Coendangered hard-ticks: threatened or threatening?

The overwhelming majority of animal conservation projects are focused on vertebrates, despite most of the species on Earth being invertebrates. Estimates state that about half of all named species of invertebrates are parasitic in at least one stage of their development. The dilemma of viewing parasites as biodiversity or pest has been discussed by several authors. However, ticks were omitted. The latest taxonomic synopses of non-fossil Ixodidae consider valid 700 species. Though, how many of them are still extant is almost impossible to tell, as many of them are known only from type specimens in museums and were never collected since their original description. Moreover, many hosts are endangered and as part of conservation efforts of threatened vertebrates, a common practice is the removal of, and treatment for external parasites, with devastating impact on tick populations. There are several known cases when the host became extinct with subsequent coextinction of their ectoparasites. For our synoptic approach we have used the IUCN status of the host in order to evaluate the status of specifically associated hard-ticks. As a result, we propose a number of 63 coendangered and one extinct hard-tick species. On the other side of the coin, the most important issue regarding tick-host associations is vectorial transmission of microbial pathogens (i.e. viruses, bacteria, protozoans). Tick-borne diseases of threatened vertebrates are sometimes fatal to their hosts. Mortality associated with pathogens acquired from ticks has been documented in several cases, mostly after translocations. Are ticks a real threat to their coendangered host and should they be eliminated? Up to date, there are no reliable proofs that ticks listed by us as coendangered are competent vectors for pathogens of endangered animals

Ticks (Ixodida)

Entomology and Plant Patholog

THE SENSORY NERVOUS SYSTEM OF THE ADULT CATTLE TICK BOOPHILUS MICROPLUS (CANESTRINI) IXODIDAE PART II. SCANNING ELECTRON MICROSCOPY

The morphology of the sensory receptors on tarsus I and on the mouthparts of the cattle tick Boophilus microplus were examined by means of scanning electron microscopy. Features not resolved by light microscopy were revealed. The number of sensilla and their morphology are unique to B. microplus though similar to those of other tick species already described. The sensory setae found include mechanoreceptors, contact and olfactory chemoreceptors. Of special interest, on each inner cheliceral digit, is a denticle bearing a papilla at its tip and a pit at its base. The functions of these two newly described features are not known but it seems likely that they may include contact chemoreceptors capable of tasting host tissue chemicals. These observations provide the foundation for transmission electron microscopy of the receptors, which is the subject of the third paper in this series. Copyrigh

THE SENSORY NERVOUS SYSTEM OF THE ADULT CATTLE TICK BOOPHILUS MICROPLUS (CANESTRINI) IXODIDAE. PART I. LIGHT MICROSCOPY

The morphology and innervation of sensory receptors on tarsus I of the foreleg and on the mouthparts of the cattle tick Boophilus microplus are described by means of light microscopy. Sixty six sensilla are located on each tarsus I and forty five on each palp. Apart from the multiply innervated olfactory and gustatory sensilla already described in other ticks, several new multiply innervated sensilla are described. A new papilla has been identified on the distal surface of each inner cheliceral digit. The papilla is associated with cell bodies situated in the cheliceral shaft and may be a contact chemoreceptor. These observations form the basis for ultrastructural and electrophysiological studies

Artificial feeding of ixodid ticks

Ixodid ticks are economically important as they cause direct damage to livestock and are vectors of several pathogens that cause diseases in humans and animals. Some of the important tick-borne pathogens of livestock are Theileria parva, T. annulata, Babesia bigemina, B. bovis, Anaplasma marginale and Cowdria ruminantium. These pathogens are responsible for causing enormous losses in livestock. Identification of factors that influence transmission and development of these pathogens in ticks will greatly facilitate development of rational strategies for control of tick-borne diseases. This research has been hampered by the lack of suitable artificial feeding methods. This paper reviews recent developments in the artificial feeding of ixodid ticks and evaluate how this method can potentially be exploited. It uses as an example the transmission of an important livestock pathogen, T. parva, by Rhipicephalus appendiculatus

Artificial feeding systems for ixodid ticks as a tool for study of pathogen transmission

Among the blood-sucking arthropods, ixodid ticks have some of the most complicated feeding behavior requirements. Feeding is preceded by an attachment process, and each instar has to remain fully attached to the same feeding site for a period of 2-14 days. These biological demands have for a long time made it relatively difficult to develop viable methods were ixodid ticks could be fed without using their natural hosts. Literature survey shows that some of the in vitro feeding methods tried include capillary feeding (1,2), feeding ticks through various membranes such as slices of bovine skin (dermatomes)) (3), rabbit/bovine skins (4), and silicone membrane (5). The capillary method had severe limitations in that ticks had to be prefed on the natural host before fixing the diet filled capillaries to the mouthparts. Furthermore, the volumes of blood taken by the tick were very small because ticks had to feed in an unnatural manner. The use of host-skin tissue had certain problems in that the skin could rot easily. In cases where rotting could be prevented, it was observed that host skins were suitable for ticks with long mouthparts like Amblyomma variegatum but unsuitable for Rhipicephalus appendiculatus with short mouthparts. Advances in our knowledge on tick sensory biology and behavior (6) facilitated the development of artificial membranes and conditions conductive to the voluntary attachment and feeding to repletion of R. appendiculatus, a vector of Theileria parva, the causative agent of East Coast fever (ECF) (7,8). Lack of efficient in vitro feeding systems for ixodid ticks has all along been a limititing factor to research efforts directed towards tick control and tick-borne disease transmission in particular. In vitro feeding systems can be used to study products injected by ticks into their hosts, the effects of substances ingested by ticks, and pathogen infection as well as transmission among ticks (9). In this paper, we discuss observations on the in vitro feeding of A. variegatum and R. appendiculatus through host skin and artificial membranes respectively. The importance of the artificial membrane as a convenient tool applicable in tick pathogen transmission studies is also discussed. This is relevant in view of the fact that the artificial membrane can be tailored to suit the feeding requirements of various ixodid ticks