The Transfer of Typhlodromus pyri on Grape Leaves for Biological Control of Panonychus ulmi (Acari: Phytoseiidae, Tetranychidae) in Vineyards in Ontario, Canada

The phytophagous mite Panonychus ulmi Koch has become a significant problem in Ontario vineyards. We attempted to introduce and establish populations of the predatory mite Typhlodromus pyri Scheuten for P. ulmi biological control. Grape leaves were transferred from a vineyard containing T. pyri in early summer 1998, by picking leaves from a donor vineyard and attaching them onto leaves in the release vineyard where T. pyri were extremely rare. Two release treatments were used with rates of 8.5 (1×) and 25.5 (3×) mobiles per vine. In the first season, T. pyri established in similar densities in both release treatments, which were significantly higher than controls. However, there were no differences among treatments in P. ulmi densities in 1998 as a result of predator release. During summer 1999, significantly fewer P. ulmi mite-days were observed in release plots compared to the control. Amblyseius fallacis (Garman) was common throughout the release vineyard in 1998 and in 1999, but appeared on the vines too late in the season to maintain low P. ulmi densities. T. pyri appeared to out-compete A. fallacis in 1999 because A. fallacis densities were significantly lower in plots where T. pyri had been released than in control plots. We conclude that T. pyri can be effective for P. ulmi biological control in Ontario vineyards and may be introduced by transferring leaves. In Europe, transferring prunings has been the standard method of inoculating T. pyri into new vineyards. Here we show that transferring leaves is another practical method.     

Life history and life table parameters of the predatory miceTyphlodromus talbii

The predatory miteTyphlodromus talbii Athias-Henriot occurs in European vineyards and is often associated with economically important species. Neither its role in vineyards nor the factors affecting its population dynamics and relationships with other phytoseiid species are well known. The development and the reproduction ofT. talbii were studied in the laboratory by rearing the predator on different kinds of food (Panonychus ulmi, Eotetranychus carpini, Colomerus vitis, Tydeus caudatus, Mesembryanthemum criniflorum pollen). Overwintered females reared on tydeids survived for long periods and laid eggs, but they died after a few days when spider mites or pollen were provided. Development occurred on all mite species but not on pollen. Developmental times on tydeids were shorter than on the other prey. Oviposition was recorded on tydeids and, to a lesser extent, on eriophyids but not on spider mites or pollen. Experiments on tydeids, which resulted as being the best food, were conducted at two temperatures (20° and 27°C). The highest temperature affected the duration of development and oviposition rates positively, but total fecundity was similar. Predators reared at 27°C consumed more prey than those reared at 20°C. The life table parameters of the species were evaluated onT. caudatus (at 20° and 27°C) and onC. vitis. The highest r_m ofT. talbii was found for individuals reared onT. caudatus at 27°C (0.165). Lower values were obtained on the same prey at 20°C (0.089) or onC. vitis (0.030). The feeding habits ofT. talbii may explain why the species coexists with the generalistAmblyseius aberrans orTyphlodromus pyri.     

Factors affecting the potential of phytoseiid mites (Acari: Phytoseiidae) as biocontrol agents in North-Italian vineyards

The results of a 5-year study on the relationships between spider mites and their predators in vineyards in Northern Italy are reported. The efficacy of the two predatory mites appeared to be strongly affected by various factors (grape variety, presence of macropredators, climatic condition, interspecific competition, phytoseiid strain). The phytoseiid mitesAmblyseius aberrans (Oud.) andTyphlodromus pyri Scheuten were released at three different density levels in two vineyards (A, B) infested byEotetranychus carpini (Oud.). One strain ofA. aberrans and two strains ofT. pyri were used for the experiments. In vineyard A,Panonychus ulmi (Koch) was recorded in the second and subsequent years of the experiments and became dominant overE. carpini from the third year onwards. The presence of anthocorids in the same vineyard increased the complexity of the system and gave us the possibility of comparing two very different situations. Release of low numbers ofA. aberrans gave a satisfactory control of spider mite populations in both vineyards. These results were even obtained on a variety non preferred by phytoseiids (Merlot) and with the continuous presence of anthocorids (vineyard A). After 5 years,A. aberrans was observed in 53% of the plots in vineyard A and in all plots of the other vineyard (B). Results of experiments in whichT. pyri was released were similar to those obtained in the experiments withA. aberrans, but only in the first year of the study. In vineyard A, theT. pyri populations declined dramatically from the second year onwards; the use of a non-preferred variety (Merlot) and the continuous presence of anthocorids seemed the most important factors causing the decline of predatory mite density. In vineyard B,T. pyri was capable of controlling spider mites even in the second year of the experiments. A very low density of macropredators and a preferred grape variety (Raboso) positively affected control. The density ofT. pyri in vineyard B decreased at the end of the second year because of adverse climatic conditions (high temperatures in combination with a low relative humidity). The decrease ofT. pyri allowed the displacement of this species byA. aberrans in all plots of vineyard B. It was also shown that the twoT. pyri strains differed in their efficacy to control spider mites. The research was partially supported by a grant from Regione Veneto (“Lotta biologica e integrata nel controllo di insetti ed acari dannosi”). The general lines of the research were planned by C. Duso and the most relevant part of the experiments was carried out by the same author. C. Pasqualetto contributed to the experimental work especially during 1989 and 1990.     

Dynamics ofPanonychus ulmi andTyphlodromus pyri: factors contributing to persistence

We addressed the question of persistence of predator and prey in a biological control system by examining temporal patterns ofPanonychus ulmi (Koch) and its predator,Typhlodromus pyri Scheuten at two geographic locations and at two spatial scales. At the scale of an orchard, bothP. ulmi andT. pyri were persistent over the time frame of 6 years. At the scale of an individual tree,T. pyri appeared to be more persistent than its prey,P. ulmi. We used a simulation model of single populations ofP. ulmi andT. pyri to determine which of several aspects of the biology of the two species could contribute to such a pattern. Spatial incongruity between predator and prey was essential for persistence of both species. The generalist food habit ofT. pyri probably contributes to the persistence ofT. pyri on individual trees, and may cause occasional extinction ofP. ulmi at this spatial scale. The presence of alternate food is likely an essential element for successful biological control in this system. Cannibalism byT. pyri results in higher prey densities, that is, it is detrimental to the biological control ofP. ulmi, but has no effect on the relative persistence of the two species.     

Toxicity of a number of pesticides to strains ofTyphlodromus pyri andAmblyseius andersoni (Acari: Phytoseiidae)

Side effects of ten pesticides used in orchards and vineyards were tested with a laboratory method on several Dutch and Italian strains of the predatory mitesTyphlodromus pyri Scheuten andAmblyseius andersoni (Chant). Resistant and susceptible strains of both species were studied. Results showed that a test which evaluates mortality of various developmental stages and fecundity of adult females is better than one that measures only survival of adult females. A definite resistance to certain pesticides was found in ItalianT. pyri andA. andersoni. The level of resistance to parathion, azinphos-methyl and carbaryl was particularly high in some strains ofA. andersoni. The high level of resistance to certain pesticides was often associated with a marked reduction in fecundity.      

Developmental times and oviposition rates of predatory mitesTyphlodromus pyri andAmblyseius andersoni (Acari: Phytoseiidae) reared on different foods

The developmental times and the reproduction of two resistant Italian strains ofTyphlodromus pyri Scheuten andAmblyseius andersoni (Chant) were studied in the laboratory by rearing them on the spider mitesPanonychus ulmi (Koch) andEotetranychus carpini (Oud.), on the eriophyidColomerus vitis (Pgst.) and on pollen ofMesembryanthemum criniflorum. The response ofT. pyri andA. andersoni females to a spider mite supply (P. ulmi orE. carpini) of 4, 8 and 16 adult female prey per female predator per day was also studied.Development ofT. pyri onE. carpini andC. vitis required a shorter period than onM. criniflorum pollen, while intermediate values were recorded forP. ulmi. When the highest number of prey was offered, the influence of different foods on oviposition rates ofT. pyri was not significant. An increase in spider mite supply favoured a shorter pre-oviposition period and higher oviposition rates.Development ofA. andersoni was faster on pollen than on spider mites, while intermediate values were found concerningC. vitis. Differences statistically significant were recorded for development onP. ulmi andC. vitis. Colomerus vitis proved to be the more suitable food in terms of oviposition. The oviposition rate decreased when feeding uponP. ulmi, but reached intermediate values onE. carpini andM. criniflorum. Increasing spider mite densities caused shorter pre-oviposition times and higher oviposition rates. Using a given number ofE. carpini females, rather than those ofP. ulmi, resulted in higher oviposition rates and shorter pre-oviposition times.For both predators, the results suggest a higher intrinsic rate of population increase onE. carpini orC. vitis than onP. ulmi.The research was supported by a grant from Regione Veneto (Lotta biologica ed integrata nel controllo di insetti ed acari dannosi).The general lines of the research have been planned by C. Duso. The authors contributed equally to the experimental work.     

Interactions among predators and phytophagous mites on apple; possible impact on biocontrol of Panonychus ulmi by Typhlodromus pyri in orchards

Laboratory experiments were conducted to determine the potential impact of the phytoseiid Euseius finlandicus, the mirid Blepharidopterus angulatus and the anthocorid Orius majusculus on the Typhlodromus pyri/Panonychus ulmi predator/prey relationship on apple. Euseius finlandicus consumed more immature spider mites than did T. pyri. When both phytoseiids were present and spider mite prey was abundant, there was no evidence of a negative interaction between the predators. In experiments where each predatory mite was confined with large numbers of the other predator, interspecific predation was exhibited by adults of each species on immatures of the other, but more so by E. finlandicus. In the predatory insect/phytoseiid experiments, when confined with spider mites and large numbers of T. pyri, both B. angulatus and O. majusculus consumed some T. pyri, but spider mites were the preferred prey. In experiments with B. angulatus, O. majusculus and T. pyri feeding on P. ulmi, there was no evidence of negative interactions between the predatory insects and T. pyri.     

Olfactory response of Typhlodromus pyri (Acari: Phytoseiidae) to synthetic methyl salicylate in laboratory bioassays

The herbivore‐induced plant volatile (HIPV) methyl salicylate (MeSA) is widely present in the chemical profile of several plant species and is known to attract natural enemies, including predatory mites. In this study, the response of Typhlodromus pyri, a key predator of pest mites in west coast vineyards, to synthetically produced MeSA was tested using a Y‐tube olfactometer in laboratory bioassays. Six doses ranging from 0.002 to 200 μg of MeSA diluted in 0.1 ml hexane were tested. Significantly higher proportions of T. pyri preferred MeSA at doses 0.02, 0.2 and 20 μg. No differences in response to MeSA were detected at the highest (200 μg), intermediate (2 μg) and lowest (0.002 μg) doses. Mite response to MeSA was a function of dose when fitting polynomial and logistic regression models using dose and square of the log dose prediction factors. Results indicate that synthetic MeSA may be applied to attract predatory arthropod populations in vineyards to enhance biological control of pest mites.     

Prey preference of the phytoseiid miteTyphlodromus pyri 1. Response to volatile kairomones

Using a Y-tube olfactometer, a study has been made of the response of females of the predatory miteTyphlodromus pyri Scheuten (Acarina: Phytoseiidae) to volatile kairomones of three prey species: the European red spider mite (Panonychus ulmi (Koch)), the two-spotted spider mite (Tetranychus urticae Koch) and the apple rust mite (Aculus schlechtendali (Nalepa)).Predators that had been reared onT. urticae responded only to the volatile kairomone ofP. ulmi. In contrast, when reared onVicia faba L. pollen, they responded to the kairomones of all three prey species. Pollen-reared predators, offered a choice between kairomones of two different prey species, prefer theP. ulmi kairomone to those ofA. schlechtendali orT. urticae.The difference in response between predators reared onV. faba pollen andT. urticae seems to be caused by the low carotenoid content ofV. faba pollen. Predators that had been reared onV. faba pollen mixed with crystalline -carotene behaved in a way similar to conspecific that had been reared on the carotenoid-rich prey miteT. urticae. Obviously, pollen-rearedT. pyri females are in need of carotenoids, which can be obtained from, e.g.,P. ulmi, T. urticae orA. schlechtendali. This may explain why pollen-reared predators respond to more prey species thanT. urticae-reared predators.WhyT. pyri females need carotenoids has not been established. The only known function of carotenoids in mites is involvement in diapause induction. However, as pollen-rearedT. pyri enter reproductive diapause under short-day conditions, they either extract sufficient amounts of carotenoids fromV. faba pollen, or do not need carotenoids for diapause induction.Apart from the effect of dietary requirements on prey selection, food deprivation also affects the predator's response to kairomones. All the data mentioned above have been obtained for predators that had been starved for 20 h. Predators that had been reared onT. urticae and starved for 48 h before the experiment did respond to the volatile kairomone ofT. urticae in contrast to predators from the same culture that had been starved for 20 h. Thus foraging decisions byT. pyri are affected by both starvation time and specific hunger for carotenoids.     

Grape downy mildew Plasmopara viticola, an alternative food for generalist predatory mites occurring in vineyards

Generalist phytoseiids are often observed for long periods on plants in the absence of prey, feeding on alternative foods and reaching high population levels. The persistence of generalist predatory mites on plants with a scarcity or absence of prey is a requirement for successful biocontrol strategies of herbivore mites. The importance of pollen as an alternative food for the support of generalist predatory mite populations is widely recognized. However, on grape the presence of pollen is often limited and thus other food sources should contribute towards generalist predatory mite persistence on perennial plants. Previous field observations reported the relationships between the population increases of generalist phytoseiids with late-season spread of grape downy mildew (GDM) Plasmopara viticola. In this study, we test the hypothesis that GDM could be a suitable food source for the predatory mites Amblyseius andersoni and Typhlodromus pyri. In the laboratory we compared the development times, oviposition rates and life-table parameters of predatory mites feeding on pollen or GDM mycelium and spores. Grape downy mildew supported the survival, development and oviposition of T. pyri and A. andersoni. Life-table parameters showed that GDM was a less suitable food source than pollen for both phytoseiid species and that it was more favorable for A. andersoni than for T. pyri. Implications for predator–prey interactions and conservation biological control in vineyards are discussed.     

Different colonization patterns of phytophagous and predatory mites (Acari: Tetranychidae, Phytoseiidae) on three grape varieties: a case study

In a vineyard having three varieties of grape (Merlot, Trebbiano and Garganega) differently colonized by two phytoseiid species,Typhlodromus pyri Scheuten andAmblyseius andersoni (Chant), the dynamics of mite populations were monitored over 5 years (1989–1993) in order to study their colonization, interspecific competition and the control of spider mites, i.e.Panonychus ulmi (Koch). These aspects were also investigated by releasingT. pyri, A. andersoni andAmblyseius aberrans (Oudemans) on some of the above varieties. In most of the experimental years (1989–1992), selective pesticides were used in order to allow a successful release of phytoseiids, in particularA. aberrans. The use of non-selective insecticides was re-established during 1993 in order to test its effect on the new mite communities originating from 1989 onwards. In the first years of the experiments an apparent relationship between grape variety and phytoseiid species was observed: in the control plots,A. andersoni occurred on Merlot whereT. pyri was rare, while the latter species was largely dominant overA. andersoni on Trebbiano and Garganega.Panonychus ulmi populations reached moderate levels only on Merlot and in the first part of experiments. The variety-phytoseiid species relationship was temporary as, at the end of experiments,T. pyri was completely dominant on all varieties. This new situation started when prey occurrence and interspecific competition decreased in importance. The moderate success of theT. pyri release on Merlot contrasts with the results of previous experiments. Two factors could be involved in this phenomenon: low interspecific competition by phytoseiids and predation by macropredators.Amblyseius aberrans was able to displaceA. andersoni andT. pyri on grape varieties where the two species were more abundant and reached higher population densities on varieties with pubescent leaf undersurfaces. In the first experimental year, spider mite densities were reduced more effectively inA. aberrans release plots than in the control or inT. pyri release plots. One year later,P. ulmi reached lower levels in the release treatments than in the control.Typhlodromus pyri andA. aberrans persisted in conditions of prey scarcity. The high competitivity ofA. aberrans over the remaining two phytoseiid species constitutes a major factor in selecting predatory species for inoculative releases in vineyards.     

Effects of acaricides,pyrethroids and predator distributions on populations of <Emphasis Type="Italic">Tetranychus urticae</Emphasis> in apple orchards

We sampled mites in three apple orchards in Nova Scotia, Canada, that had been inoculated with pyrethroid-resistant Typhlodromus pyri and had a history of Tetranychus urticae outbreaks. The objective of this study was to monitor populations of T. urticae and phytoseiid predators on the ground and in trees and to track dispersal between the two habitats. Pesticides were the chief cause of differences in mite dynamics between orchards. In two orchards, application of favourably selective acaricides (abamectin, clofentezine) in 2002, coupled with predation by T. pyri in trees and Neoseiulus fallacis in ground cover, decreased high T. urticae counts and suppressed Panonychus ulmi. By 2003 phytoseiids kept the tetranychids at low levels. In a third orchard, application of pyrethroids (cypermethrin, lambda-cyhalothrin), plus an unfavourably selective acaricide (pyridaben) in 2003, suppressed phytoseiids, allowing exponential increases of T. urticae in the ground cover and in tree canopies. By 2004 however, increasing numbers of T. pyri and application of clofentezine strongly reduced densities of T. urticae in tree canopies despite high numbers crawling up from the ground cover. Another influence on T. urticae dynamics was the distribution of the phytoseiids, T. pyri and N. fallacis. When harsh pesticides were avoided, T. pyri were numerous in tree canopies. Conversely, only a few N. fallacis were found there, even when they were present in the ground cover and on tree trunks. Low numbers were sometimes due to pyrethroid applications or to scarcity of prey. Another factor was likely the abundance of T. pyri, which not only competes with N. fallacis, but also feeds on its larvae and nymphs. The scarcity of a specialist predator of spider mites in trees means that control of T. urticae largely depends on T. pyri, a generalist predator that is not particularly effective in regulating T. urticae. The Canadian Crown's right to retain a non-exclusive, royalty-free licence in and to any copyright is acknowledged.     

Distribution of the Predatory Mite Typhlodromus pyri (Acari: Phytoseiidae) on Different Apple Cultivars

The effect of apple cultivar on the distribution of the predatory mite Typhlodromus pyri was studied in an experimental orchard where spider mites occurred at negligible densities. Seven apple scab-resistant cultivars, showing some differences in their leaf morphology, were considered. In particular, their leaf blade was classified according to four levels of pubescence. The distribution of T. pyri along the shoots was also studied. In the first experimental year the colonization of different cultivars by T. pyri showed definite patterns, sometimes influenced by the occurrence of eriophyids. One year later, T. pyri abundance again showed some differences among cultivars in conditions of prey scarcity. In both years large phytoseiid populations were recorded on the cultivar N.Y. 18491, despite the low eriophyid occurrence, probably because of its highly pubescent leaf undersurfaces. In contrast, Prima and TSR 29T219, characterized by slightly pubescent leaf undersurfaces, supported low phytoseiid densities independently of prey availability.     

Long-term residual efficacy of commerical formulations of 16 pesticides toTyphlodromus pyri Scheuten (Acari: Phytoseiidae) inhabiting commerical vineyards

The long-term residual efficacy of 16 pesticides to the predatory phytoseiid mite,Typhlodromus pyri Scheuten, inhabiting commercial sprayed vineyards in South Moravia, Czchoslovakia, was evaluated in laboratory bioassays. Omethoate, chlorpyrifos-methyl and esfenvalerate were assessed as harmful and should not be sprayed. Mancozeb-efosite-Al mixture, diazinon, dicofol, bromopropylate, azinphos-ethyl and phosmet were assessed as moderately harmful. Fenitrothion, phosalone and mancozeb were assessed as slightly harmful and some of them had delayed detrimental effect on the predatory mites. These pesticides can be used only cautiously in IPM programs. Sulphur, penconazole, trimorfamid and endosulfan were assessed as harmless and can be recommended for vineyards withT. pyri.     

Phytophagous and predatory mites (Acari: Tetranychidae,Eriophyidae, Phytoseiidae,Stigmaeidae) in South Moravian vineyards,Czechoslovakia, treated with various types of chemicals

Communities of phytophagous and predatory mites on vine can be influenced by the type of chemical treatment. Ten species of phytoseiid mites inhabit vines in the region of South Moravia. Populations ofTyphlodromus pyri Scheuten play leading roles in effective suppression of tetranychid and eriophyid mites in commercial vineyards sprayed with pesticides, except synthetic pyrethroids and mancozed, which are considered to be detrimental to the predatory phytoseiid mites.     

Increases in densities of the citrus red mite,Panonychus citri [Acarina: Tetranychidae], in association with the Argentine ant,Iridomyrmex humilis [Hymenoptera: Formicidae], in southern California citrus

We monitored the activities of the Argentine ant,Iridomyrmex humilis (Mayr), in 3 citrus orchards during 1984 and 1985. We also monitored densities of citrus red mite,Panonychus citri (McGregor), the adult spider mite destroyer,Stethorus picipes Casey [Col.: Coccinellidae], and the predatory mite,Euseius tularensis Congdon [Acarina: Phytoseiidae] during the same period in ant-present and ant-free plots in each orchard. I. humilis was excluded for at least 9 months from trees pruned 60 cm from the ground following a basal application of 1 or 2 % chlorpyrifos 4 EC. Autumn densities ofP. citri in these ant-free plots were significantly lower than those in the plots infested withI. Humilis. S. picipes appeared to be the most important predator, maintaining lowP. citri densities on citrus in southern California in the absence ofI. humilis activity.S. picipes densities increased numerically in response to the early spring and late autumn increases in the density ofP. citri populations. However, in the presence ofI. humilis activity, effective predation was apparently inhibited. Densities ofE. tularensis were unaffected by the presence ofI. humilis, nor didE. tularensis respond to spring or autumn increases in the density ofP. citri populations in any of the orchards.      

Prey preference of the phytoseiid miteTyphlodromus pyri 2. Electrophoretic diet analysis

The prey selection of the phytoseiid miteTyphlodromus pyri Scheuten was studied by using polyacrylamide gel electrophoresis to analyse the diet of field-collected predators. The predators were obtained from an orchard where the phytophagous prey mitesPanonychus ulmi (Koch) andAculus schlechtendali (Nalepa) were present in various density ratios.Esterases of both prey species were identified in the predators, but on all sampling datesP. ulmi esterases were discovered much more frequently than those ofA. schlechtendali. The data show thatT. pyri hardly fed onA. schlechtendali over a range of prey density ratios. It is therefore concluded thatT. pyri prefersP. ulmi toA. schlechtendali.     

Intraguild Predation and Feeding Preferences in Three Species of Phytoseiid Mite Used for Biological Control

The ecological impact of introduced biological control agents on native species of arthropods is a matter of considerable debate. This study investigated the ability of the non-native predatory mite Neoseiulus californicus to feed on the native Typhlodromus pyri and vice versa, as both species now co-occur in UK orchards. Typhlodromips montdorensis is a candidate for introduction into the UK as a glasshouse biological control agent. The ability of T. montdorensis to feed on the widely used N. californicus was investigated to identify possible intraguild predation, which might influence the effectiveness of either or both species as predators of Tetranychus urticae. Both N. californicus and T. pyri consumed larval stages of each other, but in choice experiments both showed a preference for T. urticae. Both N. californicus and T. montdorensis also fed on each other, but whereas N. californicus again showed a preference for T. urticae, T. montdorensis fed equally on T. urticae and N. californicus. Interactions between N. californicus and T. pyri and N. californicus and T. montdorensis are discussed in relation to their effectiveness as biological control agents in the glasshouse and the natural control of spider mite in the field.     

Detecting variability and selecting for pesticide resistance in two species of phytoseiid mites

Methods used for evaluating the effects of pesticides and selecting for pesticide resistance in phytoseiid mites are reviewed from recent literature. In particular slide dip, leaf dip, and leaf disc spray methods are compared. The selection of predatory mites (Typhlodromus pyri Scheuten andPhytoseiulus persimilis Athias-Henriot) for resistance to 3 synthetic pyrethroids (SP-cypermethrin, deltamethrin, and fenvalerate) is described. Tolerance of field populations to all 3 SP was low inP. persimilis but moderate inT. pyri. Field samples of both mite species on leaf discs were sprayed and the survivors were reared in laboratory and/or glasshouse cultures. These cultures were sprayed with repeated doses of SP; initiallyT. pyri was selected with cypermethrin andP. persimilis with fenvalerate. The survival rate ofT. pyri increased at each selection. After 6 selections the survival rate of the laboratory culture was 10 times that of the original field samples. Tests indicated crossresistance inT. pyri to fenvalerate and deltamethrin. Selection with cypermethrin is continuing. In the first 12 months repeated selections ofP. persimilis with fenvalerate gave no significant change in survival rate.

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Résumé Les méthodes utilisées pour évaluer les effets des pesticides et pour sélectionner la résistance à ces mêmes produits, des acariens phytoseiides sont analysées d'après la littérature récente. La sélection des acariens prédateurs (Typhlodromus pyri S{upcheuten} etPhytoseiulus persimilis A{upthias}-H{upenriot}) pour leur résistance aux 3 pyréthrinoides de synthèse (cyperméthrine, deltaméthrine et fenvalerate) est décrite. La tolérance des populations naturelles aux 3 pyréthrinoides de synthèse était basse pourP. persimilis, mais modérée pourT. pyri. Les échantillons des 2 espèces d'acariens prélevés à l'extérieur furent traitès sur des disques de feuilles et les survivants furent élevés au laboratoire et/ou dans des cultures en serre. Ces élevages furent traités avec des doses répétées d'un pyréthrinoide, cyperméthrine initialement pourT. pyri et fenvalerate pourP. persimilis. Le taux de survie deT. pyri augmentait à chaque sélection. Après 6 sélections, le taux de survie de l'élevage de laboratoire était 10 fois celui des échantillons d'origine. Les essais révélaient une résistance croisée deT. pyri à la fenvalerate et à la deltaméthrine. La sélection avec la cyperméthrine se poursuit. Au cours des 12 premiers mois, les sélections répétées deP. persimilis avec la fenvalerate ne donnait pas de changement significatif dans le taux de survie.

     

Die Feinde der Raubmilben als Reduzierender Faktor der Spinnmilben

Summary The relations betweenMetatetranychus ulmi living on apple trees and its different predators are complex. The most important natural enemy of this spider mite is the predacious miteTyphlodromus pyri (= T. tiliae). It destroys more spider mites than the beneficial insects do. In the district of Stuttgart-Hohenheim about 38 species of insects and spiders feed onTyphlodromus mites. For instanceT. pyri is reduced considerably byOrius minutus. This bug is a natural enemy of aphids and spider mites, however it prefers the predatory mites. It attacks the spider mites and aphids only ifTyphlodromus mites are not available.Chrysopa vulgaris andAnthocoris nemorum are similar in their feeding habits. These two destroyTyphlodromus pyri also but they are less important thanO. minutus. The other beneficial insects in our orchards have little effect on spider mites or predacious mites. If we have enough pests on our apple trees to make spraying necessary, we should look forTyphlodromus mites and be careful no to destroy them. We should always examine the composition of the biocoenosis applying chemical agents because the populations of insects and predacious mites may vary from one area to the other.