Response of Hyalomma marginatum to 20% DEET.
Description
The response of Hyalomma marginatum ticks to 20% DEET was tested in bioassays with three human volunteers.
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All testing was carried out at temperatures from 20-25°C, relative humidity above 35% and under indirect ambient light. The test apparatus was set up with two clean rectangular trays at shoulder width apart. These each contained a white wooden hand rest. A third tray was placed nearby, half-filled with water and containing a fluon treated bowl to contain ticks to be used in testing. The participant’s arm was marked with three lines; boundary line at the wrist; release line (3cm from the boundary line towards the fingers on untreated skin); and a crossing line (3 cm from the boundary line towards the elbow on treated skin). Both forearms were washed with unscented soap, rinsed and patted dry with paper towels. Using a micropipette, the calculated dose was applied to one arm, by applying small drops of product evenly between the wrist (boundary line) and the elbow and rubbed in using a single gloved finger. The hand of the untreated arm was placed onto the hand rest, with the elbow above the wrist and the forearm placed at an angle of 30°. A single tick was carefully placed on the release line and oriented towards the arm. The tick was then observed for a maximum of 3 minutes. A tick that moved steadily from the release line across the boundary line and upward along the subject’s untreated forearm was classed as actively questing, and was then used in repellency testing. Ticks that failed to do this, were removed from the arm and not used in subsequent repellency assessments. Ticks found to be questing were immediately placed on the release line on the hand of the treated arm and oriented towards the arm. The tick was observed for a maximum of 3 minutes, starting the timer after the tick’s first movement upwards. A “crossing” was recorded when a tick crossed the boundary line at least 3 cm into the treated area within 3 minutes, and remained in the treated area for at least one minute. Ticks that did not cross; crossed but turned back before 1 minute in the treated area; or fell off were classed as “repelled”. Five questing ticks were tested for each timepoint. The repellency assessment with 5 questing ticks was repeated at 30 minute intervals up to 8 hours or until treatment failure (defined as 1 tick “crossing” followed within 1 hour by a second confirmatory “crossing”). Ticks were supplied by Infravec2. They were reared at 25±3°C, at high relative humidity (>80%), with a photoperiod of approximately 16:8 hours (light:dark). While stored at test site, the same temperature, humidity and light conditions were adhered to.