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Guerin, Patrick
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Guerin, Patrick
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- PublicationMétadonnées seulementWater vapour and heat combine to elicit biting and biting persistence in tsetse(2013)
; Background: Tsetse flies are obligatory blood feeders, accessing capillaries by piercing the skin of their hosts with the haustellum to suck blood. However, this behaviour presents a considerable risk as landing flies are exposed to predators as well as the host's own defense reactions such as tail flicking. Achieving a successful blood meal within the shortest time span is therefore at a premium in tsetse, so feeding until replete normally lasts less than a minute. Biting in blood sucking insects is a multi-sensory response involving a range of physical and chemical stimuli. Here we investigated the role of heat and humidity emitted from host skin on the biting responses of Glossina pallidipes, which to our knowledge has not been fully studied in tsetse before. Methods: The onset and duration of the biting response of G. pallidipes was recorded by filming movements of its haustellum in response to rapid increases in temperature and/or relative humidity ( RH) following exposure of the fly to two airflows. The electrophysiological responses of hygroreceptor cells in wall-pore sensilla on the palps of G. pallidipes to drops in RH were recorded using tungsten electrodes and the ultra-structure of these sensory cells was studied by scanning and transmission electron microscopy. Results: Both latency and proportion of tsetse biting are closely correlated to RH when accompanied by an increase of 13.1 degrees C above ambient temperature but not for an increase of just 0.2 degrees C. Biting persistence, as measured by the number of bites and the time spent biting, also increases with increasing RH accompanied by a 13.1 degrees C increase in air temperature. Neurones in wall-pore sensilla on the palps respond to shifts in RH. Conclusions: Our results show that temperature acts synergistically with humidity to increase the rapidity and frequency of the biting response in tsetse above the levels induced by increasing temperature or humidity separately. Palp sensilla housing hygroreceptor cells, described here for the first time in tsetse, are involved in the perception of differences in RH. - PublicationMétadonnées seulementAn in Vitro Assay for Testing Mosquito Repellents Employing a Warm Body and Carbon Dioxide as a Behavioral Activator(2010)
; ; ; We describe here an in vitro behavioral assay for testing mosquito repellents applied in a dose-based manner to a warm body (34 C) in test cages. The system was used to assess the sensitivity of 4-6-day-old Anopheles gambiae to the insect repellent diethyl methyl benzamide (deet). These tests were made in the absence and presence of additional carbon dioxide (CO(2)) applied as a pulse to activate mosquitoes in the cages. In the absence of the CO(2) pulse the mosquitoes hardly responded to the warm body. Increasing the CO(2) level in the cage by 1,000 parts per million caused a 25-fold increase in the number of landings by mosquitoes on the warm body in 2-min tests. This mosquito activation allowed the measurement of a significant reduction in the number of landings to bite on the warm body with increasing doses of deet (0.4 to 3.8 mu g/cm(2)). An asymptotic nonlinear model fitted to the repellency data in the presence of CO(2) allowed estimation of the effective dose of deet that reduced landings to bite by 50% (ED(50)) at 0.95 mu g/cm(2) (5 nmol/cm(2)) and the corresponding ED(95) at 4.12 mu g/cm(2) (21.5 nmol/cm(2)). This in vitro bioassay has the advantage of permitting a fast throughput of test products under standardized conditions and is suitable for screenings designed for the purpose of discovering lead products with as yet unknown human toxicological and dermatological profiles.