Biology subjects

Ritchie, M. W.

Publications and source records attributed to Ritchie, M. W..

12 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

The disadvantage of having a big mouth: the relationship between insect body size and microplastic ingestion

Plastic pollution is ubiquitous, and animals are exposed to diverse plastic shapes and sizes. When plastics enter natural environments, they break down into microplastics (MPs; <5 mm) and likely become more accessible to smaller animals. Insects play critical environmental and economic roles, ingest plastics in the wild, and can physically degrade ingested MPs into smaller and more harmful nanoplastics. While particle size and body size undoubtedly impact plastic ingestion, we have no predictive understanding of how these factors interact to influence which plastics are a threat to which animals. To uncover these potential interactions, we studied how a model cricket species (Gryllodes sigillatus) interacts with plastics of differing sizes throughout a twentyfold change in body size during growth and development. We fed crickets a range of MP sizes of 38 to 500 {micro}m with clearly defined particle size thresholds. We investigated whether crickets would avoid MPs when given a choice and found that they do not; instead they gradually began to consume more of the plastic diet over time. We then studied how MP ingestion is influenced by body size and mouth size, and the extent of breakdown that occurs once MPs are ingested. We found that crickets would only consume whole beads when their mouth size was larger than the MP. While small MPs were more likely to be excreted whole, larger MPs were more extensively broken down as crickets grew. We conclude that crickets do not exhibit avoidance behaviour towards plastic and ingest it once a particle can be consumed whole. These effects of insect behaviour and body size on the likelihood of plastic ingestion and the degree to which MPs are degraded have important implications for regulating the size classes of plastic particles entering natural environments and how plastics move through those environments once discarded.

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

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

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↗

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

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↗

bioRxiv2022

Ingestion of microplastic fibres, but not microplastic beads, impacts growth rates in the tropical house cricket Gryllodes sigillatus

Microplastic is a growing concern as an environmental contaminant as it is ubiquitous in our ecosystems. Microplastics are present in terrestrial environments, yet the majority of studies have focused on the adverse effects of microplastics on aquatic biota. We hypothesized that microplastic ingestion by a terrestrial insect would have localized effects on gut health and nutrient absorption, such that prolonged dietary microplastic exposure would impact growth rate and adult body size. We further hypothesized that plastic form (fibres vs. beads) would influence these effects because of the nature of gut-plastic interactions. Freshly hatched tropical house crickets (Gryllodes sigillatus) were fed a standard diet containing different concentrations of either fluorescent polyethylene microplastic beads (75-105 m), or untreated polyethylene terephthalate microfibers (<5 mm) until they died or reached adulthood (approximately 8 weeks). Weight and body length were measured weekly and microplastic ingestion was confirmed through fluorescence microscopy and visual inspection of the frass. While, to our surprise, we found no effect of polyethylene bead ingestion on growth rate or final body size of G. sigillatus, females experienced a reduction in size and weight when fed high concentrations of polyethylene terephthalate microfibers. These results suggest that high concentrations of polyethylene beads of the 100 m size range can pass through the cricket gut without a substantial negative effect on their growth and development time, but high concentrations of polyethylene terephthalate microfibers cannot. Although we report the negative effects of microplastic ingestion on the growth of G. sigillatus, it remains uncertain what threats microplastics pose to terrestrial insects.

physiology↗

bioRxiv2020

A simple and dynamic thermal gradient device for measuring thermal performance in small ectotherms

The body temperature of ectothermic animals is heavily dependent on environmental temperature, impacting fitness. Laboratory exposure to favorable and unfavorable temperatures is used to understand these effects, as well as the physiological, biochemical, and molecular underpinnings of variation in thermal performance. Although small ectotherms, like insects, can often be easily reared in large numbers, it can be challenging and expensive to simultaneously create and manipulate several thermal environments in a laboratory setting. Here, we describe the creation and use of a thermal gradient device that can produce a wide range of constant or varying temperatures concurrently. This device is composed of a solid aluminum plate and copper piping, combined with a pair of programmable refrigerated circulators. As a simple proof-of-concept, we completed single experimental runs to produce a low-temperature survival curve for flies (Drosophila melanogaster) and explore the effects of daily thermal cycles of varying amplitude on growth rates of crickets (Gryllodes sigillatus). This approach avoids the use of multiple heating/cooling water or glycol baths or incubators for large-scale assessments of organismal thermal performance. It makes static or dynamic thermal experiments (e.g., creating a thermal performance or survival curves, quantifying responses to fluctuating thermal environments, or monitoring animal behaviour across a range of temperatures) easier, faster, and less costly.

ecology↗

bioRxiv2020

Multidecadal decline and recovery of aspen experiencing contrasting fire regimes: long-unburned, infrequent and frequent mixed-severity wildfire

Quaking aspen (Populus tremuloides) is a valued, minor component on western landscapes. It provides a wide range of ecosystem services and has been in decline throughout the arid west for the last century. This decline may be explained partially by the lack of fire on the landscape as aspen benefit from fire that eliminates conifer competition and stimulates reproduction through root suckering. Managers are interested in aspen restoration but there is a lack of knowledge about their spatial dynamics in response to fire. Our study area in northeastern California on the Lassen, Modoc and Plumas National Forests has experienced recent large mixed-severity wildfires where aspen was present, providing an opportunity to study the re-introduction of fire. We observed two time periods; a 54-year absence of fire from 1941 to 1993 preceding a 24-year period of wildfire activity from 1993 to 2017. We utilized aerial photos to delineate aspen stand size, location and succession to conifers. We chose aspen stands in areas where wildfires overlapped (twice-burned), where only a single wildfire burned, and areas that did not burn within the recent 24-year period. We looked at these same stands within the first period of fire exclusion for comparison (i.e., 1941-1993). In the absence of fire, all aspen stand areas declined and all stands experienced increases in conifer composition. After wildfire, stands that burned experienced a release from conifer competition and increased in stand area. Stands that burned twice or at high severity experienced a larger removal of conifer competition than stands that burned once at low severity, promoting aspen recovery and expansion. Stands with less edge:area ratio also expanded more with fire present. Across both time periods, stand movement, where aspen stand footprints were mostly in new areas compared to footprints of previous years, was highest in smaller stands. In the fire exclusion period, smaller stands exhibited greater changes in area and location (movement), highlighting their vulnerability to loss in the absence of disturbances that provide adequate growing space for aspen over time.

ecology↗

bioRxiv2020

Warm periods in repeated cold stresses protect Drosophila against ionoregulatory collapse, chilling injury, and reproductive deficits

In many insects, repeated cold stress, characterized by warm periods that interrupt cold periods, have been found to yield survival benefits over continuous cold stress, but at the cost of reproduction. During cold stress, chill susceptible insects like Drosophila melanogaster suffer from a loss of ion and water balance, and the current model of recovery from chilling posits that re-establishment of ion homeostasis begins upon return to a warm environment, but that it takes minutes to hours for an insect to fully restore homeostasis. Following this ionoregulatory model of chill coma recovery, we predicted that the longer the duration of the warm periods between cold stresses, the better a fly will recover from a subsequent chill coma event and the more likely they will be to survive, but at the cost of fewer offspring. Here, female D. melanogaster were treated to a long continuous cold stress (25 h at 0{degrees}C), or experienced the same total time in the cold with repeated short (15 min), or long (120 min) breaks at 23{degrees}C. We found that warm periods in general improved survival outcomes, and individuals that recovered for more time in between cold periods had significantly lower rates of injury, faster recovery from chill coma, and produced greater, rather than fewer, offspring. These improvements in chill tolerance were associated with mitigation of ionoregulatory collapse, as flies that experienced either short or long warm periods better maintained low hemolymph [K+]. Thus, warm periods that interrupt cold exposures improve cold tolerance and fertility in D. melanogaster females relative to a single sustained cold stress, potentially because this time allows for recovery of ion and water homeostasis.

zoology↗