Worldwide recognition of ticks and subsequent control experiences in USA, Australia and Africa is summarized. The symposium lecture includes three research challenges: (a) reduce the direct and indirect costs of ticks to African animal agriculture, (b) complete critical research required for an effective African tick control programme in spite of stable or reduced research funding, (c) learn to package and market new technology used in control schemes. Three questions are suggested for industry representatives and researchers to ask one another: (a) Is the new technology practical and affordable? (b) Is animal productivity really improved? (c) Are the schemes responsive to broader environmental and animal health concerns of society?

Five populations of the tick, Rhipicephalus appendiculatus (collected from Kilifi, South Nyanza, and Uasin Gishu districts, and a Muguga laboratory strain) were subjected to isoenzyme analysis. Isoelectric focusing (IEF) of 11 enzymes on agarose gels was used to determine genetic differences between the tick populations. The isoenzyme profile results of the 11 enzymes investigated indicated that four loci, peptidase 1 (PEP 1:EC 3.4.11.1), PEP 2:EC 3.4.11.1, malate dehydrogenase (MDH:EC 1.1.1.37) and glucose phosphate isomerase (GPI:EC 5.3.1.9) showed differences in the populations. The Uasin Gishu population was distinct from all others. Ten out of the eleven enzymes studied were polymorphic in most of the populations while only one (i.e. PEP 7) was monomorphic.

Adult female Rhipicephalus appendiculatus ticks were fed on rabbits immunized with either bovine serum albumin, solubilized tick midgut membrane proteins, a 50:50 mixture of bovine serum albumin and solubilized tick midgut membrane proteins or buffer. Haemolymph harvested from these ticks after they had fed to engorgement and sera from the immunized rabbits were assayed for the presence and quantity of both the total rabbit IgG and specific rabbit IgG raised against bovine serum albumin using the enzyme linked immunosorbent assay technique. The results obtained indicated that rabbit IgG was able to cross the midgut barrier of the tick into the haemolymph. Furthermore, the amounts of IgG crossing into the haemolymph were dependent on the antibody titres in the serum. The results also showed that feeding ticks on blood containing anti-tick midgut antibodies increased the passage of IgG into the haemolymph.

Amblyomma hebraeum differs from many ixodid tick species in that it is not susceptible to the direct effects of the host immune response. All stages of the life cycle are able to feed repeatedly on laboratory hosts and show no progressive declines in engorged weight. However, on cattle there are declines in the yield of engorged adult females over time, as animals become sensitized to the tick and grooming increases. In the field zebu, Bos indicus and sanga, B. indicus x B. taurus breeds of cattle become less heavily infested than B. taurus breeds. The apparent resistance of zebu and sanga breeds is the result of learned tick avoidance behaviour, skin sensitivity and the ability to dislodge ticks prior to attachment as well as grooming ability. Among other Amblyomma spp., the feeding of A. americanum is adversely affected by acquired host immunity, while that of A. variegatum is generally unaffected.

A comprehensive review of the acquisition of resistance in bovine and laboratory hosts as a result of natural infestation with various species of ticks is undertaken. In this review I discuss the biological aspects of the expression of resistance, deal with acquisition of resistance to ticks by bovine and laboratory animals, give details on the environmental and physiological factors which affect the resistance and explain the mechanisms of resistance in both bovine and laboratory animals. I also deal with the relationships between ticks and their bovine hosts and emphasize the difference in the acquired resistance of individuals in the breed as well as the negative correlation between the decrease in mean weight of the ticks and the increase in the levels of globulins in the serum of the different hosts.

Aspects of cross resistance by hosts to different species of ticks are also discussed in this review.

In many countries in eastern, central and southern Africa, twice-weekly to two-weekly acaricide applications are practised to prevent mortality of exotic cattle from tick-borne diseases. This practice has been extended to areas where only local cattle are present. These measures are very costly, inefficient in controlling diseases and ecologically undesirable.

In view of the many difficulties with the present method of tick control, exploitation of tick-resistant cattle breeds in enzootically stable situations would appear to be a pragmatic, alternative approach to the intensive use of acaricides. This paper reviews studies on host-tick relationships in Africa with a view to understand the role of naturally acquired resistance in limiting tick populations and hence its use in integrated pest management strategies. The levels of information required are outlined such as identification and quantification of resistance, effect of cattle breeds and productivity and economics in relation to host-resistance.

Risk-benefit considerations have stimulated efforts to develop technology to overcome the limitations of procedures that place excessive reliance on the use of acaricides for the control of ticks affecting cattle. One of the alternatives to acaricides is the selection and use of breeds of cattle with a natural propensity for developing acquired resistance to ticks. The literature on aspects of the modes of expression and mechanisms of resistance of cattle to ticks, is reviewed along with information on the successful efforts in Australia to develop productive Bos indicus ï Bos taurus breeds with the ability to develop high levels of resistance. The use of cattle resistant to ticks is discussed in relation to other factors that should be considered in the design of a programme for tick control.

ECFXPERT is a microcomputer software tool which can be used to investigate tick populations and the control of East Coast fever. The package contains four simulation models: a model for predicting the abundance and seasonality of Rhipicephalus appendiculatus ticks; a model for predicting East Coast fever prevalence within a herd of cattle; and two models for the study of disease control using either acaricidal dipping strategies or chemotherapy. In this paper, the philosophy of the ECFXPERT package, and the underlying assumptions and mathematical techniques employed are presented, along with the results of a number of computer experiments designed to validate and illustrate potential use of the model.

Tropical African ticks are found on their hosts throughout the year, but at varying infestation levels. These population changes, for most of the time, have been associated with climatic changes. Their development is inversely related to temperature. Several workers reported that development failed for a number of tick species at temperatures below 15°C, suggesting a possible lower temperature threshold for tick development. The upper development limit for most of the tropical rhipicephalids appear to be 37°C.

Ticks are particularly susceptible to attack during lethargic pre-moulting and the weak post-moulting period. Many biological features enable them, however, to survive especially well. They lay numerous eggs and withstand a comparatively wide temperature and humidity range with greater ease. They survive for months or years without food.

Their degree of host specificity varies from genus to genus or within subgroups of various genera. The requirement of two or more kinds of hosts often with divergent habits, limits their distribution to certain faunal areas.

This paper reviews our current knowledge on development and survival of ixodid ticks under tropical field conditions including some laboratory studies.

The systems analysis approach is an appropriate procedure for the effective development of a management model for the strategic control of ticks. The interacting nature of the controllable and uncontrollable factors, and the difficulty in mimicking such complex situations experimentally, should be considered in the formulation of such models. ICIPE's approach relies on the use of both deterministic and stochastic models, and assumes unambiguous definitions of management's expectations.

Selected aspects of ecological interactions with ticks, tick-borne diseases and their hosts are discussed in relation to Integrated Tick Management, The needs to preserve tick-borne disease enzootic stability and to ensure the economic justification for any interventions were emphasized.

Immature stages of Amblyomma lepidum were fed on rabbit ears and the adult ones on calf ear. There was a three-host type of development during an average period of 160.5 days. The mean larval feeding period was 5 days, 7 days for nymphs and 14.5 for females. At 27 ± 1°C and 100% r.h. the engorged larvae required 21 days for moulting and nymphs took 22 days to develop to adults. The pre-oviposition period was 14.2 days and the oviposition period was 21.4 days during which a mean number of 7564.6 eggs were laid. Hyalomma anatolicum anatolicum and Rhipicephalus evertsi evertsi were fed on rabbit ears. The larvae, nymphs and adults of Hyalomma ticks fed for 4.6 and 8.5 days, respectively. The larvae and nymphs of R. e. evertsi fed sequentially on the same host for 14 days while the females took 7.5 days to engorge. At 27 ± 1°C and 75–80% r.h. the engorged larvae and nymphs H. a. anatolicum moulted after a further 8.5 and 13 days respectively. The engorged nymphs of R. e. evertsi at 27 ± 1°C and 75–80% r.h. moulted 14.5 days after dropping off the host. At 27 ± 1°C and 75–80% r.h. the preoviposition and oviposition periods of H. a. anatolicum were 4.6 and 20.8 days, while those of R. e. evertsi were 5.4 and 14 days. The average number of eggs laid per female under the same conditions (27 ± 1°C and 75–80% r.h.), was 4684.6 for H. a. anatolicum and 3392 for R. e. evertsi.

A comprehensive review of the major investigations on the biology of African ixodid ticks is made with a view to identifying weaknesses in the life systems which may be employed as control components in an integrated package. The possibility of breeding ticks with low oviposition capacities needs to be confirmed and further studied with respect to the economically important ticks in Africa. Studies on the membrane or artificial feeding of ixodid ticks must be conclusive and more importantly the disease transmission abilities of these membrane fed ticks is worthy of being looked into. Additionally, the hybrid status of both Genus Rhipicephalus and Genus Amblyomma ticks should be studied. Efforts must also be made to intensify research on selecting resistant host breeds to multihost ticks, R. appendiculatus and A. variegatum, among the very many cattle breeds present in Africa.

Argasid ticks have been induced to feed successfully through different types of artificial membranes but this technique has not been easily applicable on ixodid ticks. In order to get hard ticks to feed artificially, two major approaches have been employed: Feeding on a diet through artificial membranes; and feeding from diet-filled capillary tubes placed over the tick's mouthparts. In both cases the ixodid ticks could not be fed to repletion. This paper gives a brief account about artificial feeding of ticks in general and the techniques used to obtain successful feeding of an ixodid tick Rhipicephalus appendiculatus through a modified Baudruche membrane.

Ticks have always been a major obstacle to livestock production due to the devastating diseases which they transmit especially in the tropics. The control of ticks which has relied heavily on the use of acaricides is now faced with serious problems e.g. increased resistance in ticks, high costs and toxicity to the environment. Over the last few decades, alternative tick control methods which utilize natural factors with little or no acaricides have been sought and those which have shown some promise are discussed in this paper. They include release or conservation of biological control agents e.g. parasitoids, predators and pathogens; anti-tick grasses and pasture spelling. The possibility of integrating some of these factors into low cost environmentally-safe tick control strategies affordable by resource limited farmers is also discussed.

The use of synthetic acaricides in tick control is increasingly becoming more expensive. As a result, a lot of Africa's resource-poor farmers are failing to dip their cattle regularly. Natural products offer these farmers a cheaper alternative to synthetic acaricides. There is indeed a great potential for the use of Africa's huge natural resources, the plants to develop sources of acaricides to reduce the cost of tick control being locally available and potentially being able to be produced and used by farmers themselves or by cottage industries. It is, however, necessary that research centres such as ICIPE encourage the development of systematic research on natural products in order to bring about the Tephrosia vogelii leaf extracts observed to be highly toxic to one-, two- and three-host ticks and cattle sprayed with the extract had a residual protection period of 10 days from re-infestation by ticks.

Paper discusses five substantive issues affecting farmer participation (FP) in the development of integrated tick management (ITM). These are the concepts, methods, incentives for and constraints to farmer participation (FP), and finally, case study material illustrating how FP has contributed to the research and development of integrated tick management.

The various methods of controlling tick infestation on livestock are reviewed, highlighting their strengths and weaknesses. A framework for developing an IPM approach including socioeconomic considerations for ticks control is proposed. Efforts at practising IPM on ticks are highlighted.