A method to assess the effects of pesticides on the predatory mite Phytoseiulus persimilis (Acari Phytoseiidae) in the laboratory

Phytoseiulus persimilis Athias-Henriot (Acari Phytoseiidae) is a major predator of Tetranychus urticae (Acari Tetranychidae). The performance of P. persimilis in controlling T. urticae may be altered by pesticides used to manage other pests. Therefore, knowledge of the side-effects of pesticides is essential for IPM. A number of laboratory methods were suggested to evaluate pesticide side-effects on predatory mites. Most methods assess residual effects only, and a number of them are characterised by high predator escape rates from experimental units. A method aimed at evaluating the topical and residual effects of pesticides on P. persimilis is herein described. Mites were treated by microimmersion and then reared in holding cells, on bean leaves previously dipped in a pesticide solution. Three insecticides (pyrethrins, spinosad and thiamethoxam), an insecticide-acaricide (abamectin), and two fungicides (azoxystrobin and tolylfluanide) were evaluated. The strain of P. persimilis used for evaluation was collected from unsprayed vegetable plants. All the pesticides affected the survival and fecundity of P. persimilis. Pesticides did not affect the egg-hatching of P. persimilis females exposed to pesticides. Pyrethrins and abamectin proved to be more toxic than other pesticides, and thiamethoxam was more toxic than spinosad, azoxystrobin and tolylfluanide. The escape rate from experimental units was lower than 5% in all trials. Additional experiments were performed on P. persimilis eggs by dipping leaves with eggs in the pesticide solution. None of the pesticides affected egg survival. Semi-field trials conducted on potted bean plants obtained results similar to those reported in laboratory trials.     

Altered host plant preference of Tetranychus urticae and prey preference of its predator Phytoseiulus persimilis (Acari: Tetranychidae, Phytoseiidae) on transgenic Cry3Bb-eggplants

The behavior of the two-spotted spider mite, Tetranychus urticae Koch and the predatory mite Phytoseiulus persimilis A.-H. was investigated in laboratory experiments with transgenic Bt-eggplants, Solanum melongena L., producing the Cry3Bb toxin and corresponding isogenic, non-transformed eggplants. In bitrophic experiments, dual-choice disc tests were conducted to reveal the effects of transgenic eggplants on host plant preference of T. urticae. Adult spider mite females were individually placed on leaf discs (2 cm diameter) and were observed during five days. Females occurred significantly more frequently on transgenic halves on which also significantly more T. urticae eggs were found. The effects of a Cry3Bb-eggplant fed prey on the feeding preference of P. persimilis were investigated in tritrophic experiments. Sixteen spider mite females, eight of which had been taken from transgenic and eight from isogenic eggplants, were offered to well-fed females of P. persimilis and numbers of respective spider mites consumed were registered 12 h later when the predators were offered new spider mites again. This procedure was repeated six times. The results revealed that predatory mites consumed significantly less Bt-fed spider mites than prey that had been raised on control eggplants. These results indicate that eggplants expressing the Cry3Bb toxin for resistance against the Colorado potato beetle are more preferred by spider mites but are less preferred by their predator P. persimilis. Possible consequences of these findings for biological control of spider mites on eggplants are discussed.     

PCR-based identification of the pathogenic bacterium, Acaricomes phytoseiuli, in the biological control agent Phytoseiulus persimilis (Acari: Phytoseiidae)

The predatory mite, Phytoseiulus persimilis is an important biological control agent of herbivorous spider mites. This species is also intensively used in the study of tritrophic effects of plant volatiles in interactions involving plants, herbivores, and their natural enemies. Recently, a novel pathogenic bacterium, Acaricomes phytoseiuli, has been isolated from adult P. persimilis females. This pathogen causes a characteristic disease syndrome with dramatic changes in longevity, fecundity, and behavior. Healthy P. persimilis use spider mite-induced volatiles to locate prey patches. Infection with A. phytoseiuli strongly reduces the attraction to herbivore-induced plant volatiles. The loss of response to herbivore-induced plant volatiles along with the other disease symptoms can have a serious impact on the success of biological control of spider mites. In this study, we have developed a molecular tool (PCR) to detect the pathogenic bacterium in individual predatory mites. PCR primers specific for A. phytoseiuli were developed based on 16S ribosomal DNA of the bacterium. The PCR test was validated with DNA extracted from predatory mites that had been exposed to A. phytoseiuli. A survey on different P. persimilis populations as well as other predatory mite species from several companies that rear predatory mites for biological control revealed that the disease is widespread in Europe and is restricted to P. persimilis. The possibility that the predatory mites get infected via their prey Tetranychus urticae could be eliminated since the PCR test run on prey gave a negative result.     

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.     

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.     

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.     

Interactions in a tritrophic acarine predator-prey metapopulation system V: Within-plant dynamics of Phytoseiulus persimilis and Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae)

To investigate the relative contributions of bottom-up (plant condition) and top-down (predatory mites) factors on the dynamics of the two-spotted spider mite (Tetranychus urticae), a series of experiments were conducted in which spider mites and predatory mites were released on bean plants. Plants inoculated with 2, 4, 8, 16, and 32 adult female T. urticae were either left untreated or were inoculated with 3 or 5 adult female predators (Phytoseiulus persimilis) one week after the introduction of spider mites. Plant area, densities of T. urticae and P. persimilis, and plant injury were assessed by weekly sampling. Data were analysed by a combination of statistical methods and a tri-trophic mechanistic simulation model partly parameterised from the current experiments and partly from previous data. The results showed a clear effect of predators on the density of spider mites and on the plant injury they cause. Plant injury increased with the initial number of spider mites and decreased with the initial number of predators. Extinction of T. urticae, followed by extinction of P. persimilis, was the most likely outcome for most initial combinations of prey and predators. Eggs constituted a relatively smaller part of the prey population as plant injury increased and of the predator population as prey density decreased. We did not find statistical evidence of P. persimilis having preference for feeding on T. urticae eggs. The simulation model demonstrated that bottom-up and top-down factors interact synergistically to reduce the density of spider mites. This may have important implications for biological control of spider mites by means of predatory mites.     

First record ofPhytoseiulus persimilis (Acari: Phytoseiidae) in Turkey

The predatory mitePhytoseiulus persimilis Athias-Henriot is widely used for biological control of spider mites in greenhouse. Despite its records from various Mediterranean countries,P. persimilis was not recorded from Turkey. Here we report the natural colonies ofP. persimilis observed along the Mediterranean coast of Turkey.     

Spider mite infestations reduce Bacillus thuringiensis toxin concentration in corn leaves and predators avoid spider mites that have fed on Bacillus thuringiensis corn

Perceived benefits of insecticidal transgenic crops include reduced usage of broad‐based insecticides, and therefore lower risk to non‐target organisms. Numerous studies have documented low or no direct toxicity of Bacillus thuringiensis (Bt)‐derived toxins against non‐target organisms, but there has been less research on (a) effects of secondary pest infestations on Bt expressing in crops and (b) behavioural responses by predators feeding on host arthropods from Bt crops – both topics are investigated in this study. We quantified predation by the obligate spider mite predator Phytoseiulus persimilis of carmine spider mites (Tetranychus cinnabarinus), reared on Bt or non‐Bt corn (Zea mays). Both no‐choice and two‐choice studies were conducted. In addition, we quantified toxin levels in corn leaves with/without spider mite infestation. Under no‐choice conditions, P. persimilis consumed non‐Bt spider mites at a faster rate than Bt spider mites. Under two‐choice conditions, P. persimilis spent more time in the vicinity of non‐Bt spider mites than near Bt spider mites. Corn infested with spider mites exhibited lower toxin levels than non‐infested plants. These results suggest potentially complex interactions among non‐target herbivores, their natural enemies and Bt crops.     

Population survey of phytoseiid mites and spider mites on peach leaves and wild plants in Japanese peach orchard

A population survey of phytoseiid mites and spider mites was conducted on peach leaves and wild plants in Japanese peach orchards having different pesticide practices. The phytoseiid mite species composition on peach leaves and wild plants, as estimated using quantitative sequencing, changed during the survey period. Moreover, it varied among study sites. The phytoseiid mite species compositions were similar between peach leaves and some wild plants, such as Veronica persica, Paederia foetida, Persicaria longiseta, and Oxalis corniculata with larger quantities of phytoseiid mites, especially after mid-summer. A PCR-based method to detect the ribosomal ITS sequences of Tetranychus kanzawai and Panonychus mori from phytoseiid mites was developed. Results showed that Euseius sojaensis (specialized pollen feeder/generalist predator) uses both spider mites as prey in the field.     

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.     

Comparative toxicity of some acaricides to the predatory mite, Phytoseiulus persimilis and the twospotted spider mite, Tetranychus urticae

The relative toxicity of someacaricides to the predatory mite, Phytoseiulus persimilis and the twospottedspider mite, Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae) wasevaluated in laboratory. Five of theacaricides tested, including bifenazate,acequinocyl, chlorfenapyr, flufenoxuron andfenbutatin oxide, were much less toxic to adultfemales and immatures of P. persimilisthan to those of T. urticae, and adultfemale predators treated with these fiveacaricides produced 84±96% as many eggs as didcontrol females. Etoxazole did not seriouslyaffect the survival and reproduction of adultfemale predators but caused high mortalityrates in eggs and larvae of P.persimilis. Milbemectin and fenazaquin werevery toxic to adult females and immatures ofP. persimilis. Adult female predatorssurvived on a diet of spider mites treated withbifenazate, acequinocyl, chlorfenapyr,flufenoxuron and fenbutatin oxide, and theirfecundity, prey consumption and the sex ratioof the progeny were not substantially affected. Based on the results, bifenazate, acequinocyl,chlorfenapyr, flufenoxuron and fenbutatin oxideappeared to be the promising candidates for usein integrated mite management programs whereP. persimilis is the major naturalenemy.     

Risk assessment of an exotic biocontrol agent: Phytoseiulus persimilis (Acari: Phytoseiidae) does not establish in rainforest in southeast Queensland

Abstract The Chilean predatory mite, Phytoseiulus persimilis Athias-Henriot, appeared in Australia in 1978 soon after being introduced into New Zealand as a specialized biological control agent of spider mites. It is known to be naturalized in agricultural habitats in southeast Queensland, Australia, although nothing is known about its distribution in native ecosystems. In order to determine whether P. persimilis is able to invade subtropical rainforest, we placed potted bean plants infested with its preferred prey, the two-spotted mite (Tetranychus urticae C.L. Koch), at 50 m intervals for 200 m on either side of the rainforest-field ecotone at four sites in southeast Queensland. Two, 4 and 6 weeks after placement, five leaves were sampled from each pot and any phytoseiid mites present were identified. The initial experiment took place in the spring and was repeated in summer and in autumn of 1997. At all four sites and in all three seasons P. persimilis rapidly colonized all of the pots in fields. In the rainforest, however, some pots were never colonized and significant populations of the predator developed only in the summer, and then only at the first stations, 50 m into the forest. These results suggest that even when its preferred prey is present, subtropical rainforest is not an appropriate habitat for P. persimilis. In addition, we reviewed extensive collections of phytoseiid mites from native forests and synanthropic habitats in Australia and found P. persimilis records only from fields, glasshouses, gardens, weeds, roadsides and similar disturbed habitats dominated by introduced plants, again suggesting that this biocontrol agent is not a rainforest invader.     

Vertical dispersal of the two-spotted spider mite Tetranychus urticae, and the predatory mite Phytoseiulus persimilis on dwarf hops

1 The pattern of dispersion within plants of the two-spotted spider mite, Tetranychus urticae, and its predator, the phytoseiid Phytoseiulus persimilis, was studied on the dwarf hop variety First Gold from May to September in 1997 and 1998. 2 Spider mite populations developed on the lower leaves initially but, by late July, as the numbers of mites increased, most were found towards the top of plants. From early August, the numbers of spider mites decreased most rapidly on the upper parts of plants. 3 Where P. persimilis was released, the predator maintained the numbers of T. urticae below those found on non-release plots throughout the season. 4 By early August, the predator’s pattern of dispersion was similar to that of the pest. 5 Predators spread to non-release plots by 20 June in 1997 and 24 July in 1998 and eventually became more numerous than on the plots where they had been released.     

Induced defence in detached uninfested plant leaves: effects on behaviour of herbivores and their predators

Summary Induction of plant defence against herbivores may include the attraction by volatile infochemicals of natural enemies of the herbivore. The emitted volatiles that mediate this attraction may also affect the behaviour of the herbivore itself. In this paper we investigate the response of the herbivorous spider miteTetranychus urticae and the predatory mitePhytoseiulus persimilis towards volatiles whose production is induced in detached Lima bean leaves. Detached uninfested Lima bean leaves were incubated on wet cotton wool on which bean leaves infested with spider mites (T. urticae) were present simultaneously or had been present previously. These treatments induce the production of volatile infochemicals in the uninfested bean leaf tissue: predatory mites are attracted and spider mites are deterred. These are the first data on the response of predators and herbivores to plant volatiles whose production was induced in detached uninfested leaves.     

Population dynamics of interacting predatory mites,Phytoseiulus persimilis and Neoseiulus californicus,held on detached bean leaves

The success of combined release of the predatory mitesPhytoseiulus persimilis and Neoseiulus californicus insuppression of spider mites may be related to the effects of the interactionsbetween the two predators on their population dynamics. We studied populationgrowth and persistence of the specialist P. persimilis andthe generalist N. californicus reared singly versus rearedin combination after simultaneous and successive predator introductions ondetached bean leaf arenas with abundant prey, Tetranychusurticae, and with diminishing prey. When reared singly with abundantprey, either predator population persisted at high densities to the end of theexperiment. In every predator combination system with abundant prey and variousinitial predator:predator ratios N. californicus displacedP. persimilis. When held singly with diminishing prey, thepopulation of P. persimilis grew initially faster than thepopulation of N. californicus but both species reachedsimilar population peaks. Irrespective whether reared singly or in combination,N. californicus persisted three to five times longer afterprey depletion than did P. persimilis. Regarding thecrucial interactions in the predator combination systems, we conclude thatintraguild predation was a stronger force than food competition and finallyresulted in the displacement of P. persimilis. Previousstudies showed that intraguild predation between the specialist P.persimilis and the generalist N. californicusisstrongly asymmetric favoring the generalist. We discuss the implications ofpotential interactions between P. persimilis andN. californicus to biological control of spider mites.     

The role of glandular and non-glandular trichomes in the negative interactions between strawberry cultivars and spider mite

In tropical countries, spider mite (Tetranychus urticae Koch) is a major pest of strawberries. This pest is mainly controlled by the application of pesticides. Use of pest-resistant cultivars is a healthy and environment-friendly alternative to pesticide use. This paper describes the role of glandular and non-glandular trichomes in the interaction between strawberry cultivars and spider mite. The methodology used in this study was based on two bioassays. First, the thumbtack bioassay of Weston and Snyder was used to differentiate strawberry cultivars in terms of the distance travelled by the mites. Second, different types of trichomes present on the abaxial surface of the strawberry leaves were identified and counted. The results of this study showed a significantly negative correlation between the distance travelled by the spider mites and the density of glandular trichomes on the strawberry plant. The cultivars Camino Real and Dover had the highest densities of glandular trichomes and the shortest distance travelled by the mites. In contrast, the cultivars Ventana and Toyonoka had the lowest density of glandular trichomes and the longest distance travelled by the spider mites. The high density of glandular trichomes might have been responsible for the spider mite non-preference to the Camino Real and Dover strawberry cultivars, whereas the non-glandular trichomes minimally contributed to this non-preference. The results of this study affirm the role of glandular trichomes in negative interactions between strawberry and spider mites.     

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.     

Mite pests and their predators on seven vegetable crops (Arachnida: Acari)

During this study the frequency of occurrence and dominance of phytophagous and predatory mites harboring seven vegetable crops in Egypt, namely common bean, cowpea, eggplant, okra, squash, sweet pepper and sweet potato during 2017–2018 were investigated to identify predatory mites that might be useful for the biological control of the phytophagous mites. Three phytophagous and nine predatory mite species were surveyed. The two spotted spider mite Tetranychus urticae Koch of the family Tetranychidae was the dominant pest on these vegetables, while phytoseiids Phytoseiulus persimilis (Athias- Henriot), Typhlodromips swirskii (Athias- Henriot) and Euseius scutalis Chant were the dominant predators. The population of the native or indigenous phytoseiid mite fauna in Egypt such as Phytoseiulus persimilis could be considered as a good biocontrol agent and a part of the Integrated Pest Management (IPM) program in the future. Mite fauna of Egypt especially local populations of Phytoseiulus persimilis can be considered for implementation in future Integrated Pest Management (IPM).     

Long-term stability in the interaction betweenTetranychus urticae andPhytoseiulus persimilis producing successful integrated control on roses in southeast Queensland

Phytoseiulus persimilis Athias-Henriot successfully controlledTetranychus urticae Koch on rose hedges in an integrated mite control programme in two unheated plastic-covered tunnels at Cleveland in southern Queensland. Mite populations were monitored fortnightly for nearly three years in one tunnel and for two years in a second. Once established,P. persimilis quickly suppressedT. urticae and then persisted. A relatively stable, long-term, low-level interaction developed between the two species under normal commercial conditions. In one tunnel, the production (upper) level of the four rose hedges contained fewer mites of both species per compound leaf (1.71 of all stages ofT. urticae, 0.38 motiles; 0.25 of all stages ofP. persimilis, 0.12 motiles) than the maintenance (lower) layer (2.02 of all stages ofT. urticae, 0.75 motiles; 0.35 of all stages ofP. persimilis, 0.21 motiles). On 68% of sampling occasions, 10% or less of compound leaves in the production layer were infested withT. urticae (all stages including eggs) and control was excellent throughout the 30-month period afterP. persimilis was established, there being no economic losses. In the second tunnel, there was no significant difference between mite numbers in the production and maintenance layers of the two hedges examined. The overall mean number of all stages ofT. urticae per compound leaf was 3.2 (1.45 motiles), and ofP. persimilis 0.46 (0.25 motiles). Control here was slightly less effective than in the first tunnel, but was still satisfactory, with 10% or less of leaves being infested on 45.5% of sampling occasions (20% or less on 66% of sampling occasions) withT. urticae (all stages including eggs).Phytoseiulus persimilis was not reintroduced or redistributed during the course of the observations. An auxiliary miticide (clofentezine) was applied on only one occasion to selected areas in the second tunnel. The influence of high temperatures on control byP. persimilis is discussed.