Species traits and environmental characteristics together regulate ant‐associated biodiversity

Host‐associated organisms (e.g., parasites, commensals, and mutualists) may rely on their hosts for only a portion of their life cycle. The life‐history traits and physiology of hosts are well‐known determinants of the biodiversity of their associated organisms. The environmental context may strongly influence this interaction, but the relative roles of host traits and the environment are poorly known for host‐associated communities. We studied the roles of host traits and environmental characteristics affecting ant‐associated mites in semi‐natural constructed grasslands in agricultural landscapes of the Midwest USA. Mites are frequently found in ant nests and also riding on ants in a commensal dispersal relationship known as phoresy. During nonphoretic stages of their development, ant‐associated mites rely on soil or nest resources, which may vary depending on host traits and the environmental context of the colony. We hypothesized that mite diversity is determined by availability of suitable host ant species, soil detrital resources and texture, and habitat disturbance. Results showed that that large‐bodied and widely distributed ant species within grasslands support the most diverse mite assemblages. Mite richness and abundance were predicted by overall ant richness and grassland area, but host traits and environmental predictors varied among ant hosts: mites associated with Aphaenogaster rudis depended on litter depth, while Myrmica americana associates were predicted by host frequency and grassland age. Multivariate ordinations of mite community composition constructed with host ant species as predictors demonstrated host specialization at both the ant species and genus levels, while ordinations with environmental variables showed that ant richness, soil texture, and grassland age also contributed to mite community structure. Our results demonstrate that large‐bodied, locally abundant, and cosmopolitan ant species are especially important regulators of phoretic mite diversity and that their role as hosts is also dependent on the context of the interaction, especially soil resources, texture, site age, and area.     

Development of species‐specific primers for rapid diagnosis of Tetranychus urticae,T. kanzawai,T. phaselus and T. truncatus (Acari: Tetranychidae)

Species diagnosis is of the utmost importance to both pest management and plant quarantine services. Because of difficulties in the morphological diagnosis of spider mites, molecular techniques are of great value to rapidly and accurately diagnose closely related species. We examined four species of genus Tetranychus (the green and red forms of T. urticae, and T. kanzawai, T. phaselus and T. truncatus), which are found in Korea and are of significance to plant quarantine services. DNA samples isolated from a single egg, larva or adult weighed 64–188 ng. We designed species‐specific primers by performing sequence alignment for 107 sequences of the ribosomal internal transcribed spacer 2 (ITS2) region, which we obtained from GenBank, and sequences generated in this study. Specific nucleotides of each species were selected for designing primers specific for each species. Each species‐specific primer pair, when used to perform PCR analyses, detected only the species from which it originated. However, a T. urticae‐specific primer pair did not discriminate between the green and red forms of this species. These species‐specific primers can be applied in practice for the rapid and accurate diagnosis of spider mite species in plant quarantine and in agricultural fields.     

New methods for the assessment of mite numbers and results obtained for several textile objects

Summary The assessment of mite numbers in textile objects is important with regard to measures aimed at mite control. The standard method is to take a dust sample and to separate the mites from the dust by means of flotation. The results of mite assessment can be improved using methods based on the natural mobility of the mites; the so-called Mobility Test makes use of the intrinsic movement tendencies of the mites, whereas the Heat Escape Method uses the mobility of the mites in connection with the effects of heat. An example concernig two jackets shows the difference in results of mite assessment when using the conventional method (dust sample and flotation) on the one hand, and the new methods (Mobility Test and Heat Escape Method) on the other. It is shown that the conventional method can only supply relative mite numbers. The new methods also enable the user to monitor more efficiently the use of acaricide agents in mite control. This is demonstrated using the example of two beds and a carpet taken from a children's bedroom. The considerably higher numbers of mites suggest that the risk of the occurence of mite allergens and their penetration into the indoor air is even greater than previously assumed.     

Dampness,mites and respiratory allergy

Summary This paper reviews the relationships between humidity, house-dust mites and respiratory allergy. In vitro relationship between relative humidity and house-dust mite growth are quite clear cut. In real conditions also, there is a significant association between relative humidity and the presence of live mites. The relevance of house-dust mites for respiratory allergy lies on clinical, physiopathological and mostly on epidemiological data. The latter demonstrate a correlation between exposure to mites and risk of sensitization and development of overt allergic diseases. Lastly, humidity of dwellings is linked to respiratory allergy. These results should lead to building safer dwellings for allergic subjects, or modifying existing dwellings. In this respect, emphasis should be put on a proper ventilation rate and also a proper behaviour of inhabitants in order to minimize humidity production.     

Control of sex ratio by female spider mites

Control of sex ratio in the progenies of mated female spider mites was investigated in two laboratory experiments. In Experiment I, a single strain of Tetranychus urticae Koch was reared in four different environments. In Experiment II, 4 different geographic strains of T. urticae were reared in a single environment.Results indicated that spider mite females were able to control the sex ratio of their progeny at two levels: an initial control of mean population ratio according to ovipositional environment. In addition, a secondary control resulted in an approximately uniform daily ratio. Although each parental female produced a varying number of eggs from day to day, a more or less constant fraction of those eggs were fertilized every day. It is concluded that both of these characteristics are probably important to the colonizing ability of the species.

---

Résumé L'étude de la régulation du sexe de la descendance de femelles inséminées d'acariens est basée sur deux expériences de laboratoire. Dans l'expérience I, une lignée de Tetranychus urticae a été élevée dans deux conditions différentes de qualité des feuilles pendant le développement des parents, d'une part, pendant leur ponte et le développement de la descendance d'autre part. Dans l'expérience II, quatre souches géographiques différentes de T. urticae ont été élevées dans les mêmes conditions.Il est apparu nettement que les femelles dans des conditions différentes ont donné des descendances avec des taux sexuels variant dans certaines limites. Ces différences étaient statistiquement significatives dans les duex lots de données expérimentales. Les taux sexuels des populations d'acariens variaient aussi avec les conditions écologiques. Dans les bonnes conditions, la proportion de femelles dans la descendance était la plus élevée. Les taux sexuels des populations variaient aussi entre les quatre souches géographiques.Les analyses ont aussi révélé que les femelles d'acariens sont capables de contrôler le taux sexuel à deux niveaux: une régulation initiale du taux de la population en fonction des conditions écologiques ou de la lignée géographique et un contrôle secondaire qui s'est traduit par un taux quotidien approximativement uniforme.En utilisant un argument mathématique simple incorporant la fécondité caractéristique des acariens, nous avons conclu que ces deux caractéristiques de la rulation sont probablement d'une importance capitale pour le pouvoir colonisateur de cette espèce.

     

Effect of water stress on abundance of twospotted spider mite on soybeans under greenhouse conditions

A rope wick technique was used to establish different levels of water stress in potted, greenhouse-grown soybean, Glycine max (L.) Merrill, plants. Water stress reduced, within a single generation, the overall abundance (number of mites/cm² leaf) of the twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) and particularly influenced female mites and eggs. Mites were most numerous in the upper strata of soybean plants on youger and possibly more nutritious leaves.

---

Influence de l'arrosage sur l'abondance de Tetranychus urticae sur soja, Glycine max en serre

Résumé Un arrosage par capillarité contrôlé a été utilisé pour maintenir différentes teneurs en eau dans des pieds empotés de G. max. Le stress hydrique a réduit, en une génération, la densité de T. urticae (nombre d'acariens/cm² de feuille), et particulièrement celle des femelles et des oeufs. Les acariens étaient plus nombreux sur les feuilles les plus jeunes et peut-être les plus nutritives des strates supérieures des pieds de soja.

     

Two new species of oribatid mites of the genus Truncozetes (Acari,Oribatida, Epactozetidae) from?Ecuador

Two new oribatid mite species of the genus Truncozetes (Oribatida, Epactozetidae), Truncozetes ecuadoriensis sp. n. and Truncozetes monodactylus sp. n., are described from the Ecuadorian soils. The morphology of the gnathosoma and the legs is presented in detail for the first time for the species of Truncozetes. An identification key to all known species of the family Epactozetidae is given.     

Mite‐y bees: bumble bees (Bombus spp., Hymenoptera: Apidae) host a relatively homogeneous mite (Acari) community,shaped by bee species identity but not by geographic proximity

1. Parasites can affect the communities of their hosts; and hosts, in turn, shape communities of parasites and other symbionts. This makes host–symbiont relationships a key but often overlooked aspect of community ecology. 2. Mites associated with bees have a range of lifestyles; however, little is known about mites associated with wild bees or about factors influencing the make‐up of bee‐associated mite communities. This study investigated how mite communities associated with bumble bees (Bombus spp.) are shaped by the Bombus community and geographic proximity. 3. Bees were collected from 15 sites in Ontario, Canada, and examined for mites. Mite abundance and species richness increased with local bee abundance. Several bee species also differed in mite abundance, species richness, prevalence, and diversity. Locally uncommon species tended to have more mites than other bees. Queen bees had the most mites, and males had more mites than workers. 4. Spatial proximity was not a predictor of mite community composition, despite a strong effect of proximity on bee community similarity. 5. On the 11 Bombus spp. examined, 33 mite species were found. Whereas nearly half of these mite species are obligate associates of bumble bees, none was restricted to particular Bombus species. 6. The best predictor of mite community composition was bee identity. Although many parasite communities show strong geographic patterns, the communities of primarily commensalistic bee‐mites in this study did not. These findings have implications for bumble bee conservation, given that pollen‐feeding commensals might become harmful at high densities or act as disease vectors.     

Double-stranded RNA analysis of strawberry plants affected by June yellows

Using an improved method for extraction of dsRNA from strawberry leaf tissue, small quantities of several dsRNA species with mol. wt greater than 1.0 × 10⁶were detected in strawberry plants free from known strawberry viruses but affected by June yellows (JY). No such dsRNA species were detected in plants of Fragaria vesca or seven strawberry cultivars known to be free from JY. Neither JY symptoms nor these dsRNA species were detected in healthy strawberry and F. vesca plants graft-inoculated with tissue from JY-affected plants. It is not known whether the JY-associated dsRNA species are those of a causal agent of JY or are a consequence of the JY condition. Nevertheless, the detection of such dsRNA species in plants affected by JY may offer a possible objective method for detecting the incipient condition in symptomless strawberry plants. However, the concentrations of dsRNA in JY-affected plants are very low and dsRNA analysis is thought not to be sufficiently reliable for routine testing of plants. The occurrence of anomalous dsRNA species in extracts from some strawberry plants was caused by dsRNA from two-spotted spider mites (Tetranychus urticae) infesting the plants.     

Induced resistance against spider mites in cotton: Field verification

Cotton plants that had been damaged by spider mites (Tetranychus spp.) or by mechanical abrasion at the cotyledon stage were less likely to develop infestations of spider mites compared to controls early in the season. These are the first field results to demonstrate that induced resistance can reduce pest populations in an agricultural system. Differences in mite populations early in the season caused by induced resistance did not translate into differences in plant growth or cotton yield at harvest.

---

Vérification au champ de la résistance du coton induite par les acariens

Résumé Les plants de coton qui ont été endommagées, au stade cotylédons, par des acariens ou par une abrasion mécanique, ont moins de chance que les témoins, de présenter ultérieurement des dégats dus aux acariens. C'est la première fois que des résultats montrent qu'une résistance induite peut réduire les populations dans un agrosystème. Les différences ultérieures dans les populations d'acariens, ne transparaissent pas au niveau de la croissance du coton ou de la production au moment de la récolte.