Laboratory evaluation of resistance to pesticides in the phytoseiid predator Typhlodromus pyri from English apple orchards

Typhlodromus pyri, reared on plate cultures and fed on pollen of Vicia faba, were bioassayed using a taped-slide technique. Mite stocks from isolated unsprayed orchards were used to establish base-line susceptibility to azinphos-methyl, parathion, carbaryl and permethrin. Stocks from English orchards with a spray history of organophosphates and carbaryl showed resistance of 4 to 6x to azinphos-methyl, c 50 x to parathion, >20x to carbaryl, and no resistance to permethrin. An orchard population derived from T. pyri imported from New Zealand in 1977 responded similarly. In other tests, mites exposed to spray residues on glass and on apple leaves were killed by lower concentrations than in taped-slide tests (glass < apple leaf < taped-slide technique); but for all three assay techniques the resistance factors to azinophos-methyl and carbaryl, comparing two stocks, were similar. All stocks from sprayed orchards were resistant to both azinphos-methyl and carbaryl, suggesting cross-resistance; and resistance to both these pesticides appeared to be stable in the field when selection pressure was relaxed. The results are discussed in relation to earlier work on T. pyri and two other resistant orchard-inhabiting phytoseiid species.     

Factors affecting biological control of apple mites by mixed populations ofMetaseiulus occidentalis andTyphlodromus pyri

Metaseiulus occidentalis (Nesbitt) andTyphlodromus pyri Scheuten have complementary features/ traits that enable them to control effectively plant-feeding mites on apple. Populations of both predators gave as good or better biological control of the apple rust mite (Aculus schlechtendali Nalepa), European red mite (Panonychus ulmi Koch) and two-spotted spider mite (Tetranychus urticae (Koch)) than single-predator populations. With mixed predators,M. occidentalis provided better control of spider mites the first season after release, butT. pyri gave better control in the second season. Several factors affected the ability of predators to provide biological control: When prey were dense,M. occidentalis rapidly increased during the warm mid-summer, whileT. pyri provided greater predation when it was cool at the start or end of the growing season. When few prey were present, searching byM. occidentalis was more confined on individual apple leaves, but it migrated between leaves and trees more often. Pollen feeding, cannibalism and interspecific predation were more common byT. pyri. In fall, oviposition byM. occidentalis stopped sooner and in the following spring,T. pyri reproduced beforeM. occidentalis. Research needs and management of mixed-predator populations are discussed.     

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.     

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.     

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.      

Dispersal and gene flow of pesticide resistance traits in phytoseiid and tetranychid mites

Dispersal and gene flow of pesticide resistance traits in phytoseiid and tetranychid mites are discussed relative to their biologies and resistance management. The focus is on deciduous fruit-tree crops whereTyphlodromus pyri Scheuten andMetaseiulus occidentalis (Nesbitt) can effectively control spider mite pests. Oregon populations ofM. occidentalis were more dispersive thanT. pyri, as evidenced by movement to small apple trees placed inside and outside of commercial apple orchards. This difference was corroborated by the spatial distributions of organophosphate resistance in populations from sprayed orchards and nearby unsprayed habitats:T. pyri showed patchy, local patterns of resistance whileM. occidentalis showed more regional, homogeneous trends. Gene flow among populations was estimated from allozymic variation ofT. pyri. Intra- and inter-population genetic variation was high enough to prevent population differentiation. Thus, allozymic estimates of gene flow were higher than that indicated by pesticide resistance patterns.Dispersal inTetranychus urticae Koch is also discussed relative to resistance evolution. Immigration of resistant phenotypes from crops or other sprayed habitats can increase the frequency of resistance. Immigration of susceptible individuals from surrounding unsprayed habitat into a sprayed crop can slow resistance or lead to its reversion, depending on the level of gene flow between populations. Dispersal within crops can have the same effect if susceptibles come from a refuge. In pears, immigration of susceptibleT. urticae from nearby habitat and groundcover aided in reversion of organotin resistance. Experiments on resistance management tactics forT. urticae are discussed.     

Fungitoxic and phytotoxic effect of some surface-active agents applied for the control of apple powdery mildew

Mixtures of methyl esters of fatty acids (‘Off-Shoot O’) and mixtures of fatty alcohols (‘Off-Shoot T’), applied during the late autumn (November), eradicated apple powdery mildew (caused by Podosphaera leucotricha) from infected buds. Applications in the spring at bud-burst were less effective. The autumn sprays caused little damage to the cultivars Bramley's Seedling, Cox's Orange Pippin and Golden Delicious but on Worcester Pearmain 50% of the buds were killed by a 5% Off-Shoot O spray. The bud-burst sprays were damaging and reduced yield on the Cox and Bramley trees. A 5% a.i. mixture of nonanol/lissapol applied to a range of commercial cultivars was effective in eradicating powdery mildew but was more phytotoxic than the Off-Shoot compounds. Spraying Cox trees later in the winter failed to reduce the damage. Eradication of the overwintering stage of the disease resulted in low spore concentrations during the following spring and early summer, enabling some economies to be made in the summer mildew fungicide programme.     

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.     

Effect of the width of the herbicide strip on mite dynamics in apple orchards

Herbicide strips are used in apple orchards to promote tree growth and survival, to increase yield and to reduce the risk of rodent damage to tree bark. However, herbicide strips, particularly wider ones, may cause problems including soil erosion, reduced organic matter, leaching of nitrates into ground water and increased incidence of plant diseases and pests, including two-spotted spider mites, Tetranychus urticae Koch. In this 2 year study we monitored mite dynamics in apple trees and used sticky bands on tree trunks to determine rates of T. urticae immigration into Nova Spy apple trees in plots with wide (2 m) or narrow (0.5 m) herbicide strips. Use of wider herbicide strips promoted two risk factors that could trigger outbreaks of tetranychid mites. First, concentrations of leaf N in apple trees were higher and those of P and K were lower with the wide strips. Such changes in nutritional quality of leaves would increase the potential for more rapid population growth of T. urticae, and to a lesser extent, the European red mite, Panonychus ulmi (Koch). Second, there were higher rates of T. urticae immigration from the ground cover vegetation into the trees. In 2006, and for most of 2007, densities of T. urticae were higher with wide herbicide strips, whereas densities of P. ulmi were not enhanced. However, by late August to early September in 2007, densities of both tetranychids were lower with wide herbicide strips. This is because both risk factors were counterbalanced, and eventually negated, by the enhanced action of phytoseiid predators, mostly Typhlodromus pyri Scheuten. From July through September 2006, ratios of phytoseiids to tetranychids were always several-fold lower with wide herbicide strips but in 2007, from mid-July onwards, predator–prey ratios were usually several-fold higher with wide strips. However, this numerical response of phytoseiids to prey density can only occur where the pesticide program in orchards is not too harsh on phytoseiids. Hence the impact of width of herbicide strip is contingent on the composition and size of the phytoseiid complex and the impact of pesticides on predation.     

Pollen availability for predaceous mites on apple: spatial and temporal heterogeneity

It has been suggested that an abundance of alternate food early in the spring may be critical to the ability of generalist predaceous mites to suppress spider mite pests. One alternate food that is typically very abundant in spring is wind-dispersed pollen. Here we investigate, at several spatial scales, the heterogeneity in the availability of pollen to predaceous mites on apple. We found pollen to be abundant on apple leaves very soon after they opened (>100 grains/cm 2 ), and that the dominant pollen types at this time were wind-dispersed tree pollens (Betulaceae and Pinaceae). We found that most of the spatial variation in pollen abundance occurred at either small spatial scales (within trees) or very large spatial scales (among orchard blocks). Variability among orchards was clearly influenced by the surrounding vegetation, and probably also by the management regime (frequency of mowing). Spatial heterogeneity in pollen availability may affect the build-up of predatory mite populations in the spring, as we found early season abundances of Typhlodromus pyri (Phytoseiidae) and Zetzellia mali (Stigmaeidae) to be better correlated with early season pollen density than with abundance of mite prey (Aculus schlechtendali).     

Sublethal effects of esfenvalerate residues on pyrethroid resistant Typhlodromus pyri (Acari: Phytoseiidae) and its prey Panonychus ulmi and Tetranychus urticae (Acari: Tetranychidae)

The effect of residues of esfenvalerate on oviposition of the resistant strain of the predatory mite Typhlodromus pyri and its main prey, European red mite Panonychus ulmi and two-spotted spider mite Tetranychus urticae, were investigated. T. pyri showed a significant linear reduction in oviposition after 24h in the presence of increasing levels of esfenvalerate residue applied at the field rate. Furthermore, when given a choice, T. pyri preferred to lay eggs on residue-free surfaces. Of the two prey species, only P. ulmi showed significant avoidance of increasing levels of residues of the field rate concentration of esfenvalerate, as measured by runoff mortality, however both P. ulmi and T. urticae, when given a choice, showed a preference for esfenvalerate-free surfaces. As with the predatory mite T. pyri, both prey species showed a significant linear reduction of oviposition with increasing esfenvalerate residues and a preference to lay eggs on esfenvalerate-free surfaces. Esfenvalerate residues as high as 15X field rate were not repellent to pyrethroid-resistant T. pyri. The possible effects of these sublethal effects on predator-prey dynamics and implications for integrated mite control programmes in apple orchards are discussed.     

Integrated control of apple pests in New Zealand 16. Progress with integrated control of European red mite

Abstract

Studies were made in an orchard near Nelson from 1974 to 1978 on integrated control of Panonychus ulmi (Koch) using the organophosphate-resistant predator Typhlodromus pyri Scheuten. Correct timing of selective acaricides during the October-January period is essential, and can be achieved by close observation of P. ulmi development. When the majority of winter eggs have hatched (late October to early November), or the majority of the summer eggs laid by the first generation (very late November to early or mid December), there is a short period when a maximum of immature mites occurs. This is before many adult females have matured, and is the most effective time for application of an acaricide such as cyhexatin. The development of P. ulmi, in particular the incubation period of the summer eggs, is controlled by temperature, and in seasons when mean temperatures are well below average in November and December the delayed mite development makes accurate timing of the December spray more difficult. Other factors which also affect mite development are the use of dormant oil, cultivar, and orchard aspect and shelter.

On the block of trees where no acaricides were used since 1968, although regular applications of azinphos-methyl were made, T. pyri maintained P. ulmi at acceptable levels over the 5 years 1973-78, a maximum of P. ulmi occurring each season in January with the third generation. In three seasons the peak was well below the threshold for commercial spraying; in two seasons this threshold was exceeded, but despite the absence of acaricides P. ulmi numbers soon fell.

A further experiment demonstrated the utility of mineral oil and cyhexatin as selective acaricides in integrated programmes. Cycloprate, tricyclotin, and fenbutatin oxide were shown to be as effective and selective as cyhexatin, a single application in early December giving good survival of T. pyri and season-long control of P. ulmi. In another experiment propargite was as effective and selective as cyhexatin; amitraz was more toxic to T. pyri and less persistent against P. ulmi, and resulted in a poor P. ulmi : T. pyri ratio; and chlorpyrifos, though not more toxic than cyhexatin to T. pyri, was less effective against P. ulmi.

Mancozeb, and dinocap + mancozeb, used in a summer-long programme of 12 treatments, were more toxic to T. pyri than were binapacryl or dinocap alone.     

Gene flow measured by allozymic analysis in pesticide resistant Typhlodromus pyri occurring within and near apple orchards

Electrophoresis of allozymes was used to estimated gene flow among populations of Typhlodromus puri Scheuten from apple orchards and nearby blackberry plants from two valleys of western Oregon, USA. Four allozyme loci unaffected by pesticides were tested. Wright's coefficient of inbreeding, F _ST, for all populations was 0.115 and the proportion of populations that migrated per generation, Nm, was 2.08. These values were higher than expected for such locally collected mites. No allelic patterns could be discerned for populations among or within valleys: however, more variation was found for mites collected within than between valleys. From other studies of dispersal and pesticide resistance, we concluded that T. pyri had a low dispersal rate, but these data from allozymic analysis indicated there was moderate gene flow among populations. We concluded that the unique features of the population dynamics of T. pyri may account for the differences seen in estimating gene flow when using different types of population assessment (i.e., dispersal distances, resistance rates and allozyme frequency studies).     

Is the predatory mite <Emphasis Type="Italic">Kampimodromus aberrans</Emphasis> a candidate for the control of phytophagous mites in European apple orchards?

The most important biocontrol agents of phytophagous mites (mainly Tetranychidae) in European apple orchards are the predatory mites Amblyseius andersoni, Typhlodromus pyri and Euseius finlandicus (Phytoseiidae). A similar situation is found in Trentino (north-eastern Italy), an important apple production area in Europe. Another phytoseiid mite, Kampimodromus aberrans, can be dominant in neglected fruit orchards but is rare in commercial orchards because of its susceptibility to pesticides. However, pesticide resistant strains of K. aberrans have recently been found in vineyards. In the late 1990s, one of these resistant strains was successfully released on an experimental farm in Trentino. Kampimodromus aberrans spread to an apple orchard, despite the fact that it was colonized by T. pyri, A. andersoni and E. finlandicus, and became the dominant species. Since K. aberrans’ colonization appeared to be affected by apple cultivars, experiments were conducted on potted plants of three selected apple cultivars (Golden Delicious, Red Chief, Reinette du Canada). The results stressed the effect of cultivars on apple colonization by K. aberrans and suggested the role of leaf morphology in influencing this phenomenon. Field releases of K. aberrans were successfully performed in four commercial apple orchards. The incidence of K. aberrans in the total phytoseiid population increased over time and the predator became dominant in the season following its release in two orchards. Kampimodromus aberrans persists in these orchards as the dominant species. The adaptation of K. aberrans to varying environmental conditions, its tolerance to pesticides, and its competitiveness towards other phytoseiid species suggest a potential role of this species in the biological control of phytophagous mites in European apple orchards. Handling editor: Eric Lucas.     

Use of spinosad and predatory mites for the management of Frankliniella occidentalis in low tunnel‐grown strawberry

Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) is a major pest of strawberry. The efficacy of three species of predatory mites, Typhlodromips montdorensis (Schicha), Neoseiulus cucumeris (Oudemans) (both: Acari: Phytoseiidae), and Hypoaspis miles (Berlese) (Acari: Laelapidae), and their compatibility with spinosad for the control of this thrips was evaluated in commercial strawberry in spring. Low tunnel‐grown strawberry was treated with ‘water then mites’, ‘spinosad then mites’, or ‘mites then spinosad’. Predatory mites were released as single‐, two‐ and three‐species combinations. Overall, spinosad‐treated plants had fewer thrips than water‐treated plants (control). In all treatment regimes, each species of predatory mite reduced the number of thrips relative to those plants that received no mites. Predatory mites were most effective in reducing thrips when released after spinosad was applied. Any multiple‐species combination of predatory mites reduced thrips numbers more than single‐species releases. The two‐species combination of T. montdorensis (foliage inhabiting) and H. miles (soil dwelling) was the most effective in suppressing thrips. The next most effective combination was a three‐species release. Of multiple‐species combinations, the two‐species combination of T. montdorensis and N. cucumeris was the least effective in suppressing thrips numbers. The spinosad and mites only temporarily reduced the numbers of F. occidentalis. This suggests that further application of predatory mites, spinosad, or both is required to maintain F. occidentalis populations below an economically damaging level.     

Simulating effects of environmental factors on biological control of Tetranychus urticae by Typhlodromus pyri in apple orchards

Successful biological control of mites is possible under various conditions, and identifying what are the requirements for robust control poses a challenge because interacting factors are involved. Process-based modeling can help to explore these interactions and identify under which conditions biological control is likely, and when not. Here, we present a process-based model for population interactions between the phytophagous mite, Tetranychus urticae, and its predator, Typhlodromus pyri, on apple trees. Temperature and leaf nitrogen concentration influence T. urticae rates of development and reproduction, while temperature and rate of ingestion of prey and pollen influence T. pyri rates of survival and reproduction. Predator and prey population dynamics are linked through a stage structured functional response model that accounts for spatial heterogeneity in population density throughout the trees. T. urticae biomass-days (BMD’s), which account for sizes of larvae, nymphs and adults, indicate level of mite-induced leaf damage. When BMD’s exceed 290 per leaf, there are economic losses. When BMD’s exceed 350 per leaf, T. urticae population growth is curbed and eventually the population decreases. Simulations were run to determine which conditions would lead to current year economic loss and increased risk of loss in the following year, i.e. where more T. urticae than T. pyri are present at the end of September. Risk was high with one or more of the following initial conditions: a high prey: predator ratio (10:1 or more); a low to intermediate (0.04–0.2 T. urticae per leaf) initial density; T. urticae with a higher initial proportion of adult females than T. pyri; and a delayed first detection of mites, whether in late July, or sometimes in late June, but not in early June. Warm summer weather, higher leaf nitrogen and T. urticae immigration into trees were also risk factors. Causes for these patterns based on biological characteristics of T. urticae and T. pyri are discussed, as are counter measures which can be taken to reduce risk.     

Pear rust mite,Epitrimerus pyri (Acari: Eriophyidae) oviposition and nymphal development on Pyrus and non-Pyrus hosts

The ovipositional response of deutogynes of the pear rust mite, Epitrimerus pyri Nalepa, and the rate of development of E. pyri nymphs differed according to the host plant to which mites were exposed. Among the fourteen Pyrus hosts examined, leaves from the Clapp's Favorite cultivar of P. communis elicited the strongest egg-laying response and the fastest rate of nymphal development, whereas egg-laying was least and nymphal development slowest on leaves from P. calleryana. Among the three non-Pyrus hosts, E. pyri oviposited and completed nymphal development on apple and quince leaves, but would not deposit eggs on apricot. Antixenosis appears to be the primary mechanism of resistance, although antibiosis may be operating to a lesser extent. These results are discussed in relation to the resistance of Pyrus to other arthropod pests.     

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.     

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.     

Diapause incidence in the two-spotted spider mite increases due to predator presence, not due to selective predation

We recently reported evidence for increased diapause incidence in the spider mite Tetranychus urticae in presence of the predatory mite Typhlodromus pyri. This effect may arise from (1) selective predation on non-diapause spider mites, (2) predator-induced diapause in spider mites, or (3) both. Using a different strain of T. urticae, we first recovered increased diapause incidence in association with predators. Then, we tested for selective feeding in two-choice experiments with equal numbers of non-diapause and diapause spider mites. We found that the predatory mite had a significant preference for the latter. This indicates that increased diapause incidence in association with predatory mites is not due to selective predation. Therefore, predator-mediated physiological induction of diapause seems a more likely explanation. The cues leading to induction appear to relate to the predators, not their effects, since predation simulated by spider-mite removal or puncturing did not significantly affect diapause incidence. Why spider mites benefit from this response, remains an open question.This revised version was published online in May 2005 with a corrected cover date.