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PubMed1997

The use of morphometrics in entomological surveillance of sylvatic foci of Triatoma infestans in Bolivia.

Jamach'uma (Cochabamba, Bolivia) is a small village surrounded by sylvatic foci of Triatoma infestans. Houses in the village were also infested with T infestans, and were sprayed in December 1992 as part of a Chagas disease vector control trial. Ten months later the houses were found to be again infested with a few fifth instar nymphs of T. infestans. These nymphs were compared by seven head measurements with 36 fifth instar nymphs collected from houses in Jamach'uma before treatment, and with two sets of nymphs originating from the surrounding sylvatic foci: eight specimens collected in 1992 and nine specimens collected in 1995. The results are discussed in relation to the possible mechanisms of the apparent reinfestation: recrudescence of a residual domestic population or reinvasion of the houses from surrounding sylvatic foci. Quantitative comparisons support the former hypothesis.

Animals↗
PubMed2001

The response of a homochrome grasshopper, Oedipoda miniata, to the dark-colour-inducing neurohormone (DCIN) of locusts.

The effect of the dark-colour-inducing neurohormone (DCIN=[His(7)]-corazonin) of locusts was investigated in nymphs of the grasshopper, Oedipoda miniata, which exhibit strong homochromy, but neither green-brown, nor phase colour polymorphism. Graded doses of synthetic DCIN were injected in 1 µl of olive oil into 0-24-h-old penultimate nymphs. DCIN induced dose-dependent darkening in the recipients, seen 4 days after injection (still in the penultimate nymphal instar), as well as in the subsequent last-instar nymphs. The dose-range obtained between discernible and maximum (almost black) darkening extended over three orders of magnitude, from 1 pmol to 1 nmol of DCIN. In spite of the darkening observed already in the penultimate nymphal instar, the exuviae in the moult from this to the last nymphal instar did not show marked dark patches. However, the exuviae of the next moult (from last-instar nymph to adult) showed such dark patches, which increased with the increase of the dose, revealing the presence of exocuticular melanin. We conclude that DCIN, or a very close peptide, is the endogenous hormone which plays the major or sole role in the control of homochromy of O. miniata and possibly also of other acridids which exhibit homochromy.

Journal Article↗
PubMed2000

The life cycle of Rhipicephalus bursa Canestrini and Fanzago, 1877 (Acarina: ixodidae) under laboratory conditions.

The biology of Rhipicephalus bursa has not been thoroughly studied. In the present study R. bursa was bred in the laboratory and its biology worked out.Larvae, nymphs and adult Rhipicephalus bursa ticks were fed on sheep and were held at 28+/-1 degrees C and 89+/-1% relative humidity (RH) in a darkened incubator. The average weight of engorged females was 0.676g (range 0.353-1.128). The average weight of eggs laid by females was 0.344g (range 0.146-0. 554g). The average number of eggs laid was 7527 (range 6263-8860) and this was significantly correlated with the weight of the females. The index of Reproduction Efficiency (number of eggs per g weight of female) was 8469.6. The index of Conversion Efficiency (weight of eggs per weight of female) was 0.5037. Peak daily oviposition, at an average of 840 eggs per female, occurred on the 6th day of oviposition. After Day 6, the rate declined steadily. The average duration of the preoviposition period was 5.1 days (range 4-7 days). The oviposition period averaged 16.5 days (range 12-21 days), and was significantly related to both the weight of the female and the number of eggs laid. The average pre-hatching period was 31.2 days (range 24-45 days). The average feeding time of larvae and nymphs of this two host tick was 15.2 days (range 14-18 days). Female ticks fed for 5.9 days on the average. Heavier nymphs produced females and a shorter premoult period was noted for lighter male nymphs. The males/females ratio was 1.38:1. The time taken to complete the life cycle was on average 142.45 days (range 99-254 days).

Animals↗
PubMed1997

Identification of an Ixodes ricinus salivary gland fraction through its ability to stimulate CD4 T cells present in BALB/c mice lymph nodes draining the tick fixation site.

BALB/c mice infested with larvae or nymphs of Ixodes ricinus develop in their lymph nodes a T cell-specific immune response triggered by salivary gland soluble antigens (SGA). SGA are apparently conserved in the 3 biological stages of I. ricinus ticks and are species specific. SGA derived from partially fed females I. ricinus stimulate lymph node T cells from mice infested with I. ricinus larvae or nymphs. In contrast, lymph node cells from mice infested with Amblyomma hebraeum nymphs do not respond. A chromatographic fraction enriched with a 65 kDa protein (IrSG65) isolated from salivary glands of I. ricinus partially fed females induces in vitro a specific T cell proliferation of lymph node cells from mice infested with I. ricinus nymphs. The depletion of CD4+ T cells drastically reduces the ability of lymphocytes from infested mice to proliferate after IrSG65 stimulation.

Animals↗
PubMed2001

Molecular individuality and adaptation of the tick Rhipicephalus appendiculatus in changed feeding environments.

The tick Rhipicephalus appendiculatus Neumann (Acari: Ixodidae) naturally infests many host species. However, the mechanisms that enable it to feed on such a wide range of hosts are unclear. One possibility is that a tick population maintains molecular (genotypic and/or phenotypic) diversity among individuals such that individuals vary in their competency in taking bloodmeals under different feeding conditions. As a first step in testing this hypothesis, we showed that the polymorphism of salivary gland proteins, previously demonstrated in unfed ticks, was maintained during feeding on guinea-pigs. We then compared feeding performance under standard laboratory rearing conditions: one instar (adults or nymphs) feeding on guinea-pigs, with three changed conditions: (1) two instars (adults and nymphs) feeding together on guinea-pigs; (2) one instar (adults or nymphs) feeding on hamsters; and (3) two instars (adults and nymphs) feeding together on hamsters. The mean engorged weight of adult females was significantly reduced under all changed conditions, indicating that most of the adult individuals were significantly challenged by the changed conditions. However, some individuals achieved successful engorgement, indicating competence to the changed condition, and demonstrating variation in adaptive ability among individuals. Engorged females produced egg masses positively correlated to the engorged weights. More interestingly, the correlation coefficient (R) increased when feeding condition was changed. This may lead to more efficient selection for population adaptation under the changed conditions. As the feeding success of ixodid ticks depends on the efficiency of the cocktail of immunomodulatory saliva, the relevance of the polymorphism of salivary gland proteins and host adaptation is discussed.

Animals↗
PubMed2001

Risk factors in habitats of the tick Ixodes ricinus influencing human exposure to Ehrlichia phagocytophila bacteria.

Ixodes ricinus L. (Acari: Ixodida) were sampled during 1996-99 in southern Scotland, on vegetation using cloth drags, on humans by removal from clothing and on roe deer (Capreolus capreolus L.) by searching legs of culled deer. Developmental microclimate was recorded by automatic recorders and questing microclimate by portable instruments during tick collections. Ticks and deer were examined for infection with Ehrlichia phagocytophila bacteria (Rickettsiales) using microscopy and polymerase chain reaction. This pathogen causes tick-borne fever of sheep in Europe and human granulocytic ehrlichiosis in North America, but in Europe human clinical ehrlichiosis due to E. phagocytophila has not been recorded despite serological evidence of exposure. Among three types of habitat, coniferous woodland was most infested with questing ticks (560 ticks/km of drag; mean numbers collected on long trousers: 24.3 larvae, 13.5 nymphs and 0.8 adult ticks/km walked), deciduous woodland had slightly lower infestation (426 ticks/km drag) and upland sheep pasture had much lower infestation (220 ticks/km drag). Of the three main vegetation types, bracken was least infested (360 ticks/km drag), ericas most (430 ticks/km drag) and grassland had intermediate infestation density (413 ticks/km drag). Questing and developmental microclimates were poor predictors of exposure within these habitats, except lower infestation of pastures was attributed to greater illumination there. Collectors who walked a total of 300 km through all habitats (taking 360 h in all seasons), wearing cotton trousers hanging outside rubber boots, were bitten by only four nymphs and 11 larvae of I. ricinus (but no adult ticks). There was a negative correlation between densities of deer and ticks collected, although presence of deer remains a major indicator of exposure. The proportion of infected ticks was fairly uniform at four sites studied. Overall prevalence of E. phagocytophila in I. ricinus was 3.3% in nymphs (40/1203) but only approximately 1.5% in adults of both sexes (although males do not bite). It was estimated that nymphs of I. ricinus gave 4.4% probability of one infected bite/person/year (for occupational exposure during this research) due to presence in all seasons and habitats, their human biting rate of 0.011 nymphs/h or 0.013 nymphs/km and widespread infection with E. phagocytophila. The frequency distribution of intensity of infection in ticks was approximately normal (mean 98 morulae/nymph infected), thus there is a high risk of receiving a high dose from any one infected tick bite.

Animals↗
PubMed2003

Longitudinal surveillance of the tick Ixodes ricinus for borreliae.

Host-seeking Ixodes ricinus (L.) (Acari: Ixodidae) were monitored for borreliae (Borrelia burgdorferi s.l.) using dark-field microscopy in South Moravia (Czech Republic) each May from 1991 to 2001 (150 nymphs, 100 females and 100 males each year). This survey revealed a mean annual percentage of infected ticks of 16.8% (range, 11.7-24.2) in nymphs, 24.9% (range, 16.5-33.6) in females and 26.1% (range, 17.1-37.3) in males. Annual incidence of Lyme borreliosis in humans of the area in the same period (range, 8.7-41.7 per 100,000) correlated significantly with the frequency (number of ticks per flag per hour) of nymphs infected with >50 borreliae or all nymphal ticks, but not with the frequency of females, infected females or the infection rate (% of ticks infected) of either nymphal or female ticks. A prediction of the annual incidence of Lyme borreliosis, based on the frequency of heavily infected or all nymphal I. ricinus ticks, is feasible. The infection rate in I. ricinus correlated significantly with the North Atlantic Oscillation winter index of the last year (in nymphs) or of the year before last (in adults).

Aging↗
PubMed2000

Effects of five insecticides used in apple orchards on Hyaliodes vitripennis (Say) (Hemiptera: Miridae).

Azinphos-methyl, carbaryl, dimethoate, phosmet and phosalone were used in apple orchards to manage apple aphid, apple maggot, woolly apple aphid and leaf eating caterpillars. Among the five insecticides evaluated, dimethoate, carbaryl and azinphosmethyl were the most toxic to the nymphs and adults of Hyaliodes vitripennis (Say) from two regions. Phosalone was the least toxic. Nymphs were more resistant than the adults. While the LC50 for dimethoate was 130 ppm for nymphs, it was 3 ppm for adults from St. Jean-Baptiste-de-Rouville. There were also significant differences in the level of resistance between the two regions where the H. vitripennis were collected. At St. Alexandre the LC50 for phosalone on nymphs was 19,250 ppm whereas, at St. Jean-Baptiste-de-Rouville it was 160,000 ppm.

Agriculture↗
PubMed2001

A relapsing fever group spirochete transmitted by Ixodes scapularis ticks.

A species of Borrelia spirochetes previously unknown from North America has been found to be transmitted by Ixodes scapularis ticks. Infected ticks are positive for Borrelia spp. by DFA test but negative for Borrelia burgdorferi by polymerase chain reaction (PCR) using species-specific primers for 16S rDNA, outer surface protein A, outer surface protein C, and flagellin genes. A 1,347-bp portion of 16S rDNA was amplified from a pool of infected nymphs, sequenced, and compared with the homologous fragment from 26 other species of Borrelia. The analysis showed 4.6% pairwise difference from B. burgdorferi, with the closest relative being Borrelia miyamotoi (99.3% similarity) reported from Ixodes persulcatus in Japan. Phylogenetic analysis showed the unknown Borrelia to cluster with relapsing fever group spirochetes rather than with Lyme disease spirochetes. A 764-bp fragment of the flagellin gene was also compared with the homologous fragment from 24 other Borrelia species. The flagellin sequence of B. burgdorferi was 19.5% different from the unknown Borrelia and showed 98.6% similarity with B. miyamotoi. A pair of PCR primers specifically designed to amplify a 219-bp fragment of the flagellin gene from this spirochete was used to survey field-collected I. scapularis nymphs from five northeastern states (Connecticut, Rhode Island, New York, New Jersey, and Maryland). Positive results were obtained in 1.9-2.5% of 712 nymphs sampled from four states but in none of 162 ticks collected from Maryland. Transovarial transmission was demonstrated by PCR of larval progeny from infected females with filial infection rates ranging from 6% to 73%. Transstadial passage occurred from larvae through adults. Vertebrate infection was demonstrated by feeding infected nymphs on Peromyscus leucopus mice and recovering the organism from uninfected xenodiagnostic larvae fed 7-21 days later. Considering the frequency of contact between I. scapularis and humans, further work is needed to determine the potential public health significance of yet another zoonotic agent transmitted by this tick species.

Animals↗
PubMed1990

Influence of fenoxycarb on German cockroach (Dictyoptera: Blattellidae) populations in public housing.

In a study examining three application rates for fenoxycarb, new interpretations of population age structure in relation to sterility levels and population reductions were used to establish important concepts in the management of German cockroaches, Blattella germanica (L.), with juvenoids. No significant differences in population reductions were noted when 0.5%, 0.25%, or 0.125% fenoxycarb was used to supplement propetamphos. However, significant differences in levels of induced sterility and in the age structure (measured as nymph-to-adult ratios) of treated populations were detected. The 0.125% rate caused lower, less consistent levels of sterility than the two higher rates, which maintained approximately 80% sterility from 4.5 mo and beyond. In addition, the 0.125% rate did not significantly reduce nymph-to-adult ratios in treated populations relative to that caused by the propetamphos alone (positive control). The two higher rates significantly reduced nymph-to-adult ratios, thereby lowering biotic potential and the capacity of a population to rebound from suppression. A relationship between the level of sterility induced by juvenoids and reductions in nymph-to-adult ratios permitted formulation of a biological action threshold for regulating treatment. This action threshold appears to be more meaningful than time intervals for scheduling retreatments in the long-term management of German cockroaches with juvenoids.

Age Factors↗
PubMed1994

Intra- and interspecific trappings of two sympatric peridomestic cockroaches (Dictyoptera: Blattidae).

Intra- and interspecific trappings of American, Periplaneta americana (L.), and smokybrown, P. fuliginosa (Serville), cockroaches were examined in laboratory experiments. More P. americana were caught in live traps than P. fuliginosa. Overall, more individuals were caught with a conspecific bait than with a heterospecific bait. Significantly more adult male, female, and total P. americana were caught in traps baited with a conspecific than with unbaited traps. Heterospecific nymphs were repellent to male and female P. americana. More P. americana were caught with conspecific females and nymphs as bait than with heterospecific nymphs. For P. fuliginosa, only more males were caught with a trap with a conspecific compared with an unbaited trap. Traps with nymphal P. fuliginosa caught more conspecifics than did unbaited traps or traps with heterospecific nymphs. Nymphal P. fuliginosa were repelled by nymphal P. americana. P. americana were captured more frequently and were more selective in interspecific associations than P. fuliginosa. These results partly account for differences in sampling these species in areas of sympatry and suggest that volatile semiochemicals are produced and detected by most stages of these cockroaches.

Animals↗
PubMed1989

Lyme disease in California: interrelationship of Ixodes pacificus (Acari: Ixodidae), the western fence lizard (Sceloporus occidentalis), and Borrelia burgdorferi.

The relationship of immature western black-legged ticks, Ixodes pacificus Cooley and Kohls, to the western fence lizard, Sceloporus occidentalis Baird and Girard, and to the Lyme disease spirochete, Borrelia burgdorferi, was investigated in chaparral and woodland-grass habitats in northern California from 1984 to 1986. Immature ticks were found on lizards in spring and summer, but the prevalence and abundance of ticks on this host were considerably greater in spring. The peak of larval abundance preceded that of nymphs by several weeks, but there was considerable seasonal overlap between these parasitic stages. Larvae and nymphs attached primarily to the lateral nuchal pockets of lizards in chaparral (99.5%) and woodland-grass (91.8%). The numbers of larvae infesting lizards in spring fit the negative binomial distribution in woodland-grass but not in chaparral; insufficient data precluded similar analyses for nymphs. Tick loads did not differ significantly with respect to age or gender of the lizard. Spirochetal infection rates (range, 0-3.7%) in I. pacificus immatures were comparable in both habitats and were similar to those reported previously for adults of this tick. Overall, 1 (0.9%) of 117 larvae and 10 (1.8%) of 552 nymphs were infected with spirochetes resembling B. burgdorferi. Spirochetes were not observed in blood smears prepared from 261 wild-caught lizards, including five lizards fed upon by infected ticks at the time of collection. These and other findings suggest that S. occidentalis, although an important host of I. pacificus immatures, may be less important as a source for infecting ticks with B. burgdorferi.

Animals↗
PubMed1989

Biology of Hyalomma impeltatum (Acari: Ixodidae) under laboratory conditions.

Completion of the life cycle of Hyalomma impeltatum Schulze & Schlottke required an average of 108 d at 26 +/- 1 degree C, 92-96% RH, and 12:12 (L:D) photoperiod. Weights of unfed larvae, nymphs, and females were 0.02, 0.16, and 15.4 mg, respectively, and increased 23-, 164-, and 55-fold, respectively, as a result of feeding on guinea pigs. Larvae and adults exhibited host-seeking behavior less than 1 d after hatching and molt, respectively; nymphs exhibited host-seeking behavior 2.9 d after molt. The mean (+/- SE) feeding period as larvae was 5.9 (+/- 2.23) d, nymphs 6.7 (+/- 1.10) d, and females 8.0 (+/- 0.19) d. Larvae molted 12.4 (+/- 0.26) d and nymphs molted 28.9 (+/- 0.22) d after engorgement. A sex ratio of 1.26:1 female/male was determined from emerged adults. Females began oviposition 8.9 (+/- 0.22) d after engorgement and produced 10,680 (+/- 300) eggs per female. Egg hatch was 84% (+/- 2.68) after an incubation period of 32.8 (+/- 0.19) d. Females converted 55% of engorged weight into eggs and produced 12,475 (+/- 188) eggs/g of engorged body weight. A freshly laid egg on the first day of oviposition weighted 47.7 (+/- 0.65) micrograms. An inverse relationship between egg weight and rate of egg production was observed.

Animals↗
PubMed1990

Feeding and host preference of immature Ixodes dammini, I. scapularis, and I. pacificus (Acari: Ixodidae).

A comparative study of feeding and host preference was made among immatures of Ixodes dammini Spielman, Clifford, Piesman & Corwin, I. scapularis Say, and I. pacificus Cooley & Kohls, using white laboratory mice, Eumeces lizards, and chickens (3-4 d old) as hosts. Larval feeding of each species when placed on hosts was greater (P less than 0.05) on mice than on chickens and lizards and higher on lizards than on chickens (P less than 0.05). When larvae of the three species were given a choice between mouse and lizard and mouse and chicken, they preferred mice (except no statistical difference was found between mice and chickens for I. pacificus larvae). When given a choice between lizard and chicken, no significant difference in host preference was seen. Nymphs of I. dammini, I. scapularis, and I. pacificus displayed no statistical difference in feeding ability between mice and lizards when placed on these hosts, but more ticks fed on mice and lizards than on chickens. Nymphs of all three species also showed no preference between mice and lizards but preferred either of these hosts to chickens (however, no statistical difference was found between mice and chickens for I. dammini nymphs or between lizards and chickens for I. pacificus nymphs).

Analysis of Variance↗
PubMed1991

Venezuelan equine encephalomyelitis virus infection in and transmission by the tick Amblyomma cajennense (Arachnida: Ixodidae).

To assess a possible role of ticks as the maintenance host for epizootic strains of Venezuelan equine encephalomyelitis (VEE) virus, laboratory experiments were conducted to determine if ticks could become infected, maintain, and transmit the virus. Larval and nymphal Amblyomma cajennense (F.) and larval Dermacentor nitens Neumann ticks were exposed to epizootic VEE virus (Trinidad donkey strain) by allowing them to feed on viremic guinea pigs (strain 13). In A. cajennense, transstadial transmission was observed from larvae to nymphs and adults. Horizontal viral transmission to a mammalian host was accomplished by nymphs. Infection rates in nymphs and adults were 2% (42/2,750) and 4% (9/244), respectively, afer ingestion of virus as larvae. Virus was detected in A. cajennense adult ticks for up to 171 d after infection in the larval stage. A cajennense, exposed as nymphs, ingested virus but did not become infected (0/164 after 10 d after taking an infective bloodmeal). No virus was detected in D. nitens 7 d after exposure. These findings suggest that A. cajennense potentially could be involved in an interepizootic maintenance cycle of epizootic VEE viral strains.

Animals↗
PubMed1995

Ticks (Acari: Ixodidae) infesting wild birds (Aves) and white-footed mice in Lyme, CT.

Birds were captured and recaptured (20.8% of 5,297) with Japanese mist nets, and white-footed mice, Peromyscus leucopus (Rafinesque), were caught and recaught (69.1% of 355) with Sherman box traps during the late spring, summer, and early fall from July 1989 through October 1991 to study tick-host relationships in Lyme, CT. Ixodes scapularis Say, a vector of Lyme disease spirochetes, Borrelia burgdorferi sensu stricto Johnson, Schmid, Hye, Steigerwalt & Brenner, infested 803 birds (15.2%) in 36 species and 148 (40.3%) of the mice. This tick dominated both birds (94.4% of 4,065 ticks) and mice (82.6% of 529 ticks). Other ticks that were recovered from birds were Haemaphysalis leporispaustris (Packard) (23 birds in seven species), I. dentatus Marx (34 birds in 14 species), and Dermacentor variabilis (Say) (two birds in two species). The latter was also collected from 12.7% of the 355 mice (n = 92 ticks). Infestations of I. scapularis were high for worm-eating warblers (30.6% of 111), ovenbirds (44.4% of 286), common yellowthroats (27.1% of 188), hooded warblers (35% of 80), Carolina wrens (50.9% of 110), house wrens (21.6% of 102), wood thrushes (23.0% of 867), veeries (32.5% of 246), and American robins (36.2% of 69). Coinfestation by larvae and nymphs of I. scapularis was significantly high for Carolina wrens (35.7% of 56 infested individuals), veeries (27.2% of 80), American robins (29.4% of 25), and common grackle (19.0% of 5), possibly enhancing transmission of B. burgdorferi. Mean crowding on larvae by nymphs, measured by Lloyd's index (1967), was highest for these four species (range 1.19-5.76). Seasonal patterns of infestation for each species of bird can account for much of the differences in degree of coinfestation. High infection rates by B. burgdorferi in larvae removed from some of these birds (14.9-20.0%) were found on those birds with both high numbers of larvae and nymphs. Spirochetemia in most avian hosts may be short and only certain species with concurrent infestations of nymphs and larvae may function effectively as reservoirs.

Animals↗
PubMed1996

Infection of Ixodes ricinus (Acari:Ixodidae) by Borrelia burgdorferi in Ile de France.

Free-living nymphs and adults from Rambouillet and Fontainebleau, 2 major forests of Ile de France, were collected to determine the infection rates of Ixodes ricinus L. by Borrelia burgdorferi (Johnson, Schmid, Hyde, Steigerwalt & Brenner). Field-collected I. ricinus nymphs and adults were screened for the presence of B. burgdorferi using direct fluorescent antibody assay. The infection rates of nymph, male and female were 12.4% (314), 2.8% (35), and 2.9% (34). No difference in infection rates of nymphs among sites were detected. Spirochetes was isolated from both sites. Isolates from Rambouillet and Fontainebleau were identified as B. burgdorferi sensu stricto and B. garinii, respectively (Baranton, Postic, Saint-Girons, Boerlin, Piffaretti, Assous, and Grimont).

Animals↗
PubMed1997

Unsuccessful rubidium marking of American dog tick (Acari:Ixodidae) adults.

In an effort to determine if Dermacentor variabilis (Say) adults could be marked with rubidium (Rb), unfed nymphs were placed on laboratory mice and the mice subsequently injected with rubidium chloride (RbCl). Nymphal feeding duration was not affected by the presence of Rb in their hosts. D. variabilis adults (24-48 h old) that had fed as nymphs on RbCl-injected hosts contained approximately 13 parts per billion (ppb) of Rb, and adults that had fed as nymphs on control mice contained approximately 20 ppb of Rb. There was no difference in Rb concentration among D. variabilis adults obtained from different RbCl-injected mice. Although Rb has been shown to be a noninvasive marker for D. variabilis nymphs, D. variabilis adults were not successfully marked using the same technique.

Animals↗