Hymenolepis diminuta (Cestoda) induces changes in expression of select genes of Tribolium confusum (Coleoptera)

Pathogen-Mediated Alterations of Insect Chemical Communication: From Pheromones to Behavior

Pathogens can influence the physiology and behavior of both animal and plant hosts in a manner that promotes their own transmission and dispersal. Recent research focusing on insects has revealed that these manipulations can extend to the production of pheromones, which are pivotal in chemical communication. This review provides an overview of the current state of research and available data concerning the impacts of bacterial, viral, fungal, and eukaryotic pathogens on chemical communication across different insect orders. While our understanding of the influence of pathogenic bacteria on host chemical profiles is still limited, viral infections have been shown to induce behavioral changes in the host, such as altered pheromone production, olfaction, and locomotion. Entomopathogenic fungi affect host chemical communication by manipulating cuticular hydrocarbons and pheromone production, while various eukaryotic parasites have been observed to influence insect behavior by affecting the production of pheromones and other chemical cues. The effects induced by these infections are explored in the context of the evolutionary advantages they confer to the pathogen. The molecular mechanisms governing the observed pathogen-mediated behavioral changes, as well as the dynamic and mutually influential relationships between the pathogen and its host, are still poorly understood. A deeper comprehension of these mechanisms will prove invaluable in identifying novel targets in the perspective of practical applications aimed at controlling detrimental insect species.

The Tapeworm Hymenolepis diminuta as an Important Model Organism in the Experimental Parasitology of the 21st Century

The tapeworm Hymenolepis diminuta is a common parasite of the small intestine in rodents but it can also infect humans. Due to its characteristics and ease of maintenance in the laboratory, H. diminuta is also an important model species in studies of cestodiasis, including the search for new drugs, treatments, diagnostics and biochemical processes, as well as its host-parasite interrelationships. A great deal of attention has been devoted to the immune response caused by H. diminuta in the host, and several studies indicate that infection with H. diminuta can reduce the severity of concomitant disease. Here, we present a critical review of the experimental research conducted with the use of H. diminuta as a model organism for over more than two decades (in the 21st century). The present review evaluates the tapeworm H. diminuta as a model organism for studying the molecular biology, biochemistry and immunology aspects of parasitology, as well as certain clinical applications. It also systematizes the latest research on this species. Its findings may contribute to a better understanding of the biology of tapeworms and their adaptation to parasitism, including complex correlations between H. diminuta and invertebrate and vertebrate hosts. It places particular emphasis on its value for the further development of modern experimental parasitology.

Comparison of the effects of multiple variables on the levels of infection of the rat tapeworm, Hymenolepis diminuta, in its intermediate host, the confused flour beetle Tribolium confusum

The interaction of the rat tapeworm, Hymenolepis diminuta, with its intermediate beetle host, Tribolium confusum, is a well-studied model system. However, there is so much variation in the methods and designs of the studies that it is difficult to draw comparisons. This study simultaneously compared several aspects of the infection protocol including beetle age, sex, density and mating status; parasite egg condition, infection environment humidity and the times for the three steps of infection: starvation, feeding and post-feeding development. Although statistically limited by low prevalence and intensity levels, we were able to detect the relative effects of the variables. The effects of these variables on prevalence (percent infection) and intensity (mean number of cysticercoids) do not necessarily correlate with each other. Egg condition, reduced starvation times, higher beetle density and longer development times reduced prevalence. However, differences in intensity were only detected with older beetles. When coupled with survivorship data, our study found that our current infection protocol is optimal for infection success. However, the results suggest extending the study to other intermediate hosts and the inclusion of additional variables.

Selection of reference genes for reverse transcription-qPCR analysis in the biomonitor macrophyte Bidens laevis L

The RT-qPCR has been the method used to analyze gene expression in plants but its benefits have not been completely exploited in the field of plants ecotoxicology when used as molecular biomarkers. The correct use of RT-qPCR demands to establish a certain number of reference genes (RG) which are expected to be invariable in their expression although it does not always happen. The main goals of this work were to: (1) analyze the stability of six potential RG, (2) establish the optimum number of RG, (3) select the most suitable RG to be applied in Bidens laevis under different test conditions and tissues and (4) confirm its convenience by normalizing the expression of one gene of interest under three different challenges. When all data were pooled together, the geNorm algorithm pointed out beta-actin and beta-tubulin (TUB) as the optimal RG pair while NormFinder algorithm selected nicotinamide adenine dinucleotide dehydrogenase (NADHD) and histone 3 (H3) as possessing the most invariable levels of expression. On the other hand, when data were grouped by tissues, ANOVA test selected H3 and TUB, while data grouped by conditions indicated that H3 and NADHD were the most stable RG under this analysis. Therefore, for a general-purpose set of RG, the overall analysis showed that a set of three RG would be optimum, and H3, TUB and NADHD were the selected ones. On the other hand, as RG can vary depending on the tissues or conditions, results achieved with ANOVA would be more reliable. Thus, appropriate normalization process would clearly need more than one RG.

Establishment Success of the Beetle Tapeworm Hymenolepis diminuta Depends on Dose and Host Body Condition

Parasite effects on host fitness and immunology are often intensity-dependent. Unfortunately, only few experimental studies on insect-parasite interactions attempt to control the level of infection, which may contribute substantial variation to the fitness or immunological parameters of interest. The tapeworm Hymenolepis diminuta—flour beetle Tenebrio molitor model—has been used extensively for ecological and evolutionary host–parasite studies. Successful establishment of H. diminuta cysticercoids in T. molitor relies on ingestion of viable eggs and penetration of the gut wall by the onchosphere. Like in other insect models, there is a lack of standardization of the infection load of cysticercoids in beetles. The aims of this study were to: (1) quantify the relationship between exposure dose and establishment success across several H. diminuta egg concentrations; and (2) test parasite establishment in beetles while experimentally manipulating host body condition and potential immune response to infection. Different egg concentrations of H. diminuta isolated from infected rat feces were fed to individual beetles 7–10 days after eclosion and beetles were exposed to starvation, wounding, or insertion of a nylon filament one hour prior to infection. We found that the establishment of cysticercoids in relation to exposure dose could be accurately predicted using a power function where establishment success was low at three lowest doses and higher at the two highest doses tested. Long-term starvation had a negative effect on cysticercoid establishment success, while insertion of a nylon filament and wounding the beetles did not have any effect compared to control treatment. Thus, our results show that parasite load may be predicted from the exposure dose within the observed range, and that the relationship between dose and parasite establishment success is able to withstand some changes in host body condition.

Longitudinal study of parasite-induced mortality of a long-lived host: the importance of exposure to non-parasitic stressors

Hosts face mortality from parasitic and environmental stressors, but interactions of parasitism with other stressors are not well understood, particularly for long-lived hosts. We monitored survival of flour beetles (Tribolium confusum) in a longitudinal design incorporating cestode (Hymenolepis diminuta) infection, starvation and exposure to the pesticide diatomaceous earth (DE). We found that cestode cysticercoids exhibit increasing morphological damage and decreasing ability to excyst over time, but were never eliminated from the host. In the presence of even mild environmental stressors, host lifespan was reduced sufficiently that extensive degradation of cysticercoids was never realized. Median host lifespan was 200 days in the absence of stressors, and 3-197 days with parasitism, starvation and/or DE. Early survival of parasitized hosts was higher relative to controls in the presence of intermediate concentrations of DE, but reduced under all other conditions tested. Parasitism increased host mortality in the presence of other stressors at times when parasitism alone did not cause mortality, consistent with an interpretation of synergy. Environmental stressors modified the parasite numbers needed to reveal intensity-dependent host mortality, but only rarely masked intensity dependence. The longitudinal approach produced observations that would have been overlooked or misinterpreted if survival had only been monitored at a single time point.

Hymenolepis diminuta infections in tenebrionid beetles as a model system for ecological interactions between helminth parasites and terrestrial intermediate hosts: a review and meta-analysis

The cestode Hymenolepis diminuta (Cyclophyllidea) uses a variety of insects as its intermediate host, where ingestion of eggs results in development in the hemocoel of a cysticercoid that is infective to a rat definitive host. Species in 2 genera, Tenebrio and Tribolium (Coleoptera: Tenebrionidae) have been used extensively as laboratory intermediate hosts. This review examines experimental studies on ecological aspects of the relationship between H. diminuta and tenebrionid beetles, including the acquisition and establishment of the parasite, host effects on the parasite, and parasite effects on the host. A meta-analysis of infection results from the literature revealed strong relationships across host species and strains between (1) prevalence and intensity of infection, (2) efficiency of cysticercoid production and exposure conditions, and (3) variance in abundance or intensity of infection relative to their respective means. The underlying mechanisms producing these patterns remain elusive. Comparative studies are infrequent, and the use of divergent methodologies hampers comparisons among studies. In spite of these problems, there is much to recommend this as a terrestrial host-parasite model system. It represents those relationships in which mostly minor, but occasionally major, responses to parasitic infection occur, and in which host genetics and environmental conditions can serve as modifying factors. Moreover, this is a tractable experimental system, and is backed by an extensive literature on host biology.

Transcription profiling of immune genes during parasite infection in susceptible and resistant strains of the flour beetles (Tribolium castaneum)

The flour beetle, Tribolium castaneum, is an intermediate host for the tapeworm Hymenolepis diminuta and has become an important genetic model to explore immune responses to parasite infection in insect hosts. The present study examined the immune responses to tapeworm infection in resistant (TIW1) and susceptible (cSM) strains of the red flour beetle, T. castaneum, using real-time quantitative reverse transcription PCR on 29 immunity-related genes that exhibit antimicrobial properties. Thirteen of the 29 genes showed constitutive differences in expression between the two strains. Fourteen to fifteen of the 29 genes exhibited significant differences in transcription levels when beetles were challenged with tapeworm parasite in the resistant and susceptible strains. Nine genes (GNBP3, cSPH2, lysozyme4, defensin1, PGRP-SA, defensin2, coleoptericin1, attacin2 and serpin29) in cSM and 13 genes (lysozyme2, proPO1, GNBP3, cSPH2, lysozyme4, defensin1, PGRP-SA, defensin2, coleoptericin1, attacin2, proPO2/3, PGRP-LE and PGRP-SB) in TIW1 were up-regulated by infections or showed parasite infection-induced expression. Seven genes (attacin2, coleoptericin1, defensin1, defensin2, lysozyme2, PGRP-SA and PGRP-SB) were more than 10 folds higher in the resistant TIW1 strain than in the susceptible cSM strain after exposure to tapeworm parasites. This study demonstrated the effects of genetic background, the transcription profile to parasite infection, and identified the immunity-related genes that were significantly regulated by the infection of tapeworms in Tribolium beetles.

The activity of drug-metabolizing enzymes and the biotransformation of selected anthelmintics in the model tapeworm Hymenolepis diminuta

The drug-metabolizing enzymes of some helminths can deactivate anthelmintics and therefore partially protect helminths against these drugs' toxic effect. The aim of our study was to assess the activity of the main drug-metabolizing enzymes and evaluate the metabolism of selected anthelmintics (albendazole, flubendazole, mebendazole) in the rat tapeworm Hymenolepis diminuta, a species often used as a model tapeworm. In vitro and ex vivo experiments were performed. Metabolites of the anthelmintics were detected and identified by HPLC with spectrofluorometric or mass–spectrometric detection. The enzymes of H. diminuta are able to reduce the carbonyl group of flubendazole, mebendazole and several other xenobiotics. Although the activity of a number of oxidation enzymes was determined, no oxidative metabolites of albendazole were detected. Regarding conjugation enzymes, a high activity of glutathione S-transferase was observed. A methyl derivative of reduced flubendazole was the only conjugation metabolite identified in ex vivo incubations of H. diminuta with anthelmintics. The results revealed that H. diminuta metabolized flubendazole and mebendazole, but not albendazole. The biotransformation pathways found in H. diminuta differ from those described in Moniezia expanza and suggest the interspecies differences in drug metabolism not only among classes of helminths, but even among tapeworms.