The Tick Blood Meal: From a Living Animalor from a Silicone Membrane ?

An artificial feeding unit with a reinforced silicone membrane to replace host skin provides ticks with a perch over blood with a tick attachment rate of 75-100%. Some 5 mg of an acaricide like fipronil is sufficient to establish survival curves over different doses down to ppb levels in blood. This in vitro feeding assay for hard ticks is more advantageous than in vivotrials on animals

Chemostimuli implicated in selection of oviposition substrates by the stable fly <i>Stomoxys calcitrans</i>

Horse and cow dung were tested as substrates for oviposition by the stable fly Stomoxys calcitrans (L) (Diptera: Muscidae) in laboratory cages. Odour alone from either horse or cow dung was sufficient to attract flies for oviposition. This was confirmed in wind tunnel experiments, where both horse and cow dung were shown to attract gravid stable flies. However, when S. calcitrans was offered a choice between these two oviposition substrates, flies always chose horse dung over cow dung, both when allowed to contact the substrates and when relying on dung odour alone. Analyses of volatile compounds emanating from horse and cow dung by gas chromatography linked antennogram recordings from S. calcitrans antennae revealed no differences in the chemostimuli released from the two substrates. The predominant chemostimulant compounds in both substrates were carboxylic acids (butanoic acid), alcohols (oct-1-en-3-ol), aldehydes (decanal), ketones (octan-3-one), phenols (p-cresol), indoles (skatole), terpenes (β-caryophyllene) and sulphides (dimethyl trisulphide). Higher levels (20–40 p.p.m.) of carbon dioxide were recorded over horse dung compared with cow dung, a factor that may contribute to the preference exhibited by S. calcitrans for this substrate for oviposition

Ixodid ticks avoid contact with liquid water

Larvae of the cattle tick Boophilus microplus and all life stages of the European sheep tick Ixodes ricinus avoid walking on a wet membrane surface surrounding a dry patch. Of 170 reactions made at a border with liquid water by 22 B. microplus larvae, 40% consisted of immediate turns to the opposite side to bring all the legs back onto a dry patch, 41% were walks along the border, during which the ticks maintained contact with both the dry and wet zones, and 19% were returns to the dry patch after a short excursion onto the wet surround. Since contact with one front leg tip was sufficient to cause return reactions from the wet surface in most of the border contacts, the water receptor(s) that enable ticks to perceive the wet surface are probably located in terminal pore sensilla on the first-leg tarsi. Observations on the return reactions of ticks with different groups of chemosensilla masked confirmed this. Ticks have an ambiguous relationship with water: they appear to avoid direct contact with it, but they need a high humidity to compensate for any deficit in body water

Olfactory and behavioural responses of the blood-sucking bug <i>Triatoma infestans</i> to odours of vertebrate hosts

Olfactory receptors in basiconic and grooved-peg sensilla on the antenna of fifth-instar Triatoma infestans nymphs respond to host odours. Gas chromatography analyses of host odour extracts coupled to electrophysiological recordings from basiconic sensillum receptors indicate that nonanal is a constituent of sheep wool and chicken feather odour that stimulates one of the receptors in this type of sensillum. Similar analyses revealed isobutyric acid in rabbit odour to be a chemostimulant for one of the receptors in grooved-peg sensilla. The response of the aldehyde receptor was higher to heptanal, octanal and nonanal than to other aliphatic aldehydes, and the response of the acid receptor was higher to isobutyric acid than to other short-chain branched and unbranched acids. The behavioural responses of fifth-instar T. infestans nymphs to nonanal and isobutyric acid in an air-stream on a servosphere indicate that, whereas nonanal causes activation of the bugs, isobutyric acid induces an increase in upwind displacement, i.e. odour-conditioned anemotaxis. Binary mixtures of these compounds did not improve the attraction obtained with isobutyric acid alone. A comparison of the behavioural and electrophysiological responses of the bugs to different amounts of isobutyric acid in air suggests that attraction is obtained at concentrations that causes low-to-moderate increases in the firing rate of the acid-excited receptor in the grooved-peg sensilla, whereas at a dose that evokes relatively high firing rates (>40 Hz) no attraction is obtained

Components from Sri Lankan <i>Piper betle</i> L. leaf oil and their analogues showing toxicity against the housefly, <i>Musca domestica</i>

The essential oil extracted from Piper betle L. leaf using pilot plant steam distillation was tested against the adult housefly, Musca domestica, for insecticidal activity. LC50 values at the end of 24 and 48 h exposure periods were 10.3 and 8.7 mg/dm3, respectively. Ceylon citronella oil (Cymbopogon nardus) used as a standard showed LC50s of 26.5 and 24.2 mg/dm3 for the same exposure periods. Bioassay-guided fractionation of P. betle leaf oil revealed safrole and eugenol as the active principles against M. domestica, safrole showing LC50 values of 4.8 and 4.7 mg/dm3, and eugenol 7.3 and 6.2 mg/dm3 for the 24 and 48 h exposure periods, respectively, while citronellal (synthetic standard) showed equal LC50 values of 14.3 mg/dm3 for the same exposure periods. Using safrole as the starting compound, eight analogues were prepared to study structure–activity relationships. Among the eight analogues, dihydrosafrole gave almost equal mortality at LC50 4.7 mg/dm3 as that of the parent compound safrole after 24 and 48 h exposure, but isosafrole was twice as active as safrole, showing LC50 values of 2.3 and 2.2 mg/dm3 for the 24 and 48 h exposure periods. Our GC–MS studies on Sri Lankan P. betle leaf oil show that it contains safrole (52.7%), allylpyrocatechol diacetate (15.4%), eugenol (6.4%) and eugenyl acetate (5.8%) as the major components. Here we also present the GC–MS profile of fractions of Sri Lankan P. betle leaf oil

<i>In vitro</i> assays for repellents and deterrents for ticks: differing effects of products when tested with attractant or arrestment stimuli

Most in vivo and in vitro tests with repellents or deterrents against ticks have not considered which sensory channel is being targeted. We have recorded the responses of two hard tick species (Acari: Ixodidae) in vitro to determine if such products can disrupt the perception of an attractant in a repellent assay or the perception of an arrestment stimulus in a deterrent assay. Ethyl butylacetylaminopropionate (EBAAP), N,N-diethyl-methyl-benzamide (deet), permethrin and indalone were chosen to test their capacity to inhibit the attraction of Amblyomma variegatum Fabricius to its aggregation-attachment pheromone. Vapours of each test product plus those from a synthetic blend of the pheromone were delivered to the walking tick in an air stream on a locomotion compensator. Neither EBAAP, deet, permethrin nor indalone could inhibit attraction of A. variegatum even when each of the test products was delivered at 106 times the pheromone. Indalone did decrease the attraction of A. variegatum to the pheromone and induced repulsion of A. variegatum when presented on its own in the air stream. The effect of permethrin, a sodium channel blocker, was also tested in a deterrent assay measuring the arrestment of Ixodes ricinus (L.) adults on its own faeces and faecal constituents. Permethrin deterred arrestment at doses of 670 fg/cm2 to 67 ng/cm2, i.e. at levels five times lower than the dose of chemostimuli present in the arrestment stimulus. This sensitivity to permethrin suggests that it acts via the contact chemoreception channel

The sugar meal of the African malaria mosquito <i>Anopheles gambiae</i> and how deterrent compounds interfere with it: a behavioural and neurophysiological study

In this study, we show that female African malaria mosquitoes Anopheles gambiae starved for 3–5 h start to engorge on sucrose at concentrations between 50 and 75 mmol l−1. Half of the feeding response (ED50) is reached at 111 mmol l−1 and the maximum response (0.4 mg) occurs at 250 mmol l−1. Two receptor cells in a trichoid sensillum of the labellum, called the ‘sucrose’ and ‘water’ neurones, are activated by sucrose and water, respectively. The electrophysiological response of the sucrose receptor cell starts well below the level of sugar necessary to induce engorgement. The sugar receptor cell is most sensitive to small increments in sucrose concentration up to 10 mmol l−1 with a response plateau from 25 mmol l−1. Fructose has a mild phagostimulatory effect on A. gambiae, whereas no significant differences in meal sizes between water and glucose were found. However, when 146 mmol l−1 fructose plus glucose are mixed, the same engorgement as on 146 mmol l−1 sucrose is observed. Likewise, even though the sucrose receptor cell is not activated by either fructose or glucose alone, equimolar solutions of fructose plus glucose activate the neurone. We conclude that there is a behavioural and neurophysiological synergism between fructose and glucose, the two hexose sugars of sucrose. We show that some bitter-tasting products for humans have a deterrent effect on feeding in A. gambiae. When 1 mmol l−1 quinidine, quinine or denatonium benzoate is added to 146 mmol l−1 sucrose, feeding is almost totally inhibited. The effect of berberine is lower and no significant inhibition on engorgement occurs for caffeine. The deterrent effect depends on the concentration for both quinine and quinidine. Capillary feeding experiments show that contact chemosensilla on the mouthparts are sufficient for the detection of sucrose and bitter products. The feeding assay findings with deterrents correlate with the neurophysiological responses of the sucrose and water labellar neurones, which are both inhibited by the bitter compounds denatonium benzoate, quinine and berberine between 0.01 and 1 mmol l−1, but not by the same concentrations of caffeine. In conclusion, sucrose stimulates feeding and activates the labellar sucrose neurone, whereas feeding deterrents inhibit both the sucrose and water neurones. This study provides an initial understanding of the physiological mechanisms involved in sugar feeding in A. gambiae and shows how some bitter products interfere with it

A standardised <i>in vivo</i> and <i>in vitro</i> test method for evaluating tick repellents

The threat of transmission of Lyme borelliosis and tick-borne encephalitis by ixodid ticks has resulted in an increasing number of tick repellents coming onto the market. To allow proper evaluation of the efficacy of different types of compounds and their formulations, there is a need for standardised methods for testing ticks repellents. Ticks show a marked negative geotactic response following contact with a potential host, i.e., they climb up in order to locate attachment and feeding sites, whereas exposing ticks to repellents induces positive geotaxis, i.e., ticks walk downwards or drop off the treated host or substrate. We describe here complementary tests that employ these geotactic responses to evaluate repellents: one in vitro on a warm glass plate and the other on the lower human leg (shin). The compounds tested were DEET, EBAAP, icaridin, capric acid, lauric acid, geraniol, citriodiol, citronella essential oil and lavender essential oil, all non-proprietary ingredients of widely distributed tick repellent formulations. In controls on both the warm glass plate and the human leg, the majority of Ixodes ricinus nymphs walk upwards. By contrast, in both the in vitro and in vivo tests, effective doses of repellents cause ticks to either walk downwards or fall off the substrates, termed here “affected ticks”. The ED75 values for affected ticks on the human leg indicate that the test products can be divided into three groups: (1) icaridin, EBAAP, DEET and capric acid with values between 0.013 and 0.020 mg/cm2, (2) citriodiol and lauric acid with values between 0.035 and 0.058 mg/cm2, and (3) geraniol, citronella oil and lavender essential oil with values between 0.131 and 1.58 mg/cm2. The latter three products can be considered as less effective repellents. The tests on the warm glass plate resulted in very similar efficacy rankings for the products tested in vivo, and the ticks’ behavioural responses also corresponded closely to those observed on the treated human leg. The ED75 values on the glass plate ranged from half to one sixth needed on the leg. The warm glass plate test thus provides a reliable alternative to human subjects for an initial evaluation of new repellents, and is particularly appropriate for testing products with still to be determined human toxicity and dermatological effects

Learning affects host preference in tsetse flies

Les glossines sont des vecteurs cycliques très efficaces des trypanosomoses animales. Etant généralement infectées dès le premier repas de sang, en particulier dans le cas de la maladie du sommeil, toute tendance à retourner sur la première espèce hôte rencontrée se traduirait par une augmentation de la transmission intra-spécifique du parasite au détriment de sa transmission interspécifique. Pour tester cette hypothèse, un choix entre deux hôtes (vache et varan) a été proposé en étable sous moustiquaire à des glossines marquées (Glossina palpalis gambiensis, Diptera : Glossinidae) préalablement nourries sur un de ces deux hôtes. Quatre-vingts pourcent des glossines ténérales choisirent d’exploiter la vache lorsque le choix leur fut proposé. Parmi les glossines nourries une première fois sur un des deux hôtes, une proportion significativement supérieure de glossines sont retournées sur le premier hôte rencontré. Les avantages énergétiques et les implications épidémiologiques de ce comportement dans la transmission du parasite de la maladie du sommeil du réservoir animal à l’homme sont discutés. Enfin, la question de l’impact de l’apprentissage dans l’épidémiologie des zoonoses à transmission vectorielle est posée.Tsetse flies are very efficient cyclic vectors of African trypanosomosis. Since tsetse are generally infected by the first blood meal, as in the case of sleep-ing sickness for example, any propensity to feed on the same host a second time will improve transmission within this host species, whereas transmission between host species will decrease. To test this hypothesis we presented a monitor lizard and a cow in a stable to marked tsetse flies that had first fed on one of these two hosts. 80% of the teneral flies that fed did so on the cow when provided the choice. Among the flies having feeding experience, a dis-proportionately high number of flies that had fed on one host returned to this host for the second meal. We discuss the energetic advantages of such a learn-ing behavior and its importance in sleeping sickness epidemiology. The find-ings are of relevance to the role played by such learning behavior in disease transmission by other insect vectors of zoonoses.Las moscas tse-tse son vectores cíclicos muy eficientes de la tripanosomosis africana. En vista de que las tse-tse generalmente se infectan con su primera alimentación de sangre, como por ejemplo en el caso de la enfermedad del sueño, cualquier propensión a alimentarse una segunda vez en el mismo huésped mejora la transmisión al interior de las especies huéspedes mientras que la transmisión entre especies huéspedes disminuye. Para probar esta hipótesis, presentamos una lagartija monitor y una vaca en un establo, para marcar las moscas tse-tse que se alimentan por primera vez en uno de estos huéspedes. 80% de las moscas tenerales que se alimentaron, lo hicieron en la vaca cuando la escogencia les fue propuesta. Entre las moscas que experimentaron la alimentación, un número desproporcionado de moscas que se alimentaron en uno de los huéspedes volvieron a este huésped para su segunda comida. Discutimos las ventajas energéticas de este comportamiento aprendido y su importancia en la epidemiología de la enfermedad del sueño. Estos hallazgos son relevantes para el papel que juegan estos comportamientos aprendidos en la transmisión de la enfermedad por otros insectos vectores de zoonosis