Both host and diet shape bacterial communities of predatory mites.

Microbial communities, derived from food, ambient, and inner, can affect host ecological adaption and evolution. Comparing with most phytophagous arthropods, predators may have more opportunities to develop specific microbiota depending on the level of prey specialization. To explore how diet sources affect host microbial communities and vary across predator species, we considered 3 types of predators from Phytoseiidae (Acari: Mesostigmata): polyphagous (Amblyseius orientalis Ehara, Neoseiulus barkeri Hughes, and Amblyseius swirskii Athias-Henrio), oligophagous (Neoseiulus californicus McGregor), and monophagous (Phytoseiulus persimilis Athias-Henriot) predatory mites. The polyphagous species were fed on 2 types of diets, natural prey and alternative prey. By using 16S rRNA sequencing, we found that diet was the main source of microbiota in predatory mites, while there was no clear pattern affected by prey specialization. Among 3 polyphagous predators, host species had a larger impact than prey on microbial composition. Unlike A. orientalis or N. barkeri which showed consistency in their microbiota, prey switching significantly affected ß-diversity of bacterial composition in A. swirskii, with 56% of the microbial alteration. In short, our results confirmed the substantial influence of diet on host microbial construction in predatory species, and highlighted species differences in shaping the microbiota which are not necessarily related to prey specialization.

Amblyseius orientalis shows high consumption and reproduction on Polyphagotarsonemus latus in China.

The broad mite, Polyphagotarsonemus latus (Banks) (Acari: Tarsonemidae), is a cosmopolitan pest that infests many greenhouse crops. Biological control is an important way to control P. latus, with predatory mites being the most widely used natural enemies of this pest. The purpose of this study is to evaluate the capabilities of three native phytoseiids in China (Neoseiulus californicus, Neoseiulus barkeri and Amblyseius orientalis) in controlling P. latus, using Amblyseius swirskii as a control, a commercial biocontrol agent of this pest widely used in Europe. Consumption, development, and reproduction of the four species when fed with P. latus were assessed, and their life table parameters were estimated and compared. Among the three native species, A. orientalis has the highest consumption rate of P. latus (29.0 per day), the shortest developmental duration (5.3 days), and the highest cumulative fecundity (13.5 eggs/female). Overall, its intrinsic rate of increase (rm) is 0.12, comparable to that of A. swirskii. Among the three candidates, A. orientalis is the only one whose population increase might be expected when fed with P. latus. Therefore, we propose A. orientalis to be a potential biocontrol agent for this pest in China.

Predatory mite Amblyseius orientalis prefers egg stage and low density of Carpoglyphus lactis prey.

Amblyseius orientalis (Ehara) (Acari: Phytoseiidae) is an effective predatory mite for spider mite control on fruit trees in China. In recent decades, it has been produced massively at a commercial natural enemy producer, feeding on the storage mite Carpoglyphus lactis (L.). In the predator production process, the ratio of predatory mites to their prey was found to be critical for the population increase of A. orientalis in large-scale rearings. In this study, we investigated the predatory capacity of A. orientalis on various developmental stages of the prey C. lactis, and the effect of prey numbers on predator reproduction. The maximum predation rate of A. orientalis adults on C. lactis adults was 2.21 per day at the lowest density of five prey adults, and on C. lactis eggs it was 45.07 at the highest density of 60 prey eggs. The preference index Ci of A. orientalis on C. lactis eggs and adults was 0.4312 and - 0.9249, respectively, suggesting that A. orientalis preferred eggs to adults. Amblyseius orientalis could reproduce when it preyed on either eggs or deutonymphs of C. lactis. However, the fecundity of the predatory mites is not always proportional to the provided prey number. Higher density of prey deutonymphs resulted in lower fecundity, whereas more prey eggs resulted in higher fecundity of A. orientalis. Therefore, our study indicated that the choice of suitable density and developmental stage of prey can significantly improve A. orientalis production on a large scale.

Expression and functional analysis of transformer-2 in Phytoseiulus persimilis and other genes potentially participating in reproductive regulation.

Transformer-2 (tra-2) is an important sex-determining gene in insects. It also plays a role in the reproduction of phytoseiid mites. We performed bioinformatic analyses for the tra-2 ortholog in Phytoseiulus persimilis (termed Pptra-2), measured its expression at different stages and quantitatively identified its function in reproduction. This gene encodes 288 amino acids with a conserved RRM domain. The peak of its expression was observed in adult females, especially ca. 5 days after mating. In addition, expression is also higher in eggs than in other stages and adult males. When Pptra-2 was silenced through RNA interference with oral delivery of dsRNA, 56% of the females had their egg hatching rates decreased in the first 5 days, from ca. 100% to ca. 20%, and maintained at low levels during the rest of the oviposition period. To detect other genes functionally related to Pptra-2, transcriptome analyses were performed on day 5 after mating. We compared mRNA expressions among interfered females with significantly reduced egg hatching rate, interfered females without significant hatching rate and CK. In total 403 differential genes were identified, of which 42 functional genes involved in the regulation of female reproduction and embryonic development were screened and discussed.

Expression and functional analysis of Niemann-Pick C2 gene in Phytoseiulus persimilis.

As a new protein class of semiochemical binding and transporting, Niemann-Pick proteins type C2 (NPC2) in arthropods have received more attentions in recent decade. However, the gene function has not been studied in phytoseiid mites with biocontrol potential. In the current study, we cloned a NPC2 gene PpNPC2a from the transcriptome of Phytoseiulus persimilis Athias-Henriot. By encoding 181 amino acids with a conserved ML domain, PpNPC2a was found a homolog of NPC2-1 in Galendromus occidentalis Nesbitt. We then measured the spatio-temporal expression of PpNPC2a in P. persimilis, and found the highest expression in female adults compared to other stages. Due to the tiny body size of predatory mites, we only examined tissue expressions in two sections: the anterior part (gnathosoma and the first pair of legs) and the posterior part (idiosoma without the first pair of legs). Higher transcription of PpNPC2a was found in the posterior part. To investigate the potential function of PpNPC2a in P. persimilis, we interfered gene expression in female adults by feeding dsRNA, which resulted in a decrease of relative expression by 59.1 and 78.2% after 24 and 72 h, respectively. Compared with the control, dsNPC2a-treated P. persimilis were insensitive to the scent of leaves or plants infested by spider mites, suggesting a role of PpNPC2a in response to plant volatiles. However, the dsNPC2a-interfered mites could still respond to four representative compounds of herbivore-induced plant volatiles, including 4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT), methyl salicylate (MeSA), ß-caryophyllene and linalool. In short, our results indicated PpNPC2a may be involved in the chemosensory process of P. persimilis in response to whole-plant volatiles.

Detection, Detrimental Effects, and Transmission Pathways of the Pathogenic Bacterium Acaricomes phytoseiuli in Commercial Predatory Mites.

Arthropod pathogens and other microorganisms have been documented from mass production systems aimed at producing natural enemies for pest control. If losses due to pathogens are encountered in such systems, they could lead to uneconomical production of natural enemies and/or a loss of predator quality for effective field control of target pests. Here, we identify and describe the laboratory transmission of a bacterial pathogen, Acaricomes phytoseiuli, in a Chinese strain of the local predatory mite Neoseiulus californicus following contact with Phytoseiulus persimilis, a predatory mite imported for the control of small sap-sucking pests in greenhouses. Analysis of the 16S rRNA gene and whole-genome sequences of A. phytoseiuli isolated from the Chinese strain of N. californicus showed 99.6 and 99.78% similarity, respectively, to the pathogen isolated from a European population (DSM14247 strain). This is the first report of P. persimilis infected with A. phytoseiuli outside Europe and transmitting to a local predatory mite species. A. phytoseiuli severely damaged local N. californicus, leading to a dorso-ventrally flattened body and reduced prey consumption and reproduction as well as early death. Through fluorescence in situ hybridization, A. phytoseiuli was shown to accumulate in the digestive tract of mites and in the oviductal bulb of adult females. Infected males had no obvious symptoms, but they still were able to pass on the infection to healthy females through contact and mating. The pathogen was transmitted vertically to offspring by either infected parent through adherence to eggshells. A. phytoseiuli could also persist in other herbivorous arthropods from the same habitat, suggesting wider potential risks. Our study highlights pathogen risk to predators in local biocontrol industries through pathogen spread from imported material. IMPORTANCE Predatory mites are important natural enemies for biological control of pests, but mass rearing of the mites can be affected by pathogens. In particular, the mite pathogen Acaricomes phytoseiuli may pose a threat to predatory mite production, and we have now detected this pathogen in China. We explored the pathogen's transmission within species, its ability to transfer to a locally important predatory mite species, and symptoms following transfer. The detection of A. phytoseiuli and its ability to transfer to a local predator where it reduces performance highlight the importance of ongoing monitoring and hygiene in the predatory mite industry.

Star Polycation Mediated dsRNA Improves the Efficiency of RNA Interference in Phytoseiulus persimilis.

RNA interference (RNAi) is one of the most widely used techniques to study gene functions. There is still a lack of RNAi techniques that can be applied in Phytoseiidae conveniently and efficiently. Star Polycation is a new nanomaterial commonly used as a carrier of dsRNA in RNAi. Five genes of P. persimilis (PpATPb, PpATPd, PpRpL11, PpRpS2, and Pptra-2) were selected to verify whether SPc promotes the delivery of dsRNA into P. persimilis through soaking. When each of the five genes were interfered using SPc-mediated dsRNA, the total number of success offspring produced per female in six days decreased by ca. 92%, 92%, 91%, 96%, and 64%. When PpATPb, PpATPd, PpRpL11, or PpRpS2 was interfered, both the fecundity and egg hatching rate decreased. In contrast, when Pptra-2 was interfered, reduction in the reproductive capability was mainly the result of the decreased egg hatching rate. Correspondingly, when the target gene was interfered, P. persimilis expression of PpRpL11 reduced by 63.95%, while that of the other four genes reduced by at least 80%. Our studies showed that nanomaterials, such as SPc, have the potential to be used in RNA interference of phytoseiid mites.

Impact of starvation on paternal reproductive investment in Neoseiulus californicus.

Neoseiulus californicus is an important biological control agent of small arthropod pests, widely used in preventive releases at low prey densities. Therefore, it is important to study reproductive investment of this species, both females and males, under environmental pressure of limited prey availability. Laboratory experiments were performed to investigate N. californicus male reproductive investment after short-time fasting or long-term starvation. When fasted for 36 h, males are still able to complete a single mating with no significant change in reproductive parameters of its mate. But the total mating duration became 24% longer, especially timing for the male to fill the first spermatheca of its mate increased by 35%. If daily food availability was less than 20% of demand, males were still able to mate until the end of life, but their fertility reduced after ca. the seventh mating. Mating of some males at the end of their lives are invalid, with their mates failing to oviposit. Overall, we summarized that reproductive investment demand for a single mating was low in N. californicus males, but its priority in energy allocation was high. When starved, males tried to guarantee their mating capability, but their fertility decreased gradually.

Combining predatory mites and film mulching to control Bradysia cellarum (Diptera: Sciaridae) on Chinese chives, Allium tuberosum.

The subterranean insect Bradysia cellarum Frey (Diptera: Sciaridae) is a notorious and major pest of Chinese chives, Allium tuberosum Rottler ex Sprengle (Amaryllidaceae) in China. Current chemical control of B. cellarum results in low insecticide efficacy, high cost and pesticide resistance, therefore there is an urgent need for sustainable management. Here, greenhouse experiments were conducted to evaluate the potential biocontrol agent Stratiolaelaps scimitus Womersley (Acari: Laelapidae) against B. cellarum. The number of B. cellarum larvae in soil declined from 17.6 to 0 in 4 months after releasing predatory mites in high density (5,000 adults per row); treatment was less effective under low densities of 2500 adults per row. To determine whether S. scimitus can be used in combination with soil solarization by film mulching over 40 °C for 4 h, we also evaluated heat tolerance of S. scimitus in laboratory and its control efficacy against B. cellarum after high-temperature treatment mimicking the film mulching in greenhouse. As our results showed that egg hatchability of S. scimitus was 2.6% at 38 °C and adult survival rate was 2% at 40 °C for 4 h, respectively, we concluded S. scimitus was largely inviable and could not reproduce at 40 °C. This temperature was the baseline of soil solarization, suggesting predatory mites should be released after soil solarization. When using S. scimitus after soil solarization or when using soil solarization as single treatment, fly larvae declined similarly from initial density of 18 to 0 or 17.2 to 0, respectively, within a month. Thus, our study suggests the potential of S. scimitus as a biocontrol agent of B. cellarum in greenhouse, and the most effective strategy is to combine film mulching and predatory mites (after soil heating) to control B. cellarum in chive productions.

Massive gene rearrangement in mitogenomes of phytoseiid mites.

Mitochondrial (mt) gene sequences have been widely used to infer phylogeny in animals. The relative order of mt genes in the mitogenome can also be a useful marker for evolution, but the propensity of mt gene rearrangements vary tremendously among taxa. Ticks and mites in Acari exemplify this trend as some families retain the ancestral arthropod gene order, while others show highly divergent gene orders. Mites in Phytoseiidae, many of which are effective biological control agents, show some of the most divergent gene orders. However, the diversity of mitogenome order within this family is little known. We thus sequenced three mt genomes of phytoseiid mites from two of the most speciose genera: Amblyseius swirskii (Athias-Henriot), Amblyseius tsugawai (Ehara) and Neoseiulus womersleyi (Schicha). We find differences in mt GC skew and nucleotide composition, especially between N. womersleyi and the two Amblyseius species. Each species within Phytoseiidae (including three previously available sequences) present a unique gene order. Phytoseiid mitogenomes show some of the highest numbers of breakpoints when compared to the ancestral arthropod order (up to 33), as well as high numbers of breakpoints within the family (14-30). This suggests a history of massive, ongoing mitogenome rearrangements in the family. Phylogenetic analyses of mt sequences confirm that the degree of gene rearrangements follows phylogenetic relatedness. We discuss possible causes for the high degree of mt gene rearrangement within phytoseiid mites as well as selection in the mt and nuclear genome tied to the independent evolution of many diverse feeding strategies in the family. Finally, we suggest N. womersleyi should be used instead of the synonym Amblyseius pseudolongispinosus.

Spermatophore producing process and sperm transfer in Phytoseiulus persimilis.

In phytoseiid mites, the spermatophore is an intermediate, isolated structure where sperms are stored during mating. In the present study, the producing process of Phytoseiulus persimilis spermatophore is described in details. Its shape, and the number and shape of sperms inside, are also analyzed, each as affected by coupling time. Based on our results, the spermatophore of P. persimilis is pyriform, and is produced from the male genital opening within 3 min since mating started. When produced, the spermatophore is transferred along the capitular groove to the cheliceral base, where it is adhered to one of the two small holes at the bases of the chelicerae. Seminal fluid passes through the hole, the hollow spermatodactyl, the opening on the spermatodactyl tip, and enters the insemination pore to reach the spermatheca of the female. No sperm was observed in spermatophores obtained 5 min after mating started. The number of sperms increased in the next 10 min, reached its maximum (ca. 52 sperms per spermatophore), and then decreased. All sperms were released in 75 min after mating started. Sperms are slender in shape and on average 3.9 ± 0.3 µm long.

Effects of Beauveria bassiana on predation and behavior of the predatory mite Phytoseiulus persimilis.

Determination of intraguild interactions between entomopathogens and predators is important when attempting to use a combination of these two natural enemy groups for biological control of their shared arthropod pest species. This study assessed the effects of Beauveria bassiana on the predation and associated behavior of the predatory mite, Phytoseiulus persimilis, against Tetranychus urticae. The functional response tests showed that P. persimilis exhibited a Holling type II response on the spider mite, Tetranychus urticae, when treated with either a B. bassiana or Tween-80 suspension. There were no significant differences between the treatments in the number of T. urticae consumed. The laboratory choice test indicated that P. persimilis displayed a significant avoidance response to B. bassiana on bean leaves immediately following spray application. They also spent significantly longer time in self-grooming behavior on leaf disks sprayed with fungal conidia than on discs treated with Tween-80. There were no significant differences in the predation rates on T. urticae eggs between the different treatments. The potted plant investigations indicated that P. persimilis showed significant aversion behavior to the initial fungal spray, but gradually dispersed over the entire bean plants. Observations using scanning electron microscopy revealed that fungal conidia were attached to the body of P. persimilis after mounting the leaf disk treated with B. bassiana, which would account for its varied behavioral responses. Our study suggests that fungal spray did not affect the predation capability of P. persimilis and poses a negligible risk to their behavior.

Highly virulent Beauveria bassiana strains against the two-spotted spider mite, Tetranychus urticae, show no pathogenicity against five phytoseiid mite species.

Entomopathogenic fungi and predatory mites can independently contribute to suppressing the two-spotted spider mite, Tetranychus urticae Koch. It is important to assess the risk of possible fungal infections in predators when a combination of them are being considered as a tandem control strategy for suppressing T. urticae. The first part of this study tested 12 Beauveria bassiana isolates for virulence in T. urticae. Strains SCWJ-2, SDDZ-9, LNSZ-26, GZGY-1-3 and WLMQ-32 were found to be the most potent, causing 37.6-49.5% adult corrected mortality at a concentration of 1 × 107 m/L conidia 4 days post-treatment. The second part evaluated the pathogenicity of these five strains in five species of predatory phytoseiid mites. The bioassay results indicated that all adult predatory mite mortalities ranged from 7.5 to 9.1% 4 days post-treatment. No viable fungal hyphae were found on predator cadavers. Observations with scanning electron microscopy revealed that conidia were attached to the cuticle of predatory mites within 2-12 h after spraying with strain LNSZ-26, and had germinated within 24-36 h. After 48 h, conidia had gradually been shed from the mites, after none of the conidia had penetrated the cuticular surfaces. In contrast, the germinated conidia successfully penetrated the cuticle of T. urticae, and within 60 h the fungus colonized the mite's body. Our study demonstrated that although several B. bassiana strains displayed a high virulence in T. urticae there was no evident pathogenicity to phytoseiid mites. These findings support the potential use of entomopathogenic fungus in combination with predatory mites in T. urticae control programs.

Insight into the feeding behavior of predatory mites on Beauveria bassiana, an arthropod pathogen.

Interactions between fungal entomopathogens and pest predators are particularly relevant in control of agricultural insect pests. In a laboratory study, we confirmed that the predatory mite, Neoseiulus barkeri, exhibited feeding behavior on the entomopathogenic fungus Beauveria bassiana conidia through DNA extracts. Using transmission electron microscopy, we determined that the majority of conidia found in the mite gut tended to dissolve within 24 h post ingestion, suggesting that the conidia had probably lost their viability. To our knowledge this is the first report of feeding behavior of phytoseiid mites on entomopathogenic fungus. The findings expand our knowledge of fungus-predator interactions.

Intraguild predation between Amblyseius swirskii and two native Chinese predatory mite species and their development on intraguild prey.

Amblyseius swirskii, native to the east and southeast Mediterranean region, is a successful biological control agent of whiteflies. In this study, we investigated intraguild predations (IGP) between each stage of A. swirskii and each stage of two Phytoseiid species that occur in China, Amblyseius orientalis and Neoseiulus californicus. When there was no whitefly egg provided as the extraguild prey, IGP between A. swirskii and A. orientalis, and between A. swirskii and N. californicus, was observed in 10 and 20 out of 35 combinations, respectively. When IGP was observed, A. swirskii was the intraguild predator in 70% and 65% cases of A. orientalis and N. californicus predation, respectively. These results suggest that A. swirskii is a more aggressive intraguild predator compared to either A. orientalis or N. californicus. When whitefly eggs were provided as the extraguild prey, IGP between A. swirskii and N. californicus decreased greatly, but no significant decrease of IGP was observed between A. swirskii and A. orientalis. Amblyseius swirskii was able to complete development on both heterospecific predatory mites, and both heterospecific predatory mites completed their development on A. swirskii. Possible impacts that A. swirskii may have on local predatory mite populations in China are discussed.

Prey Preference and Life Table of Amblyseius orientalis on Bemisia tabaci and Tetranychus cinnabarinus.

Amblyseius orientalis (Ehara) (Acari: Phytoseiidae) is a native predatory mite species in China. It used to be considered as a specialist predator of spider mites. However, recent studies show it also preys on other small arthropod pests, such as Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). Experiments were conducted to investigate (1) prey preference of A. orientalis between Tetranychus cinnabarinus (Boisd.) (Acari: Tetranychidae) and B. tabaci, and (2) development, consumption and life table parameters of A. orientalis when reared on T. cinnabarinus, B. tabaci or a mix of both prey species. When preying on different stages of T. cinnabarinus, A. orientalis preferred protonymphs, whereas when preying on different stages of B. tabaci, A. orientalis preferred eggs. When these two most preferred stages were provided together (T. cinnabarinus protonymphs and B. tabaci eggs), A. orientalis randomly selected its prey. Amblyseius orientalis was able to complete its life cycle on B. tabaci eggs, T. cinnabarinus protonymphs, or a mix of both prey. However, its developmental duration was 53.9% and 30.0% longer when reared on B. tabaci eggs than on T. cinnabarinus and a mix of both prey, respectively. In addition, it produced only a few eggs and its intrinsic rate of increase was negative when reared on B. tabaci eggs, which indicates that B. tabaci is not sufficient to maintain A. orientalis population. The intrinsic rates of increase were 0.16 and 0.23 when A. orientalis was fed on the prey mix and T. cinnabarinus, respectively. These results suggest that although B. tabaci is a poor food resource for A. orientalis in comparison to T. cinnabarinus, A. orientalis is able to sustain its population on a mix of both prey. This predatory mite may thus be a potential biological control agent of B. tabaci when this pest co-occurs with the alternative minor pest T. cinnabarinus.

Feeding on Beauveria bassiana-treated Frankliniella occidentalis causes negative effects on the predatory mite Neoseiulus barkeri.

The entomopathogenic fungus Beauveria bassiana and the predatory mite Neoseiulus barkeri are both potential biocontrol agents for their shared host/prey Frankliniella occidentalis. The combination of the two agents may enhance biological control of F. occidentalis if the fungus does not negatively affect N. barkeri. This study evaluated the indirect effects of B. bassiana strain SZ-26 on N. barkeri mediated by F. occidentalis using the age-stage, two-sex life table. When fed on the first instar larvae of F. occidentalis that had been exposed for 12 h to the SZ-26 suspension, the developmental time of preadult N. barkeri was significantly longer, and the longevity and fecundity were significantly lower than that of N. barkeri fed on untreated F. occidentalis. The mean generation time (T), net reproductive rate (R0), finite rate of increase (λ), intrinsic rate of natural increase (rm) and predation rates were correspondingly affected. The data showed that B. bassiana has indirect negative effects on N. barkeri population dynamics via influencing their prey F. occidentalis larvae, which indicates that there is a risk in combining B. bassiana with N. barkeri simultaneously for the biocontrol of F. occidentalis. The probable mechanism for the negative effects is discussed.

An entomopathogenic strain of Beauveria bassiana against Frankliniella occidentalis with no detrimental effect on the predatory mite Neoseiulus barkeri: evidence from laboratory bioassay and scanning electron microscopic observation.

Among 28 isolates of Beauveria bassiana tested for virulence against F. occidentalis in laboratory bioassays, we found strain SZ-26 as the most potent, causing 96% mortality in adults at 1×10(7) mL(-1)conidia after 4 days. The effect of the strain SZ-26 on survival, longevity and fecundity of the predatory mite Neoseiulus (Amblyseius) barkeri Hughes were studied under laboratory conditions. The bioassay results showed that the corrected mortalities were less than 4 and 8% at 10 days following inoculation of the adult and the larvae of the predator, respectively, with 1×10(7) conidia mL(-1) of SZ-26. Furthermore, no fungal hyphae were found in dead predators. The oviposition and postoviposition durations, longevity, and fecundity displayed no significant differences after inoculation with SZ-26 using first-instar larvae of F. occidentalis as prey in comparison with untreated predator. In contrast, the preoviposition durations were significantly longer. Observations with a scanning electron microscope, revealed that many conidia were attached to the cuticles of F. occidentalis at 2 h after treatment with germ tubes oriented toward cuticle at 24 h, penetration of the insect cuticle at 36 h, and finally, fungal colonization of the whole insect body at 60 h. In contrast, we never observed penetration of the predator's cuticle and conidia were shed gradually from the body, further demonstrating that B. bassiana strain SZ-26 show high toxicity against F. occidentalis but no pathogenicity to predatory mite.

Prey preference of the predatory mite, Amblyseius swirskii between first instar western flower thrips Frankliniella occidentalis and nymphs of the twospotted spider mite Tetranychus urticae.

The prey preference of polyphagous predators plays an important role in suppressing different species of pest insects. In this study the prey preference of the predatory mite, Amblyseius swirskii (Athias-Henriot) (Acari: Phytoseiidae) was examined between nymphs of the twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) and first instar larvae of the western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), as well as between active and chrysalis spider mite protonymphs and active and chrysalis spider mite deutonymphs. The study was done in the laboratory on bean leaf discs at 25 ± 1° C and 70 ± 5% RH. Amblyseius swirskii had a clear preference for thrips compared to both spider mite protonymphs and deutonymphs. About twice as many thrips as spider mites were consumed. Amblyseius swirskii did not show a preference between active and chrysalis stages of spider mites.