Amblyseius Fallacis Research Articles

PREDATORY COMPLEX OF PHYTOPHAGOUS MITES AND THEIR ROLE IN INTEGRATED PEST MANAGEMENT IN APPLE ORCHARD

ABSTRACT Predatory complex of phytophagous mites, their diversity, abundance, predatory potential and their role in integrated mite management (IPM) in apple orchards was studied. Two species of predatory mites viz., Amblyseius fallacis A-H and Zetzellia mali (Ewing); one species of black coccinellid beetle, Stethorus punctum Le Conte; a mirid, Chrysoperla spp. ; anthocorid bug, Orius spp; the black hunter thrip, Leptothrips mali (Fitch) and various species of spiders were recorded feeding on phytophagous mites. Predatory mites were the most abundant species. The black coccinellid beetle was the next most predominant species. Amblyseius fallacis consumed 2.0 and Stethorus punctum 12-18 European red mites per day. Population of phytophagous mites remained high in orchards heavily sprayed with insecticides adults, whereas predatory mites population was highest in orchards receiving zero insecticidal applications. Stoppage of insecticidal applications resulted in a rise of predacious mite populations, which in turn brought decline in spider mite populations.

Effects of pesticides on mite predators (Acari: Phytoseiidae) and colonization of apple trees byTetranychus urticae

A 2-year survey of mite populations and pesticide use was carried out in Nova Scotia, Canada, in apple orchards where the two-spotted spider mite (Tetranychus urticae Koch) was the dominant phytophagous mite. Fungicides were the only class of pesticides that affected cumulative number ofT. urticae-days per leaf in tree canopies and colonization success — the ratio ofT. urticae-days to number of immigratingT. urticae caught in sticky bands on tree trunks. In 2000, increased numbers ofT. urticae-days in the tree canopy were associated with more frequent applications of ethylene bis-dithiocarbamate (EBDC) fungicides and with higher fungicide toxicity scores, which indicate cumulative level of suppression of the phytoseiid predatorTyphlodromus pyri Scheuten by all fungicide applications. Higher rates of colonization success were also associated with higher toxicity scores. EBDC’s applied in 2000 promotedT. urticae immigration as indicated by their counts on sticky bands. In 2000 and 2001, number ofT. pyri-days in the tree canopies was decreased by more frequent EBDC applications and by higher fungicide toxicity scores. Promotion ofT. urticae in tree canopies by EBDC’s was attributed to their toxicity toT. pyri. BothT. pyri and another phytoseiid,Amblyseius fallacis (Garman), were found in ground cover vegetation. Hence, increased immigration from the ground cover attributed to the toxicity of EBDC’s toT. pyri and, especially, toA. fallacis, which is a specialist predator of spider mites and an effective natural enemy ofT. urticae.

Inventory of Predacious Mites in Quebec Commercial Apple Orchards Where Integrated Pest Management Programs Are Implemented

Abstract The commercial apple (Malus spp.) orchard ecosystem in Quebec has a diverse fauna of predacious mites. A systematic 2-yr survey showed Amblyseius fallacis (Garman), Typhlodromus caudiglans Schuster (Acari: Phytoseiidae), and Agistemus fleschneri Summers (Acari: Stigmaeidae) to be the most abundant species. Other phytoseiids, Typhlodromus conspicuous (Garman), Typhlodromus herbertae Chant, Typhlodromus longipilus Nesbitt, Typhlodromus bakeri (Garman), Typhlodromus pyri Scheuten, Amblyseius okanagensis (Chant), and Amblyseius finlandicus (Oudemans), were found in low numbers. Two of these species, A. finlandicus and T. conspicuus, were identified for the first time in Quebec. Other occasional species included Anystis baccarum (L.) (Acari: Anystidae) and Balaustium sp. (Acari: Erythraeidae). Tetranychid mite numbers were always less than two mites per leaf throughout the study, and none of the commercial orchards required an acaricide treatment. A notable aspect of this study was that seasonal total...

Prey preference of Hyaliodes vitripennis as an intraguild predator: Active predator choice or passive selection?

Prey vulnerability is a major factor influencing predator preferences. This study evaluated the preference of the glassy-winged mirid bug Hyaliodes vitripennis for two prey types: a slow-moving extraguild prey, the two-spotted spider mite Tetranychus urticae, and a faster intraguild prey, the phytoseiid mite Amblyseius fallacis. Tests were done in the presence of mobile and frozen individuals. Searching and handling time, defensive mechanisms and prey value of the two prey species were also evaluated. Results demonstrated that H. vitripennis had a constant preference for T. urticae over A. fallacis independently of prey mobility. Hence, H. vitripennis preference for T. urticae may be considered as an active predator choice rather than a passive selection. H. vitripennis searching time was longer in the presence of mobile prey than in the presence of the frozen prey regardless of the species. However, prey handling time was not affected by prey mobility. T. urticae did not show any effective defensive mechanisms to avoid the predator attacks while A. fallacis escaped 33.3% of the attacks by fleeing. Defensive mechanisms could reduce attack efficiency of H. vitripennis and increase its foraging costs. Evaluation of prey value showed that T. urticae provided higher weight gain and longer developmental time to H. vitripennis. H. vitripennis preference for T. urticae could be the result of nutritional suitability of this intraguild prey.

The effect of indoxacarb and five other insecticides on Phytoseiulus persimilis (Acari: Phytoseiidae), Amblyseius fallacis (Acari: Phytoseiidae) and nymphs of Orius insidiosus (Hemiptera: Anthocoridae)

A laboratory study assessed the contact toxicity of indoxacarb, abamectin, endosulfan, insecticidal soap, S-kinoprene and dimethoate to Amblyseius fallacis (Garman), Phytoseiulus persimilis Athias-Henriot and nymphs of Orius insidiosus (Say). Amblyseius fallacis is a predacious phytoseiid mite and an integral part of integrated pest management (IPM) programmes in North American apple orchards. The other two beneficials are widely used in greenhouses to manage various arthropod pests infesting vegetable and ornamental crops. Indoxacarb is a slow-acting insecticide, so toxicity data were recorded 7 days post-treatment when the data had stabilised. It showed no toxicity to O. insidiosus nymphs or to A. fallacis or P. persimilis adults. The LC50 values for O. insidiosus nymphs and P. persimilis could not be estimated with their associated confidence limits, because the g values were greater than 0.5 and under such circumstances the lethal concentration would lie outside the limits. The LC50 for A. fallacis was 7.6x the label rate. The fecundity of P. persimilis was reduced by 26.7%. The eclosion of treated eggs from both species of beneficial mites was not affected adversely. Among the other pest control products, S-kinoprene and endosulfan affected adversely at least one species of the predators, whereas dimethoate, abamectin and insecticidal soap were very toxic to all three beneficials. Indoxacarb should be evaluated as a pest control product in IPM programmes.

Does altering patch number and connectivity change the predatory functional response type? Experiments and simulations in an acarine predator–prey system

In multipatch landscapes, understanding the role of patch number and connectivity is key for the conservation of species under processes such as predation. The functional response is the most basic form of the predator–prey interaction. Two common response types exist: a decelerating curvilinear increase in prey consumption with prey density to a plateau (type II) and a sigmoidal-shaped curve (type III). Type II responses have been observed for a variety of predators, though only type III responses allow long-term persistence and are demographically stabilizing. We tested the hypothesis that the functional response type can change from a type II to a type III with increasing patch number and (or) decreasing connectivity. The predatory mite Amblyseius fallacis (Garman, 1948) has previously been shown to have a type II response when feeding on Panonychus ulmi (Koch, 1839). We examined this predator–prey interaction using experiments that varied in patch number, and simulations that varied in both patch number and connectivity. In no experimental or simulation trial did altering patch number or connectivity change the predator's functional response from type II to type III, even with an 80-fold decrease in patch connectivity. How do predators with this demographically destabilizing functional response persist? Hypotheses regarding metapopulations and alternative prey are discussed.

Effects of Dispersal, Predators (Acari: Phytoseiidae), Weather, and Ground Cover Treatments on Populations of <I>Tetranychus urticae</I> (Acari: Tetranychidae) in Apple Orchards

In a 2-yr study of causes of mite outbreaks in apple (Malus spp.) orchards in Nova Scotia, we monitored immigration of Tetranychus urticae Koch from orchard ground cover into trees populated by the generalist phytoseiid predator Typhlodromus pyri Scheuten. In both years, T. urticae-days in the tree canopy increased with number of T. urticae caught in sticky bands on tree trunks. In 2000, T. urticae-days were negatively correlated with T. pyri-days. Lack of correlation in 2001 was attributed to higher rates of immigration, which would mask the effects of predation. Weather also affected mite dynamics. Rainfall in July and August was less in 2001 than in 2000. Heat units were sufficient for six generations of T. urticae in 2001 but only for five in 2000. Consequently, T. urticae-days in the tree canopy and immigration rates were significantly greater in 2001 than in 2000, despite three-fold greater use of miticides. We also tested the effects of herbicides on T. urticae immigration. Application of selective herbicides in laneways reduced coverage of reproductive hosts of T. urticae, but these changes did not reduce immigration. In 2001, application of a miticidal herbicide, glufosinate, in tree rows reduced captures of T. urticae on sticky bands in high immigration orchards but not in low immigration orchards. We conclude that generalist predators and modified herbicide use are insufficient remedies and that effective biological control of T. urticae in the ground cover by a specialist phytoseiid such as Amblyseius fallacis Garman is essential to prevent outbreaks.

Impact of intraguild predation and lambda‐cyhalothrin on predation efficacy of three acarophagous predators

This laboratory study reports the interaction of three predators found in commercial apple orchards in Quebec, Hyaliodes vitripennis (Say) (Hemiptera: Miridae), Harmonia axyridis Pallas (Coleoptera: Coccinellidae) and Amblyseius fallacis (Garman) (Acarina: Phytoseiidae). First, intraguild predation between H vitripennis and the two other predators was characterized in the absence and presence of their extraguild prey, Tetranychus urticae Koch. The results showed an asymmetrical interaction in favour of the larger predator and the levels of intraguild predation were weak for the two predatory combinations. Presence of the phytophagous mite reduced the intensity of intraguild predation in the predatory combination of H axyridis and H vitripennis. Second, the effects of intraguild predation and the application of lambda-cyhalothrin on predation efficacy of the predators were evaluated. The application of the insecticide reduced prey consumption of H vitripennis and H axyridis but did not affect that of A fallacis. Combination of predators and an insecticide application resulted in two different situations depending on the species involved: a reduced predation efficacy for the combination of H vitripennis and H axyridis due to a knockdown effect caused by the insecticide, and no effect on T urticae consumption for H vitripennis and A fallacis. It is suggested that an integrated pest management program based on H vitripennis, A fallacis and lambda-cyhalothrin may be evaluated to repress phytophagous mites in Quebec orchards.

Toxicity of indoxacarb to two species of predacious mites and a predacious mirid.

Indoxacarb is a novel oxadiazine pro-insecticide that has no toxic effects on the adults, fecundity and eclosion of Amblyseius fallacis (Garman), a predacious phytoseiid, or Agistemus fleschneri Summers, a predacious stigmaeid. It is toxic to Hyaliodes vitripennis (Say), a predacious mirid that has been reported from several Quebec orchards where IPM programs are used. The LC50 for this mirid is about one-half of the recommended dose (0.054 g AI litre(-1)) of indoxacarb for apple orchards. Following an application, the intoxicated mirids remained motionless as their prolegs and posterior had paralyzed. Twenty-four hours later, they appeared smaller, shrunken and severely desiccated.

Impact of Lambda-cyhalothrin on Intraguild Predation Among Three Mite Predators

The impact of a sublethal dose of lambda-cyhalothrin on intraguild predation between three mite predators, Hyaliodes vitripennis (Say), Harmonia axyridis Pallas, and Amblyseius fallacis (Garman) was evaluated in laboratory. The symmetry and level of intraguild predation in selected predator combinations were recorded in the absence and presence of lambda-cyhalothrin. The mobility of the different predatory stages was also recorded in the absence and presence of insecticide. The results showed that lambda-cyhalothrin did not significantly modify intraguild predation but it affected the mobility. A knockdown effect was observed in H. axyridis larvae and in H. vitripennis nymphs, whereas A. fallacis showed an increased mobility. Exposure to a sublethal dose of lambda-cyhalothrin modified predator behavior and must be considered in the implementation of a mite control program in apple orchards.

Functional and numerical responses do not always indicate the most effective predator for biological control: an analysis of two predators in a two‐prey system

Summary Functional and numerical responses are key components in the selection of predators for biological control. We examined the relevance of these responses for predicting the effectiveness of generalist predators, taking into account effects of alternative prey and multiple predators. Our system involved two acarine predators of two prey species on apple. Responses were measured on leaf discs in the laboratory, and predictions assessed on small potted apple trees. In particular, we tested three hypotheses. Hypothesis I: the species with the higher predatory responses will be more effective in limiting prey populations. Neither predator had a consistently higher functional response, which depended on prey stage and species. Amblyseius fallacis had a (approximately two times) higher ovipositional response than Typhlodromus pyri. We therefore hypothesized that A. fallacis would be more effective in controlling prey. No evidence was found to support this hypothesis. Hypothesis II: alternative prey reduce the functional response of predators to target prey. Alternative prey did or did not reduce the functional response to target prey, depending on the predator, stage and species of alternative prey. The only consistent trend for both predators was that the predation of Panonychus ulmi deutonymphs was reduced when Tetranychus urticae was present. Hypothesis III: the predator species with the highest mean ovipositional response will out‐compete the other predator species. The number of predators observed in the mixed predator treatments depended on the prey composition. Although A. fallacis had a higher ovipositional response, it was never more abundant. Intraguild predation probably played a role in determining predator abundance, although prey composition altered intraguild effects. These results highlight the complex nature of predator and prey interactions. Because of these interactions, functional and numerical assays on single predator–single prey systems in simplified laboratory environments do not allow predictions of the growth of mixed populations in realistic habitats, or of the effectiveness of predators as biological control agents in the field.

Evaluation of Two Commercial Strains of Phytoseiuluspersimilis Athias-Henriot (Acarina: Phytoseiidae) and Laboratory-Selected, Pyrethroid-Resistant and Susceptible Strains of Amblyseius fallacis (Garman) (Acarina: Phytoseiidae) for Pesticide Resistance on Greenhouse Cucumber

To evaluate the pesticide resistance of two commercial strains of Phytoseiulus persimilis Athias-Henriot (Koppert, strain A; Applied Bio-Nomics, strain B) and two strains of Amblyseius fallacis (Garman) (resistant and susceptible), residual toxicity trials were conducted on greenhouse cucumber crops that were sprayed with two pesticides (pyridaben and dicofol), respectively. Strain A had significantly higher mortalities than strain B when exposed to foliage residues of pyridaben and dicofol. Strain B showed 3–18% higher survivorship than strain A when exposed to 7- to 14-day foliage residues of pyridaben at 213 and 426 ppm. When exposed to 1- and 8-day foliage residues of dicofol at 152 and 303 ppm, strain A exhibited 8–10% higher mortalities as compared to strain B. Residual toxicity of both pesticides to P. persimilis decreased significantly at the lower concentrations and over time under greenhouse conditions. Mortalities of both strains of P. persimilis were reduced by 50% when exposed to the 1-week residues of both pesticides at the lowest concentrations. With the treatment of dicofol (303 ppm), mortalities for the two strains of P. persimilis decreased from 53.54–42.68% at 1-day residues to 28.18–21.21% at 8-day residues. At 500 ppm of dicofol, mortalities decreased from 60.09–60.90% at 1-day residue to 35.75–34.14% at 22-day residues. However, with dicofol (1000 ppm), mortalities were as high as 61.73% at 22-day residue. The resistant strain of A. fallacies showed significantly lower mortality, as compared to the susceptible strain, when exposed to 1- and 7-day foliage residue of pyridaben at 213 and 426 ppm concentrations. Mortality of A. fallacis to pyridaben was lower than that of P. persimilis. This suggests that A. fallacis may be more compatible with the application of this pesticide to greenhouse crops than that of P. persimilis. In addition, strain B of P. persimilis may be more advantageous after the application of these pesticides in a greenhouse IPM program than strain A.

Migration of specialist insect predators to exploit patchily distributed spider mites

AbstractIt is believed that specialist predators of spider mites often migrate by flight or aerial transport to exploit patchily distributed prey. The migration is an important factor in determining the seasonal occurrence of the predators in a field. Several species of specialist insect predators, such as Oligota kashmirica benefica (Coleoptera: Staphylinidae) and Scolothrips takahashii (Thysanoptera: Thripidae), migrate between orchard trees and plants near the trees (e.g., groundcover, weeds, or windbreaks) to exploit abundant spider mites. This migration is at least partly triggered by prey scarcity in the original local habitats. Although these predators are tiny insects, they have flight abilities. For example, adult O. kashmirica benefica (body length, ∼1 mm) could move at least 5–16 m in one flight. Presumably, migration of the insect predators between prey‐infested plants occurs mainly by flights. Predatory mites, such as Amblyseius fallacis and Amblyseius womersleyi (Acari: Phytoseiidae), migrated to spider mite‐infested plants outside an orchard by aerial transport when they suffered from prey scarcity in the orchard. S. takahashii can use plant volatiles from lima bean plants induced by the spider mite Tetranychus urticae as cues for prey location during migration in Satsuma mandarin groves. However, it remains unknown how far from the trap boxes S. takahashii could respond to herbivore‐induced plant volatiles in the groves.

Release, establishment, and movement of the predator Typhlodromus pyri (Acari: Phytoseiidae) on apple

AbstractIn Ontario apple [Malus × domestica Mill. (Rosaceae)] orchards, the application of certain pesticides kills phytoseiid predatory mites and causes outbreaks of phytophagous mites. We released a strain of the predatory mite Typhlodromus pyri Scheuten (Acari: Phytoseiidae), obtained from Nova Scotia and with organophosphate- and pyrethroid-resistant traits, into adjacent ’McIntosh’ and ’Red Delicious’ apple orchards and followed its progress over four seasons. The T. pyri strain established in the orchards, became the dominant predator, and was associated with low densities of the phytophagous mites Panonychus ulmi Koch and Tetranychus urticae Koch (Acari: Tetranychidae) and Aculus schlechtendali (Nalepa) (Acari: Eriophyidae). It moved slowly through the orchards and took 4 years to reach the 28th tree (84 m) from the release point in both orchards. The predominant wind direction did not appear to influence T. pyri movement. It was present in high numbers on release trees, or trees near these release trees, each summer after release, unlike other predatory species including Typhlodromus caudiglans (Schuster) (Acari: Phytoseiidae), Amblyseius fallacis (Garman) (Acari: Phytoseiidae), and Zetzellia mali (Ewing) (Acari: Stigmaeidae). This species appears particularly useful for biological control of phytophagous mites in Ontario and is worthy of further testing for conservation and augmentative release.

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 (13) and 25.5 (33) 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. © 2001 Academic Press

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.

Seasonal Abundance of Spider Mites and Their Predators on Red Raspberry in Quebec, Canada

Seasonal abundance of spider mites and their predators on red raspberry was studied in 1993 and 1994 at 2 agricultural locations near Quebec City, Canada. Three raspberry systems, wild raspberry, pesticide-free cultivated raspberry, and commercial raspberry treated with a variety of pesticides, were sampled at frequent intervals. Tetranychus mcdanieli McGregor accounted for 87.5, 80.6, and 95.0% of the identified spider mites collected in the commercial, untreated, and wild systems, respectively. Tetranychus urticae Koch was observed in low numbers in both years. Spider mites were more abundant in the commercial and untreated systems than in the wild system, and there was generally no difference between commercial and untreated systems in 1993, whereas in 1994 there was more spider mites in the commercial system than in the untreated one. Predatory mites were present in all systems. Amblyseius fallacis (Garman) was the most abundant predator in the commercial system, whereas a complex of other predatory mites species dominated the wild system. The coccinellid Stethorus punctillum Weise was abundant in the untreated system and rare in the commercial and the wild systems. Variations of predator abundance among treatments did not correlate with variations of spider mite abundance, and could be explained by seasonal predator-prey asynchrony.

Pyrethroid Encapsulation for Conservation of Acarine Predators and Reduced Spider Mite (Acari: Tetranychidae) Outbreaks in Apple Orchards

We examined the effects of a microencapsulated formulation of the pyrethroid cypermethrin on the predator Amblyseius fallacis (Garman) and the biological control of tetranychid mites. In functional response analysis, susceptible field-collected and mass-reared pyrethroid resistant strains of A. fallacis consumed similar numbers of Tetranychus urticae Koch eggs on unsprayed leaf-disks (14–16 eggs per day). Fewer prey were consumed on microencapsulated cypermethrin sprayed disks, but consumption was similar between strains (10.3–11.3 eggs per day). The functional response on cypermethrin EC (emulsifiable concentrate)-sprayed disks was associated with resistance. Susceptible A. fallacis mites (cypermethrin LC50 = 7.2 ppm) consumed a maximum of 1.0 eggs per day; field-collected predators (LC50 = 13.3 ppm) consumed a maximum of 4.0 eggs per day, and mass-reared A. fallacis (LC50 = 28.2 ppm) consumed a maximum of 4.33 eggs per day. Encapsulated cypermethrin was much less toxic to predators, and was similar in toxicity between strains (LC50 range = 87.0–100.4 ppm). In an experimental orchard, a commercial formulation of cypermethrin EC almost eliminated A. fallacis. On trees sprayed with the microencapsulated formulation, mean A. fallacis densities were reduced from 0.81 ± 0.26 per leaf to 0.26 ± 0.12 per leaf. On microencapsulated sprayed trees this predator density, together with the stigmaeid predator Zetzellia mali (Ewing), appeared to regulate Panonychus ulmi Koch to a peak density of 21.7 ± 11.7 per leaf, compared to 87.2 ± 15.6 per leaf on cypermethrin EC treated trees, and 10.4 ± 4.6 per leaf on unsprayed trees. The microencapsulated cypermethrin formulation conserved natural biological control in pyrethroid sprayed orchards better than the cypermethrin EC formulation.

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.

Microsatellite sequences are under-represented in two mite genomes.

Microsatellites are known to be a common feature of eukaryote genomes. Here we investigate the presence of microsatellite sequences in the genome of two mite species, Tetranychus urticae and Amblyseius fallacis, based on screening of both mite genomic libraries and Southern blots of these mites that we compare to two vertebrates. No signal with GT15 or a faint smear with CT10 were obtained in Southern analysis for the two mites, whereas both probes strongly bound with vertebrate DNA. Genomic libraries constructed in plasmid and lambda vectors were probed and only two CT microsatellites were isolated for T. urticae. Among eight trinucleotides probes tested, the strongest hybridization signal was detected for T. urticae with CAT and TGA probes. These two classes of repeats were also the most represented in genomic library screenings. However, only sequences with short numbers of units could be detected (<CAT4 or TGA9). Congruency of Southern analysis and screening of partial genomic libraries indicates an under-representation of microsatellite sequences in the two mite genomes. The potential of the scarce repetitive DNA isolated from mites to serve as population genetics markers is discussed on the basis of preliminary assessment of their polymorphism.