marine systems, and less is known about interactions between terrestrial organisms. 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 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 (likely into the nanoplastic range), and this fragmentation occurs early in the digestive process of this insect. These findings suggest that generalist insects can act as agents of plastic transformation in their environment if/when encountering MPs.

physiology↗

bioRxiv2022

Characterizing microplastic ingestion, transformation, 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 microplastics. Microplastics 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, transformation, and elimination can be quantified and related to molecular, physiological, and organismal traits. Here we propose a complete method for isolating and characterizing 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 animals (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 characterized plastic particles within the gut and frass.

zoology↗