Cannibalism in mosquito larvae during microbial larvicide potency tests.

We observed instances of cannibalism (intraspecific predation) among intra-instar larvae of Culex pipiens Linnaeus, 1758 while performing a bioassay of Lysinibacillus sphaericus (formerly named Bacillus sphaericus) larvicide, when the larvae were exposed to the larvicide for 48 h in the absence of food. Larvae without symptoms of poisoning attacked and devoured those visibly affected. Cannibalism was more prevalent in 1st-2nd instar larvae than in 3rd-4th instar. This phenomenon should be taken into account when interpreting the results of larvicide bioassays, especially when the exposure lasts over 24 h. The necessity of creating optimal conditions for organisms tested is emphasised.

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.

Tick pests and vectors (Acari: Ixodoidea) in European towns: Introduction, persistence and management.

Ticks have always been a part of fauna in and around human settlements, and their significance changed concurrently with the enlargement of settlements and their transformation into towns. The increased rate of urbanization during the last decades has created a new reality for tick existence. Two groups of ticks are of major concern for modern towns: those living under natural conditions of urban surroundings and those well-adapted to urban conditions. During the process of urbanization, encroachment into forested and uncultivated areas as well as protection of existing green spaces create opportunities for ticks living in nature to also exist under urban and suburban conditions. Conditions of modern urban and especially suburban environment in developed European countries adequately meet tick requirements. Tick species having an advantage in urban areas are those that can use one and the same host at all parasitic stages, can starve for a prolonged time, can use either urban pests or domesticated animals as hosts, and can live in man-made buildings. The ticks of the Argas reflexus group (Argasidae) and the brown dog tick Rhipicephalus sanguineus (Ixodidae) comply with practically all conditions necessary for successful survival in urban areas. The ability of ticks to transmit numerous human and animal pathogens and the presence of many reservoir hosts in urban and suburban areas create persistent danger for human populations and domestic animals. Impact on urban ticks should be directed against the two major requirements of tick existence: reducing populations of potential tick hosts (feral pigeons, stray dogs and cats, and urban rodents), and changing other environmental conditions to make them less suitable for ticks. It is especially important that urban inhabitants be properly informed about the danger posed by ticks, the sites of possible tick attacks, and basic self-protection techniques.

Attachment of nymphal Rhipicephalus sanguineus (Acari: Ixodidae) to a human in an urban area followed by severe adverse reaction shortly before drop-off.

A case of attachment and complete engorgement of a Rhipicephalus sanguineus (Latreille, 1806) nymph on a woman with severe pain shortly before nymphal drop-off is described. The pain continued for about 2 weeks after tick removal. Apparently, this is the first documented case of human adverse reaction developed at the very last stage of engorgement of nymphal R. sanguineus. The infestation most likely took place inside the enclosed household garden in the southern area of Jerusalem where the woman took care of the plants. The importance of immature R. sanguineus ticks in attacking humans is discussed.

Physiological age of field-collected female taiga ticks, Ixodes persulcatus (Acari: Ixodidae), and their infection with Borrelia burgdorferi sensu lato.

In some studies the prevalence of tick infection (infection rate) and the intensity of infection are negatively correlated with unfed tick age (in the broad sense of this term). However, no special research has been carried out to consider the phenomenon thoroughly. The infection indices of the female taiga ticks, Ixodes persulcatus, infected with Borrelia burgdorferi s.l. were related to tick physiological age, an index that more precisely reflects tick physiological state than the time of tick collection in the field or the duration of tick survival under laboratory conditions. A novel quantitative technique of physiological age determination based on the evaluation of the ratios between sizes of the stable (scutum) and the changing (alloscutum) structures of the tick body was used. The age was estimated in accordance with the classical age-grade scale introduced by Balashov and a more fractional scale determined by the new technique. In total, 131 female ticks were examined for their infection and physiological age, 46 of which were infected with B. burgdorferi s.l. (mean infection rate 35.1%). The minimal intensity of infection was 0.4 bacterial cells per 100 fields of view whereas the maximal infection was 172 cells. There was no difference between the prevalence of infection in ticks of different physiological age. The intensity of infection obviously differed between ticks of different age groups in the scale introduced by Balashov but did not significantly differ between ticks of different age groups according to the fractional age-grade scale. The data concerning the relationships between Borrelia burgdorferi and unfed Ixodes ticks are considered.

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 taiga tick Ixodes persulcatus (Acari: Ixodidae) in the Sakha Republic (Yakutia) of Russia: distributional and reproductive ranges.

The finding of an unfed adult female of the taiga tick Ixodes persulcatus Schulze is reported from the northern part of Eastern Siberia (the central part of the Sakha Republic [former Yakutia]) of Russia. This finding supplements other reported single findings of the taiga tick in different sites of the central part of the Sakha Republic, thus increasing its distributional range. The reproductive range of the taiga tick is limited to two separate areas in the southern parts of the Republic. The most probable mode of tick introduction northwards from the border of the reproductive range is by spring bird migrations from their wintering areas to breeding sites. The possibility of the establishment of stable tick populations in the areas of introduction is also considered.

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.

Tightly bound binary toxin in the cell wall of Bacillus sphaericus.

We have shown that urea-extracted cell wall of entomopathogenic Bacillus sphaericus 2297 and some other strains is a potent larvicide against Culex pipiens mosquitoes, with 50% lethal concentrations comparable to that of the well-known B. sphaericus binary toxin, with which it acts synergistically. The wall toxicity develops in B. sphaericus 2297 cultures during the late logarithmic stage, earlier than the appearance of the binary toxin crystal. It disappears with sporulation when the binary toxin activity reaches its peak. Disruption of the gene for the 42-kDa protein (P42) of the binary toxin abolishes both cell wall toxicity and crystal formation. However, the cell wall of B. sphaericus 2297, lacking P42, kills C. pipiens larvae when mixed with Escherichia coli cells expressing P42. Thus, the cell wall toxicity in strongly toxic B. sphaericus strains must be attributed to the presence in the cell wall of tightly bound 51-kDa (P51) and P42 binary toxin proteins. The synergism between binary toxin crystals and urea-treated cell wall preparations reflects suboptimal distribution of binary toxin subunits in both compartments. Binary toxin crystal is slightly deficient in P51, while cell wall is lacking in P42.

Preliminary observations on specific adaptations of exophilic ixodid ticks to forests or open country habitats.

Some features of three-host exophilic ticks important for their survival differ at the generic level in relation to the types of their habitat. Ixodes and Haemaphysalis are typical forest genera. Hyalomma is an open country genus, whereas Dermacentor and Rhipicephalus, having some features of forest ticks, are closer to the ticks of open country. Forest ticks encounter rather stable and favorable temperature, humidity and illumination conditions as compared with open country ticks. A few differences determining every-day survival, hostseeking. and reproduction of ticks are considered. (1) Tolerance to desiccation is very low in forest ticks and much greater in ticks of open country. (2) Lack of eyes in forest ticks (having, however, epithelial photoreceptor cells) and formation of eyes as special morphological structures in ticks of open country. (3) Capability of mating and insemination of unfed specimens both on and off hosts in forest ticks (Ixodes) and insemination of partially engorged females only on hosts by fed males in open country ticks. (4) Reciprocal sexual dimorphism where in forest ticks females have a larger body than males and in open country ticks this correlation is opposite. (5) Linear dependence between female weight and number of eggs laid is established in forest ticks after the female weight becomes higher than 50% of mean engorgement weight whereas in open country ticks linear dependence begins to reveal itself much earlier. (6) In forest ticks the compensatory growth occurs only during adult feeding whereas in open country ticks such a growth occurs both during nymphal and adult feeding. The adaptive nature of the above differences and their evolutionary trends have been hypothesized.