Behavioral and population consequences of acarodomatia in grapes on phytoseiid mites (Mesostigmata) and implications for plant breeding

We examined the influence of acarodomatia in the riverbank grape Vitis riparia Michaux (Vitaceae) on the distribution and abundance of predatory mites (Phytoseiidae) and their interactions with herbivorous mites. Acarodomatia are tufts of nonglandular trichomes or pits located in major leaf vein axes of many species of woody perennial plants and are often occupied by predatory and mycophagous mites. In common garden plantings of different accessions of V. riparia we found a significant positive relationship between size of domatia and the abundance of naturally occurring predatory mites. Behavior of adult predatory mites may explain this positive association, in part. In separate laboratory experiments, gravid females of Typhlodromus pyri Scheuten and Amblyseius andersoni Chant spent more time and deposited more eggs on half of a V. riparia leaf with accessible domatia versus the other half in which access to domatia was blocked with pruning tar. Domatia also had population consequences. In an outdoor experiment using potted grapevines, population size of T. pyri and A. andersoni mites was greater on V. riparia with open domatia compared to V. riparia in which domatia were blocked with pruning tar. Population size of predatory mites was also greater on V. riparia with domatia than on Vitis vinifera L., whether their axils were blocked or not. Since V. vinifera have very small domatia, these results indicate that the presence of domatia is important, not just access to vein axils. Elevated predatory mite populations in response to domatia, however, did not translate into differences in the abundance of European red mite Panonychus ulmi (Koch), an important pest of grapes.Overall, these results indicate that domatia in uncultivated V. riparia promote higher densities of some species of generalist phytoseiid mites. However, domatia are small in most cultivated grapes. We crossed females and males of V. riparia that varied in domatia size and reared their offspring and found that average domatia size in the parents was highly correlated (r² = 0.77, slope = 0.55) with average domatia size in offspring (high narrow-sense heritability). Given that V. riparia possesses many other desirable agronomic traits, this result suggests it should be practical to breed for well-developed domatia in cultivated accessions.     

Leaf domatia and mites on Australasian plants: ecological and evolutionary implications

Leaf domatia, specialized chambers in the vein axils on the underside of leaves of many plant species, have remained an enigma for over a century. In this study we show a strong association between foliar domatia and mites in 37 plant species in Australasia. Overall, mites accounted for 91% of the arthropods observed in domatia. Across all species, a median of 51% of domatia were occupied and 71% of leaves showed mite evidence in domatia. The level of mite association did not depend on domatia type (pit, pouch, pocket, or tuft) or provenance (Papua New Guinea, Queensland, Victoria, or New Zealand). Mite association with domatia commonly varied between plant species, between individuals within species, and between shoots within individuals. The leaf developmental stage probably explains much of the variation in association for many of these species. The presence of a variety of life history stages of mites within domatia indicates that these structures act as shelters for development and reproduction. Furthermore, in 12 of 13 plant species examined, domatia concentrate mites in particular locations on the leaf. Mite taxa that we classify as largely predaceous (e.g. phytoseiids, stigmaeids and tydeids) or fungivorous (e.g. acarids and oribatids) were most common in domatia and dominated the association in 21 of 24 plant species in which the relative abundance of herbivorous, fungivorous and predaceous groups was quantified. We evaluate hypotheses that explain the role of leaf domatia, including non-functional hypotheses (e.g. architectural constraints), physiological function (e.g. gas exchange and water uptake), bacterial symbiosis and antagonistic and mutualistic associations with mites. Our quantitative results confirm anecdotal accounts of mite association with leaf domatia and are most consistent with Lundströem's century-old hypothesis of plant-mite mutualism in which leaf domatia billet predaceous and fungivorous mites that prey on plant enemies. Leaf domatia are widespread among woody angiosperms and abundant in many temperate and tropical regions of Australasia. Mites, an ancient group of arthropods whose diversity and abundance parallels that of insects, are likely to be important selective agents on terrestrial plants. Our results (1) indicate that mite-domatia association represents a relationship of comparable scope to plant-ant associations mediated by specialized plant structures such as extrafloral nectaries, food bodies and specialized domatia; (2) suggest that sociality is not a necessary prerequisite for widespread and diverse mutualisms between arthropods and plants; and, (3) extend the diversity of organisms that produce specialized mite ‘houses’ from lizards, and wasps and bees to woody angiosperms.     

In search of artificial domatia for predatory mites

Banker plants can enhance biological pest control by providing both floral resources and appropriate oviposition sites, e.g. through acarodomatia, to predator species. The use of materials mimicking domatia i.e. artificial domatia may be an economically favourable alternative to the use of banker plants bearing domatia. The aim of the present study was to identify materials that are able to host eggs of the Neoseiulus californicus predatory mite but not those of the Tetranychus urticae pest mite. In a laboratory experiment, the oviposition of predatory and phytophagous mites were compared in Petri dishes containing leaves. The different modalities compared were (i) natural domatia of Viburnum tinus or (ii) one of twelve potential artificial domatia materials. The overall oviposition response of predatory mites to all artificial domatia was similar to that of the natural domatia. The oviposition of the Tetranychus urticae pest mite did not increase in response to the artificial domatia. Five artificial domatia hosted as many eggs of the predatory mite as observed in the natural domatia. The effect of the physical properties of artificial domatia was also tested and N. californicus was found to favour the artificial domatia that had high heat retention capacities for oviposition. Three of these artificial domatia were tested on rose plants in a greenhouse experiment; none of which enhanced the biological control on the plants under these conditions. The present study highlights the difficulty in identifying and using suitable artificial domatia as substitutes to banker plants in biological pest control efforts.     

Do leaf domatia mediate a plant–mite mutualism? An experimental test of the effects on predators and herbivores

1. Leaf domatia are tiny structures in leaf vein axils that are widespread among plant taxa and have been described to be typically inhabited by predatory and fungivorous mites. The mutualism hypothesis for the function of leaf domatia predicts that predatory and/or fungivorous mites benefit from having a favourable place to take refuge and reproduce and that plants benefit indirectly from reduced herbivory and/or pathogen attack.
2. The effect of leaf domatia on populations of predatory and herbivorous mites was examined for avocado, Persea americana . In separate experiments, domatia were added to leaves of a variety of avocado plants lacking domatia (Hass) and domatia were blocked on a domatia-bearing variety (Toro Canyon).
3. In two out of the five experiments conducted, domatia-bearing plants had significantly higher numbers of predatory mites compared with controls. Although herbivore numbers were consistently lower on plants with domatia than on plants without domatia, in no case did the presence of leaf domatia result in a statistically significant decrease in herbivorous mite populations.
4. These results suggest that domatia may frequently benefit predatory mites, however, indirect effects on herbivorous mites may not commonly exist or may be too difficult to detect.     

Leaf domatia and foliar mite abundance in broadleaf deciduous forest of north Asia

Plant morphology may be shaped, in part, by the third trophic level. Leaf domatia, minute enclosures usually in vein axils on the leaf underside, may provide the basis for protective mutualism between plants and mites. Domatia are particularly frequent among species of trees, shrubs, and vines in the temperate broadleaf deciduous forests in north Asia where they may be important in determining the distribution and abundance of mites in the forest canopy. In lowland and montane broadleaf deciduous forests at Kwangn;akung and Chumbongsan in Korea, we found that approximately half of all woody species in all forest strata, including many dominant trees, have leaf domatia. Pooling across 24 plant species at the two sites, mites occupied a mode of 60% (range 20-100%) of domatia and used them for shelter, egg-laying, and development. On average, 70% of all active mites and 85% of mite eggs on leaves were found in domatia; over three-quarters of these were potentially beneficial to their hosts. Further, mite abundance and reproduction (expressed as the proportion of mites at the egg stage) were significantly greater on leaves of species with domatia than those without domatia in both forests. Effects of domatia on mite abundance were significant only for predaceous and fungivorous mite taxa; herbivore numbers did not differ significantly between leaves of species with and without domatia. Comparable patterns in broadleaf deciduous forest in North America and other biogeographic regions suggest that the effect of leaf domatia on foliar mite abundance is general. These results are consistent with several predictions of mutualism between plants and mites, and indicate that protective mutualisms may be frequent in the temperate zone.     

Do domatia mediate mutualistic interactions between coffee plants and predatory mites?

Many plant species possess structures on their leaves that often harbour predatory or fungivorous mites. These so‐called domatia are thought to mediate a mutualistic interaction; the plant gains protection because mites decimate plant pathogenic fungi or herbivores, whereas the mites find shelter in the domatia. We tested this hypothesis using two species of coffee (Coffea spp.) plants that posses domatia consisting of small cavities at the underside of the leaves, and which often harbour mites. We assessed densities of domatia, of the predatory mite Iphiseiodes zuluagai Denmark and Muma (Acari: Phytoseiidae) and of herbivorous mites Oligonychus ilicis (McGregor) (Acari: Tetranychidae) and Brevipalpus phoenicis (Geijskes) (Acari: Tenuipalpidae) on Coffea arabica L. (Rubiaceae) and Coffea canephora Pierre in the field. Over a period of 50 days, C. arabica harboured on average 7.5 times more predatory mites and 0.4–0.66 fewer prey mites than C. canephora. Hence, the higher density of predatory mites on C. arabica could not be explained by higher densities of prey. However, the density of domatia on C. arabica was on average 1.65 times higher than on C. canephora, and within each species, leaves with higher densities of domatia also harboured more predators. This suggests a positive effect of domatia on predatory mites. In the laboratory, survival of adult female predatory mites on leaves of C. arabica with open domatia was indeed significantly higher than on leaves with closed domatia. Hence, predatory mites benefited from the domatia. However, plants with higher densities of domatia did not harbour fewer herbivores. Taken together, our study only provides partial evidence for a mutualistic interaction between coffee plants and predatory mites, mediated by domatia.     

Host plant manipulation of natural enemies: leaf domatia protect beneficial mites from insect predators

Acarodomatia are small tufts of hair or invaginations in the leaf surface and are frequently inhabited by several taxa of non-plant-feeding mites. For many years, ecologists have hypothesized that these structures represent a mutualistic association between mites and plants where the mites benefit the plant by reducing densities of phytophagous arthropods and epiphytic microorganisms, and domatia benefit the mite by providing protection from stressful environmental conditions, other predaceous arthropods, or both. We tested these hypothesized benefits of domatia to domatia-inhabiting mites in laboratory and growth chamber experiments. In separate experiments we examined whether domatia on the wild grape, Vitis riparia, provided protection against drying humidity conditions or predaceous arthropods to two species of beneficial mite: the mycophagous species Orthotydeus lambi, and the predaceous species Amblyseius andersoni. For both taxa of beneficial mite, domatia significantly increased mite survivorship in the presence of the predatory bug, Orius insidiosus and the coccinellids Coccinella septempunctata and Harmonia varigata. There was no evidence for a protective effect of domatia with a third species of predatory arthropod, lacewing larvae Chrysoperla rufilabris. In contrast, there was no evidence for either species of beneficial mite that domatia provided any protection against low humidity. Thus in this system the primary mechanism by which domatia benefit beneficial mites is by protecting these organisms from other predatory arthropods on the leaf surface.     

Oviposition patterns in a predatory mite reduce the risk of egg predation caused by prey

Abstract 1. Predatory arthropods lay their eggs such that their offspring have sufficient prey at their disposal and run a low risk of being eaten by conspecific and heterospecific predators, but what happens if the prey attacks eggs of the predator? 2. The egg distribution and time allocation of adult female predatory mites Iphiseius degenerans as affected by predation of their eggs by prey, the western flower thrips Frankliniella occidentalis, were studied on sweet pepper plants. The predatory mites attack the first instar of thrips but all active stages of thrips are capable of killing the eggs of the predator; however the predatory mite is used for biological control of thrips. 3. The majority of predatory mite eggs was laid on the underside of leaves in hair tufts (domatia). During the experiment, females spent increasing amounts of time in flowers where they fed on pollen and thrips larvae. The risk of predation on predator eggs by thrips was lower on leaves than in flowers where the majority of thrips resides. Moreover, predation risk was higher outside leaf domatia than inside. 4. This suggests that predators avoid ovipositing in places with abundant prey to prevent their eggs from being eaten by thrips.     

Domatia reduce larval cannibalism in predatory mites

Abstract.  1. Acarodomatia are small structures on the underside of leaves of many plant species, which are mainly inhabited by carnivorous and fungivorous mites.
2. Domatia are thought to protect these mites against adverse environmental conditions and against predation. They are considered as an indirect plant defence; they provide shelter to predators and fungivores and these in turn protect the plants against herbivores and fungi.
3. We studied the possible role of domatia of coffee ( Coffea arabica L.) (Rubiaceae) and sweet pepper ( Capsicum annum L.) (Solanaceae) in reducing cannibalism in the mites inhabiting the domatia. We measured cannibalism of larvae by adults of the predatory mites Iphiseiodes zuluagai Denmark & Muma and Amblyseius herbicolus Chant on coffee leaf discs and of the predatory mite Iphiseius degenerans (Berl.) on sweet pepper leaf. Domatia were closed with glue or left open.
4. Cannibalism in all three species increased when domatia were closed. With I. degenerans , moreover, we found that the previous diet of the cannibal attenuated the effect of domatia on cannibalism.
5. We conclude that domatia can protect young predatory mites against cannibalism by adults and that the diet of cannibals affects the rate of cannibalism.     

Domatia morphology and mite occupancy of Psychotria horizontalis (Rubiaceae) across the Isthmus of Panama

Leaf domatia are small plant structures in vein axials on the undersides of leaves that are often inhabited by mites of several species. The mites are presumed to benefit the plant because they are predatory or fungivorous. The domatia are thought to provide the mites shelter from predators and changes in relative humidity, and in exchange, the mites protect the plant from small herbivores and fungal spores. Differences in relative humidity can affect food availability, changing the interaction between plants and mites. We examined domatium morphology of the shrub Psychotria horizontalis (Rubiaceae) and its associated mite diversity at three sites along the rainfall gradient of the Isthmus of Panama, during the dry and wet seasons. The dry forest had a domatium morphology consistent with providing greater desiccation protection, with trichomes and a smaller domatium opening relative to domatium size (size/opening ratio). Additionally, this size/opening ratio was significantly higher in the dry season than in the wet season at all three sites. Mite diversity was highest at the intermediate rainfall site with a large degree of overlap with the other sites, whereas the dry site and wet site shared few mite species. More fungivorous mites were present in the moist forests and more facultative feeders on fungal spores and small mites in the dry forest. The average mite size at each site matched the average domatium size at each site. The dry forest had small mites in small domatia, whereas the moist forests had larger mites in larger domatia. While these data are primarily observational, the site and seasonal differences in domatium morphology and mite diversity are consistent with two main hypotheses: (1) that protection from changes in humidity would be particularly important when humidity was low, such as in the dry forest and during the dry season (2) more fungivorous mites would be found in domatia of the moist forests. The data presented here further highlight the close adaptive relationship between leaf domatia on plants and the mites that inhabit them.     

Dynamics of refuge use: diurnal, vertical migration by predatory and herbivorous mites within cassava plants

Plants may protect themselves against herbivorous arthropods by providing refuges to predatory arthropods, but they cannot prevent herbivores from taking countermeasures or even from reaping the benefits. To understand whether plants benefit from providing self‐made refuges (so‐called domatia), it is not only necessary to determine the fitness consequences for the plant, but also to assess (1) against which factors the refuge provides protection, (2) why predatory arthropods are more likely to monopolise the refuge, and (3) how herbivorous and predatory arthropods respond to and affect each other in and outside the refuge. In this article, we focus on the last aspect by studying the dynamics of refuge use of a predatory mite (Typhlodromalus aripo) and its consequences for a herbivorous mite (Mononychellus tanajoa) on cassava plants in Benin, West Africa. The refuge, located in‐between the leaf primordia of the cassava apex, is thought to provide protection against abiotic factors and/or intraguild predators. To test whether the predator waits for prey in the apex or comes out, we sampled predator‐prey distributions on leaves and in the apex at 4 hour‐intervals over a period of 24 hours. The predatory mites showed pronounced diurnal changes in within‐plant distribution. They were in the apices during the day, moved to the young leaves during night and returned to the apices the next morning. Nocturnal foraging bouts were more frequent when there were more herbivorous mites on the leaves near the apex. However, the foraging predators elicited an avoidance response by mobile stages of their prey, since these were more abundant on the first 20 leaves below the apex during late afternoon, than on the same leaves during night. These field observations on cassava plants show that (1) during daytime predatory mites monopolise the apical domatia, (2) they forage on young leaves during night and (3) elicit avoidance by within‐plant, vertical migration of mobile stages of the herbivorous mites. We hypothesize that cassava plants benefit from apical domatia by acquiring protection for their photosynthetically most active, young parts, because predatory mites (1) protect primordial leaves in the apex, (2) reduce the densities of herbivorous mites on young leaves, and (3) cause herbivorous mites to move down to less profitable older leaves.     

Benefits associated with the domatia mediated tritrophic mutualism in the shrub Coprosma lucida

The fitness benefits of plant structural adaptations that increase the effectiveness of fungivores against leaf pathogenic fungi are poorly understood. In a 12‐month field experiment, we investigated the effect of domatia on mite density, the role of these mites in limiting leaf fungi, and the associated effects on plant fitness in the endemic New Zealand shrub, Coprosma lucida. The presence of domatia on mite density was controlled using combinations of domatia blocking, sham blocking, mite addition and mite control using miticide. Limiting access to domatia reduced mite density and increased the proportion of leaves without mites. Mite families represented were predominantly fungivorous/detritivorous (97.2%), and predaceous (2.6%); herbivorous mites were absent. Mites significantly reduced fungal hyphae, fungal spores and pollen, but the effect was surface‐(upper/lower) and density‐dependent with the greatest reduction in fungi occurring over low mite densities. Fungal hyphae reduced leaf longevity, but were associated with increased production of new leaves. Hyphae density on old leaves was negatively correlated with the number of domatia produced on new leaves. New leaves in the mite reduction treatment had slightly reduced levels of carbon but not nitrogen. High levels of fungal infection on the lower surface increased the number of fruit fascicles per shoot, however on the upper surface where fungi were reduced by mites, hyphae density was negatively related to reproduction. The data support a limited interpretation of a fitness benefit for plants with domatia. While domatia increased mite density, control of fungi by mites occurred at lower average densities than supported by plants without functioning domatia. We suggest the primary function of leaf domatia in this mutualism is to increase the probability of a leaf‐level beneficial mite presence rather than to maximise mite density. Many mites are not necessarily better than few mites, but some mites are better than none.     

Abundance of phytoseiid mites on Vitis species: effects of leaf hairs,domatia, prey abundance and plant phylogeny

We observed the number of predatory mites (Phytoseiidae:Typhlodromus caudiglans) on the foliage of 20 North American species of grapes (Vitis spp) plus the domesticated EuropeanVitis vinifera, all grown in a common garden. We found relatively few phytophagous mites. The numbers of phytophagous mites were not correlated with the plant characteristics that we measured. We found approximately five times as many predatory mites as phytophagous mites and the numbers of these phytoseiid predators were not affected by the availability of prey. Similarly, numbers of phytoseiids were unaffected by plant gender and, hence, the availability of pollen, another source of food. The numbers of phytoseiids were not clustered according to the taxonomic grouping of the tested plant species. Leaf surface characteristics explained over 25% of the variance in the numbers of phytoseiids. Numbers of phytoseiids were positively associated with the density of vein hairs, the density of bristles in leaf axils, and the presence of leaf domatia. These results suggest that sheltered habitats rather than food availability may limit the numbers of phytoseiid mites on grapevines.     

Leaf domatia do not affect population dynamics of the predatory mite Iphiseiodes zuluagai

Leaves of plants of several families possess small cavities or tufts of hair where leaf veins bifurcate. These so-called acarodomatia are usually inhabited by predatory and fungivorous mites, which utilize domatia as shelter against adverse conditions or against other predators and cannibals. Plants may benefit from the presence of the mites through reduced densities of herbivores or plant-pathogenic fungi. It has therefore been suggested that domatia mediate a mutualistic interaction between plants and mites. We tested the hypothesis that cavity-like domatia on coffee plants benefit the predatory mite Iphiseiodes zuluagai through providing protection against adverse weather conditions and other predators in three field experiments. We manipulated plant domatia by blocking all on one group of plants, whereas a second group of plants with open natural domatia served as a control. Predatory mite populations were provided with pollen as a food source during part of two experiments. Experiments were done in the dry and rainy season to test the effects of adverse weather conditions and with or without an insect glue barrier on the plant to prevent access of ground-dwelling hyperpredators. High temperatures had a significant negative effect on predator densities in all experiments, whereas rainfall and humidity affected densities in one and two experiments respectively. None of the experiments showed a significant effect of domatia manipulation on mite numbers, or a significant interaction between weather parameters and domatia, suggesting that domatia did not protect against these adverse weather conditions. Nevertheless, predatory mites were frequently observed inside the domatia, suggesting that the mites benefit from using domatia. Perhaps domatia offer protection against hyperpredators, which were rarely observed during our experiments.     

Leaf domatia: carbon‐limited indirect defence?

Plant‐based defence mutualisms utilize plant morphology to reduce the performance of plant parasites through their natural enemies. Leaf domatia primarily occur in the axials of secondary veins and are often inhabited by microbivorous and predaceous mites which often increase plant growth rates and reproductive success by controlling plant pests. Our study investigated if domatia investment is limited by plant primary productivity. To our knowledge no studies have tested if foliar domatia are resource‐limited. We tested our hypothesis using the genus Coprosma (Rubiaceae), conducting correlative field surveys and manipulative experiments measuring domatia production in new leaves along temperature, nutrient and irradiance gradients. Field surveys indicated a strong positive association between leaf area, the number of secondary veins, and domatia per leaf. The number of potential sites for domatia is underutilised, with leaves on selected Coprosma species having on average 47 to 72% of the ‘maximum’ number of available sites where domatia could occur. Foliar carbon was positively associated with domatia investment. Coprosma plants held under elevated night‐time temperatures showed a 34–91% decrease in daily carbon gain, a 38% decrease in domatia per leaf mass, and a positive relationship between domatia investment and integrated daily carbon gain. Under irradiance and nutrient stress, our data indicated evidence of a positive relationship between domatia investment and foliar carbon. We found a significant negative association between relative investment in domatia produced and investment in new leaf biomass. Our findings suggest investment in foliar domatia is limited by primary productivity. We propose that domatia are discretionary goods and not intrinsic structures produced automatically on leaves that mites utilize. We suggest that plants have the ability to regulate domatia formation during leaf ontogeny, with investment controlled by resource availability and some intrinsic allocation mechanism to defence.     

OCCURRENCE OF PREDATORY AND FUNGIVOROUS MITES IN LEAF DOMATIA

Domatia are small invaginations and hair tufts usually found at vein junctions on the undersides of leaves in many woody dicots. Domatia of 32 plant species (of worldwide origin from 18 families) growing in California, Hawaii, and Costa Rica were examined for mites. Domatia of 31 of 32 (97%) of these plants contained mites, and 24 of 32 (75%) contained mite eggs. Mites were found within the domatia of 48% of the sampled leaves. The domatia of 26 of 31 (84%) plants had mite species considered beneficial (primarily in the families Phytoseiidae and Tydeidae, but also Bdellidae, Cheyletidae and Stigmaeidae), while 6 of 31 (19%) had mite species considered harmful (Tenuipalpidae and Eriophyidae). Based on these findings (and in part upon Lundström's 1887 domatia theory), we hypothesize the existence of a widespread facultative mutualism between plants with leaf domatia and beneficial mites: leaf domatia serve as shelters and nurseries for mites which in turn eat phytophagous arthropods and pathogens using the plants. This proposed mutualism could be of importance to agriculture since domatia are known to occur in some crop plants, including coffee, grape, and walnut.     

Biotic interactions of mites, plants and leaf domatia

Leaf domatia, minute structures that typically house mites and other small arthropods, are produced by an impressive number of plants; however, their role in mediating plant-mite mutualism has only recently been elucidated. New evidence indicates that domatia function primarily as refuges for beneficial mites against predators. The presence of domatia therefore results in more beneficial mites on leaves, fewer pathogen attacks and reduced leaf herbivory. Unexpectedly, herbivorous mites are specialized domatia inhabitants of some plants. By providing refuges for herbivores, however, domatia may stabilize interactions between predator and their mite prey and thereby reduce the chances of herbivore outbreaks. Understanding the ecological mechanisms that promote beneficial interactions between mites and plants could have important implications for pest management.     

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.     

Oviposition-site shift in phytophagous mites reflects a trade-off between predator avoidance and rainstorm resistance

Predators can reduce prey population densities by driving them to undertake costly defences. Here, we report on a remarkable example of induced antipredator defence in spider mites that enhances the risk to rainstorms. Spider mites live on the undersides of host plant leaves and usually oviposit on the leaf undersurface. When they are threatened by predatory mites, they oviposit on three-dimensional webs to avoid egg predation, although the cost of ovipositing on webs has not yet been clearly determined. We prepared bean plants harbouring spider mite (Tetranychus kanzawai) eggs on either leaf surfaces or webs and exposed them to rainstorms outdoors. We found that fewer eggs remained on webs than on leaf surfaces. We then examined the synergistic effect of wind and rain by simulating both in the laboratory. We conclude that ovipositing on webs comes at a cost, as eggs are washed off the host plants by wind and rain. This may explain why spider mite populations decrease drastically in the rainy season, although they inhibit leaf undersides where they are not directly exposed to rainfall.     

Predatory mites avoid ovipositing near counterattacking prey

Attacking prey is not without risk; predators may endure counterattackby the prey. Here, we study the oviposition behaviour of a predatory mite(Iphiseius degenerans) in relation to its prey, thewesternflower thrips (Frankliniella occidentalis). This thrips iscapable of killing the eggs of the predator. Thrips and predatory mites - apartfrom feeding on each other - can also feed and reproduce on a diet of pollen.Because thrips may aggregate at pollen patches, such patches may be risky foroviposition by the predatory mites. We found that, in absence of thrips,predatory mites lay their eggs close to pollen, but further away when thripsarepresent. Predatory mite eggs near pollen were killed more frequently by thripsthan when they were deposited further away. The oviposition behaviour of thepredatory mite was also studied in absence of thrips, but in presence of thealarm pheromone of thrips. This pheromone is normally secreted upon contactwithpredators or competitors. When applied close to the pollen, predatory mitesoviposited significantly further away from it. When the alarm pheromone wasapplied away from the food source, most eggs were found near the pollen. Theseresults indicate that female predatory mites show flexible ovipositionbehaviourin response to the presence of their counterattacking prey.