HYALOMMA-TRUNCATUM (ACARI, IXODIDAE) - INVESTIGATIONS INTO THE SCOTOTAXIS OF UNFED ADULT TICKS

Under controlled test conditions, unfed male and female Hyalomma trunc atum ticks exhibited a positive scototaxis to stationary, two-dimensio nal targets. Upright-positioned rectangles were the most attractive ta rgets. The attractiveness of these targets increased with their size. Significantly more ticks responded scototactically positively to the t argets under a luminance contrast ratio of 5:1, as compared with other luminance contrast ratios. Targets with an elevation angle of 13 degr ees were occupied more frequently than objects with higher elevation a ngles. Scototaxis was the same towards a stationary and a sinusoid osc illating target. When an upright-positioned rectangle was combined wit h a CO2 gradient, the number of ticks that migrated into the CO2 gradi ent and contacted the target did not increase significantly. The inter val between exposure and first locomotion of the ticks, however, was s ignificantly shorter under the influence of a CO2 gradient than in all other experiments without a CO2 gradient. A temperature gradient simu lating a natural host (cattle) did not alter the scototaxis. The resul ts of these investigations suggest that the positive scototaxis exhibi ted by adult H. truncatum ticks is not likely to be part of their appe tence behaviour but rather searching behaviour to find adequate protec tion from harsh climatic conditions.