Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Nymph”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30Linked to original sources
PubMed2002

Glass capillary tube feeding: a method for infecting nymphal Ixodes scapularis (Acari: Ixodidae) with the lyme disease spirochete Borrelia burgdorferi.

We evaluated an artificial capillary feeding method to infect nymphal Ixodes scapularis (Say) ticks with Borrelia burgdoeferi, the causative agent of Lyme disease. Thirty to 70% of the nymphs were infected after feeding for 2.5 h from glass capillary tubes filled with a solution of spirochetes. Capillary infection was stable and persisted in the nymphs for at least 10 d after feeding. Capillary feeding also maintained natural vector competence patterns because I. scapularis ticks acquired infection unlike Dermacentor variablis (Say), which did not become infected. Capillary infected I. scapularis nymphs were capable of transmitting the infection to naive mice although not as efficiently as naturally infected nymphs. The capillary infection method is convenient and is a better alternative to syringe inoculation as a means of infecting animals with B. burgdorferi.

Animals↗
PubMed2002

Geographical information systems and bootstrap aggregation (bagging) of tree-based classifiers for Lyme disease risk prediction in Trentino, Italian Alps.

The risk of exposure to Lyme disease in the province of Trento, Italian Alps, was predicted through the analysis of the distribution of Ixodes ricinus (L.) nymphs infected with Borrelia burgdorferi s.l. with a model based on bootstrap aggregation (bagging) of tree-based classifiers within a geographical information system (GIS). Data on L ricinus density assessed by dragging the vegetation in 438 sites during 1996 were cross-correlated with the digital cartography of a GIS, which included the variables altitude, exposure and slope, substratum, vegetation type and roe deer density. Ticks were more abundant at altitudes below 1,300 m a.s.l., in the presence of limestone and vegetation cover with thermophile deciduous forests and high densities of roe deer. A bootstrap aggregation procedure (bagging) was used to produce a model for the prediction of tick occurrence, the accuracy of which was tested on actual tick counts assessed by a further dragging campaign carried out during 1997 to determine infection prevalence and resulted in average 77%. Other tests of the model were made on additional and independent data sets. The prevalence of infection with Borrelia burgdorferi s.l, determined by polymerase chain reaction on 2,208 nymphs collected by random dragging in 245 transects selected within eight areas where the model predicted the occurrence of I. ricinus during 1997, was 17.5% and was positively correlated to tick abundance and roe deer density. These findings were used to relate the output of the bagged model (probability of tick occurrence) to the density of infected nymphs through a stepwise model selection procedure and thus to produce a GIS digital map of the probability distribution of infected nymphs in the Province of Trento at high resolution scale (50 by 50-m cell resolution). The application of the bagging procedure increased the accuracy of the prediction made by a single classification tree, a well-known classification method for the analysis of epidemiological data.

Animals↗
PubMed2000

Competence of the African tortoise tick, Amblyomma marmoreum (Acari: Ixodidae), as a vector of the agent of heartwater (Cowdria ruminantium).

The ability of the African tortoise tick, Amblyomma marmoreum, to acquire and transmit Cowdria ruminantium infection was investigated experimentally with transmission trials and with a C. ruminantium-specific polymerase chain reaction (PCR) detection assay. Laboratory-reared A. marmoreum larvae and nymphs were fed on small ruminants with clinical heartwater. After molting, the resultant nymphs were fed on Cowdria ruminantium-naive sheep (n = 3), and the adults were ground and inoculated intravenously into sheep (n = 5). Fatal heartwater developed in the 5 recipient animals, demonstrating larvae-nymph transmission and nymph-adult acquisition of infection. Cowdria ruminantium infection was also detected in adult A. marmoreum by PCR analysis, although at lower frequency (10%) than in Amblyomma hebraeum ticks (43%), the major vector of C. ruminantium in southern Africa, which had been fed simultaneously on the infected animals (P<0.0001). Amblyomma marmoreum, therefore, can be an effective vector of C. ruminantium. The potential role of this species in heartwater epidemiology and in the spread of the disease to new areas is highlighted by these results and by the fact that immature stages of this tick feed readily on domestic and wild animals susceptible to C. ruminantium.

Animals↗
PubMed2003

Effects of photoperiod, temperature and melatonin on nymphal development, polyphenism and reproduction in Halyomorpha halys (Heteroptera: Pentatomidae).

Influences of photoperiod, temperature and melatonin were examined on development and color patterns of nymphs, and sternum color and reproductive fate of adults in Halyomorpha halys (brevis). Short-day accelerated nymphal development, whereas long-day accelerated reproductive maturation. The two types of photoperiodic responses at different stages may help maintain the univoltinism of this species in the field, assuring the right timing for diapause and reproduction. The pronotum of fifth instar nymphs reared under LD 11:13 shows a brown-marbled color pattern darker, with less creamy-yellowish speckles, than that of nymphs reared under LD 16:8. Short-day-reared fifth instar nymphs, which are destined to diapause in adults, had shorter white stripes on the pronotum, smaller body size, less frequent feeding and more lipid accumulation than the long-day-reared. The longer the exposure to LD 13:11 at 20 degrees C during the nymphal stage, the greater the expression of short-day associated characteristics observed in the fifth nymphal instar and adult stage. Melatonin orally administered (500 microg/ml) to insects under LD 16:8 produced slightly reduced body size, suppressed feeding, extended nymphal period and increased accumulation of lipid compared to the untreated bugs, but did not affect the incidence of diapause in females. In males, melatonin retarded gonadal development under LD16:8. These results may suggest a possible role of melatonin for the control of seasonal polyphenism and development.

Animals↗
PubMed1996

Experimental transmission of Powassan virus (Flaviviridae) by Ixodes scapularis ticks (Acari:Ixodidae).

Transmission experiments were performed with Ixodes scapularis ticks from an uninfected laboratory colony. Immature and adult ticks were exposed to Powassan (POW) viremic hamsters and rabbits, respectively. Oral infection rates for engorged larvae, nymphs and females fed on POW-infected hosts were 10%, 40%, and 57%, respectively. Transstadial transmission rates for nymphs exposed to POW virus as larvae, adults exposed as larvae, and adults exposed as nymphs, were 9.5%, 10%, and 54%, respectively. Evidence of transovarial transmission occurred when two uninfected hamsters, exposed to F2 larvae and nymphs originally exposed to POW virus in the F1 nymphal stage, seroconverted to POW virus with hemagglutination inhibition titers of 80 and 5,120, respectively; the transovarial transmission rate was 16.6%. All developmental stages were able to transmit virus orally to uninfected hosts regardless of when the ticks were originally exposed to the virus. These results suggest that I. scapularis is a competent vector of POW virus under experimental conditions.

Animals↗
PubMedDate not supplied

[A trial at using the systemic action of ivermectin for suppressing the vector capacity of ticks (Ixodidae) infected with the tick-borne encephalitis virus].

Adult Dermacentor marginatus hatched from nymphs infected with TBE virus and poisoned with ivermectin retain their vector abilities. Even small individuals with a 1.5-2 times lesser mass as against the reference mass contain the virus in the body in the same titers and the virions in salivary gland alveoli. Administration of an oil solution of ivermectin into the stomach of white mice, nymph feeders, in a dose surpassing threefold the dose recommended for intramuscular injection of this agent completely suppressed shedding of intact nymphs but did not suppress it in those infected. The nymph mass, size and mass of adult ticks hatched from them dropped under the effect of ivermectin dosage build-up in both intact and infected ticks, but these processes were slower in ticks infected with TBE virus. The authors suggest that the ticks infected with TBE virus are much more resistant to the process of gamma-aminobutyric acid depression, the mechanism of ivermectin action. They emphasize the necessity of bearing in mind the possible differences in the reactions to systemic poisons of intact and infected ticks when organizing vector control measures.

Animals↗
PubMed2004

A laboratory comparison of the life cycles of the dog ticks Haemaphysalis leachi and Rhipicephalus sanguineus.

Engorged female Haemaphysalis leachi and Rhipicephalus sanguineus as well as their eggs, flat and engorged larvae and nymphs were incubated at combinations of five temperatures and three relative humidities. Mean pre-oviposition periods for H. leachi varied between 4.3 days and 12.1 days and for R. sanguineus between 4.8 days and 21.0 days. Haemaphysalis leachi converted up to 65.7% of their body mass into eggs and produced up to 16.3 eggs/mg body mass, with 4801 eggs the maximum number deposited by a single female. Peak egg production of 520 eggs/day was recorded 3 days after the commencement of oviposition. Rhipicephalus sanguineus converted up to 68.1% of their body mass into eggs and produced up to 17.2 eggs/mg body mass, with a maximum of 3,232 eggs, and peak egg production of 400 eggs/day 4 days after the commencement of oviposition. Mean incubation periods for eggs of H. leachi varied between 15.5 days and 66.7 days, and for R. sanguineus between 19.0 days and 72.0 days. Mean pre-moult periods for engorged larvae and nymphs of H. leachi varied between 14.0 days and 192.0 days, and 13.0 days and 41.0 days respectively, and for R. sanguineus between 9.5 days and 36.5 days, and 15.0 days and 44.5 days respectively. Allowing 7 days for female engorgement and 7 days for hardening of the exoskeletons and mouthparts of each of the three parasitic stages before they attach to a host, the life cycle of H. leachi would require 97-190 days and that of R. sanguineus 99-236 days to complete at the various regimes of temperature and relative humidity. The greatest proportion of H. leachi larvae engorging on mice detached between 18:00 and 19:00 on the first day of detachment and between 06:00 and 08:00 in the morning and 14:00 and 18:00 in the afternoon of the following day, while the greatest proportion of nymphs engorging on dogs detached around 19:00 on the first day of detachment and between 13:00 and 17:00 on the following day. The greatest proportion of R. sanguineus larvae engorging on dogs detached between 11:00 and 21:00 on the second day of detachment, and the greatest proportion of nymphs detached between 03:00 and 5:00 on the second and third days of detachment.

Animals↗
PubMed2003

[Occurrence of Babesia microti in ticks Ixodes ricinus on selected areas of western Pomerania].

The aim of present study was to evaluate acquisition risk of babesiosis in human population exposed to ticks Ixodes ricinus by examination of Babesia microti DNA occurrence in ticks of all development stages. The polymerase chain reaction (PCR) was applied to estimate the occurrence of DNA Babesia microti in Ixodes ricinus. The Bab1 and Bab4 primers were used to amplify fragment. 238bp in length, of 18S rRNA gene for small ribosomal subunit. Amplicons were electroforeticaly separated in agarose gels. Ticks were collected in year 1999 and 2000, twice in each year in spring-summer (May-July) and summer-autumn (August-October) seasons from Goleni6w Forest and Pobierowo. These places have been classified as people attendance and tourist areas. The 716 I. ricinus ticks were collected in 1999 with 61.3% of nymphs, 17.8% larvae, 10.9% females and 9.9% males. Highest range of infection was observed in females--28.8% studied, than males--18.3%, nymphs--7.7% and larvae--3.l1%. The total number of 416 I. ricinus was collected in year 2000 with 64% of nymphs. 13.4%/males. 11.9% females and 10.7% larvae. The infection with Babesia microtri occurred only in three nymphs, which was 0.7% of studied population.

Animals↗
PubMed2006

Experimental infection of Hyalomma marginatum ticks with West Nile virus.

To define the possible role of Hyalomma marginatum ticks in the transmission of West Nile virus (WNV) in Portugal an experimental infection was established. Ticks were fed on viremic rabbits previously infected with WNV. In different developmental stage of H. marginatum virus isolation and detection of viral antigen and viral RNA were attempted. The oral infection rates were 3%, 33% and 75% for engorged larvae, nymphs and females after oviposition, respectively. Transstadial transmission rates for nymphs exposed to virus as larvae, for adults exposed as larvae, and for adults exposed as nymphs were 33%, 11% and 46%, respectively. No evidence of transovarial transmission was obtained. Ticks in the stages of nymphs and adults were able to transmit the infection to uninfected hosts. This study demonstrated that H. marginatum could be involved in the natural circulation of WNV in Portugal.

Animals↗
PubMedDate not supplied

[Effect of the diapause in the Ixodes ricinus (Ixodidae) tick on the multiplication of the tick-borne encephalitis virus in its body].

The tick encephalitis virus was found to multiply more intensively in ticks developing without diapause. Thus, in larvae developing with diapause, in 4 and 8 weeks after they feed on infected animals, the virus titers were 3.0 and 3.5 lg LD50 respectively. At the development without diapause the titers were 4.3 and 5.3, respectively (P less than 0.05). The virus titers in infected nymphs developing without diapause were 2.5 to 3.9 lg LD50 higher than those of the diapausing individuals. In diapausing larvae and nymphs the tick encephalitis virus remained for a long time (8 to 10 weeks) without fall of titers. The fall of virus titers was not recorded either during the moulting of larvae for nymphs and nymphs for imago but in hungry ticks, which were maintained for a long time at 18 to 23 C, the amount of virus gradually diminished.

Animals↗
PubMed1995

Prevalence of ticks in relation to their role as vector of Borrelia burgdorferi under autochthone conditions.

A total of 59 (78.7%) of 75 areas were found to be inhabitated by ticks; all the 4335 collected ticks were identified as Ixodes ricinus. Both nymphs and adults were found to be more active during the late spring and early summer months. Ticks of 29 recreation areas were found to be carrying spirochaetes. Considering the total number of 75 recreation areas examined and the total number of 59 areas inhabitated by ticks the percentage was 38.7 and 49.2 respectively. The positivity rate by dark field microscopy was 16.7% in 653 tick samples (single nymphs 8.8%, pooled nymph samples 21.5%, single females 10.9% and single males 10.8%). Overall positivity rate by culture examination of 245 samples was 22.8%. It was maximal in nymphs (24.7%) followed by males (21.1%) and females (19.7%). 10.2% of the 177 samples, found negative by DFM, were positive by this method. A positivity rate of 23.9% in 96 tick samples was found by IFAT. A total of 56 spirochaete-strains were obtained of which 51 could be maintained further; 50 strains were identified as Borrelia burgdorferi.

Animals↗
PubMed2001

Endocrine mechanisms controlling body-color polymorphism in locusts.

The present article reviews recent published and unpublished findings on the hormonal mechanisms for the control of body-color polymorphism in locusts. Emphasis is placed on the dark color-inducing factors and their role in the induction of various types of body coloration observed under different environmental conditions. Implantation of corpora cardiaca (CC) taken from normal nymphs of Locusta migratoria induced dark color in nymphs of an albino strain. Using the albino strain for the bioassay, a neuropeptide, [His7]-corazonin, was identified as a dark color-inducing factor for L. migratoria and Schistocerca gregaria. In the former, depending upon the dose and timing of the injection, this peptide and juvenile hormone developed various body colors looking like those found in nature. The body coloration characteristic of gregarious forms was also induced in isolated albino nymphs and field-collected solitary nymphs. In S. gregaria, on the other hand, the peptide induced black patterns, but the orange or yellow background color observed in gregarious forms was not induced when the peptide was injected into solitary individuals. [His7]-corazonin also induced darkening in other grasshoppers and locusts, but not in katydids. Albino L. migratoria developed dark color when implanted with brains or CC taken from other insects belonging to 10 major insect orders, but not with those from Coleoptera. [His7]-corazonin or a similar compound is widespread among insects and plays a pivotal role in controlling body color in some species and presumably other physiological roles in other species. Arch.

Animals↗
PubMed1998

Pathogenicity of the entomopathogenic fungi paecilomyces spp. and Beauveria bassiana against the silverleaf whitefly, Bemisia argentifolii.

Pathogenicities of three species of entomopathogenic fungi against preimaginal Bemisia argentifolii were measured and compared. Third-instar nymphs on excised leaves of Hibiscus rosa-sinensis were exposed to spray applications of 14 isolates of Beauveria bassiana, 22 isolates of Paecilomyces fumosoroseus, and five isolates of Paecilomyces farinosus. B. bassiana and P. fumosoroseus isolates of diverse origins were highly pathogenic to the whitefly nymphs; median lethal doses of 14 of the 22 P. fumosoroseus and four of the 13 B. bassiana isolates ranged between 50 and 150 conidia/mm2. Five isolates of P. farinosus were also pathogenic; however, LC50s were relatively high, ranging between 350 and 4000 conidia/mm2. Nymphs infected with all but one isolate of B. bassiana displayed a pronounced red pigmentation. Postmortem hyphal growth and sporulation of B. bassiana was relatively slow and usually confined to the region immediately surrounding the dead host. Whitefly nymphs patently infected with P. fumosoroseus and P. farinosus were lightly pigmented yellow or orange. Postmortem hyphal growth and sporulation of P. fumosoroseus rapidly covered the dead host and extended several millimeters onto the surrounding leaf surface. The results indicate that highly virulent strains of P. fumosoroseus and B. bassiana with considerable whitefly control potential are widespread and numerous.

Animals↗
PubMed2000

Effects of fluctuating moisture and temperature regimes on the infection potential of Beauveria bassiana for Rhodnius prolixus.

The effect of both moisture and temperature on the infective potential of Beauveria bassiana to the Chagas' disease vector, Rhodnius prolixus, was studied under fluctuating regimes. At constant 25 degrees C, contaminated first-instar nymphs exposed to increasing daily periods of initial exposure to 97% RH, followed by transfer to reduced humidity (43, 53, 75, and 86% RH), showed a significant reduction in mortality when the 97% RH exposure time declined from 12 to 8 h per day. The duration of disease incubation depended on the daily 97% RH exposure time. Under fluctuating regimes of both humidity (97% RH versus 75% RH) and temperature (15/28, 20/25, 25/28, and 25/35 degrees C), first-instar mortality was affected by weather conditions, daily 97% RH exposure time (8, 12, and 16 h per day), and number of temperature and humidity fluctuations before transferring tested insects to constant unfavorable conditions. In most cases, at 12/12 h alternating cycles, high and rapid mortality required five cycles. Under these fluctuating regimes, fungus-induced mortality and mortality time were similarly affected in third- and fifth-instar nymphs by the daily 97% RH exposure time. Despite a lower susceptibility of older larval stages, mortality rates in insects exposed for at least 12 h per day at 97% RH remained very high except at 15 degrees C. Moisture and temperature regimes at 12/12 h cycling significantly affected the dose-mortality response in first-instar nymphs. The most favorable conditions consisted of 97%-20 degrees C combined with either 75%-25 degrees C or 43%-25 degrees C. Under less favorable alternating conditions (lower and higher temperatures) the amounts of inoculum required for killing 50% of first-instar nymphs were 10 or 20 times higher. From a vector control standpoint, daily high humidity appears to be the most crucial climatic constraint. B. bassiana has the potential to control R. prolixus populations with applications made during the rainy seasons when humidity is high.

Animals↗
PubMed2003

Prevalence of borreliae in ixodid ticks from a floodplain forest ecosystem.

Host-seeking ixodid ticks were sampled in a floodplain forest ecosystem along the lower reaches of the Thaya (Dyje) river in South Moravia (Czech Republic) and Lower Austria during the period 1989-2002. The ticks were examined by dark-field microscopy for borreliae (Borrelia burgdorferi sensu lato, the agent of Lyme borreliosis), and attempts were made to culture the spirochetes in BSK-H medium from preparations containing their high numbers. Isolated borreliae were identified by PCR-RFLP analysis using probes directed against ribosomal spacer genes. A total of 797 nymphal and 719 adult (391 female, 328 male) Ixodes ricinus were examined: 16.2% of nymphs, 28.6% of females and 29.0% of males were positive. Dermacentor reticulatus (70 females, 30 males) and Haemaphysalis concinna (12 nymphs, 8 females, 2 males) were negative for spirochetes. The overall prevalence rate of borreliae in I. ricinus from the floodplain forest is slightly higher than the mean European data (i.e., 14% for nymphs, 21% for adults). The difference in infection rate between nymphal and adult ticks was significant, including the proportion of heavily infected (with > 100 borreliae) nymphs (2.1%) vs. adults (7.6%). Prevalence of borreliae in I. ricinus showed a significant decrease during autumn in this ecosystem. Three strains of spirochetes, all of the Borrelia afzelii genomic group, were isolated from female I. ricinus. Moreover, Trypanosoma/Crithidia sp. protozoa and Dipetalonema rugosicauda nematodes were detected in 0.4% and 1.0%, respectively, of all I. ricinus.

Animals↗
PubMed2004

Appetence behaviours of the triatomine bug Rhodnius prolixus on a servosphere in response to the host metabolites carbon dioxide and ammonia.

A combination of 1,000 ppm CO(2) plus 30-40 ppb NH(3) in an air stream induced Rhodnius prolixus nymphs walking on a servosphere to perform a series of appetence behaviours. Shortly after the onset of stimulation the nymphs turned sharply upwind towards the source of the chemostimuli (within 13 +/- 9 s) from mostly downwind and crosswind walks in the air stream alone. The mean vector angles of these upwind tracks were concentrated in a cone 60 degrees either side of due upwind. The upwind walking bugs stopped more frequently but for a shorter duration and walked at a higher speed than before stimulation. During stops in the presence of the chemostimuli the bugs frequently corrected their course angles and extended their forelegs to reach higher with their antennae in the air. In the air stream alone, R. prolixus nymphs frequently sampled the sphere surface with the antennae and cleaned their antennae with the foreleg tarsi. However, the nymphs only briefly tapped the left or right antennal flagellum on the corresponding first leg tarsus and never touched the servosphere surface in the presence of the chemostimuli. After chemostimulus removal from the air stream the bugs continued to respond with the same appetence responses as during stimulation, but walked more tortuously in a crosswind direction in an effort to regain contact with the chemostimuli.

Administration, Inhalation↗
PubMed2005

Susceptibility of Amblyomma variegatum ticks to acaricides in Ghana.

Abstract. The susceptibility of unfed and fed stages of larvae, nymphs and adult females of Amblyomma variegatum ticks were tested using Shaw's filter paper dip method against four acaricides; chlorfenvinphos and dioxathion, chlorfenvinphos, gamma benzene hexachloride and amitraz at four different concentrations including the recommended dose rates. Based on their lethal concentrations (LC50 & LC90) chlorfenvinphos and dioxathion combined and chlorfenvinphos alone placed first and second, respectively, in all stages except at the unfed nymphal stage where gamma benzene hexachloride topped with a LC50 of 0.001629, while chlorfenvinphos and dioxathion combined and chlorfenvinphos alone had LC50 of 0.001794 and 0.002258, respectively. Amitraz appeared to have a quick knock-down effect on larvae and nymphs but at the recommended dose rate, showed no mortality of the ticks at that stage. However, at a concentration of 0.040%, amitraz showed a 100% inhibition of oviposition and hatching of laid eggs. Gamma benzene hexachloride produced only 66% inhibition of oviposition while chlorfenvinphos and dioxathion combined and chlorfenvinphos alone produced 100% inhibition of oviposition at their recommended dose rates. Fed nymphs were more susceptible than the unfed nymphs. Eggs laid by engorged female ovipositing ticks, applied with gamma benzene hexachloride, hatched.

Animals↗
PubMed1994

Effect of GSH depletion mediated by l-BSO on the insecticidal activity of DDT and fenitrothion in Triatoma infestans (Hemiptera).

l-BSO injected at a sublethal dose in nymph V of Triatoma infestans produces a transient GSH depletion in the abdomen. A depletion of the total content of GSH was observed in nymph II fed with a sublethal concentration of l-BSO. Either ingestion or injection pretreatments of T. infestans nymph V with sublethal concentrations of l-BSO produced a slight synergism on the toxicity of fenitrothion. Feeding administration of a sublethal concentration of l-BSO to nymphs II of T. infestans resulted in a weak potentiation of the acute toxicity of DDT.

Animals↗