Spatial scale of aggregation in three acarine predator species with different degrees of polyphagy

Aggregative responses by the predatory mites, Phytoseiulus persimilis, Typhlodromus occidentalis, and Amblyseius andersoni (Acari: Phytoseiidae), to spatial variation in the density of mobile stages of Tetranychus urticae (Acari: Tetranychidae) were studied over different spatial scales on greenhouse roses. Significant spatial variations in prey numbers per leaflet, per leaf, per branch or per plant were present in all experimental plots. None of the predator species responded to prey numbers per plant, and all searched randomly among plants. Within a plant, the oligophagous P. persimilis searched randomly among branches, but aggregated strongly among leaves within a branch and among leaflets within a leaf. The narrowly polyphagous T. occidentalis searched randomly among leaflets within a leaf and amond leaves within a branch, but aggregated strongly among leaflets or leaves within a plant. The boradly polyphagous A. andersoni searched randomly among leaflets within a leaf, a branch or a plant, and among leaves within a branch or a plant, but distributed themselves more often on branches with lower prey densities. Thus, specialist predators aggregate strongly at lower spatial levels but show random search at higher spatial levels, whereas generalist predators show random search at lower spatial levels but aggregate at higher spatial levels. This is the first empirical evidence demonstrating the relation between the degree of polyphagy and the spatial scale of aggregation. It is also concluded that both the prey patch size (i.e. grain) and predator foraging range (i.e. extent) are important for analyzing spatial scales of predator aggregation. The importance of studying spatial scale of aggregation is also discussed in relation to predator-prey metapopulation dynamics.     

Phytoseiulus persimilis response to herbivore-induced plant volatiles as a function of mite-days

The predatory mite, Phytoseiulus persimilis (Acari: Phytoseiidae), uses plant volatiles (i.e., airborne chemicals) triggered by feeding of their herbivorous prey, Tetranychus urticae (Acari: Tetranychidae), to help locate prey patches. The olfactory response of P. persimilis to prey-infested plants varies in direct relation to the population growth pattern of T. urticae on the plant; P. persimilis responds to plants until the spider mite population feeding on a plant collapses, after which infested plants do not attract predators. It has been suggested that this represents an early enemy-free period for T. urticae before the next generation of females is produced. We hypothesize that the mechanism behind the diminished response of predators is due to extensive leaf damage caused by T. urticae feeding, which reduces the production of volatiles irrespective of the collapse of T. urticae population on the plant. To test this hypothesis we investigated how the response of P. persimilis to prey-infested plants is affected by: 1) initial density of T. urticae, 2) duration of infestation, and 3) corresponding leaf damage due to T. urticae feeding. Specifically, we assessed the response of P. persimilis to plants infested with two T. urticae densities (20 or 40 per plant) after 2, 4, 6, 8, 10, 12 or 14 days. We also measured leaf damage on these plants. We found that predator response to T. urticae-infested plants can be quantified as a function of mite-days, which is a cumulative measure of the standing adult female mite population sampled and summed over time. That is, response to volatiles increased with increasing numbers of T. urticae per plant or with the length of time plant was infested by T. urticae, at least as long at the leaves were green. Predatory mites were significantly attracted to plants that were infested for 2 days with only 20 spider mites. This suggests that the enemy-free period might only provide a limited window of opportunity for T. urticae because relatively low numbers of T. urticae per plant can attract predators. Leaf damage also increased as a function of mite-days until the entire leaf was blanched. T. urticae populations decreased at this time, but predator response to volatiles dropped before the entire leaf was blanched and before the T. urticae population decreased. This result supports our hypothesis that predator response to plant volatiles is linked to and limited by the degree of leaf damage, and that the quantitative response to T. urticae populations occurs only within a range when plant quality has not been severely compromised.     

Olfactory response of the predator <Emphasis Type="Italic">Zetzellia mali</Emphasis> to a prey patch occupied by a conspecific predator

While searching for food, predators may use volatiles associated with their prey, but also with their competitors for prey. This was tested for the case of Zetzellia mali (Ewing) (Acari: Stigmaeidae), an important predator of the hawthorn spider mite, Amphitetranychus viennensis (Zacher) (Acari: Tetranychidae), in black-cherry orchards in Baraghan, Iran. Using a Y-tube olfactometer, the response of this predatory mite was tested to odour from black-cherry leaves with a conspecific female predatory mite, either with or without a female of the hawthorn spider mite when the alternative odour came from black-cherry leaves with the hawthorn spider mite only. Female predators avoided odours from leaves with both a hawthorn spider mite and a conspecific predator, as well as leaves with a conspecific predator only. We discuss whether avoidance emerges in response to cues from the competitor/predator, the herbivore/prey or the herbivore-damaged plant.     

Plant spatial distribution and predator–prey ratio affect biological control of the twospotted spider mite Tetranychus urticae (Acari: Tetranychidae) by the predatory mite Phytoseiulus persimilis (Acari: Phytoseiidae)

A greenhouse experiment was conducted to determine the effect of plant spacing and predator–prey ratio on dispersal and foraging efficiency of the predatory mite, Phytoseiulus persimilis, on the twospotted spider mite, Tetranychus urticae. When predators were released at the end of spider mite-infested arrays of lima bean plants that had either no spacing or two different patterns of spacing among plant rows, plant damage was uniformly low throughout the experiment at both predator–prey ratios (1:10 and 3:10) in the treatment with no spacing. In contrast, damage was higher in both treatments where plant rows were interrupted by spacing. At the 1:10 ratio, more plants closer to the predator release point experienced moderate damage than at the 3:10 ratio where only the plant rows farthest from the release point had unacceptable damage. Our findings suggest that point releases of P. persimilis at the standard 1:10 predator–prey ratio should be effective within a diameter of at least 65?cm on mite-infested patches of plants where pots are touching. However, if gaps in plant rows exist, even large numbers of predators may not be sufficient to protect parts of the crop unless predators are released at shorter fixed points in the greenhouse crop.     

Effects of feeding frequency and sugar concentration on behavior and longevity of the adult aphid parasitoid: Aphidius ervi (Haliday) (Hymenoptera: Braconidae)

The effectiveness of the predatory mite, Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseidae), as a suppressive agent of the twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), was evaluated on greenhouse ivy geraniums at predator:prey release ratios of 1:60, 1:20, and 1:4. Releases at each predator:prey ratio were made at moderate and high T. urticae densities to determine if initial pest population size influenced the suppressive ability of the predator. At ratios of 1:4 and 1:20, P. persimilis significantly reduced T. urticae populations 1 week after release and kept them at low levels thereafter. Plant damage also was significantly reduced at these densities. After 4 weeks, the P. persimilis that were released at a ratio of 1:4 consistently reduced T. urticae populations from densities as high as 30 T. urticae per leaf to fewer than 0.6 per leaf. We found no interaction between release ratio and T. urticae density, indicating that predator effectiveness remains constant, at least within the range of T. urticae densities used. Our work demonstrates the potential of P. persimilis to provide effective control of T. urticae on a greenhouse-grown floricultural crop at a moderately low predator:prey ratio (1:20) and over a range of initial pest densities. However, we recommend that P. persimilis be released at a ratio of 1:4 for greatest reliability and successful control of T. urticae on ivy geraniums.     

Arbuscular mycorrhiza enhances preference of ovipositing predatory mites for direct prey‐related cues

Most terrestrial plants are associated with arbuscular mycorrhizal fungi but research on the effects of arbuscular mycorrhizal symbiosis on aboveground plant‐associated organisms is scarcely expanded to tri‐trophic systems. The arbuscular mycorrhizal fungus Glomus mosseae Nicol. & Gerd. enhances fitness of the two‐spotted spider mite Tetranychus urticae Koch and its natural enemy, the predatory mite Phytoseiulus persimilis Athias‐Henriot, via changes in host plant and prey quality, respectively. In the present study, it is hypothesized that gravid P. persimilis are able to recognize arbuscular mycorrhiza‐enhanced prey quality and behave accordingly. In two experiments, on leaf arenas and in cages, P. persimilis is given a choice between prey patches deriving from mycorrhizal and non‐mycorrhizal bean plants (Phaseolus vulgaris L.) as feeding and oviposition sites. The use of cages allows the manipulation of distinct patch components acting as possible cues to guide predator foraging and oviposition behaviours, such as eggs produced and traces (webbing and faeces) left by the spider mite females. Both experiments show that P. persimilis preferentially resides close to prey fed on mycorrhizal plants. The cage experiment reveals that P. persimilis uses direct prey‐related cues, mainly derived from eggs, to discern prey quality and preferentially oviposits close to prey from mycorrhizal plants. This is the first study to document that predators recognize arbuscular mycorrhiza‐induced changes in herbivorous prey quality via direct prey‐related cues.     

Behavioral responses to prey density by three acarine predator species with different degrees of polyphagy

Behavioral responses by three acarine predators, Phytoseiulus persimilis, Typhlodromus occidentalis, and Amblyseius andersoni (Acari: Phytoseiidae), to different egg and webbing densities of the spider mite Tetranychus urticae (Acari: Tetranychidae) on rose leaflets were studied in the laboratory. Prey patches were delineated by T. urticae webbing and associated kairomones, which elicit turning back responses in predators near the patch edge. Only the presence of webbing affected predator behavior; increased webbing density did not increase patch time. Patch time increased with increased T. urticae egg density in the oligophagous P. persimilis, but was density independent in the polyphagous species T. occidentalis and A. andersoni. Patch time in all three species was more strongly correlated with the number of prey encounters and attacks than with the actual prey number present in the patch. Patch time was determined by (a) the turning back response near the patch edge; this response decayed through time and eventually led to the abandonment of the patch, and (b) encounters with, and attacks upon, prey eggs; these prolonged patch time by both an increment of time spent in handling or rejecting prey and an increment of time spent searching between two successive prey encounters or attacks. Although searching efficiency was independent of prey density in all three species, the predation rate by P. persimilis decreased with prey density because its searching activity (i.e. proportion of total patch time spent in searching) decreased with prey density. Predation rates by T. occidentalis and A. andersoni decreased with prey density because their searching activity and success ratio both decreased with prey density. The data were tested against models of predator foraging responses to prey density. The effects of the degree of polyphagy on predator foraging behavior were also discussed.     

Intraguild Interactions Between the Predatory Mites Neoseiulus californicus and Phytoseiulus persimilis

Species at the same trophic level may interact through competition for food, but can also interact through intraguild predation. Intraguild predation is widespread at the second and third trophic level and the effects may cascade down to the plant level. The effects of intraguild predation can be modified by antipredator behaviour in the intraguild prey. We studied intraguild predation and antipredator behaviour in two species of predatory mite, Neoseiulus californicus and Phytoseiulus persimilis, which are both used for control of the two-spotted spider mite in greenhouse and outdoor crops. Using a Y-tube olfactometer, we assessed in particular whether each of the two predators avoids odours emanating from prey patches occupied by the heterospecific predator. Furthermore, we measured the occurrence and rate of intraguild predation of different developmental stages of P. persimilis and N. californicus on bean leaves in absence or in presence of the shared prey. Neither of the two predator species avoided prey patches with the heterospecific competitor, both when inexperienced with the other predator and when experienced with prey patches occupied by the heterospecific predator. Intraguild experiments showed that N. californicus is a potential intraguild predator of P. persimilis. However, P. persimilis did not suffer much from intraguild predation as long as the shared prey was present. This is probably because N. californicus prefers to feed on two-spotted spider mites rather than on its intraguild prey.     

Foraging time and spatial patterns of predation in experimental populations

Summary Responses of the predaceous mites Phytoseiulus persimilis, Typhlodromus (=Metaseiulus) occidentalis, and Amblyseius andersoni to spatial variation in egg density of the phytophagous mite, Tetranychus urticae, were studied in the laboratory.The oligophagous predator P. persimilis showed initially a direct density dependent foraging time allocation and variation in foraging time increased with prey density. With changes in prey density due to predation, predator foraging rates (per hour) decreased with time and density dependent foraging gradually became density independence, because P. persimilis continued to respond to initial prey density, instead of the changing prey density and distribution. The consequent spatial pattern of predation by P. persimilis was density independent, although slopes of predation rate-prey density regressions increased with time.Compared with P. persimilis, the narrowly polyphagous predator T. occidentalis responded relatively slowly to the the presence or absence of prey eggs but not to prey density: the mean and variation of foraging time spent in patches with prey did not differ with prey density, but was significantly greater in patches with prey eggs than in patches without eggs. Prey density and distribution changed only slightly due to predation and overall foraging rates remained more or less constant. The consequent spatial pattern of predation by T. occidentalis was inversely density dependent. As with P. persimilis, slopes of predation rate-prey density regressions increased with time (i.e. the inverse density dependence in T. occidentalis became weaker through time).The broadly polyphagous predator A. andersoni showed density independent foraging time allocation with variation independent of prey density. With changes in prey density over time due to prey depletion, overall foraging rates decreased. The consequent spatial pattern of predation by A. andersoni also changed through time; it initially was inversely density dependent, but soon became density independent.Overall, P. persimilis and T. occidentalis spent more time in prey patches than A. andersoni, suggesting that A. andersoni tended to spend more time moving outside patches. The overall predation rates and searching efficiency were higher in P. persimilis than in A. andersoni and T. occidentalis. Predator reproduction was highest in P. persimilis, lower in T. occidentalis and the lowest A. andersoni.The differences in response to prey distribution among the three predaceous species probably reflect the evolution of these species in environments with different patterns of prey distribution. The degree of polyphagy is a major determinant of the aggregative response, but other attributes such as handling time are also important in other aspects of phytoseiid foraging behavior (e.g. searching efficiency or predation rate).     

Allocating time between feeding, resting and moving by the two-spotted spider mite, Tetranychus urticae and its predator Phytoseiulus persimilis

This study characterizes the timing of feeding, moving and resting for the two-spotted spider mite, Tetranychus urticae Koch and a phytoseiid predator, Phytoseiulus persimilis Athias-Henriot. Feeding is the interaction between T. urticae and plants, and between P. persimilis and T. urticae. Movement plays a key role in locating new food resources. Both activities are closely related to survival and reproduction. We measured the time allocated to these behaviours at four ages of the spider mite (juveniles, adult females immediately after moult and adult females 1 and 3 days after moult) and two ages of the predatory mite (juveniles and adult females). We also examined the effect of previous spider mite-inflicted leaf damage on the spider mite behaviour. Juveniles of both the spider mite and the predatory mite moved around less than their adult counterparts. Newly emerged adult female spider mites spent most of their time moving, stopping only to feed. This represents the teneral phase, during which adult female spider mites are most likely to disperse. With the exception of this age group, spider mites moved more and fed less on previously damaged than on clean leaves. Because of this, the spider mite behaviour was initially more variable on damaged leaves. Phytoseiulus persimilis rested at all stages for a much larger percentage of the time and spent less time feeding than did T. urticae; the predators invariably rested in close proximity to the prey. Compared to adult predators, juveniles spent approximately four times as long handling a prey egg. The predator-prey interaction is dependent upon the local movement of both the predators and prey. These details of individual behaviours in a multispecies environment can provide an understanding of population dynamics.     

The Predatory Mite Phytoseiulus persimilis Adjusts Patch-leaving to Own and Progeny Prey Needs

Integration of optimal foraging and optimal oviposition theories suggests that predator females should adjust patch leaving to own and progeny prey needs to maximize current and future reproductive success. We tested this hypothesis in the predatory mite Phytoseiulus persimilis and its patchily distributed prey, the two-spotted spider mite Tetranychus urticae. In three separate experiments we assessed (1) the minimum number of prey needed to complete juvenile development, (2) the minimum number of prey needed to produce an egg, and (3) the ratio between eggs laid and spider mites left when a gravid P. persimilis female leaves a patch. Experiments (1) and (2) were the pre-requirements to assess the fitness costs associated with staying or leaving a prey patch. Immature P. persimilis needed at least 7 and on average 14±3.6 (SD) T. urticae eggs to reach adulthood. Gravid females needed at least 5 and on average 8.5±3.1 (SD) T. urticae eggs to produce an egg. Most females left the initial patch before spider mite extinction, leaving prey for progeny to develop to adulthood. Females placed in a low density patch left 5.6±6.1 (SD) eggs per egg laid, whereas those placed in a high density patch left 15.8±13.7 (SD) eggs per egg laid. The three experiments in concert suggest that gravid P. persimilis females are able to balance the trade off between optimal foraging and optimal oviposition and adjust patch-leaving to own and progeny prey needs.     

Spatial distribution of predators and prey affect biological control of twospotted spider mites by Phytoseiulus persimilis in greenhouses

We evaluated the effects of predator release pattern and prey distribution on rate of suppression of the twospotted spider mite, Tetranychus urticae Koch (Acari, Tetranychidae) and visual damage to the ornamental plant, Impatiens wallerana Hook.f., in a greenhouse. Sixteen impatiens plants were arranged in a square and infested with the same total number of spider mites distributed either evenly (equal numbers on all plants) or clumped (divided equally among the 4 central plants), simulating a “hot spot.” The predatory mite, Phytoseiulus persimilis Athias-Henriot, was released at a 1:4 predator:prey ratio based on total spider mites in the experimental unit, but the pattern of release was either even or clumped, which simulated broadcast or point-release strategies, respectively. Nine days after predator release, spider mite populations were reduced in all treatments, but only in the clumped pest-clumped predator treatment were spider mites undetectable. Poorest pest suppression occurred in the clumped spider mite-even predator treatment. Eighteen days after predator release, spider mites were eliminated in all treatments, but a reduction in average plant damage occurred only in treatments in which the predator release pattern matched the spider mite distribution (i.e., even-even or clumped-clumped) with the greatest reduction in the even-even treatment. Results suggest that there is an advantage to releasing predators in “hot spots” provided that the recommended predator:prey ratio is maintained within infested patches. If more uniform predator releases are planned, overall predator numbers need to be kept sufficiently high so that the predator:prey ratio of 1:4 shown to prevent damage on impatiens is achieved in higher-density spider mite patches.     

Response of a phytoseiid predator to herbivore-Induced plant volatiles: Selection on attraction and effect on prey exploitation

Bean plants infested with herbivorous spider mites emit volatile chemicals that are attractive toP. persimilis, a predator of spider mites. In Y-tube olfactometer tests we evaluated involvement of a genetic component in predator response to herbivore-induced plant volatiles. Replicated bidirectional selection resulted in a significant increase in attraction after one generation of selection, but no decrease even after three generations of selection, indicating significant, but unbalanced, additive genetic variation in predator perception of, or response to, herbivore-induced plant volatiles. Selected lines responded differently than an unselected population to food deprivation, pointing to an interaction between their internal state and response to plant volatiles. Selected lines also differed from unselected ones in behaviors associated with local prey exploitation, such as residence time, prey consumption, and reproduction. At lower prey densities,P. persimilis from both “+” lines left spider mite-infested leaves more rapidly and consumed fewer prey eggs than an unselected population. Defining olfactory components of predator search behavior is one step in understanding the effect of plant volatiles on predator foraging efficiency. By selecting lines differing in their attraction to herbivore-induced plant volatiles we may experimentally investigate the link between this behavior, predator foraging efficiency, and local and regional predator-prey population dynamics. The impact of significant additive genetic variation in predator response to plant volatiles on evolution in a tritrophic context also remains to be uncovered.     

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

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

The Effects of Prey Patchiness, Predator Aggregation, and Mutual Interference on the Functional Response of Phytoseiulus persimilis Feeding on Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae)

The spatial distributions of two-spotted spider mites Tetranychus urticae and their natural enemy, the phytoseiid predator Phytoseiulus persimilis, were studied on six full-grown cucumber plants. Both mite species were very patchily distributed and P. persimilis tended to aggregate on leaves with abundant prey. The effects of non-homogenous distributions and degree of spatial overlap between prey and predators on the per capita predation rate were studied by means of a stage-specific predation model that averages the predation rates over all the local populations inhabiting the individual leaves. The empirical predation rates were compared with predictions assuming random predator search and/or an even distribution of prey. The analysis clearly shows that the ability of the predators to search non-randomly increases their predation rate. On the other hand, the prey may gain if it adopts a more even distribution when its density is low and a more patchy distribution when density increases. Mutual interference between searching predators reduces the predation rate, but the effect is negligible. The stage-specific functional response model was compared with two simpler models without explicit stage structure. Both unstructured models yielded predictions that were quite similar to those of the stage-structured model.     

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.     

Compensatory growth following transient intraguild predation risk in predatory mites

Compensatory or catch‐up growth following growth impairment caused by transient environmental stress, due to adverse abiotic factors or food, is widespread in animals. Such growth strategies commonly balance retarded development and reduced growth. They depend on the type of stressor but are unknown for predation risk, a prime selective force shaping life history. Anti‐predator behaviours by immature prey typically come at the cost of reduced growth rates with potential negative consequences on age and size at maturity. Here, we investigated the hypothesis that transient intraguild predation (IGP) risk induces compensatory or catch‐up growth in the plant‐inhabiting predatory mite Phytoseiulus persimilis. Immature P. persimilis were exposed in the larval stage to no, low or high IGP risk, and kept under benign conditions in the next developmental stage, the protonymph. High but not low IGP risk prolonged development of P. persimilis larvae, which was compensated in the protonymphal stage by increased foraging activity and accelerated development, resulting in optimal age and size at maturity. Our study provides the first experimental evidence that prey may balance developmental costs accruing from anti‐predator behaviour by compensatory growth.     

Do spider mite-infested plants and spider mite trails attract predatory mites?

We questioned the well-accepted concept that spider mite-infested plants attract predatory mites from a distance. This idea is based on the preference demonstrated by predatory mites such as Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae) for volatiles produced by spider mite-infested plants in a closed environment (Y-tube wind tunnel). However, in natural open environments, kidney bean leaves heavily infested with Tetranychus urticae Koch (Acari: Tetranychidae) did not attract P. persimilis from the same distances as were used in the Y-tube tests. Therefore, the attraction of predatory mites for spider mite-infested plant volatiles in the Y-tube tests may reflect a preference in a closed environment and should be carefully interpreted as a basis for extrapolating predator–prey attraction mechanisms in the wild. On the other hand, we showed that adult female P. persimilis could follow trails laid down by adult female T. urticae in the laboratory and in natural open environments. Consequently, we propose that following spider mite trails represents another prey-searching cue for predatory mites.     

Coincidental intraguild predation by caterpillars on spider mites

Intraguild predation (IGP) is defined as the killing and eating of prey species by a predator that also can utilize the resources of the prey. It is mainly reported among carnivores that share common herbivorous prey. However, a large chewing herbivore could prey upon sedentary and/or micro herbivores in addition to utilizing a host plant. To investigate such coincidental IGP, we observed the behavioral responses of the polyphagous mite Tetranychus kanzawai Kishida (Acari: Tetranychidae) when its host plant Cayratia japonica (Thunb.) Gagnep. (Vitaceae) was attacked by hornworms, Theretra japonica Boisduval (Sphingidae) and T. oldenlandiae Fabricius (Sphingidae). We also examined an interaction between the oligophagous mite Panonychus citri McGregor (Acari: Tetranychidae) and caterpillars of the swallowtail Papilio xuthus L. (Papilionidae) that share citrus plants as their main food source. Although all T. kanzawai and some active stage P. citri tried to escape from the coincidental IGP, some were consumed together with eggs, quiescent mites, and host plant leaves, suggesting that coincidental IGP occurs on spider mites in the wild. Moreover, neither hornworms nor swallowtail caterpillars distinguished between spider mite-infested and uninfested leaves, suggesting that the mite-infested leaves do not discourage caterpillar feeding. The reasons that the mites have no effective defense against coincidental IGP other than escaping are discussed.     

Social Familiarity Governs Prey Patch-Exploitation, - Leaving and Inter-Patch Distribution of the Group-Living Predatory Mite Phytoseiulus persimilis

Background

In group-living animals, social interactions and their effects on other life activities such as foraging are commonly determined by discrimination among group members. Accordingly, many group-living species evolved sophisticated social recognition abilities such as the ability to recognize familiar individuals, i.e. individuals encountered before. Social familiarity may affect within-group interactions and between-group movements. In environments with patchily distributed prey, group-living predators must repeatedly decide whether to stay with the group in a given prey patch or to leave and search for new prey patches and groups.

Methodology/Principal Findings

Based on the assumption that in group-living animals social familiarity allows to optimize the performance in other tasks, as for example predicted by limited attention theory, we assessed the influence of social familiarity on prey patch exploitation, patch-leaving, and inter-patch distribution of the group-living, plant-inhabiting predatory mite Phytoseiulus persimilis. P. persimilis is highly specialized on herbivorous spider mite prey such as the two-spotted spider mite Tetranychus urticae, which is patchily distributed on its host plants. We conducted two experiments with (1) groups of juvenile P. persimilis under limited food on interconnected detached leaflets, and (2) groups of adult P. persimilis females under limited food on whole plants. Familiar individuals of both juvenile and adult predator groups were more exploratory and dispersed earlier from a given spider mite patch, occupied more leaves and depleted prey more quickly than individuals of unfamiliar groups. Moreover, familiar juvenile predators had higher survival chances than unfamiliar juveniles.

Conclusions/Significance

We argue that patch-exploitation and -leaving, and inter-patch dispersion were more favorably coordinated in groups of familiar than unfamiliar predators, alleviating intraspecific competition and improving prey utilization and suppression.