Aspects of cold hardiness in Steganacarus magnus (Acari: Cryptostigmata)

Supercooling points and the presence of antifreeze compounds were measured for both nymphs and adults of Steganacarus magnus (Nicolet) collected from a coniferous forest soil in southern England in March, June and November. The mean supercooling point of nymphs was –14.4°C and of adults, –11.7°C. Acclimation to low temperatures (1–2°C) did not alter these values significantly. The total concentration of antifreeze compounds in the nymphs was 4.46 g mg^-1 and in the adults 0.91 g mg^-1. These results are compared with similar data for other species of cryptostigmatic mites.     

Investigation on the taxonomic status of Steganacarus magnus and Steganacarus anomalus (Acari: Oribatida) using mitochondrial DNA sequences

To test the previously suggested synonymization of S. anomalus with the older S. magnus, a fragment of the mitochondrial COI gene was amplified via the polymerase chain reaction and sequenced. The sequence variation was examined in a total of 327 base pairs for four steganacarid mite populations, two of which belong to S. anomalus, one to S. magnus and one to S. hirsutus. The sequence variation suggests that S. magnus and S. anomalus are not distinct species and that the population from Fioreta (Siena) is more similar to that from Apulia than to the nearer population from the Apuan Alps. The results show the usefulness of this molecular approach as a tool for determining taxonomic status and for suggesting faunistic movements in the past millions of years.     

A new mite superfamily (Acari: Cryptostigmata)

The new superfamily Eutegaeoidea (Acari: Cryptostigmata) is defined and subdivided into three families, viz. Eutegaeidae, Compactozetidae nov., Pterozetidae nov. The Eutegaeidae is considered to possess six genera ( Eutegaeus, Neoeutegaeus, Neseutegaeus, Pareutegaeus, Birotegaeus nov., Atalotegaeus nov.), the Pterozetidae three genera ( Pterozetes, Porrhotegaeus, Dudichella ), and the Compactozetidae four genera ( Compactozetes, Bornebuschia, Hamotegeus, Sadocepheus ). Keys are provided to all taxa down to species and Pareutegaeus similis (Trägardh, 1931) is redescribed from the lectotype.     

Printed in Great Britain The genus Phyllhermannia (Acari: Cryptostigmata)

The genus Phyllhermannia Berlese, 1916 is redefined. Two main groups of species are postulated within the genus, each being further divided into two subgroups. Known species reviewed completely or in part are: P. dentata, P. bimaculata, P. mollis and P. pulcher . New distribution records are given for the New Zealand species P. foliata, P. forsteri, P. mollis, P. phyllophora and P. rubra , together with a distribution map of all species. Some biogeographical comments are included for the genus. P. africana Balogh, 1958 is redescribed and a new species, P. collofi sp.n., is established. A key to the species of the world is provided.     

Species of the genus Crotonia (Acari: Cryptostigmata) from New Zealand

Five new species of Crotonia from New Zealand ( C. cervicorna, C. cupulata, C. longibulbula, C. tuberculata and C. reticulata ) are described as new, and two species ( C. cophinana (Michael 1908) and C. caudatis (Hammer 1966)) are redescribed. Five species groups of the genus are characterized and a key to the adequately described species of the world is presented.     

Seasonality of some Chihuahuan Desert soil oribatid mites (Acari: Cryptostigmata)

1. Reproductive strategies of four species of oribatid mites were investigated in the Chihuahuan Desert from 1981 to 1984.
2. Breeding activity coincided with the summer rainfall period in three of the four cases: Passalozetes neomexicanus, P. californicus and Jornadia larreae. This pattern was not changed by the application of simulated rainfall at other times of the year. The strict seasonality of reproductive behaviour is interpreted as an outcome of strong selection pressure to recruit only when food quality and quantity and microclimate are most favourable.
3. Joshuella striata showed a more flexible pattern which was essentially bimodal. Periods of egg production occurred in winter and also during the summer rainfall period. This pattern is consistent with the known distribution of this species in winter- and summer-rainfall deserts in south-western USA.     

Population dynamics of intertidal oribatid mites (Acari: Cryptostigmata) from the subtropical archipelago of Bermuda

The population dynamics of the three intertidal oribatid species, Alismobates inexpectatus, Fortuynia atlantica and Carinozetes bermudensis, have been studied on the archipelago of Bermuda over the course of a year. All three species are univoltine, showing a clear seasonal demographic pattern, with reproduction from spring to late autumn and a complete standstill of egg production in winter. A seasonal shift in sex ratio could also be observed in all three species and is supposed to be based on sex-dependent mortality. The subtropical climate of Bermuda allows longer reproductive periods than shown in other intertidal or edaphic temperate species and temperature is supposed to be the main factor influencing the demography of these intertidal dwelling mites. Although all three Bermudian species exhibit the same basic seasonal demographic pattern, there are slight temporal shifts in population dynamics, presumably caused by local microclimatic differences among the populations. Larviparity, shown in other littoral oribatid mites, is clearly absent in the present species.     

The seasonal abundance of oribatid mites (Acari: Cryptostigmata) on an irrigated Kikuyu grass pasture

The seasonal abundance of oribatid mites, the intermediate hosts of anoplocephaline cestodes, was studied on an irrigated Kikuyu grass pasture in Transvaal, South Africa. The following species were consistently present: Galumna nuda. Galumna rasilis, Scheloribates elsi and Tectocepheus sarekensis. The mean total number of mites on the herbage peaked in January (3.7 mites g ¹dry herbage) and correlated positively with temperature, relative humidity, rainfall and soil moisture on the day of collection. The mean total number of mites on the herbage including the top 5 cm of soil peaked in April (3.757 mites m ²) and May (3.761 mites m ²), and these numbers correlated positively with radiation on the day of collection. There was a significant decline in the number of mites on the herbage at midday and in the afternoon, but there was no difference in the number on the herbage including the top 5 cm of soil at different times of day. The trends in abundance are also discussed separately for each of the four species.     

Distribution and temperature tolerance of the Antarctic free-living mite Antarcticola meyeri (Acari,Cryptostigmata)

The ecology and physiology of a free-living mite species Antarcticola meyeri, Cryptostigmata, rarely discovered in the Continental Antarctic Zone, were studied near the Japanese Antarctic Base, Syowa Station. The distribution of this mite species correlated noticeably with the distribution of its food, the imperfect lichen species, which grow in moss carpets. Within a limited habitat, this mite species preferred dry carpets to wet carpets. Low humidity appeared disadvantageous to the species at high temperatures (ca. 30°C), but at low temperatures (ca. -25°C), low humidity appeared advantageous. This may explain why this species preferred dry carpets. The mean supercooling point of starved individuals was -30.6°C (nymphs) to-33.9°C (eggs). When fed with lichens, however, it was significantly raised, probably because the gut contents functioned as ice nucleators or contained ice-nucleating agents. Acclimation to low temperatures significantly lowered the supercooling point of larvae but not of other growth stages.     

Distribution of Cryptostigmata and Mesostigmata (Acari) within the litter and soil layers of two subtropical forests

Differences in the litter and soil of northern temperate and tropical and subtropical forest soil and soil faunas are noted. Analyses of the distribution and abundance of Cryptostigmata and Mesostigmata mites in the litter and soil of two Australian subtropical forests are presented. The faunal associations in the litter and soil of these forests are different. It is suggested that the litter and soil habitats of subtropical and tropical forests should be regarded as separate but connected habitats in relation to their fauna. This contrasts with the assumption, for temperate forests, that litter and soil communities are portions of a single system.     

Morphology of the Eyes in adult Hyalomma Truncatum Ticks (Acari: Ixodidae)

The eyes of Hyalomma truncatum ticks are morphologically similar in both sexes. They appear aspaired hemispherical structures situated dorsally between the first and second pair of legs on thelateral scutal margin. Each eye consists of a lens and photoreceptor cells, which are separated by afine fibrillar layer and the hypodermis. The lens contains numerous channels which open beneaththe epicuticle, converge uninterruptedly to the interior of the lens and end below the fine fibrillarlayer. The inner closure of the lens is formed as an oval plateau with a cone-like projectionsituated caudolaterally and eccentrically to the longitudinal axis of the lens. The hypodermis is asingle layer of cells, situated immediately below the fine fibrillar layer. Beneath the hypodermis,directly below the cone-like projection of the inner lens are the photoreceptor cells localized in arosette-like arrangement. Facing the hypodermis, each photoreceptor cell is provided withnumerous microvilli. The microvilli consistently border the microvilli regions of other cells atdifferent angles but are always oriented at a right angle to the lenticular channels. Thephotoreceptor cells are unipolar neurons, whose axons arise from the basal portion of the cell andjoin to nerve fibre bundles forming the optic nerve. It is concluded that the eyes in adult H.truncatum ticks possess all the structures necessary to perceive and conduct light stimuli andvisual signals.     

Geometric morphometric study of geographic and host-related variability in Aceria spp. (Acari: Eriophyoidea) inhabiting Cirsium spp. (Asteraceae)

The russet mite, Aceria anthocoptes (Nalepa), is the only eriophyoid that has been recorded on Cirsium arvense (L.) Scop. It has been noted in several European countries and recently in the USA. In this study we explored the geographic and host-related variability of Aceria spp. inhabiting different Cirsium spp. We applied landmark-based geometric morphometric methods to study morphological variability of three body regions (ventral, coxigenital and prodorsal) of 13 Aceria spp. populations inhabiting five Cirsium spp. in Serbia (Europe) and four Cirsium spp. in Colorado (North America). Analyses of size and shape variation revealed statistically significant differences between Aceria spp. living on European native and North American native Cirsium spp., as well as between A. anthocoptes s.s. inhabiting European C. arvense and North American C. arvense. The coxigenital region was the most informative when considering inter-population shape differences. European Aceria spp. dwelling on Cirsium spp., including A. anthocoptes s.s. from C. arvense, are characterized by higher inter-population size and shape variability than their North American counterparts. This finding supports a Eurasian origin of A. anthocoptes, presumed to consist of a complex of cryptic taxa probably coevolved with host plants in the native environment. Morphological similarity among Aceria spp. inhabiting North American native Cirsium spp. may indicate that speciation of A. anthocoptes started relatively soon after the host shift to plants different from C. arvense in the invaded region.     

Intra- and interspecific predation by adult female Metaseiulus occidentalis and Typhlodromus pyri (Acari: Phytoseiidae) when provisioned with varying densities and ratios of Tetranychus urticae (Acari: Tetranychidae) and phytoseiid larvae

The phytoseiid mites Metaseiulus occidentalis (Nesbitt) and Typhlodromus pyri Schueten are used together and alone as biological control agents against tetranychid pest mites of apple. Their effectiveness as control agents may be impacted by intraguild predation. The effects of prey species and prey density on the rates of inter- and intraspecific predation and oviposition by these two predators were investigated through a series of experiments. Adult female predators were given prey as mixed populations of phytoseiid larvae and larvae of a more preferred species, the spider mite, Tetranychus urticae Koch, at different densities and ratios. Typhlodromus pyri, more of a generalist predator, showed higher rates of predation and cannibalism on phytoseiid immatures at most prey densities and ratios. Manly preference indices indicated that T. pyri switched to feed on phytoseiid larvae at higher prey levels and ratios of T. urticae than M. occidentalis. This greater ability to use phytoseiid larvae as prey may help stabilize T. pyri populations when more preferred prey is unavailable. This may, in part, explain the observed persistence of T. pyri populations when M. occidentalis populations were decreasing in orchard test plots.     

Predation of Galendromus helveolus (Acari: Phytoseiidae) on Brevipalpus californicus (Acari: Tenuipalpidae)

The false spider mite, Brevipalpus californicus (Banks), is a major citrus pest in Texas. This phytophagous mite causes damage to fruit, leaves and stems of citrus, and is also a vector of citrus leprosis virus. Galendromus helveolus (Chant) is one of the most prevalent predacious mite species found on Texas citrus. The predation potential of G. helveolus on different stages of B. californicus was evaluated in the laboratory. An individual immature G. helveolus mite consumed an average of 30.7 eggs, 53.6 larvae, or 22.7 nymphs of B. californicus before developing to an adult. An individual adult female G. helveolus consumed an average of 164.8 eggs, 369.6 larvae, or 80.9 nymphs of B. californicus. Both immature and adult G. helveolus never fed on adult stage of B. californicus and never completed development. The development times of the immature stages of G. helveolus were 4.5, 4.1 and 4.6 days when fed on eggs, larvae and nymphs of B. californicus, respectively. When G. helveolus fed on the larval stage of B. californicus, the adults had the longest longevity (18.5 days) and the highest fecundity (14.0 eggs/female).