The efficiency of Rhadinopsylla rothschildi and R. dahurica fleas as vectors of the causative agent of plague in a Transbaikal natural focus

Experiments have shown that a block of proventriculus arises in 2.1 to 12.5% of infected fleas of R. rothschildi and in 7.2 to 10.5% of R. dahurica. These fleas transmit the plague agent to different animals (Brandt's vole, narrow-skulled vole, Dahurian suslik). The plague microbe is preserved in the organism of infected insects till the end of the experiment, 74 and 24 days respectively. Therefore, the fleas can play a part in the maintenance of plague epizootics in the Transbaikal natural nidus.     

Efficiency of Neopsylla abagaitui fleas as plague vectors in Transbaikalia

Experiments have shown that the block of proventriculus develops in 1.1 to 1.5% of individuals of the flea Neopsylla abagaitui infected with plague microbe. These insects transmit the agent during bloodsucking to different plague carriers (Citellus dauricus, C. undulatus, Meriones unguiculatus, Microtus gregalis). The plague microbe is preserved in fleas for 65 days (the observation period).     

Relationship of the flea Citellophilus tesquorum altaicus (Siphonaptera: Ceratophyllidae) with the plague agent

Some aspects of relationships of the flea Citellophilus tesquorum altaicus and bacterium Yersinia pestis of two strains isolated from different parts of the Tuva natural plague focus were studied. Peculiarities of elimination and blood meal activity of fleas infected with two strains of the plague agent were not revealed. Differences in mortality and alimentary activity are considerably determined by the sex of insects. The ability of examined strains to form a proventriculus block was not identical in the strains examined. This ability was expressed higher in the strain I-3428, which originated from the same part of the natural focus as the insectarium flea culture, than in the strain I-3327. During the spring and first half of summer, the proventriculus block appeared more frequently in females. The increasing of the fraction of blocked individuals was observed in both sexes from spring to summer. As for the ability to transmit the plague agent, similar seasonal increasing was noted in males, but in females, the ability to inoculate the plague microbe was always maintained at the same level.     

Experimental study of the infecting ability of the flea Coptopsylla lamellifer rostrata in the Kyzylkum natural focus of plague

Experimental infecting of the fleas Coptopsylla lamellifer rostrata by plague was carried out. The fleas were infected by feeding through biomembrane (skin of a white mouse) with a mixture of defibrinated blood of guinea-pig and plague microbes. Under concentration 2-3 milliard of the microbes in 1 millilitre, from 60 to 100% of the fleas were infected. Forming of the block of proventriculus was observed in 9-13 day. Mean percent of blocking for all experiments was less than 1%. Maximal rate of blocking (2.8%) was observed in the experiment under everyday 3-hour feeding. After planting of the fleas with blocks on great gerbil (2 fleas on one gerbil) 20% of the gerbils were infected. The conclusion had been made that C. lamellifer rostrata has only insignificant effectiveness as a vector of plague agent in Kyzylkum. Probably it is caused by some specific features of this subspecies.     

Seasonal dynamics of epizootic process of the plague agent <Emphasis Type="Italic">Yersinia pestis</Emphasis> transmission to the long-tailed suslik <Emphasis Type="Italic">Citellus undulatus</Emphasis> by the flea <Emphasis Type="Italic">Citellophilus tesquorum</Emphasis> in Tuva

Transmission of Yersinia pestis to the long-tailed suslik (Citellus undulatus) by fleas (Citellophilus tesquorum) in the Tuva natural plague focus in different seasons (spring, summer, and autumn) was studied experimentally. Between feeding periods, insects were kept in an artificial nest under temperature and humidity closely corresponding to seasonal ones. The character of the agent transmission was estimated according to the fraction of fleas with the agent in the aggregated state (bacterial lumps, partial blocks of proventriculus), the fraction of blocked individuals, and the fraction of infected susliks and of those with the generalized form of infection. Seasonal dynamics of epizootic process of the Y. pestis transmission corresponded to the results obtained in the epizootic examination of the Tuva natural plague focus and reflected the dynamics of the epizootic process (increase-peak-decline). The activity of the formation of a proventriculus block in C. t. altaicus, the infection ability of the fleas, and the sensitivity of long-tailed Siberian susliks to Y. pestis were the highest in mid-summer (July-first ten days of August), during the period of epizooty activation in the focus. The maximal number of C. t. altaicus with the plague agent at the aggregated state was observed in the cold period, before wintering of insects and after their hibernation.     

The formation of proventriculus block, alimentary activity and mortality of flea Amphipsylla primaris primaris infected with Yersinia pestis

The results of experiments held in 1982-1983 in Tuva plague natural focus with flea Amphipsylla primaris primaris (Jordan et Rothschild, 1915) from natural populations, whish were inflected and fed on specific host--flat-headed vole (Alticola strelzovi), are analyzed. The initial infectivity of the insects in autumn was higher than in spring: 90 and 50 % respectively. Accumulation of the agent in aggregated form in the organism of A. p. primaris, estimated by the quantity of fleas with and partial blocks, was more active in imago of both sexes in autumn than in spring, while sucking flea were observed in spring more often than in autumn. Irrespective of season, the part of males with visible accumulations of Y. pestis was more, and their alimentary activity was higher than that of females. Fleas died much more quickly in spring. Part of the males with proventriculus block exceeded that of females in spring experiment. Females with alimentary canal obstruction prevailed in autumn. Thus, sex of the insect and season of the experiment conducting influenced on all studied indices. Besides that, Y pestis ability for the proventriculus block formation in fleas during different seasons can change by the opposite way depending on sex of the ectoparasites.     

Costs of cannibalism in the presence of an iridovirus pathogen of Spodoptera frugiperda

Abstract.  1. The costs of cannibalism were examined in larvae of Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) in the presence of conspecifics infected by a lethal invertebrate iridescent virus (IIV). The hypothesis of a positive correlation between insect density and the likelihood of disease transmission by cannibalism was examined in laboratory microcosms and a field experiment.
2. Transmission was negligible following peroral infection of early instars with purified virus suspensions or following coprophagy of virus-contaminated faeces excreted by infected insects. In contrast, 92% of the insects that predated infected conspecifics acquired the infection and died prior to adult emergence in the laboratory. Diseased larvae were more likely to be victims of cannibalism than healthy larvae.
3. The prevalence of cannibalism was density dependent in laboratory microcosms with a low density (10 healthy insects + one infected insect) or high density (30 healthy insects + one infected insect) of insects, and field experiments performed on maize plants infested with one or four healthy insects + one infected insect.
4. Cannibalism in the presence of virus-infected conspecifics was highly costly to S. frugiperda ; in all cases, insect survival was reduced by between ≈ 50% (laboratory) and ≈ 30% (field) in the presence of the pathogen. Contrary to expectations, the prevalence of disease was not sensitive to density because cannibalism resulted in self-thinning. As infected individuals are consumed and disappear from the population, the prevalence of disease will be determined by the timescale over which transmission can be achieved, and the rate at which individuals that have acquired an infection become themselves infectious to conspecific predators.     

Host Avian Beta-Defensin and Toll-Like Receptor Responses of Pigeons following Infection with Pigeon Paramyxovirus Type 1

The high morbidity and mortality in pigeons caused by pigeon paramyxovirus type 1 (PPMV-1) highlights the need for new insights into the host immune response and novel treatment approaches. Host defense peptides (HDPs) are key components of the innate immune system. In this study, three novel avian β-defensins (AvBDs 2, 7, and 10) were characterized in pigeons and shown to possess direct antiviral activity against PPMV-1 in vitro. In addition, we evaluated the mRNA expression of these AvBDs and other immune-related genes in tissues of 2-month-old infected pigeons at 3 and 7 days postinfection. We observed that the expression of AvBD2 in the cecal tonsil, lungs, and proventriculus, as well as the expression of AvBD10 in the spleen, lungs, proventriculus, and kidneys, was upregulated in infected pigeons. Similarly, the expression of both Toll-like receptor 3 (TLR3) and TLR7 was increased in the spleen, trachea, and proventriculus, while TLR15 expression was increased only in the lungs of infected pigeons. In addition, inducible nitric oxide synthase (iNOS) expression was upregulated in the spleen, the bursa of Fabricius, the trachea, and the proventriculus of infected pigeons. Furthermore, we observed a high correlation between the expression of AvBD2 and the expression of either TLR7 or TLR15, as well as between AvBD10 expression and either TLR3 or TLR7 expression in respective tissues. The results suggest that PPMV-1 infection can induce innate host responses characterized by the activation of TLRs, particularly TLR3 and TLR7, AvBDs (2 and 10), and iNOS in pigeons.     

Effects of gamma irradiation on the development of Trypanosoma rangeli in the vector Rhodnius prolixus

Studies on the effects of gamma radiation on the infectivity of Trypanosoma rangeli (strain H14) for the vector Rhodnius prolixus revealed that (i) the LD(50) (lethal dose for 50% of bugs) for uninfected insects was 4147 rads; (ii) irradiated insects with a dose of 1200 rads subsequently infected with the flagellates exhibited a mortality of 45%, while uninfected irradiated insects showed a mortality of 5%, and infected nonirradiated insects exhibited 10% mortality; (iii) flagellates were present in the hemolymph of irradiated insects 7 days postinfection (p.i.), while in nonirradiated insects the parasites appeared in the hemocoel 18 days p.i.; (iv) T. rangeli infection decreased the number of hemocytes significantly and induced the formation of nodules in the hemolymph of both irradiated and nonirradiated insects; and (v) gamma irradiation affected the ultrastructural organization of the epithelial cells of the small intestine, principally the perimicrovillar membranes and microvilli. In this paper, we discuss the significance of the intestinal microenvironment of R. prolixus with regard to its interaction with T. rangeli.     

Epizootiological importance of Frontopsylla hetera (Siphonaptera) fleas in the Gorno-Altai natural plague focus

Experiments conducted during all seasons have established that F. hetera, one of the mass species of fleas in Mountain Altai, can be infected both by the strain of selective virulence typical to this nidus and by the non-typical non-virulent mountain-altai strain of plague agent. The non-virulent strain does not form in fleas the block of proventriculus and within 1.5-2 months they become free from the microbe. At the infection with the typical strain of the altai subspecies rare transmissions of the agent to Pallas' pika can take place as well as its long preservation in fleas.     

A computer simulation of the epidemiology of the rice dwarf virus

An epidemiological system model was developed to evaluate the role of factors which were responsible for the prevalence of rice dwarf virus (RDV) transmitted by the green rice leafhopper, Nephotettix cincticeps. Simulation tests were conducted by varying values of the following three parameters: the vector density, the coefficient of the efficiency of feeding acquisition of RDV of the vector, and that of efficiency of RDV transmission by the vector. The effect of each parameter was assessed in terms of changes in percentages of infected insects and of infected rice hills. Both the percentages of infected insects and of infected rice hills increased rapidly with increasing vector density within a range of low vector density. The former increased linearly when the acquisitive coefficient was increased. But the percentage of infected rice hills was affected to a lesser extent. The percentage of infected insects and that of infected rice hills increased exponentially with increasing values of the transmission coefficient. The results obtained from the simulation tests were discussed in relation to the ecological factors which caused the recent prevalence of RDV.     

Physical and physiological characteristics of Trogoderma glabrum infected with the schizogregarine pathogen Mattesia trogodermae

Physical and physiological characteristics of an infection of Trogoderma glabrum by Mattesia trogodermae were studied. Weights of infected larvae drop markedly between 10 and 20 days post-infection at 30° and 35°C. This loss is less abrupt and not as great when the incubation temperature is 25°C. Reduction of dry matter is gradual during the first 12 days of infection, but drops 70% from 12 to 20 days post-infection.Glycogen reserves in both infected and control insects drop 50% within 3 days after deprivation of food. Healthy insects recover and begin to reconstitute lost glycogen; however, infected larvae continue to deplete glycogen to 15% of prestarvation levels. Similarly, insect protein is reduced 40% within 7 days after starvation and noninfected insects apparently halt protein metabolism at this level. Diseased larvae continue to lose protein to 20% of prestarvation amounts. These losses are at least partially attributable to insect metabolism since infected insects defecate significantly more than control larvae. It is thought that defecation is an effective route of water loss which occurs during the first 20 days of infection. Relative humidities ranging from 0 to 84% had no obvious effects on mortality rates, indicating that water loss is effected through routes other than evaporation through the cuticle, e.g., failure of water retention systems and elimination of body water with feces.     

The proventriculus of the carpenter bee, Xylocopa virginica virginica (L.), with special reference to bacteria-containing luminal tunnels

Abstract. Four tunnels off the lumen of the proventriculus of the carpenter bee, Xylocopa virginica virginica , have been discovered. Light and electron micrographs revealed the presence in the tunnels of gram-positive, rod-shaped bacteria, some of which showed division stages. The occurrence of the bacteria exclusively in the tunnels—not in the lumen of the proventriculus—makes speculation as to their function difficult. The function of the tunnels is also obscure, as no glands were seen emptying into them. The bacteria may be symbionts that release enzymes into the tunnels, which are subsequently transported to the midgut to aid digestion. They could also be parasites. This is the first report of such bacterial-containing tunnels in insects.     

Metalloproteases in Trypanosoma rangeli-infected Rhodnius prolixus

Protease activities in the haemolymph and fat body in a bloodsucking insect, Rhodnius prolixus, infected with Trypanosoma rangeli, were investigated. After SDS-polyacrylamide gel electrophoresis containing gelatin as substrate, analysis of zymograms performed on samples of different tissues of controls and insects inoculated or orally infected with short or long epimastigotes of T. rangeli, demonstrated distinct patterns of protease activities: (i) proteases were detected in the haemolymph of insects which were fed on, or inoculated with, short epimastigotes of T. rangeli (39 kDa and 33 kDa, respectively), but they were not observed in the fat body taken from these insects; (ii) protease was also presented in the fat bodies derived from naive insects or controls inoculated with sterile phosphate-saline buffer (49 kDa), but it was not detected in the haemolymph of these insects; (iii) no protease activity was observed in both haemolymph and fat bodies taken from insects inoculated with, or fed on, long epimastigotes of T. rangeli. Furthermore, in short epimastigotes of T. rangeli extracts, three bands of the protease activities with apparent molecular weights of 297, 198 and 95 kDa were detected while long epimastigotes preparation presented only two bands of protease activities with molecular weights of 297 and 198 kDa. The proteases from the insect infected with T. rangeli and controls belong to the class of either metalloproteases or metal-activated enzymes since they are inhibited by 1,10-phenanthroline. The significance of these proteases in the insects infected with short epimastigotes of T. rangeli is discussed in relation to the success of the establishment of infection of these parasites in its vector, R. prolixus.     

Vertical transmission of TnSNPV,TnCPV, AcMNPV,and possibly recombinant NPV in Trichoplusia ni

Four viruses were tested for vertical transmission in Trichoplusia ni: T. ni nucleopolyhedrovirus (TnSNPV), T. ni cypovirus (TnCPV), Autographa californica nucleopolyhedrovirus (AcMNPV), and AcMNPV engineered to express a scorpion toxin (AcMNPV.AaIT). Fifth instars were exposed to each virus, the survivors were reared and mated, and second-generation (F(1)) insects were examined for infection. TnSNPV was transmitted to offspring at a prevalence rate of 15.4%, TnCPV at 10.2%, and AcMNPV at 10.1%. Only one of 2484 F(1) insects was infected with AcMNPV.AaIT; this experiment was repeated, and none of 4774 insects was infected. Thus, vertical transmission is unlikely to contribute to AcMNPV.AaIT contacting non-target organisms after its field release. There was evidence that TnCPV and possibly TnSNPV were activated to overt infections by ingestion of a different virus. TnCPV, but not the NPVs, routinely infected 0.3-1.7% of non-treated insects, probably indicating that it is vertically transmitted at enzootic levels.     

Age-dependent reduction of ghrelin- and motilin-induced contractile activity in the chicken gastrointestinal tract

Ghrelin is an endogenous ligand for growth hormone secretagogue-receptor 1a (GHS-R1a) and stimulates gastrointestinal (GI) motility in the chicken. Since ghrelin stimulates GH release, which regulates growth, it might be interesting to compare ghrelin-induced responses in GI tract of different-aged chickens. Motilin is a ghrelin-related gut peptide that induces strong contraction in the small intestine. Aim of this study was to clarify age-dependent changes in ghrelin- and motilin-induced contractions of the chicken GI tract and expression of their receptor mRNAs. Chicken ghrelin caused contraction of the crop and proventriculus. Ghrelin-induced contraction in the proventriculus decreased gradually up to 100 days after hatching, but the responses to ghrelin in the crop were the same during the growth period. GHS-R1a mRNA expression in the crop tended to increase, but that in the proventriculus decreased depending on the age. Chicken motilin caused contraction of the chicken GI tract. Atropine decreased the responses to motilin in the proventriculus but not in the ileum. Motilin-induced contraction in the proventriculus but not that in the ileum decreased depending on post-hatching days. On the other hand, motilin receptor mRNA expression in every region of the GI tract decreased with age, but the decrease was more marked in the proventriculus than in the ileum. In conclusion, ghrelin- and motilin-induced GI contractions selectively decreased in the chicken proventriculus depending on post-hatching days, probably due to the age-related decrease in respective receptors expression. The results suggest an age-related contribution of ghrelin and motilin to the regulation of chicken GI motility.     

Effects of insect-vector preference for healthy or infected plants on pathogen spread: insights from a model

Insects vector many plant pathogens and often have higher or lower densities on infected plants than on healthy plants. Two hypotheses may explain this observation: insects may preferentially orient toward and select one plant type (referred to as orientation preference) or insects may reside on infected plants for longer or shorter periods than on healthy plants (referred to as feeding preference). The effects of feeding preference and orientation preference were compared alone and in combination using a spatially explicit model. With feeding preference for healthy or infected plants, the qualitative relationship between the percentage of plants infected and the rate of pathogen spread was not affected. However, feeding preference for healthy plants increased rates of pathogen spread, whereas feeding preference for infected plants decreased rates of pathogen spread. Unlike feeding preference, orientation preference for healthy and infected plants produced qualitatively different relationships between the percentage of plants infected and the rate of pathogen spread. With orientation preference for healthy plants, the pathogen spread slowly when few plants were infected, but quickly once most plants were infected. In contrast, with orientation preference for infected plants, the pathogen spread quickly when few plants were infected, but slowly once most plants were infected. In sensitivity analyses, we found that assumptions about the latent period (time between infection and when insects can recognize a plant as being infected) and persistence (length of time an insect remains inoculative) altered the aforementioned effects in some cases. The results illustrate that feeding and orientation preference affect pathogen spread differently, highlighting the importance of elucidating the mechanisms that control vector preference for healthy versus infected plants.     

Investigations concerning the symbiosis of bacteria inTriatoma Infestans (KLUG)

Summary 1. From the proventriculus ofTriatoma infestans aPseudomonas species could always be obtained in pure culture by simple means.2. The bacteria isolated out of the ventriculus of various bugs appeared to agree, not only morphologically but also biochemically and agglutinatorically.3. Further evidence for the identity of the intracellular and the lumen form of this bacterium could be furnished by serological means.4. The assumption expressed byWigglesworth that the infection of the young bug would occur already in the egg and his view on the means by which the egg is infected are very much open to question.5. It does not appear probable that the bacterium, isolated byWigglesworth fromRhodnus prolixus is identical with the proventriculus bacterium ofTriatoma infestans.6. The intracellular bacteria set free into the lumen of the proventriculus have in virtue of their haemodigestive capacity, probably a function in the digestion of the blood sucked by the bug.