Plants,mites and mutualism: leaf domatia and the abundance and reproduction of mites on Viburnum tinus (Caprifoliaceae)

Associations between mites and leaf domatia have been widely reported, but little is known about their consequences for either plants or mites. By excising domatia from leaves of the laureltinus, Viburnum tinus L. (Caprifoliaceae), in the garden and laboratory, we showed that domatia alter the abundance, distribution, and reproduction of potential plant mutualists. Over 4 months, leaves with domatia on six garden shrubs had 2–36 times more predatory and microbivorous mites, and more mite eggs than leaves without domatia. However, this effect varied among plants and was weaker on one shrub with few mites on its leaves. Domatia also influenced the distribution of mites on leaves. A significantly higher fraction of mites, representing all life stages, was found in vein axils of leaves with domatia than in vein axils on leaves without domatia. Single-leaf experiments in the laboratory showed that domatia enhanced reproduction by the predatory mite, Metaseiulus occidentalis, especially at low relative humidity (30–38%). When domatia were removed, oviposition was reduced significantly only at low relative humidity, suggesting that domatia provide mites with refuge from environmental extremes on the leaf surface. Moreover, the use of domatia by predatory mites may reduce the impact of some plant enemies. In two experiments where prey consumption was measured, M. occidentalis ate significantly higher percentages of the eggs of the two-spotted spider mite (Tetranychus urticae). Our results are consistent with the viewpoint that mite-domatia associations are mutualistic. By directly aiding and abetting the third trophic level, plants with leaf domatia may increase the efficiency of some predaceous and microbivorous mites in consuming plant enemies.     

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.     

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.     

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.     

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.     

How leaf domatia and induced plant resistance affect herbivores, natural enemies and plant performance

Predators and plant resistance may act together to control herbivorous arthropod populations or antagonistically, which would reduce the control of pest populations. In a field experiment we enhanced predation by adding simulated leaf domatia to plants. Leaf domatia are small structures that often harbor predaceous arthropods that are potentially beneficial to the plant. We also manipulated host plant quality by inducing resistance with controlled, early season exposure of seedlings to spider mite herbivory.
Our manipulations had profound consequences for the natural community of arthropods that inhabited the plants. Leaf domatia had a direct positive effect on abundances of two species of bugs and one species of thrips, all of which are largely predators of herbivores. On leaves with domatia, each of the predators was found inside the domatia two to three times more often than outside the domatia. Eggs of predaceous bugs inside leaf domatia were protected from parasitism compared to eggs outside the domatia. The positive effects of leaf domatia on predator abundances were associated with reduced populations of herbivorous spider mites, aphids, and whiteflies. Plants with experimental leaf domatia showed significantly enhanced reproductive performance.
Induced resistance also affected the community of arthropods. Of the abundant predators, all of which also fed on the plant, only minute pirate bugs were negatively affected by induced resistance. Populations of herbivorous spider mites and whiteflies were directly and negatively affected by induction. In contrast, aphid populations were higher on plants with induced resistance compared to uninduced plants. Effects of induced resistance and domatia were additive for each of the predators and for aphids. However, spider mite and whitefly populations were not suppressed further by employing both induced resistance and domatia compared to each strategy alone. Our manipulations suggest that plant defense strategies can have positive effects on some species and negative effects on others. Negative effects of “resistance traits” on predators and positive effects on some herbivores may reduce the benefits of constitutive expression of resistance traits and may favor inducible defense strategies. Multiple plant strategies such as inducible resistance and morphological traits that aid in the recruitment of predators of herbivores may act together to maximize plant defenses, although they may also be redundant and not act additively.     

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.     

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.     

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.     

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.     

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.     

Does microhabitat structure affect foliar mite assemblages?

1. Habitat structure is an important factor influencing population dynamics and trophic organisation of terrestrial invertebrates. The phylloplane zone on vascular plant leaves is topographically complex, containing a multitude of microhabitats such as leaf hairs, lesions, and structural refugia such as domatia, which may modify interactions between resident invertebrate communities, colonisers, and subsequent trophic relationships. Leaf domatia are small indentations on the underside of leaves and are often inhabited by potentially beneficial mites and other arthropods. 2. This study investigated the relationship between domatia availability and foliar mite assemblages in contrasting habitats (native forest, plantation forest, and pasture) using a standard test plant (the endemic New Zealand shrub Coprosma lucida, J.R. & G. Forst.). 3. Diverse woody native vegetation types supported higher numbers of mite species than either plantation forest or pastoral grasses. The highest number of mite species occurred in the native forest (63%), plantation forest (38%), and pastoral grasses (25%). In the native vegetation type, experimental C. lucida leaves with domatia supported higher mite densities, greater colonisation success, and more diverse mite assemblages than those without domatia. Mite assemblages within the pastoral site were significantly different from the other two vegetation types. Only one fungivorous mite species, Orthotydeus californicus, occurred compared to five mite species in native and plantation forests. 4. This study indicated that foliar mite assemblages in native vegetation on experimental C. lucida shrubs are influenced by domatia availability, resident foliar mites, and local mite assemblages.     

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.     

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.     

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.     

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.     

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.     

Trichomes and spider-mite webbing protect predatory mite eggs from intraguild predation

Predaceous arthropods are frequently more abundant on plants with leaves that are pubescent or bear domatia than on plants with glabrous leaves. We explored the hypothesis that for some predatory mites this is because pubescence affords protection from intraguild predation. In laboratory experiments, we tested whether apple leaf pubescence protected Typhlodromus pyri eggs from predation by western flower thrips, Frankliniella occidentalis. To investigate the effect of pubescence further, we added cotton fibers to trichome-free leaves. We also determined whether webbing produced by Tetranychus urticae protected Phytoseiulus persimilis eggs from predation by F. occidentalis. Predation by thrips on T. pyri eggs oviposited on field-collected pubescent "Erwin Bauer" apple leaves was significantly less than on glabrous "Crittenden" apple leaves. Phytoseiid eggs oviposited in the cotton fibers were preyed upon significantly less than those on the trichome-free bean disk. Increasing the cotton fiber density from 5 to 20 fibers only slightly further reduced predation by thrips on T. pyri eggs. Thrips fed upon significantly fewer P. persimilis eggs oviposited in Te. urticae webbing than eggs oviposited on a surface that differed only in the absence of Te. urticae web. We conclude that a complex leaf topography reduces intensity of intraguild predation in this system.