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Notes: Abstract Scanning-electron-microscopic investigations of Haller's organ in larvae, nymphs I, II, III and IV, and male and female adultArgas (Persicargas) walkerae ticks showed that morphology and structural organization change during postembryonic development. Stage-dependent differences existed regarding setal numbers of the anterior pit as well as formation and reticulation of cuticular projections in the capsule cavity. The anterior pit increased in size in the course of postembryonic development. It contained only seven setae in larvae, one conical, setiform and grooved seta each as well as two porose and fine setae. Nymphs I, II, III and IV and adult ticks had equal numbers of setae; however, one additional unilaterally serrate and grooved seta each were present. Setal length increased continuously during postembryonic development and attained maximum values in adult ticks. The capsule consisted of roof and cavity and was located distinctly lateral in larvae, slightly lateral in nymphs I and II, and in all other stages directly on the longitudinal axis of tarsus. The capsule roof showed a reticular structure. The slit-like main aperture was located peripherally and arranged transversally to the longitudinal axis of tarsus I in larvae. Nymphs and adult ticks had a central, circular main aperture. Stage-dependent cuticular projections of varying form protruded into the capsule cavity. Larvae had only single, free-standing projections which ramified slightly and communicated with each other. Projections were more heavily reticulated in nymphs I and II. In nymphs III and IV as well as male and female adult ticks, a long centrally situated tube of reticular appearance was seen, which was supported by a large number of radially organized and interlocking pillars and communicated with the capsule roof. In all tick stages there were always four porose setae present, arranged on the capsule floor.

Notes: Abstract A monoclonal antibody directed against a paralysis toxin of Rhipicephalus evertsi evertsi ticks was used to localize the toxin in cytoplasmic granules and, surprisingly, chromatin of the nuclei of cells which resemble the “b” cell type in the salivary glands of Rhipicephalus appendiculatus, Boophilus microplus and Ixodes holocyclus. The association of toxin with chromatin indicates that the toxin may have a regulatory function. Evidence is provided to support the view that the toxin is made up of three identical sub-units, with only the trimeric form being toxic.

Notes: Abstract Investigations concerning the reactions of unfed Hyalomma truncatum and Rhipicephalus evertsi mimeticus female and male ticks to vertically incident narrow- and wideband optical radiation at irradiances of 0.115 mWcm-2 and 0.98 mWcm-2, respectively, revealed that, independent of sex, adults of the two species are capable of perceiving a wide range of wavelengths. Considering the migration into the entry area of the optical radiation at the test chamber's ceiling as a positive phototaxis, H. truncatum always reacted with higher percentages than R. e. mimeticus. Compared to the controls, R. e. mimeticus ticks occupied the entry area of the optical radiation significantly more frequently only in the wavelength ranges of 415–474 nm, 529–628 nm, 611–707 nm and 190–2,600 nm, but always with low rates. High percentages of H. truncatum ticks, however, consistently reacted with a positive phototaxis in all the offered monochromatic sectors between 292–707 nm and also in the wide spectral range of 190–2,600 nm, particularly in the range of 470–520 nm. When ticks of both species were additionally confronted with a stable CO2 gradient, continuously increasing from 0.18 vol% at the bottom to 0.90 vol% at a height of 40 cm in the test chamber, they moved less frequently to the entry area of the optical radiation, compared to ticks tested without CO2, regardless of their exposure to darkness or to narrow- and wideband radiation. The percentages of ticks, however, that moved in a vertical direction, but did not reach the chamber's ceiling were always higher, with the exception of R. e. mimeticus at the wavelength range of 415–474 nm. A total of 30 unfed male and 30 unfed female adult ticks of both tick species were investigated at each combination of a narrow- and wideband spectral range, with and without the influence of a CO2 gradient. Considering moving ticks only, the interval between exposure and first movement of ticks was shorter under the influence of an additional CO2 gradient. The average delay in reaction with and without the stimulus of the CO2 gradient was 156.2 s and 195.6 s, respectively, for H. truncatum and 126.6 and 226.3 s, respectively, for R. e. mimeticus.

Notes: Abstract The immune response of a natural host of Rhipicephalus evertsi evertsi to feeding by this tick species was investigated with respect to the effects of tick salivary gland extracts on the transformation of peripheral blood lymphocytes and the release of histamine by basophils obtained from repeatedly infested sheep. The results indicated that there was no stimulation of lymphocyte transformation but that histamine release was elevated 10 fold after four infestations. Although this suggests a hypersensitivity reaction, believed to be a major factor in resistance to tick feeding, it was observed that ticks fed normally even after four infestations with 28 day intervals in between. These results emphasize the adaptation of ticks to feeding on their natural hosts.

Notes: Abstract Cross-reactivity between all the paralysis inducing tick species of veterinary relevance in Africa was demonstrated, by using a monoclonal antibody directed against the paralysis inducing toxin of Rhipicephalus evertsi evertsi. Western blot results, together with amino acid composition studies indicated that this monoclonal antibody recognizes protein bands of similar molecular mass and amino acid composition in R. evertsi evertsi and Ixodes rubicundus. This suggests that the Karoo paralysis toxin of I. rubicundus is possibly also a trimer with a high degree of homology to the spring lamb paralysis toxin of R. evertsi evertsi. The conclusive identity of these protein bands of 1. rubicundus could not be shown. Bio-assay studies performed on 1-day-old chickens suggested that the anti-spring lamb paralysis toxin monoclonal antibody also recognizes the paralysis toxin present in Argas (Persicargas) walkerae, by rendering some degree of protection against the effect of this toxin.

Notes: Abstract Investigations by scanning and transmission electron microscopy and freeze-etching revealed that eyes of adultRhipicephalus evertsi mimeticus consist of a lens and photoreceptor cells, which are separated by an acellular layer and the hypodermis. The lens contains numerous pore channels, which open beneath the epicuticula of the outer portion, converge uninterrupted to the inner closure and end in approximately 420 pore fields. The inner closure of the lens is formed as a deep circular invagination. Beneath the hypodermis and perpendicular to the lens, a group of approximately 20 highly differentiated photoreceptor cells in a rosette-like arrangement is localized within the invagination of the lens. Each photoreceptor cell is characterized terminally by numerous, tightly packed and parallel-running microvilli, which are oriented perpendicularly to the lenticular pore channels.

Notes: Abstract In investigations concerning the influence of stimuli emitted by chickens on the host-finding behaviour of hungry female adultArgas walkerae ticks, we found that 92.5% of the ticks migrated to the stimulus source following their simultaneous exposure to odours and to a CO2 gradient increasing in the direction of the chicken, as opposed to 67.5% following their exposure to kairomones of chickens in the absence of CO2. Migration of the ticks toward the stimulus source was precipitated by a wide range of CO2 concentrations (varying from 0.06 to 1 vol% within the odour mixture) but always required an increasing CO2 gradient in the direction of the chicken, whereby differences in concentration of 0.01 vol% over a distance of 2.5 cm were sufficient. During exclusive confrontation with either CO2 or heat in a gradient otherwise analogous to that emitted by a chicken, only 27.5% and 55% of the female ticks migrated to the stimulus source, respectively. Accordingly, odours emitted by chickens are considered to represent an essential stimulus modality, whereas body heat and CO2 are regarded merely as secondary, non-specific stimulatory agents. Investigations involving the exposure of ticks to a habitat similar to a chicken roost revealed that host seeking and finding are not influenced by gravity and occur only in darkness and that the portion of host-finding ticks diminishes with increasing distance from the blood donor.

Notes: Abstract The valence of horizontally incidenting light/optical radiation for host-seeking-inclined ixodid ticks was investigated by exposing male and female adults ofRhipicephalus evertsi mimeticus andHyalomma 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 ofR. e. mimeticus andH. 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 ofH. truncatum consistently showed a faster and stronger response and reacted phototactically positively in higher percentages than adults ofR. e. mimeticus. Independent of wavelength range and irradiance, predominantly only fewR. e. mimeticus ticks were stimulated to positive phototaxis, whereas at least 33.3% (in most cases, 50%) and maximally 〉80% ofH. truncatum adults reacted phototactically positively. Spectral sensitivity maxima were demonstrated at the yellow and red light and at the UV-A waveband width forR. e. mimeticus and at the violet, blue, green and yellow light wavelength forH. 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 ofRhipicephalus evertsi mimeticus andHyalomma truncatum to horizontally incidenting monochromatic radiation of various wavelength sectors and irradiances and to optical radiation of a sun-simulating spectral range.