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.     

Optimum release times for biological control of the two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) by Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseidae) on the strawberry in greenhouses

The effectiveness of the predatory mite Phytoseiulus persimilis Athias‐Henriot (Acari: Phytoseidae) in controlling the two‐spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) was evaluated in commercial strawberry greenhouses in two areas of Korea. Optimum release times for P. persimilis were investigated by case studies. Control effects of the two‐spotted spider mite by release of the predatory mite were shown. There was mostly good control by the release of P. persimilis when there were fewer than 0.9 T. urticae per leaf. We recommend it would be ideal to release P. persimilis twice in December and once in February for very early strawberry harvest, and three times from February to March (after overwintering) for early harvest.     

Integrated pest management of two-spotted mite Tetranychus urticae on greenhouse roses using petroleum spray oil and the predatory mite Phytoseiulus persimilis

From 1995 to 1999, four experiments were conducted on greenhouse roses to assess the effectiveness of the nC24 petroleum spray oil (PSO), D-C-Tron Plus, against two-spotted mite, Tetranychus urticae Koch (Acarina: Tetranychidae), and to determine how the oil could be most efficiently and effectively used in combination with the predatory mite Phytoseiulus persimilis Athias-Henriot (Acarina: Phytoseiidae) in an integrated pest management program. The results showed that 0.5% PSO applied fortnightly to roses gave excellent protection from T. urticae infestation when the mite population was not already established. However, PSO applied after roses were infested with T. urticae above the economic threshold only stabilised populations without reducing them below that threshold. Populations of P. persimilis in the upper and lower canopies were unchanged after two sprays of PSO at 7-day intervals, and application of PSO to the upper canopy was as effective in controlling T. urticae in the presence of P. persimilis as spraying the entire plant. Combining PSO with P. persimilis gave better control of T. urticae than using P. persimilis alone. The most cost-effective use of PSO in the presence of P. persimilis is, therefore, to apply spray only to the upper canopy. This will not affect control of powdery mildew with PSO. Comparison of a control program for T. urticae based on the monitored use of synthetic miticides with that based on calendar application of PSO revealed that both gave equally effective control. The benefits of combining PSO and P. persimilis in an integrated pest management program for T. urticae on roses over a program based on synthetic fungicides are discussed.     

Demographic examination of sex ratio in the two-spotted spider mite, Tetranychus urticae

Primary sex ratio of arrhenotokous tetranychid mites depends on the age-specific schedule of ratios of progeny produced by individual females. Since primary sex ratio is conditional upon female age and since the proportion of females of a given age in a population is influenced by the rate of increase, both the agespecific ratio of males to females and the overall ratio of males to females depends on the rate of increase. We given an expression for this dependence and compare it to experimental results for the two-spotted spiter mite. These results imply that there is no standard sex ratio of spider mites because of interpopulation variation in rates of increase.

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Résumé Le taux sexuel des acariens tétranychidés arrhénotoques est défini comme le rapport de la somme des nombres de mâles sur la somme des nombres de femelles pour chaque âge de la distribution en âges. Comme le taux sexuel primaire dépend de l'âge de la femelle et comme la proportion de femelles d'un âge donné dans la population est influencée par le taux d'accroissement, alors le rapport mâle/femelle spécifique d'un âge déterminé et le rapport global mâle/femelle dépendent du taux d'accroissement. Nous avons cherché à exprimer cette dépendance et à la comparer aux résultats expérimentaux pour Tetranychus urticae. Ces résultats signifient qu'il n'y a pas de taux sexuel caractéristique de Tétranyques par suite des variations du taux d'accroissement suivant les populations.

     

Discrimination through silk recognition: The case of the two-spotted spider mite Tetranychus urticae

Choosing a suitable habitat is a main step in the settlement process, particularly for species having weak movement abilities. Reliable cues are thus needed for habitat selection. In silk-spinning arthropods, silk can be used as a social cue to select an appropriate location. Silk can also provide information on the presence of related or non-related individuals. In this article, we compare the settlement behaviour of two strains of the two-spotted spider mite, Tetranychus urticae, in response to the presence of silk woven by an individual of its own or another strain. We then examined how individuals behaved when confronted with both types of silk (own/another strain) simultaneously. Both strains were sensitive to related silk. Settlement decision for both strains did not differ according to the origin of the silk. Mites used the silk as a communication cue for habitat selection and strain discrimination. Our results provide experimental evidence for the use of multiple social cues in the settlement decision by weaving mites.     

Arrestment responses of the predatory mite, Phytoseiulus persimilis, to steep odour gradients of a kairomone

ABSTRACT. The response of the predatory mite, Phytoseiulus persimilis Athias-Henriot, to steep gradients of a volatile kairomone emitted by its prey, Tetranychus urticue Koch, was studied in a vertical air flow chamber. The orientation to wind direction was eliminated by using an olfactometer that had an air stream approaching the predator from below a gauze screen upon which the predator walked. The steep gradient of odour was obtained by putting a cylinder filled with prey-infested leaves vertically below the screen. Starved predators were arrested in the odour patch by walking more slowly and tortuously than well-fed predators. The latter mites did not show a significant ortho- or klinokinetic response to the presence of odour. Both well-fed and starved predators showed a chemotactic response to steep gradients at the border of the circular odour patch. Predators that happened to walk out of the patch, frequently turned back to it. This response is presumably based on idiothetic information about the predator's immediately previous walking directions, because it occurred in the odour-free zone after passing the steep gradient of prey odour. Right-about turns can help the predator to stay in static odour plumes with steep gradients at the borders. This type of plume is present only close to the odour source. Further away from the source the odour plume tends to move to and fro due to variation in wind direction. For the predator to keep track of these snaking plumes the right-about turns are unlikely to be of any value because the response is of short duration and because the response to a moving plume appeared to be inadequate; by moving the cylinder below the screen (and consequently the odour patch) it was found that the predator turned back even if the odour gradient was made to pass the predator in the same direction as that of the predator's movement.     

Olfactory response of predatory mite Phytoseiulus persimilis to synthetic methyl salicylate

We studied the role of methyl salicylate as an important part of volatile blends in searching behaviour of the predatory mite, Phytoseiulus persimilis (Athias-Henriot). We showed that Methyl Salicylate (MeSa) attracted the predatory mites (1 h starved) in a dose range of 0.02–20?μg. The highest attraction was recorded at the dose of 0.2?μg. The dose of 0.002?μg was considered under the detection level of the predator. P. persimilis could not detect the extra amount of MeSa (100 and 200?μg). The probable effect of starvation period on the predator response is discussed.     

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.     

Biocontrol of Two-spotted Spider Mite Tetranychus urticae on Dwarf Hops by the Phytoseiid Mites Phytoseiulus persimilis and Neoseiulus californicus

Two female Phytoseiulus persimilis and their offspring eliminated two-spotted spider mite Tetranychus urticae from hop leaf discs faster than two female Neoseiulus californicus and their offspring at 25°C. A combination of one female of each species and their offspring eliminated spider mites faster than the N. californicus alone, but slower than P. persimilis alone. Air relative humidities of 55% and 93% had no effect on predation. Both predator species cannibalised eggs and juveniles when spider mite numbers were low. In field experiments in 1996, fewer spider mites were recorded where P. persimilis was released, irrespective of the presence of N. californicus. Pest numbers on cv. 'First Gold' were lower than on cv. 'Herald'. No differences were recorded between the numbers of spider mite eggs in predator release treatments on 'First Gold', but fewer active stages of spider mites were recorded on plots with P. persimilis than controls soon after the time of peak pest population densities. On 'Herald', fewer spider mite active stages and eggs were recorded where predators were released than on untreated controls.     

Effects of pesticides on spin down and webbing production by the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae)

Spin down in response to pesticides is a known phenomenon. This study aimed at investigating the effects of varying acaricide concentrations and acaricidal combinations on the rate of spin down and thread length, the fate of mites after spinning down and, thus, the implications of spin down in the context of mite control and the relationship between webbing and the efficacy of ovicides. In response to cyhexatin at a concentration of up to 100 mg dm-3 the rate of spin down did not change, but in response to higher concentrations it occurred earlier and ceased before the end of the experiment. The mean thread length did not vary with the concentration of acaricide and, whilst the proportion of mites spinning down increased with a cyhexatin concentration of up to 10 mg dm-3, it did not increase further with higher concentrations thereafter. It is therefore postulated that at any given time only a certain proportion of mites have a propensity to spin down. In combination with cyhexatin, only amitraz (at low concentrations) increased the proportion of mites spinning down, but amitraz (at higher concentrations), flubenzimine and permethrin all inhibited spin down, which may be a useful attribute in pesticide formulations. With regard to the fate of mites after spinning down, they were able to climb back up threads, but the proportion doing so was too small to be of practical importance. Mites which spin down and remain at the end of a thread die, but those which reached another leaf were able to spin down again and were more likely to do so if the leaf bore a cyhexatin residue. Mites reaching another leaf are also able to lay eggs, the number being greater if the leaf which they reach is untreated. Spin down is therefore likely to be of significant advantage to Tetranychus urticae in avoidance of the effects of acaricides. Finally, some eggs were observed to be laid on webbing and not to come into direct contact with clofentezine residues. The use of a fine water spray to simulate dew increased the ovitoxicity of clofentezine, probably by resuspension of the pesticide, but not of amitraz, which inhibits webbing production. The avoidance of acaricides should be added to the several known advantages of webbing production for spider mites. It is concluded that, all other factors being equal, pesticide formulations which inhibit spin down and webbing production are likely to be more effective in control programmes than those which stimulate such behaviour.     

Interactions in a trirophic acarine predator-prey metapopulation system: effects of Tetranychus urticae on the dispersal rates of Phytoseiulus persimilis (Acarina: Tetranychidae, Phytoseiidae)

The dispersal behaviour of the predatory mite Phytoseiulus persimilis Athias-Henriot between bean plants was studied in a greenhouse. The aim of the study was to estimate the rate of predator emigration affected by different densities of Tetranychus urticae Koch and different numbers of between-plant connections (bridges). The results show that predators emigrate from a plant almost exclusively as a response to the local prey density whereas the loss rate (the per capita rate at which predators disappear from the system) also depends on the prey density on the surrounding plants, provided they are connected to the central plant by bridges. © Rapid Science Ltd. 1998     

Aerial dispersal of the two-spotted spider mite (Tetranychus urticae) from field corn

Field data from 48 plots monitored during diverse weather conditions in two separate years were subjected to multiple regression analysis to determine which factors were related to spider-mite aerial dispersal. With the number of aerially dispersing mites as the dependent variable, partial regression coefficients (b) for mite population density and percent corn-leaf area infested with mites were positive, while those for percentNeozygites-infected mites and hours per week 90% r.h. were negative. When an aerial dispersal index (number of aerially dispersing mites/mites per plant) was used as the dependent variable, the partial regression coefficient for percent leaf area infested was positive, while coefficients for hours per week 90% r.h. and percentNeozygites-infected mites were negative. Mite aerial dispersal was greatest in predator-suppressed field plots under dry weather conditions. Mite aerial dispersal was substantially reduced in plots where moist weather conditions induced epizootics ofNeozygites floridana before corn plants became entirely infested with mites.     

Effects of triflumuron on the two-spotted spider mite,Tetranychus urticae (Acari: Tetranichydae)

The effects of triflumuron on the mortality, fecundity, and fertility of the two-spotted spider mite, Tetranychus urticae, were evaluated in the laboratory. No differences in toxicity for larvae, protonymphs and deutonymphs were observed, but immature stages were 3.8-times more susceptible than adults at the LC₅₀. The compound exhibited a direct contact ovicidal activity influenced by eggs age. 48–72 hold eggs were significantly more sensitive than eggs of the other age classes. No hatch inhibition was observed in eggs laid by treated adult females using a sublethal dose at two physiological times (<12 and 48–72h old). However, fecundity decreased in younger treated females, but it increased in the older-ones. The toxicity for immatures and eggs, and the sublethal effects described suggest that triflumuron could be an interesting incorporation in integrated pest programs of T. urticae. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of mating status and age on dispersal behavior in the twospotted spider mite, Tetranychus urticae in response to fenvalerate-treated leaf surfaces

Effects of variation in age and mating status on dispersal of the twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), from fenvalerate-treated leaf surfaces were investigated. Unmated and mated female mites, 1 to 6 days in age, were scored for walkoff and spindown dispersal response on bean leaves treated with a sub-lethal, residual dose of fenvalerate. Variation in mite age did not have a pronounced effect on dispersal response. Significant differences in dispersal response due to mating type were observed, yet the mean differences in dispersal response between unmated and mated females was generally small. Our data suggest that the current practice of using mated female mites of unknown age when testing for among-population differences in dispersal response, in most cases, provides an adequate estimate of population response when differences among treatments in dispersal response are large. However, when testing for within-population differences in dispersal response, small treatment effects may be more easily measured using a single age class of mites, because this could decrease within-treatment variance.     

Differential Effects of Plant Species on a Mite Pest (Tetranychus Urticae) and its Predator (Phytoseiulus Persimilis): Implications for Biological Control

The influence of plant species on the population dynamics of the spider mite pest, Tetranychus urticae, and its predator, Phytoseiulus persimilis, was examined as a prerequisite to effective biological control on ornamental nursery stock. Experiments have been done to investigate how the development, fecundity and movement of T. urticae, and the movement of P. persimilis were affected by plant species. A novel experimental method, which incorporates plant structure, was used to investigate the functional response of P. persimilis. Development times for T. urticae were consistent with published data and did not differ with plant species in a biologically meaningful way. Plant species was shown to have a major influence on fecundity (P < 0.001) and movement of the pest mite (P < 0.01), but no influence on the movement of the predator. The movement of both pest and predator was shown to be related to the density of the adult pest mites on the plant (P < 0.001). Plant structure affected the functional response, particularly in relation to the ability of the predator to locate prey at low densities. The impact of these findings on the effective use of biological control on ornamental nursery stock is discussed.     

Laboratory and glasshouse evaluation of entomopathogenic fungi against the two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae), on tomato, Lycopersicon esculentum

Forty isolates of entomopathogenic fungi from six genera were assessed against the two-spotted spider mite, Tetranychus urticae, in a single dose, direct application laboratory bioassay on tomato leaflets. Only three isolates caused greater mortality than the control: these were Metarhizium anisopliae 442.99, Hirsutella spp. 457.99, and Verticillium lecanii 450.99. These isolates were assessed in a multiple dose bioassay, together with three isolates cultured from commercial biopesticides as follows: Beauveria bassiana 432.99 (cultured from 'Naturalis-L', Troy Biosciences, Phoenix, TX, USA); Hirsutella thompsonii 463.99 (cultured from 'Mycar', Abbott Laboratories USA); and V. lecanii 19.79 (used in 'Mycotal' Koppert BV, The Netherlands). Beauveria bassiana 432.99, H. thompsonii 463.99, M. anisopliae 442.99, and V. lecanii 450.99 were all pathogenic to T. urticae in this bioassay. In addition, it was found that the mortality caused by B. bassiana 432.99 and Naturalis-L was increased when the mites were exposed to tomato leaflets sprayed previously with conidia suspensions, compared to spraying the mites directly. In a glasshouse experiment, sprays of B. bassiana 432.99, H. thompsonii 463.99, M. anisopliae 442.99, V. lecanii 450.99 and Naturalis-L reduced T. urticae populations in a tomato crop grown according to commercial practice. Naturalis-L reduced T. urticae numbers by up to 97%. In a second glasshouse experiment, single sprays of Naturalis-L and the acaricide fenbutatin oxide (Torq) were compared as supplementary treatments to release of the predatory mite, Phytoseiulus persimilis. Supplementary sprays of fenbutatin oxide reduced the numbers of T. urticae nymphs (80% reduction), while Naturalis-L reduced numbers of T. urticae adults, nymphs and eggs (98% reduction in all three cases). It is concluded that Naturalis-L has the potential to be used against T. urticae on glasshouse tomato crops.     

Suitability of the spider mite Tetranychus evansi as prey for Phytoseiulus persimilis

Expeirments conducted to evaluate the suitability of T. evansi as a source of food for P. persimilis revealed that the primary factor responsible for the low oviposition rate and survivorship of the predator when fed T. evansi was the low amount of food ingested. P. persimilis detected and initiated feeding on T. evansi equally as well as on T. urticae. However, a feeding depressant was apparently responsible for a longer time spent by P. persimilis feeding on eggs of T. evansi than on eggs of T. urticae. Eggs of the former prey were totally consumed only occasionally. The depressant effect influenced subsequent feeding on T. urticae, increasing the time required for consumption and the number of partially consumed eggs for at least 3 days.

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Résumé Les expérience d'évaluation de l'adéquation de T. evansi comme proie pour P. persimilis ont montré que le principal facteur responsable des faibles taux de ponte et de survie du prédateur alimenté sur T. evansi est la faible quantité d'aliments ingérés. P. persimilis avait découvert et commencé à s'alimenter sur T. evansi aussi bien que sur T. urticae. Cependant, un facteur réduisant la prise de nourriture a été responsable du temps plus important consacré à s'alimenter sur oeufs de P. persimilis que sur oeufs de T. urticae. Les oeufs de la première proie n'ont été que rarement consommés intégralement. Cet effet dépressif a influencé l'alimentation ultérieure sur T. urticae, en augmentant le temps nécessaire pour la consommation et le nombre d'oeufs partiellement utilisés au moins pendant les trois jours suivants.

     

Ultrahistology of oogenesis and vitellogenesis in the spider mite Tetranychus urticae

Histology of the ovary of the spider mite Tetranychus urticae is described light and electron microscopically with special reference to oogenesis and vitellogenesis of this mite. Morphology of the ovary is comparable to the typical sac-like chelicerate ovary with oocytes protruding from the ovarian surface, thus resulting in a grape-like appearance. According to different oogenetic stages, a germ, pre-vitellogenic and vitellogenic region can be observed. Oogonia and primary oocytes characterized by extranuclear material or 'yolk nuclei' are situated in the germ region. Primary oocytes develop into three-nucleated nurse cells situated in the periphery of the pre-vitellogenic region, and into pre-vitellogenic oocytes protruding from the ovarian surface. Growth of oocytes is performed while they are in ovarian pouches by uptake of nurse cell cytoplasm and following extraovarian yolk precursors. Intraoocyte yolk synthesis interpreted from altered cytoplasmic organelles also occurs. Processes taking place during oogenesis and vitellogenesis in T. urticae are compared to published information on yolk synthesis of other animal species.     

Genetics of diapause supression in the two-spotted spider mite,Tetranychus urticae Koch

Starting from the Sambucus strain of the two-spotted spider miteTetranychus urticae Koch, the strains ND₁ and ND₂ were selected for lack of diapause under a short-day regimen (LD 1014, 18°C). The genetic basis of the suppression of diapause in ND₁ and ND₂ was analysed by means of mendelian crosses and backcrosses, using the photoperiodic cycle LD 1014 as diagnostic for the distinction of diapausing and non-diapausing phenotypes. Suppression of diapause is inherited as a recessive trait. From backcross analysis it was concluded that the suppression of diapause in ND₁ and ND₂ is under monogenic control. The major genes for suppression of diapause in ND₁ and ND₂ are alleles at a locus designated asd. A mutation for albinism of the locusa-p is pleiotropic for suppression of diapause. It was shown from crosses between ND₁ and the albino strain, thatd anda-p are distinct loci.     

联苯肼酯对智利小植绥螨的安全性及二者对二斑叶螨的联合控制作用

【目的】评价联苯肼酯对智利小植绥螨Phytoseiulus persimilis的安全性,以及该药剂与捕食性天敌智利小植绥螨联合使用的效果。【方法】采用室内生物测定与田间试验的方法测定了联苯肼酯对智利小植绥螨成螨和若螨致死率与繁殖能力的影响,以及二者联合使用对茄子上二斑叶螨的控制效果。【结果】结果表明143 mg/L联苯肼酯对智利小植绥螨成螨和若螨的存活和生殖能力均无显著影响,处理后96 h对若螨的最高致死率为2.30%,成螨为2.04%;处理组8 d的平均产卵量为15.08粒/雌,与对照平均产卵量15.45粒/雌无显著差异;处理组所产卵的平均孵化率为98.63%,与对照组平均孵化率98.13%无显著差异;联苯肼酯悬浮剂在143 mg/L浓度下对二斑叶螨的控制效果表现为速效性高于单独使用智利小植绥螨,但持效性低于智利小植绥螨,防效在第22天时开始下降。二者联合使用表现出较好的速效性与持效性,处理后第2天防效达97.35%,第18天时达100%。【结论】联苯肼酯对智利小植绥螨具有极高的安全性,该药剂与智利小植绥螨联合使用对二斑叶螨具有良好的控制效果。