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PubMed2000

Repellency of deet to nymphs of Triatoma infestans.

The repellency of N,N-diethyl-3-methylbenzamide (deet) to Triatoma infestans (Klug) (Hemiptera: Reduviidae) was evaluated using third-instar nymphs and a video tracking technique. Three experimental designs were used: (a) the test arena floor was divided into two halves, only one of which was treated with deet; (b) the arena floor was divided into an inner circle and an outer ring, only the latter treated with deet; (c) half of the test arena was covered by a filter paper roof treated with deet (out of reach of the nymphs). In all three types of experiment, a repellent effect was demonstrated proportional to the dose of deet. When a host (pigeon) was shielded by deet-treated gauze, the rate of blood-feeding by the nymphs was inhibited. Topical pre-treatment of the nymphs with N-ethylmaleimide, to block chemoreception, inhibited the repellency.

Animals↗

PubMed2000

Cytokine responses of C3H/HeN mice infested with Ixodes scapularis or Ixodes pacificus nymphs.

Lyme borreliosis, caused by Borrelia burgdorferi, is transmitted by Ixodes scapularis in the eastern and midwestern United States and by Ixodes pacificus in the far-Western United States. Studies have shown that infestation with I. scapularis nymphs modulates host cytokine production; however, the influence of I. pacificus infestation on host cytokines remains uninvestigated. This study demonstrated how repeated infestations with pathogen-free I. scapularis or I. pacificus nymphs affects the production of the macrophage cytokines IL-1beta, IL-6 and tumour necrosis factor-alpha and the T lymphocyte cytokines IL-2, IL-4, IL-5, IL-6, IL-10 and IFN-gamma by C3H/HeN mice. Female mice were infested once or twice with pathogen-free I. scapularis or I. pacificus nymphs, with a 14-day tick-free period between exposures. After each infestation, tick biology parameters were assessed and macrophage and T lymphocyte cytokine production measured by antigen capture ELISA. Acquired resistance to tick feeding did not develop after infestation with either tick species. Differences in cytokine production were observed between infested and noninfested mice, and between mice infested with either I. scapularis or I. pacificus nymphs. Infestations polarized cytokine production towards a Th2 cytokine profile, with suppression of pro-inflammatory Th1 cytokines. This pattern of cytokine production is more pronounced for I. pacificus infested mice.

Animals↗

PubMed2001

Fine-scale tissue distribution of cadmium, inorganic mercury, and methylmercury in nymphs of the burrowing mayfly Hexagenia rigida studied by whole-body autoradiography.

The distribution of inorganic 109Cd(II), inorganic 203Hg(II), and [203Hg] methylmercury (MeHg) in nymphs of the burrowing mayfly Hexagenia rigida after exposure via water and sediments was studied. To better understand the mechanisms underlying the fate of Cd, Hg, and MeHg in this animal and to identify target organs, autoradiography of whole-body cryosections was used to obtain a detailed view of the distribution of the radiolabels. The gut and exoskeleton were the only structures labeled in nymphs exposed to Cd via water or sediments. After exposure to inorganic Hg via water, the Malpighian tubules exhibited a very high labeling, indicating that these organs may be a target for Hg toxicity. The distribution of Hg after exposure via sediments was similar, though the labeling of Malpighian tubules was less intense. Distribution of MeHg strongly differed between treatment groups. Nymphs were rather uniformly labeled after exposure via water, whereas in those exposed to MeHg in sediments, the intense labeling of all internal tissues contrasted with the very low labeling of the hemolymph, indicating that the translocation rate of the absorbed MeHg was faster in the latter group. This may be related to the complexation of MeHg by small thiol ligands in the gut as a result of the digestion process.

Animals↗

PubMed1993

Oxygen consumption of engorged nymphs and unfed adults of Hyalomma asiaticum ticks (Acari: Ixodidae) exposed to various photoperiods.

The oxygen consumption of engorged nymphs of Hyalomma asiaticum was measured at various intervals after drop-off from mice hosts. Duration of nymphal development to the emergence of adults was 25-32 days at 25 degrees C. The oxygen consumption was high immediately after completing the blood meal (193-248 mm3 g-1 h-1 but decreased significantly 18 days later (at 25 degrees C) to 45-65 mm3 g-1 h-1. It increased again before ecdysis (81-102 mm3 g-1 h-1, and also after ecdysis in freshly moulted adults (177-220 mm3 g-1 h-1. The oxygen consumption in 8-month-old adult ticks was very variable ranging from 40-42 to 172 mm3 g-1 h-1. Neither engorged nymphs nor unfed adult ticks showed any dependence of their respiratory metabolism on the photoperiodic regimes tested (LD 20:4 and LD 12:12, with or without transfer to an alternative photoperiod after engorgement of nymphs).

Animals↗

PubMed1992

Responses of the ticks Amblyomma hebraeum and A. variegatum to known or potential components of the aggregation-attachment pheromone. IV. Attachment stimulation of nymphs.

Ten known or potential components of the aggregation-attachment pheromone (AAP) of the ticks Amblyomma hebraeum and A. variegatum, as well as a mixture of these components and extracts of prefed males of the two species, were tested as attachment stimulants for nymphs. Unfed nymphs were confined in linen bags on the ears of rabbits that had been treated with the test compounds, mixture or extracts; the numbers attached were recorded after 24 h. In A. hebraeum, attachment was induced by four compounds (2-methyl propanoic acid, methyl salicylate, o-nitrophenol and salicylaldehyde), the mixture and extracts from both species. In A. variegatum, attachment was induced by three compounds (methyl salicylate, o-nitrophenol and salicylaldehyde), the mixture and extracts from both species. Methyl salicylate and o-nitrophenol are primary components of the AAP of both A. hebraeum and A. variegatum. 2-methyl propanoic acid is a species-specific attachment stimulant for A. hebraeum. Salicylaldehyde, a phenolic compound, is not a naturally occurring AAP component. Nymphs of both species respond to fewer attachment stimulants than the adults and, as shown by their respective host ranges, are less dependent on the AAP in the regulation of attachment than the adults.

Animals↗

PubMed1988

Field sampling of unfed nymphs of Amblyomma hebraeum.

Unfed nymphs of Amblyomma hebraeum Koch, 1844 shelter under debris on the soil surface and become active in host-seeking when stimulated with carbon dioxide. The active nymphs are not attracted to sources of carbon dioxide and hence cannot be effectively sampled using static carbon dioxide traps. However, these nymphs will cling to flannelette and can be sampled by flagging. Larger numbers are recovered if the soil surface is sampled using a vacuum device.

Animals↗

PubMed1998

Susceptibility of BALB/c mice to nymphs and larvae of Ixodes ricinus after modulation of IgE production with anti-interleukin-4 or anti-interferon-gamma monoclonal antibodies.

BALB/c mice infested three times with nymphs or larvae of Ixodes ricinus ticks do not acquire resistance as assessed by evaluation of both tick attachment and the weight of engorged nymphs or larvae. Tick challenge causes a gradual increase in total IgE antibody production from the first to the third infestation. Anti-tick IgG antibodies are never detected. When the mice are treated with anti-interleukin-4 (anti-IL-4) or anti-interferon-gamma (anti-IFN-gamma) monoclonal antibodies (mAbs) 1 day before each infestation, they produce fewer or more IgE antibodies, respectively. No effect is observed on IgG antibodies. In IL-4-deficient mice, no IgE or IgG antibody is produced. However, these treatments and the use of IL-4-deficient mice have no negative effect on either tick attachment or the weight of engorged nymphs or larvae. Treatment with anti-IL-4 mAb and the use of IL-4-deficient mice inhibits and abolishes the switching of IgE, respectively, but these are apparently not sufficient to shift the response toward Th1 cells.

Animals↗

PubMed1990

Infection rates with Cowdria ruminantium of nymphs and adults of the bont tick Amblyomma hebraeum collected in the field in Zimbabwe.

Cowdria ruminantium (heatwater) infection rates of field populations of the bont tick, Amblyomma hebraeum, were determined at two locations in the southern lowveld of Zimbabwe. At Mbizi Quarantine Station, unfed adult males and females, and nymphs were collected at intervals over a 2-year period using traps. At Lemco Ranch, engorged nymphs were collected on three occasions from weaner calves and allowed to moult to adults. The unfed ticks were fed in small pools on heartwater-susceptible sheep, some of which became infected. The infection rates of the ticks were then estimated statistically. Depending on the date of collection and locality, these rates were in the range 0.0-44.9% for males, 20.0-36.1% for females and 0.0-13.4% for nymphs. Most of these rates are considerably higher than those previously believed to occur.

Animals↗

PubMed2006

Differential gene expression in Perillus bioculatus nymphs fed a suboptimal artificial diet.

Fragments of two artificial diet up-regulated and two prey up-regulated transcripts were isolated from the predatory Pentatomid Perillus bioculatus using suppression subtractive hybridization. A BlastX search found similarities for two diet-upregulated clones, i.e., the tyrosine-3-monooxygenase gene and the gene for the chitin binding protein, Gasp. The probe generated from the tyrosine-3-monooxygenase clone hybridized to two transcripts 2.3 and 1.2kb in size. The two transcripts were differentially regulated: the 2.3kb transcript was upregulated in the first and late third instar diet-fed nymphs, whereas the 1.2kb transcript was upregulated in the second and early third instar diet-fed nymphs. The Gasp gene was upregulated in late third instar nymphs. A positive correlation was found between levels of expression of the isolated genes and the number of generations the insects had been reared on the artificial diet.

Animal Nutritional Physiological Phenomena↗

PubMed1976

The feeding behaviour of larvae, nymphs and adults of Rhipicephalus appendiculatus.

The pre-feeding and feeding periods of larvae, nymphs and adults of Rhipicephalus appendiculatus on rabbits (Oryctolagus cuniculus) were investigated. Larvae and nymphs required at least 8-9 days after hatching and moulting respectively before they could attach and start feeding, while adults required at least 6-9 days. But longer periods of starvation improved the proportion of ticks that successfully fed. After attachment, there was always an initial period of slow feeding, which was followed by a phase of very rapid feeding before the engorged ticks detached from the host. Larvae detached 4-5 days after attachment, nymphs detached after 5-6 days and adults detached 7-9 days after attachment.

Animals↗

PubMed2002

Seasonal activity patterns of Ixodes pacificus nymphs in relation to climatic conditions.

In western North America, the tick Ixodes pacificus Cooley & Kohls (Acari: Ixodidae) is the primary vector to humans and domestic animals of the disease agents causing Lyme disease and granulocytic ehrlichiosis. We examined the seasonal activity patterns of I. pacificus nymphs over a 4-year period, including the wet and cold El Niño winter/spring of 1998, in a dry oak/madrone woodland, and for one year in a cooler and moister redwood/tanoak woodland in Mendocino County, California. Linear regressions were used to estimate when nymphal densities first exceeded and then fell below 25, 50 and 75% of the recorded yearly peak densities. In oak/madrone woodland, nymphs typically were active by mid-March, reached 50% of their yearly peak densities in early to mid-April, peaked by early May, fell below 50% of their peak densities by early to mid-June, and were absent by late July to mid-August. The lengths of the periods with nymphal densities exceeding 50 and 75% of the recorded yearly peaks in oak/madrone woodland were associated positively with rainfall and negatively with maximum air temperatures during April-May. Moreover, nymphal numbers typically reached 50% of their peak 10-15 days later, remained at levels above 50% of the peak 1.3-1.5 times longer, and started declining 4-6 weeks later under cooler, moister climatic conditions (oak/madrone woodland in 1998 and redwood/tanoak woodland in 2000) relative to warmer, drier conditions (oak/madrone woodland in 2000-2001). In oak/madrone woodland, nymphal densities typically started to decline when mean maximum daily air temperatures exceeded 23 degrees C. Nymphal densities were higher in dry oak/madrone relative to moist redwood/tanoak woodland from mid-March to late May 2000, similar in both habitat types in early June, but higher in redwood/tanoak woodland from late June onwards. We conclude that large-scale studies of the density of I. pacificus nymphs in California need to consider spatial variation in the length of nymphal activity periods and select temporal sampling regimens that yield representative data for all included habitat types.

Animals↗

PubMed2004

Sigmodontinae rodents as hosts for larvae and nymphs of Ixodes loricatus Neumann, 1899 (Acari: Ixodidae).

Larvae and nymphs of Ixodes loricatus Neumann, 1899 ticks (confirmed by morphological characters and by comparison of 16S mitochondrial rDNA sequences) were collected from Sigmodontinae Wagner, rodents in central and northern Argentina and Uruguay. A total of 100 larvae and 38 nymphs of I. loricatus were collected on the genera Akodon Meyen (n = 36 individuals), Calomys Waterhouse (n = 2), Oligoryzomys Bang in = 12), Oxymycterus Waterhouse (n = 9), and Scapteromys Waterhouse (n = 13). 72 larvae and 18 nymphs were collected on Akodon. Adults of I. loricatus were found in central Argentina and Uruguay on Didelphimorphia of the genera Didelphis Linnaeus and Lutreolina Thomas. Ixodes loricatus has been considered a species with strict total specificity to Didelphimorphia. Our results show that this statement may not be justified. Sigmodontinae rodents are sympatric and share habitats with the phylogenetically distant Didelphimorphia; infestation with I. loricatus seems to be its consequence. We tentatively consider I. loricatus moderately specific to Didelphimorphia.

Animals↗

PubMed1991

Effectiveness of carbaryl applications for the control of Ixodes dammini (Acari: Ixodidae) nymphs in an endemic residential area.

Ground applications of carbaryl in early June 1989 reduced populations of nymphal Ixodes dammini Spielman, Clifford, Piesman & Corwin by 100% in five 0.4-ha residential sites 72 h after application. High levels of control (greater than 90%) persisted for almost 2 mo. Five nymphs were recovered at the periphery of the sprayed plots at two sites 2 wk after spraying and nine nymphs were collected at the periphery of the sprayed plots at three of the sites 4-5 wk after application. At 8 wk after application, I. dammini nymphs were recovered within three of the sprayed plots. Chemical control of nymphal I. dammini may be a viable management practice for homeowners living in endemic areas to reduce the chances of acquiring Lyme disease.

Animals↗

PubMed1992

Tick sweep: modification of the tick drag-flag method for sampling nymphs of the deer tick (Acari: Ixodidae).

We describe a version of the standard tick drag-flag modified for use in close-growing and tangled vegetation, as well as under ornamental shrubbery and fallen branches. Two major features of the sweep are: (1) it allows the user to remain upright with the flag parallel to the ground, thus sampling effectively beneath low and fallen branches and around shrubs, as well as capturing host-seeking ticks in advance of the operator; and (2) the use of a flannel rubberized-laminate fabric (crib sheet) for the flag that is snag-proof and highly durable in dense and thorny vegetation. In simultaneous 100-m samples, the sweep was as effective as the 1-m standard tick drag for capturing nymphs of the deer tick, Ixodes dammini Spielman, Clifford, Piesman & Corwin, where understory vegetation was sparse, but was twice as effective in dense vegetation, capturing significantly more I. dammini nymphs. The sweep also captured nymphs of the American dog tick, Dermacentor variabilis (Say); rabbit tick, Haemaphysalis leporispalustris (Packard); and lone star tick, Amblyomma americanum (L.).

Animals↗

PubMed1997

Density-dependent seasonal dynamics of blacklegged tick (Acari:Ixodidae) nymphs.

The midsummer seasonal decline in abundance of unfed Ixodes scapularis Say nymphs on experimental plots in New Jersey was density-dependent. Nymph density was manipulated on 9 plots (10 by 10 m each) in Morristown. National Historical Park, NJ, in early June 1994. Subsequent rates of decline were directly proportional to initial density (linear regression, R2 = 0.83). A 6-fold manipulation of density caused more than a 10-fold increase in per-capita disappearance rate. Absence of density-dependent mortality in simultaneous field cage experiments implicated dispersal at rates higher than reported previously, positive-density-dependent host finding success, or predation, possibly in the form of host grooming. Each of these possibilities has important implications for the role of unfed nymphs in the regulation of I. scapularis populations.

Animals↗

PubMed2005

Remote sensing (normalized difference vegetation index) classification of risk versus minimal risk habitats for human exposure to Ixodes pacificus (Acari: Ixodidae) nymphs in Mendocino County, California.

In California, Ixodes pacificus Cooley & Kohls nymphs have been implicated as the primary bridging vectors to humans of the spirochetal bacterium causing Lyme disease (Borrelia burgdorferi). Because the nymphs typically do not ascend emergent vegetation, risk of human exposure is minimal in grasslands, chaparral, and woodland-grass. Instead, woodlands with a ground cover dominated by leaf litter (hereinafter referred to as woodland-leaf) have emerged as a primary risk habitat for exposure to B. burgdorferi-infected nymphs. As a means of differentiating woodland-leaf habitats from others with minimal risk (e.g., chaparral, grassland, and woodland-grass), we constructed a maximum likelihood model of these habitat types within a 7,711-ha area in southeastern Mendocino County based on the normalized difference vegetation index derived from Landsat 5 Thematic Mapper imagery (based on a 30 by 30-m pixel size) over four seasons. The overall accuracy of the model to discriminate woodland-leaf, woodland-grass, open grassland, and chaparral was 83.85% (Kappa coefficient of 0.78). Validation of the accuracy of the model to classify woodland-leaf yielded high values both for producer accuracy (93.33% of validated woodland-leaf pixels correctly classified by the model) and user accuracy (96.55% of model-classified validation pixels correctly categorized as woodland-leaf). Woodland-leaf habitats were found to be highly aggregated within the examined area. In conclusion, our model successfully used remotely sensed data as a predictor of habitats where humans are at risk for Lyme disease in the far-western United States.

Animals↗

PubMedDate not supplied

Incoordination, paralysis and recovery after pyrethroid treatment on nymphs III of Triatoma infestans (Hemiptera: Reduviidae).

Symptoms of poisoning for deltamethrin and cis-permethrin on nymphs III of Triatoma infestans were described. The time required for incoordination and paralysis were determined. Deltamethrin was equal or more rapid in the onset of the first effect (accordingly to dose), and cis-permethrin in the onset of the second one. There were no significant differences between incoordination doses 50% (IncD50s) at different times for the two pyrethroids. They showed equivalent incoordination power, but the nymphs treated with deltamethrin recovered slightly more rapid and in greater amount than the nymphs treated with cis-permethrin. The recovery was inhibited by the simultaneous application of piperonyl butoxide. This result suggests that biotransformation by mixed-function microsomal oxidases are involved in the process of recovery.

Animals↗

PubMed2002

Spatial distribution of Plecoptera nymphs in streams of a mountainous area of Central Brazil.

In this paper the spatial distribution of Plecoptera nymphs in the Almas' River basin, Pirenópolis, GO, was studied. Two Surber samples, each comprising 20 sampling units and totalling 2 m2, were taken in each of the 13 stations, one during the rainy season (January 1994) and the second during the dry season (July 1994). In 5 of these stations, monthly samplings were made from June 1993 to July 1994; in these, temperature, velocity, discharge, electrical conductivity and pH were measured. Regional rainfall was also obtained. To ascertain the distribution of nymphs in the habitat, a separate sample was taken. Of the factors considered, the most important affecting the spatial distribution of the stonefly nymphs were altitude, stream order, and anthropic influence. Locally, the genera Anacroneuria and Kempnyia showed clumped distributions, but the data for Gripopteryx and Tupiperla were inconclusive due to low numbers.

Animals↗