Showing papers in "Experimental and Applied Acarology in 1999"

Ticks feeding on humans: a review of records on human-biting Ixodoidea with special reference to pathogen transmission.

Abstract: In this article, literature records of argasid and ixodid ticks feeding on humans worldwide are provided in view of increased awareness of risks associated with tick bites. Ticks can cause paralyses, toxicoses, allergic reactions and are vectors of a broad range of viral, rickettsial, bacterial and protozoan pathogens. Approximately 12 argasid species (Argas and Ornithodos) are frequently found attached to humans who intrude into tick-infested caves and burrows. Over 20 ixodid tick species are often found on humans exposed to infested vegetation: four of these are Amblyomma species, 7 Dermacentor spp., 3 Haemaphysalis spp., 2 Hyalomma spp. and 6 Ixodes species. Personal protection methods, such as repellents and acaricide-impregnated clothing are advised to minimize contact with infected ticks. Acaricidal control of ixodid ticks is impractical because of their wide distribution in forested areas, but houses infested with soft ticks can be sprayed with acaricidal formulations. Attached ticks should be removed without delay. The best way is to grasp the tick as close to the skin as possible with fine tweezers and pull firmly and steadily without twisting. Finally, despite the fact that most people who are bitten destroy the offending tick in disgust, it is recommended that they preserve specimens in ethanol for taxonomic identification and detection of pathogens by molecular methods.

Pollen as food for the predatory mites Iphiseius degenerans and Neoseiulus cucumeris (Acari: Phytoseiidae): dietary range and life history

Abstract: Although all known phytoseiid mites (Acari: Phytoseiidae) are predators of mites or small insects, many readily feed and reproduce on pollen as well. This ability to feed on food from plant origin increases their survival during periods when prey is locally sparse, but might occur at the expense of the ability to utilize food as efficiently as specialized predators. In this study we compare two predatory mite species used as biological control agents against thrips, Neoseiulus cucumeris and Iphiseius degenerans, with respect to (1) the range of pollen species that may serve as food sources for a sustained oviposition; and (2) the life history and expected intrinsic growth rates on some suitable pollen diets. The results show that I. degenerans is, compared to N. cucumeris, able to utilize a larger proportion of approx. 25 pollen species tested, but does not show equally high ovipositional rates as N. cucumeris. Consequently, the highest intrinsic growth rate for I. degenerans (0.21 day −1) will be surpassed by N. cucumeris.

Leaf hairs influence searching efficiency and predation rate of the predatory mite Phytoseiulus persimilis (Acari: Phytoseiidae)

Abstract: The effect of leaf hairs on searching efficiency of adult female Phytoseiulus persimilis was investigated. For this purpose we used the ornamental crop Gerbera jamesonii and determined the predator’s searching efficiency on three cultivars that differ largely in density of leaf hairs on the undersurface of the leaves. Walking speed of the mites was highest on the cultivar with the lowest leaf hair density. Walking activity, defined as the percentage of time spent walking, was not dependent on leaf hair density of the cultivars. At both prey densities tested, time until first predation increased with leaf hair density. Predation rate of adult female P. persimilis is affected by trichome density, especially when prey density is low. At prey densities of 1.3 and 2.5 T. urticae eggs/cm2, predation rate was inversely related to leaf hair density. At a prey density of 8.0 eggs/cm2 no significant effect of leaf hair density on predation rate was found. These negative effects on searching efficiency and predation success at low prey density of P. persimilis suggest that biological control of T urticae on gerbera may be hampered by leaf hairs.

Origin and Evolution of Feather Mites (Astigmata)

Abstract: Feather mites are highly specialized plumage and skin ectoparasites that are variously adapted for inhabiting certain microhabitats on a bird’s body. Different feather mite taxa of higher (familial) rank adapted to the same microhabitats display similar main morphological adaptations even if they are rather distantly related to one another. Hypotheses on the evolution of general adaptations in morphology of feather mites during colonization and establishment in different microhabitats are presented. According to recent data feather mites are a paraphyletic group consisting of three superfamilies: Analgoidea, Pterolichoidea and Freyanoidea. We present our view on the general feather mite phylogeny course at the familial rank for the Analgoidea by means of cladistic analysis. Co-speciation of parasites with their hosts is postulated as a main factor driving feather mite evolution. Examples are given of non-coevolutionary events, e.g. recolonization from one host species onto another, extinction and multiple speciation.

Molecular detection of pathogen DNA in ticks (Acari: Ixodidae): a review

Abstract: Ticks play an important role in human and veterinary medicine, in particular due to their ability to transmit a wide spectrum of pathogenic micro-organisms of protozoal, rickettsial, bacterial and viral origin. Pathogens in ticks can be identified by conventional methods such as indirect immunofluorescence, isolation in cell culture or by using histological staining techniques. However, the advent of the polymerase chain reaction (PCR) has resulted in tremendous improvements in the specific and sensitive detection of pathogen DNA in ticks. In this paper, literature on DNA extraction methods, PCR protocols, primers and probes, which are in use for the successful detection and identification of pathogens in ticks, are critically reviewed. Some recommendations are also given towards the end of this review.

Sequence Variation of Ribosomal Internal Transcribed Spacers (ITS) in Commercially Important Phytoseiidae Mites

Abstract: Preliminary work is needed to assess the usefulness of different markers at different taxonomic scales when a new group is analyzed, such as the commercially important Phytoseiidae mites. We investigate here the level of sequence variation of the nuclear ribosomal spacers ITS 1 and 2 and the 5.8S gene in six species of Phytoseiidae: Neoseiulus culifornicus, N. fallacis, Euseius concordis, Metaseiulus occidentalis, Typhlodromus pyri and Phytoseiulus persimilis. As expected, the 5.8S gene (148 base pairs) is markedly conserved and displays little variation in between genera comparisons. ITS1 and ITS2 show contrasting patterns: while the ITS2 is short (80-89 bp) and shows little variation, the ITS1 is longer (303-404 bp) and is very variable in sequence. This fact compromises reliable nucleotide homologies when comparing the genera. The comparison of ITS1 sequence similarity at the species level might be useful for species identification, however, the value of ITS in taxonomic studies does not extend to the level of the family. The intraspecific variations of ITS were investigated in three species: N. californicus, N. fallacis and E. concordis. The first species has identical ITS1 sequences and the last two display low polymorphism (2 nucleotide substitutions). The ITS2 and 5.8S sequences were identical in all three subspecies comparisons.

The contribution of extrafloral nectar to survival and reproduction of the predatory mite Iphiseius degenerans on Ricinus communis

Abstract: The phytoseiid mite Iphiseius degenerans (Berlese) is an effective predator of western flower thrips, Frankliniella occidentalis (Pergande), in Dutch greenhouses. In the Mediterranean area, castor bean, Ricinus communis L., is known as a year-round host plant for this predatory mite. On flowering castor bean plants in greenhouses, I. degenerans can be found in densities of more than 100 per leaf. For this reason, the plant is being used as a ‘banker’ plant to augment biological control. It has been shown that pollen produced by the large apical flowers sustains reproduction and development for these mites. The objective of this study was to measure the contribution of the extrafloral nectar of this plant to the reproductive success of this predatory mite. A study conducted at 25°C in presence of free water showed that (1) I. degenerans is unable to develop beyond the protonymphal stage when fed only nectar and leaf tissue, (2) its ovipositional rate is higher when pollen is supplemented with nectar, (3) its reproduction ceases within a few days when fed on nectar only, but the predator can survive for several weeks and resume oviposition when fed pollen again and (4) the feeding of young females for one or two weeks with nectar only extends their longevity by approximately the same period and only slightly diminishes their lifetime reproductive potential (R0), as compared to mites continuously fed pollen. It can be concluded that extrafloral nectar can provide an important contribution to population growth and maintenance of I. degenerans on R. communis, particularly in pre- and post-blooming periods. Assuming these predators are beneficial to the plant in clearing them of herbivorous mites and thrips, this relationship may be regarded as an example of plant–predator mutualism. The combination of pollen and extrafloral nectar makes castor bean an ideal rearing and banker plant for I. degenerans.

High temperatures eliminate Wolbachia, a cytoplasmic incompatibility inducing endosymbiont, from the two-spotted spider mite

Abstract: Wolbachia can induce cytoplasmic incompatibility (CI) in the arrhenotokous two-spotted spider mite between uninfected females and infected males. Cytoplasmic incompatibility is expressed through a male-biased sex ratio and a low hatchability, and can be suppressed by removing Wolbachia from spider mites reared on a diet with antibiotics. Here we investigated whether heat-treatment can elimate Wolbachia from infected mites. Using a PCR assay with a Wolbachia-specific primer pair (ftsZ), and by standard crosses, we were able to show that 71 per cent of the mites had lost the Wolbachia infection after rearing the infected population at 32 ± 0.5 °C for four generations. The infection could be completely removed when mites were reared at 32 ± 0.5 °C for six generations. Curing through high temperatures could be one of the reasons why mixed infected/uninfected populations occur in the field. An additional consequence of rearing mites at 32 ± 0.5 °C was the shortened development time. The effect of environmental temperature on the abundance of Wolbachia and possible behavioural consequences for the spider mite are discussed.

Effect of long-term feeding history on functional and numerical response of Neoseiulus californicus (Acari: Phytoseiidae)

Abstract: The functional and numerical responses of the predatory mite Neoseiulus californicus to eggs and protonymphs of Tetranychus urticae were studied on excised strawberry leaflet discs under laboratory conditions (25 ± 1°C, 75–85% RH and 16L : 8D) Four strains of the phytoseiid were compared: three originated from a long-term mass-rearing with different food (T urticae, Dermatophagoides farinae and Quercus spp pollen) and under controlled conditions, while the fourth was directly collected from a natural environment and therefore considered a wild strain The different nutritional histories affected the responses of N californicus on tetranychids On the whole, the wild strain gave better performance When egg prey was administered this strain and the one mass-reared on two-spotted spider mites showed similar functional as well as numerical responses; on the contrary, when protonymphs were furnished, the wild strain did not differ from that mass-reared on pollen The strain previously fed on house dust mites gave the worst performance and also showed the lowest percentages of females in the progeny The functional responses obtained were predominantly type II curves In all cases considered, no stored energy was allocated for reproduction and, with the exception of the wild strain on eggs, the prey was exploited less efficiently as the consumption increased In spite of the differences evidenced in this experiment all strains were characterized by high predation and oviposition rates Thus the results obtained suggest no drawbacks in the use of mass-reared N californicus as biocontrol agents © Rapid Science Ltd 1998

Sequence variations in the Boophilus microplus Bm86 locus and implications for immunoprotection in cattle vaccinated with this antigen.

Abstract: Cattle tick infestations constitute a major problem for the cattle industry in tropical and subtropical regions of the world. Traditional control methods have been only partially successful, hampered by the selection of chemical-resistant tick populations. The Boophilus microplus Bm86 protein was isolated from tick gut epithelial cells and shown to induce a protective response against tick infestations in vaccinated cattle. Vaccine preparations including the recombinant Bm86 are used to control cattle tick infestations in the field as an alternative measure to reduce the losses produced by this ectoparasite. The principle for the immunological control of tick infestations relies on a polyclonal antibody response against the target antigen and, therefore, should be difficult to select for tick-resistant populations. However, sequence variations in the Bm86 locus, among other factors, could affect the effectiveness of Bm86-containing vaccines. In the present study we have addressed this issue, employing data obtained with B. microplus strains from Australia, Mexico, Cuba, Argentina and Venezuela. The results showed a tendency in the inverse correlation between the efficacy of the vaccination with Bm86 and the sequence variations in the Bm86 locus (R2 = 0.7). The mutation fixation index in the Bm86 locus was calculated and shown to be between 0.02 and 0.1 amino acids per year. Possible implications of these findings for the immunoprotection of cattle against tick infestations employing the Bm86 antigen are discussed.

Mite population dynamics on different grape varieties with or without phytoseiids released (Acari: Phytoseiidae).

Abstract: In a three-year study, mite populations were monitored in two vineyards, each having two grape varieties with different leaf hair density. In both vineyards native phytoseiids were present: Amblyseius andersoni in one vineyard, and Phytoseius finitimus in the other. The economically important predators Kampimodromus aberrans and Typhlodromus pyri were released in both vineyards in order to study their efficacy in controlling tetranychids and eriophyids and their persistence during periods of prey scarcity. In both vineyards, relative abundances of the mite species, especially phytoseiids, were found to differ on different varieties in the same vineyard. In the first experiment, A. andersoni reached higher densities and was more persistent on the variety with slightly pubescent leaf under-surface (Merlot). Typhlodromus pyri and K. aberrans releases were successful and the mites became more abundant on the variety with pubescent leaf under-surface (Verduzzo). In the second experiment, P. finitimus was more abundant on a variety with pubescent leaf under-surface (Prosecco) than with glabrous leaf under-surface (Riesling). The most interesting results of the present study concerned the interactions between native and released predators. In the first vineyard, different results were obtained when releasing T. pyri on the two varieties. On the variety with pubescent leaves, A. andersoni was rapidly displaced by T. pyri, whereas the former species persisted on the other variety throughout the three-year study, apparently becoming dominant during the last season. In contrast to T. pyri, interactions between K. aberrans and A. andersoni in this vineyard did not depend on variety. The results of the experiments carried out in the second vineyard stressed the importance of interspecific competition for phytoseiid releases. Typhlodromus pyri colonization failed on both varieties. Kampimodromus aberrans releases appeared to be more successful on Riesling than on Prosecco; where P. finitimus was more abundant. At the end of the experiments, K. aberrans displaced P. finitimus on both varieties.

Borrelia burgdorferi sensu lato in Ixodes ricinus ticks and rodents in a recreational park in south-western Ireland.

Abstract: Ixodes ricinus ticks infected with Borrelia burgdorferi sensu lato were numerous on the edges of paths and roads in a recreational park in south-western Ireland. The abundance of ticks at different sites was related to the presence of deer, but a negative relationship was shown between tick abundance and tick infection rates. This is thought to be due to the deposition of large numbers of uninfected ticks by deer, which are apparently not good reservoir hosts of B. burgdorferi s.l. Blood meal analysis only detected deer DNA in uninfected nymphs. Reservoir competent rodents, Apodemus sylvaticus and Clethrionomys glareolus, were abundant at all sites and a high proportion of captured specimens were infested with larval ticks. However, very few rodents were infected with B. burgdorferi s.l. and none of the unfed infected nymphs analysed for the identity of their larval blood meal had fed on rodents. The spirochaetes detected in I. ricinus in the study area may be poorly adapted to rodents or are not transmitted readily because of the absence of nymphal infestation. The majority of spirochaetes in these ticks were apparently acquired from non-rodent hosts, such as birds.

The effect of temperature on life history parameters of Tetranychus evansi (Acari: Tetranychidae)

Abstract: The effect of four constant temperatures (21, 26, 31 and 36°C) on biological (survival and duration of developmental stages, fecundity and longevity of females and sex ratio) and demographic parameters (R0, G, rm and ) of Tetranychus evansi was studied in the laboratory under controlled conditions: 75 ± 10% RH and 12L : 12D. The lower thermal threshold was 10.3°C. The shortest developmental time (6.3 days) was obtained at 36°C. Maximum fecundity was recorded at 31°C with 123.3 eggs per female. The highest intrinsic rate of increase (rm) (0.355) was obtained at 31°C. The optimal temperature for population growth seems to be 34°C. © Rapid Science Ltd. 1998

Biological control of Tetranychus urticae (Acari: Tetranychidae) with naturally occurring predators in strawberry plantings in Valencia, Spain

Abstract: Naturally occurring beneficials, such as the phytoseiid mite Amblyseius californicus McGregor and the insects Stethorus punctillum Weise, Conwentzia psociformis (Curtis) and others, controlled Tetranychus urticae Koch in 11 strawberry plots near Valencia, Spain, during 1989–1992 The population levels of spider mites in 17 subplots under biological control were low or moderate, usually below 3000 mite days and similar to seven subplots with chemical control In most of the crops A californicus was the main predator, acting either alone or together with other beneficials Predaceous insects colonized the crop when tetranychids reached medium to high levels For levels above one spider mite per leaflet, a ratio of one A californicus per five to ten T urticae resulted in a decline of the prey population in the following sample (1–2 weeks later) These results suggest that naturally occurring predators are able to control spider mites and maintain them below damaging levels in strawberry crops from the Valencia area

A Comparative Study of Varroa Jacobsoni Reproduction in Worker Cells of Honey Bees ( Apis Mellifera ) in England and Africanized Bees in Yucatan, Mexico

Abstract: The aim of this study was to investigate an underlying mechanism of the apparent tolerance of Africanized honey bees (AHB) to Varroa jacobsoni mites in Mexico. This was achieved by conducting the first detailed study into the mites' reproductive biology in AHB worker cells. The data was then compared directly with a similar study previously carried out on European honey bees (EHB) in the UK. A total of 1071 singly infested AHB worker cells were analyzed and compared with the data from 908 singly infested EHB worker cells. There was no significant difference between the number of mother mites dying in the cells (AHB = 2.0%, EHB = 1.8%); the mean number of eggs laid per mite (AHB = 4.86, EHB = 4.93); the number of mites producing no offspring (AHB = 12%, EHB = 9%); and developmental times of the offspring in worker cells of AHB and EHB. However, there was a major difference between the percentage of mother mites producing viable adult female offspring (AHB = 40%, EHB = 75%). This was caused by the increased rate of mite offspring mortality suffered by the first (male) and second (female) offspring in AHB worker cells. Therefore, only an average of 0.7 viable adult female offspring are produced per mite in AHB, compared to 1.0 in EHB.

Integrated control of acaricide-resistant Boophilus microplus populations on grazing cattle in Mexico using vaccination with Gavac and amidine treatments.

Abstract: Throughout most of the twentieth century, tick infestations on cattle have been controlled with chemical acaricides, typically administered by dipping or spraying. This approach can cause environmental and residue problems and has created a high incidence of acaricide resistance within tick populations in the field. Recently we developed a vaccine against Boophilus microplus employing a recombinant Bm86 antigen preparation (Gavac)™, (Heber Biotec S.A., Havana, Cuba) which has been shown to induce a protective response in vaccinated animals. Here we show for the first time under field conditions a near 100% control of B. microplus populations resistant to pyrethroids and organophosphates, by an integrated system employing vaccination with Gavac™ and amidine treatments. This method effectively controls tick infestations while reducing the number of chemical acaricide treatments and consequently the rise of B. microplus populations resistant to chemical acaricides.

Evolution and systematics of the Chelicerata

Abstract: After approximately 40 years of discussion about the question whether the Arthropoda are a monophyletic or a paraphyletic group, or even a polyphyletic assemblage of unrelated taxa, most morphologists, palaeontologists and molecular taxonomists agree that the Arthropoda are a monophylum. The Euarthropoda are composed of the Arachnomorpha and Mandibulata. Myriapods are usually considered to be mandibulates; however, new molecular data as well as some morphological characters show similarities which the Myriapoda share with the Chelicerata, suggesting that there is no taxon Antennata or Atelocerata. Chelicerata are usually considered to be the sister group of Trilobita or, more correctly, Trilobita branch off from the chelicerate stem line. The first adaptive radiation of the Chelicerata took place in the Cambrian. All extant and some extinct orders were present during the Carboniferous. Two systems are compared. It is suggested that the Chelicerata contain the Pantopoda and Euchelicerata. The Euchelicerata are divided into Xiphosura and terrestrial Arachnida. Scorpiones are considered to be the sister group of all other arachnids, the Lipoctena, and these are further divided into the Megoperculata (Uropygi, Amblypygi and Araneae) and Apulmonata (all other groups). The Acari are tentatively considered to be a monophylum and the sister group of the Ricinulei. However, the Actinotrichida and Anactinotrichida diverged early and therefore have had a long history of independent evolution.

Spider mites avoid plants with predators

Abstract: While searching for food, prey can use cues associated with their predators to select patches with a reduced predation risk In many cases, odours indicate the presence of both food and predators Spider mites are known to use odours to locate food and mates, but also to avoid interspecific competitors We studied the response of the two-spotted spider mite, Tetranychus urticae, to cues associated with the presence of their predators, the phytoseiid Phytoseiulus persimilis We found that the spider mites strongly avoid plants defended by this predator, but do not avoid plants with another predatory mite, Neoseiulus californicus Since P persimilis is commonly used in the greenhouse where our strain of T urticae was collected and strains of this pest are known to adapt to greenhouse environments, we hypothesize that there has been selection on the pest to recognize its enemy We further hypothesize that there has been no selection to recognize N californicus, as it has not been used against two-spotted spider mites in the greenhouse where our spider mites were collected We discuss the implications of avoidance of predation by spider mites and non-lethal effects of predators for biological control of this pest in greenhouses

Host plant associations in the spider mite Tetranychus urticae (Acari: Tetranychidae): insights from molecular phylogeography

Abstract: This article integrates studies on the genetic variation of T. urticae populations and the interspecific variation of several tetranychid species. It aims at obtaining insights into the roles of the historical, geographical and ecological factors in the partitioning of variation of species. Two types of molecular markers were used to determine whether the patterns of genetic variation in mites inhabiting different host plants can shed light on the existence of host plant associations. The ribosomal sequences of the second internal transcribed spacer (ITS2), which evolves through concerted evolution, are good indicators of long-term isolation between populations and reveal exceptional homogeneity in a worldwide sampling of T. urticae. The mitochondrial cytochrome oxidase I (COI) sequences do not disclose old divergences related to host plant in this mite but rather suggest recent geographic colonization patterns of the species. Allozyme variation on a fine scale gives some evidence of host associations in the case of citrus trees. However, if any divergence of mites related to this host plant exists, it probably prevails in local populations only and it should not be old enough to be revealed by a phylogenetic analysis of mitochondrial COI sequences. The phyletic constraint in the evolution of feeding specificity in the family Tetranychidae is investigated based on a phylogenetic analysis of mitochondrial sequences. The results provide some support for the hypothesis that an evolutionary trend towards polyphagy has occurred in the family. Overall, it seems that the major characteristic of T. urticae is its high colonization potential. Polyphagy has enhanced its successful spread and may have led to connectivity between populations worldwide.

Biology and ecology of trombidiid mites (Acari: Trombidioidea)

Abstract: Most mites of the family Trombidiidae are ectoparasites in the larval stage and free-living predators in the deutonymphal and adult stages on a variety of arthropods, among which are pests of many economic crops. This paper provides an updated review of their systematics, life history, reproduction, behaviour, predator—prey and parasite—host relationships, and population dynamics, with particular reference to their possible role in biological control.

Sequential histopathology at the Rhipicephalus sanguineus tick feeding site on dogs and guinea pigs.

Abstract: The tick Rhipicephalus sanguineus is a very common parasite of dogs worldwide. Dogs seem unable to acquire resistance against this tick species, whereas guinea pigs demonstrate a very strong resistance following primary infestation. We studied the inflammatory reaction at the R. sanguineus tick feeding site on dogs and guinea pigs during primary and tertiary infestations at different time intervals after attachment. Biopsies were collected after 4, 24, 48 and 96 hours. Changes that were found in all experimental groups included a cone of cement around the mouthparts of the tick, epidermal hyperplasia, edema and inflammatory cell infiltration in the dermis directly underneath the tick attachment site. Dogs reacted to ticks mainly with neutrophils, particularly after repeated exposure. Mast cells and mononuclear leukocytes were also present. Guinea pigs reacted to R. sanguineus mainly with mononuclear cells, eosinophils and basophils. These cells were particularly numerous after repeated exposure to R. sanguineus. Our results suggest that basophils and eosinophils are involved in resistance of guinea pigs to R. sanguineus and that neutrophils in dogs have little effect against this tick species.

Spatial distribution and coincidence of Neoseiulus californicus and Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae) on strawberry

Abstract: In strawberry greenhouses in La Plata (Buenos Aires, Argentina), Tetranychus urticae is a major pest and Neoseiulus californicus is its most important established phytoseiid predator. The purpose of this study was to determine the spatial distribution and coincidence of N. californicus and T. urticae on strawberry. T. urticae populations exhibited density variations that were followed, with some temporal delay, by those of the predator. In general terms, N. californicus exhibited lower aggregation than T. urticae. The index of dispersion (I) of T. urticae had values significantly greater than 1 in 100% of the sampling dates. The percentage of infested leaflets increased with prey density in a curvilinear way, ranging from 80 to 100% when density was higher than 100 individuals/leaflet. N. californicus had values of I higher than unity in 86.7% (G1) and 53.8% (G2) of the cases. TaylorOs b and IwaoOs β values were greater than 1 for both populations, this indicating aggregation. IwaoOs results showed larger aggregation units of T. urticae (α=53.24) than of N. californicus (α=3.61), probably due to its higher fecundity and oviposition behaviour of laying eggs in clumps. Both populations were overdispersed, although in general terms, N. californicus exhibited lower aggregation than T. urticae. This would create refuges for the prey, thus increasing the persistence of the system. Index of coincidence of predator (Ic) was high most of the time even at low densities of both populations, decreased abruptly at the end of an interaction cycle and was similar at greenhouse and plant spatial scales. The high spatial coincidence of N. californicus with T. urticae suggests an important dispersal capacity of the predator and a high ability to detect leaflets with prey. The refuge index for the prey decreased with predator density and was higher at greenhouse scale than at plant scale, both at similar predator densities. At greenhouse scale and despite high predator density, the prey had a 10%-refuge, which would lead to the system persistence. Results of the present study suggest that N. californicus is a promising established natural enemy for controlling T. urticae on strawberry.

Density of deer in relation to the prevalence of Borrelia burgdorferi s.l. in Ixodes ricinus nymphs in Rambouillet forest, France.

Abstract: The Rambouillet Forest, a Lyme disease-endemic area near Paris, France, was surveyed from September 1994 to October 1995 to determine the risk periods and zones for humans. Firstly, during the period of Ixodes ricinus activity, abundance of nymphs is greater in spring than in autumn. Secondly, we observed significant variation in nymphal abundance between zones according to the density of cervids. The polymerase chain reaction (PCR) was used to detect DNA of Borrelia burgdorferi sensu lato in 461 unfed nymphs. DNA was detected in 38 nymphs (8.2%). By genospecific PCR based on the OspA gene, we detected the three pathogenic spirochetes with occurrences of 10.3, 31.1 and 58.6 for B. burgdorferi s.s., Borrelia garinii and Borrelia afzelii, respectively, indicating that B. afzelii is probably the main Borrelia species in the Rambouillet Forest. Finally, 11.5% of positive nymphs exhibited a double infection. Infection rates of I. ricinus nymphs by B. burgdorferi s.l. were not significantly different throughout the year for a given area, indicating that the risk periods of acquiring Lyme disease are mainly linked to nymph activity and correspond to spring and autumn. Likewise infection rates of nymphs were not significantly different between zones with a high density of deer (more than 100 animals per 100 ha) and zones with lower deer density (less than 20 animals per 100 ha). In addition to the role of deer as an amplifier of tick populations, these data indicate that zones with a high density of cervids should be considered as higher risk areas. © Rapid Science Ltd. 1998

Geostatistics as Predictive Tools to Estimate Ixodes ricinus (Acari: Ixodidae) Habitat Suitability in the Western Palearctic From AVHRR Satellite Imagery

Abstract: Geostatistics (cokriging) were used to model the cross-correlated information between satellite-derived vegetation and climate variables and actual records of the tick Ixodes ricinus in the western Palearctic. The output was used to map the habitat suitability for I. ricinus on a continental scale. A database of collecting localities of I. ricinus was built up from a total of 812 records. This database has been cross-tabulated with satellite NOAA AVHRR pictures obtained from 1982 to 1994 over the Palearctic at 10 day intervals, with a resolution of 8 km per pixel. A cokriging system was generated to exploit satellite-derived data and to estimate the distribution of I. ricinus. Three vegetation (standard NDVI values) and four temperature variables output the habitat suitability prediction with a sensitivity of 0.98 and a specificity of 0.92. Results obtained with the model closely agreed with actual records of the tick, with 4 and 3% of false-positive and false-negative sites, respectively. Such statistical analysis can guide field work towards the correct interpretation of the distributional limits of ticks and may also be used to make predictions about the impact of global change on tick distributional ranges.

Abundance of ticks (Acari: Ixodidae) infesting the western fence lizard, Sceloporus occidentalis, in relation to environmental factors.

Abstract: We examined the impact of environmental characteristics, such as habitat type, topographic exposure and presence of leaf litter, on the abundance of Ixodes pacificus ticks infesting the western fence lizard (Sceloporus occidentalis) at the University of California Hopland Research and Extension Center (HREC), Mendocino County, California. A total of 383 adult lizards were slip-noosed and examined for tick infestation in April and May 1998. At least 94% of the lizards were infested by ticks and at least 20% of the females and 33% of the males carried > 15 ticks. This intensive utilization of western fence lizards (which do not serve as natural reservoirs for Lyme disease spirochetes) by subadult ticks, is probably the primary reason for the low prevalence of infection with Borrelia burgdorferi in I. pacificus nymphs and adults previously recorded at the HREC. Tick loads were higher on male than female lizards. Also, male lizards were generally more heavily infested in late April than in late May. The prevalence of tick infestation exceeded 88% in all habitat types but males collected in woodland and grass/woodland edges had higher tick loads than those collected in open grassland. Male lizards captured in open, exposed grassland tended to carry heavier tick loads in northern/eastern, as compared to southern/western, exposures, and when leaf litter was present.

Larval size relative to larval feeding, cannibalism of larvae, egg or adult female size and larval–adult setal patterns among 13 phytoseiid mite species

Abstract: Phytoseiid mite larvae vary in size and feeding type We compared larval size to feeding by larvae, cannibalism of larvae by adult females, egg and adult female size and the setae lengths of larvae and adults among 13 species There was no relationship between size of larvae and either feeding by larvae or cannibalism of larvae by adult female mites Correlations were highest between larval size as measured by idiosoma plus extended leg lengths and adult female size of idiosoma plus extended leg lengths (r2=0746), while next highest was larval idiosoma length and adult female idiosoma length (r2=0662) and then larval idiosoma length and egg length (r2=0579) Based on idiosoma length, Phytoseiulus persimilis had the largest larvae (non-feeding) among species and Euseius finlandicus had the smallest larvae (obligatory feeding) However, based on idiosoma length plus extended leg length, obligatory feeding larvae (on pollen or mites) of E finlandicus and Euseius hibisci were largest and facultative feeding larvae (on mites) of Neoseiulus californicus and obligatory feeding larvae (on mites) of Galendromus occidentalis were the smallest Among species with non- or facultative feeding larvae, Amblyseius andersoni and Neoseiulus barkeri had larger larvae and Typhlodromus pyri and Neoseiulus fallacis had smaller larvae when leg lengths were included in larval size Setae lengths of larvae versus adult females (after adjustment for body sizes) showed high correlation for j6 (r2=0942) and s4 (r2=0854), but low correlation for larval Z4 versus adult female Z4 (r2=0084) or Z5 (r2=0063) Overall, larval morphological traits were most closely correlated to traits of other life stages, although for setae there were some exceptions Differences in the functions of setae j6, s4 and Z4 in the larva versus adult female are discussed

Interactions in a tritrophic acarine predator– prey metapopulation system: prey location and distance moved by Phytoseiulus persimilis (Acari: Phytoseiidae)

Abstract: The between-plant movement of the predatory mite Phytoseiulus persimilis was studied in a greenhouse. The aims were to determine the distance moved by P. persimilis and the response of the predator to the location of a plant infested with two-spotted spider mite, Tetranychus urticae. In addition, we tested whether the predator exhibits random movement between plants or whether its dispersal is oriented. We found that a high proportion of the predators released on a central plant were able to reach plants at the periphery provided the plants were connected to the central plant with 'bridges'. The results further showed that P. persimilis does not disperse randomly to the surrounding plants. The distribution of immigrants was influenced by the position of an infested plant in the neighbourhood, but light/shadow effects in the greenhouse may also influence the choice of direction. The likely implications of the findings for biological control are discussed. © Rapid Science Ltd. 1998

Population dynamics of ticks on indigenous cattle in a pastoral dry to semi-arid rangeland zone of Uganda.

Abstract: Studies on seasonality and population dynamics of ticks on indigenous cattle and their crosses (calves) were carried out in Buruli Ranching Scheme, Nabiswera, Luwero district of Uganda on three treatment groups of animals: group 1 (twice a week dipping), group 2 (once a month dipping) and group 3 (no tick control). During this study, four major species of ticks of economic importance were recorded in decreasing order of abundance: Rhipicephalus appendiculatus, Rhipicephalus evertsi evertsi, Amblyomma variegatum and Boophilus decoloratus. Of these ticks, a seasonal pattern of activity was only observed in R. appendiculatus ticks, with peak activities occurring during rainy seasons. Greater numbers of ticks were recorded on cows than calves in the three treatment groups, with the exception of A. variegatum where the reverse occurred. The mean numbers of ticks per animal were highly significantly different (p 0.05) were observed in mean tick numbers between group 2 and 3 animals. Highly significant differences (p < 0.01) were observed in mean tick numbers on cows and calves (more than 12 months old) in different calving seasons. The state of lactation only affected tick counts on cows in group 1; significantly more ticks (p < 0.01) were observed in lactating than non-lactating cows. Furthermore, significantly greater (p < 0.05) numbers of ticks (with the exception of B. decoloratus) were recorded during the second year of study (March 1992–May 1993) than the first year (January 1991–February 1992), despite lower rainfall during the former period. © Rapid Science Ltd. 1998

Juvenile survival and development in Euseius finlandicus, Typhlodromus pyri and Kampimodromus aberrans (Acari: Phytoseiidae) feeding on con- and heterospecific immatures

Abstract: Juvenile survival and development in Euseius finlandicus (Oudemans), Typhlodromus pyri Scheuten and Kampimodromus aberrans (Oudemans) feeding on con- and heterospecific phytoseiid immatures were investigated in the laboratory at 25 ± 1 °C and 65 ± 5% RH. More than 50% of T. pyri protonymphs preying on larvae of K. aberrans or E. finlandicus reached the adult stage. The mean developmental time of T. pyri from the protonymphal stage to adulthood was 6.3 days when feeding on K. aberrans and 7.5 days when feeding on E. finlandicus. The majority (approximately 90%) of K. aberrans protonymphs feeding on larvae of T. pyri or E. finlandicus died before reaching the deutonymphal stage; in both cases only one individual completed juvenile development. Euseius finlandicus larvae require food to reach the subsequent life stage, in contrast to larvae of T. pyri and K. aberrans, which usually do not feed at all: 10% of E. finlandicus immatures feeding on larvae of K. aberrans or T. pyri completed juvenile development (mean developmental time from larva to adult 7.0 and 6.7 days, respectively). Cannibalizing immatures of T. pyri and K. aberrans were able to reach adulthood, whereas those of E. finlandicus were not. Unfed immatures of T. pyri lived longer than the corresponding stages of E. finlandicus and K. aberrans. The present study indicates that phytoseiid immatures are suitable prey for developing stages of polyphagous phytoseiids. Since E. finlandicus, T. pyri and K. aberrans partly inhabit the same plant species, their immatures can be regarded as potential prey for competitive phytoseiids in times of food scarcity.

Differential Effects of Plant Species on a Mite Pest (Tetranychus Urticae) and its Predator (Phytoseiulus Persimilis): Implications for Biological Control

Abstract: The influence of plant species on the population dynamics of the spider mite pest, Tetranychus urticae, and its predator, Phytoseiulus persimilis, was examined as a prerequisite to effective biological control on ornamental nursery stock. Experiments have been done to investigate how the development, fecundity and movement of T. urticae, and the movement of P. persimilis were affected by plant species. A novel experimental method, which incorporates plant structure, was used to investigate the functional response of P. persimilis. Development times for T. urticae were consistent with published data and did not differ with plant species in a biologically meaningful way. Plant species was shown to have a major influence on fecundity (P < 0.001) and movement of the pest mite (P < 0.01), but no influence on the movement of the predator. The movement of both pest and predator was shown to be related to the density of the adult pest mites on the plant (P < 0.001). Plant structure affected the functional response, particularly in relation to the ability of the predator to locate prey at low densities. The impact of these findings on the effective use of biological control on ornamental nursery stock is discussed.