Physiological Measurements and Transcriptomics Reveal the Fitness Costs of Monochamus saltuarius to Bursaphelenchus xylophilus.

The pine wood nematode (PWN) uses several Monochamus species as vehicles, through a temporary hitchhiking process known as phoresy, enabling it to access new host plant resources. Monochamus saltuarius acts as a new and major vector of the PWN in Northeastern China, showing lower PWN carrying capacity and a shorter transmission cycle compared to established vectors. The apparently altered symbiotic relationship offers an interesting area for researching the costs and adaptions involved in nematode-beetle, a specialized phoresy. We analyzed the response and fitness costs of M. saltuarius through physiological measurements and transcriptomics. The PWN exerted adverse repercussions on the growth and development of M. saltuarius. The PWN accelerated larval development into pupae, while beetle adults carrying the PWN exhibited an elevated abnormality rate and mortality, and reduced starvation resistance. During the pupal stage, the expression of growth-related genes, including ecdysone-inducible genes (E74EA), cuticle proteins, and chitin genes (CHTs), markedly increased. Meanwhile, the induced immune response, mainly by the IMD and Toll signaling pathways, could be a contributing factor to adult abnormality and mortality. Adult gonads and trachea exhibited enrichment in pathways related to fatty acid elongation, biosynthesis, and metabolism. FASN, ELOVL, and SCD possibly contributed to resistance against PWN. Our research indicated that phoretic interactions between vector beetles and PWN vary throughout the vector's lifespan, particularly before and after entry into the trachea. This study highlighted the fitness costs of immunity and metabolism on the vector beetle, indicating the adaptation mechanisms and evolutionary trade-offs to PWN.

Phoretic behavior of the pseudoscorpion Megachernes ryugadensis on the Japanese wood mouse Apodemus speciosus.

Phoresy is a passive transportation behavior where one organism (phoront) disperses to a new location by attaching to another organism. Pseudoscorpions are arthropod predators that mainly live in soil, subterranean habitats, and under tree bark. Some species also live in animal nests and engage in phoresy on small mammals, suggesting close associations with these animals. However, the relationship between phoretic pseudoscorpions and hosts as well as the ecological significance of phoresy remain largely unexplored. Here, to understand the function of phoresy of Megachernes ryugadensis, phoretic on small mammals, their phoretic behavior was investigated in a deciduous forest in northern Japan; individual-level dynamics of phoresy were examined by over 3-year mark-recapture surveys that concurrently marked the host and phoront; and host characteristics, such as sex and age class, were analyzed based on a 2-year small mammal trapping survey. The primary host species was the abundant Japanese wood mouse Apodemus speciosus. Out of 132 pseudoscorpions marked, 5 were recaptured approximately 1 month later. No pseudoscorpions were recaptured within the same census period (3-4 days) when they were marked, indicating that phoresy events last less than one night, and pseudoscorpions are unlikely to engage in phoresy again within a few weeks of their initial engagement. Furthermore, analysis of host characteristics revealed a tendency for female mice and adult individuals to have a higher probability of being hosts compared with males and subadults, respectively. Based on the findings in this and previous studies, the function of phoresy in this species is discussed.

Feeding-induced plant metabolite responses to a phoretic gall mite, its carrier psyllid and both, after detachment.

Phoresy is one of the most distinctive relationships between mites and insects, and the off-host interaction between phoretic mites and their carriers is the most critical factor sustaining the phoretic association. As phoretic associations commonly occur in temporary habitats, little is known about off-host interactions between phoronts and carriers. However, an off-host interaction has been reported, in which the plant-mediated competition between a phoretic gall mite, Aceria pallida, and its psyllid vector, Bactericera gobica, after detachment decreases leaf abscission caused by B. gobica and then directly facilitates their phoretic association. In this obligate phoresy, A. pallida seasonally attaches to B. gobica for overwinter survival and they share the same host plant, Lycium barbarum, during the growing season. It is unknown how the host plant responds to these two herbivores and what plant metabolites are involved in their interspecific interaction. Here, effects of A. pallida and B. gobica on the host plant's transcriptome and metabolome, and on enzymes involved in plant defence, at various infestation stages were studied by inoculating A. pallida and B. gobica either separately or simultaneously on leaves of L. barbarum. Our results showed that (a) A. pallida significantly promoted primary and secondary metabolite accumulation, (b) B. gobica markedly inhibited primary and secondary metabolite accumulation and had little influence on defence enzyme activity, and (c) under simultaneous A. pallida and B. gobica infestation, an intermediate response was predicted. These findings indicate that A. pallida and B. gobica have different effects on host plants, A. pallida inhibits B. gobica mainly by increasing the secondary metabolism of L. barbarum, whereas B. gobica inhibits A. pallida mainly by decreasing the primary metabolism of L. barbarum. In conjunction with our previous research, we speculate that this trade-off in host plant metabolite response between A. pallida and B. gobica after detachment promotes a stable phoretic association.

Dispersal patterns of oribatid mites across habitats and seasons.

Oribatid mites are tiny arthropods that are common in all soils of the world; however, they also occur in microhabitats above the soil such as lichens, mosses, on the bark of trees and in suspended soils. For understanding oribatid mite community structure, it is important to know whether they are dispersal limited. The aim of this study was to investigate the importance of oribatid mite dispersal using Malaise traps to exclude sole passive wind-dispersal. Oribatid mite communities were collected over a 3-year period from five habitat types (coniferous forests, deciduous forests, mixed forests, meadows, bog/heathlands sites) and three seasons (spring, summer, autumn) in Sweden. Mites entered traps either by walking or by phoresy, i.e., by being attached to flying insects. We hypothesized (1) that oribatid mite communities in the traps differ between habitats, indicating habitat-limited dispersal, and (2) that oribatid mite communities differ among seasons suggesting that dispersal varies due to changing environmental conditions such as moisture or resource availability. The majority of the collected species were not typically soil-living species but rather from habitats such as trees, lichens and mosses (e.g., Carabodes labyrinthicus, Cymbaeremaeus cymba, Diapterobates humeralis and Phauloppia lucorum) indicating that walking into the traps or entering them via phoresy are of greater importance for aboveground than for soil-living species. Overall, oribatid mite communities collected in the traps likely originated from the surrounding local habitat suggesting that long distance dispersal of oribatid mites is scarce. Significant differences among seasons indicate higher dispersal during warm and dry periods of the year. Notably, 16 species of oribatid mites collected in our study were sampled for the first time in Sweden. This study also demonstrates that Malaise traps are a meaningful tool to investigate spatial and temporal patterns of oribatid mite communities.

Emigrating Together but Not Establishing Together: A Cockroach Rides Ants and Leaves.

AbstractSymbionts of ant colonies can hitchhike on winged ant reproductives (alates) during colony nuptial flights. Attaphila fungicola Wheeler, a miniature cockroach that lives in the nests of Texas leaf-cutter ants (Atta texana Buckley), hitchhikes on female alates (winged queens). Hitchhiking roaches are presumably vertically transmitted from leaf-cutter parent colonies to daughter colonies, remaining with female alates as they transition into foundresses (workerless queens); however, foundresses have limited resources and high mortality rates. Rather than remaining with foundresses likely to die (vertical transmission), roaches might abandon them during dispersal to infect higher-quality later stages of colony development (female alate-vectored transmission). In field experiments, I find evidence for female alate-vectored transmission and discover that roaches use a second hitchhiking step (riding foraged plant material) to infect established colonies. This work reveals a novel relationship between host dispersal and symbiont transmission and shows that colony development can be an important selection pressure on transmission.

Hopping on: Conspecific traveller density within a vehicle regulates parasitic hitchhiking between ephemeral microcosms.

Hitchhikers (phoretic organisms) identify their vehicles using species-specific visual, chemical and vibrational cues. However, what factors influence their choice between vehicles of the same species has rarely been investigated. Hitchhikers must not only avoid overcrowded vehicles but may also need to travel with conspecifics to ensure mates at their destination. Hence, a trade-off between overcrowding and presence of conspecifics likely determines the choice of a vehicle especially when destination sites are distant, ephemeral and unique. Here, we investigate whether a trade-off between the presence of conspecifics versus overcrowding by conspecifics or heterospecifics on a vehicle affects hitchhiker choice. We also investigate the sensory modality responsible for this choice. We experimentally examine these questions using a phoretic nematode community (containing plant- and animal-parasitic taxa) obligately associated with a brood-site pollination mutualism. In this model system, nematodes co-travel with conspecifics and heterospecifics on pollinators as vehicles, between ephemeral plant brood sites to complete their developmental life cycle. In this system, hitchhiker overcrowding has proven negative impacts on vehicle and plant fitness. We expected nematodes to respond to conspecifics and heterospecific density on offered vehicles when making their choice. We found that animal-parasitic nematodes preferred vehicles containing some conspecifics within a certain density range. However, plant-parasitic nematodes preferentially boarded vehicles that were devoid of conspecifics or had few conspecifics. Plant parasites that preferred empty vehicles likely hitchhiked in pairs. Both nematode types employed volatile cues to discriminate between vehicles with different conspecific nematode densities. Our results suggest that vehicle overcrowding by conspecifics, most likely, guaranteed access to mates at the destination determined hitchhiker choice. Surprisingly, and contrary to our expectations, plant- and animal-parasitic nematodes did not respond to heterospecific crowding on vehicles and did not discriminate between vehicles with different heterospecific nematode densities. The reason for this lack of response to heterospecific presence is unknown. This study not only shows that phoretic organisms use different strategies while choosing a vehicle but also confirms that density-dependent effects can ensure the stability and persistence of phoretic interactions in a mutualism by balancing overcrowding against reproductive assurance.

The Scent of Life: Phoretic Nematodes Use Wasp Volatiles and Carbon Dioxide to Choose Functional Vehicles for Dispersal.

Hitchhikers (phoretic organisms) need vehicles to disperse out of unsuitable habitats. Therefore, finding vehicles with the right functional attributes is essential for phoretic organisms. To locate these vehicles, phoretic organisms employ cues within modalities, ranging from visual to chemical senses. However, how hitchhikers discriminate between individual vehicles has rarely been investigated. Using a phoretic nematode community associated with an obligate fig-fig wasp pollination mutualism, we had earlier established that hitchhiking nematodes make decisions based on vehicle species identity and number of conspecific hitchhikers already present on the vehicle. Here we investigate if hitchhikers can differentiate between physiological states of vehicles. We asked whether phoretic nematodes choose between live or dead vehicles present in a chemically crowded environment and we investigated the basis for any discrimination. We conducted two-choice and single-choice behavioral assays using single nematodes and found that plant- and animal-parasitic nematodes preferred live over dead vehicles and used volatiles as a sensory cue to make this decision. However, in single-choice assays, animal-parasitic nematodes were also attracted towards naturally dead or freeze-killed wasps. The volatile profile of the wasps was dominated by terpenes and spiroketals. We examined the volatile blend emitted by the different wasp physiological states and determined a set of volatiles that the phoretic nematodes might use to discriminate between these states which is likely coupled with respired CO2. We determined that CO2 levels emitted by single wasps are sufficient to attract nematodes, demonstrating the high sensitivity of nematodes to this metabolic product.

Patterns of intraspecific morphological variability in soil mites reflect their dispersal ability.

The ability to disperse is one of the most important factors influencing the biogeography of species and speciation processes. Highly mobile species have been shown to lack geographic population structures, whereas less mobile species show genetically strongly subdivided populations which are expected to also display at least subtle phenotypic differences. Geometric morphometric methods (GMM) were now used to analyze morphological differences between European populations of a presumed non-phoretic, little mobile mite species in comparison to a highly mobile, phoretic species. The non-phoretic species Scutacarus carinthiacus showed a phenotypic population structure, whereas the phoretic species S. acarorum displayed homogeneity. These different patterns most probably can be explained by different levels of gene flow due to different dispersal abilities of the two species. GMM proved to be a sensitive tool that is especially recommendable for the analysis of (old) museum material and/or specimens in microscopic slides, which are not suitable for molecular genetic analysis.

Hitchhiking or hang gliding? Dispersal strategies of two cereal-feeding eriophyoid mite species.

Dispersal shapes the dynamics of populations, their genetic structure and species distribution; therefore, knowledge of an organisms' dispersal abilities is crucial, especially in economically important and invasive species. In this study, we investigated dispersal strategies of two phytophagous eriophyoid mite species: Aceria tosichella (wheat curl mite, WCM) and Abacarus hystrix (cereal rust mite, CRM). Both species are obligatory plant parasites that infest cereals and are of economic significance. We investigated their dispersal success using different dispersal agents: wind and vectors. We hypothesised that in both mite species the main mode of dispersal is moving via wind, whereas phoretic dispersal is rather accidental, as the majority of eriophyoid mite species do not possess clear morphological or behavioural adaptations for phoresy. Results confirmed our predictions that both species dispersed mainly with wind currents. Additionally, WCM was found to have a higher dispersal success than CRM. Thus, this study contributes to our understanding of the high invasive potential of WCM.

Neurogenetics of nictation, a dispersal strategy in nematodes.

Nictation is a behaviour in which a nematode stands on its tail and waves its head in three dimensions. This activity promotes dispersal of dauer larvae by allowing them to attach to other organisms and travel on them to a new niche. In this review, we describe our understanding of nictation, including its diversity in nematode species, how it is induced by environmental factors, and neurogenetic factors that regulate nictation. We also highlight the known cellular and signalling factors that affect nictation, for example, IL2 neurons, insulin/IGF-1 signalling, TGF-ß signalling, FLP neuropeptides and piRNAs. Elucidation of the mechanism of nictation will contribute to increased understanding of the conserved dispersal strategies in animals.

The dynamic eggs of the Phasmatodea and their apparent convergence with plants.

The egg stages of animal life cycles are underappreciated in terms of their capacity for dispersal, protection, and biotic and abiotic interactions. Some of the most intriguing egg morphologies are seen in stick and leaf insects (Phasmatodea). Phasmids are charismatic insects, particularly due to their incredible camouflage, though a lesser-known fact is that their eggs are incredibly diverse in shape and structure, reflecting varying ecological niches. Perhaps most remarkable are those eggs which appear to resemble plant seeds in both their appearance and means of dispersal, such as via water and animal vectors. Numerous hypotheses surrounding the function of these egg morphologies and their apparent convergence with seeds have been proposed; however, empirical evidence remains lacking. Here, we present an initial synthesis of available evidence surrounding the ecology and dispersal strategies of phasmid eggs and weigh up the evidence for convergent evolution between phasmid eggs and seeds. In doing so, we highlight areas where further research is needed and discuss how the ecology of phasmid eggs may interplay with other aspects of phasmid ecology, distribution, and evolution.

Dispersal and resistance to starvation in Raoiella indica (Acari: Tenuipalpidae).

Raoiella indica Hirst (Tenuipalpidae) is an obligate phytophagous mite that has rapidly colonized wide areas of tropical America and causes severe injuries, mainly to plants in the families Arecaceae, Heliconiaceae, Zingiberaceae and Musaceae. This study evaluates biological attributes of the species that could explain its potential as invasive pest, its capacity to survive when deprived of food and its dispersal mechanisms, including passive displacement by wind and possible phoretic association with insects. This mite has a higher resistance to starvation than other phytophagous mites, with a maximum 12 days for adult females. Its main dispersal is by wind, even at low velocities. Phoresy on insects was not observed.

Estimates of phoretic mite abundance on bark beetles as affected by beetle capture method: a case study with Mesostigmata mites and Ips typographus (Coleoptera: Curculionidae).

The spectrum of Mesostigmata mite species that are phoretic on the bark beetle Ips typographus has been well described. However, phoretic mite abundance has mostly been quantified by researchers who used only a single method for capturing bark beetles: pheromone traps. We therefore compared mite abundance using two beetle-capture methods. At a single location with high numbers of I. typographus in the eastern Czech Republic in 2013, beetles were collected with pheromone traps and from infested logs placed in emergence traps. In total 29,589 I. typographus beetles were captured using the two methods. Mite abundance was assessed on 2400 beetles from pheromone traps and on 955 beetles from emergence traps; in total 5805 phoretic mesostigmatid mites were detected. Six species of phoretic mites were captured using pheromone traps and four species using emergence traps. The number of phoretic mites per beetle was higher for beetles captured in emergence traps than for beetles captured in pheromone traps. The most abundant mite species overall were Dendrolaelaps quadrisetus, Uroobovella ipidis, and Trichouropoda polytricha. The seasonal dynamics of phoretic mites paralleled the seasonal dynamics of their hosts.

A comprehensive and cost-effective approach for investigating passive dispersal in minute invertebrates with case studies of phytophagous eriophyid mites.

Dispersal is a fundamental biological process that operates at different temporal and spatial scales with consequences for individual fitness, population dynamics, population genetics, and species distributions. Studying this process is particularly challenging when the focus is on microscopic organisms that disperse passively, whilst controlling neither the transience nor the settlement phase of their movement. In this work we propose a comprehensive approach for studying passive dispersal of microscopic invertebrates and demonstrate it using wind and phoretic vectors. The protocol includes the construction of versatile, modifiable dispersal tunnels as well as a theoretical framework quantifying the movement of species via wind or vectors, and a hierarchical Bayesian approach appropriate to the structure of the dispersal data. The tunnels were used to investigate the three stages of dispersal (viz., departure, transience, and settlement) of two species of minute, phytophagous eriophyid mites Aceria tosichella and Abacarus hystrix. The proposed devices are inexpensive and easy to construct from readily sourced materials. Possible modifications enable studies of a wide range of mite species and facilitate manipulation of dispersal factors, thus opening a new important area of ecological study for many heretofore understudied species.

Fossil amber reveals springtails' longstanding dispersal by social insects.

BACKGROUND: Dispersal is essential for terrestrial organisms living in disjunct habitats and constitutes a significant challenge for the evolution of wingless taxa. Springtails (Collembola), the sister-group of all insects (with Diplura), are reported since the Lower Devonian and are thought to have originally been subterranean. The order Symphypleona is reported since the early Cretaceous with genera distributed on every continent. This distribution implies an ability to disperse over oceans, however symphypleonan Collembola have never been reported in marine water contrary to other springtail orders. Despite being highly widespread, modern springtails are rarely reported in any kind of biotic association. Interestingly, the fossil record has provided occasional occurrences of Symphypleona attached by the antennae onto the bodies of larger arthropods. RESULTS: Here, we document the case of a ~ 16 Ma old fossil association: a winged termite and ant displaying not some, but 25 springtails attached or in close proximity to the body. The collembola exhibit rare features for fossils, reflecting their courtship and phoretic behaviours. By observing the modes of attachment of springtails on different arthropods, the sex representation and ratios in springtail antennal anatomies in new and previously reported cases, we infer a likely mechanism for dispersal in Symphypleona. By revealing hidden evidence of modern springtail associations with other invertebrates such as ants and termites, new compelling assemblages of fossil springtails, and the drastic increase of eusocial insects' abundance during the Cenozoic (ants/termites comprising more than a third of insects in Miocene amber), we stress that attachment on winged castes of ants and termites may have been a mechanism for the worldwide dispersal of this significant springtail lineage. Moreover, by comparing the general constraints applying to the other wingless soil-dwelling arthropods known to disperse through phoresy, we suggest biases in the collection and observation of phoretic Symphypleona related to their reflexive detachment and infer that this behaviour continues today. CONCLUSIONS: The specific case of tree resin entrapment represents the (so far) only condition uncovering the phoretic dispersal mechanism of springtails - one of the oldest terrestrial arthropod lineages living today.

Life history of Macrocheles muscaedomesticae (Parasitiformes: Macrochelidae): new insights on life history and evidence of facultative parasitism on Drosophila.

Macrocheles muscaedomesticae is a cosmopolitan macrochelid mite whose populations have likely diverged considering the many locations they inhabit, but most of the work published on this mite species has been on the basis of their association with the house fly, Musca domestica. Here, we studied several aspects of the biology of M. muscaedomesticae associated with drosophilid flies collected in Alberta, Canada. We assessed the degree of divergence of our populations from others, compared their life history to other published populations and experimentally tested whether M. muscaedomesticae feeds on Drosophila hydei hosts by comparing the body mass of mites that attached to hosts to those that did not. There was no strong phylogenetic differentiation among any of the M. muscaedomesticae specimens, suggesting multiple recent introductions of this species to Canada. Compared to other populations, our mites exhibited lower fecundity, which may have been a result of the temperature or nematode-only diet in which they were maintained. Finally, mites that attached to hosts for 4 h weighed significantly more than those that did not. Without direct evidence for host tissue transfer to the mites, it is difficult to determine whether the mites are indeed feeding on their hosts while attached. However, the existing evidence for the costs fly hosts endure at the expense of these mites makes this relationship antagonistic.

[Overwintering status and species identification of gall mite in major wolfberry production areas].

To identify the wolfberry gall mite species and their overwintering situation in different wolfberry production areas and to provide a scientific basis for their prevention and control. We investigate the phoresy overwintering situation of gall mite, and identify the species of gall mite. Our results showed that the phoretic gall mite was Aceria pallida in all the production areas. The phoresy of gall mite was a common occurrence in different production areas, and the phoresy probability was above 75%. The phoretic behavior of wolfberry gall mite occurred commonly in the other production areas. The control of this mite in different production areas should pay attention to their phoretic behavior.

Standing on the shoulders of giants: young aphids piggyback on adults when searching for a host plant.

BACKGROUND: Upon the detection of imminent peril, pea aphids (Acyrthosiphon pisum) often drop off their host plant. Dropping in response to insect enemies is intermittent in nature, but when a mammalian herbivore feeds on their host plant, a large mixed-age group of aphids usually drops off the plant at once. Aphids that reach the ground are confronted with new, hostile environmental conditions and must therefore quickly walk toward a suitable host plant. The longer it takes an aphid to reach a host plant, the more it is exposed to the risks of starvation, desiccation and predation. RESULTS: We found that young nymphs, which have limited mobility and high mortality on the ground, quickly climb on conspecific (not necessarily parental) adults and cling to them before the latter start walking in search of a plant. This "riding" behavior is likely to be adaptive for the nymphs, for it shortens their journey and the time they spend off a host plant. Adults however, seem to be irritated by the riding nymphs, as they often actively try to remove them. CONCLUSIONS: After dropping from the host plant, young aphid nymphs travel at least part of the way back to a plant on the backs of adults. For the riding behavior to take place, nymphs need to successfully find adults and withstand removal attempts.

Birds Mediate a Fungus-Mite Mutualism.

Mutualisms between ophiostomatoid fungi and arthropods have been well documented. These fungi commonly aid arthropod nutrition and, in turn, are transported to new niches by these arthropods. The inflorescences of Protea trees provide a niche for a unique assemblage of ophiostomatoid fungi. Here, mites feed on Sporothrix fungi and vector the spores to new niches. Protea-pollinating beetles transport the spore-carrying mites between Protea trees. However, many Protea species are primarily pollinated by birds that potentially play a central role in the Protea-Sporothrix-mite system. To investigate the role of birds in the movement of mites and/or fungal spores, mites were collected from Protea inflorescences and cape sugarbirds, screened for Sporothrix fungal spores and tested for their ability to feed and reproduce on the fungal associates. Two mite species where abundant in both Protea inflorescences and on cape sugarbirds and regularly carried Sporothrix fungal spores. One of these mite species readily fed and reproduced on its transported fungal partner. For dispersal, this mite (a Glycyphagus sp.) attached to a larger mite species (Proctolaelaps vandenbergi) which, in turn, were carried by the birds to new inflorescences. The results of this study provide compelling evidence for a new mite-fungus mutualism, new mite-mite commensalisms and the first evidence of birds transporting mites with Sporothrix fungal spores to colonise new Protea trees.

Plant-mediated competition facilitates a phoretic association between a gall mite and a psyllid vector.

Phoretic associations between mites and insects commonly occur in patchy and ephemeral habitats. As plants provide stable habitats for herbivores, herbivorous mites are rarely dependent on other animals for phoretic dispersal. However, a phoretic gall mite, Aceria pallida, which is found on plants, seasonally attaches to a herbivorous insect, Bactericera gobica, for overwintering survival. After detachment, the gall mite shares a habitat with its vector and is likely to compete with this vector for plant resources. However, excessive competition works against the sustainability of the seasonal phoretic association. How the gall mite, as an obligate phoretic mite, balances this relationship with its vector during the growing season to achieve phoresy is unknown. Here, the plant-mediated interspecific interaction between the gall mite and the psyllid after detachment was studied in the laboratory and field. The laboratory results showed that infestation by the gall mite had detrimental effects on the survival and development of psyllid nymphs. Meanwhile, the mite population and the gall size were also adversely affected. The results from the field showed that the mean densities of the mite galls and psyllids were lower in the mixed-species infestation treatment than in the single-species infestation treatment across the investigation period. However, the interspecific interaction between the gall mite and the psyllid decreased rather than accelerated leaf abscission caused by the psyllid, which promoted the persistence of the psyllid population and then indirectly contributed to phoretic association. Our results suggest that the plant-mediated competition between the phoretic gall mite and its vector after detachment facilitates the maintenance of the phoretic association.