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PubMed1993

Prevalence of Theileria in the tick Hyalomma detritum detritum in the Doukkala region, Morocco.

The overall prevalence of Theileria species, mainly, if not exclusively, T.annulata, in 901 Hyalomma detritum detritum collected from cattle in the Doukkala region of Morocco over a period of 2 years was 21.5%. The quantity of infection (number of sporoblasts per infected tick) followed the negative binomial distribution with between one and 250 sporoblasts per infected tick. Infected ticks were found in eight of fourteen areas examined whilst T.annulata was present in all fourteen. There were significant differences in both the prevalence and the quantity of infection between ticks collected from different farms, and between nymphs collected in the autumn from these farms, and moulted in the laboratory, and adults collected in the following summer. The prevalence, but not the quantity, of infection was higher in female than in male ticks. No correlations were established between infection of engorged nymphs and the breed, sex and Theileria piroplasm parasitaemia of the host animal. However, calves infected a greater proportion of nymphs than adult cattle and the heavier the infestation of nymphs on an animal, up to a plateau, the higher the prevalence of infection in those nymphs. There were no differences in infection between ticks moulted at 24 degrees C and 37 degrees C, after the engorged nymphs had been stored at 18 degrees C to simulate over-wintering.

Animals↗
PubMedDate not supplied

[Xenodiagnosis in chronic Chagas' disease. I. The sensitivity of Panstrongylus megistus and Triatoma infestans].

From January 1986 to February 1994, 563 xenodiagnosis (XD) were applied in 563 chronic chagasic patients from different areas of Brazil; 292 were women and 271 were men between 6 and 89 years (average: 41.4 +/- 14.7 years). To each XD 40 nymphs on the 4th stage were used: 20 from Panstrongylus megistus (Pm) and 20 from Triatoma infestans (Ti) in fast, during at least 14 days. The exam in each nymph was made 45 days after being applied on the patient, by observation in optical microscopy of the drugs and/or the grinded from the digestive tube. The results are: a) 205 (36.4%) positive XD, including 85 (15.1%) due only nymphs of Pm, 44 (7.8%) Ti and 76 (13.5%) Pm and Ti; b) positively in 4.9% of the nymphs from Pm and in 3.0% of the Ti nymphs examined. These results' analysis showed that the Pm nymphs were more sensitive that Ti's ones to the infection by Trypanosoma cruzi, increasing considerably the xenopositivity, independently from birthplace, sex or age of the patients. These results point out that to increase the efficacy of XD in chronic Chagas' disease, the exam must have more than a species of triatomine with different sensibilities to the T. cruzi infection, and in case of using one species on XD, Pm must substitute Ti.

Adolescent↗
PubMed2001

Evaluation of three methods for detecting permethrin resistance in adult and nymphal Blattella germanica (Dictyoptera: Blattellidae).

The insecticide resistance status of the German cockroach, Blattella germanica (L.), against permethrin was evaluated with three different bioassay methods. The LT50 and KT50 in adults were measured by glass jar test, the LT50 and KT50 in nymphs were assessed by glass petri dish-test, and the LD50 in adults and nymphs was measured by topical application. The results indicate that in all three bioassays, cockroaches showed different degrees of resistance to permethrin. Resistance ratios of 6.7-, 12.8-, and 7.5-fold for KT50, LD50, and LT50, respectively, were obtained for adult cockroaches compared with those from a susceptible strain. Similarly, resistance ratio values of 17-fold for KT50, 8-fold for LD50, and 6.4-fold for LT50 were obtained for nymphs compared with those from a susceptible strain. Although both adults and nymphs exhibited a similar level of susceptibility to permethrin, adults showed a higher degree of susceptibility to topical application than to the other exposure method. The order of sensitivity (based on resistance ratio values) was topical application (LD50) > LT50 > KT50 in adults. For nymphs, the resistance ratio in the knockdown test was higher than in other tests (resistance ratio = 17-fold). Therefore, the order of test sensitivity based on comparisons of resistance ratio values was KT50 > topical application (LD50) > LT50 in nymphs. Topical application exhibited a higher sensitivity than the LT and KT methods in adults. Thus, the results suggest that topical application and knockdown testing methods are the most sensitive assays for measuring resistance of adult and nymphal German cockroaches, respectively, to permethrin.

Animals↗
PubMed2001

Prevalence and abundance of Ixodes pacificus immatures (Acari: Ixodidae) infesting western fence lizards (Sceloporus occidentalis) in northern California: temporal trends and environmental correlates.

The prevalence and abundance of immature Ixodes pacificus ticks on western fence lizards (Sceloporus occidentalis) were examined in relation to time of year, host attributes (i.e., age, gender, and presence or absence of blood parasites), and 5 environmental characteristics, including topographic exposure and ground cover substrate, over a 2-year period in northern California. Lizards were infested with subadult ticks from early March until late July or early August, with peak median numbers of larvae and nymphs recorded in late April and early May of both years. Peak larval and nymphal abundances differed between years. The overall ratio of larvae to nymphs on adult male lizards was low, ranging from 0.80 in 1999 to 2.41 in 2000. Such intensive feeding of nymphs versus larvae on these lizards, which are reservoir-incompetent for Borrelia burgdorferi spirochetes, may explain previous observations of decreasing spirochetal infection prevalence from the nymphal to adult stage in northwestern California. Adult male lizards were more likely to be infested with nymphs and harbored greater abundances of larvae and nymphs than adult females. Lizards uninfected with blood parasites had more nymphs than infected lizards. The measured environmental characteristics could explain only a small percentage of the total variation observed in larval prevalence (22%) and in larval and nymphal abundance (12 and 3%, respectively).

Animals↗
PubMed1995

Evidence implicating nymphal Ixodes pacificus (Acari: ixodidae) in the epidemiology of Lyme disease in California.

To clarify the role of nymphal versus adult western black-legged ticks (Ixodes pacificus) in the epidemiology of Lyme disease, the seasonal distribution, abundance, and spirochetal infection rates in these stages, and the seasonal occurrence of ticks biting humans and of incident cases of Lyme disease were determined in northern California. Although their seasonal activity periods overlapped for about one-third of the year, nymphs and adults predominated in different seasons, the former from late spring to summer and the latter from fall to early spring. At one site, four (4%) of 100 adults from low vegetation bordering a hardwood forest and 44 (13.6%) of 324 nymphs from leaf litter in the forest were found to contain Borrelia burgdorferi. Biting-collection records revealed that nymphs attach to people more commonly than recognized previously; I. pacificus nymphs comprised 12.5% of 967 ticks of various species and stages and 42% of all nymphs submitted for identification. Attachments by nymphs occurred primarily between April and August, which coincided with the seasonal occurrence of most incident cases of Lyme disease. Collectively, these findings strongly implicate the nymphal stage of I. pacificus as the primary vector of B. burgdorferi to humans in this region.

Animals↗
PubMed2001

The attraction of Zonocerus variegatus (Orthoptera: Pyrgomorphidae) to different types of lure.

Zonocerus variegatus is a common grasshopper in parts of west and equtorial Africa. The distribution in Nigeria extends from the lowland rainforest zone to the savannah in the north. The influence of lure on the behaviour of grasshopper inside cages (120 insect per cage) was investigated. Nymphs and adults of Zonocerus variegatus responded positively to intact leaves, crushed leaves and inflorescence of the common compositae weed Chromolaena odorata inside muslin bags, and intact plants. There were significant differences in the attraction recorded for starved nymphs, fed nymphs and starved adults. Attraction was more to intact leaves and is by olfaction. The increase in the attraction of starved nymphs is time dependent. Attraction to plant parts ceased after the plants were dried for 24 and 48 hours at room temperature and when plants were placed in transparent polythene bags. Gut motility and gut activity were higher during the day than at night. Nymphs, adults and egg pods placed separately inside muslin bags were not attractive to adults or nymphs.

Animals↗
PubMedDate not supplied

[Plant smells---important determinants in the behavior and rate of development of ixodid disease vectors].

Experiments with nymphs of Ixodes persulcatus and Dermacentor marginatus have shown that the rate and degree of engorgement, dropping off from the mouse, metamorphosis longevity and weight of emerging imagoes change under plant odour influence. The influence of acetone extract vapours of pepper, poplar buds, linden and aspen was tested. Under the influence of the vapour, acting as an attractant for the adults, engorgement weight of their nymphs and the weight of imagoes emerging from them increased; attractants change the nymph-imago metamorphosis duration as well. Repellent acting odours, as a rule, produce an opposite reaction. The phenomenon of the inversion of the infected D. marginatus reaction to the odour is proved in nymphs. Attractant for naive adult ticks (poplar buds) increased the time of feeding and weight of nymphs in comparison with the control. Just the opposite: nymphs infected with tick-borne encephalitis (TBE) virus produce an opposite reaction--weight decrease under influence of poplar buds as the repellent. Importance of the above phenomena for the ticks distribution and TBE epizootiology is discussed.

Animals↗
PubMed2001

Baseline toxicity of several pesticides to Hyaliodes vitripennis (Say) (Hemiptera: Miridae).

Hyaliodes vitripennis (Say) is a univoltine indigenous predacious mirid. It has been reported in several orchards where IPM programmes are used. It is a generalist, and feeds on phytophagous mites in addition to other arthropods. In Quebec, a foliar application of imidacloprid, deltamethrin or lambda-cyhalothrin is used at least once per season to manage arthropod pests such as leafhoppers and leaf-eating caterpillars. Meanwhile, several applications of metiram, flusilazole, myclobutanil and mancozeb are made to control apple scab [Venturia inaequalis (Cooke) Winter]. In laboratory trials, comparison of lethal concentrations of the three insecticides against H vitripennis nymphs and adults showed no significant difference. However, when lethal concentrations were compared between two growth stages for each insecticide, a significant difference was noted between adults and nymphs treated with lambda-cyhalothrin, adults being more susceptible than nymphs. No such difference could be detected for imidacloprid or deltamethrin. When LC50 values were compared with the manufacturer's label rates, deltamethrin and imidacloprid were toxic to the nymphs and adults, and lambda-cyhalothrin was slightly toxic to the nymphs and moderately toxic to the adults. Among the fungicides evaluated in the laboratory, myclobutanil showed moderate toxicity to adults at the manufacturer's label rate. The remaining fungicides had no toxic effects to adults or nymphs, even at four times the manufacturer's label rate.

Age Factors↗
PubMed1994

New findings in the development of Babesia (Theileria) equi (Laveran, 1901) in the salivary glands of the vector ticks, Hyalomma species.

The development of the piroplasm Babesia equi was studied by light microscopy in the salivary glands of three different Hyalomma species during and after the engorgement of nymphs on experimentally infected horses and after adults had fed on a vertebrate host following ecdysis. The stock of B. equi used was isolated from a horse imported from Turkmenistan (CIS) in 1991. The findings, being identical in all three Hyalomma species, differ with regard to the chronological order of the development stages in several respects from the results of previous studies based upon light or electron microscopy. A first sporogony phase of B. equi was found to develop in the salivary glands of the engorged nymphs before the ticks moulted to adults. Beginning at day 6 postinfestation (p. infest.) of the nymphs, spindle-shaped sporozoites appeared to be formed by both rapid sequential fission of a multinucleated complex and a process of radial budding from multiple fission bodies. Sporozoites isolated from the salivary glands of the engorged nymphs proved to be infectious when they were injected into a susceptible horse. After the nymphs had moulted, a second sporogony phase similar to the first one observed in the salivary glands of engorged nymphs could also be initiated in the salivary glands of adults when they were attached to a vertebrate host. Sporozoites produced in the salivary glands of adults were equally infectious for horses. Thus, two completely separate sporogony phases in B. equi seem to develop successively in the salivary glands of Hyalomma species during a transstadial transmission.

Acari↗
PubMed1999

Transmission of the blood parasite Hemolivia mariae between its lizard and tick hosts.

The haemogregarine Hemolivia mariae is found in the erythrocytes of a natural population of the lizard Tiliqua rugosa. It infects two tick species, Amblyomma limbatum and Aponomma hydrosauri, which parasitise lizards. In laboratory experiments, engorged Amb. limbatum nymphs from infected lizards transmitted the haemogregarine to uninfected lizards significantly more often than engorged Ap. hydrosauri nymphs. Dissections of larvae and nymphs of both species fed on the same infected hosts showed that Amb. limbatum ticks were significantly more likely to become infected than Ap. hydrosauri ticks. In Amb. limbatum, oval cysts containing parasite stages thought to be infective to the lizard host had developed within 15 days of engorged nymphs detaching from an infected host. The chance of Ap. hydrosauri becoming infected and the intensity of infection in Amb. limbatum increased when ticks were fed on infected hosts as larvae and as nymphs compared with those fed on an infected host only as a nymph. This suggests that infections can accumulate over the tick life stages. Since the two tick species have broadly parapatric distributions, the boundary between the tick species may have implications for the distribution of H. mariae.

Animals↗
PubMed1995

The life-cycle of the bont tick Amblyomma hebraeum in vitro.

The life-cycle of the hard tick Amblyomma hebraeum was completed in vitro by feeding all life-stages of the tick through silicone membranes on bovine blood from an abattoir. Ticks were placed in a simple feeder membranes on bovine blood from an abattoir. Ticks were placed in a simple feeder consisting of a honey jar containing the blood with a glass tube insert (o.d. 42 mm) across the end of which the membrane was stretched. This feeding unit was held in a water bath (38 degrees C). Larvae and nymphs fed on a membrane (< 90 microns thick) made of silicone reinforced with Kodak lens cleaning paper, and adults on a silicone membrane (0.5 mm thick) reinforced with Terylene netting. To control microbial growth, gentamicin (5 micrograms/ml) and nystatin (100 i.u./ml) were added to the weekly open-collected blood, which was manually defibrinated. The blood was changed twice daily for nymphs and three times for adults and larvae. Attachment of ticks was induced with combinations of host hair, tick faeces, a bovine pelage extract and a synthetic aggregation-attachment pheromone mixture. The in vitro life-cycle started with unengorged "natural" adults, which had moulted from nymphs fed on steer. The life-cycle closed with unengorged, first in vitro generation adults which had moulted from nymphs fed in vitro. Although the feeding and development of larvae and nymphs were similar to in vivo controls, females fed and developed poorly in vitro. The toxicity of the systemic acaricide Ivermectin for nymphs of A. hebraeum was confirmed using the in vitro feeding method.

Animals↗
PubMed2002

Field evidence for density-dependent facilitation amongst Ixodes ricinus ticks feeding on sheep.

Engorged Ixodes ricinus nymphs collected from sheep resident in an upland UK field site were significantly lighter than nymphs that engorged on previously tick-naïve sheep, indicating that site-resident sheep continually exposed to ticks acquired anti-tick resistance. The weights of engorged nymphs that fed on naturally tick-resistant sheep increased significantly, however, when increasingly high numbers of adult female ticks fed on the sheep during seasonal peaks of tick activity. This relationship was unaffected by variations in nymph weight amongst individual sheep, between seasons and years, and potential effects of sheep infection with Ehrlichia phagocytophila; this suggests that high adult tick infestations may directly inhibit the expression of acquired anti-tick resistance by sheep. The length, width and weight of adult ticks and the scutum length of adult females were linearly related to their weight as an engorged nymph. The mean scutum length of adult female ticks feeding on sheep in the field site was greater than that of adult females obtained from engorged nymphs collected from sheep of the same site. This suggests that larger ticks have a survival advantage and that I. ricinus ticks exhibit density-dependent intraspecific facilitation at high infestation levels with potential consequences for the transmission of tick-borne diseases.

Animals↗
PubMed1999

The life cycle of Amblyomma neumanni Ribaga, 1902 (Acari: Ixodidae) in the laboratory.

A colony of Amblyomma neumanni was started with engorged females collected from cattle in the province of Salta (24 degrees 51'S, 65 degrees 33'W), Argentina. The larvae and nymphs were fed on rabbits and the adults on calves. The non-parasitic stages were maintained in darkness at 27 +/- 1 degrees C and 83-86% RH. The life cycle (pre-feeding period not tested) had a mean duration of 205.7 days. The mean time (days) for the different phases of the cycle were as follows: feeding of females 8.8, pre-oviposition 23.8, oviposition 41.4, minimum egg incubation 76.1, feeding of larvae 8.5, pre-moult to nymphs 16.4, feeding of nymphs 7.9 and pre-moult to adults 22.8. The mean recovery rates of larvae, nymphs and females were 83.8, 85.6 and 89.3%, respectively. The nymphs moulting to females were heavier (8.1 +/- 2.34 mg) than those moulting to males (6.0 +/- 2.34 mg; p < 0.01), but their range of engorgement weight showed overlap (2.3-16.2 versus 2.2-12.8 mg, respectively). Two gynandromorphs were detected between the nymphs. A comparison of biological parameters of A. neumanni with other American Amblyomma species from mammals is presented.

Animals↗
PubMed2001

Host plant effects on activity of the mitosporic fungi Beauveria bassiana and Paecilomyces fumosoroseus against two populations of Bemisia whiteflies (Homoptera: Aleyrodidae).

Laboratory bioassays were conducted to determine the effect of host plant on mycosis in two geographically distinct populations of early 2nd-instar nymphs of Bemisia argentifolii Bellows & Perring from the entomopathogenic fungi Beauveria bassiana (Balsamo) Vuillemin and Paecilomyces fumosoroseus (Wize) Brown & Smith. Mycosis in B. argentifolii nymphs varied according to the host plant on which the nymphs were reared but not according to the population. Both populations of whiteflies reared on cotton were consistently significantly less susceptible to infection by either fungus than when reared on melon. We hypothesized that the cotton plant produced a fungal inhibitor that may confer protection on whiteflies feeding (and possibly sequestering) upon it. Germination of conidia of both fungi was strongly inhibited (below 12% germination) on the cuticle of nymphs reared on cotton but was over 95% on the cuticle of nymphs reared on melon. We further hypothesized that the terpenoid gossypol, produced by many cultivars of cotton, might have been involved in antibiosis. Gossypol mixed with Noble agar at five concentrations was tested for its effects on germination of conidia of both fungi. P. fumosoroseus was highly tolerant of gossypol, even at the relatively high concentration of 1000 ppm, while B. bassiana tolerated gossypol at concentrations up to 500 ppm and strong inhibition only occurred in presence of gossypol at 1000 ppm. Our in vivo findings on cotton and on the insect's cuticle pointed at a potential host plant-mediated antibiosis. The in vitro tolerance of P. fumosoroseus and partial tolerance of B. bassiana to gossypol disagreed with our in vivo data. Gossypol concentrations higher than 1000 ppm might have increased the sensitivity of the fungi in our in vitro tests. Sequestered gossypol (and/or other cotton plant allelochemicals) by B. argentifolii nymphs would explain, at least partially, the insect's defense against the pathogens.

Animals↗
PubMed2002

Evidence of an assembly pheromone in the black-legged deer tick, Ixodes scapularis.

The responses of Irodes scapularis (Acari: Ixodidae) nymphs and adults to extracts of cast larval skins were tested in a Petri dish bioassay. Assembly was elicited in nymphs and adults in the presence of skins, exudate from ticks, and filter paper exposed to ticks compared to untreated controls. Assembly was noted by 1 hr after exposure with little change between 1 and 24 hr. The assembly response increased in the presence of an increased number of skins. Similar assembly was elicited in nymphs and adults in the presence of cast larval skins and a saline (0.95% NaCl) skin extract. Methanol and hexane extracts were not attractive. When chemical standards were tested against nymphs, they responded to guanine, uric acid, hypoxanthine, xanthine, inosine, and hematin. Adults were tested against guanine, inosine, and xanthine, and all elicited significant assembly. Responses of nymphs increased significantly with increase in dose of uric acid and guanine. Responses of nymphs to a mixture of guanine, xanthine, and adenine (25:1:1 ratio) were similar to responses to cast skins. This study provides the first evidence of an assembly pheromone in I. scapularis.

Animals↗
PubMed2003

Life cycle and host specificity of Amblyomma triste (Acari: Ixodidae) under laboratory conditions.

We report biological data of two generations of Amblyomma triste in laboratory and compared the suitability of different host species. Infestations by larval and nymphal stages were performed on guinea pigs (Cavia porcellus), chickens (Gallus gallus), rats (Rattus norvegicus), rabbits (Oryctolagus cuniculus), wild mice (Calomys callosus), dogs (Canis familiaris) and capybaras (Hydrochaeris hydrochaeris). Infestations by adult ticks were performed on dogs, capybaras and rabbits. Tick developmental periods were observed in an incubator at 27 degrees C and RH 90%. Guinea pigs were the most suitable hosts for larvae and nymphs, followed by chickens. The remaining host species were less suitable for immature ticks as fewer engorged ticks were recovered from them. Mean larval feeding periods varied from 3.8 to 4.7 d between different host species. Mean larval premolt periods ranged from 8.9 to 10.4 d. Nymphal mean feeding periods varied from 4.2 to 6.2 d for ticks fed on different host species. Premolt period of male nymphs (mean: 15.4 d) was significantly longer than that of female nymphs (14.7 d). Female nymphs were significantly heavier than male nymphs. The overall sex ratio of the adult ticks emerged from nymphs was 0.9:1 (M:F). Capybaras were the most suitable host for the tick adult stage as significantly more engorged females were recovered from them and these females were significantly heavier than those recovered from dogs or rabbits. The life cycle of A. triste in laboratory could be completed in an average period of 155 d. The potential role of guinea pigs, birds and capybaras, as hosts for A. triste in nature, is discussed.

Animals↗
PubMed2005

Phenology and demography of Homalodisca coagulata (Hemiptera: Cicadellidae) in southern California citrus and implications for management.

Populations of Homalodisca coagulata (Say) were sampled from citrus orchards in southern California, USA to characterize and quantify seasonal occurrences of nymphs and adults with the goal of identifying management opportunities through well-timed treatments and/or natural enemy releases. Higher densities of H. coagulata in 2001 contributed to a complete seasonal profile that began in early spring with the emergence of first instar nymphs and their progression through five nymphal instars lasting until mid-August. Adult emergence began in mid-June with peak adult densities attained from mid to late August followed by a gradual decline through autumn. A persistent and significant male bias was observed in the adult sex ratio from the time of first emergence through mid-October in oranges; the same trend was present in lemons, but with more variability. Adult densities gradually declined through the winter months into the following spring before rapidly increasing again in June as the 2002 spring generation of nymphs began emerging as adults. The seasonal timing of nymphs and adults in 2002 was nearly identical to that observed the previous year. Phenology data from both years were incorporated into a stochastic, temperature-dependent model that predicts the occurrences of H. coagulata stages through time. Applications of imidacloprid early in the spring generation of nymphs proved very effective at reducing nymphs and sustaining lower densities of adults through summer.

Animals↗
PubMed1989

Changes in the concentration of globulins in naive guinea pigs during feeding by the immature stages of Rhipicephalus evertsi evertsi (Acari: Ixodidae).

The weight of Rhipicephalus evertsi evertsi Neumann nymphs, which as larvae and nymphs completed the entire blood meal on the same individual guinea pig, was significantly lower than the weight of those that as larvae and nymphs fed on two separate naive hosts. Nymphs of the latter category spent 1 wk (from unfed larvae to unfed nymphs) on one animal before their transfer to the second host to complete the blood meal. The albumin concentration of the host blood decreased and was related to the time that the immature ticks spent on the hosts. The albumin/globulin ratio also decreased. The alpha 1 globulin fraction increased soon after the guinea pigs were infested with ticks. No further changes in the levels of the alpha 1 globulin fraction were observed with time. The concentration of serum beta globulins increased only in guinea pigs infested with immature ticks for the entire larval and nymphal feeding period. A second infestation of those guinea pigs with larvae of R. e. evertsi resulted in further increases in the levels of serum beta globulins. The relationships among serum beta globulin levels, the weight of engorged nymphs, and host immunity are discussed.

Animals↗