Survival of unfed Rhipicephalus appendiculatus and Rhipicephalus zambeziensis adults

Two ixodid tick species, Rhipicephalus appendiculatus (Neumann) and Rhipicephalus zambeziensis (Walker et al.) (Acari: Ixodidae), both originating from the southern province of Zambia, were used to study the survival time of adults at a range of different humidities and temperatures. In general, the experiment clearly demonstrates the different survival times of the two species in relation to the climatic conditions tested: survival of R. zambeziensis was better under more extreme conditions of temperature and humidity. These findings offer an explanation for the different distribution ranges of the two tick species. Rhipicephalus appendiculatus is more confined to cooler and wetter conditions, whereas R. zambeziensis is adapted to hotter and drier areas.     

Artificial-membrane feeding of the ixodid tick,Rhipicephalus appendiculatus,to repletion

An artificial feeding device was constructed with a Baudruche, membrane bearing olfactory and tactile stimuli, to induce voluntary attachment and feeding of the brown ear tick,Rhipicephalus appendiculatus. Preparation of the membrane and experimental conditions used are described. Unfed adults ofR. appendiculatus, 2–3 weeks after moulting, were confined on the membrane, which was treated with cattle ear-wash and other stimuli. They attached and commenced sucking blood within 12–48 h. Fully engorged ticks started detaching from the membrane on the 6th day. After a 5–6-day incubation period, they started laying eggs which hatched into normal larvae.     

Diapause induction in adults of three Rhipicephalus appendiculatus stocks

Newly-moulted adults of three Rhipicephalus appendiculatus stocks, originating from Kenya, Zambia and Zimbabwe, were kept in different photoperiods (12h : 12h, 13h : 11h and 14h : 10h light : dark). The stock originating from Kenya showed almost no behavioural diapause in any of these day lengths, whereas virtually all individuals of the Zimbabwean stock entered a behavioural diapause irrespective of day length. Adults from the Eastern Province of Zambia, a transition zone between the multivoltine phenology in equatorial Africa and the univoltine in southern Africa, exhibited a photoperiod-dependent diapause response. The possible mechanisms of diapause regulation and their origin are discussed.     

Questing activity of Rhipicephalus appendiculatus (Acari: Ixodidae) nymphs: a random process?

Abstract.  In Zambia, an experiment under quasi-natural conditions indicated that Rhipicephalus appendiculatus nymphs react to prevailing climatic conditions. Higher temperatures and higher vapour pressure deficits lead to decreased activity. The majority of nymphs (>75%) were recorded at ground level. Simulations showed that larval phenology and temperature during the nymphal premoulting period largely explain the seasonal abundance patterns of nymphs, as observed on cattle, given the absence of a behavioural diapause. Consequently, the effect of climate, as observed in our studies, is masked. However, the results of the present study indicate that daily climatic conditions probably have a much larger effect on the transmission dynamics of Theileria parva . The vertical distribution of questing instars is a function of temperature and humidity. In years of unfavourable conditions, nymphs might feed mainly on hosts other than cattle, and this could govern the infection prevalence in the adult population. This suggestion is supported by previous epidemiological studies.     

Structural and histochemical changes in the salivary glands of Rhipicephalus appendiculatus during feeding

The salivary glands of the brown ear tick of cattle, R. appendiculatus, from both sexes and at all stages of feeding, were examined as whole glands and as sections for ultrastructural and histochemical changes. The type 1 acinus consists of a basal labyrinth formed by the interdigitations of a central cell and four peripheral cells. These cells form a specialized border with a central constrictor cell which surrounds the acinar duct. The plasma membrane of the central cell is exposed to the duct. The type 1 acini do not appear to secrete active saliva components involved in feeding. The type 2 acini undergo a great increase in synthetic and secretory activity during feeding in both sexes and secrete a lipoprotein probably to form part of the attachment cone and also glycoproteins and esterases of unknown functions. The type 3 acini of both sexes also secrete a lipoprotein probably to form part of the attachment cone. The f cells of these acini in the females transiently secrete a glycoprotein of unknown function and then transform to become part of a water excreting unit. In the males the secretory activity of the granular cells of the type 2 and 3 acini is maintained for further attachments. The type 4 acini of the males accumulate masses of proteinaceous granules. The system of interstitial cells and intercellular spaces in types 2, 3 and 4 acini is large and increasingly active during feeding.     

Molecular individuality and adaptation of the tick Rhipicephalus appendiculatus in changed feeding environments

The tick Rhipicephalus appendiculatus Neumann (Acari: Ixodidae) naturally infests many host species. However, the mechanisms that enable it to feed on such a wide range of hosts are unclear. One possibility is that a tick population maintains molecular (genotypic and/or phenotypic) diversity among individuals such that individuals vary in their competency in taking bloodmeals under different feeding conditions. As a first step in testing this hypothesis, we showed that the polymorphism of salivary gland proteins, previously demonstrated in unfed ticks, was maintained during feeding on guinea-pigs. We then compared feeding performance under standard laboratory rearing conditions: one instar (adults or nymphs) feeding on guinea-pigs, with three changed conditions: (1) two instars (adults and nymphs) feeding together on guinea-pigs; (2) one instar (adults or nymphs) feeding on hamsters; and (3) two instars (adults and nymphs) feeding together on hamsters. The mean engorged weight of adult females was significantly reduced under all changed conditions, indicating that most of the adult individuals were significantly challenged by the changed conditions. However, some individuals achieved successful engorgement, indicating competence to the changed condition, and demonstrating variation in adaptive ability among individuals. Engorged females produced egg masses positively correlated to the engorged weights. More interestingly, the correlation coefficient (R) increased when feeding condition was changed. This may lead to more efficient selection for population adaptation under the changed conditions. As the feeding success of ixodid ticks depends on the efficiency of the cocktail of immunomodulatory saliva, the relevance of the polymorphism of salivary gland proteins and host adaptation is discussed.     

Rhipicephalus appendiculatus feeding on rabbits and cattle: Salivary-gland responses to varying host resistance

AdultRhipicephalus appendiculatus ticks were fed as three sequential infestations on both rabbits and cattle. The feedings at first infestation on naive hosts were optimum for the ticks, whereas at third infestation the hosts were resistant, as expressed by reduced tick feeding performance. Ticks from naive and resistant hosts were examined for histological differences of salivary glands. In ticks fed on resistant rabbits there was a large increase in the synthesis of glycoprotein secretory granules in thec ₁ cells compared with ticks fed on naive rabbits. In ticks fed on naive and resistant cattle, the activity of thec ₁ cells was less than in ticks fed on naive and resistant rabbits. It was concluded that the salivary glands are able to respond selectively to conditions at the feeding site, and that this may be advantageous to the tick.     

Antigens and glycoproteins of larvae, nymphs and adults of the tick Ixodes ricinus

Abstract Protein components of homogenates of unfed larvae and nymphs of Ixodes ricinus (L.), and of ovary, haemolymph, Malpighian tubules, rectal ampulla, fat body, integument, salivary glands and midgut of partially fed adult females were studied for their antigenicity and carbohydrate moieties using immunoblotting and lectin affinity blotting (LAB) techniques. Comparing the individual anti-larval, anti-nymphal and anti-adult immune sera for their capacity to recognize the specific and trans-stadially cross-reactive antigenic proteins, larval feeding induced the most effective humoral response. The majority of immunogens recognized by rabbit anti-tick immune sera are glycoproteins. Most of the glycosylated antigens were modified with N-type glycans; however, O-type glycans were also demonstrated in some antigens. The correlation of the type of glycosylation with antigenicity, and the sharing of common antigenic epitopes by various tissues, are discussed.     

A study of the diapausing behaviour of Rhipicephalus appendiculatus and R. zambeziensis under quasi-natural conditions in Zambia

Abstract. The diapausing behaviour of Rhipicephalus appendiculatus was studied under quasi-natural conditions in the Eastern Province of Zambia. Newly-moulted adults of ticks indigenous to the study area entered a behavioural diapause when exposed to daylengths below a critical photoperiod, provisionally a daylength between 11 h 20min and 11 h 45min. In the Eastern Province of Zambia the diapause was apparently not terminated by a long-day signal, but by a weakening of the photoperiodic maintenance of the diapause because of increasing age of the ticks. Adults of a reference stock indigenous to Kenya also entered a diapause when exposed to daylengths below the same threshold and maintained this diapause for the same length of time. Adults of a reference stock of Rhipicephalus zambeziensis indigenous to Zimbabwe did not enter a diapause when exposed to the same daylengths. The relevance of the findings is discussed in relation to the distributions of the two species.     

Variation in body size in the tick complex Rhipicephalus appendiculatus/Rhipicephalus zambeziensis.

We examined the relationship between body size and the phenology of the tick complex Rhipicephalus appendiculatus/Rhipicephalus zambeziensis. These ticks transmit Theileria parva in cattle. In Africa, the body size of R. appendiculatus increases with latitude while the body size of the morphologically similar Rhipicephalus zambeziensis is constant at two different latitudes. A larger body size is necessary once survival becomes a constraint. The most plausible explanation for the smaller R. appendiculatus in equatorial Africa is the cost to produce a larger egg. The consequences of these findings for the introduction of R. appendiculatus in new environments are discussed. New field observations from southern Zambia indicate that R. appendiculatus body size does not vary seasonally as compared to eastern Zambia. This is an additional indication of the presence of a single diapausing population of larger ticks.     

Rhipicephalus appendiculatus: characterization of a testis-associated protein

A novel gene coding for Rhipicephalus appendiculatus Male-specific Protein (RAMP) was identified in a cDNA library constructed from the testis/vas deferens of R. appendiculatus ticks. This gene encodes a secreted protein exclusively expressed in the testis/vas deferens. The putative RAMP amino acid sequence contains a signal peptide and has 29% amino acid identity with male-specific Is5 gene of Ixodes scapularis. Gene expression studies revealed that RAMP mRNA was up-regulated in male ticks during blood feeding. RAMP was detected not only in the testis/vas deferens of males but also in postcoitum female ticks based on Western blotting, indicating that this protein is transferred to the female tick during copulation. Virgin female ticks, microinjected with recombinant RAMP, had significantly prolonged attachment duration during feeding, but there was no effect on fed weight. These results suggest that RAMP is a male-specific molecule in the spermatophore, and is related to female attachment behavior in R. appendiculatus ticks.     

The aggregation of questing ticks, Rhipicephalus pulchellus, on grass stems, with observations on R.appendiculatus

Rhipicephalus pulchellus was observed to aggregate on the tips of grass stems in the field in Kenya. Laboratory studies of this behaviour, using simulated glass ‘stems’ in sand-trays, showed that this aggregation was not due to responses to either (a) chemical marks placed on the stems by climbing ticks, or (b) other stimuli transmitted down the stems by ticks already at their tips. Instead, the aggregation on stems appeared to be an adventitious result of the ticks aggregating on the ground (in the lab., under filter paper covering the sand substrate of the apparatus) and then climbing the nearest stem in due course. Briefer, comparative observations on R. appendiculatus indicated that it was much more mobile on the stems, spending less time at their tips, and not obviously aggregating.     

Genetic variation in Rhipicephalus appendiculatus (Acari: Ixodidae) from Zambia: correlating genetic and ecological variation with Rhipicephalus appendiculatus from eastern and southern Africa.

Based on their ecology, Rhipicephalus appendiculatus ticks from eastern and southern Africa have been divided into three groups. We investigated how two geographic genetically differentiated stocks of R. appendiculatus from the southern and the eastern provinces of Zambia, representing two ecological groups, i.e., southern African and transition groups, respectively, genetically compare to stocks from east Africa (Rwanda) and southern Africa (Zimbabwe and South Africa). The ITS2 and two mitochondrial genes segments, 12s rDNA and COI, were used in the investigations. The ITS2 tree did not show support for differentiation into any groups, while the two mitochondrial genes trees (12s rDNA and COI) showed two genetically differentiated groups: an east African genetic group which included specimens from Rwanda and the plateau area of the eastern province of Zambia, and a southern African genetic group represented by specimens from South Africa, Zimbabwe and specimens collected on the fringes of the eastern province plateau in the Nyimba district of Zambia. This suggests that the two geographically differentiated stocks of the southern and eastern provinces of Zambia might be part of two wider geographic genetically differentiated R. appendiculatus groups that extend beyond Zambia. Stocks of "transition" ecology (eastern province) belong to the east African genetic group and the differences in ecology within this genetic grouping may be due to genetic polymorphism, phenotypic plasticity, and other local factors.     

The effects of the brown ear-tick, Rhipicephalus appendiculatus, on milk production of Sanga cattle

Abstract. Lactating Sanga cows of the Mashona breed from Zimbabwe, receiving either a low or a high level of nutritional supplement, were exposed to two levels of infestation of adults of the brown ear-tick, Rhipicephalus appendiculatus in the highveld of Zimbabwe. The effect of the ticks on the milk yield was measured over an 11-week period during the rainy season from January to April 1986. A technique in which calves were weighed before and after suckling was used to estimate milk yield. There were significant treatment effects of ticks (P < 0.05) on milk production but no significant differences in liveweight gain between calves from tick-free and tick-infested dams. The loss in milk production was poorly related to the number of female ticks that engorged, being 9 g (SEM 4) per tick. A Friesian x Hereford (Bos taurus) reference group of cattle carried 50% more ticks than the Mashona cows, illustrating a difference in resistance between the breeds. Thirteen screw-worm (Chrysomya bezziana) strikes were recorded amongst the thirty-two Mashona cows compared with twenty-one amongst the ten Friesian × Hereford animals between January and the end of March.     

The effects of the brown ear-tick, Rhipicephalus appendiculatus, on milk production in dairy cattle

Abstract. The effect is reported of artificially controlled levels of infestation with adults of Rhipicephalus appendiculatus on the milk yield of twenty commercial Bos taurus dairy cattle on a high plane of nutrition and eighteen crossbed B.taurus × Sanga cattle on a lower plane of nutrition in the highveld of Zimbabwe. The results showed no significant effect on milk yield of infestations averaging twenty engorging ticks per animal per day, despite severe ear damage in some animals. They indicate that milk production of dairy cattle under commercial management is not sensitive to infestation with R.appendiculatus. The results have important implications for management of ticks in Africa, but need to be interpreted within the context of the control of tick-borne diseases.