UV radiation elevates arylalkylamine N-acetyltransferase activity and melatonin content in the two-spotted spider mite, Tetranychus urticae

Effects of low dose radiation on behavior rhythm of zebrafish (Danio rerio)

Biological rhythm refers to the internal regulation of various life activities of an organism, which are determined by the specific time structure sequences of each individual. Behavior rhythm is the most intuitive embodiment of biological rhythm. To study the effect of low dose radiation on behavioral rhythm, zebrafish (Danio rerio) was used as a model organism in this study. The early embryos of zebrafish were irradiated at doses of 0.01, 0.1, and 1 Gy to observe the changes in zebrafish development, circadian rhythm, key clock genes, related RNA and protein expression, and melatonin. The results revealed that 0.1 and 1 Gy radiation could lead to different degrees of telencephalic nerve cell apoptosis and the formation of vacuolar structures. 0.1 and 1 Gy radiation could reduce the hatching rate of zebrafish embryos at 72 hpf and delay embryo hatching. The analysis of circadian behavior at 120 hpf demonstrated that 1 Gy dose of radiation altered the circadian rhythm of zebrafish, as well as decreased the distance, amplitude, and phase of movement. RT-PCR analysis of the key clock genes (bmal1b, clock1a, per1b, per2, cry2, and nr1d1) involved in regulating circadian rhythm was performed. The results showed that 1 Gy radiation could interfere with the expression of clock genes in zebrafish embryos and upregulate bmal1b, clock1a, and per1b. Western blot experiments further verified the protein expression of key clock genes, bmal1b and clock. Detection of melatonin secretion at different time points over 24 h showed that radiation doses of 0.1 and 1 Gy could increase melatonin secretion. Based on these findings, it is speculated that a certain dose of radiation may affect melatonin secretion, which impacts the telencephalon structure and ontogeny of zebrafish, delays hatching, and changes the circadian rhythm. This effect is thought to be achieved through upregulating the expression of circadian rhythm genes, clock1a and per1b and related proteins, which may be responsible for the abnormal circadian rhythm caused by radiation.

Circadian and Neuroendocrine Basis of Photoperiodism Controlling Diapause in Insects and Mites: A Review

The photoperiodic system is concealed in the highly complex black-box, comprising four functional subunits: 1) a photo/thermo-sensitive input unit, 2) a photoperiodic clock based on a circadian system, 3) a condenser unit counting the number of inductive signals, and 4) a neuroendocrine switch that triggers a phenotypic shift. This review aims to summarize the research history and current reach of our understanding on this subject to connect it with the molecular mechanism of the circadian clock rapidly being unveiled. The review also focuses on the mode of intersubunit information transduction. It will scan the recent advancement in research on each functional subunit, but special attention will be given to the circadian clock-endocrine conjunct and the role of melatonin signaling in the regulation of insect photoperiodism. Prothoracicotropic hormone (PTTH) probably plays the most crucial role in the regulation of pupal diapause, which is the simplest model system of diapause regulation by hormones investigated so far, particularly in the Chinese oak silkmoth (Antheraea pernyi). A search for the trigger to release the PTTH found some candidates, that is, indoleamines. Indolamine metabolism is controlled by arylalkylamine N-acetyltransferase (aaNAT). Indolamine dynamics and aaNAT enzymatic activity changed according to photoperiods. aaNAT activity and melatonin content in the brain showed not only a photoperiodic response but also a circadian fluctuation. aaNAT had multiple E-boxes, suggesting that it is a clock-controlled gene (ccg), which implies that cycle (cyc, or brain-muscle Arnt-like 1 = Bmal1)/Clock (Clk) heterodimer binds to E-box and stimulates the transcription of aaNAT, which causes the synthesis of melatonin. RNAi against transcription modulators, cyc, or Clk downregulated aaNAT transcription, while RNAi against repressor of cyc/Clk, per upregulated aaNAT transcription. Immunohistochemical localization showed that the circadian neurons carry epitopes of melatonin-producing elements such as aaNAT, the precursor serotonin, HIOMT, and melatonin as well as clock gene products such as cyc-ir, Per-ir, and dbt-ir, while PTTH-producing neurons juxtaposed against the clock neurons showed hMT2-ir in A. pernyi brain. Melatonin probably binds to the putative melatonin receptor (MT) that stimulates Ca2+ influx, which in turn activates PKC. This induces Rab 8 phosphorylation and exocytosis of PTTH, leading to termination of diapause. All the PTTH-expressing neurons have PKC-ir, and Rab8-ir. When diapause is induced and maintained under short days, serotonin binding to 5HTR1B suppresses PTTH release in a yet unknown way. RNAi against this receptor knocked out photoperiodism; short day response is blocked and diapause was terminated even under the short day condition. The result showed that a relatively simple system controls both induction and termination in pupal diapause of A. pernyi: the circadian system regulates the transcription of aaNAT as a binary switch, the enzyme produces a melatonin rhythm that gates PTTH release, and 5HTR1B and MT are probably also under photoperiodic regulation. Finally, we listed the remaining riddles which need to be resolved, to fully understand this highly complex system in future studies.

Within-plant Distributions and Density of Amblyseius swirskii (Acari: Phytoseiidae) as Influenced by Interactions Between Plastic Mulch and Vegetable Crop Species

Plastic mulch of different colors and ultraviolet (UV) reflectivity individually or combined with released arthropod predators is an important component of an integrated pest management strategy. In 2015 and 2016, we evaluated the density and within-plant distribution of a released predatory mite, Amblyseius swirskii Athius-Henriot (Acari: Phytoseiidae) in snap bean (Phaseolus vulgaris L.), cucumber (Cucumis sativus L.), yellow squash (Cucurbita pepo L.), eggplant (Solanum melongena L.), Jalapeno pepper (Capsicum annuum L.), and tomato (Solanum lycopersicum L.) grown on different plastic mulches. The mulch treatments evaluated were: metalized top and black bottom, metalized top and white bottom, black-on-black, black-on-white, white-on-black, and bare soil with no mulch. Crop species had a significant effect on the density of A. swirskii. Eggplant and cucumber had higher numbers of A. swirskii than the other crops tested in 2015. In 2016, the density of A. swirskii was higher on eggplant than on cucumber. There was a variation in the distribution of A. swirskii in different strata of the plant canopies with the highest number in the bottom stratum of each crop, which was positively correlated with the population of Thrips palmi Karny (Thysanoptera: Thripidae). Mulch type had no effect on the density or distribution of A. swirskii in any strata of any of the crops tested. The results of this study indicate that releasing A. swirskii is compatible with the use of UV-reflective mulch. This information about host preference and within-plant distribution of A. swirskii should be of value in pest management programs for the crops studied.

Comparative transcriptome and metabolome analysis of Ostrinia furnacalis female adults under UV-A exposure

Ultraviolet A (UV-A) radiation is a significant environmental factor that causes photoreceptor damage, apoptosis, and oxidative stress in insects. Ostrinia furnacalis is an important pest of corn. To understand the adaptation mechanisms of insect response to UV-A exposure, this study revealed differentially expressed genes (DEGs) and differently expressed metabolites (DEMs) in O. furnacalis under UV-A exposure. Three complementary DNA libraries were constructed from O. furnacalis adult females (CK, UV1h, and UV2h), and 50,106 expressed genes were obtained through Illumina sequencing. Of these, 157 and 637 DEGs were detected in UV1h and UV2h after UV-A exposure for 1 and 2 h, respectively, compared to CK, with 103 and 444 upregulated and 54 and 193 downregulated genes, respectively. Forty four DEGs were detected in UV2h compared to UV1h. Comparative transcriptome analysis between UV-treated and control groups revealed signal transduction, detoxification and stress response, immune defense, and antioxidative system involvement. Metabolomics analysis showed that 181 (UV1h vs. CK), 111 (UV2h vs. CK), and 34 (UV2h vs. UV1h) DEMs were obtained in positive ion mode, while 135 (UV1h vs. CK), 93 (UV2h vs. CK), and 36 (UV2h vs. UV1h) DEMs were obtained in negative ion mode. Moreover, UV-A exposure disturbed amino acid, sugar, and lipid metabolism. These findings provide insight for further studies on how insects protect themselves under UV-A stress.

Identification of differentially expressed proteins in Ostrinia furnacalis adults after exposure to ultraviolet A

Ultraviolet A (UVA), the major component of solar UV irradiation, is an important environmental factor inducing damage to insects including cell death, photoreceptor damage, and oxidative stress. In order to improve understanding of the adaptation mechanisms of insect after UVA exposure, a comparative proteomic analysis was carried out to reveal differential protein expression in Ostrinia furnacalis. Three-day-old adults were treated with UVA for 1 h. Total proteins of control and UVA-treated insects were examined using two-dimensional electrophoresis (2-DE). 2-DE analysis demonstrated that 19 proteins were increased and 18 proteins were decreased significantly in O. furnacalis after UVA exposure, respectively. Thirty differentially expressed proteins were successfully identified by mass spectrometry. The identified proteins were involved in diverse biological processes, such as signal transduction, transport processing, cellular stress, metabolisms, and cytoskeleton organization. Our results reveal that the response patterns of O. furnacalis to UVA irradiation are complex and provide novel insights into the adaptation response to UVA irradiation stress.

Egg hatching response to a range of ultraviolet-B (UV-B) radiation doses for four predatory mites and the herbivorous spider mite Tetranychus urticae

Egg hatchability of four predatory mites-Phytoseiulus persimilis Athias-Henriot, Iphiseius [Amblyseius] degenerans Berlese, Amblyseius swirskii Athias-Henriot, and Euseius finlandicus Oudemans (Acari: Phytoseiidae)-and the spider mite Tetranychus urticae Koch (Acari: Tetranychidae) was determined under various UV-B doses either in constant darkness (DD) or with simultaneous irradiation using white light. Under UV-B irradiation and DD or simultaneous irradiation with white light, the predator's eggs hatched in significantly lower percentages than in the control non-exposed eggs, which indicates deleterious effects of UV-B on embryonic development. In addition, higher hatchability percentages were observed under UV-B irradiation and DD in eggs of the predatory mites than in eggs of T. urticae. This might be caused by a higher involvement of an antioxidant system, shield effects by pigments or a mere shorter duration of embryonic development in predatory mites than in T. urticae, thus avoiding accumulative effects of UV-B. Although no eggs of T. urticae hatched under UV-B irradiation and DD, variable hatchability percentages were observed under simultaneous irradiation with white light, which suggests the involvement of a photoreactivation system that reduces UV-B damages. Under the same doses with simultaneous irradiation with white light, eggs of T. urticae displayed higher photoreactivation and were more tolerant to UV-B than eggs of the predatory mites. Among predators variation regarding the tolerance to UV-B effects was observed, with eggs of P. persimilis and I. degenerans being more tolerant to UV-B radiation than eggs of A. swirskii and E. finlandicus.

Physiological and molecular mechanisms underlying photoperiodism in the spider mite: comparisons with insects

Photoperiodism is an adaptive, seasonal timing system that enables organisms to coordinate their development and physiology to annual changes in the environment using day length (photoperiod) as a cue. This review summarizes our knowledge of the physiological mechanisms underlying photoperiodism in spider mites. In particular, the two-spotted spider mite Tetranychus urticae is focussed, which has long been used as a model species for studying photoperiodism. Photoperiodism is established by several physiological modules, such as the photoreceptor, photoperiodic time measurement system, counter system, and endocrine effector. It is now clear that retinal photoreception through the ocelli is indispensable for the function of photoperiodism, at least in T. urticae. Visual pigment, which comprised opsin protein and a vitamin A-based pigment, is involved in photoreception. The physiological basis of the photoperiodic time measurement system is still under debate, and we have controversial evidence for the hourglass-based time measurement and the oscillator-based time measurement. Less attention has been centred on the counter system in insects and mites. Mite reproduction is possibly regulated by the ecdysteroid, ponasterone A. Prior physiological knowledge has laid the foundation for the next steps essential for the elucidation of the molecular mechanisms driving photoperiodism.

Determination of melatonin in Acyrthosiphon pisum aphids by liquid chromatography-tandem mass spectrometry

Melatonin is a hormone mainly involved in the regulation of circadian and seasonal rhythms in both invertebrates and vertebrates. Despite the identification of melatonin in many insects, its involvement in the insect seasonal response remains unclear. A liquid chromatography tandem mass spectrometry (LC-MS/MS) method has been developed for melatonin analysis in aphids (Acyrthosiphon pisum) for the first time. After comparing two different procedures and five extraction solvents, a sample preparation procedure with a mixture of methanol/water (50:50) was selected for melatonin extraction. The method was validated by analyzing melatonin recovery at three spiked concentrations (5, 50 and 100 pg/mg) and showed satisfactory recoveries (75-110%), and good repeatability, expressed as relative standard deviation (<10%). Limits of detection (LOD) and quantitation (LOQ) were 1 pg/mg and 5 pg/mg, respectively. Eight concentration levels were used for constructing the calibration curves which showed good linearity between LOQ and 200 times LOQ. The validated method was successfully applied to 26 aphid samples demonstrating its usefulness for melatonin determination in insects. This is -to our knowledge- the first identification of melatonin in aphids by LC-MS/MS.

Structures and functions of insect arylalkylamine N-acetyltransferase (iaaNAT); a key enzyme for physiological and behavioral switch in arthropods

The evolution of N-acetyltransfeases (NATs) seems complex. Vertebrate arylalkylamine N-acetyltransferase (aaNAT) has been extensively studied since it leads to the synthesis of melatonin, a multifunctional neurohormone prevalent in photoreceptor cells, and is known as a chemical token of the night. Melatonin also serves as a scavenger for reactive oxygen species. This is also true with invertebrates. NAT therefore has distinct functional implications in circadian function, as timezymes (aaNAT), and also xenobiotic reactions (arylamine NAT or simply NAT). NATs belong to a broader enzyme group, the GCN5-related N-acetyltransferase superfamily. Due to low sequence homology and a seemingly fast rate of structural differentiation, the nomenclature for NATs can be confusing. The advent of bioinformatics, however, has helped to classify this group of enzymes; vertebrates have two distinct subgroups, the timezyme type and the xenobiotic type, which has a wider substrate range including imidazolamine, pharmacological drugs, environmental toxicants and even histone. Insect aaNAT (iaaNAT) form their own clade in the phylogeny, distinct from vertebrate aaNATs. Arthropods are unique, since the phylum has exoskeleton in which quinones derived from N-acetylated monoamines function in coupling chitin and arthropodins. Monoamine oxidase (MAO) activity is limited in insects, but NAT-mediated degradation prevails. However, unexpectedly iaaNAT occurs not only among arthropods but also among basal deuterostomia, and is therefore more apomorphic. Our analyses illustrate that iaaNATs has unique physiological roles but at the same time it plays a role in a timezyme function, at least in photoperiodism. Photoperiodism has been considered as a function of circadian system but the detailed molecular mechanism is not well understood. We propose a molecular hypothesis for photoperiodism in Antheraea pernyi based on the transcription regulation of NAT interlocked by the circadian system. Therefore, the enzyme plays both unique and universal roles in insects. The unique role of iaaNATs in physiological regulation urges the targeting of this system for integrated pest management (IPM). We indeed showed a successful example of chemical compound screening with reconstituted enzyme and further attempts seem promising.

Superoxide dismutases, SOD1 and SOD2, play a distinct role in the fat body during pupation in silkworm Bombyx mori

One way that aerobic biological systems counteract the generation of reactive oxygen species (ROS) is with superoxide dismutase proteins SOD1 and SOD2 that metabolize superoxide radicals to molecular oxygen and hydrogen peroxide or scavenge oxygen radicals produced by the extensive oxidation-reduction and electron-transport reactions that occur in mitochondria. We characterized SOD1 and SOD2 of Bombyx mori isolated from the fat body of larvae. Immunological analysis demonstrated the presence of BmSOD1 and BmSOD2 in the silk gland, midgut, fat body, Malpighian tubules, testis and ovary from larvae to adults. We found that BmSOD2 had a unique expression pattern in the fat body through the fifth instar larval developmental stage. The anti-oxidative functions of BmSOD1 and BmSOD2 were assessed by exposing larvae to insecticide rotenone or vasodilator isosorbide dinitrate, which is an ROS generator in BmN4 cells; however, exposure to these compounds had no effect on the expression levels of either BmSOD protein. Next, we investigated the physiological role of BmSOD1 and BmSOD2 under environmental oxidative stress, applied through whole-body UV irradiation and assayed using quantitative RT-PCR, immunoblotting and microarray analysis. The mRNA expression level of both BmSOD1 and BmSOD2 was markedly increased but protein expression level was increased only slightly. To examine the differences in mRNA and protein level due to UV irradiation intensity, we performed microarray analysis. Gene set enrichment analysis revealed that genes in the insulin signaling pathway and PPAR signaling pathway were significantly up-regulated after 6 and 12 hours of UV irradiation. Taken together, the activities of BmSOD1 and BmSOD2 may be related to the response to UV irradiation stress in B. mori. These results suggest that BmSOD1 and BmSOD2 modulate environmental oxidative stress in the cell and have a specific role in fat body of B. mori during pupation.

Developmental and light-entrained expression of melatonin and its relationship to the circadian clock in the sea anemone Nematostella vectensis

Background

The primary hormone of the vertebrate pineal gland, melatonin, has been identified broadly throughout the eukaryotes. While the role for melatonin in cyclic behavior via interactions with the circadian clock has only been reported in vertebrates, comparative research has shown that the transcription-translation loops of the animal circadian clock likely date to the cnidarian-bilaterian ancestor, leaving open significant questions about the evolutionary origin of melatonin signaling in circadian behavior by interacting with the molecular clock.

Results

Expression of melatonin in adult anemones showed peak expression at the end of light period (zeitgeber time (ZT) = 12) when cultured under diel conditions, coinciding with expression of genes and enzyme activity for members of the melatonin synthesis pathway (tryptophan hydroxylase and hydroxyindol-O-methyltransferase), which also showed rhythmic expression. During embryogenesis and juvenile stages, melatonin showed cyclic oscillations in concentration, peaking in midday. Spatial (in situ hybridization) and quantitative (real-time PCR) transcription of clock genes during development of N. vectensis showed these ‘clock’ genes are expressed early in the development, prior to rhythmic oscillations, suggesting functions independent of a function in the circadian clock. Finally, time-course studies revealed that animals transferred from diel conditions to constant darkness lose circadian expression for most of the clock genes within 4 days, which can be reset by melatonin supplementation.

Conclusions

Our results support an ancient role for melatonin in the circadian behavior of animals by showing cyclic expression of this hormone under diel conditions, light-dependent oscillations in genes in the melatonin synthesis pathway, and the function of melatonin in initiating expression of circadian clock genes in the cnidarian N. vectensis. The differences in expression melatonin and the circadian clock gene network in the adult stage when compared with developmental stages of N. vectensis suggests new research directions to characterize stage-specific mechanisms of circadian clock function in animals.

Melatonin production in the sea star Echinaster brasiliensis (Echinodermata)

The primary hormone of the vertebrate pineal gland, melatonin, has been identified broadly throughout the tree of life, in animals, plants, and fungi, supporting a deep evolutionary origin for this signaling molecule. However, some key groups have not been studied. Echinoderms, deuterostome animals, are one of these groups. Herein we study the presence of melatonin and enzymes of its pathway in the sea star Echinaster brasiliensis. We demonstrate that E. brasiliensis produces endogenous melatonin, in the gonads, under a circadian pattern with a nocturnal peak of production. We also show that the enzymes arylalkylamine N-acetyltransferase (AANAT) and tryptophan hydroxylase (TPH) are present and are probably regulating the melatonin production.

An LED-based UV-B irradiation system for tiny organisms: System description and demonstration experiment to determine the hatchability of eggs from four Tetranychus spider mite species from Okinawa

We developed a computer-based system for controlling the photoperiod and irradiance of UV-B and white light from a 5×5 light-emitting diode (LED) matrix (100×100mm). In this system, the LED matrix was installed in each of four irradiation boxes and controlled by pulse-width modulators so that each box can independently emit UV-B and white light at irradiances of up to 1.5 and 4.0Wm(-2), respectively, or a combination of both light types. We used this system to examine the hatchabilities of the eggs of four Tetranychus spider mite species (T. urticae, T. kanzawai, T. piercei and T. okinawanus) collected from Okinawa Island under UV-B irradiation alone or simultaneous irradiation with white light for 12hd(-1) at 25°C. Although no eggs of any species hatched under the UV-B irradiation, even when the irradiance was as low as 0.02Wm(-2), the hatchabilities increased to >90% under simultaneous irradiation with 4.0Wm(-2) white light. At 0.06Wm(-2) UV-B, T. okinawanus eggs hatched (15% hatchability) under simultaneous irradiation with white light, whereas other species showed hatchabilities <1%. These results suggest that photolyases activated by white light may reduce UV-B-induced DNA damage in spider mite eggs and that the greater UV-B tolerance of T. okinawanus may explain its dominance on plants in seashore environments, which have a higher risk of exposure to reflected UV-B even on the undersurface of leaves. Our system will be useful for further examination of photophysiological responses of tiny organisms because of its ability to precisely control radiation conditions.

Characterization of arylalkylamine N-acetyltransferase from silkmoth (Antheraea pernyi) and pesticidal drug design based on the baculovirus-expressed enzyme

Arylalkylamine N-acetyltransferase (AANAT; EC 2.3.1.87) catalyzes the N-acetylation of arylalkylamines. A cDNA encoding AANAT (ApAANAT) was cloned from Antheraea pernyi by PCR. The cDNA of 1966 bp encodes a 261 amino acid protein. The amino acid sequence was found to have a high homology with Bombyx mori AANAT (BmNAT) but had very low homology with vertebrate AANATs. Amino acid sequence analysis revealed that four insect AANATs cloned from three species including ApAANAT formed a distinct cluster from the vertebrate group. A recombinant ApAANAT protein was expressed in Sf9 cells using a baculovirus expression system, having AANAT activity. The transformed cell extract acetylated tryptamine, serotonin, dopamine, tyramine, octopamine and norepinephrine. The AANAT activity was inhibited at over 0.03 mM tryptamine. Although insect AANATs have been considered as a target of insecticide, this type of insecticide has never been developed. Screening a chemical library of Otsuka Chemical Co., Ltd., we found a novel compound and its derivatives that inhibited the AANAT activity of ApAANAT. This may facilitate investigation of the monoamine metabolic pathway in insects and the development of new types of insecticides and inhibitors of AANATs.

The molecular characterization of antioxidant enzyme genes in Helicoverpa armigera adults and their involvement in response to ultraviolet-A stress

Ultraviolet (UV) radiation can cause oxidative stress in insects. To gain insight into the roles of different antioxidant enzymes of Helicoverpa armigera adults in response to oxidative stress caused by UV-A at a molecular level, three antioxidant enzyme genes [encoding copper zinc superoxide dismutase (Cu/ZnSOD), catalase (CAT) and glutathione peroxidase (GPX)] were cloned. The deduced amino acid sequences of these genes are similar to that of other insects. In addition, the expression profiles of genes from a classic antioxidant defense system, comprising Cu/ZnSOD, manganese superoxide dismutase (MnSOD), CAT, thioredoxin peroxidase, GPX and glutathione-S-transferase, were also determined. The results indicated that all antioxidant enzyme genes (except MnSOD in females) were significantly upregulated at certain time points (from 30 to 90min) in both male and female adults of H. armigera following UV-A radiation. We also found that longer periods of radiation exposure did not yield higher levels of mRNA expression. Furthermore, changes of determined physiological parameters (glutathione, Cu/ZnSOD and MnSOD activity) were basically consistent with the gene expression profiles. We therefore infer that the different antioxidant enzymes of H. armigera act in a coordinated manner at the transcriptional level against oxidative stress caused by UV-A radiation.

Do plant mites commonly prefer the underside of leaves?

The adaxial (upper) and abaxial (lower) surfaces of a plant leaf provide heterogeneous habitats for small arthropods with different environmental conditions, such as light, humidity, and surface morphology. As for plant mites, some agricultural pest species and their natural enemies have been observed to favor the abaxial leaf surface, which is considered an adaptation to avoid rain or solar ultraviolet radiation. However, whether such a preference for the leaf underside is a common behavioral trait in mites on wild vegetation remains unknown. The authors conducted a 2-year survey on the foliar mite assemblage found on Viburnum erosum var. punctatum, a deciduous shrub on which several mite taxa occur throughout the seasons, and 14 sympatric tree or shrub species in secondary broadleaf-forest sites in Kyoto, west-central Japan. We compared adaxial-abaxial surface distributions of mites among mite taxa, seasons, and morphology of host leaves (presence/absence of hairs and domatia). On V. erosum var. punctatum, seven of 11 distinguished mite taxa were significantly distributed in favor of abaxial leaf surfaces and the trend was seasonally stable, except for Eriophyoidea. Mite assemblages on 15 plant species were significantly biased towards the abaxial leaf surfaces, regardless of surface morphology. Our data suggest that many mite taxa commonly prefer to stay on abaxial leaf surfaces in wild vegetation. Oribatida displayed a relatively neutral distribution, and in Tenuipalpidae, the ratio of eggs collected from the adaxial versus the abaxial side was significantly higher than the ratio of the motile individuals, implying that some mite taxa exploit adaxial leaf surfaces as habitat.

UV tolerance in the two-spotted spider mite, Tetranychus urticae

The two-spotted spider mite, Tetranychus urticae was exposed to UV-C (250 nm), UV-B (300 nm), and UV-A (350 nm). In non-diapausing females, the median effective doses for 50% mortality plus escape incidence (ED(50)) were 21 (UV-C) and 104 kJm(-2) (UV-B); those for 50% oviposition rate in continuous darkness-treated mites were 6.2 (UV-C) and 41 kJm(-2) (UV-B). No significant effects of UV-A on mortality and oviposition rate were observed. The ED(50) values for UV-B were similar to the natural UV-B observed for 2-5 days in summer when T. urticae inhabits the undersides of leaves. Therefore, T. urticae possibly uses leaves as a filter to avoid the deleterious effects of UV-B. In diapausing females, low mortality was observed even at high doses of UV radiation, but more than half escaped even at low doses. The orange body color of diapausing females results from accumulation of carotenoids, a scavenger for UV-induced reactive oxygen species; this may explain the low mortality of diapausing females. Diapausing females may overcome the deleterious effects of UV-B during winter in the absence of leaves by emigrating to UV-free environments and by accumulating carotenoids.