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 505 records · Page 28Linked to original sources
PubMed2005

Altitudinal distribution limit of the tick Ixodes ricinus shifted considerably towards higher altitudes in central Europe: results of three years monitoring in the Krkonose Mts. (Czech Republic).

The aim of the study was to monitor present status of the Ixodes ricinus tick vertical distribution in the Krkonose Mts. (Czech Republic) and evaluate its potential changes. Two methods were used: monitoring of tick presence on dogs in 2001-2002 and direct monitoring of host-seeking ticks by flagging on two vertical transects reaching from 620 to 1270 m above sea level (a. s. l.) and from 600 to 1020 m in 2002-2003. Moreover ticks were monitored by flagging at another 13 localities situated in 800-1299 m a. s. l. in 2003. Both monitoring methods revealed an obvious shift in altitudinal distribution limit of the tick I. ricinus in the Krkonose Mts. They both showed that ticks recently penetrate even up to a timberline (approximately 1250 m a. s. l.). The number of recorded host-seeking ticks rapidly decreased with increasing altitude. Whereas the average number of recorded nymphs converted per 60 minutes of flagging reached 15.2-25.7 nymphs in 700-799 m a. s. l. and 3.3-23.3 in 800-899 m, it was 4-9.6 nymphs in 900-999 m, 1.5-1.7 nymphs in 1000-1099 m and only 0.2 nymph in 1100-1299 m a. s. l. The observed shift of the tick altitudinal distribution limit at the same time results in extension of areas with potential risk of tick-borne diseases.

Altitude↗
PubMedDate not supplied

[Abundance levels of populations of the virus carriers and vectors in a focus of tick-borne encephalitis].

In 10 altitude-belt complexes of Dzhoysky ridge (West Sajans) during the summer period of 14-17 years the abundance of small mammals and imago of the taiga tick and the abundance of engorged larvae and nymphs of I. persulcatus was studied. The obtained results have shown that fluctuations in abundance of mammals and imago of ticks are not, as a rule, beyond the limits of a range of critical levels of abundance, which is defined as ee = 15.15. Fluctuations in the abundance of nymphs can cover two ranges and those of larvae up to three ranges. The amplitude of fluctuations in abundance of all groups of animals in question is minimum in optimal altitude-belt complexes and rises with an increasing effect of limiting factors. The decrease in the amplitude of fluctuations of nymphs as compared to larvae and that of imago as compared to nymphs can be, apparently, explained by a stabilizing effect of larval diapause on the abundance of nymphs and larval and nymphal diapause on the abundance of imago. Critical levels of abundance are assumed to be used as criteria of co-members stability in a parasitic system of the tick-borne encephalitis nidus and for classification of nidi with a regard for this character.

Animals↗
PubMed1994

[Transstadial transmission of Francisella tularensis by Ixodes ricinus ticks infected during the nymphal stage].

The degree of infection of nymphs of Ixodes ricinus which finished their feeding on experimentally infected mice on the day of their death from tularaemia represented more than 10(7) cells of Francisella tularensis per tick after feeding. The high degree of positivity was preserved in ticks also during one month of metamorphosis. Transstadial transmission of the agent from the stage of nymph to the stage of imago was confirmed in adults either by cultivation or by experiments attempting to transmit the infection to white mice, even after more than a year after infection of nymphs or more than a year after metamorphosis. Some of the ticks which did not transmit the infection while feeding were found to be positive subsequently. Results of quantitative examination of the degree of infection indicate also the possibility of reproduction of the agent in imagines after feeding on hosts. Incompletely engorged nymphs which fed repeatedly on mice after being collected from their host dead from tularaemia, were able to transmit the infection during interrupted feeding. Further possibilities of transmission were indicated by findings of consumption of infected ticks by hosts or by elimination of F. tularensis in faeces of infected nymphs and adults.

Animals↗
PubMed1988

Postembryonic development of the dorsal ocellus of the American cockroach.

Postembryonic development of the dorsal ocellus of the cockroach Periplaneta americana was examined. Small ocelli (20 micron in diameter) with less than 100 cells in the newly hatched nymph become adult ocelli (more than 500 micron in diameter) with more than 10,000 retinular cells, through ten to 11 nymphal stages. Thus, sequential steps of morphogenesis of rhabdomeres from loose interdigitations of apposed cell membranes to regularly arranged microvilli can be seen in the nymphal ocelli. Some retinular axons appear to extend into the brain as a bundle in the first-instar nymph. Retinular axons differentiated later also extend toward the brain, but there is no evidence that they enter it. The ultrastructure of the ocellus and component analysis of the ocellar electroretinogram suggest that functional connections between retinular axons and ocellar interneurons do not occur in the ocellar capsule until mid (the fifth or sixth)-instar nymphs. The ocellar diameter increases linearly with increase in body length during the nymphal stages, but it increases by a factor of 1.5-2.0 during the final molting: the body length of the adult is almost the same as that of the last-instar nymph. These data suggest that the function of the dorsal ocelli may be closely related to specific adult behavior such as flight.

Animals↗
PubMed1991

The life cycle of Amblyomma parvum Aragao, 1908 (Acari: Ixodidae) under laboratory conditions.

A colony of Amblyomma parvum was started with engorged females collected from cattle in the Province of Salta (25 degrees 01' S, 63 degrees 56' W), Argentina. The progeny of those ticks were fed on rabbits and the non-parasitic stages maintained at 27 +/- 1 degrees C, 83-86% RH in darkness. The life cycle (prefeeding period not evaluated) had a mean duration of 99.6 days. The mean time (days) for the different phases of the cycle were as follows: feeding period of females, 8.0; pre-oviposition period, 5.7; oviposition period, 17.5; minimum incubation period of the eggs, 31.8; feeding period of larvae, 3.2; premoult period to nymphs, 10.9; feeding period of nymphs, 4.7; premoult period to adults, 17.8. The oviposition pattern was typical of an ixodid tick, including a linear relationship between weights of engorged females and the number of eggs laid (r = 0.8659). The males increased 18% in weight after feeding on hosts (P less than 0.01). The mean recovery rates of larvae, nymphs and females were 28.2%, 95.3% and 90.7%, respectively. The nymphs moulting to females were heavier (6.8 +/- 0.69 mg) than those moulting to males (3.2 +/- 0.29 mg) (P less than 0.01). A comparison of biological values of A. parvum with American and non-American Amblyomma species is presented.

Animals↗
PubMed1984

Development of ixodid ticks under natural conditions in Nigeria.

The developmental periods of five tick species were recorded from egg to adult stages under natural conditions. The ticks were Amblyomma variegatum, Boophilus decoloratus, B. geigyi, Hyalomma rufipes and H. truncatum and the natural condition was a grazing field on which "open" site and "shade" were recognised. The investigation took place between April 1980 and March 1981. The hatching patterns of larvae, attachment, engorgement, larvo-nymphal and nympho-adult moulting periods and the survival of larvae and nymphs during different climatic periods of the year were recorded. While the attachment and engorgement periods which were recorded on the animal were relatively constant for each tick species throughout the period of investigation the hatching patterns and moulting periods were influenced by rainfall and temperature. The moulting periods of larvae and nymphs kept in the open as well as the total duration of the life cycle were lower than those of ticks kept in the shade. The survival of larvae and nymphs of all tick species was lowest during the peak of rains and highest during the dry season; the survival was also generally higher among larvae and nymphs kept in the shade than those kept in the open. The results were related to the distribution pattern and seasonal occurrence of some of the tick species in Nigeria.

Animals↗
PubMed1993

Temperature effect on the insecticidal activity of pyrethroids on Triatoma infestans.

1. The toxic effect of deltamethrin, asymmethrin, alphamethrin, cypermethrin and cypermethrin High cis in nymphs III of Triatoma infestans was lower at 28 than 16 degrees C. 2. Prostration in treated nymphs III occurred more rapidly at 28 than 16 degrees C. 3. Symptoms of poisoning rapidly disappeared when nymphs III intoxicated were moved from 16 to 28 degrees C. 4. Nymphs III exposed to low doses of pyrethroids at 28 degrees C, which did not show symptoms of poisoning, were rapidly affected when they were moved to 16 degrees C.

Animals↗
PubMed2004

Cold shock injury and ecological costs of rapid cold hardening in the grain aphid Sitobion avenae (Hemiptera: Aphididae).

The ability of first instar nymphs and newly moulted pre-reproductive adults of the grain aphid S. avenae to rapidly cold harden was investigated. When nymphs reared at 20 degrees C were transferred directly to -8 degrees C for 3 h, there was 18% survival. This exposure was selected as the discriminating temperature. Maximum increases in survival were achieved by acclimating nymphs for 2 h at 0 degrees C and adults for 3 h at 0 degrees C, resulting in survival of 83% and 68%, respectively. Cooling nymphs from 10 to 0 degrees C at different rates (1, 0.1 and 0.05 degrees C min(-1)) also increased cold hardiness, with the slowest rate of 0.05 degrees C min(-1) conferring the highest survival following exposure to the discriminating temperature. Adult aphids also expressed a rapid cold hardening response but to a lesser extent, with survival increasing from 16% to 68% following 3 h at 0 degrees C. There were no 'ecological costs' associated with rapid cold hardening in terms of development, longevity or fecundity. The data support the hypothesis that rapid cold hardening can be induced during the cooling phase of natural diurnal temperature cycles, allowing insects to track daily changes in environmental temperatures.

Acclimatization↗
PubMed1998

Experimental transmission of Hepatozoon americanum Vincent-Johnson et al., 1997 to dogs by the Gulf Coast tick, Amblyomma maculatum Koch.

Experimental transmission of Hepatozoon americanum to dogs was attempted with four ixodid ticks, viz., Rhipicephalus sanguineus, Amblyomma americanum, Amblyomma maculatum and Dermacentor variabilis. Ticks that dogs ingested included some that were laboratory-reared and experimentally fed as nymphs on a dog with naturally occurring hepatozoonosis; other ticks were collected as replete or partially engorged larvae, nymphs and adults from dogs that had hepatozoonosis and natural infestations of ticks. Whole ticks used to expose susceptible dogs orally were partially dissected to help release oocysts. Among eight dogs exposed, only the three that were fed A. maculatum adults experimentally acquisition fed as nymphs became infected. Dogs developed elevated body temperature and other evidence of clinical disease starting 4 weeks after exposure. 'Cysts' typical of H. americanum were found in skeletal muscle when samples were first examined 5 weeks after dogs ingested ticks, and parasites were also observed in peripheral blood smears at approximately the same time. Our study demonstrates that A. maculatum nymphs can acquire H. americanum by feeding on a parasitemic dog and that transstadial transmission of the protozoan occurs, with dogs acquiring infection when they ingest newly molted adult ticks.

Animals↗
PubMed1983

Transmission of Theileria parva by a population of Rhipicephalus appendiculatus under simulated natural conditions.

A 2 hectare paddock on the Muguga Estate, Kiambu District of Kenya (altitude 2100 m) free of Theileria parva-infected ticks was seeded by applying Rhipicephalus appendiculatus nymphs to cattle infected with Theileria parva (Kiambu 4). It was estimated that over 50 000 engorged nymphs fell onto the pasture from 4 cattle with high parasitaemias during the cold season (June). Samples of these ticks were placed in plastic cylinders under the vegetation in the paddock and sexual stages of T. parva were detected in gut lumen smears in these samples up to 21 days after repletion. Zygotes were first observed to transform into kinetes on day 55 and parasites were first detected in salivary glands of adults on day 64. Moulting of the nymphs started on day 60 after repletion and was completed by day 87. Cattle introduced into the paddock showed their first infestation with adult R. appendiculatus on day 64 after repletion of the nymphs and the infestation level gradually increased. On day 76 after repletion, 17% of a sample of adult ticks infesting cattle showed salivary gland infections with T. parva and this increased to over 70% by day 150. From day 360 onwards, a decrease in both the percentage of ticks infected and the number of salivary gland acini infected/tick was noted. In addition, T. parva infections within the salivary glands required a longer period of feeding in the older ticks before they developed into sporozoites. Cycling of Theileria through ticks was prevented by the removal of female ticks before they completed repletion. Lethal challenge levels of T. parva for cattle existed in the paddock up to day 547 after repletion, after which introduced cattle showed no infection or only a sub-lethal infection. Cattle introduced into the paddock on day 808 after repletion showed no evidence of T. parva infection. The tick infestation of introduced cattle decreased markedly from day 368 and infestation had virtually ceased by day 808.

Animals↗
PubMed1983

Transmission of Theileria annulata (Dschunkowsky & Luhs, 1904) by Hyalomma excavatum (Koch, 1844).

Theileria annulata was transmitted transtadially by an Israeli strain of Hyalomma excavatum from larvae to nymphs and from nymphs to adults. However, the adults developing from larvae which engorged on infected calves and fed during the nymphal stage on non-infected calves, rabbits or gerbils (Meriones tristrami), did not transmit theileriosis. Suspensions of infected unfed nymphs or adults did not produce theileriosis but both nymphs and adults of the same batch became infective to cattle after 2 days of feeding. Suspensions of salivary glands or of whole ticks derived from infected adults that remained attached to rabbits for more than 7 days, were not infective to cattle.

Animals↗
PubMed1996

The activity periods and life-cycle of the tick Ixodes uriae (Acari: Ixodidae) in relation to host breeding strategies.

We investigated the timing of seasonal activity of the seabird tick Ixodes uriae by examining engorgement rates of off-host ticks and the prevalence of infested common guillemots (Uria aalge) and kittiwakes (Rissa tridactyla) on the Isle of May, Scotland. More than 99% of I. uriae fed during the period late April to early August which coincided with the seabird breeding season. No ticks fed in the autumn and winter, and none over-wintered in the engorged state. Peak tick feeding activity was during the hosts' incubation period in May and early June, when over 70% of birds were parasitized. Few ticks were active when guillemot chicks were being brooded, or during the early part of kittiwake chick-rearing. Adult female tick feeding peaked in the first week of June, while nymphal and larval activity peaked in the third week of May. Adult female ticks fed later than nymphs on guillemots and larvae on both guillemots and kittiwakes; however, there was considerable temporal overlap in the feeding periods of the 3 stages of both hosts. All larvae and nymphs fed in May and early June, but up to 18% of adult females remained unengorged at this time, and probably deferred feeding by 1 year. A small proportion of individuals which fed as larvae in May appeared to feed again as nymphs in July of the same season, thereby shortening their life-cycle by 1 year. The duration of the life-cycle of I. uriae on the Isle of May is typically 3 years but varies from 2 to 4 years. Ticks feeding on guillemots did so significantly earlier than those feeding on kittiwakes, possibly because guillemots start breeding earlier in the year. Breeding of both guillemots and kittiwakes was later in 1994 than in 1993. This delayed the activity of all tick stages on kittiwakes and adult female ticks on guillemots, but did not affect the timing of activity of nymphs or larvae feeding on guillemots.

Animals↗
PubMed1999

Incidence from coincidence: patterns of tick infestations on rodents facilitate transmission of tick-borne encephalitis virus.

Tick-borne encephalitis (TBE) virus has a highly focal distribution through Eurasia. Endemic cycles appear to depend on the transmission of non-systemic infections between ticks co-feeding on the same rodent hosts. The particular features of seasonal dynamics and infestation patterns of larval and nymphal Ixodes ricinus, but not Dermacentor reticulatus, from 4 regions within TBE foci in Slovakia, are such as to promote TBE virus transmission. The distributions of larvae and nymphs on their principal rodent hosts are highly aggregated and, rather than being independent, the distributions of each stage are coincident so that the same ca. 20% of hosts feed about three-quarters of both larvae and nymphs. This results in twice the number of infectible larvae feeding alongside potentially infected nymphs compared with the null hypothesis of independent distributions. Overall, co-feeding transmission under these circumstances brings the reproductive number (R0) for TBE virus to a level that accounts quantitatively for maintained endemic cycles. Essential for coincident aggregated distributions of larvae and nymphs is their synchronous seasonal activity. Preliminary comparisons support the prediction of a greater degree of coincident seasonality within recorded TBE foci than outside. This identifies the particular climatic factors that permit such patterns of tick seasonal dynamics as the primary predictors for the focal distribution of TBE.

Animals↗
PubMed2000

The effect of male ticks on the feeding performance of immature stages of Rhipicephalus sanguineus and Amblyomma americanum (Acari: Ixodidae).

A unique group of immunoglobulin-binding proteins (IGBPs), produced by ixodid male ticks during the latter half of their prolonged feeding period, improves the feeding performance of co-feeding females. As a follow-up to this observation, we investigated whether male tick feeding also affects the feeding of other developmental stages. Immature stages of Rhipicephalus sanguineus (Latreeille) and Amblyomma americanum (L.) were fed on rabbits in the presence or absence of conspecific males. The mean weight of larvae and nymphs of both species that fed around males and detached from the host on the first day of dropping was significantly higher than when the immature ticks fed on rabbits in the absence of males. However, larvae of both species and nymphs of R. sanguineus that fed slower and detached on the second day of dropping did not show significant differences in weight. A similar pattern was observed for A. americanum nymphs although, unlike R. sanguineus, the presence of males also influenced the feeding performance of the nymphs that fed slowly and detached on the second day of drop-off. The improved feeding performance demonstrated by immature ticks in the presence of males may be due to immunomodulatory saliva proteins, such as immunoglobulin-binding proteins (IGBPs) that are introduced into the co-feeding site. The results are considered in relation to the distribution of ixodid tick species on their natural hosts.

Animals↗
PubMedDate not supplied

Studies on the development of Theileria annulata Dschunskowsky and Luhs, 1904 in the tick--Hyalomma anatolicum anatolicum Koch, 1844.

The endogenous development of Theileria annulata in the vector tick--Hyalomma anatolicum anatolicum has been described. Parasites within and outside the erythrocytes were seen in the gut contents of larvae and nymphs immediately after their removal from the infected cattle but not after 24 hours. Two bodies resembling the intra-erythrocytic stage of the parasite, lying close to each other were seen near the gut epithelium of a larva on the 4th day of its dropping off the infected host. Neither multiplication nor union of the parasite resulting in zygote formation in the gut of the tick, was noticed. Next stage of the parasite was seen in the salivary glands of nymphs and adults. The pre-infective stage characterized by indistinct chromatin dots (nuclei) surrounded with cytoplasm was seen in alveolar cells of the salivary glands of nymphs and adult ticks from the first to the third day of their feeding of the host. This stage progressed to the infective stage consisting of distinct chromatin particles (the infective particles) surrounded with cytoplasm in the salivary glands of nymphs and adult ticks after the second and first day, respectively of feeding on the host. The infective particles were also seen within ducts of the salivary glands.

Animals↗
PubMed2000

Spatial risk assessment for Lyme borreliosis in Denmark.

A study of nymphal and adult Ixodes ricinus density was performed in well-defined spruce and beech forest habitats with different levels of roe deer abundance and soil water capacity. In 35 habitats, a total of 489 larvae, 1,611 nymphs and 193 adult I. ricinus ticks were collected. Tick density was found to be influenced by roe deer abundance and soil water capacity. Based on this evaluation, a model predicting increasing number of ticks with increasing roe deer abundance and soil water capacity was suggested. A total of 1,045 nymphs and 106 adult ticks were tested for infection with Borrelia burgdorferi sensu lato Of these, 53 nymphs and 6 adults were found to be infected, leading to an general infection rate of 5% and 6% for nymphs and adults, respectively. Prevalences of Borrelia burgdorferi sensu lato in nymphal I. ricinus were found to be independent of roe deer abundance and soil water capacity. The correlation between human neuroborreliosis incidence and the estimated number of I. ricinus based on roe deer abundance and soil water capacity was examined. Differences in human neuroborreliosis incidence were found to correspond with the expected spatial differences in tick density in 12 counties in Denmark.

Animals↗
PubMed2004

Evaluation of immunocompetent and immunocompromised mice (Mus musculus) for infection with Ehrlichia chaffeensis and transmission to Amblyomma americanum ticks.

Experiments on the natural history of Ehrlichia chaffeensis, the agent of human monocytic ehrlichiosis (HME), would be facilitated by the availability of a laboratory animal model for transmission to vector ticks. Five strains of mice were evaluated for their susceptibility to infection with E. chaffeensis and transmission competence: C57BL/6 mice, inducible nitric oxide synthase (iNOS) deficient mice, MHC I deficient (beta2m /) mice, MHC II deficient mice (Abb /), and B and T cell deficient (Rag1 /) mice. Mice were inoculated with a low passage isolate of E. chaffeensis, and infection and morbidity were monitored for 57 days. Three xenodiagnostic infestations with A. americanum nymphs were performed 1, 8, and 15 days following inoculation. C57BL/6 mice cleared the organism in less than 17 days, with no indication of morbidity, and mounted a rapid, strong antibody response. Transmission to feeding A. americanum nymphs was seen in 1/30 nymphs fed on C57BL/6 mice immediately after inoculation. In MHC I and iNOS deficient mice, pathogen DNA was detected up to 17 or 24 days, respectively, after inoculation. Persistent infection for the duration of the experiment (57 days) was observed in MHC II deficient mice. However, E. chaffeensis was not detected in ticks fed on iNOS, MHC I, or MHC II deficient mice. Susceptibility to infection was greatest in Rag1 knockout mice, with significant morbidity and mortality within 24 days after inoculation. E. chaffeensis DNA was detected in up to 55% of replete nymphs that fed on Rag1 mice. However, E. chaffeensis was not detected in molted adult ticks from the same cohorts.

Animals↗
PubMed2005

Experimental infection models of ticks of the Rhipicephalus sanguineus group with Rickettsia conorii.

Rhipicephalus sanguineus group ticks collected on dogs in Thailand were maintained in the laboratory over several generations to test methods to infect these ticks with Rickettsia conorii, the agent of Mediterranean spotted fever. Three methods were tested: (1) infection of adults and nymphs through artificially induced bacteremic rabbit, (2) capillary feeding of solution containing 5 x 10(3) and 5 x 10(5)pfu/mL of R. conorii to adult female ticks, and (3) immersion of engorged nymphs which were "one leg-cut," "two leg-cut," or "cuticle cut" in solution containing R. conorii. The most efficient method to infect adult ticks with R. conorii was infection of ticks through the bacteremic rabbit (71.4%). The best method to infect nymphs with R. conorii was immersion of "one leg-cut" engorged nymphs in solution containing R. conorii (30%). Interestingly, a high mortality of the ticks infected with R. conorii was observed regardless of the method used. The harmful effect of R. conorii on Rh. sanguineus group ticks from Thailand is discussed including the role of the geographic origin of the ticks and the difficulties to identify ticks within this group to the species level.

Animals↗