ON THE REACTION OF ADULT RHIPICEPHALUS-EVERTSI-MIMETICUS AND HYALOMMA-TRUNCATUM TO HORIZONTALLY INCIDENTING OPTICAL RADIATION OF VARIOUS WAVELENGTH RANGES AND DIFFERENT IRRADIANCES AND TO OPTICAL RADIATION OF A SUN-SIMULATING WAVELENGTH SPECTRUM

The valence of horizontally incidenting light/optical radiation for host-seeking-inclined ixodid ticks was investigated by exposing male and female adults of Rhipicephalus evertsi mimeticus and Hyalomma truncatum to narrow-band monochromatic radiation in the wavelength range of 300-801 nm at irradiances corresponding to an overcast to clear sunny day, a cloudy day and a full-moon night as well as to optical radiation of a sun-simulating wavelength spectrum of 190-2600 nm within a test chamber from which other stimuli were excluded. It was demonstrated that independent of sex, adult ticks of R. e. mimeticus and H. truncatum responded to a wide wavelength spectrum in the visible and UV range, even at irradiances corresponding to a full-moon night. Interspecific differences existed in the degree and extent of the response as well as in the spectral sensitivity. Ticks of H. truncatum consistently showed a faster and stronger response and reacted phototactically positively in higher percentages than adults of R. e. mimeticus. Independent of wavelength range and irradiance, predominantly only few R. e. mimeticus ticks were stimulated to positive phototaxis, whereas at least 33.3% (in most cases, 50%) and maximally > 80% of H. truncatum adults reacted phototactically positively. Spectral sensitivity maxima were demonstrated at the yellow and red light and at the UV-A waveband width for R. e. mimeticus and at the violet, blue, green and yellow light wavelength for H. truncatum. With decreasing irradiance, the spectral sensitivity shifted to the blue wavelength range. In the search for adequate blood donors, ticks are confronted with numerous natural stimuli, which must be sorted and processed and are possibly used selectively if a host is to be located successfully. The questions as to whether and to what extent optical radiation may precipitate a reaction and/or an orientationally determining influence on ticks has been only partially and insufficiently investigated. Studies on two-host ixodid species of ticks that inhabit the same regions south of the Sahara have not been performed at all in this regard. Accordingly, the present study was intended to investigate the reactions of hungry male and female ticks of Rhipicephalus evertsi mimeticus and Hyalomma truncatum to horizontally incidenting monochromatic radiation of various wavelength sectors and irradiances and to optical radiation of a sun-simulating spectral range.