Prey–predator mutualism in a tritrophic system on a camphor tree

We report the discovery of a mutualistic system encompassing prey–predator interactions. A domatium is a small space in a vein axil on the underside of leaves of woody angiosperms. Cinnamomum camphora Linn. has domatia that harbor a microphytophagous eriophyid mite (sp. 1). We previously reported that a predatory mite, Euseius sojaensis (Ehara), depends on this eriophyid mite as food. We revealed that E. sojaensis also preyed upon another eriophyid mite (sp. 2) that induces galls on leaves, and that the mean area of C. camphora leaves with galls was usually less than half that of leaves without galls. We experimentally tested the effect of E. sojaensis on galls, and confirmed that the presence of E. sojaensis reduced gall induction. Therefore, C. camphora, eriophyid mite sp. 1, and E. sojaensis comprise a mutualistic system, in spite of the prey–predator interactions among them. The conventional concept of mutualism does not apply to such prey–predator interactions, so we defined them as systematic mutualism. Here, the system consists of three trophic levels, and individuals that constitute this system benefit from the other species that constitute this system.     

Micro-morphological alterations in young rosette leaves of Dipsacus laciniatus L. (Dipsacaceae) caused by infestation of the eriophyid mite Leipothrix dipsacivagus Petanovic et Rector (Acari: Eriophyoidea) under laboratory conditions

The present study describes micro-morphological and histological changes to rosette leaves of the native Eurasian plant species Dipsacus laciniatus (Dipsacaceae) provoked by infestation of the eriophyid mite Leipothrix dipsacivagus Petanovic et Rector. Conspicuous injuries to the leaf tissue were induced by mites feeding on leaves of D. laciniatus rosettes that were propagated from seed under laboratory conditions. Anatomical injuries extended into epidermal cells on the upper and lower leaf surface as well as to the mesophyll layer of infested D. laciniatus leaves. Statistical analysis (by ANOVA and MANOVA) showed significant differences between control and infested plants, particularly in total leaf thickness. The most striking change observed was the decrease in thickness of infested leaves, beginning from the 8th week, associated with the progressive replacement of epidermal cells with an acellular layer. Measures of mite density on test leaves indicated that mites vacated leaves as russeting symptoms intensified. They also appeared to vacate all leaves, whether symptomatic or not, after populations peaked 10–12 weeks after infestation. Comparisons were made between these studies and those on naturally infested, field-collected D. laciniatus plants, as well as with similar studies of other mite-plant interactions.     

A new mite-plant association: mites living amidst the adhesive traps of a carnivorous plant

Non-antagonistic interactions between arthropods and leaves of insectivorous plants with adhesive traps so far have never been reported. The mites are common prey of such plants, but we have found a new subspecies of the mite Oribatula tibialis living on the leaves of Pinguicula longifolia. Because of its small size and the low glandular density of the host, the mite moves without being trapped by the mucilaginous droplets of the leaf surface. P. longifolia provides shelter and food for the mite, while the plant may also benefit because of its fungivorous and scavenging activities. This new interaction is another dramatic example of widespread miteplant associations.     

Field assessment of host plant specificity and potential effectiveness of a prospective biological control agent, Aceria salsolae, of Russian thistle, Salsola tragus

The eriophyid mite, Aceria salsolae de Lillo and Sobhian, is being evaluated as a prospective classical biological control agent of invasive alien tumbleweeds, including Salsola tragus, S. collina, S. paulsenii and S. australis, in North America. Previous laboratory experiments to determine the host specificity of the mite indicated that it could sometimes persist and multiply on some nontarget plants, including Bassia hyssopifolia and B. scoparia. These are both European plants whose geographic range overlaps that of the mite, but the mite has never been observed on them in the field. A field experiment was conducted in Italy to determine if the mite would infest and damage these plants under natural outdoor conditions. The results indicate that this mite does not attain significant populations on these nontarget plants nor does it significantly damage them. Salsola tragus was heavily infested by A. salsolae, and plant size was negatively correlated to the level of infestation. Although S. kali plants were also infested, their size did not appear to be affected by the mites. The other nontarget plants were not as suitable for the mite in the field as in previous laboratory experiments. We conclude that there would be no significant risk to nontarget plants as a result of using A. salsolae as a biological agent to control Salsola species in North America.     

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.     

Stratospheric Ozone Depletion: High Arctic Tundra Plant Growth on Svalbard is not Affected by Enhanced UV-B after 7 years of UV-B Supplementation in the Field

The response of tundra plants to enhanced UV-B radiation simulating 15 and 30% ozone depletion was studied at two high arctic sites (Isdammen and Adventdalen, 78° N, Svalbard).The set-up of the UV-B supplementation systems is described, consisting of large and small UV lamp arrays, installed in 1996 and 2002. After 7 years of exposure to enhanced UV-B radiation, plant cover, density, morphological (leaf fresh and dry weight, leaf thickness, leaf area, reproductive and ecophysiological parameters leaf UV-B absorbance, leaf phenolic content, leaf water content) were not affected by enhanced UV-B radiation. DNA damage in the leaves was not increased with enhanced UV-B in Salix polaris and Cassiope tetragona. DNA damage in Salix polaris leaves was higher than in leaves of C. tetragona. The length of male gametophyte moss plants of Polytrichum hyperboreum was reduced with elevated UV-B as well as the number of Pedicularis hirsuta plants per plot, but the inflorescence length of Bistorta vivipara was not significantly affected. We discuss the possible causes of tolerance of tundra plants to UV-B (absence of response to enhanced UV-B) in terms of methodology (supplementation versus exclusion), ecophysiological adaptations to UV-B and the biogeographical history of polar plants     

Climbing of Leaf Trichomes by Eriophyid Mites Impedes Their Location by Predators

Eriophyid mites are plant parasites that are well adapted to hide away from predators. Tiny and wormlike, they can invade very narrow spaces in plants or form galls that, apart from other functions, serve as a shelter from predation. Previous observations showed that some free-living eriophyids as well as tetranychid mites spend their quiescence on the top of leaf trichomes. Here, I investigated climbing leaf trichomes by the eriophyid, Rhinophytoptus concinnus, and tested whether it enables the herbivores to avoid phytoseiid mites. Climbing behavior took place just prior to the quiescent period of juveniles. Larvae and nymphs raised the hind part of their stiffening bodies and walked, turning around on their axis. Having found a hair, juveniles attached their anal suckers to its tip, and, pushing back from a leaf surface or the base of the hair, they lifted their bodies up to become motionless. As revealed by the playback experiments with the phytoseiid mite, Typhloctonus tiliarum, predatory females needed much more time to find quiescent nymphs perching on hairs than those placed on a leaf surface. The time of nymph handling was similar in both situations. Also, a similar number of predators gave up feeding on nymphs in both locations. I conclude that climbing leaf trichomes enables the herbivorous mite to hide from predators. After detection, however, placement on trichomes does not give the quiescent juveniles any advantage over those placed on a leaf blade.     

Pathogen-activated induced resistance of cucumber: response of arthropod herbivores to systemically protected leaves

Summary Restricted (non-systemic) inoculation of cucurbits, green bean, tobacco, and other plants with certain viruses, bacteria, or fungi has been shown to induce persistent, systemic resistance to a wide range of diseases caused by diverse pathogens. The non-specificity of this response has fueled speculation that it may also affect plant suitability for arthropod herbivores, and there is limited evidence, mainly from work with tobacco, which suggests that this may indeed occur. Young cucumber plants were immunized by restricted infection of a lower leaf with tobacco necrosis virus (TNV), and upper leaves were later challenged with anthracnose fungus, Colletotrichum lagenarium, to confirm induction of systemic resistance to a different pathogen. The response of arthropod herbivores was simultaneously measured on non-infected, systemically protected leaves of the same plants. As has been reported before, immunization with TNV gave a high degree of protection from C. lagenarium, reducing the number of lesions and the area of fungal necrosis by 65–93%. However, there was no systemic effect on population growth of twospotted spider mites, Tetranychus urticae Koch, on upper leaves, nor did restricted TNV infection of leaf tissue on one side of the mid-vein systemically affect mite performance on the opposite, virus-free side of the leaf. Similarly, there were no effects on growth rate, pupal weight, or survival when fall armyworm larvae were reared on systemically protected leaves from induced plants. In free-choice tests, greenhouse whiteflies oviposited indiscriminately on induced and control plants. Feeding preference of fall armyworms was variable, but striped cucumber beetles consistently fed more on induced than on control plants. There was no increase in levels of cucurbitacins, however, in systemically-protected foliage of induced plants. These findings indicate that pathogen-activated induced resistance of cucumber is unlikely to provide significant protection from herbivory. The mechanisms and specificity of induced resistance in cucurbits apparently differ in response to induction by pathogens or herbivores.     

“HAIRY CANOLA” – Arabidopsis GL3 Induces a Dense Covering of Trichomes on Brassica napus Seedlings

Transformation with the Arabidopsis bHLH gene 35S:GLABRA3 (GL3) produced novel B. napus plants with an extremely dense coverage of trichomes on seedling tissues (stems and young leaves). In contrast, trichomes were strongly induced in seedling stems and moderately induced in leaves of a hairy, purple phenotype transformed with a 2.2 kb allele of the maize anthocyanin regulator LEAF COLOUR (Lc), but only weakly induced by BOOSTER (B-Peru), the maize Lc 2.4 kb allele, or the Arabidopsis trichome MYB gene GLABRA1 (GL1). B. napus plants containing only the GL3 transgene had a greater proportion of trichomes on the adaxial leaf surface, whereas all other plant types had a greater proportion on the abaxial surface. Progeny of crosses between GL3⁺ and GL1⁺ plants resulted in trichome densities intermediate between a single-insertion GL3⁺ plant and a double-insertion GL3⁺ plant. None of the transformations stimulated trichomes on Brassica cotyledons or on non-seedling tissues. A small portion of bHLH gene-induced trichomes had a swollen terminal structure. The results suggest that trichome development in B. napus may be regulated differently from Arabidopsis. They also imply that insertion of GL3 into Brassica species under a tissue-specific promoter has strong potential for developing insect-resistant crop plants. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Chlorophyll fluorescence and leaf chlorophyll content of bean leaves injured by spider mites (Acari: Tetranychidae)

The use of chlorophyll fluorescence as a method for detecting and monitoring plant stress arising from Tetranychus urticae (Koch) feeding injury was investigated. The effect of mite density (1–32 mites per 1.5 cm² of leaf) and the duration of the feeding period (1–5 days) on the chlorophyll fluorescence parameters of bean (Phaseolus vulgaris) leaves were examined. Changes in chlorophyll fluorescence parameters were dependent both on mite density and duration of feeding. Decreases in F _o, the initial fluorescence and F _m, the maximum fluorescence led to a decrease in the ratio of variable to maximum fluorescence, F _v/F _m. The decrease in F _v/F _m is typical of the response of many plants to a wide range of environmental stresses and indicates a reduced efficiency of photosystem II (PSII) photochemistry. T _1/2, which is proportional to the pool size of electron acceptors on the reducing side of PSII, was also reduced in response to mite-feeding injury. The leaf chlorophyll content decreased with increasing mite density and duration of feeding but did not appear to contribute to the decrease in F _v/F _m. Chlorophyll fluorescence is an effective method for detecting and monitoring stress in T. urticae-injured bean leaves.     

Leaf domatia mediate mutualism between mites and a tropical tree

Although associations between mites and leaf domatia have been widely reported, their consequences for plants, especially for natural tree populations, particularly in the tropics, are largely unknown. In experiments with paired Cupania vernalis (Sapindaceae) saplings in a semi-deciduous forest in south-east Brazil, we blocked leaf domatia to examine their effect: (1) on mites and other arthropods, and (2) on damage caused by fungi and herbivorous arthropods. In general, plants with resin-blocked domatia had fewer predaceous mites on leaves than control plants with unaltered domatia, but the total abundances of fungivorous and of phytophagous mites remained unchanged. However, phytophagous eriophyid mites, the most numerous inhabitants of domatia, decreased on leaf surfaces with the blocking treatment. In a second experiment, treated plants lacking functional domatia developed significantly greater numbers and areas of chlorosis, apparently due to increased eriophyid attacks, whereas fungal attack, epiphyll abundance and leaf-area loss were unaffected. This seems to be the first experimental study to demonstrate that leaf domatia can benefit plants against herbivory in a natural system. The possible stabilizing effect of leaf domatia on predator-prey interactions is discussed.     

罗汉松雌雄株叶形态结构的比较研究

该研究以雌雄异株植物罗汉松(Podocarpus macrophyllus)成熟叶为研究材料,采用光学显微镜、扫描电镜和透射电镜观察比较罗汉松雌、雄植株叶在形态、显微结构和超显微结构的差异,以明确罗汉松雌、雄株在进化过程中叶对环境功能的适应性。结果显示:(1)罗汉松雌株的叶片大于雄株,且两者的叶长、叶宽和叶柄长差异极显著,而叶柄厚、叶面积、叶体积、叶质量、比叶重(SLW)、面积与体积之比(A/V)等性状无显著差异。(2)雌株叶片的气孔相对较大,密度较高,且雌株气孔宽度极显著大于雄株;雌株叶片的上表皮长细胞宽度和下表皮短细胞宽度均显著大于雄株,但雌株叶片的上表皮长细胞和短细胞的长度则显著小于雄株。(3)罗汉松雌株叶片的栅栏组织厚度、海绵组织厚度、传输组织长度和宽度、上下角质层厚度、维管束厚度、叶片紧密度(CTR)及疏松度(SR)均极显著大于雄株,而雌株的下表皮厚度极显著小于雄株,但雌雄株叶片的上表皮细胞厚度和栅海比差异不显著;雌株叶片的栅栏组织细胞、叶绿体和线粒体均较雄株的长而细,且雌株的线粒体宽度极显著小于雄株。(4)罗汉松雌株叶片上表皮蜡质饰纹、下表皮角质层纹饰、气孔外拱盖纹饰及内缘类型等4个微形态特征与雄株差异明显。(5)叶表皮蜡质层能谱分析表明,罗汉松雌株叶片含有9种元素,而雄株叶片仅有8种(缺少K元素);且雌株的Si元素含量高于雄株,而雄株的C、O、Na、Mg、Al、Ca和Au元素含量均高于雌株。研究表明,罗汉松雌、雄植株之间存在明显的第二性征,雌株叶片结构有助于提高光合等性能以满足生殖需求;罗汉松雌、雄株叶形态结构的差异是其长期进化形成的有利于物种繁衍的适应策略。     

Control of the broad mite (Polyphagotarsonemus latus (Banks)) on organic greenhouse sweet peppers (Capsicum annuum L.) with the predatory mite, Neoseiulus cucumeris (Oudemans)

The predatory mite Neoseiulus cucumeris (Oudemans) (Acarina: Phytoseiidae) successfully controlled the broad mite Polyphagotarsonemus latus (Banks) (Acarina: Tarsonemidae) on two varieties of greenhouse-grown sweet peppers (Capsicum annuum L.). A survey of pre-plant seedlings showed that nurseries were a source of infestation for the broad mite. The predatory mites were released twice (on day 1 and 5, or 15 days later) on each plant, every second plant or every fourth plant. Broad mite populations were evaluated by sampling young leaves from the top of the plant. The effect of the broad mite on plant height, dry mass and yield was evaluated. Additionally, since N. cucumeris is known to control thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), blue sticky traps and flower sampling were used to evaluate changes in thrips populations. All three release rates of N. cucumeris significantly (P<0.05) controlled broad mite populations, but when the predatory mites were released only on every fourth plant, the overall height and yield of the plants were adversely affected by broad mites. Releasing N. cucumeris on each or every second plant was as efficacious in controlling broad mites as sulfur treatments in terms of plant height, dry mass and yield. Plants treated with sulfur, however, had significantly higher thrips populations and fruit damage.     

ERECTA is required for protection against heat-stress in the AS1/ AS2 pathway to regulate adaxial-abaxial leaf polarity in Arabidopsis

In seed plants, formation of the adaxial–abaxial polarity is of primary importance in leaf patterning. Since Arabidopsis thaliana (L.) Heynh. genes ASYMMETRIC LEAVES1 (AS1) and ASYMMETRIC LEAVES2 (AS2) are key regulators in specifying adaxial leaf identity, and ERECTA is involved in the AS1/AS2 pathway for regulating adaxial–abaxial polarity [L. Xu et al. (2003) Development 130:4097–4107], we studied the physiological functions of the ERECTA protein in plant development. We analyzed the effects of different environmental conditions on a special leaf structure in the as1 and as2 mutants. This structure, called the lotus-leaf, reflects a severe loss of adaxial–abaxial polarity in leaves. Higher concentrations of salt or other osmotic substance and lower temperature severely affected plant growth both in the wild type and the mutants, but did not affect lotus-leaf frequency in the as1 and as2 mutants. as1 and as2 mutants exhibited a very low lotus-leaf frequency at 22°C, a temperature that favors Arabidopsis growth. The lotus-leaf frequency rose significantly with an increase in growth temperature, and only in plants that are in the erecta mutation background. These results suggest that ERECTA function is required for reducing plant sensitivity to heat stress during adaxial–abaxial polarity formation in leaves.Abbreviations AS1, AS2 ASYMMETRIC LEAVES1, 2 - ER ERECTA     

Response of predatory mites with different rearing histories to volatiles of uninfested plants

The behavioural response of the predatory mite Phytoseiulus persimilis to volatiles from several host plants of its prey, spider mites in the genus Tetranychus, was investigated in a Y-tube olfactometer. A positive response to volatiles from tomato leaves and Lima bean leaves was recorded, whereas no response was observed to volatiles from cucumber leaves, or leaves of Solanum luteum and Solanum dulcamara.Different results were obtained for predators that differed in rearing history. Predators that were reared on spider mites (Tetranychus urticae) on Lima bean leaves did respond to volatiles from Lima bean leaves, while predators that had been reared on the same spider mite species but with cucumber as host plant did not respond to Lima bean leaf volatiles. This effect is compared with the effect of rearing history on the response of P. persimilis to volatile allelochemicals of prey-infested plant leaves.     

Predator avoidance in phytophagous mites: response to present danger depends on alternative host quality

We studied whether volatiles released by putative host plants affect the antipredator response of an herbivorous mite, Tetranychus urticae, when the patch was invaded by Phytoseiulus persimilis. Tetranychus urticae laid a lower number of eggs on tomato leaves than on lima bean leaves, suggesting that lima bean is a preferred host food source for T. urticae. In addition, T. urticae preferred lima bean plant volatiles to tomato plant volatiles in a Y-tube olfactometer test. To investigate the antipredator response of T. urticae, we examined the migration of T. urticae from a lima bean leaf disc to a neighbouring leaf disc (either a tomato or lima bean leaf disc) when ten predators were introduced into the original lima bean disc. A Parafilm bridge allowed for migration between the leaf discs. No migrations occurred between leaf discs when there were no predators introduced to the original leaf disc. However, when predators were introduced migrations did occur. When the neighbouring leaf disc was upwind of the original disc, the migration rate of the mite from original lima bean leaf disc to a neighbouring tomato leaf disc was significantly lower than that to a neighbouring lima bean leaf disc. By contrast, when the neighbouring leaf disc was downwind of the original leaf disc, there was no difference in the migration rates between lima bean leaf discs and tomato leaf discs. The number of T. urticae killed by P. persimilis for each treatment was not different, and this clearly shows that the danger was the same in all treatments regardless of the decision made by T. urticae. From these results, we conclude that T. urticae change their antipredator response by evaluating the difference in host plant volatiles in the patch they inhabit.     

Effects of simulated herbivory on photosynthesis and N resorption efficiency in <Emphasis Type="Italic">Quercus</Emphasis><Emphasis Type="Italic">pyrenaica</Emphasis> Willd. saplings

We examined the effects of simulated folivory by caterpillars on photosynthetic parameters and nitrogen (N) resorption efficiency in Quercus pyrenaica saplings. We analyzed the differences between intact leaves in control plants, punched leaves in damaged plants, and intact leaves in damaged plants. We then established two levels of simulated folivory: low (≈13% of the leaf area of one main branch removed per plant) and high (≈26% of the leaf area of one main branch removed per plant) treatments. No differences were found in net assimilation rate and conductance between either leaf type or treatment during the most favourable period for photosynthesis. However, the N content was lower in punched than in intact leaves, and as a result PNUE was higher in damaged leaves from treated trees. In leaf-litter samples, N mass was significantly higher in punched than in intact leaves in treated plants, and LMA was significantly higher in damaged than in intact leaves of both the treated and control plants. Consequently, N resorption efficiency was around 15% lower in damaged leaves as compared with intact leaves from treated and control plants. Mechanical injury to leaves not only triggered no compensatory photosynthetic response to compensate a lower carbon uptake due to leaf area loss, but also affected the resorption process that characterizes leaf senescence.     

The fine structure and photosynthetic cost of structural leaf variegation

The leaves of some plants display an optical patchiness on their upper side, displaying light- and dark-green areas with high and low reflectance, respectively. In this investigation, we studied the fine structure of the corresponding sectors and we asked whether the lost reflected light entails a photosynthetic cost to these leaves. Four species, i.e. Arum italicum, Ranunculus ficaria, Cyclamen hederifolium and Cyclamen persicum were investigated. Scanning electron microscope examination revealed that epidermal cells of light-green sectors of all species are more bulgy than corresponding cells of neighboring dark-green leaf sectors. The comparative anatomical study revealed that (i) epidermis thickness of the light-green areas and the number of mesophyll cell layers does not differ from those of the adjacent dark-green leaf sectors and (ii) palisade cells of light-green sectors are slightly larger and more loosely arranged, allowing a much higher percentage of intercellular air spaces. The latter histological feature seems to provide the structural basis for the different optical properties between the two leaf sectors. Contrary to expectations, net photosynthetic rates (expressed on a leaf area basis) were similar in the light-green and the dark-green areas of the two cyclamen species. Yet, in C. persicum net photosynthesis was higher in the light-green areas, if expressed on a dry mass basis. The small size of the light-green spots in the rest of the test plants precluded CO₂ assimilation measurements, yet maximum linear photosynthetic electron transport rates displayed no differences between the two sectors in all plants. Thus, the assumption of a photosynthetic cost in the light-green areas was not confirmed. On the contrary, a higher construction cost was evident in the dark-green areas of three species, displaying a significantly higher specific leaf mass, without any photosynthetic benefit. The results on net photosynthesis were compatible with leaf optical properties and pigment levels. Thus, in spite of the considerably higher reflectance of the light-green areas and their lower (yet normal for a green leaf) chlorophyll levels, corresponding differences in absorptance were slight. In addition, dry mass-based pigment contents in dark-green areas were higher, while chlorophyll a/b (in two species) and carotenoid/chlorophyll ratios (in three species) were lower, pointing to a shade adaptation in these sectors. We conclude that in variegated leaves of this kind, dark-green areas are more costly to build and probably less photosynthetically active. We argue that the high pigment contents of dark-green areas establish steep light gradients in the corresponding mesophyll, rendering deeper chloroplast layers more shade adapted.     

Pearl bodies of Cayratia japonica (Thunb.) Gagnep. (Vitaceae) as alternative food for a predatory mite Euseius sojaensis (Ehara) (Acari: Phytoseiidae)

On the young leaves, shoots, and buds of Cayratia japonica (Thunb.) Gagnep. (Vitaceae), we observed nutritious bodies called pearl bodies and hypothesized that they are utilized by generalist predators as alternative foods. Some ambulate organisms consume pearl bodies in the wild and the predatory mite Euseius sojaensis (Ehara) (Acari: Phytoseiidae) was considered as a primary candidate. Pearl bodies promoted E. sojaensis settlement on C. japonica leaves and E. sojaensis could prey on the phytophagous mite Tetranychus kanzawai Kishida (Acari: Tetranychidae) when the predators settle on a leaf before the prey. In addition, the presence of pearl bodies did not reduce predation of E. sojaensis on T. kanzawai. This was seemingly because food quality of T. kanzawai was higher than pearl bodies. These results implied that pearl bodies on C. japonica leaves are utilized by E. sojaensis as alternative foods.     

Induced Response of Tomato Plants to Injury by Green and Red Strains of Tetranychus Urticae

We studied the induced response of tomato plants to the green strain and the red strain of the spider mite Tetranychus urticae. We focused on the olfactory response of the predatory mite Phytoseiulus persimilis to volatiles from T. urticae-infested tomato leaves in a Y-tube olfactometer. Tomato leaves attracted the predatory mites when slightly infested with the red strain, or moderately or heavily infested with the green strain. In contrast, neither leaves that were slightly infested with green-strain mites, nor leaves that were moderately or heavily infested with the red strain attracted the predators. We discuss the specific defensive responses of tomato plants to each of the two strains.