The life cycle of Gregarina cuneata in the midgut of Tribolium castaneum and the effects of parasitism on the development of insects

Tribolium castaneum Herbst 1797 (Coleoptera: Tenebrionidae), an important pest of stored grains and byproducts, is naturally infected by Gregarina cuneata Stein 1848 (Apicomplexa: Gregarinidae). Changes in the life cycle of insects caused by the parasite development in the midgut were studied. Trophozoites, gamonts (solitary and associated), and gametocysts were present in the midgut of the insects. In young trophozoites, the apical region differentiated into an epimerite that firmly attached the parasite to the host epithelial cells. With maturation, trophozoites developed in gamonts that were associated with the initiation of sexual reproduction in the cell cycle, culminating in the formation of the spherical gametocyst. Morpho-functional analyses indicated that gregarines absorb nutrients from infected cells and can occlude the midgut as they develop. Consequently, nutritional depletion may interfere with the host's physiology, causing decreased growth, delayed development, and high mortality rates of the parasitized insects. These results suggest G. cuneata could be an important biological agent for controlling T. castaneum in integrated pest management programs.

Response of Tribolium castaneum to elevated copper concentrations is influenced by history of metal exposure, sex-specific defences, and infection by the parasite Steinernema feltiae

We studied how copper toxicity in the red flour beetle, Tribolium castaneum changed as a result of infection by the entomopathogenic nematode Steinernema feltiae. Measured traits were: respiration, growth and survival, as well as the concentrations of copper within beetle tissues and in its diet. By comparing F1 and F5 generation we were able to answer how long-term metal exposure changed the responses to both copper and the parasite. The beetles did accumulate copper; however, the results indicated that copper concentrations in beetle tissues were affected by nematode infection, the sex of the experimental animals, and the number of generations of exposure. Five generations of exposure to copper resulted in the highest dry body mass of infected beetles of both sexes; additionally, this group also had the lowest copper concentrations in their tissues. The only factor that had a significant effect on respiration was infection by nematodes: infected beetles of both sexes in both generational groups had significantly decreased respiration rates. Survival was lowest in nematode-infected animals of both sexes from both generations, regardless of exposure to copper. Our results confirm that an organism's response to metal pollution is dependent on its health status and sex. We also found that the history of exposure to metal was equally important-we found enhanced resistance to copper intoxication after only five generations of exposure.

A Ni hyperaccumulator and a congeneric non-accumulator reveal equally effective defenses against herbivory

The defense hypothesis is commonly used to explain the adaptive role of metal hyperaccumulation. We tested this hypothesis using two Brassicaceae congeneric species: Alyssum pintodasilvae, a Ni hyperaccumulator, and the non-accumulator Alyssum simplex both growing on serpentine soils in Portugal. Artificial diet disks amended with powdered leaves from each plant species were used to compare the performance (mortality, biomass change) and feeding behavior of Tribolium castaneum in no-choice and choice tests. The performance of T. castaneum was not affected at several concentrations of A. pintodasilvae or A. simplex in no-choice tests. However, the consumption of plant-amended disks was significantly lower than that of control disks, irrespectively of the species fed. Accordingly, when insects were given an alternative food choice, disks of both plant species were significantly less consumed than control disks. Moreover, insects did not discriminate between disks in the combination "A. pintodasilvae+A. simplex". Contrary to our expectations, these results suggest that both plant species have equally effective defenses against herbivory. While Ni is believed to be part of the deterrence mechanism in the hyperaccumulator A. pintodasilvae, it seems likely that organic compounds, possibly glucosinolates, play an important role in the defense of A. simplex or in both species.

SHAPE VARIATION OF CYSTICERCOIDS OF HYMENOLEPIS DIMINUTA (CYCLOPHYLLIDEA) FROM FED, PARTIALLY FED, AND FASTED TRIBOLIUM CONFUSUM (COLEOPTERA)

Quantitative studies of a crowding effect on cysticercoids of Hymenolepis diminuta in the intermediate host are few and limited in scope. In this study, we developed a technique to rapidly collect morphological information on large numbers of parasites, and verified the utility of geometric models for simple and accurate estimation of cysticercoid size for quantitative studies. These models were tested using measurements from 4,899 H. diminuta obtained from 666 Tribolium confusum exposed 1-4 wk previously. Length, width, and depth of the body and cercomer (when present) can be used in conjunction with these models to provide the most accurate estimation of parasite size. However, parasite body length alone can be used, with adjustment for effects of host diet and infection intensity, to predict the remaining measurements in incomplete specimens. Parasites that developed in higher intensity infections, or in hosts with reduced food intake, were narrower and had a proportionately shorter cercomer. Host age, sex, and mating status, and parasite age also had statistically significant, but small-magnitude, effects on parasite shape.

Determinants of virulence for the parasite Nosema whitei in its host Tribolium castaneum

For many parasites, especially those that obligately kill the host for transmission, host age is crucially important to determine success. Here, we have experimentally investigated this relationship with the microsporidian parasite, Nosema whitei, in its host, the Red Flour Beetle, Tribolium castaneum. We find that infection is only possible in young larvae and that spore load at the time of transmission (i.e., host death) correlates with host body size. The data suggested that an infection by N. whitei prolongs the life span of the infected larva and prevents them from pupation. Together, virulence to the host and success for the parasite is mainly determined by the host age at infection. The patterns are consistent with theoretical predictions for obligate killer parasites.

Spread of parasites in metapopulations: an experimental study of the effects of host migration rate and local host population size

We established experimental metapopulations of the flour beetle, Tribolium castaneum, and its ectoparasitic mite, Acarophenax tribolii, to investigate the effects of host migration rate and local host population size on the spread of mite infections. Global prevalence across our metapopulations was less than half the observed within-patch prevalence, so that spatial structure alone afforded a great deal of protection to hosts against parasite infection. Our results showed further that migration played a determining role in occupancy, the number of patches infected within a metapopulation, while host population size played a determining role in local prevalence, the fraction of hosts infected within local patches. Local and global prevalence appeared to reach equilibrium levels on 2 different time-scales. Local host prevalence reached equilibrium values within 30 days of receiving an infected host migrant. Global prevalence increased more slowly and was clearly dependent upon occupancy, the number of host patches with at least 1 infected host, which in turn depended on the level of host migration among host patches. The effect of population size was not limited to local prevalence in patches without spatial structure but extended to sets of patches across the metapopulation. Lloyd's index of patchiness differed significantly between metapopulations with small versus large numbers of hosts. Although parasites were aggregated on hosts for both local patch sizes, they tended to aggregate to a much greater degree at the smaller host patch size. We discuss our empirical findings in light of current epidemiological theory.

Parasite prevalence and the size of host populations: an experimental test

Although important in epidemiological theory, the relationship between the size of host populations and the prevalence of parasites has not been investigated empirically. Commonly used models suggest no relationship, but this prediction is sensitive to assumptions about parasite transmission. In laboratory populations, I manipulated the size of Tribolium castaneum flour beetle populations and measured the prevalence and distribution of a parasitic mite, Acarophenax tribolii. I found that parasite prevalence did not vary for a wide range of host population sizes. However, prevalence was lower in populations with less than 40 hosts. This effect cannot be attributed to changes in host population density because host density was held constant among treatments. The reduction in prevalence of small populations below a threshold that I observed is predicted by the extinction debt model, but it is not expected from models of host-parasite interactions that assume density-dependent transmission. The distribution of parasites, measured using Lloyd's patchiness index, was not affected by host population size. The mean crowding of parasites, however, was negatively related with host density. Finally, the prevalence of parasites in large populations did not differ from that found in sets of smaller patches as long as the smaller populations in aggregate were equivalent in size to the large population.

The Hymenolepis diminuta–Golden Hamster (Mesocricetus auratus) Model for the Evaluation of Gastrointestinal Anticestode Activity

A novel laboratory anticestode assay was developed using Hymenolepis diminuta in the hamster. The commercial anticestode compounds, praziquantel, bunamidine, and niclosamide were active against patent infections of Hymenolepis diminuta in golden hamsters (Mesocricetus auratus) when given orally at 3.125, 100, and 200 mg/kg, respectively. The gastrointestinal nematode anthelmintics, cambendazole and mebendazole, were active at 50 mg/kg. Rafoxanide (fasciolicide) was active at 25 mg/kg, the lowest level tested. The coccidiostat, nicarbazin, was active at experimental levels (800 mg/kg and up). The anthelmintic-ectoparasiticide (endectocide), ivermectin, was inactive against the tapeworm at 0.5 mg/kg, as expected.

Effects of tapeworm infection on male reproductive success and mating vigor in the red flour beetle, Tribolium castaneum

Parasites may exert negative effects on host survivorship and reproductive success. The effects of parasites on female host fitness have been well documented; however, the effects of parasites on the reproductive success of male hosts and particularly the underlying mechanisms that alter male fitness are not well understood. Previous studies demonstrated that infection by rat tapeworm (Hymenolepis diminuta) reduced the fitness of male red flour beetles (Tribolium castaneum) in an environment of female mate choice and strong male-male competition. The present study determined the role of female mate choice and male insemination capacity on observed fitness reduction of male beetles by the tapeworm parasites. We found that infected males showed reduced mating vigor and consequently inseminated fewer females than did uninfected males. Specifically, tapeworm infection reduced the number of offspring sired by a male by 14-22% even when male-male competition and female mate choice were absent. Further, the insemination capacity of males diminished by 30% because of infection. Female beetles did not discriminate against infected males in precopulatory mate choice experiments. Copulatory courtship, a determinant of postcopulatory female choice, was not significantly different between infected and uninfected males. Hence, we concluded that female beetles did not show either pre- or postcopulatory choice against tapeworm-infected males. Therefore, tapeworm-induced reduction in the reproductive success of male beetles possibly results from altered reproductive biology, such as lower mating vigor and decreased sperm quantity or quality.

[Establishment of Hymenolepis diminuta-animal model and morphology of cysticercoid]

AIM

To observe the morphological changes in the process of the development of Hymenolepis diminuta.

METHODS

The life cycle of Hymenolepis diminuta was established between Rattus domesticus albus and Triboliun castaneum. The morphology of cysticercoid were observed microscopically, and the ultrastructure of the body surface of cysticercoid were observed by scanning electron microscopy.

RESULTS

Three phases including the mature stage, the blister stage and the protective outer membrane-forming stage during the growing course of cysticercoid were observed microscopically. Under scanning electron microscope, lots of sieve-like micropores on the surface of mature cysticercoid were seen in the second week after infection. The blister phase was found in the third week and the outer membrane measuring about 45 microns in thickness were found surrounding the cysticercoid and vesicular surface, forming a smooth cyst wall in the fourth week.

CONCLUSION

The life cycle of Hymenolepis diminuta has been established in the animal-model. The finding of the three phases during the growing course of cysticercoid is reported for the first time.

Failure to infect laboratory rodent hosts with human isolates of Rodentolepis (= Hymenolepis) nana

Confusion exists over the species status and host-specificity of the tapeworm Rodentolepis (= Hymenolepis) nana. It has been described as one species, R. nana, found in both humans and rodents. Others have identified a subspecies; R. nana var. fraterna, describing it as morphologically identical to the human form but only found in rodents. The species present in Australian communities has never been identified with certainty. Fifty one human isolates of Rodentolepis (= Hymenolepis) nana were orally inoculated into Swiss Q, BALB/c, A/J, CBA/ CAH and nude (hypothymic) BALB/c mice, Fischer 344 and Wistar rats and specific pathogen free (SPF) hamsters. Twenty four human isolates of R. nana were cross-tested in flour beetles, Tribolium confusum. No adult worms were obtained from mice, rats or hamsters, even when immunosuppressed with cortisone acetate. Only one of the 24 samples developed to the cysticercoid stage in T. confusum; however, when inoculated into laboratory mice the cysticercoids failed to develop into adult worms. The large sample size used in this study, and the range of techniques employed for extraction and preparation of eggs provide a comprehensive test of the hypothesis that the human strain of R. nana is essentially non-infective to rodents.

Gregarina triboliorum (Eugregarinida: Gregarinidae) n. sp. from Tribolium confusum and resolution of the confused taxonomic history of Gregarina minuta Ishii, 1914

The septate gregarine parasites of flour beetles (Tribolium spp.) include Gregarina minuta Ishii, 1914, a relatively small species in which both primite and satellite possess an obvious protomerite, and a larger species that lacks the satellite protomerite. The latter species has been placed in the genera Didymophyes and Hirmocystis by various authors, but studies reported here demonstrate that this species, herein described as Gregarina triboliorum, exhibits early pairing and produces oocyst chains, both characteristics of the genus Gregarina. The oocysts of this new species are described for the first time. In addition, experimental infections using oocyst from single gametocysts reveal that oocyst chain number is variable but is typically 1, 2, or 4. Prior experiments involving a related beetle, Tenebrio molitor, demonstrated extreme host specificity within the 4 Gregarina species parasitizing larval and adult hosts. However, G. triboliorum is not limited either stadially or specially, infecting both adults and larvae of Tribolium confusum and Tribolium castaneum.

Influence of tapeworm infection on the production of aggregation pheromone and defensive compounds in Tribolium castaneum

Recent studies suggest that parasites affect host development, reproduction, and behavior through alterations of host hormones and pheromones, or other hormone-triggered biochemical events. We previously reported that Hymenolepis diminuta infection affects surface-seeking and cannibalism behaviors, and reduces male sperm precedence of Tribolium castaneum beetles. This study examined the quantitative effects of H. diminuta on the production of aggregation pheromone and 3 defensive compounds in male T. castaneum beetles, using 2 wild-caught, geographically distinct T. castaneum strains. For the c-Madison strain, infected beetles exhibited a 2- to 22-fold increase in defensive compounds; conversely, no changes were observed in strain c-Africa. Parasite infection did not significantly influence aggregation pheromone secretion in either strain. Because defensive compounds function as repellents or deterrents to other insects, parasite-induced increases in the secretion of defensive compounds may be a physiologic clue for the behavioral changes in infected T. castaneum beetles. Significant among-strain variation in defensive compound production seen in infected beetles suggests that caution is needed before generalizing about changes in volatile production and in host behavior induced by a parasite.

The minimum effective dose of praziquantel in treatment of Hymenolepis diminuta in rats

To determine the minimum effective dose of praziquantel against Hymenolepis diminuta in rats, 5.0 mg/kg, 2.5 mg/kg, 1.0 mg/kg, 0.5 mg/kg, 0.1 mg/kg, or 0.05 mg/kg praziquantel were given to each of five experimentally infected rats in six groups. Faecal samples from each rat were examined on ten consecutive days following treatment. The rats were killed and examined for worms on day 10. Based on the results of faecal examination and autopsy, the minimum effective dose of praziquantel against Hymenolepis diminuta in rats was determined to be 0.5 mg/kg.

Infection of Tribolium beetles with a tapeworm: variation in susceptibility within and between beetle species and among genetic strains

Host susceptibility and resistance to parasites are often hypothesized to be genetically variable traits. We tested 2 species of Tribolium flour beetles for among-strain variation in susceptibility to the rat tapeworm Hymenolepis diminuta. Twelve genetic strains of Tribolium confusum and 11 strains of Tribolium castaneum were examined. We found T. castaneum was more susceptible to the tapeworm than T. confusum. There was significant among-strain and between-sex variation for both beetle species in infection intensity and prevalence. Among-vial variation was marginally significant. These results add to evidence that host susceptibility to a parasite is a genetically variable trait. We view these results as important findings for understanding natural selection on host-parasite interactions. Traits that are genetically variable can respond to natural selection. Thus, if a beetle's susceptibility to the tapeworm is correlated with fitness and heritable, susceptibility can evolve. Susceptibility is likely to be pleiotropic and have important consequences on issues ranging from parasite transmission to host species interactions and community structure.

FMRFamide-related peptides in Hymenolepis diminuta: immunohistochemistry and radioimmunoassay

The localization of FMRFamide-related peptide (FaRP) immunoreactivity was determined during different stages of development of the rat tapeworm Hymenolepis diminuta. In the adult worm (14 days old), FaRP immunostaining was most intense in the scolex and concentrated in the central nervous system (cerebral ganglia and transverse commissures) and around the lips of the suckers. In the strobila, medial and lateral longitudinal nerve cords (LNCs) and ladder-like connecting commissures were the only tissue stained. Immunoreactivity in the medial LNCs of the adult tapeworms extended only to and included proglottides containing developing testis and seminal receptacle but disappeared in proglottides in which primordial ovaries were first detected. Radioimmunoassay confirmed that FaRPs were concentrated in the scolex/neck region of the adult worm (3.9 +/- 1.5 pmol mg protein-1), whereas the lowest concentrations (0.2 +/- 0.19 pmol mg protein-1) were recovered from the regions of the strobila containing shelled eggs. The pattern of FaRP immunoreactivity observed in 5- and 7-day-old worms was similar to that seen in adult worms, but in 2- and 3-day-old worms the pattern of immunoreactivity observed in the cerebral ganglia, transverse commissures, and LNCs differed significantly as compared with that seen in older worms. These results indicate differential utilization and/or roles for FaRPs during development and suggest both central and sensory roles in this tapeworm.

A study on the life-cycle and epidemiology of Pseudanoplocephala crawfordi Baylis, 1927

A study of the life-cycle and epidemiology of Pseudanoplocephala crawfordi Baylis, 1927 is reported. Intermediate hosts are Tenebrio obscurus, T. molitor, Carpophilus dimidiatus and Tribolium castaneum. The first three species are new host records. Development in the intermediate host takes 1-1.5 months. The completion of the life-cycle takes 2-2.5 months. Surveys of intermediate hosts, pigs, humans and rats were carried out. In Rattus norvegicus, the prevalence was as high as 22%. Epidemiological factors and suggestions for control measures are discussed.

Differences in biological characteristics of two strains of the cestode Hymenolepis diminuta

Biological characteristics of infectivity, growth rate and fecundity of Hymenolepis diminuta isolated from wild Rattus rattus in Japan were compared with parasites of Texas origin maintained for several generations in this and many other laboratories in laboratory bred Rattus norvegicus. The timing of development and maturation was similar in parasites from both sources, but the mean parasite dry weight was less and the mean egg production lower in Japanese parasites in both single and multiple infections. The differences persisted over 10 weeks in single infections, and were unaffected by rat strain. In all experiments there was much greater variation and heterogeneity in the biological characteristics of the Japanese parasites. It was concluded that the Texas parasites were better adapted to R. norvegicus and in the course of adaptation had become more homogeneous, and that the difference between the parasite strains had a complex genetic basis. Some Japanese parasites of the early isolated generations failed to produce normal eggs, but the proportion of these decreased in later generations. However, selected individual Japanese parasites whose egg production was equal to that of parasites of Texas origin did not produce offspring of larger mean size or higher mean fecundity, and heterogeneity of these characteristics was maintained. In the intermediate host, the mean number of cysticercoids of the Japanese isolate per beetle was higher than that of the Texas strain in Tribolium confusum but lower in Tenebrio molitor. The greater heterogeneity exhibited by Japanese parasites and the genetic basis of the strain difference are discussed with particular reference to geographical isolation, differences in definitive hosts and co-evolution of wild and laboratory host and parasite populations.

Experimental infection of Tribolium confusum (Coleoptera) by Hymenolepis diminuta (Cestoda): host fecundity during infection

Some effects of Hymenolepis diminuta on the fecundity of Tribolium confusum are described. Host fecundity is observed to be reduced exponentially with increasing parasite burden/host, although there are differences in the ability of individual hosts to respond to parasitism. Of particular interest is the finding that host fecundity is greatly reduced in young beetles on or by day 14 post-infection (p.i.). This age-related reduction in host fecundity is discussed in relation to the population dynamics of this host-parasite relationship.

Interactions of the cysticercoids of Hymenolepis diminuta and raillietina cesticillus in their intermediate host, Tribolium confusum

This study was based on the experimental exposure of beetles to homologous and heterologous infections of Hymenolepis diminuta and Raillietina cesticillus. The results demonstrated that, for both species over the range of parasite densities employed, the presence of a primary infection had no effect on the establishment success of an homologous challenge infection. The establishment success of R. cesticillus cysticercoids was not affected by the presence of an H. diminuta infection. The existence of an R. cesticillus infection, however, severely reduced the establishment success of an H. diminuta infection. The reduction in H. diminuta establishment was greatest in R. cesticillus infections less than 10 days old. The plausibility of some of the mechanisms that are potentially responsible for the reduction in H. diminuta establishment success is discussed, as is the possible ecological significance of these results.

Comparison of the effects of imidazo[1,2-a]pyridine-2-carbamates and benzimidazole-2-carbamates on the development of Hymenolepis nana in Tribolium confusum

The anthelmintic properties of several imidazo[1,2-a]pyridine carbamates and benzimidazole carbamates against Hymenolepis nana are compared. The results of this study, coupled with previous work, indicate that methyl 6-(trichloroethenyl)-imidazo[1,2-a]pyridine-2-carbamate has the potential of being a broad spectrum anthelmintic effective against both nematodes and cestodes.

The dynamics of infection of Tribolium confusum by hymenolepis diminuta: the influence of exposure time and host density

Survival of Hymenolepis diminuta eggs (as measured by their infectivity to the intermediate host) was found to be age-dependent with an expected value of 11 days when the eggs were retained within the faecal pellet at 10 degree C. The expected life-span of eggs under experimental conditions (i.e. extracted from faecal material and placed on filter paper at 30 degree C) was estimated as 33 min. The mean parasite burden of populations of Tribolium exposed to known densities of H. diminuta eggs was found to rise to a plateau with increasing exposure time. The experimental results provided a method of estimating the instantaneous rate of parasite transmission: a value of 0.0004/egg/min/host/13 cm2 was obtained. The mean parasite burden of populations of T. confusum exposed to known densities of H. diminuta eggs was found to decrease exponentially with increasing host density. A second estimate of the instantaneous rate of parasite transmission of 0.004/egg/min/host/13 cm2 was obtained from the experimental results. No differences in susceptibility to infection between 2-week-old male and female beetles were found. A marked decrease, however, was apparent with increasing beetle age up to 14 weeks post-eclosion.

Evolutionary implications of Tribolium confusum-Hymenolepis citelli interactions

Hymenolepis citellicaused a marked mortality inTribolium confusumduring the first 14 days of infection. The mortality was higher when the beetles were starved for 6 days immediately prior to infection (73–93%) than when they were starved for 1 day (51%). Regardless of the starvation time, the majority of beetle deaths occurred between days 8 and 11 post-infection (p.i.) and the precise survival time for individuals tended to vary inversely with the number of parasites they contained. With few exceptions beetles that survived until day 15 p.i., when the experiments were terminated, contained 14 or fewer cysticercoids, whereas those that died on or before day 14 p.i. contained 20 or more parasites. Mortality was equally high in both sexes but the mean survival time was significantly shorter for female beetles (8·8 days) than for males (9·6 days). Also, parasite development rate varied with the sex of the host. When parasite populations recovered from beetles that died on the same day were compared, the degree of development attained by those from males was significantly higher than in the populations grown in female hosts. The line ofH. citelliused in these experiments has been maintained in the laboratory for the past 5 years. The results obtained with the current generation of this line were compared with those obtained with it 2 years earlier (approximately 16 generations ago). Mortality was lower with the current generation (67%) than with the earlier generation (93%). However, with the latter generation, the mean parasite population size in beetles that survived to day 15 p.i. was significantly higher (14·1 cysticercoids/beetle) than in those infected with the recent generation (7·3–7·9) cysticercoids/beetle). These findings suggest that relatively high selection pressures have been applied byT. confusumtoH. citelli, thereby reducing the number of parasite lines with high infectivity and consequently improving host survivorship. The host also responded to artificial, directed selection for reduced cysticercoid number (heritability estimates of 0·30 ± 0·12 and 0·26 ± 0·12) and increased survival (heritability estimates of 0·28 ± 0·12 and 0·15 ± 0·083). The realized heritability was 0·37 for cysticercoid number and 0·17 for increased survival.

A comparison of the effect of albendazole, cambendazole, and thiabendazole on the larval development of three hymenolepidid cestodes

Flour beetles (Tribolium confusum) parasitized either by Hymenolepis diminuta, H. nana, or H. microstoma were fed continuously on flour mixed either with thiabendazole, cambendazole, or albendazole (drug concentration was always 10%) from day 1 (24 hr) to day 10 postinfection when the experiments were terminated. All drugs markedly inhibited the development of H. diminuta and H. nana. Populations of these species recovered from beetles fed anthelmintics were composed mostly of under-developed forms, many of which still retained the size and appearance of newly hatched oncospheres, whereas all the parasites recovered from the control beetles (fed only flour) reached full development. Parasites inhibited by cambendazole and albendazole recovered and reached full development within 9 days after treatment was terminated. Also, results were obtained which implied that some parasites were able to continue their development at a reduced rate in the presence of the drugs. Hymenolepis microstoma differed from the other species in its response to the drugs. Albendazole and thiabendazole had no effect on its development and it was only slightly inhibited by cambendazole. Larvae recovered from beetles fed the latter drug had all developed beyond the oncosphere stage but 3 to 5% of them repeatedly failed to reach full development. The drugs varied in their effects on the flour beetles. An average of 63% and 33% of those fed thiabendazole and cambendazole, respectively, died before the 10th day of infection. Albendazole, on the other hand, had no effect on beetle survival.

The influence of Hymenolepis diminuta on the survival and fecundity of the intermediate host, Tribolium confusum

An experimental study of the effects of parasitism by H. diminuta on the intermediate host, Tribolium confusum, is described. No density-dependent constraints on parasite establishment within individual hosts are evident, although a reduction in cysticercoid size at high parasite burdens is demonstrated. The relationship between parasite burden, host mortality and host fecundity is investigated. Host mortality is linearly related to parasite burden, whereas the relationship between parasite burden and host fecundity is non-linear. There is no difference in viability between eggs from infected and uninfected females. The generative causes of these effects are not investigated experimentally, although it is postulated that survival is related to the degree of damage to the midgut wall caused by parasite penetration, and fecundity to the biomass of parasites harboured by the host. The significance of these effects is discussed in relation to the overall dynamics of the host-parasite association.

The dynamics of infection of Tribolium confusum by Hymenolepis diminuta: the influence of infective-stage density and spatial distribution

The mean parasite burden of a population of Tribolium confusum is shown to rise to a plateau as the exposure density of infective eggs of Hymenolepis diminuta increases. The level of this plateau is shown to be dependent on the nutritional status of the host population, being depressed from approximately 18 cysticeroids/beetle in hosts which have been starved prior to experimentation, to approximately 2 cysticercoids/beetle in satiated hosts. A simple model is used to describe the shape of this infection functional response in terms of the predator-prey interaction between hosts (T. confusum) and parasite infective stages (H. diminuta eggs). The distribution of successful infections/host is shown to be over-dispersed, even when hosts are exposed to infective stages arranged in a uniform spatial pattern. The over-dispersion of parasite numbers/host is shown to become more severe as the spatial pattern of infective stages changes from under-dispersed, through random, to over-dispersed. Experimental results are discussed in relation to the dynamics of parasite-host interactions, in which infection takes place by host ingestion of a free-living infective stage.

[Effect of parasitic protozoa on the physiological state of the body of the confused flour beetle (Coleoptera, Tenebrionidae)]

Studies were conducted of diseases of Tribolium destructor and T. confusum caused by parasites of the fat body, microsporidians of Nosema whitei and coccidians of Adelina tribolii. The infection of larvae of tenebrionid beetles with microsporidians and coccidians results in substantial changes in the metabolism of insects-hosts (respiratory metabolism is disturbed and activity of tissue catalase is reduced). Physiological characteristics of uninfected larvae of T. confusum and T. destructor differ considerably. In T. destructor the disease is more acute in its character and is accompanied by more sharp changes in metabolism as compared to T. confusum. On the basis of experiments conducted the author came to the conclusion that parasitic protozoans affect the physiological state of tenebrionid beetles in many ways. On the other hand the tenebrionids themselves are somehow affected by the host that apparently is stipulated by physiological and biochemical peculiarities of the organism of the latter.

The effect of mebendazole on different developmental stages of Hymenolepis diminuta cysticercoids

Tribolium confusum beetles infected with Hymenolepis diminuta were fed continuously from day 1, 3, 5, 6, or 7 to day 10 post infection (p.i.) on a mixture composed of two parts Telmin (containing 16.67% of mebendazole) and one part flour. The drug inhibited the worm development and this effect decreased as the age of larvae at the time of the first exposure increased. Lowered incidence of infection, decreased population size, and retarded development were apparent when the beetles were given drug from day 3 p.i. or earlier. Retarded development was also observed in cysticercoids from beetles given drug from day 5 p.i. When given from day 6 or later, it had no effect on worm development. However, when compared with larvae from beetles fed only flour, cysticercoids exposed to the drug from day 6 or later showed reduced infectivity and a decrease in their ability to excyst in vitro. Fully developed infective cysticercoids exposed to the drug from day 10 p.i. or later were not affected by it.

The growth and development of Hymenolepis peromysci Tinkle, 1972 (Cestoda: Cyclophyllidea)

The growth and development of the metacestode and the adult stages of Hymenolepis peromysci Tinkle. 1972 in Tribolium confusum and Mesocricetus auratus, respectively, have been examined. These aspects of the worm's biology follow a general pattern similar to those established for other members of Hymenolepis which have been extensively studied. The primary differences observed are in the time scale of development and the final size of the adult worm, A high degree of variability has been noted and it is speculated that this variability is due to the relatively short time that this species has been maintained under laboratory conditions.

Qualitative distribution of neutral lipids and phospholipids in Hymenolepis microstoma from the cysticercoid to the egg producing adult

The distribution of neutral lipids and phospholipids in Hymenolepis microstoma has been studied using Fettrot, Sudan Black B, Sudan IV and copper phthalocyanin staining techniques. In the cysticercoid, neutral lipids are found in the outer membrane, the lining of the cysticercoid cavity, the tegument of the larval worm and the calcareous corpuscles. A decreasing gradient of phospholipids is found starting from the acellular layer, through the circular fibrous layer, the longitudinal fibrous layer, the adjacent dense zone and ending with the lining of the cysticercoid cavity. Phospholipids are also found in the calcareous corpuscles and the tegument of the larval worm. In the young adult (3 days p.i.) fat globules are first seen to accumulate in the last 2-3 proglottids. Until the 6th day p.i. they are found in the posterior third of the worm, surrounding developing gonads, but mostly concentrated along the transverse line. The mature proglottids contain fat, (a) in both granular and globular forms: in the folds of the uterus, sperm ducts, cirrus pouch and tegument (proximal cytoplasm), (b) in a diffuse form: in the vitellaria, ovary, testes and the tegument (distal cytoplasm). Pre-gravid and gravid proglottids show the largest fat globules. From the cleaving embryo to the fully developed oncosphere the concentrations of neutral lipids and phospholipids vary in form, intensity and location. In all strobilar forms of the parasite neutral lipids and phospholipids are found in the tegument and calcareous corpuscles. Although in H. microstoma lipid droplets are found in the excretory canals, all lipids in the proglottids are not absolutely waste products. From the results it would appear that they play a role in the maturation of gonads and transformation of the fertilized ovum to the oncosphere.

The effect of mebendazole on the development of Hymenolepis diminuta in Tribolium confusum

Tribolium confusum parasitized by Hymenolepis diminuta were allowed to feed on mixtures composed of 0.005 to 20 g of mebendazole (Telmin: methyl-5-benzoyl benzimidazole-2-carbamate) in 10 g of flour from day 1 (24 h) to day 9 post infection. Retarded cysticercoid development, lowered incidence of infection, and reductions in the number of cysticercoids recovered per beetle were produced by drug levels of 0.1, 1.0, and 10 g respectively. None of the drug concentrations tested produced 100% mortality, and developing cysticercoids varied considerably in their tolerance of mebendazole.

A comparative study of the two alternative larval forms of Hymenolepis nana, the dwarf tapeworm, with special reference to the process of excystment

Studies of the cysticercoids of Hymenolepis nana from insects and from mouse villi revealed important differences in cyst structure and function. The insect form resists low pH unless treated with bile salts which render the cyst permeable and reduce infectivity to mice. Bile salts are not essential for scolex activation. Activation is inhibited by pH 2.5 and under and by 1% succinic acid up to pH 4.0. The importance of scolex immobility and energy conservation in relation to cyst impermeability is discussed. The villus cysticercoid has no special insulating layer. It is vulnerable to low pH and cannot infect mice orally. Bile salts are without effect and excystment occurs unaided by external agents. The structural differences between the two forms revealed by the electron microscope may be attributed to changes in the relative rates of development of the various tissues.

Immunity to intestinal tapeworms: the rejection of Hymenolepis citelli by mice

Approximately 90% of Hymenolepis citelli cysticercoids given to 6-week-old male CFLP mice by stomach tube became established. Equally high recovery rates were obtained from administering 1, 3 and 6 cysticercoids.

In 1-worm infections worms increase in weight until about day 25–28 post infection. After a few days at maximum weight (mean weights of worms 24–42 mg) there is a small, 10–25%, decrease in weight, after which there is little change in weight up to day 90 (as long as studied).

One-worm infections survived without loss until day 30, after which a slow loss occurred, but only in two experiments, both with older mice, did loss exceed 50% by day 80. In 3-worm infections worms were rejected between days 17 and 30, but loss varied from 50 to 80% during this period in replicate experiments. With 6-worm infections rejection occurred over a shorter period (days 17–22), was more uniform between experiments and was more complete, over 75% of worms being lost. In both 3- and 6-worm infections a residual population, usually of only a single worm, persisted in 20–50% of the mice until the end of the experiments (day 63–78).

Cortisone prevented loss of worms from both 3- and 6-worm infections; worms continued to grow until day 25 ± 2 (as in 1-worm infections), by which time they were considerably larger than (the surviving) worms in mice not receiving cortisone. The biomass (worm burden per mouse) remained constant from day 25 to 55 in mice receiving cortisone.

The results are discussed with particular reference to: H. diminuta and the evidence that mice do mount an immunological response against tapeworms in the intestine; the existence of an antigenic threshold in mice; the apparent existence of a similar rejection pattern in a natural population of H. citelli in Peromyscus maniculatus, and hence the importance of immunity as a factor preventing gradual increase in number of tapeworms in the intestine during the life of a host.