The influence of preprandial insemination on feeding and oviposition of Ixodes persulcatus females (Acari: Ixodidae) and some thoughts concerning mating strategies in ticks of the genus Ixodes.

Prostriate ticks (subfamily Ixodinae, genus Ixodes) can copulate and the females can be inseminated before attachment to the host. In tests with Ixodes persulcatus females collected in the field and fed without males on the host, it was shown that this preprandial insemination is necessary and sufficient for successful engorgement and oviposition if female feeding took place in up to 1 month after collection. A 2-month period between preprandial insemination and female feeding was followed by a significant decrease in the proportion of normally engorged females and significant increase in egg mortality. If a small number of males were added to feeding females in this case, the number of normally engorged females increased but the egg mortality remained as high. Spermatophore destruction during the 2-month period is assumed to have a negative effect on the viability of eggs produced after additional (perprandial) insemination. Prostriate ticks are believed to be an intermediate group between argasid and metastriate ticks. Transition from nidicolous parasitism in argasid ticks to exophily (pasture parasitism) in metastriate ticks determines the change in mating strategy from off-host to on-host copulation. We review the available data concerning mating strategies in representatives of different subgenera of the genus Ixodes in the context of this evolutionary relationship.

Potential risk of pathogen transmission by acaricide-poisoned ticks.

Many aspects of tick poisoning with acaricides have yet to be elucidated. One of them is the influence of acaricide poisoning on tick infectivity to their hosts. To clarify this problem, we should know how tick poisoning develops after acaricide application. Data obtained during more than three decades of work with ticks of various species and with acaricides of different groups are presented in the paper. The first important phenomenon found was the gradual and progressive development of toxic symptoms after acaricide application, with death of the treated ticks delayed for days or even weeks ('slow-death syndrome'). The development of symptoms was much faster after the application of fenthion, an organophosphorous acaricide, when compared to DDT, a chlorinated hydrocarbon. The larger the adult ticks of a particular species, the more refractory they were to acaricide action. The duration of the development of toxic symptoms directly correlates with the degree of species-specific refractoriness. A special index T(LD(50)) (T(LC(50)) was introduced for comparing the duration of the poisoning development between different tick species, populations etc. The index determines the time when the final mortality is reached after using the LD(50) of a particular acaricide. Another index , T(LD(90)), was used for practical purposes. The values of these indices decreased with increasing age of tick populations. The prolonged duration of poisoning was also observed in nymphal ticks of species with a prolonged life-span and the ability to over-winter (Ixodes, Haemaphysalis) but not in ticks characterized by a short life-span (Dermacentor). During the entire period of poisoning, from acaricide application until tick death, the individual tick passes through six stages defined by its locomotor capabilities. The stages are the same for nymphs and adults of both hard and soft ticks after treatment with various acaricides. When ticks are at the initial stages of poisoning (1st to 3rd stage for DDT or 1st to 2nd for fenthion), they can attach to hosts and imbibe blood. The average body weight of such ticks after repletion corresponded to that of control ticks. Engorged nymphal ticks normally molted to adults, engorged females normally oviposited, and their progeny did not differ from the progeny of control females. This second important phenomenon, called 'overcoming the poisoning', was observed in all studied species of ticks from several genera. Thus, the slow development of tick poisoning creates a potential for ticks to attach to hosts and to gorge blood, and for infected ticks to transmit pathogens to those hosts, while the ability to overcome the poisoning allows the ticks to survive and makes possible the subsequent trans-stadial and transovarial passage of pathogens. These data can be considered as strong circumstantial evidence of the risk that ticks can present to humans and animals at the initial stages of poisoning after acaricide treatment.

The dog factor in brown dog tick Rhipicephalus sanguineus (Acari: Ixodidae) infestations in and near human dwellings.

Three cases of the tick Rhipicephalus sanguineus infiltration in or near human dwellings caused by dogs, and their influence on epidemiological features of human habitats have been investigated. (a) The observation of dogs kept indoors proved that single tick females could engorge and oviposit inside apartments followed by the development of subadults. (b) Abundant micropopulations of ticks were formed in small yards or gardens near the dwellings where dogs lived in kennels. (c) A huge field population of R. sanguineus was observed on a farm where watchdogs constantly patrolled along the farm perimeter. Tick abundance near the kennels and in the permanent resting sites of the dogs reached more than 30 adults per 10 min of collecting, while the number of adults on a dog reached 100. Unfed adult females under conditions of constant dog availability had a larger scutal index than females collected in the control field site. On the basis of circumstantial evidence it is possible to conclude that under the above conditions tick development may change from the normal 3-host cycle to a 2-host cycle. Ticks in the field had one complete generation per year. Ticks on the farm, as well as ticks in kennels, developed faster and a significant part of their population had two complete generations per year. R. sanguineus is the main vector and reservoir of a pathogen from the Rickettsia conorii complex, the causative agent of Israeli tick typhus. The described conglomerations of R. sanguineus create a great risk to humans who can be attacked by infected ticks in and around their homes, even in large towns. Such a feature of the tick life history most likely exists not only in Israel but in other countries as well.