SUMMARY Spontaneous walking by Ixodes ricinus nymphs in the horizontal plane was investigated within choice arenas to test whether these ticks move preferentially up a humidity gradient, and whether they are attracted towards host odour, specifically volatile substances from the back of a dog's ear. Responses by ticks with high and low fat contents and in different states of hydration were compared. Ticks with higher energy reserves were more likely to walk horizontally over short distances. Only if they were slightly dehydrated were they more likely to walk towards fully saturated air than drier air, and only if the atmosphere was sufficiently wet were they likely to walk towards odour secreted by host skin. It seems that, under certain circumstances, ticks of this ambushing species will move short distances towards host odour.

SUMMARY Hard ticks spend most of their life isolated from passing vertebrates but require a blood meal to proceed to the next life stage (larva, nymph or adult). These opportunist ectoparasites must be capable of anticipating signals that render suitable hosts apparent. Large ungulates that tolerate a high ectoparasite burden are the favoured hosts of adult hard ticks. Ruminants, comprising the majority of ungulate species, must regularly eruct gases from the foregut to relieve excess pressure and maintain a chemical equilibrium. Through eructations from individuals, and particularly herds,ruminants inadvertently signal their presence to hard ticks. Here, we report that all adult hard tick species we tested are attracted to cud and demonstrate that these acarines possess olfactory receptor cells for the carboxylic acid, phenol and indole end-products of the rumen bioreactor. Compounds from each of these classes of volatiles attract ticks on their own,and mixtures of these volatiles based on rumen composition also attract. Appetence for rumen metabolites represents a fundamental resource-tracking adaptation by hard ticks for large roaming mammals.

SUMMARY The behaviour of Ixodes ricinus nymphs was recorded in 10-day experiments using computer-assisted video-tracking, in the absence of any host stimuli. These ticks switch spontaneously from questing in a desiccating atmosphere to quiescence in a water-saturated atmosphere after dark. Quantification of both questing and quiescence duration demonstrates that questing duration is inversely related to saturation deficit whereas quiescence duration is not. Distance walked after quiescence increased with desiccating conditions, while the distance walked after questing remained unchanged. Almost all locomotor activities of I. ricinus occurred during darkness under either a 14 h:10 h L:D or a 8 h:4 h L:D cycle. We established that all life stages of I. ricinus are equipped to sense shifts in light intensity with bilaterally placed strings of photoreceptors. This permits I. ricinus to use onset of darkness to trigger mobility when desiccation risk is reduced in nature.

SUMMARY The hard tick Boophilus microplus ingests large volumes of cattle blood, as much as 100 times its own mass before feeding. Huge amounts of haem are produced during haemoglobin digestion, which takes place inside acidic lysosomal-type vacuoles of the digest cells of the midgut. Haem is a promoter of free radical formation, so haemoglobin digestion poses an intense oxidative challenge to this animal. In the present study we followed the fate of the haem derived from haemoglobin hydrolysis in the digest cells of the midgut of fully engorged tick females. The tick does not synthesize haem, so during the initial phase of blood digestion, absorption is the major route taken by the haem, which is transferred from the digest cells to the tick haemocoel. After this absorptive period of a few days, most of the haem produced upon haemoglobin degradation is accumulated in the interior of a specialized, membrane-delimited, organelle of the digest cell, herein called hemosome. Haem accounts for 90% of the hemosome mass and is concentrated in the core of this structure, appearing as a compact, non-crystalline aggregate of iron protoporphyrin IX without covalent modifications. The unusual FTIR spectrum of this aggregate suggests that lateral propionate chains are involved in the association of haem molecules with other components of the hemosome, which it is proposed is a major haem detoxification mechanism in this blood-sucking arthropod.

SUMMARY To attempt description of the set of mRNA and protein (sialome) expressed in the salivary glands of the tick Ixodes scapularis , we randomly sequenced 735 clones of a full-length salivary gland cDNA library of this arthropod and performed Edman degradation of protein bands from salivary gland homogenates (SGH) and saliva separated by SDS-PAGE. The sequences were grouped into 410 clusters, of which 383 are not associated with known I. scapularis sequences. 15- and 17-protein bands from PAGE yielded amino-terminal information on the saliva and salivary gland gels,respectively. We attributed 19 of these sequences to translation products of the cDNA library. Full-length sequences were obtained for 87 clones. Among these protein sequences are several protease inhibitors of distinct classes,metalloproteases, novel proteins with histamine-binding domains, and several peptide families of unknown function displaying different conserved cysteine residues, many of which contain single Kunitz domains. This work provides information into the diversity of messages expressed in the salivary glands of I. scapularis , describes novel sequences that may be responsible for known biological activites, indicates further biological activities that may be present in I. scapularis saliva and identifies novel vaccine targets that may be used in Lyme disease prevention.