Gromphadorhina Portentosa Research Articles

Morphology and ultrastructure of the tarsal adhesive organs of the Madagascar hissing cockroach Gromphadorhina portentosa.

The present transmission and scanning electron microscopic study of the ultramorphology of the pliable attachment pads (arolium, euplantulae) of the Madagascar hissing cockroach Gromphadorhina portentosa reveals structural evidence for their function in producing, storing, and secreting an adhesion-mediating secretion and releasing it to the exterior. The exocrine epidermal tissue of both the arolium and the euplantula is significantly enlarged by numerous invaginations stretching into the hemolymph cavity. Its cells show large nuclei, numerous mitochondria, Golgi complexes, and a prominent rough-surfaced endoplasmic reticulum integrated within an electron-dense cytoplasm that contains numerous vesicles of diverse electron density and size. Invaginations of the cell membrane provide evidence for strong membrane turnover. The glandular epithelium of both the arolium and the euplantula releases the adhesion-mediating secretion into a subcuticular void from which it has to permeate the thick cuticle of the adhesive pads. The subcuticular void is compartmentalized by cuticle bands through which the adhesion-mediating secretion permeates via small canals. The secretion subsequently enters a larger storage reservoir before being received by a prominent sponge-like cuticle. The structural differences between the arolium and the euplantula consist of the number and length of the interdigitations spanning the hemolymph cavity, of the subdivision of the subcuticular reservoir by cuticle bands, and of the thickness of the sponge-like cuticle. The structural results are discussed with respect to the production of a chemically complex (emulsion-like) adhesive, its controlled release to the exterior, and the micromechanical properties of the cuticle of the pliable pad.

Adhesion and friction of the smooth attachment system of the cockroach Gromphadorhina portentosa and the influence of the application of fluid adhesives.

ABSTRACTTwo different measurement techniques were applied to study the attachment of the smooth foot pads of the Madagascar hissing cockroach Gromphadorhina portentosa. The attachment of the non-manipulated adhesive organs was compared with that of manipulated ones (depletion or substitution by artificial secretions). From measurements of the friction on a centrifuge, it can be concluded that on nanorough surfaces, the insect appears to benefit from employing emulsions instead of pure oils to avoid excessive friction. Measurements performed with a nanotribometer on single attachment organs showed that, in the non-manipulated euplantulae, friction was clearly increased in the push direction, whereas the arolium of the fore tarsus showed higher friction in the pull direction. The surface of the euplantulae shows an imbricate appearance, whereupon the ledges face distally, which might contribute to the observed frictional anisotropy in the push direction. Upon depletion of the tarsal adhesion-mediating secretion or its replacement by oily fluids, in several cases, the anisotropic effect of the euplantula disappeared due to the decrease of friction forces in push-direction. In the euplantulae, adhesion was one to two orders of magnitude lower than friction. Whereas the tenacity was slightly decreased with depleted secretion, it was considerably increased after artificial application of oily liquids. In terms of adhesion, it is concluded that the semi-solid consistence of the natural adhesion-mediating secretion facilitates the detachment of the tarsus during locomotion. In terms of friction, on smooth to nanorough surfaces, the insects appear to benefit from employing emulsions instead of pure oils to avoid excessive friction forces, whereas on rougher surfaces the tarsal fluid rather functions in improving surface contact by keeping the cuticle compliable and compensating surface asperities of the substratum.

Effects of diet on growth rates in Aleuropoda insignis.

Aleuropoda insignis are a species of Madagascar Hissing Cockroach that typically live in colonies with males generating courtship calls (whistles or ‘hisses’, Comer & Conley 2016). Variability in individual courtship songs may be a factor in sexual selection within and between species of hissing cockroaches. Diet may influence effects of sexual selection since individuals in sparse populations may have to travel longer distances to find mates and may grow to a larger size (Kasumovic & Andrade 2006). To observe effects of diet on growth rates, Aleuropoda insignis were isolated from birth and put on one of three distinct diets. Ten individuals were fed a grain-based commercial cricket food, ten individuals were fed a corn-based commercial dog food and ten individuals were fed certified organic grain/corn/soybean-based human-grade food. Since social isolation may affect growth rate (simulating a sparse population), some animals were maintained in a colony and the growth rate of a representative sample individuals from the colony was calculated. Growth rate was calculated as the change in the area of the animals’ body over the number of days, measured from photographs. The data suggest a growth spurt at about 12 weeks of age across all diets. The average growth rate was lower for the corn-based dog food diet, but not significant (p<0.17); however a larger sample size may provide a significant difference. Differences in growth rates (or size) between colonial versus isolated animals may be insignificant since colonial species should not have to travel far to find mates. This work was funded in part by the Research Challenge Fund through a Summer Undergraduate Research Experience Grant from the West Virginia Higher Education Policy Commission Division of Science and Research

Susceptibility of cockroaches (Gromphadorhina portentosa, Nauphoeta cinerea and Blaptica dubia) exposed to entomopathogenic nematodes

ABSTRACTCockroaches are major pests, vectors of pathogenic bacteria and induce allergies. Current control methods use chemical pesticides, but they can be ineffective and costly and there are reports of resistance in the field; hence new control methods are needed. There are conflicting reports about the susceptibility of cockroaches to entomopathogenic nematodes (EPNs); so we investigated if EPNs could kill several diverse cockroach species, including the Madagascan hissing roach (Gromphadorhina portentosa), the Lobster roach (Nauphoeta cinerea) and Blaptica dubia. Female adult cockroaches were exposed to either commercial products containing Steinernema kraussei or a combination of Heterorhabditis spp. and Steinernema spp. at 50 and 150 nematodes per cm2 for 21 days. We also monitored feeding and the numbers of infective juveniles that were produced from each cockroach corpse. We found that S. kraussei were harmless to all cockroach species (at both doses) but when exposed to a mixture of Heterorhabditis spp. and Steinernema spp. B. dubia died after 6 days and its feeding was strongly inhibited. We also found that the mixture of Heterorhabditis spp. and Steinernema spp. could proliferate in the cadavers of B. dubia whilst S. kraussei could only reproduce in G. portentosa and B. dubia but not N. cinerea. In conclusion, S. kraussei was harmless to all three cockroach species but B. dubia was killed when exposed to Heterorhabditis spp. and Steinernema spp., highlighting the differences in the host range of EPNs.

First protein and peptide characterization of the tarsal adhesive secretions in the desert locust, Schistocerca gregaria, and the Madagascar hissing cockroach, Gromphadorhina portentosa.

Peptides and proteins have been largely neglected in the analysis of insect tarsal adhesives. After extraction of the protein fraction of the tarsal secretion of the desert locust, Schistocerca gregaria, and Madagascar hissing cockroach, Gromphadorhina portentosa, we combined Fourier transform infrared spectroscopy (FTIR), sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS) analyses for protein mass detection. In both these insects, SDS-PAGE analysis revealed several protein bands ranging from 8-190 kDa in both the tarsal secretion and the tibia control sample. Two (S. gregaria) and one (G. portentosa) protein bands exclusively occurred in the tarsal secretion and can be considered to belong to peptides and proteins specific to this secretion. MALDI-TOF analyses revealed 83 different proteins/peptides of 1-7 kDa in S. gregaria, and 48 of 1-11 kDa in G. portentosa. 59 (S. gregaria) and 27 (G. portentosa) proteins exclusively occurred in the tarsal secretion. In G. portentosa, a characteristic series of signal peaks occurred in the range of c. 10-12 kDa, each peak being approximately 160 Da apart. Such a pattern is indicative of proteins modified by glycosylation. Our approach demonstrates that extensive sampling involving considerable time and manpower to sample the adhesive fluid directly from the tarsi opens up a perspective for extracting peptides and proteins in sufficient quantities. This makes them accessible to the field of proteomics and thus to elucidate their possible function in the adhesive process.

The complete mitochondrial genomes of four cockroaches (Insecta: Blattodea) and phylogenetic analyses within cockroaches

Three complete mitochondrial genomes of Blaberidae (Insecta: Blattodea) (Gromphadorhina portentosa, Panchlora nivea, Blaptica dubia) and one complete mt genome of Blattidae (Insecta: Blattodea) (Shelfordella lateralis) were sequenced to further understand the characteristics of cockroach mitogenomes and reconstruct the phylogenetic relationship of Blattodea. The gene order and orientation of these four cockroach genomes were similar to known cockroach mt genomes, and contained 13 protein-coding genes (PCGs), 2 ribosomal RNA (rRNA) genes, 22 transfer RNA (tRNA) genes and one control region. The mt genomes of Blattodea exhibited a characteristics of a high A+T composition (70.7%–74.3%) and dominant usage of the TAA stop codon. The AT content of the whole mt genome, PCGs and total tRNAs in G. portentosa was the lowest in known cockroaches. The presence of a 71-bp intergenic spacer region between trnQ and trnM was a unique feature in B. dubia, but absent in other cockroaches, which can be explained by the duplication/random loss model. Based on the nucleotide and amino acid datasets of the 13 PCGs genes, neighbor-joining (NJ), maximum parsimony (MP), maximum likelihood (ML) and bayesian inference (BI) analyses were used to rebuild the phylogenetic relationship of cockroaches. All phylogenetic analyses consistently placed Isoptera as the sister cluster to Cryptocercidae of Blattodea. Ectobiidae and Blaberidae (Blaberoidea) formed a sister clade to Blattidae. Corydiidae is a sister clade of all the remaining cockroach species with a high value in NJ and MP analyses of nucleotide and amino acid datasets, and ML and BI analyses of the amino acid dataset.

The effect of diet on the metabolic rate and microbiome of Gromphadorhina portentosa

The metabolic phenotype of an animal is shaped by the developmental trajectory of its gut microbiome. Although the core microbiota of an organism is stable throughout adulthood, there are certain parts of the microbiome that can be altered through an array of environmental stressors, such as diet. So far, there is a lot of research focused on the effects that diet has on the metabolism and gut microbiome of vertebrate mammals. However, not a lot of work is focused on how a change in diet can affect the metabolic rates, or the microbiome, of invertebrates. In its natural habitat Gromphadorhina portentosa, the hissing cockroach, feeds opportunistically on fruits and may also consume decaying animal material and small insects. In this study we measured the effects of diet on the metabolic rate, and microbiota, of G. portentosa. Prior to data collection we normalize the microbiota of forty male cockroaches by placing them on a control diet. Preliminary data showed that roaches would move all gut contents through their digestive system within 7 days. Resting metabolic rates for normalized cockroaches was measured after cockroaches had been placed for 2 weeks under the control diet. Fecal samples were also collected at this time. Ten male roaches were placed under one of four diet treatments (control, high protein, high carbohydrate or high lipid) for a total of 8 weeks. During this experimental period, resting metabolic rates were obtained on a weekly basis using flow through respirometry. Fecal samples were once again collected at the end of the 8‐week experimental period. Cultivation independent metagenomic sequencing was accomplished so that changes in the microbiota of roaches could be identified. Previous work has shown a shift in the microbiota of organisms fed varying amounts of fat vs. protein, were animals fed a high protein diet showed an increase in bacteroidetes with was an inverse relationship to the firmicute population. Furthermore, an increase in metabolic rates have also been seen when animals are given a high protein diet. We expect G. portentosma to respond in a similar manner when their diet is altered.Support or Funding InformationULV Faculty Research Grant

Temperature and the Ventilatory Response to Hypoxia in Gromphadorhina portentosa (Blattodea: Blaberidae).

In general, insects respond to hypoxia by increasing ventilation frequency, as seen in most other animals. Higher body temperatures usually also increase ventilation rates, likely due to increases in metabolic rates. In ectothermic air-breathing vertebrates, body temperatures and hypoxia tend to interact significantly, with an increasing responsiveness of ventilation to hypoxia at higher temperatures. Here, we tested whether the same is true in insects, using the Madagascar hissing cockroach, Gromphadorhina portentosa (Schaum) (Blattodea: Blaberidae). We equilibrated individuals to a temperature (beginning at 20 °C), and animals were exposed to step-wise decreases in PO2 (21, 15, 10, and 5 kPa, in that order), and we measured ventilation frequencies from videotapes of abdominal pumping after 15 min of exposure to the test oxygen level. We then raised the temperature by 5 °C, and the protocol was repeated, with tests run at 20, 25, 30, and 35 °C. The 20 °C animals had high initial ventilation rates, possibly due to handling stress, so these animals were excluded from subsequent analyses. Across all temperatures, ventilation increased in hypoxia, but only significantly at 5 kPa PO2 Surprisingly, there was no significant interaction between temperature and oxygen, and no significant effect of temperature on ventilation frequency from 25 to 35 °C. Plausibly, the rise in metabolic rates at higher temperatures in insects is made possible by increasing other aspects of gas exchange, such as decreasing internal PO2, or increases in tidal volume, spiracular opening (duration or amount), or removal of fluid from the tracheoles.

ω-Tbo-IT1-New Inhibitor of Insect Calcium Channels Isolated from Spider Venom.

Novel disulfide-containing polypeptide toxin was discovered in the venom of the Tibellus oblongus spider. We report on isolation, spatial structure determination and electrophysiological characterization of this 41-residue toxin, called ω-Tbo-IT1. It has an insect-toxic effect with LD50 19 μg/g in experiments on house fly Musca domestica larvae and with LD50 20 μg/g on juvenile Gromphadorhina portentosa cockroaches. Electrophysiological experiments revealed a reversible inhibition of evoked excitatory postsynaptic currents in blow fly Calliphora vicina neuromuscular junctions, while parameters of spontaneous ones were not affected. The inhibition was concentration dependent, with IC50 value 40 ± 10 nM and Hill coefficient 3.4 ± 0.3. The toxin did not affect frog neuromuscular junctions or glutamatergic and GABAergic transmission in rat brains. Ca2+ currents in Calliphora vicina muscle were not inhibited, whereas in Periplaneta americana cockroach neurons at least one type of voltage gated Ca2+ current was inhibited by ω-Tbo-IT1. Thus, the toxin apparently acts as an inhibitor of presynaptic insect Ca2+ channels. Spatial structure analysis of the recombinant ω-Tbo-IT1 by NMR spectroscopy in aqueous solution revealed that the toxin comprises the conventional ICK fold containing an extended β-hairpin loop and short β-hairpin loop which are capable of making “scissors-like mutual motions”.

Immunochemical detection of the crustacean cardioactive peptide in the cephalic ganglia of cockroaches (Blattodea: Blattidae)

In insects, the crustacean cardioactive peptide (CCAP) is involved mainly in the regulation of ecdysis and is both a hormone secreted into the haemolymph and a neuromodulator or neurotransmitter in the nervous system. However, this peptide has only been recorded in the brains of a few species of insects. The present study examined the distribution of CCAP in the cephalic ganglia of the cockroach, Periplaneta americana, using two kinds of specific antibodies. The antibody directed against synthetic CCAP detected a large number of CCAP-immunoreactive neurons in the protocerebrum, deutocerebrum, tritocerebrum, suboesophageal ganglion, optic lobes, frontal ganglion and neurohemal organs, while the antibody directed against CCAP precursor (pre-propeptide) stained only a few neurons within the central brain and frontal ganglion. The latter antibody also revealed similar sets of neurons in another species of cockroach, Gromphadorhina portentosa, and identified the CCAP precursor of approximately 15 kDa in size in Western blot analyses.

Cold induced changes in lipid, protein and carbohydrate levels in the tropical insect Gromphadorhina coquereliana

Insects cope with thermal stressors using mechanisms such as rapid cold hardening and acclimation. These mechanisms have been studied in temperate insects, but little is known about their use by tropical insects in response to cold stress. Here, we investigated whether cold stress (1×8h and 3×8h at 4°C) triggers a metabolic response in the Madagascar cockroach Gromphadorhina coquereliana. We examined the effects of cold on the levels of selected metabolites in the fat body tissue of G. coquereliana. After cold exposure, we found that the quantity of total protein increased significantly in the insect fat body, whereas glycogen decreased slightly. Using antibodies, we observed upregulation of AQP-like proteins and changes in the HSP70 levels in the fat body of G. coquereliana when exposed to cold. We also examined the content and nature of the free sugars in the G. coquereliana hemolymph and discovered an increase in the levels of polyols and glucose in response to cold stress. These results suggest an important role of the fat body tissue of tropical insects upon cold exposure.

Towards fenceless boundaries for solar powered insect biobots.

Demonstration of remote navigation with instrumented insects, such as the Madagascar Hissing Cockroach, Gromphadorhina portentosa, has enabled the concept of biobotic agents for search and rescue missions and environmental monitoring applications. The biobots can form the nodes of a mobile sensor network to be established, for example, in unknown and dynamic environments after natural disasters to pinpoint surviving victims. We demonstrate here, for the first time, the concept of an invisible fence for insect biobots with an ultimate goal of keeping insect biobots within a certain distance of each other or a base station to ensure a reliable wireless network. For extended mission durations, this fenceless boundary would also be used to guide insects towards light sources for autonomous solar charging of their on-board batteries.

Neural responses from the wind-sensitive interneuron population in four cockroach species

The wind-sensitive insect cercal sensory system is involved in important behaviors including predator detection and initiating terrestrial escape responses as well as flight maintenance. However, not all insects possessing a cercal system exhibit these behaviors. In cockroaches, wind evokes strong terrestrial escape responses in Periplaneta americana and Blattella germanica, but only weak escape responses in Blaberus craniifer and no escape responses in Gromphadorhina portentosa. Both P. americana and B. craniifer possesses pink flight muscles correlated with flight ability while B. germanica possesses white flight muscles that cannot support flight and G. portentosa lacks wings. These different behavioral combinations could correlate with differences in sensory processing of wind information by the cercal system. In this study, we focused on the wind-sensitive interneurons (WSIs) since they provide input to the premotor/motor neurons that influence terrestrial escape and flight behavior. Using extracellular recordings, we characterized the responses from the WSI population by generating stimulus–response (S–R) curves and examining spike firing rates. Using cluster analysis, we also examined the activity of individual units (four per species, though not necessarily homologous) comprising the population response in each species. Our main results were: (1) all four species possessed ascending WSIs in the abdominal connectives; (2) wind elicited the weakest WSI responses (lowest spike counts and spike rates) in G. portentosa; (3) wind elicited WSI responses in B. craniifer that were greater than P. americana or B. germanica; (4) the activity of four individual units comprising the WSI population response in each species was similar across species.

Wireless Communication By an Autonomous Self-Powered Cyborg Insect

Wireless Communication By an Autonomous Self-Powered Cyborg Insect

Testing the disturbance hiss of the Madagascar hissing Cockroach (Gromphadorhina portentosa) as an anti-predatory response

The display of the disturbance hiss by the Madagascar Hissing Cockroach (Gromphadorhina portentosa) is considered to be an anti-predatory response despite there being little direct evidence linking the hiss with survival. Many studies have investigated the roles of the aggression and courtship hisses, displayed in this social species, but few have considered the role of the disturbance hiss. This study looked at the stimulus for the disturbance hiss response by placing unfamiliar individuals into different social contexts. A total of 10 male and 10 female G. portentosa were kept separately before being placed into four different social situations for 5 min at a time. The individuals were placed into an established colony of all females, an established colony of all males and an established colony of mixed sex G. portentosa. The subjects were also placed in the presence of a predator, an Emperor Scorpion (Pandinus imperator Koch). All interactions and hisses were recorded both by video and on a sound-recording device. There was a highly significant difference in the setting in which the disturbance hiss was shown and a highly significant difference in the display rates of the disturbance hiss between the sexes in general, with most displays of the disturbance hiss being when introduced to a mixed sex colony. The findings suggest that the role of the disturbance hiss is not an anti-predatory response when presented with a predator of limited auditory senses. Further study into the behavioural ecology of this species is recommended to understand the range of anti-predatory responses used by this species when presented with different predators. It was also found that there is some social context for the display of the disturbance hiss which warrants further study.

Boldness is influenced by sublethal interactions with predators and is associated with successful harem infiltration in Madagascar hissing cockroaches

One of the contemporary challenges of the behavioral syndromes literature is to identify how individual variation in behavior is determined, and whether this variation impacts ecological success. Although variation in experience is an obvious potential driver of intraspecific behavioral variation, predicting the impact of experience on suites of correlated behavioral traits is less intuitive. Specifically, if experience impacts traits that shape individuals' success in multiple contexts (e.g., foraging and anti-predator behavior), then experience could generate cross-contextual performance trade-offs associated with behavioral spillover. In the present study, we explore how sublethal experience with predators impacts various aspects of male behavioral tendencies in the Madagascar hissing cockroach, Gromphadorhina portentosa. First, we found that males' activity level and boldness were correlated together in the form of a behavioral syndrome. Second, we found that repeated sublethal interactions with predators shifted male boldness but not activity level, thus suggesting that the syndrome's constituent traits can respond to experience at least semi-independently. Third, we discovered that although predator exposure only influenced boldness, we found that boldness was highly correlated with males' ability to obtain rewarding positions in the harems of rival males. Taken together, our data suggest (but do not yet confirm) that although sublethal exposure to predators influences only a narrow subset of male's behavioral tendencies, these effects could still have nonintuitive consequences for males' success in functionally dissimilar ecological contexts (i.e., social and sexual encounters).

Upper Thermal Limits of Insects Are Not the Result of Insufficient Oxygen Delivery

Most natural environments experience fluctuating temperatures that acutely affect an organism's physiology and ultimately a species' biogeographic distribution. Here we examine whether oxygen delivery to tissues becomes limiting as body temperature increases and eventually causes death at upper lethal temperatures. Because of the limited direct, experimental evidence supporting this possibility in terrestrial arthropods, we explored the effect of ambient oxygen availability on the thermotolerance of insects representing six species (Acheta domesticus, Hippodamia convergens, Gromphadorhina portentosa, Pogonomyrmex occidentalis, Tenebrio molitor, and Zophobus morio), four taxonomic orders (Blattodea, Coleoptera, Hymenoptera, and Orthoptera), and multiple life stages (e.g., adults vs. larvae or nymphs). The survival curves of insects exposed to temperatures (45° or 50°C) under normoxic conditions (21% O(2)) were compared with those measured under altered oxygen levels (0%, 10%, 35%, and 95% O(2)). Kaplan-Meier log rank analyses followed by Holm-Sidak pairwise comparisons revealed that (1) anoxia sharply diminished survival times in all groups studied, (2) thermotolerance under moderate hyperoxia (35% O(2)) or moderate hypoxia (10% O(2)) was the same as or lower than that under normoxia, (3) half of the experimental treatments involving extreme hyperoxia (95% O(2)) caused reduced thermotolerance, and (4) thermotolerance differed with developmental stage. Adult G. portentosa exhibited much higher thermotolerance than their first-instar nymphs, but responses from larval and adult Z. morio were equivocal. We conclude that some factor(s) separate from oxygen delivery is responsible for death of insects at upper lethal temperatures.

Coordinated ventilation and spiracle activity produce unidirectional airflow in the hissing cockroach,Gromphadorhina portentosa

Insects exchange respiratory gases via an extensive network of tracheal vessels that open to the surface of the body through spiracular valves. Although gas exchange is known to increase with the opening of these spiracles, it is not clear how this event relates to gas flow through the tracheal system. We examined the relationship between respiratory airflow and spiracle activity in a ventilating insect, the hissing cockroach, Gromphadorhina portentosa, to better understand the complexity of insect respiratory function. Using simultaneous video recordings of multiple spiracular valves, we found that abdominal spiracles open and close in unison during periods of ventilation. Additionally, independent recordings of CO2 release from the abdominal and thoracic regions and observations of hyperoxic tracer gas movement indicate that air is drawn into the thoracic spiracles and expelled from the abdominal spiracles. Our video recordings suggest that this unidirectional flow is driven by abdominal contractions that occur when the abdominal spiracles open. The spiracles then close as the abdomen relaxes and fills with air from the thorax. Therefore, the respiratory system of the hissing cockroach functions as a unidirectional pump through the coordinated action of the spiracles and abdominal musculature. This mechanism may be employed by a broad diversity of large insects that respire by active ventilation.

Alteration of carbohydrates metabolism and midgut glucose absorption in Gromphadorhina portentosa after subchronic exposure to imidacloprid and fenitrothion

This study was undertaken to test the hypothesis that following exposure to insecticides, changes take place in the metabolism of carbohydrates and absorption in the midgut of insects. The Madagascar hissing cockroach (Gromphadorhina portentosa) was chosen for the experiment as a model organism, due to it being easy to breed and its relatively large alimentary tract, which was important when preparing the microperfusion midgut bioassay. In each group of cockroaches treated with imidacloprid and fenitrothion, absorption of glucose, expressed as the area under the curve (AUC), was elevated compared to the control group. Glucose in the hemolymph of the examined insects was present in a vestigial amount, often below the threshold of determination, so the determinable carbohydrate indices were: hemolymph trehalose concentration and fat body glycogen content. The level of trehalose found in the hemolymph of insects when exposed to fenitrothion, and irrespective of the level of concentration mixed into food, were significantly lower when comparing to the control samples. Imidacloprid acted analogically with one exception at the concentration of 10 mg·kg−1 dry food where trehalose concentration did not differ from the control values. Coupling with fat body glycogen concentration was less visible and appeared only at the concentrations of 5 and 10 mg imidacloprid·kg−1 dry food. As described in this study changes in the sugar distribution and midgut glucose absorption indicate that insects cover the increased energy needs induced by insecticides; also at the gastrointestinal tract level. The result indicates that the midgut glucose absorption parameters could be considered as a non-specific biomarker of insecticide toxicity.

Madagascar hissing cockroach mite, Gromphadorholaelaps schaeferi, prevents fungal infection in its cockroach host: evidence for a mutualistic symbiosis

In this study, we provide the first evidence that the mite Gromphadorholaelaps schaeferi is beneficial to the Madagascar hissing cockroach Gromphadorhina portentosa by participating in a cleaning symbiosis and thus prolonging the life of its host. Gromphadorholaelaps schaeferi is a permanent resident of the cockroach and reduces mould levels by removing the food debris from the cockroach that acts as a substrate for fungal growth. To investigate the mould clearance attributes of these mites, we determined the effectiveness of mite infestation for decreasing cockroach mortality from a topically applied entomopathogenic fungus Metarhizium anisopliae. We further determined the effects of regulating cockroach food levels on altering the mycoflora profile of the cockroaches, with and without mites. Results showed that the lifespan of the cockroaches is extended by approximately 9 months when infested with mites. When treated with M. anisopliae (107 conidia/ml), which is pathogenic to the cockroach but not to the mite, mite infestation increases cockroach longevity by 65% as compared to uninfested cockroaches. Also, the effects of limiting the food offered to the cockroaches synergize with the cleaning symbiosis relationship to further reduce cockroach surface moulds. As a side observation, limiting food input in the cockroach colony not only reduces total cockroach moulds, but also shifts the fungal competition to favour those strains that are less medically significant, that is, away from an otherwise heavy zygomycete load of Rhizopus spp. and Mucor spp. to mitosporic fungi. Maintaining a healthy mite population, and reducing the amount of food kept in the cages, when keeping the hissing cockroach in captivity can potentially reduce fungal load and therefore any associated (human) allergies.