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Kroeber, Thomas
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Kroeber, Thomas
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- PublicationMétadonnées seulementA standardised in vivo and in vitro test method for evaluating tick repellents(2013)
; ; 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 Nodes 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/cm(2), (2) citriodiol and lauric acid with values between 0.035 and 0.058 mg/cm(2), 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. (C) 2013 Elsevier Inc. All rights reserved. - PublicationMétadonnées seulementThe tick blood meal: From a living animal or from a silicone membrane?(2007)
; 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 vivo trials on animals. - PublicationMétadonnées seulementIn vitro assays for repellents and deterrents for ticks: differing effects of products when tested with attractant or arrestment stimuli(2003)
; 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 10(6) 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/cm(2) to 67 ng/cm(2), 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. - PublicationMétadonnées seulementThe dynamics of an avoidance behavior by ixodid ticks to liquid water(2000)
; Life stages of different tick species avoid walking on a wet surface surrounding a dry patch by systematically returning to the dry each time they contact the wet surface beyond the border with the tip of a first leg tarsus. Sequential analysis of the border behaviors shows that repetitive contact with the water increases the probability of walks astride the border. Ticks accept this unilateral contact with the water for longer intervals and eventually walk on to the wet surface after a combination of a short patch walk followed by a border walk which is longer than the foregoing ones. Staying time on a small circular patch is shorter than on a large one, arising probably from faster adaptation of peripheral receptors following a higher frequency of border contacts. However, an equal number of border reactions on patches of different sires and shapes suggests that a 'counter' in the CNS may also influence dry patch departure.