Zur Sensitivität von Argas (Persicargas) walkerae auf optische Strahlung sowie zur Lokalisation und Organisation lichtperzipierender oder ‐durchlässiger Areale des Integumentes

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Considering a negative phototaxis as a stimulus reaction to narrow - or wideband monochromatic radiance of varying ranges of wavelengths and different irradiance it was established that both unfed and engorged I. and II. nymphs, as well as male and female adult ticks of Argas (Persicargas) walkerae, responded almost to the whole spectrum of the investigated wavelengths from 246-809nm, however, depending on the irradiance. Peaks of sensitivity with 50-100% of phototactically negative reacting ticks, however, were only registered in the range of 415 nm to 604 nm at moderate and high irradiance. Interstadially unfed and fed ticks showed no or only slight differences of reaction. Engorged ticks responded analogously to the unfed ticks but usually with smaller percentages. The lower readiness of reaction of the engorged stages was also established by the comparison of the temporal threshold values, which were ca. 1 min shorter for unfed ticks. Ablation tests for localizing light perception in or through the integument by means of covering the integumental areas in various combinations and simultaneously confronting them with the highly sensitive range of wavelengths from 446-568 nm revealed that unfed female adults probably perceived the light stimuli primarily through the dorsum. Covering the entire dorsum with white or black paint caused a phototactically negative response in 10-30% of the ticks. Untreated control ticks reacted to the light stimuli with a proportion of 50-75%. Scanning electron microscopical examinations of the dorsum, ventral surface and supracoxal folds of unfed female ticks gave no evidence of morphologically recognizable, superficially organized or integument-integrated photoreceptor areas or optical organs similar to lenses.