The long-acting walking control of a cockroach bio-bot for vision-aided pipeline navigation.

Many small bionic crawling robots have been invented for search and rescue missions in narrow spaces. However, their locomotion capability is far from that of insects of the same size. Transforming a cockroach into a bio-bot has been a hot topic in the past decade. Herein, we modified this insect to perform surveillance work in dark confined environments. The synergistic electrical stimulation for turning control was proposed by alternating electrical stimulation of the cerci and antennae every 5 trials. The result showed that this method was able to control cockroaches turning steadily 117 times. An electronic backpack was designed, which was capable of transmitting images in real time, and a light emitting diode (LED) was installed on the backpack providing a light source for the camera. Thus, a vision-aided navigation system was formed for dark confined environments, e.g. pipelines. With a host computer software, the operator controlled the bio-bot to pass through a completely dark and closed pipeline. The electronic backpack and the host computer were connected via transmission control protocol (TCP), which allows the operator to manipulate the bio-robot remotely. This technology can be applied in pipeline surveillance in the future.

Histological Findings in Captive Madagascar Hissing Cockroaches (Gromphadorhina portentosa) and a Literature Review.

Madagascar hissing cockroaches (MHC, Gromphadorhina portentosa) are members of the Blaberidae (giant cockroaches) family of the Insecta class. They are native to the African island of Madagascar where they live within leaf litter on the rainforest floor. Due to their large size, relative tameness, and general easy keeping, they have become popular in classrooms, zoological collections, museums, research laboratories, and as private exotic pets; however, descriptions of diseases of MHC in the literature are rare. The objective of this study is to describe and characterize postmortem histological findings in 18 captive MHC from a single zoological collection. In this retrospective study, 18 (4 females and 14 males) adult MHC necropsies were submitted to Northwest ZooPath between 2016 and 2020 for evaluation. The main organs with histological lesions were chitinous gut (foregut and/or hindgut; n = 17), tracheae (n = 15), fat body (n = 14), ventriculus (midgut) (n = 13), body wall (n = 12), Malpighian tubules (n = 12), and hemolymphatic sinuses (n = 12). All animals had inflammatory lesions affecting various organs. Inflammatory lesions typically consisted of aggregates of hemocytes with variable amounts of melanization and/or encapsulation. Bacterial, fungal, and parasitic infections were common and variably associated with hemocytic inflammation. Many of these organisms may represent symbiotic organisms of the MHC that cause opportunistic infections. This study contributes to the current knowledge of pathological findings and disease response of MHC and reviews diseases reported in multiple cockroach species.

Multielectrode recordings of cockroach antennal lobe neurons in response to temporal dynamics of odor concentrations.

The initial representation of the instantaneous temporal information about food odor concentration in the primary olfactory center, the antennal lobe, was examined by simultaneously recording the activity of antagonistic ON and OFF neurons with 4-channel tetrodes. During presentation of pulse-like concentration changes, ON neurons encode the rapid concentration increase at pulse onset and the pulse duration, and OFF neurons the rapid concentration decrease at pulse offset and the duration of the pulse interval. A group of ON neurons establish a concentration-invariant representation of odor pulses. The responses of ON and OFF neurons to oscillating changes in odor concentration are determined by the rate of change in dependence on the duration of the oscillation period. By adjusting sensitivity for fluctuating concentrations, these neurons improve the representation of the rate of the changing concentration. In other ON and OFF neurons, the response to changing concentrations is invariant to large variations in the rate of change due to variations in the oscillation period, facilitating odor identification in the antennal-lobe. The independent processing of odor identity and the temporal dynamics of odor concentration may speed up processing time and improve behavioral performance associated with plume tracking, especially when the air is not moving.

Parasitoid wasp venom re-programs host behavior through downmodulation of brain central complex activity and motor output.

The parasitoid wasp Ampulex compressa hunts down its host, the American cockroach (Periplaneta americana), and envenomates its brain to make it a behaviorally compliant food supply for its offspring. The primary target of the wasp sting is a locomotory command center called the central complex (CX). In the present study, we employ, for the first time, chronic recordings of patterned cockroach CX activity in real time as the brain is infused with wasp venom. CX envenomation is followed by sequential changes in the pattern of neuronal firing that can be divided into three distinct temporal phases during the 2 h interval after venom injection: (1) reduction in neuronal activity for roughly 10 min immediately after venom injection; (2) rebound of activity lasting up to 25 min; (3) reduction of ongoing activity for up to 2 h. Long-term reduction of CX activity after venom injection is accompanied by decreased activity of both descending interneurons projecting to thoracic locomotory circuitry (DINs) and motor output. Thus, in this study, we provide a plausible chain of events starting in the CX that leads to decreased host locomotion following brain envenomation. We propose that these events account for the onset and maintenance of the prolonged hypokinetic state observed in stung cockroaches.

Cockroaches adjust body and appendages to traverse cluttered large obstacles.

To traverse complex terrain, animals often transition between locomotor modes. It is well known that locomotor transitions can be induced by switching in neural control circuits or driven by a need to minimize metabolic energetic cost. Recent work revealed that locomotor transitions in complex 3D terrain cluttered with large obstacles can emerge from physical interaction with the environment controlled by the nervous system. For example, to traverse cluttered, stiff grass-like beams, the discoid cockroach often transitions from using a strenuous pitch mode pushing across the beams to using a less strenuous roll mode rolling into and through the gaps. This transition can save mechanical energetic cost substantially (∼100-101 mJ) but requires overcoming a potential energy barrier (∼10-3-10-2 mJ). Previous robotic physical modeling demonstrated that kinetic energy fluctuation of body oscillation from self-propulsion can help overcome the barrier and facilitate this transition. However, the animal was observed to transition even when the barrier still exceeded kinetic energy fluctuation. Here, we further studied whether and how the cockroach makes active adjustments to facilitate this transition to traverse cluttered beams. The animal repeatedly flexed its head and abdomen, reduced hindleg sprawl, and depressed one hindleg and elevated the other during the pitch-to-roll transition, adjustments which were absent when running on a flat ground. Using a refined potential energy landscape with additional degrees of freedom to model these adjustments, we found that head flexion did not substantially reduce the transition barrier (by ∼10-3 mJ), whereas leg sprawl reduction did so dramatically (by ∼10-2 mJ). We speculate that head flexion is for sensing the terrain to guide the transition via sensory feedback control.

Parasitoid wasp venom manipulates host innate behavior via subtype-specific dopamine receptor activation.

The subjugation strategy employed by the jewel wasp is unique in that it manipulates the behavior of its host, the American cockroach, rather than inducing outright paralysis. Upon envenomation directly into the central complex (CX), a command center in the brain for motor behavior, the stung cockroach initially engages in intense grooming behavior, then falls into a lethargic sleep-like state referred to as hypokinesia. Behavioral changes evoked by the sting are due at least in part to the presence of the neurotransmitter dopamine in the venom. In insects, dopamine receptors are classified as two families, the D1-like and the D2-like receptors. However, specific roles played by dopamine receptor subtypes in venom-induced behavioral manipulation by the jewel wasp remain largely unknown. In the present study, we used a pharmacological approach to investigate roles of D1-like and D2-like receptors in behaviors exhibited by stung cockroaches, focusing on grooming. Specifically, we assessed behavioral outcomes of focal CX injections of dopamine receptor agonists and antagonists. Both specific and non-specific compounds were used. Our results strongly implicate D1-like dopamine receptors in venom-induced grooming. Regarding induction of hypokinesia, our findings demonstrate that dopamine signaling is necessary for induction of long-lasting hypokinesia caused by brain envenomation.

Thermal tolerance of an invasive drywood termite, Cryptotermes brevis (Blattodea: Kalotermitidae).

West Indian drywood termites (Cryptotermes brevis, Blattodea: Kalotermitidae) are an important invasive termite in many countries including Australia where they are spreading across two eastern states. Fumigation is often used to eliminate infestations, but it is costly, has negative environmental effects and does not prevent reinfestation. Heat treatment has been suggested as an alternative. Many insect pest mitigation strategies recommend 30 min exposure at 56 °C, but this may be difficult to achieve in structural applications. The potential for heating at lower temperatures was explored to determine the effect on termite survival and gut fauna. Exposure to 40 °C up to an hour did not kill the termites; however, 1-h exposure at 45 °C was lethal. Exposure for little as 3 min at 50 °C or 2 min at 55 °C was lethal. Protozoa levels were lower in termites that survived shorter exposures, but there appeared to be some recovery over time. The results suggest that short term exposures to 50 or 55 °C could be used to eliminate infestations, creating an opportunity for localized spot heating as a mitigation measure.

Feeding Behaviour of a Pyrethroid-Resistant Strain of the German Cockroach Blattella germanica (Linnaeus, 1767).

Many authors report biological differences among insecticide-resistant pest species, mainly associated with parameters of life history, but only a few studies approach differences at the behavioural level. Feeding behaviour in Blattella germanica (L.) is modulated by the detection of chemical volatiles emitted from food sources in order to be located a long-median distance, and also by the physicochemical properties of food. This work aimed to study the differences in the feeding behaviour of a susceptible and a pyrethroid-resistant strain of B. germanica, in the location and exploitation of a food source. Resistant males showed a lower performance in the feeding behaviour compared to susceptible males. Particularly, the time taken to locate the source was significantly higher in the resistant individuals, suggesting a lower capacity in the detection of food odours. In addition, although the Intake rate was negatively related to the stiffness of food for both strains, resistant individuals showed a lower intake rate compared to susceptible ones, when exploiting a food source of the same stiffness. In a control context, the phenotypic characteristics associated to feeding of pyrethroid-resistant individuals could induce a behavioural resistance mechanism caused by a reduction in the amount of toxic gel bait ingested. If that is the case, resistance of this strain would not be associated to physiological changes affecting the toxicity of the active principle of gel baits, but to a lower efficacy of these products against resistant individuals due to less amount of gel consumed, generating control problems of this pest.

Discontinuous gas exchange in Madagascar hissing cockroaches is not a consequence of hysteresis around a fixed PCO2 threshold.

It has been hypothesised that insects display discontinuous gas-exchange cycles (DGCs) as a result of hysteresis in their ventilatory control, where CO2-sensitive respiratory chemoreceptors respond to changes in haemolymph PCO2 only after some delay. If correct, DGCs would be a manifestation of an unstable feedback loop between chemoreceptors and ventilation, causing PCO2 to oscillate around some fixed threshold value: PCO2 above this ventilatory threshold would stimulate excessive hyperventilation, driving PCO2 below the threshold and causing a subsequent apnoea. This hypothesis was tested by implanting micro-optodes into the haemocoel of Madagascar hissing cockroaches and measuring haemolymph PO2 and PCO2 simultaneously during continuous and discontinuous gas exchange. The mean haemolymph PCO2 of 1.9 kPa measured during continuous gas exchange was assumed to represent the threshold level stimulating ventilation, and this was compared with PCO2 levels recorded during DGCs elicited by decapitation. Cockroaches were also exposed to hypoxic (PO2 10 kPa) and hypercapnic (PCO2 2 kPa) gas mixtures to manipulate haemolymph PO2 and PCO2. Decapitated cockroaches maintained DGCs even when their haemolymph PCO2 was forced above or below the putative ∼2 kPa ventilation threshold, demonstrating that the characteristic oscillation between apnoea and gas exchange is not driven by a lag between changing haemolymph PCO2 and a PCO2 chemoreceptor with a fixed ventilatory threshold. However, it was observed that the gas exchange periods within the DGC were altered to enhance O2 uptake and CO2 release during hypoxia and hypercapnia exposure. This indicates that while respiratory chemoreceptors do modulate ventilatory activity in response to haemolymph gas levels, their role in initiating or terminating the gas exchange periods within the DGC remains unclear.

Distribution and daily oscillation of GABA in the circadian system of the cockroach Rhyparobia maderae.

Gamma-aminobutyric acid (GABA) is the prevalent inhibitory neurotransmitter in nervous systems promoting sleep in both mammals and insects. In the Madeira cockroach, sleep-wake cycles are controlled by a circadian clock network in the brain's optic lobes, centered in the accessory medulla (AME) with its innervating pigment-dispersing factor (PDF) expressing clock neurons at the anterior-ventral rim of the medulla. GABA is present in cell clusters that innervate different circuits of the cockroach's AME clock, without colocalizing in PDF clock neurons. Physiological, immunohistochemical, and behavioral assays provided evidence for a role of GABA in light entrainment, possibly via the distal tract that connects the AME's glomeruli to the medulla. Furthermore, GABA was implemented in clock outputs to multiple effector systems in optic lobe and midbrain. Here, GABAergic brain circuits were analyzed further, focusing on the circadian system in search for sleep/wake controlling brain circuits. All GABA-immunoreactive neurons of the cockroach brain were also stained with an antiserum against the GABA-synthesizing enzyme glutamic acid decarboxylase. We found strong overlap of the distribution of GABA-immunoreactive networks with PDF clock networks in optic lobes and midbrain. Neurons in five of the six soma groups that innervate the clock exhibited GABA immunoreactivity. The intensity of GABA immunoreactivity in the distal tract showed daily fluctuations with maximum staining intensity in the middle of the day and weakest staining at the end of the day. Quantification via enzyme-linked immunosorbent assay and quantitative liquid chromatography coupled to electrospray ionization tandem mass spectrometry, likewise, showed higher GABA levels in the optic lobe during the inactivity phase of the cockroach during the day and lower levels during its activity phase at dusk. Our data further support the hypothesis that light- and PDF-dependently the circadian clock network of the cockroach controls GABA levels and thereby promotes sleep during the day.

Propelling and perturbing appendages together facilitate strenuous ground self-righting.

Terrestrial animals must self-right when overturned on the ground, but this locomotor task is strenuous. To do so, the discoid cockroach often pushes its wings against the ground to begin a somersault which rarely succeeds. As it repeatedly attempts this, the animal probabilistically rolls to the side to self-right. During winged self-righting, the animal flails its legs vigorously. Here, we studied whether wing opening and leg flailing together facilitate strenuous ground self-righting. Adding mass to increase hind leg flailing kinetic energy increased the animal's self-righting probability. We then developed a robot with similar strenuous self-righting behavior and used it as a physical model for systematic experiments. The robot's self-righting probability increased with wing opening and leg flailing amplitudes. A potential energy landscape model revealed that, although wing opening did not generate sufficient kinetic energy to overcome the high pitch potential energy barrier to somersault, it reduced the barrier for rolling, facilitating the small kinetic energy from leg flailing to probabilistically overcome it to self-right. The model also revealed that the stereotyped body motion during self-righting emerged from physical interaction of the body and appendages with the ground. Our work demonstrated the usefulness of potential energy landscape for modeling self-righting transitions.

Midgut transcriptome assessment of the cockroach-hunting wasp Ampulex compressa (Apoidea: Ampulicidae).

The emerald jewel wasp Ampulex compressa (Hymenoptera: Ampulicidae) is a solitary wasp that is widely known for its specialized hunting of cockroaches as larvae provision. Adult wasps mainly feed on pollen and nectar, while their larvae feed on the cockroachs' body, first as ecto- and later as endoparsitoids. Little is known about the expression of digestive, detoxification and stress-response-related genes in the midgut of A. compressa, or about its transcriptional versatility between life stages. To identify gut-biased genes related to digestion, detoxification, and stress response, we explored the midgut transcriptome of lab-reared A. compressa, for both adults and larvae, by focusing on the top 100 significantly up- and down-regulated genes. From the top 100 significantly differentially expressed genes (DEGs), we identified 39 and 36 DEGs putatively related to digestion and detoxification in the adult wasps and larvae, respectively. The two carbohydrases alpha-glucosidase (containing an alpha-amylase domain) and glycosyl hydrolase family 31, as well as the two proteinases chymotrypsin and trypsin, revealed the highest gene diversity. We identified six significant DEGs related to detoxification, which comprise glutathione S-transferase, cytochrome P450s and UDP-glucuronosyltransferase. The gene expression levels that were significantly expressed in both life stages vary strongly between life stages, as found in genes encoding for chymotrypsin and trypsin or glycosyl hydrolases family 31. The number of genes related to alpha-glucosidase, glycosyl hydrolase family 31, and cytochrome P450s was found to be similar across nine reference hymenopteran species, except for the identified glycosyl hydrolase family 31 gene, which was absent in all reference bee species. Phylogenetic analyses of the latter candidate genes revealed that they cluster together with their homologous genes found in the reference hymenopteran species. These identified candidate genes provide a basis for future comparative genomic and proteomic studies on (ontogenetic) dietary transitions in Hymenoptera.

From cockroaches to tanks: The same power-mass-speed relation describes both biological and artificial ground-mobile systems.

This paper explores whether artificial ground-mobile systems exhibit a consistent regularity of relation among mass, power, and speed, similar to that which exists for biological organisms. To this end, we investigate an empirical allometric formula proposed in the 1980s for estimating the mechanical power expended by an organism of a given mass to move at a given speed, applicable over several orders of magnitude of mass, for a broad range of species, to determine if a comparable regularity applies to a range of vehicles. We show empirically that not only does a similar regularity apply to a wide variety of mobile systems; moreover, the formula is essentially the same, describing organisms and systems ranging from a roach (1 g) to a battle tank (35,000 kg). We also show that for very heavy vehicles (35,000-100,000,000 kg), the formula takes a qualitatively different form. These findings point to a fundamental similarity between biological and artificial locomotion that transcends great differences in morphology, mechanisms, materials, and behaviors. To illustrate the utility of this allometric relation, we investigate the significant extent to which ground robotic systems exhibit a higher cost of transport than either organisms or conventional vehicles, and discuss ways to overcome inefficiencies.

Emigrating Together but Not Establishing Together: A Cockroach Rides Ants and Leaves.

AbstractSymbionts of ant colonies can hitchhike on winged ant reproductives (alates) during colony nuptial flights. Attaphila fungicola Wheeler, a miniature cockroach that lives in the nests of Texas leaf-cutter ants (Atta texana Buckley), hitchhikes on female alates (winged queens). Hitchhiking roaches are presumably vertically transmitted from leaf-cutter parent colonies to daughter colonies, remaining with female alates as they transition into foundresses (workerless queens); however, foundresses have limited resources and high mortality rates. Rather than remaining with foundresses likely to die (vertical transmission), roaches might abandon them during dispersal to infect higher-quality later stages of colony development (female alate-vectored transmission). In field experiments, I find evidence for female alate-vectored transmission and discover that roaches use a second hitchhiking step (riding foraged plant material) to infect established colonies. This work reveals a novel relationship between host dispersal and symbiont transmission and shows that colony development can be an important selection pressure on transmission.

Neotropical Melyroidea group cockroaches reveal various degrees of (eu)sociality.

Eusociality in its various degrees represents an animal social system characterised by cooperative brood care, differentiation into castes and generational overlap. The fossil record indicates that eusociality is likely to have originated in hymenopterans and blattodeans during the Cretaceous. In this study, we present findings from surveys in Peruvian (Villa Carmen) and Ecuadorian (Rio Bigal, El Reventador) cloud forests revealing the first extant cockroach species living in complex, structured groups (n = 90-200 individuals, ˃ 20 adults). We observed and described behaviours that suggest the existence of cooperative care, nest guarding, nest chamber preparation within hardwood Casearia sp. (Salicaceae) and bamboo (Bambusoideae), multiple overlapping generations ('different stages of' instars), colony translocation, possibly a sole reproductive female (1.25 times larger white 'queen', but no potential 'king' observed), and morphologically diversified immature stages. In order to define the lineage where this type of sociality originated and occurs, the forms of Melyroidea magnifica Shelford, 1912, M. ecuadoriana sp. n., M. mimetica Shelford, 1912 and an undescribed species from Peru are also described in a separate section of this study. Blattoid morphological characteristics such as typical styli suggest categorisation within distinct Oulopterygidae (Rehn, 1951), outside Corydiidae Saussure 1864. Transitional advanced sociality or semisociality in related Aclavoidea socialis gen. et sp. n. is documented in a rotting stump (n = 80 individuals, few adults). Close phylogenetic relation between the genera, conserved morphology of numerous characters and their diverse feeding strategies generally lacking specialisation suggests a rather recent origin of a social way of life in this group. Eusociality in invertebrates and vertebrates can thus originate in various phylogenetical and ecological trajectories including predation, parasitism, care for herbs and the new one, documented through diet shift from detritivory to fungivory and algaevory. Interdisciplinary approaches reveal the low degree of knowledge of rainforest ecosystems, with fundamental groups remaining still systematically and also behaviourally undescribed.

Three-dimensional analysis of the heart function and effect cholinergic agonists in the cockroach Gromphadorhina portentosa.

Many relevant aspects of mammal's cardiac physiology have been mainly investigated in insect models such as Drosophila melanogaster and Periplaneta americana. Cardiac function has been poorly studied in the cockroach Gromphadorhina portentosa, which has some advantages for experimental purposes such as an easier culture, bigger organs and a robust physiology. On the other hand, the study of cardiac physiology in insects has been largely improved since the arrival of digital imaging technologies for recording purposes. In the present work, we introduce a methodology of video recording coupled to an isotonic transducer for a three-dimensional analysis of the heart and intracardiac valves of G. portentosa. We used this methodology for assessing the physiological responses of the cockroach heart upon the application of different cholinergic neurotransmitters (acetylcholine, nicotine and muscarine). We recorded in detail the relationship between intracardiac valves movement, hemolymph flow, diastole and systole. Acetylcholine and nicotine induced a biphasic effect on the cardiac frequency. Acetylcholine increased the diastolic opening. Nicotine at high concentration caused paralysis. Muscarine induced no major effects. These findings suggest a combined action of cholinergic agonists for a finely tuned the cardiac frequency, intracardiac valves function and cardiac cycle.

Insect-machine hybrid robot.

Recently, insect-machine hybrid robots have been developed that incorporate insects into robots or incorporate machines into insects. Most previous studies were motivated to use the function of insects for robots, but this technology can also prove to be useful as an experimental tool for neuroethology. We reviewed hybrid robots in terms of the closed-loop between an insect, a robot, and the real environment. The incorporated biological components provided the robot sensory signals that were received by the insects and the adaptive functions of the brain. The incorporated artificial components permitted us to understand the biological system by controlling insect behavior. Hybrid robots thus extend the roles of mobile robot experiments in neuroethology for both model evaluation and brain function analysis.

Neither per, nor tim1, nor cry2 alone are essential components of the molecular circadian clockwork in the Madeira cockroach.

Circadian clocks control rhythms in physiology and behavior entrained to 24 h light-dark cycles. Despite of conserved general schemes, molecular circadian clockworks differ between insect species. With RNA interference (RNAi) we examined an ancient circadian clockwork in a basic insect, the hemimetabolous Madeira cockroach Rhyparobia maderae. With injections of double-stranded RNA (dsRNA) of cockroach period (Rm´per), timeless 1 (Rm´tim1), or cryptochrome 2 (Rm´cry2) we searched for essential components of the clock´s core negative feedback loop. Single injections of dsRNA of each clock gene into adult cockroaches successfully and permanently knocked down respective mRNA levels within ~two weeks deleting daytime-dependent mRNA rhythms for Rm´per and Rm´cry2. Rm´perRNAi or Rm´cry2RNAi affected total mRNA levels of both genes, while Rm´tim1 transcription was independent of both, also keeping rhythmic expression. Unexpectedly, circadian locomotor activity of most cockroaches remained rhythmic for each clock gene knockdown employed. It expressed weakened rhythms and unchanged periods for Rm´perRNAi and shorter periods for Rm´tim1RNAi and Rm´cry2RNAi.As a hypothesis of the cockroach´s molecular clockwork, a basic network of switched differential equations was developed to model the oscillatory behavior of clock cells expressing respective clock genes. Data were consistent with two synchronized main groups of coupled oscillator cells, a leading (morning) oscillator, or a lagging (evening) oscillator that couple via mutual inhibition. The morning oscillators express shorter, the evening oscillators longer endogenous periods based on core feedback loops with either PER, TIM1, or CRY2/PER complexes as dominant negative feedback of the clockwork. We hypothesize that dominant morning oscillator cells with shorter periods express PER, but not CRY2, or TIM1 as suppressor of clock gene expression, while two groups of evening oscillator cells with longer periods either comprise TIM1 or CRY2/PER suppressing complexes. Modelling suggests that there is an additional negative feedback next to Rm´PER in cockroach morning oscillator cells.

Characterization of Gromphadorhina coquereliana hemolymph under cold stress.

Low temperatures in nature occur together with desiccation conditions, causing changes in metabolic pathways and cellular dehydration, affecting hemolymph volume, water content and ion homeostasis. Although some research has been conducted on the effect of low temperature on Gromphadorhina coquereliana, showing that it can survive exposures to cold or even freezing, no one has studied the effect of cold on the hemolymph volume and the immune response of this cockroach. Here, we investigated the effect of low temperature (4 °C) on the abovementioned parameters, hemocyte morphology and total number. Cold stress affected hemocytes and the immune response, but not hemolymph volume. After stress, the number of circulating hemocytes decreased by 44.7%, but the ratio of apoptotic cells did not differ significantly between stressed and control individuals: 8.06% and 7.18%, respectively. The number of phagocyting hemocytes decreased by 16.66%, the hemocyte morphology drastically changed, and the F-actin cytoskeleton differed substantially in cold-stressed insects compared to control insects. Moreover, the surface area of the cells increased from 393.69 µm2 in the control to 458.38 µm2 in cold-treated animals. Together, our results show the links between cold stress and the cellular immune response, which probably results in the survival capability of this species.

Viscoelastic legs for open-loop control of gram-scale robots.

Gram-scale insects, such as cockroaches, take advantage of the mechanical properties of the musculoskeletal system to enable rapid and robust running. Engineering gram-scale robots, much like their biological counterparts, comes with inherent constraints on resources due to their small sizes. Resource-constrained robots are generally limited in their computational complexity, making controlled, high-speed locomotion a challenge, especially in unstructured environments. In this paper we show that embedding control into the leg mechanics of robots, similarly to cockroaches, results in predictable dynamics from an open-loop control strategy that can be modified through material choice. Tuning the mechanical properties of gram-scale robot legs promotes high-speed, stable running, reducing the need for active control. We utilize a torque-driven damped spring-loaded inverted pendulum model to explore the behavior and the design space of a spring-damper leg at this scale. The resulting design maps show the trade-offs in performance goals, such as speed and efficiency, with stability, as well as the sensitivity in performance to the leg properties and the control input. Finally, we demonstrate experimental results with magnetically actuated quadrupedal gram-scale robots, incorporating viscoelastic legs and demonstrating speeds up to 11.7 body lengths per second.