Assessment of Amblyseius fallacis (Acari: Phytoseiidae) for biological control of tetranychid mites in an Ontario peach orchard

We introduced a mass-reared pyrethroid-resistant strain of the predatory phytoseiid mite Amblyseius fallacis (Garman) into an Ontario peach orchard in an attempt to control populations of the phytophagous mites Panonychus ulmi Koch and Tetranychus urticae Koch (Acari: Tetranychidae). Releases of 1,000 and 2,000 mites per tree were made, at three different times. The release of 2,000 mites per tree in June and in July resulted in significantly higher phytoseiid densities than was observed on control trees. However, densities of P. ulmi or T. urticae were not significantly affected by any release rate or by timing. The release of 1,000 A. fallacis per tree, or of any density in August, did not significantly increase phytoseiid abundance. In the following year, population dynamics of both phytoseiid and phytophagous mites were not significantly affected by the previous year's release. Amblyseius fallacis can be a useful predator in some fruit orchards. However, further research is necessary into the timing and rate of release, modified spray programmes, and with different crops, in order to clarify the role of this species for biological control in Ontario peach orchards.     

Functional response of Euseius finlandicus and Amblyseius andersoni to Panonychus ulmi on apple and peach leaves in the laboratory

The functional response of adult females of the predatory mites Euseius (Amblyseius) finlandicus and Amblyseius andersoni to larvae and adult females of the fruit tree red spider mite Panonychus ulmi was determined on apple and peach leaf disks in the laboratory at 25°C and 16:8 (L:D). For adult females of P. ulmi the predation efficiency of E. finlandicus was higher on peach than on apple, whereas that of A. andersoni was higher on apple than on peach. Efficiency of predation on larvae of P. ulmi by either predator did not differ significantly between apple and peach. On both plants, A. andersoni had a higher predation rate than E. finlandicus on larvae of P. ulmi. It is concluded that in the laboratory the host plant has a substantial effect on predation efficiency of A. andersoni and E. finlandicus when they preyed on adults but not when they preyed on larvae of P. ulmi.     

Some effects of pre-release host-plant on the biological control of Panonychus ulmi by the predatory mite Amblyseius fallacis

Amblyseius fallacis Garman has been selected for pyrethroid resistance and mass reared for experimental release as a biological control agent for tetranychid mites on a number of crops in Canada. Several releases of this predator onto apple and peach trees have failed to result in the establishment of A. fallacis, or in the biological control of Panonychus ulmi Koch. Here, we test the hypothesis that the change of host-plant at the time of release is a critical factor in the establishment of A. fallacis for biological control of P. ulmi. Functional and numerical response studies were undertaken on two populations of A. fallacis: a wild strain collected from the canopy foliage of an apple orchard near Vineland, Ontario; and a second strain reared on bean plants in a commercial insectary with Tetranychus urticae as prey. Each population consumed significantly more P. ulmi and produced significantly more eggs when on leaf disks from the plant species they were reared on, than on leaf disks from the novel host plant. A further experiment was conducted to determine if establishment and biological control of mass-reared A. fallacis could be affected by rearing a population for a short term on apple leaves prior to release on apple trees. Three release treatments were made into potted apple trees in a glasshouse, using predators commercially mass-reared on bean and T. urticae: A. fallacis released directly; A. fallacis reared in the laboratory for four weeks on bean and T. urticae; A. fallacis reared on apple leaves and T. urticae for four weeks. They were compared with a control treatment lacking predator release. Contrary to results of the functional and numerical response studies, no difference was observed between release treatments. All release treatments adding A. fallacis resulted in a similar, if limited, degree of biological control of P. ulmi. These results indicated that there may be short-term effects of host plant on the establishment of A. fallacis and biological control of P. ulmi, which in our study were observed as an initial reduction of the predatory response. However, in a test, the predators appeared to overcome these short-term effects and successfully established on the new host-plant to control P. ulmi.     

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.     

The effect of pyrethroid lambdacyhalothrin applications on the spatial distribution of phytophagous and predatory mites in apple orchards

The spatial distribution of three phytophagous mites,Panonychus ulmi (Koch),Tetranychus urticae Koch andAculus schlechtendali (Nalepa), and two predacious mites,Zetzellia mali (Ewing) andAmblyseius fallacis (Garman), and the effect of pyrethroid lambdacyhalothrin applications on mite spatial dispersion were investigated over a 3-year period in an apple orchard in Ontario. The index of dispersion and the slope of Taylor's power law were used to evaluate dispersion patterns of mites. Panonychus ulmi showed that between-tree spatial variation decreased with an increase of population densities, whereas between-leaf variation increased with population densities. With all other four species it appeared that between-tree variation is much greater than between-leaf variation at all field population density levels. The values ofb by Taylor's power law suggested that all five species of mites are aggregated, but that in generalP. ulmi andT. urticae (b=1.427–1.872) are more aggregated than their predators (b=1.254–1.393). Taylor's regression technique suggests that pyrethroid applications causedP. ulmi, T. urticae, Z. mali andA. fallacis to be less aggregated whileA. schlechtendali was more aggregated. The impact of changes in mite spatial distribution following pyrethroid applications on sampling plans is 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.     

Tebufenpyrad: compatibility with integrated mite control on apples

Successful integrated mite control (IMC) depends on the availability of acaricides which act selectively on pest mites with minimal effects on predators. Laboratory bioassays of tebufenpyrad against adult female Panonychus ulmi (Koch) provided baseline toxicity data and showed it to be highly active. Bioassays also showed tebufenpyrad was toxic to the predatory mite Typhlodromus pyri Scheuten but it was approximately 70 times less toxic to the predators than to P. ulmi at the lc ₅₀. Field trials using four concentrations of tebufenpyrad (10, 7.5, 5 and 2.5 g a.i./100 l) confirmed it was selectively more toxic to the pest mites than to predators and showed that it is compatible with IMC. It is suggested that a concentration of 5 g a.i./100 l would be suitable for IMC. A resistance management strategy for tebufenpyrad is proposed.     

Amensalism via webs causes unidirectional shifts of dominance in spider mite communities

Competitive displacement is considered the most severe consequence of interspecific competition; if a superior competitor invades the habitat of an inferior species, the inferior species will be displaced. Most displacements previously reported among arthropods were caused by exotic species. The lack of investigation of displacement among native species may be due to their apparently harmonious coexistence, even if it is equivalent to an outcome of interspecific association. A seasonal change in the species composition of spider mites, from Panonychus ulmi to Tetranychus urticae, is observed in apple trees worldwide. Previous laboratory experiments have revealed amensal effects of T. urticae on P. ulmi via their webs. Using manipulation experiments in an orchard, we tested whether this seasonal change in species composition occurred as the result of interspecific competition between these spider mites. Invasion by T. urticae prevented an increase in P. ulmi densities throughout the experimental periods. Degree of overlap relative to the independent distribution on a leaf-surface basis (ω _S) changed from positive to negative with increasing density of T. urticae. T. urticae invasion drove P. ulmi toward upper leaf surfaces (competitor-free space). The niche adjustment by P. ulmi occurred between leaf surfaces but not among leaves. Our findings show that asymmetrical competition between T. urticae and P. ulmi plays an important role in this unidirectional displacement and that the existence of refuges within a leaf produces the apparently harmonious coexistence of the mites and obscures their negative association.     

Analysis of prey preference in phytoseiid mites by using an olfactometer,predation models and electrophoresis

Prey preference of three phytoseiid species,Typhlodromus pyri Scheuten,Amblyseius potentillae (Garman) andA. finlandicus (Oudemans) which occur in Dutch orchards, was analysed with respect to two economically important phytophagous mites, the European red spider mitePanonychus ulmi (Koch), and the apple rust miteAculus schlechtendali (Nalepa). Two types of laboratory experiments were carried out: (1) olfactometer tests to study the response when volatile kairomones of both prey species were offered simultaneously; and (2) predation tests in mixtures of the two prey species and comparison with calculated predation rates, using a model provided with parameters estimated from experiments with each prey species alone. In addition, the diet of field-collected predators was analysed using electrophoresis. For each predator species the results of the different tests were consistent, in thatT. pyri andA. potentillae preferredP. ulmi overA. schlechtendali, whereasA. finlandicus preferredA. schlechtendali overP. ulmi.     

Feeding preference of Zetzellia mali: does absolute or relative abundance of prey matter more?

The importance of the acarine predator, Zetzellia mali, in the control of phytophagous mites in apple orchards is not well understood. Zetzellia mali tends to prefer the eriophyid, Aculus schlechtendali, over the economically more significant tetranychid, Panonychus ulmi, but quite a wide range of preference values have been reported in the literature. In sets of laboratory choice trials, we determined that prey preference of this predator varies with the relative but not absolute density of its prey. We attempt to explain these results in terms of behavioural mechanisms and discuss the potential implications of our results for the effectiveness of Z. mali in the biological control of phytophagous mites in apple orchards.     

Factors influencing the acaricidal activity of flucycloxuron

Contact activities of flucycloxuron on immature stages of the two-spotted spider mite (Tetranychus urticae (Koch)) and the European red mite (Panonychus ulmi (Koch)) gradually decrease in the successive developmental stages. The levels of contact activity of flucycloxuron on larvae and protonymphs ofT. urticae andP. ulmi are of the same order. Deutonymphs ofT. urticae are less susceptible to contact activity than the similar stage ofP. ulmi. In adultT. urticae, the transovarial ovicidal activity was used as an indicator for cuticular penetration. More than 90% of the maximal penetration into adult mites occurs within 8 h. Reversibility of the transovarial activity was not observed after 24 h, but did occur after a subsequent 48 h stay on untreated leaves. The ovo-larvicidal activity of flucycloxuron onP. ulmi after treatment of apple leaves is strongly negatively influenced by leaf age, partly by lower retention of the spray liquid on the leaves. Leaf penetration was measured by application of flucycloxuron on leaf uppersides and assessment of the transovarial activity in mites (P. ulmi orT. urticae) infested on the undersides, one day after treatment. In this test system, leaf penetration was found to be strongly species dependent. Penetration was high in cucumber, moderate in French beans, cotton, roses and strawberry, but low in apple and pepper. Leaf penetration in French bean plants is drastically reduced at increasing leaf age. The overall positive effect of increase in relative air humidity on leaf penetration, is statistically highly significant (P=0.001) for French beans and almost significant (P=0.08) for cucumbers. WithT. urticae on French bean it was found that in this test flucycloxuron needs more than one day for maximal leaf penetration. Although in apple leaves penetration from uppersides was low, penetration from undersides was much higher. The surfactants Arkopal N 130, Silwet L-77 and X2-5309 enhance penetration from leaf under-sides.     

Abundance of phytoseiid mites on Vitis species: effects of leaf hairs,domatia, prey abundance and plant phylogeny

We observed the number of predatory mites (Phytoseiidae:Typhlodromus caudiglans) on the foliage of 20 North American species of grapes (Vitis spp) plus the domesticated EuropeanVitis vinifera, all grown in a common garden. We found relatively few phytophagous mites. The numbers of phytophagous mites were not correlated with the plant characteristics that we measured. We found approximately five times as many predatory mites as phytophagous mites and the numbers of these phytoseiid predators were not affected by the availability of prey. Similarly, numbers of phytoseiids were unaffected by plant gender and, hence, the availability of pollen, another source of food. The numbers of phytoseiids were not clustered according to the taxonomic grouping of the tested plant species. Leaf surface characteristics explained over 25% of the variance in the numbers of phytoseiids. Numbers of phytoseiids were positively associated with the density of vein hairs, the density of bristles in leaf axils, and the presence of leaf domatia. These results suggest that sheltered habitats rather than food availability may limit the numbers of phytoseiid mites on grapevines.     

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.     

Aerial dispersal of European red mites (Acari: Tetranychidae) in commercial apple orchards

Aerial dispersal of European red mite, Panonychus ulmi (Koch), in commercial apple orchards was estimated by trapping windborne mites. Studies were conducted at four orchards in eastern New York during 1989 and 1990 and at three orchards in western New York during 1989. In each orchard mites were trapped in three locations; the interior of the orchard, at the border of the orchard and in a field or woodlot beyond the orchard. Large numbers of mites were captured, even when the numbers of mites on apple foliage were well below levels where mite injury to leaves was visible (less than five per leaf). The log numbers of mites trapped were linearly related to the log density of mites on leaves and this relationship was consistent for each year and region the study was conducted. The trap captures among the three locations in and outside an orchard were highly correlated. The implications these findings may have on metapopulation dynamics and resistance to acaricide dynamics are discussed.     

Species association among predaceous and phytophagous apple mites (Acari: Eriophyidae, Phytoseiidae, Stigmaeidae, Tetranychidae)

Predator–predator, predator–prey, and prey–prey associations among nine species of mites were studied in a plot of 100 Red Delicious apple (Malus pumila Miller) trees from 1990 to 1997. In 1990, seven-year-old trees were inoculated with Panonychus ulmi (Koch), Tetranychus urticae Koch (Acari: Tetranychidae) or both, and sprayed with azinphosmethyl (alone or plus endosulfan), or nothing. The species Zetzellia mali (Ewing) (Acari: Stigmaeidae), Amblyseius andersoni Chant (Acari: Phytoseiidae), Eotetranychus sp., Bryobia rubrioculus (Scheuten) (Acari: Tetranychidae), and Aculus schlechtendali Nalepa (Acari: Eriophyidae) were already present or immigrated into plots, and Galendromus occidentalis (Nesbitt) and Typhlodromus pyri Scheuten (Acari: Phytoseiidae) were introduced. Yule's V association index was used to measure positive, neutral, or negative interspecific associations for each species pair, because of its robustness with spatially autocorrelated data. We found that pesticide and release treatments did not greatly affect the association results, but there were strong seasonal differences. Predator–predator associations were the strongest and most consistent, showing negative associations in the early and mid seasons, and neutral ones in late season. Negative associations of T. pyri with other predators were the strongest, which is consistent with evidence that this mite can detect other predators on a leaf. Predator–prey seasonal associations were mixed, with some positive and others negative, with most significant associations occurring in the mid season. One prey–prey interaction was positive, again in mid season, most likely because of similar habitat preferences.     

Variation in the olfactory response of 13 populations of the predatory mite Amblyseius womersleyi to Tetranychus urticae-infested plant volatiles (Acari: Phytoseiidae, Tetranychidae)

We studied the response of the predatory mite Amblyseius womersleyi collected in 13 different sites in Japan toward Tetranychus urticae-infested kidney bean leaf volatiles in a Y-tube olfactometer. The predatory mites were collected from eight plant species infested by one of three tetranychid mite species. The predators' responses to the infested-leaf volatiles varied from 33% to 97% among the populations. The predators collected at 10 sites showed a significant preference for infested-leaf volatiles, whereas those collected at three tea plantations did not distinguish between the infested- and uninfested-leaf volatiles. We discussed the possible factors that affected the olfactory response of A. womersleyi towards the infested leaf volatiles.     

Hierarchical structure in kairomone preference of the predatory mite Amblyseius potentillae: dietary component indispensable for diapause induction affects prey location behaviour

ABSTRACT.

• 1 The phytoseiid predator Amblyseius potentillae (Garman) responded to volatile kairomones emitted from leaves infested by the two-spotted spider mite (Tetranychus urticae Koch), the apple rust mite (Aculus schlechtendali (Nalepa)) or the thrips Frankliniella pallida (Uzel), only when the predators had been reared on a carotenoid-free diet. In contrast A.potentillae responded to the European red spider mite (Panonychus ulmi (Koch)) both when the predators had been reared on a carotenoid-containing and a carotenoid-free diet.
• 2 Carotenoid-deficient predators did not respond to odour emitted from a host plant that was infested by larvae of the fruit-tree leaf roller (Adoxophyes orana (F.v.R)), a carotenoid-containing phytophage, that cannot be preyed upon by A.potentillae.
• 3 Carotenoids are indispensable for diapause induction in A.potentillae. Hence, carotenoid-deficient predators can increase their fitness by feeding from a carotenoid source. This may explain the response of carotenoid-deficient predators to the kairomones of the two-spotted spider mite, F.pallida and the apple rust mite (all containing ingestible carotenoids). As the fruit-tree leaf roller cannot serve as prey and thus as a carotenoid source, it makes sense that the predators lacking carotenoids do not respond to the kairomone of this phytophagous insect.
• 4 Two-choice experiments in a Y-tube olfactometer showed that the kairomone preference of A.potentillae has a hierarchical structure: the kairomone of the European red spider mite is the most preferred one, followed by that of apple rust mite, whereas the kairomone of the two-spotted spider mite is the least preferred of these three.

     

Selection for non-diapause inAmblyseius cucumeris andAmblyseius barkeri and exploration of the effectiveness of selected strains for thrips control

In Europe and North America the western flower thrips,Frankliniella occidentalis, is an important pest in various greenhouse crops, such as sweet pepper and cucumber. Two species of predatory mite are commercially applied for biological control of this pest:Amblyseius cucumeris andA. barkeri. Thrips control is generally successful from March onwards. During winter, however, thrips control by these predatory mites is less effective. An important reason for this is that the commercially applied strains of both mite species enter reproductive diapause under short-day photoperiods, whereas the western flower thrips does not enter diapause. In this paper we report on selection experiments for non-diapause in strains of both mite species, aimed at obtaining predators that do not enter diapause under light- and temperature conditions prevailing in winter. Additional experiments were done to estimate the potential of the selected lines as control agents ofF. occidentalis. Selection for non-diapause proved highly successful in both predatory mite species. In a New Zealand strain ofA. cucumeris diapause incidence decreased from 41% to 0% in about ten generations; in a Dutch strain ofA. barkeri diapause incidence decreased from 67% to 0% in about six generations. Furthermore, selection for non-diapause had no influence on predator performance, measured as predation rate and oviposition rate on a diet of first instar thirps larvae. Rates of predation and oviposition were the same for selected and unselected lines in both species; rates of predation and oviposition were higher forA. cucumeris than forA. barkeri. After 18 months under non-diapause conditions, no less than 92% of a sample of the selected non-diapause line ofA. cucumeris did not enter diapause when tested under diapause-inducing conditions. This indicates that ‘non-diapause’ is a stable trait in these predatory mites. Finally, a small-scale greenhouse experiment in a sweet pepper crop showed that the selected non-diapause line ofA. cucumeris established successfully under diapause-inducing short-day conditions.     

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.     

Washing technique for monitoring mites in apple orchards

A shake-and-wash technique for monitoring the predatory phytoseiid mitesTyphlodromus pyri, Amblyseius finlandicus, and their prey,Panonychus ulmi, Tetranychus urticae andAculus schlechtendali in commercial apple orchards was developed. The removal and recovery of mites from leaves, shoots and spurs is based on agitating the plant material by hand in alcohol and subsequently removing the mites using a separating funnel. The mites are quickly killed and easily washed off the plant material, and are thus well preserved for further study. The technique is more efficient than directly counting the mites on plant material under a dissection microscope and can be easily employed both in the laboratory and in the field.