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PubMed2000

Efficiency of drag sampling for estimating population sizes of Ixodes pacificus (Acari: Ixodidae) nymphs in leaf litter.

Drag sampling is a commonly used method to obtain relative estimates of the density of questing nymphal Ixodes scapularis Say and I pacificus Cooley & Kohls ticks, which are primary vectors of Lyme disease spirochetes to humans in North America. However, the efficiency of drag sampling in determining absolute population densities of questing nymphs has not been evaluated previously. Therefore, we assessed the efficiency of a single drag-sampling occasion to estimate the total population size of questing I pacificus nymphs in a leaf-litter habitat in California. Repeated daily removal sampling was carried out in four areas, each covering 300 m2, on 17 occasions over a 23-d period in the spring of 1999. In total, 573 I. pacificus nymphs were collected, of which 55 (9.6%) were collected on the initial sampling occasion and 20 (3.5%) on the last occasion. The total population size of questing nymphs, i.e., the intersection with the horizontal axis of a linear regression of daily nymphal catch rates on the number of nymphs caught previously, was estimated to be 936. Thus, the efficiency of the initial sampling occasion to estimate the total population size was 5.9% (4.8, 5.0, 5.8, and 9.1%, respectively, for the four individual sampling areas). Further, the overall mean efficiencies of the two, five, and 10 first removal sampling occasions to estimate the absolute nymphal density was 5.2, 4.7, and 4.3%, respectively, and 13 sampling occasions were required to collect 50% of the estimated total nymphal population.

Animals↗
PubMed1997

Evaluation of hyperactivity produced by pyrethroid treatment on third instar nymphs of Triatoma infestans (Hemiptera:Reduviidae).

The hyperactivity produced in third instar nymphs of Triatoma infestans by their exposure to films of deltamethrin or cis-permethrin was evaluated. Both pyrethroids produced a significant increase in locomotor activity at 26 and 36 degrees C but not at 16 degrees C. At 26 degrees C, only deltamethrin produced hyperactivity when topically applied on the dorsal side of the nymph's abdomen. However, both pyrethroids produced hyperactivity when topically applied on the head of the nymphs. Hyperactivity was not observed when nymphs were treated with N-ethylmaleimide (20 micrograms/insect) before exposure to the pyrethroids. The effect of both insecticides on locomotor activity reversed the inhibitory influence on locomotion elicited by contact with the walls of the experimental arena (thigmotaxis).

Animals↗
PubMed1999

Ixodes scapularis: effects of repeated infestations with pathogen-free nymphs on macrophage and T lymphocyte cytokine responses of BALB/c and C3H/HeN mice.

Schoeler, G. B., Manweiler, S. A., and Wikel, S. K. 1999. Ixodes scapularis: Effects of repeated infestations with pathogen-free nymphs on macrophage and T lymphocyte cytokine responses of BALB/c and C3H/HeN mice. Experimental Parasitology 92, 239-248. Ixodes scapularis is the principal vector in the United States of Borrelia burgdorferi, the causative agent of Lyme borreliosis, the human granulocytic ehrichiosis agent, and Babesia microti. Infestation with I. scapularis nymphs has previously been shown to modulate host T lymphocyte cytokine production. Tick-induced host immunomodulation is increasingly recognized as a contributing factor in successful transmission and/or establishment of tick-borne pathogens. This study was conducted to determine the effects of repeated infestations with pathogen-free I. scapularis nymphs on the production of the macrophage cytokines interleukin (IL)-1beta and tumor necrosis factor-alpha and the T lymphocyte cytokines IL-2, IL-4, IL-10, and interferon-gamma in both BALB/c and C3H/HeN mice. The pattern of T lymphocyte cytokine production was evaluated to determine if repeated tick infestation polarizes the immune response toward a Th-1 or Th-2 cytokine profile. Female BALB/c and C3H/HeN mice were infested one to four times with pathogen-free I. scapularis nymphs, with a 14-day tick-free period between each exposure. After each infestation, tick biology parameters were measured and macrophage and T lymphocyte cytokine production was assessed. Elaboration of T lymphocyte and macrophage cytokines was quantitated by antigen capture enzyme-linked immunosorbent assay. Acquired resistance to I. scapularis feeding was not developed by either mouse strain. Significant differences in cytokine production were observed between infested and noninfested mice, as well as between the two mouse strains, following tick infestation. Infestation of both strains with pathogen-free I. scapularis results in a polarization of the host immune response toward a Th-2, anti-inflammatory pattern, with a corresponding suppression of Th-1 responses.

Animals↗
PubMed1992

A comparison of the attraction of nymphs and adults of the ticks Amblyomma hebraeum and A. variegatum to carbon dioxide and the male-produced aggregation-attachment pheromone.

The attraction of nymphs of the ticks Amblyomma hebraeum and A. variegatum to CO2 alone and CO2 together with the male-produced aggregation-attachment pheromone (AAP) was investigated. Matching experiments on the attraction of the adults of the two species were run for comparison. Nymphs of A. hebraeum were strongly attracted to sources of CO2 and CO2/AAP at distances of 10 and 15 m. At distances of 20 and 25 m significantly more nymphs were attracted to CO2/AAP than to CO2 alone. Adults of A. hebraeum were not attracted to CO2 alone at any distance; these ticks were attracted to CO2 and AAP together for distances of up to 25 m. The patterns of attraction of nymphs and adults of A. variegatum at 10 m were similar to those recorded in A. hebraeum.

Animals↗
PubMed2005

Response properties of wind-sensitive giant interneurons in the fourth-instar nymphs of the cricket, Gryllus bimaculatus.

The response properties of four wind-sensitive giant interneurons (GIs) 8-1, 9-1, 9-2 and 9-3 in the fourth-instar nymphs of the cricket Gryllus bimaculatus were investigated to clarify the differences and/or similarities of the escape eliciting neural system between nymphs and adults. Air current was presented to the animal from 12 different directions in the horizontal plane, and the intensity-response curves for each GI were obtained at each stimulus direction. The intensity-response curves showed that the response magnitudes of GI 8-1 in the fourth-instar crickets increased with stimulus velocity up to 300 mm/s regardless of the stimulus direction. The response magnitudes of GI 9-1 in the nymphs reached a plateau at a stimulus velocity of 30 mm/s in most stimulus directions. The response magnitudes of GIs 9-2 and 9-3 increased with stimulus velocity up to 300 mm/s regardless of the stimulus direction. The directional sensitivity curves plotted on the basis of threshold velocities revealed that the preferential directions of the GIs were the ipsilateral-side in GI 8-1, the ipsilateral-front and contralateral-rear in GI 9-1, the ipsilateral-rear in GI 9-2 and the ipsilateral-front in GI 9-3, designated with respect to the side of the ventral nerve cord containing the axons. Although the GIs in nymphs occasionally showed higher threshold velocities and larger response magnitudes, the directional sensitivities, i.e., the preferred directions, of the GIs were basically the same with those of adults.

Animals↗
PubMed2006

Determining the tick scutal index allows assessment of tick feeding duration and estimation of infection risk with Borrelia burgdorferi sensu lato in a person bitten by an Ixodes ricinus nymph.

The risk of Borrelia burgdorferi sensu lato transmission from an infected vector tick to a host increases with increasing duration of tick feeding. In Ixodes ricinus nymphs, the main vector of B. burgdorferi s.l. in most parts of Europe, the transmission risk appears low to moderate within the first 24h of feeding but increases to >70% after only 36 h. In this study, the so-called scutal index, the ratio between tick abdominal length and scutum width, a very good measure of the level of tick engorgement, was investigated for its potential to assess the feeding duration of detached I. ricinus nymphs, thereby indicating the level of human infection risk with B. burgdorferi s.l. I. ricinus nymphs were allowed to feed in capsules on tick-naive Mongolian gerbils for 0, 12, 24, 36 h, or to repletion, in groups of up to 9 individuals. After tick removal, the scutal index of each tick (n=516) was determined using a stereomicroscope with an ocular micrometer. This was also possible, if the tick mouthparts were damaged. Although the scutal indices determined at 24 h versus 36 h post-attachment (a critical interval for B. burgdorferi transmission) differ significantly, there was some overlap between the two groups. However, by choosing a scutal index of 1.1 as a cut-off, it was possible to assign 93.2% of the ticks attached for 24h (n=310) to one group (low-risk group ticks) and 85.6% of those attached for 36 h (n=97) to the other (high-risk group ticks). This means that those people from whom I. ricinus nymphs with a scutal index >1.1 detached have a distinctly elevated risk of Borrelia infection and therefore more likely require medical attention.

Animals↗
PubMed2005

Stimuli inducing gregarious colouration and behaviour in nymphs of Schistocerca gregaria.

Solitarious nymphs of Schistocerca gregaria were reared under various conditions in both Jerusalem and Oxford to tease apart cues involved in behavioural and colour phase change. Treatments included rearing nymphs from the IInd or IIIrd until the final nymphal stadium in physical contact with similarly aged conspecific groups or with another locust species, Locusta migratoria migratorioides, as well as confining single nymphs in mesh cages, which were kept within crowds of S. gregaria or L. migratoria migratorioides, providing visual and olfactory but no physical contact with other locusts. In the Oxford experiments, an extra treatment was included which provided olfactory cues without visual or contact stimulation. Our results confirm that transformation from the solitarious to the gregarious phase of locusts is complex, and that different phase characteristics not only follow different time courses, but are also controlled by different suites of cues. As predicted from earlier studies, behavioural phase change was evoked by non-species-specific cues. Rearing in contact with either species was fully effective in inducing gregarious behaviour, as was the combination of the sight and smell of other locusts, but odour alone was ineffective. Colour phase change was shown to comprise two distinct elements that could be dissociated: black patterning and yellow background. The former of these could be induced as effectively by rearing S. gregaria nymphs in a crowd of L. migratoria migratorioides as by rearing with conspecifics. Sight and smell of other locusts also triggered black patterning and, unlike behavioural change, some black patterning was induced by odour cues alone. Hence, physical contact was not needed to induce gregarious black patterning. Yellow colouration, however, was only fully induced when locusts were reared in contact with conspecifics, implying the presence of a species-specific contact chemical cue.

Analysis of Variance↗
PubMed2004

Estimation of the density of nymphs of the bush tick, Haemaphysalis longicornis (Acari: Ixodidae), by the catch effort method.

The density of nymphs of the bush tick, Haemaphysalis longicornis, was investigated by the catch effort method with flagging. The spatial distribution of H. longicornis nymphs fit the model of contagiously distributed colonies by Iwao's m*-m analysis (Iwao 1968). A sequential sampling method was used to predict the theoretical point at which to stop sampling. Our analysis showed that five quadrats (4 m x 4 m) were sufficient to estimate the density of H. longicornis nymphs with a mean density of 5.39 per quadrat. We estimated the tick density by two methods with respect to the sampling interval. The estimated density of ticks based on ticks collected during short sampling intervals (within a half hour) was 511.34 in the 18 quadrats with the extrapolation of the linear regression equation. On the other hand, for the long interval sampling, the total number of ticks estimated by the linear regression equation was 635.47 in six quadrats in which ticks had been collected by long interval sampling. There was a significant difference between the slopes of the two linear regression equations, suggesting that the rate of reduction in the number of H. longicornis nymphs in the study area by the catch effort method differed between the two sampling methods.

Animals↗
PubMed2005

The shield-backed bug, Pachycoris stallii: description of immature stages, effect of maternal care on nymphs, and notes on life history.

The life history of the shield-backed bug, Pachycoris stallii Uhler (Heteroptera: Scutelleridae), immatures was studied on its host plant, Croton californicus Muell.-Arg. (Euphorbiaceae), in Baja California Sur, Mexico. Immature stages are described and illustrated. Pachycoris stallii is bi- or multivoltine and occurs in xeric areas with sandy soil where it is rarely encountered away from C. californicus. Nymphs and adults feed on seeds within C. californicus fruit. Bugs oviposit on the underside of leaves, and females guard their eggs and first-instar nymphs from natural enemies. Embryonic orientation of prolarvae is nonrandom; each embryo is oriented with its venter directed toward the ground. This orientation may facilitate aggregation of first instars. The longitudinal axes of eggs are always oriented upward at about a 16 degree angle of deviation from a line perpendicular to the leaf surface. This is the first recorded observation of this phenomenon in Pentatomoidea. Experimental removal of females guarding first instars results in 100% loss of nymphs, and this is attributed to disruption of the aggregative behavior of nymphs. Maternal guarding appears to be a net benefit to P. stallii, despite possible costs to the brooding female.

Animals↗
PubMed1997

Pyriproxyfen effects on newly engorged larvae and nymphs of the lone star tick (Acari:Ixodidae).

Newly engorged larvae and nymphs of the lone star tick, Amblyomma americanum (L.), were exposed to 9 treatments of pyriproxyfen in glass vials consisting of dosages of 4, 8, and 16 micrograms/cm2 for 7 d, 14 d, and continuous exposure periods at each concentration. Treatment of newly engorged larvae resulted in decreased molting, altered postmolt defecation, and nymphal survival with results being dose and exposure dependent. Molting inhibition ranged from 35.9 to 68.4%. Successfully molted nymphs were lethargic, exhibited altered defecation patterns, and were short-lived compared with untreated adults. By 65 d after treatment, cumulative inhibition of molting and hastened mortality of molted adults resulted in 82.6-100% control, depending on dosage and exposure. Treatment of newly engorged nymphs showed minimal to no effect on molting; however, adults were lethargic and displayed altered postmolt defecation patterns. Subsequent adult longevity was most dramatically affected with 87.9-100% control achieved by 82-84 d after treatment. Fecal patterns and survivorship were dose and exposure dependent. Estimates of subsequent feeding success of adults treated as engorged nymphs, show reduced capacities of attachment, engorgement and reproduction.

Animals↗
PubMed2003

Self-sacrificing gall repair by aphid nymphs.

Insect galls are vulnerable to invasion by moth larvae that can tunnel into the wall. We report that nymphs of the aphid Nipponaphis monzeni repair their gall self-sacrificingly. When a hole was bored into their gall, many globular nymphs discharged a large amount of body fluid from their cornicles onto the gall's wound, and kneaded the fluid, which soon became viscous and eventually congealed, plastering over the hole. Having discharged the fluid, the nymphs shrivelled to approximately one-third of their original volume. Several nymphs were buried in the plaster, like 'aphid sacrifices'. This is the most elaborate social behaviour so far known among aphids.

Animals↗
PubMed1990

Circadian rhythms of locomotor activity in cockroach nymphs: free running and entrainment.

The temporal organization of locomotor activity was investigated in nymphs of the cockroach Leucophaea maderae. Approximately 40% of the animals examined between 1 and 50 days of age exhibited a circadian activity rhythm in constant darkness (n = 172) with an average free-running period of 23.7 +/- 0.68 hr. Twelve of 17 animals in which activity was recorded for most or all of the final instar also exhibited periods of rhythmic activity. The rhythms of the nymphs could be entrained by light-dark (LD) cycles with periods of 22, 24, or 26 hr. In contrast, neither maternal influences during embryogenesis nor hatching from the egg was effective in synchronizing the rhythms. Although adult cockroaches can be readily entrained by temperature cycles, in nymphs temperature appeared at best to be a weak zeitgeber. Embryonic exposure to an LD cycle until 6 days prior to egg hatch was effective in synchronizing the activity rhythms of the nymphs, indicating that differentiation of an entrainable pacemaking system occurs prior to hatching.

Aging↗
PubMed2006

Disruption of the salivary protein 14 in Ixodes scapularis nymphs and impact on pathogen acquisition.

We previously examined the physiological role of the anticoagulant salivary protein 14 (salp14) in adult Ixodes scapularis and showed that Salp14 played a role in tick feeding and engorgement. We now analyze whether the disruption of the salp14 family expression by RNA interference affects tick weight in naïve nymph I. scapularis. Salp14 expression after dsRNA injection was significantly reduced, as shown by mRNA and protein analysis. However, nymph engorgement weight was not altered in salp9pac (salp14 paralog) dsRNA-injected ticks. We also determined Borrelia burgdorferi and Anaplasma phagocytophilum acquisition in I. scapularis nymphs that had reduced Salp14 expression. B. burgdorferi and A. phagocytophilum acquisition was not affected 72 hours after feeding. Our results suggest that different mechanisms govern nymph and adult feeding in I. scapularis.

Anaplasma phagocytophilum↗
PubMedDate not supplied

[The development of methods for the absolute count of the population of ixodid pasture ticks in open landscapes. 3. The count of hungry Dermacentor nuttalli Olen., 1919 larvae and nymphs in the steppe regions of the Transbaikal area].

Methods for absolute registration of the number of hungry larvae and nymphs directly in the places of their natural habitation have been elaborated. Specific features of the activation of these phases in Transbaikal conditions have been studied. Peaks of their seasonal activity can be observed in July. It has been shown that the results of single (during seasonal peak in their number) capture of larvae and nymphs from all animal holes over a 100 m2 area can be used for characterization of density. Single capture accounts for 9-15% larvae and 12-16% nymphs of the total number of activized individuals. To assess reliably mean larval and nymph density, with the inadequacy of the results of absolute registration being 30%, not less than 100-130 areas should be examined.

Animals↗
PubMed1990

Development and infectivity of Anaplasma marginale in Dermacentor andersoni nymphs.

The development of Anaplasma marginale was studied in Dermacentor andersoni nymphs after they had fed on a calf with ascending Anaplasma infection. Gut tissues were collected on day 4 of tick feeding, from newly replete (fed) nymphs and on postfeeding days (PFD) 5, 10, 15, 20, and were processed for light and electron microscopy to determine density of A marginale colonies. Homogenates of gut tissues were prepared from nymphs collected on the same days and inoculated into susceptible, splenectomized calves to test for infectivity. Anaplasma colonies were detected in gut cells on PFD 5, 10, 15, and 20. Although colony density appeared to be higher on PFD 10 and 15, differences were not significant. Nymphal type-1 colonies were detected in highest numbers on PFD 5 and 10, transitional colonies were seen in highest numbers at PFD 10 and 15, and nymphal type-2 colonies were observed only on PFD 20. Gut homogenates that were collected from ticks at 4 days of feeding, when newly replete, and on PFD 20 caused anaplasmosis when injected into susceptible calves, but homogenates made from ticks collected on PFD 5, 10, and 15 were not infective. The data indicate that of the colony types of A marginale that develop in replete nymphs, nymphal type-1 and transitional colonies may contain organisms that are not infective for cattle.

Anaplasma↗
PubMed1980

The use of dragonfly nymphs in the control of Aedes aegypti.

The predatory rates of the dragonfly nymphs on Aedes aegypti were studied in the laboratory and under field conditons. Labellulid nymphs were found to predate on Ae. aegypti larvae and pupae readily. The rate of consumption was found to be 133 +/- 21 all stages of larvae per medium size nymph per 24 hours. In container habitats complete elimination of all larvae and pupae were achieved between day 4 and 9 depending on density of aquatic stages. The dragonfly nymphs as predators could be used in biological control of Aedes mosquitoes.

Aedes↗
PubMed1995

Transmission of Borrelia burgdorferi by Ixodes pacificus nymphs and reservoir competence of deer mice (Peromyscus maniculatus) infected by tick-bite.

The transmission of Borrelia burgdorferi to deer mice (Peromyscus maniculatus) by Ixodes pacificus nymphs was investigated experimentally. Deer mice were exposed to infected nymphs for 24, 48, or 72 hr, or until ticks had fed to repletion (> or = 96 hr). Infection status of hosts was assessed 4 wk later by culture of ear-punch biopsies in BSK II medium and by indirect immunofluorescence. Eight mice exposed to ticks for 24 hr did not become Infected. In contrast, infection was acquired by 1 of 9 (11%), 2 of 8 (25%), and 8 of 10 (80%) mice exposed for 48, 72, and > or = 96 hr, respectively. Eight weeks after exposure to infected nymphs, the infectivity of 5 deer mice for I. pacificus larvae was assessed. Overall, 33% of I. pacificus larvae fed on these mice acquired and transstadially passed spirochetes. We conclude that most I. pacificus nymphs require 4 days or longer to transmit spirochetes to deer mice, and that larvae efficiently acquire and maintain spirochetes from mice that have been infected by tick-bite.

Animals↗
PubMed1994

Effect of repeated infestations of BALB/c mice with Ixodes ricinus nymphs on tick-borne encephalitis virus infection.

The effect of repeated infestations of BALB/c mice with Ixodes ricinus (L.) nymphs on tick borne encephalitis (TBE) virus infection was studied. Enhancement of nymphal feeding, occurring in noninfected mice during the quaternary infestations, was less apparent or absent in female nymphs engorged on TBE virus infected mice. The mice infected with TBE virus during quaternary tick infestation survived significantly longer (P < 0.01) than mice infected with TBE virus during the primary tick infestation. The mean titre of virus in murine blood (determined by plaque assay) was significantly lower (P < 0.01) and the number of nymphs acquiring virus was reduced (P < 0.05) when feeding on hosts infected during the quaternary infestation. The results indicate that repeated infestations of I. ricinus nymphs on BALB/c mice, although enhancing tick feeding, reduced infection with TBE virus when inoculated intraperitoneally.

Animals↗