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PubMed2006

Silverleaf whitefly induces salicylic acid defenses and suppresses effectual jasmonic acid defenses.

The basal defenses important in curtailing the development of the phloem-feeding silverleaf whitefly (Bemisia tabaci type B; SLWF) on Arabidopsis (Arabidopsis thaliana) were investigated. Sentinel defense gene RNAs were monitored in SLWF-infested and control plants. Salicylic acid (SA)-responsive gene transcripts accumulated locally (PR1, BGL2, PR5, SID2, EDS5, PAD4) and systemically (PR1, BGL2, PR5) during SLWF nymph feeding. In contrast, jasmonic acid (JA)- and ethylene-dependent RNAs (PDF1.2, VSP1, HEL, THI2.1, FAD3, ERS1, ERF1) were repressed or not modulated in SLWF-infested leaves. To test for a role of SA and JA pathways in basal defense, SLWF development on mutant and transgenic lines that constitutively activate or impair defense pathways was determined. By monitoring the percentage of SLWF nymphs in each instar, we show that mutants that activate SA defenses (cim10) or impair JA defenses (coi1) accelerated SLWF nymphal development. Reciprocally, mutants that activate JA defenses (cev1) or impair SA defenses (npr1, NahG) slowed SLWF nymphal development. Furthermore, when npr1 plants, which do not activate downstream SA defenses, were treated with methyl jasmonate, a dramatic delay in nymph development was observed. Collectively, these results showed that SLWF-repressed, JA-regulated defenses were associated with basal defense to the SLWF.

Animals↗
PubMed2002

Inbreeding alters resistance to insect herbivory and host plant quality in Mimulus guttatus (Scrophulariaceae).

Previous studies have demonstrated genetic variation for resistance to insect herbivores and host plant quality. The effect of plant mating system, an important determinant of the distribution of genetic variation, on host plant characteristics has received almost no attention. This study used a controlled greenhouse experiment to examine the effect of self- and cross-pollination in Mimulus guttatus (Scrophulariaceae) on resistance to and host plant quality for the xylem-feeding spittlebug Philaenus spumarius (Homoptera: Cercopidae). Spittlebugs were found to have a negative effect on two important fitness components in M. guttatus, flower production and above ground biomass. One of two M. guttatus populations examined showed a significant interaction between the pollination and herbivore treatments. In this case, the detrimental effects of herbivores on biomass and flower production were much more pronounced in inbred (self) plants. The presence of spittlebug nymphs increased inbreeding depression by as much as three times. Pollination treatments also had significant effects on important components of herbivore fitness, but these effects were in opposite directions in our two host plant populations. Spittlebug nymphs maturing on self plants emerged as significantly larger adults in one of our host plant populations, indicating that inbreeding increased host plant quality. In our second host plant population, spittlebug nymphs took significantly longer to develop to adulthood on self plants, indicating that inbreeding decreased host plant quality. Taken together these results suggest that the degree of inbreeding in host plant populations can have important and perhaps complex effects on the dynamics of plant-herbivore interactions and on mating-system evolution in the host.

Animals↗
PubMed2005

Capillary feeding of specific dsRNA induces silencing of the isac gene in nymphal Ixodes scapularis ticks.

Ixodes scapularis transmits several pathogens including Borrelia burgdorferi. Bioactive compounds in tick saliva support tick feeding and influence pathogen transmission to the mammalian host. These studies utilized oral delivery of dsRNA to silence an anticomplement gene (isac) in I. scapularis nymphs. Silencing of isac significantly reduced fed-tick weight compared to delivery of control lacZ dsRNA, and immunoblots specific for FlaB protein indicated a reduction in spirochete load in isac-silenced infected nymphs. SDS-PAGE demonstrated that isac gene silencing affected expression of a number of salivary and non-salivary gland proteins in ticks. Finally, multiple isac cDNA homologues were cloned, and these may represent a new gene family coexpressed during tick feeding. This work presents a novel oral delivery approach for specific gene silencing in I. scapularis nymphs and characterizes the effect of isac on blood-feeding in an attempt to block transmission of B. burgdorferi.

Animals↗
PubMed1994

Immunological response in rabbits infested with Rhipicephalus sanguineus.

In order to clarify the importance of humoral antibody in host resistance to ticks, in the present work we studied the immunological response of rabbits infested with larvae, nymphs or adults of Rhipicephalus sanguineus, using extracts of eggs (EE), larvae (LE), nymphs (NE), male salivary glands (MSGE), male midguts (MME), female salivary glands (FSGE) and female midguts (FME). When serum from rabbits infested with larvae or nymphs was tested using enzyme-linked immunosorbent assay, no reactions were observed with any of the extracts including the homologous LE or NE. In sera from rabbits infested with adult ticks, the reactions were observed in both homologous (MSGE, MME, FSGE and FME) and heterologous (EE, LE and NE) system. However, differences were seen regarding the type of antigen used. When the experiment was carried out using extracts from adults higher responses were found. With FSGE and FME antigens, antibody levels were systematically higher than those observed when MSGE and MME were used.

Animals↗
PubMed1997

Efficacy of acaricidal tags and pour-on as prophylaxis against ticks and louping-ill in red grouse.

This paper examines the efficacy of 10% lambdacyhalothrin-impregnated plastic tags and a deltamethrin pour-on preparation in protecting red grouse chicks from parasitism by ticks and subsequent infection with the louping-ill virus. In 1995, ten red grouse hens (Lagopus lagopus scoticus) in a free-living population in north-east Scotland were fitted with lambdacyhalothrin-impregnated plastic tags, glued to radio transmitters. Chicks of more than 10 days of age from a further ten untreated radio-collared hens were caught and fitted with individual tags to the ptagium. Both treatments significantly reduced tick burdens in the short term. The number of larvae and nymphs on chicks up to 45 days was less under both treatments than on control chicks and tagged chicks had fewer nymphs than chicks from treated hens. Nevertheless, treatments did not reduce viral infection rates nor increase survival to 10 weeks, possibly explained by incomplete treatment of tagged broods and/or direct or indirect mortality due to tags. In 1996 chicks in ten broods from hens with radio transmitters were individually treated at 14 days of age at a rate of 1 mg/kg of chick with a deltamethrin pour-on preparation. This preparation significantly reduced the number of larvae and nymphs on grouse chicks 7-10 days after application below the number on untreated controls. At 20 days from application, however, only larval numbers were lower on treated chicks. Nevertheless louping-ill virus infection prevalences were significantly reduced at 35 days of age and survival of chicks to 10 weeks increased.

Animals↗
PubMed2006

Quantification of blood intake of the head louse: Pediculus humanus capitis.

Although head lice, Pediculus humanus capitis, are globally prevalent blood-sucking ectoparasites, the amount of blood imbibed by head lice has not been determined. This study investigated this parameter, as regular loss of a small quantity of blood may lead to an iron deficiency and anaemia. Adult female lice (66), adult males (46), and nymphs (152) were weighed before and after feeding in groups of 17-109 lice. The average amounts of blood imbibed at a single feed were: adult female louse (0.0001579 ml), adult male (0.0000657 ml) and nymph (0.0000387 ml). Assuming three feeds per day by an average infection of 30 lice (10 females, 10 males, and 10 nymphs), the average child with active pediculosis would loose 0.008 ml of blood per day. This amount of blood loss is of no clinical significance even in iron-deficient children. The most heavily infected child observed with 2657 lice could be expected to loose 0.7 ml/day or 20.8 ml/month, which may be of clinical importance in a child on an adequate diet, and would be significant in an iron-deficient child. However, if head lice feed more often than three times a day, a heavy infestation would have a greater potential to lead to iron deficiency. The frequency of feeding of head lice on the head of the human host needs to be determined.

Anemia, Iron-Deficiency↗
PubMed1996

Potential impact of wildlife on the tropical bont tick eradication program in the Caribbean.

Wildlife are hosts for A. variegatum throughout its range in Africa, and have been demonstrated to serve as hosts for larvae and nymphs on several islands in the Caribbean. Studies conducted in the Caribbean have indicated that most larvae and nymphs and all adults of the tick feed on livestock; therefore, eradication can be approached through the treatment of livestock. However, since small numbers of animals such as the mongoose are infested with larvae and nymphs, these animals may represent a short-term alternative host system. Such infestations potentially could result in a presence of small numbers of ticks for up to 46 months after the onset of a treatment program and could serve as a source to reinfest livestock during the eradication process. Wildlife surveys have been conducted in St. Croix, Puerto Rico, Guadeloupe, and Antigua; but the host status of species present on other islands such as the white-tailed deer on St. Kitts has not been evaluated. As part of the eradication program, the species of wildlife present on each island and the association of these species with infested pastures should be determined. Surveys of wildlife can be used during the eradication to determine if wildlife are serving as an alternative host system. Cattle egrets may serve to disseminate the tick among islands in the region, and to areas outside the region. Cattle egrets have been shown to serve as hosts for the tick, and to move throughout the eastern Caribbean and to North America. The potential for interisland dissemination of ticks by cattle egrets, as well as by other means, substantiates the need for a region-wide eradication program.

Animals↗
PubMed1998

Attempts to feed Amblyomma variegatum ticks on artificial membranes.

Feeding jars were used to feed nymphs of Amblyomma variegatum on blood of goats or cattle. Sterile blood was collected daily or weekly (kept at 4 degrees C or frozen until use), with addition either of heparin alone or of heparin and antibiotics/fungicide or of heparin, adenosine triphosphate and glutathione. Membranes were made of a thin (0.12-0.32 mm) film of silicone mastic. Blood in the jars was replaced twice a day, and reached a temperature of 39 degrees C in a waterbath before it became available to the ticks. Attachment of nymphs was stimulated by dropping on the membrane fresh goat hair and squamae collected close to prefed males, skin washing and natural pheromone extracts. Using these devices, attachment of nymphs is rapid and intense (68%). Their body mass when engorged and the molting success, were lower than that of naturally fed ticks. Furthermore, the proportion of engorging ticks was usually much less and the length of the blood meal was much longer than of naturally fed ticks. The best results were obtained with fresh goat blood or cattle blood with antibiotics. Further developments are needed before this method can be used routinely.

Animals↗
PubMed1993

Accelerated transmission of Lyme disease spirochetes by partially fed vector ticks.

To determine how rapidly Lyme disease spirochetes (Borrelia burgdorferi) can be transmitted by partially fed vector ticks (Ixodes dammini), attached nymphs were removed from their hosts at various intervals post-attachment and subsequently permitted to re-feed to repletion on noninfected mice. We confirm previous reports that ticks deposit Lyme disease spirochetes in the skin of their hosts mainly after 2 days of attachment. Those that have been removed from a host within this interval can reattach and commence feeding. Spirochete-infected nymphs that have previously been attached to a host for 1 day become infectious to other hosts within another day. Noninfected nymphs acquire infection from spirochete-infected hosts within a day of attachment and become infectious to other hosts 3 to 5 days later. Virtually all ticks transmitted infection when reattaching after first feeding for 2 days. We conclude that partially fed nymphal ticks transmit spirochetal infection more rapidly than do ticks that have never been attached to a host and that infected ticks become infectious before they molt.

Animals↗
PubMed2002

Transmission studies of Babesia microti in Ixodes ricinus ticks and gerbils.

In order to investigate the possible role of Ixodes ricinus as a vector of zoonotic Babesia microti infection in Europe, a European rodent isolate (HK) and a zoonotic American isolate (GI) were studied in transmission experiments. PCR detected B. microti in the blood and spleens of infected gerbils (Meriones unguiculatus) and also in laboratory-induced infections of I. ricinus ticks. B. microti DNA was detected by PCR in all pooled samples of nymphs and the majority of adults that had fed as larvae and nymphs, respectively, on gerbils with acute infection of the European isolate, confirming that I. ricinus could serve as a vector in Europe. The American isolate, GI, proved to be equally infective for larval and nymphal I. ricinus as the HK strain, despite a very different appearance in gerbil erythrocytes. Nymphs infected with the HK and GI strains readily infected gerbils. In contrast to the finding in acute infections, ticks that fed on gerbils with chronic infections of HK and GI did not become infected. It was also found that the HK strain was not transmitted transovarially. The finding that a B. microti strain (GI) from a distant geographical region (United States) can infect and be transmitted by I. ricinus suggests that other European B. microti strains, in addition to the HK strain used here, are probably infective for I. ricinus, supporting the view that infection of humans with European B. microti may be a regular occurrence.

Animals↗
PubMed2004

Escape behavior and escape circuit activation in juvenile crayfish during prey-predator interactions.

The neural systems that control escape behavior have been studied intensively in several animals, including mollusks, fish and crayfish. Surprisingly little is known, however, about the activation and the utilization of escape circuits during prey-predator interactions. To complement the physiological and anatomical studies with a necessary behavioral equivalent, we investigated encounters between juvenile crayfish and large dragonfly nymphs in freely behaving animals using a combination of high-speed video-recordings and measurements of electric field potentials. During attacks, dragonfly nymphs rapidly extended their labium, equipped with short, sharp palps, to capture small crayfish. Crayfish responded to the tactile stimulus by activating neural escape circuits to generate tail-flips directed away from the predator. Tail-flips were the sole defense mechanism in response to an attack and every single strike was answered by tail-flip escape behavior. Crayfish used all three known types of escape tail-flips during the interactions with the dragonfly nymphs. Tail-flips generated by activity in the giant neurons were predominantly observed to trigger the initial escape responses to an attack, but non-giant mediated tail-flips were often generated to attempt escape after capture. Attacks to the front of the crayfish triggered tail-flips mediated either by the medial giant neuron or by non-giant circuitry, whereas attacks to the rear always elicited tail-flips mediated by the lateral giant neuron. Overall, tail flipping was found to be a successful behavior in preventing predation, and only a small percentage of crayfish were killed and consumed.

Action Potentials↗
PubMed2002

Development of Spinitectus inermis (Nematoda: Cystidicolidae), a parasite of eel, Anguilla anguilla, in Europe.

The development of the nematode Spinitectus inermis (Zeder, 1800), a parasite of the stomach of eels, Anguilla anguilla (L.) in Europe, was experimentally studied. Mayfly nymphs Caenis macrura, Ecdyonurus dispar, Heptagenia sulphurea, Potamanthus luteus and Seratella ignita from Portugal and the Czech Republic were found to serve as experimental intermediate hosts. After ingestion of the nematode eggs by the mayfly nymphs, the toothed first-stage larvae were released and penetrated into the body cavity of the intermediate host. There they moulted twice (on day 4 and 6 post infection [p.i.] at water temperatures of 20-25 degrees C), attaining the third infective stage. The definitive host, A. anguilla, undoubtedly acquires infection by feeding on mayfly nymphs harbouring infective-stage larvae. In an experimentally infected eel, the fourth-stage larva undergoing the third moult was observed 28 days p.i. at water temperature of 20 degrees C. The larval stages, including moulting forms, are described and illustrated. The prepatent period of S. inermis is estimated to be about two months.

Anguilla↗
PubMedDate not supplied

[Parasitemia in chronic chagasic patients evaluated using the index of infected Triatoma in xenodiagnosis].

As part of a pre-treatment study of chronic Chagas infections, the parasitemia of 206 patients (85 men and 121 women, aged 7 to 80 y) from Virgem da Lapa, Minas Gerais State Brazil, was evaluated by three xenodiagnoses per patient during a one year period. Each time, 40 3rd or 4th instar nymphs of Triatoma infestans were applied. The parasitemia was arbitrarily classified as: not detected (when all nymphs were negative), low (when the number of infected nymphs was less than 2%), medium (when it was higher than 2% and up to 7%) and high (when higher than 7%). The parasitemia was not detected in 105 (51%) of the patients, and was considered low in 55 (26.7%), medium in 27 (13.1%) and high in 19 (9.2%). There was no significant differences in levels of parasitemia in relation to sex or age, but the high parasitemia was more frequent among the patients with chagasic cardiomyopathy. Persistent parasitemia (all three xenodiagnoses positive) was observed in 100% of the patients with high parasitemia, in 22.2% with medium and in none with low parasitemia.

Adolescent↗
PubMedDate not supplied

Resistance to starvation of Triatoma rubrofasciata (De Geer, 1773) under laboratory conditions (Hemiptera: Reduviidae: Triatominae).

The present work aims at learning the period of resistance to starvation (molting/death) of Triatoma rubrofasciata in different stages of development and the respective loss of weight until death. Eggs of specimens from the greater area of the city of São Luis in the State of Maranhão, Brazil, yielded approximately 300 nymphs. These nymphs were placed in labelled Borrel glasses, in which they were weekly fed on rats (Rattus norvegicus), until reaching the stage to be observed. The experiments were conducted in a climatic chamber regulated at 29 +/- 1 degrees C, 70% relative humidity and 12 hr photoperiod. The resistance to starvation increased according to the stage of development, except for adult bugs, whose results were similar to the 3rd stage nymphs. In all these development stages there was an abrupt loss of weight in the first week, followed by a gradual loss until death. Comparing this work with those of other authors, it was observed that T. rubrofasciata is among the less resistant triatomine species.

Animals↗
PubMedDate not supplied

Changes in nuclear phenotypes following cold shock in Panstrongylus megistus (Burmeister).

The nuclear phenotypes of Malpighian tubule epithelial cells of 5th instar male nymphs of the blood-sucking insect Panstrongylus megistus were studied immediately after a short (1 h) cold shock at 0 degrees C, and 10 and 30 days later. The objective was to compare the responses to a cold shock with those known to occur after hyperthermia in order to provide insight into the cellular effect of cold in this species. Nuclei which usually exhibited a conspicuous Y chromosome chromocenter were the most frequent phenotype in control and treated specimens. Phenotypes in which the heterochromatin was unravelled, or in which there was nuclear fusion or cell death were more abundant in the shocked specimens. Most of the changes detected have also been found in heat-shocked nymphs, except for nuclear fusion which generates giant nuclei and which appeared to be less effective or necessary than that elicited after heat shock. Since other studies showed that a short cold shock does not affect the survival of more than 14% of 5th instar nymphs of P. megistus with domestic habit and can induce tolerance to a prolonged cold shock, heat shock proteins proteins are probably the best candidates for effective protection of the cells and the insects from drastic damage caused by low temperature shocks.

Animals↗
PubMed2001

Biology of Triatoma flavida Neiva, 1911 (Hemiptera: Reduviidae) under laboratory conditions.

The complete life cycle of Triatoma flavida, weekly fed on hens, was studied at 28+/-2 degrees C and 80+/-10% RH. Aspects related to hatching, life span, mortality and feeding behavior for each stage of its life cycle were evaluated. The hatching rate observed for 100 eggs was 93% with an average incubation period of 27.2 days. Sixty-two nymphs completed the cycle and the mean egg to adult development time was 230.4 days. Mean duration of 1st, 2nd, 3rd, 4th and 5th instar nymphs was 22.1, 25.3, 36.7, 49.7 and 69.4 days, respectively. The number of blood meals on each nymphal stage varied from 1 to 7. The mortality rate was 6.5% for NI, 23% for NIII and 7.5% for NV nymphs. Mean number of laid eggs per female was 283.1. Adult survival rates were 344.8 +/- 256.4 days for males and 285.3 +/- 201.8 days for females.

Animals↗
PubMed2004

[Life cycle of Rhodnius brethesi Matta, 1919 (Hemiptera, Reduviidae, Triatominae), a potential vector of Chagas disease in the Amazon region].

R. brethesi is a sylvatic species from the Amazon region; it has been incriminated as responsible for the transmission of Chagas disease in collectors of piacaba in this region. The aim of present study was to investigate the efficiency of these insects as potential vectors of Trypanosoma cruzi. Aspects related with feeding and defecation patterns, life time, and mortality had been observed in each instar of R. brethesi. We use 5th instar nymphs to get adults virgins, after the moulting 3 groups with 6 females and 2 males each were created to obtain eggs. After hatching, 1st instar nymphs had been weighed and kept in bottles until the next moult. Insects were fed once a week in mice. Results showed that the average period of incubation was 17 days, the number of blood meal was increasing from the 1st to the 5th instar nymph with 7 (average) to become adult, a significative numbers of the defecations occurring immediately after the bloodmeals. The total percentual of mortality was 16%. This results suggests that this species presents a good exploitation of blood meals and a brief nymphal development in laboratory conditions reflecting its behavior in sylvatic environments.

Animals↗
PubMed2006

Biology of three species of the Meccus phyllosomus complex (Hemiptera: Reduviidae: Triatominae) fed on blood of hens and rabbits.

Aspects related to hatching, life time, number of blood meals to molt, mortality, feeding time and postfeed defecation delay for each instar of Meccus phyllosomus, M. mazzottii, and M. bassolsae, life-cycle were evaluated and compared in two cohorts of each of those three species, fed on hens or rabbits. No significant (p > 0.05) differences were recorded among cohorts fed on hens respect to cohorts fed on rabbits in M. phyllosomus and M. mazzottii and the average time of hatching was 21.5 days for cohorts fed on hens and 22.5 for cohorts fed on rabbits. Average egg-to-adult development times were no significant (p > 0.05) different between both cohorts of M. phyllosomus and M. mazzotti, independent of the blood meal source. The average span in days for each instar fed on hens was not significantly different to the average span for each instar fed on rabbits, when comparisons were made by species. The number of blood meals at each nymphal instar varied from 1 to 6 in both cohorts of each species. The mortality rates were higher on older nymphs, in both cohorts of M. phyllosomus and M. bassolsae, whereas they were higher on first instar nymphs on M. mazzottii. Mean feeding time was no significant (p > 0.05) different in triatomines fed on hens or fed on rabbits, when each species were compared separately. A similar number of nymphs of each cohort, completed the cycle. Defecation delay was no significant (p > 0.05) different when cohorts fed on hens and fed on rabbits were compared by species. Most of the studied parameters showed no significant (p > 0.05) differences among those cohorts fed on hens and for fed on rabbits, which could mean a high degree of association of those species with birds as much as mammals, under wild conditions, increasing their capacity to colonize human dwellings.

Animals↗