Pest species diversity enhances control of spider mites and whiteflies by a generalist phytoseiid predator

To test the hypothesis that pest species diversity enhances biological pest control with generalist predators, we studied the dynamics of three major pest species on greenhouse cucumber: Western flower thrips, Frankliniella occidentalis (Pergande), greenhouse whitefly, Trialeurodes vaporariorum (Westwood), and two-spotted spider mites, Tetranychus urticae Koch in combination with the predator species Amblyseius swirskii Athias-Henriot. When spider mites infested plants prior to predator release, predatory mites were not capable of controlling spider mite populations in the absence of other pest species. A laboratory experiment showed that predators were hindered by the webbing of spider mites. In a greenhouse experiment, spider mite leaf damage was lower in the presence of thrips and predators than in the presence of whiteflies and predators, but damage was lowest in the presence of thrips, whiteflies and predators. Whitefly control was also improved in the presence of thrips. The lower levels of spider mite leaf damage probably resulted from (1) a strong numerical response of the predator (up to 50 times higher densities) when a second and third pest species were present in addition to spider mites, and (2) from A. swirskii attacking mobile spider mite stages outside or near the edges of the spider mite webbing. Interactions of spider mites with thrips and whiteflies might also result in suppression of spider mites. However, when predators were released prior to spider mite infestations in the absence of other pest species, but with pollen as food for the predators, we found increased suppression of spider mites with increased numbers of predators released, confirming the role of predators in spider mite control. Thus, our study provides evidence that diversity of pest species can enhance biological control through increased predator densities.     

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.     

The Effects of Timing and Rates of Release of Phytoseiulus persimilis against Two-spotted Spider Mite Tetranychus urticae on Dwarf Hops

Single inoculative releases of the phytoseiid mite Phytoseiulus persimilis were made against the two-spotted spider mite, Tetranychus urticae, on two varieties of dwarf hops in 1996 and 1997 at means of 20, 10, 5, 2.5 and nil per plant, and at up to three timings. The numbers of spider mites recorded on leaves after the predators were released were related inversely to the rates of release. The earliest releases of the predator maintained spider mites at lower population densities than did those made later in the year. In all treatments the numbers of spider mites decreased when the prey:predator ratio reached approximately 10:1.     

Evaluation of the predatory mite, Neoseiulus californicus, for spider mite control on greenhouse sweet pepper under hot arid field conditions

The efficacy of Neoseiulus californicus (a generalist predatory mite) for the biological control of Tetranychus urticae, was compared to release of Phytoseiulus persimilis (a specialist predatory mite) and an acaricide treatment in sweet pepper plants grown in greenhouse tunnels in a hot and arid climate. To ensure uniform pest populations, spider mites were spread on pepper plants in two seasons; a natural infestation occurred in one season. Predators were released prophylactically and curatively in separate tunnels when plants were artificially infested with spider mites, and at low and moderate spider mite populations when infestations occurred naturally. Although spider mite populations did not establish well the first year, fewer spider mites were recovered with release of N. californicus than with all other treatments. In the second year, spider mites established and the prophylactic release of N. californicus compared favorably with the acaricide-treated plants. In the course of monitoring arthropod populations, we observed a significant reduction in western flower thrips (Frankliniella occidentalis) populations in tunnels treated with N. californicus as compared with non-treated control tunnels. Our field trials validate results obtained from potted-plant experiments and confirm that N. californicus is a superior spider mite predator at high temperatures and low humidities.     

Evaluation of dry-adapted strains of the predatory mite Neoseiulus californicus for spider mite control on cucumber, strawberry and pepper

The goal of this study was to evaluate spider mite control efficacy of two dry-adapted strains of Neoseiulus californicus. Performance of these strains were compared to a commercial strain of Phytoseiulus persimilis on whole cucumber, pepper and strawberry plants infested with Tetranychus urticae at 50 +/- 5% RH. Under these dry conditions predators' performance was very different on each host plant. On cucumber, spider mite suppression was not attained by any of the three predators, plants 'burnt out' within 4 weeks of spider mite infestation. On strawberry, all predators satisfactorily suppressed spider mites yet they differed in short term efficacy and persistence. Phytoseiulus persimilis suppressed the spider mites more rapidly than did the BOKU and SI N. californicus strains. Both N. californicus strains persisted longer than did P. persimilis. The BOKU strain was superior to SI in population density reached, efficacy in spider mite suppression and persistence. On pepper, in the first 2 weeks of the experiment the BOKU strain was similar to P. persimilis and more efficacious in spider mite suppression than strain SI. Four weeks into the experiment the efficacy of P. persimilis dropped dramatically and was inferior to the SI and BOKU strains. Overall, mean predator density was highest on plants harbouring the BOKU strain, lowest on plants with P. persimilis and intermediate on plants with the SI strain. Implications for biocontrol of spider mites using phytoseiid species under dry conditions are discussed.     

Absence of odour-mediated avoidance of heterospecific competitors by the predatory mite Phytoseiulus persimilis

Arthropods use odours associated with the presence of their food, enemies and competitors when searching for patches. Responses to these odours therefore determine the spatial distribution of animals, and are decisive for the occurrence and strength of interactions among species. Therefore, a logical first step in studying food web interactions is the analysis of behaviour of individuals that are searching for patches of food. We followed this approach when studying interactions in an artificial food web occurring on greenhouse cucumber in the Netherlands. In an earlier paper we found that one of the predators of the food web, the predatory mite Phytoseiulus persimilis Athias-Henriot, used to control spider mites, discriminates between odours from plants with spider mites, Tetranychus urticae Koch, and plants with spider mites plus conspecific predators. The odours used for discrimination are produced by adult prey in response to the presence of predators, and probably serve as an alarm pheromone to warn related spider mites. Other predator species may also trigger production of this alarm pheromone, which P. persimilis could use in turn to avoid plants with heterospecific predators. We therefore studied the response of the latter to odours from plants with spider mites and 3 other predator species, i.e. the generalist predatory bug Orius laevigatus (Fieber), the polyphagous thrips Frankliniella occidentalis and the spider-mite predator Neoseiulus californicus (McGregor). Both olfactometer and greenhouse release experiments yielded no evidence that P. persimilis avoids plants with any of the 3 heterospecific predators. This suggests that these predators do not elicit production of alarm pheromones in spider mites, and we argue that this is caused by a lack of coevolutionary history. The consequences of the lack of avoidance of heterospecific predators for interactions in food webs and biological control are discussed.     

Prey preference,intraguild predation and population dynamics of an arthropod food web on plants

The theory of intraguild predation (IGP) largely studies effects on equilibrium densities of predators and prey, while experiments mostly concern transient dynamics. We studied the effects of an intraguild (IG) predator, the bug Orius laevigatus, on the population dynamics of IG-prey, the predatory mite Phytoseiulus persimilis, and a shared prey, the phytophagous two-spotted spider mite Tetranychus urticae, as well as on the performance of cucumber plants in a greenhouse. The interaction of the predatory mite and the spider mite is highly unstable, and ends either by herbivores overexploiting the plant or predators exterminating the herbivores. We studied the effect of IGP on the transient dynamics of this system, and compared the dynamics with that predicted by a simple population-dynamical model with IGP added. Behavioural studies showed that the predatory bug and the predatory mite were both attracted to plants infested by spider mites and that the two predators did not avoid plants occupied by the other predator. Observations on foraging behaviour of the predatory bug showed that it attacks and kills large numbers of predatory mites and spider mites. The model predicts strong effects of predation and prey preference by the predatory bugs on the dynamics of predatory mites and spider mites. However, experiments in which the predatory bug was added to populations of predatory mites and spider mites had little or no effect on numbers of both mite species, and cucumber plant and fruit weight.     

Functionally different predators break down antipredator defenses of spider mites

Prey that lives with functionally different predators may experience enhanced mortality risk, because of conflicts between the specific defenses against their predators. Because natural communities usually contain combinations of prey and functionally different predators, examining risk enhancement with multiple predators may help to understand prey population dynamics. It is also important in an applied context: risk enhancement with multiple biological control agents could lead to successful suppression of pests. We examined whether risk enhancement occurs in the spider mite Tetranychus kanzawai Kishida (Acari: Tetranychidae) when exposed to two predator species: a generalist ant, Pristomyrmex punctatus Mayr (Hymenoptera: Formicidae), and a specialist predatory mite, Neoseiulus womersleyi Schicha (Acari: Phytoseiidae). We replicated microcosms that consisted of spider mites, ants, and predatory mites. Spider mites avoided generalist ants by staying inside their webs on leaf surfaces. In contrast, spider mites avoided specialist predatory mites that intruded into their webs by exiting the web, which obviously conflicts with the defense against ants. In the presence of both predators, enhanced mortality of spider mites was observed. A conflict occurred between the spider mites’ defenses: they seemed to move out of their webs and be preyed upon by ants. This is the first study to suggest that risk enhancement occurs in web‐spinning spider mites that are exposed to both generalist and specialist predator species, and to provide evidence that ants can have remarkable synergistic effects on the biological control of spider mites using specialist predatory mites.     

Oviposition Behavior of Interacting Predatory Mites: Response to the Presence of Con- and Heterospecific Eggs

Oviposition behavior may be affected by the presence of potential future competitors, mates, or predators of offspring. We examined patch choice, oviposition site preference and egg production in the predaceous mites Phytoseiulus persimilis and Neoseiulus californicus (Acari: Phytoseiidae) when given a choice between paired spider mite patches with and without conspecific eggs, with and without heterospecific eggs, and with conspecific or heterospecific eggs. Neoseiulus californicus females had no patch preference and distributed their eggs randomly in all choice situations. This was also the case with P. persimilis females given a choice between patches with and without conspecific eggs and between patches with either con- or heterospecific eggs. Phytoseiulus persimilis females confronted with patches with and without heterospecific eggs preferentially stayed and oviposited in the predator free patches. We discuss the oviposition strategies of P. persimilis and N. californicus with respect to food competition, cannibalism and intraguild predation.     

Evaluation of predatory mite (Acari: Phytoseiidae) releases to suppress spruce spider mites, Oligonychus ununguis (Acari: Tetranychidae), on juniper

A laboratory trial evaluated four phytoseiid species for their potential as biological control agents of spruce spider mite, Oligonychus ununguis (Jacobi) (Acari: Tetranychidae). An augmentative biological control approach, using the predatory mites Neoseiulus fallacis Garman and Galendromus occidentalis Nesbitt (Acari: Phytoseiidae), was evaluated for reducing pest mite densities and injury, and economic costs on Juniperus chinensis 'Sargentii' A. Henry (Cupressaceae) in an outdoor nursery. Sequential releases of predator species, individually and in combination, were tested and compared with two commonly used miticides, a low-toxicity miticide, horticultural oil, and a conventional miticide, hexythiazox. Timing of treatments was based on grower-determined need, and predator release rates were based on guidelines in literature received from producers of beneficial organisms. Predator releases were more expensive and provided less effective suppression of spruce spider mites, resulting in greater spider mite injury to plants, compared with conventional pesticides. However, spider mite damage to plants did not differ in an economically meaningful way between treatments. Unsatisfactory levels of control seem related to under estimations of actual spider mite abundance based on grower perceptions and the beat sampling technique used to estimate predator release rates. These data suggest that when initial populations of spruce spider mite are high, it is unlikely that sequential releases of predator species, individually or in combination, will suppress spider mite populations. In this trial, augmentative biological control control was 2.5-7 times more expensive than chemical controls.     

Combined versus Single Species Release of Predaceous Mites: Predator–Predator Interactions and Pest Suppression

Interactions such as competition, intraguild predation (IGP), and cannibalism affect the development and coexistence of predator populations and can have significance for biological control of commonly exploited pest organisms. We studied the consequences of combined versus single release of two predaceous mite species (Phytoseiidae), with differing degrees of diet specialization, on their population dynamics and the suppression of the carmine spider mite, Tetranychus cinnabarinus Boisduval (Tetranychidae), on greenhouse-grown gerbera. Population growth of the specialist predator Phytoseiulus persimilis Athias-Henriot was greater and population decline steeper when released in combination with the generalist Neoseiulus californicus McGregor than when released alone. In contrast, the N. californicus population grew and declined more gradually when released in combination with P. persimilis, compared to the single species release. The differential impact on each other's population dynamics can be primarily attributed to contrasting properties in competition, IGP, and cannibalism. At the same overall predator density and as long as prey was abundant, the specialist P. persimilis was more strongly affected by intraspecific competition than by interspecific competition with the generalist N. californicus. In contrast, interspecific competition with P. persimilis had a greater impact on N. californicus than intraspecific competition. After prey depletion, the generalist predator N. californicus was more likely to engage in IGP than was the specialist predator P. persimilis. Overall, the study demonstrates that prey specificity has significance for the quality and intensity of predator–predator interactions and indicates potential implications for biological control of spider mites. All predator releases (i.e., either species alone and both species in combination) resulted in reduction of the spider mite population to zero density. Individual release of the specialist P. persimilis led to the most rapid spider mite suppression. Nonetheless, in perennial greenhouse-grown crops P. persimilis and N. californicus could have complementary effects and a combination of the two predators could enhance long-term biological control of spider mites. The potential risks and benefits associated with the release of both species are discussed.     

Predatory role of Neoseiulus fallacis (Acari: Phytoseiidae): spatial and temporal dynamics in Washington red raspberry fields

The seasonal abundance of spider mites and their predator Neoseiulus fallacis (Garman) (Acari: Phytoseiidae) was determined during three consecutive years in Washington State red raspberry fields. Tetranychus urticae Koch (Acari: Tetranychidae), Eotetranychus carpini borealis (Ewing) (Acari: Tetranychidae), and N. fallacis were commonly found in Skagit and Whatcom Counties. E. carpini borealis colonized the fruiting canes earlier in the season than T. urticae. The two phytophages overlapped in midseason, but T. urticae entered diapause earlier than E. carpini borealis and N. fallacis. Densities of N. fallacis increased with increase in spider mite densities. However, the numerical response of the predator was more evident for T. urticae than for E. carpini borealis. Nevertheless, the predator was spatially associated with the two prey species. The spatial and seasonal distribution of N. fallacis in relationship to host plant phenology and prey distribution may influence the effectiveness of this predator as a biological control agent against spider mites in red raspberry. Densities of the predator increased too late to prevent spider mite damage. The predatory role of N. fallacis could be enhanced by introducing or conserving predators that are more tolerant to climatic factors that prevail in and around the cane canopy in the beginning of the season.     

Plants with spider-mite prey attract more predatory mites than clean plants under greenhouse conditions

Although many predators and parasitoids are known to respond to odours produced by plants infested with their prey under laboratory conditions, there are actually few studies that show that this response leads to higher numbers of predators or parasitoids on the plants under natural conditions. Here we study the response of predatory mites (Phytoseiulus persimilis Athias-Henriot, Acari, Phytoseiidae) to odours from cucumber plants infested with two-spotted spider mites (Tetranychus urticae Koch, Acari, Tetranychidae) in greenhouse release experiments, where predators were released in the centre of a hexagon of cucumber plants. Forty to 57% of all predators released were recaptured on plants within 7 h. Of these, an average of 79.5% were found on infested plants, indicating that these attract about 4 times as many predators as do clean plants. Hence, the blind predatory mites were guided to the plants with prey by herbivore-induced odours produced by the plant, as was indicated by olfactometer experiments, where it was found that P. persimilis preferred odours from infested cucumber plants to odours from clean cucumber plants. The long-range searching behaviour of P. persimilis is discussed.     

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.     

Spider Mites Avoid Plants with Predators

While searching for food, prey can use cues associated with their predators to select patches with a reduced predation risk. In many cases, odours indicate the presence of both food and predators. Spider mites are known to use odours to locate food and mates, but also to avoid interspecific competitors. We studied the response of the two-spotted spider mite, Tetranychus urticae, to cues associated with the presence of their predators, the phytoseiid Phytoseiulus persimilis. We found that the spider mites strongly avoid plants defended by this predator, but do not avoid plants with another predatory mite, Neoseiulus californicus. Since P. persimilis is commonly used in the greenhouse where our strain of T. urticae was collected and strains of this pest are known to adapt to greenhouse environments, we hypothesize that there has been selection on the pest to recognize its enemy. We further hypothesize that there has been no selection to recognize N. californicus, as it has not been used against two-spotted spider mites in the greenhouse where our spider mites were collected. We discuss the implications of avoidance of predation by spider mites and non-lethal effects of predators for biological control of this pest in greenhouses.     

Host-plant-mediated interaction between populations of a true omnivore and its herbivorous prey

Western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), are competitors with twospotted spider mites, Tetranychus urticae Koch (Acari: Tetranychidae), for plant resources and potential predators on spider mites when the opportunity arises. Which interaction predominates may depend on relative population densities and individual species’ responses to the plants on which they co‐occur. We examined interactions between populations of thrips and spider mites on several cultivars of two bedding plants: impatiens (Impatiens wallerana Hook.f) cultivars ‘Impulse Orange’ and ‘Cajun Carmine’, and ivy geranium [Pelargonium peltatum (L.) L’Her ex Aiton] cultivars ‘Sybil Holmes’ and ‘Amethyst 96’. Four combinations of thrips and mite numbers were studied: thrips alone, mites alone, and two densities of thrips and mites together. We compared population numbers after 4 weeks. Overall, mite numbers increased more rapidly than thrips did, but both species increased more rapidly on impatiens than on ivy geraniums. Between impatiens cultivars, thrips and mites increased more slowly on ‘Cajun Carmine’ (i.e., it was more resistant) than on ‘Impulse Orange’. On ivy geraniums, spider mites increased more slowly on ‘Sybil Holmes’ than on ‘Amethyst 96’ but the reverse was the case for thrips. Regardless of plant species or cultivar, thrips had a strong negative effect on spider mites whenever they co‐occurred, suppressing mite population growth by around 50% compared to when mites were alone. However, the effect of spider mites on western flower thrips depended on the quality of the plant species. On impatiens, thrips co‐occurring with spider mites increased slightly more than thrips alone did, while on ivy geranium mites had a small negative effect on thrips. Contrary to expectations, thrips had a larger negative impact on spider mites on plants that were more susceptible to thrips than they did on plants more resistant to thrips. We suggest that host plants mediate the interaction between an omnivore and its herbivorous prey not only by altering individual diet choice but by changing the relative population dynamics of each species.     

Evaluation of predatory mites and Acramite for control of twospotted spider mites in strawberries in north central Florida

Greenhouse and field experiments were conducted from 2003 to 2005 to determine the effectiveness of two predatory mite species, Phytoseiulus persimilis Athias-Henriot and Neoseiulus californicus (McGregor), and a reduced-risk miticide, Acramite 50 WP (bifenazate), for control of twospotted spider mite, Tetranychus urticae Koch, in strawberries (Fragaria x ananassa Duchesne). In greenhouse tests, three treatments consisting of releases of P. persimilis, N. californicus, and an untreated control were evaluated. Both species of predatory mites significantly reduced twospotted spider mite numbers below those found in the control during the first 3 wk of evaluation. However, during week 4, twospotted spider mite numbers on the plants treated with P. persimilis increased and did not differ significantly from the control. Field studies used releases of P. persimilis and N. californicus, applications of Acramite, and untreated control plots. Both N. californicus and P. persimilis significantly reduced populations of twospotted spider mite below numbers recorded in the control plots. During the 2003-2004 field season P. persimilis took longer than N. californicus to bring the twospotted spider mite population under control (< 10 mites per leaflet). Acramite was effective in reducing twospotted spider mite populations below 10 mites per leaflet during the 2003-2004 field season but not during the 2004-2005 field season, possibly because of a late application. These findings indicate that N. californicus releases and properly timed Acramite applications are promising options for twospotted spider mite control in strawberries for growers in north Florida and other areas of the southeast.     

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.     

The possibilities for control of two‐spotted spider mite Tetranychus urticae on field‐grown strawberries in the UK by predatory mites

The potential of two species of predatory phytoseiid mites to control the two‐spotted spider mite, Tetranychus urticae, on unprotected field‐grown strawberries in the UK was investigated. Typhlodromus pyri, a native species, was able to control T. urticae in some circumstances, but was less effective under hot, dry conditions. Natural colonization by this species is likely to be too slow in plantations of 1–2 years life. Attempts to introduce this predator to strawberry fields on cut apple shoots were unsuccessful. The exotic predator Phytoseiulus persimilis, which is available from commercial sources, gave very good control of T. urticae when released onto strawberry plants in June. A release earlier in the year was less successful, so to prevent early build‐up of mites and possible plant damage it may sometimes be necessary to reduce spider mite numbers early in the year with an acaricide, before a later release of P. persimilis. The success of this integrated control strategy was demonstrated.     

Improved control capacity of the mite predator Phytoseiulus persimilis (Acari: Phytoseiidae) on tomato

The predatory mite Phytoseiulus persimilis is frequently reported to perform poorly on greenhouse tomatoes. As the predators are mass-reared on another host plant (bean), we supposed that they are poorly adapted to tomato, a plant densely packed with poisonous and sticky glandular hairs. This hypothesis was tested by comparing the control capacity of a stain of P. persimilis directly obtained from a mass rearing with the same strain after four generations on tomato. Both strains were released in a tomato crop in two identical compartments of a greenhouse and the population dynamics of prey (a tomato strain of Tetranychus urticae) and predator were recorded at weekly time intervals. It was found that the strain previously exposed to a tomato environment performed better than the unexposed strain: (1) its population increased faster; (2) the prey population declined faster; and (3) the damage to new-grown tomato leaves was considerably lower. To investigate the causes of the difference in performance between the exposed and unexposed strains, oviposition and survival rates were assessed on a diet of two-spotted spider mites on tomato leaf sections. In addition, the unexposed strain was tested on a diet of two-spotted spider mites on bean leaf sections. The difference in oviposition rates of both predator strains was small compare to the overall mean. However, the oviposition rate of the first generation of predators since transfer from bean to tomato dropped to less than half of the original value. Moreover, mortality in the first generation increased from 14% to 89%, whereas it decreased to 0% after four generations. Future research should clarify whether these changes in life history are due to selection or to physiological adaptation.