Mite Outbreaks Research Articles

Use of vapor pressure deficit to predict humidity and temperature effects on the mortality of mold mites, Tyrophagus putrescentiae

The mold mite, Tyrophagus putrescentiae (Shrank), frequently infests a variety of stored food products in ideal, but rather limited conditions. Major factors limiting survival of this mite are the temperature and humidity imposed on T. putrescentiae as it develops within and disperses among sites. However, since relative humidity is dependent upon air temperature, determining survivability in a habitat can be difficult in the presence of structural temperature variations. Vapor pressure deficit (VPD) provides a method of combining both relative humidity and temperature into a single number that can be used to determine conditions detrimental to mite survival. This study utilized a bioassay format to measure mortality of T. putrescentiae when exposed to a range of seven temperatures (5-35 degrees C), 10 relative humidities (0-100% RH), 17 exposure times (0.5-240 h), with and without food. With these combinations of temperature and RH, mortality curves (mortality versus time) that displayed a sigmoidal relationship were used to calculate LT(50) and LT(90) estimates. These mortality estimates were then regressed on their associated VPD and the resulting regressions (LT(50) and LT(90)) were significant at P < 0.0001, and provided acceptable R(2) values >or=0.83, regardless of whether food was present or not. At room temperature, threshold of VPD for T. putrescentiae development was below 8.2 mbar, this estimate being initially calculated from published values. For mites exposed to drier conditions, above 8.2 mbar, survival time was curtailed dependant on the magnitude of VPD. As the VPD exceeded 12 mbar, mites experienced substantial (>90%) mortality within 58 (33, 101) h; and further increasing VPD decreased the time of exposure to achieve mortality. This study demonstrates that making subtle changes in humidity or temperature to reach a target VPD may provide control of mite outbreaks and reduce areas inhabitable for T. putrescentiae.

Professional and Consumer Insecticides for Management of Adult Japanese Beetle on Hybrid Tea Rose

In many states, Japanese beetle, Popillia japonica Newman (Coleoptera: Scarabeidae), is no longer quarantined, and management is left to professional applicators and consumers. Adult management in hybrid tea rose, Rosa L., was compared among biorational insecticides, novel imidacloprid applications (tablet, gel, and root dip), and conventional insecticides. Efficacy of biorational insecticides used by consumers varied widely and may not offer predictable management: mortality was 3.0% with Garlic Barrier, 5.0% with Monterey Neem Oil, 15.1% with Pygenic (1.4% pyrethrins), and 27.3% with Orange Guard (d–limonene). Only JB Killer (0.02% pyrethrins plus 0.2% piperonyl butoxide) had mortality of 90.9%, probably due to piperonyl butoxide. Professional biorationals did not show significant mortality: 7.7% with Azatin XL (azadirachtin) and 3.7% Conserve (spinosad). In contrast, conventional insecticides demonstrated significant mortality; 88.4% with Decathlon 20 WP (cyfluthrin) and 83.3% with Discus SC (imidacloprid plus cyfluthrin). New imidacloprid applications (tablet, gel, and root dip) worked as well as standard drench and granular methods, but they showed 9.1–42.7% mortality. However, beetles were incapacitated as demonstrated by inability to walk (82–106-s flip time) compared with controls (30-s flip time). No phytotoxicity was observed in any treatments. However, some imidacloprid treatments produced growth enhancement: higher leaf chlorophyll (1X, 3X granular, and one tablet), and larger leaf area and higher nitrogen (3X granular, drench). The highest (active ingredient) imidacloprid was in 3X granular treatment, which in an unplanned infestation, showed highest numbers of twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). Effects of imidacloprid on leaf quality and mite outbreaks deserves research.

Professional and Consumer Insecticides for Management of Adult Japanese Beetle on Hybrid Tea Rose

In many states, Japanese beetle, Popilliajaponica Newman (Coleoptera: Scarabeidae), is no longer quarantined, and management is left to professional applicators and consumers. Adult management in hybrid tea rose, Rosa L., was compared among biorational insecticides, novel imidacloprid applications (tablet, gel, and root dip), and conventional insecticides. Efficacy of biorational insecticides used by consumers varied widely and may not offer predictable management: mortality was 3.0% with Garlic Barrier, 5.0% with Monterey Neem Oil, 15.1% with Pygenic (1.4% pyrethrins), and 27.3% with Orange Guard (D-limonene). Only JB Killer (0.02% pyrethrins plus 0.2% piperonyl butoxide) had mortality of 90.9%, probably due to piperonyl butoxide. Professional biorationals did not show significant mortality: 7.7% with Azatin XL (azadirachtin) and 3.7% Conserve (spinosad). In contrast, conventional insecticides demonstrated significant mortality; 88.4% with Decathlon 20 WP (cyfluthrin) and 83.3% with Discus SC (imidacloprid plus cyfluthrin). New imidacloprid applications (tablet, gel, and root dip) worked as well as standard drench and granular methods, but they showed 9.1-42.7% mortality. However, beetles were incapacitated as demonstrated by inability to walk (82-106-s flip time) compared with controls (30-s flip time). No phytotoxicity was observed in any treatments. However, some imidacloprid treatments produced growth enhancement: higher leaf chlorophyll (1X, 3X granular, and one tablet), and larger leaf area and higher nitrogen (3X granular, drench). The highest (active ingredient) imidacloprid was in 3X granular treatment, which in an unplanned infestation, showed highest numbers of twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). Effects of imidacloprid on leaf quality and mite outbreaks deserves research.

PEST MANAGEMENT IN QUEENSLAND STRAWBERRIES: REALITY BITES, AND GROWERS´ PERSPECTIVES CHANGE!

Prior to the 1980s, arthropod pest control in Queensland strawberries was based entirely on calendar sprays of insecticides (mainly endosulfan, triclorfon, dimethoate and carbaryl) and a miticide (dicofol). These chemicals were applied frequently and spider mite outbreaks occurred every season. The concept of integrated pest management (IPM) had not been introduced to growers, and the suggestion that an alternative to the standard chemical pest control recipe might be available, was ignored. Circumstances changed when the predatory mite, Phytoseiulus persimilis Athios-Henriot, became available commercially in Australia, providing the opportunity to manage spider mites, the major pests of strawberries, with an effective biological agent. Trials conducted on commercial farms in the early 1980s indicated that a revolution in strawberry pest management was at hand, but the industry generally remained sceptical and afraid to adopt the new strategy. Lessons are learnt from disasters and the consequent monetary loss that ensues, and in 1993, such an event relating to ineffective spider mite control, spawned the revolution we had to have. Farm-oriented research and evolving grower perspectives have resulted in the acceptance of biological control of spider mites using Phytoseiulus persimilis and the 'pest in first' technique, and it now forms the basis of an IPM system that is used on more than 80% of the Queensland strawberry crop.

Effects of Dispersal, Predators (Acari: Phytoseiidae), Weather, and Ground Cover Treatments on Populations of &lt;I&gt;Tetranychus urticae&lt;/I&gt; (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.

Role of neonicotinyl insecticides in Washington apple integrated pest management. Part II. Nontarget effects on integrated mite control

The effect of neonicotinyl insecticides on integrated mite control in Washington apple was examined from 0 In a series of 20 field trials (54 treatments) designed primarily to look at efficacy against the codling moth, Cydia pomonella, nearly half of the treatments using four or more applications of acetamiprid had peak mite densities exceeding the economic threshold of 5 mites per leaf. Overall, acetamiprid treatments had 4.6-fold higher mite densities than the standard organophosphate insecticide treatment. Of the treatments with high mite populations, Panonychus ulmi, the European red mite, and Tetranychus urticae, the twospotted spider mite, were the dominant species in roughly equal numbers of cases. Only 11.1% of the thiacloprid treatments exceeded 5 mites per leaf; these experimental treatments included eight applications, whereas the current label restricts the number of applications at the rate for C. pomonella to two applications. One out of six clothianidin treatments caused a significantly higher mite density than the standard treatment; however, this material appeared to suppress predatory mites. Neonicotinyl insecticides did not eliminate predatory mites, but they inhibited their ability to respond normally to increasing prey populations. In field trials designed specifically to examine mite population densities where neonicotinyl insecticides were used, significantly higher levels of tetranychid mites occurred in one or more acetamiprid treatments (one, two or four applications) in five out of six trials. In the sixth trial (in a commercial orchard), only two acetamiprid applications were made, and mite populations were low in all treatments. While elevated mite densities were more likely to occur with four applications, in one case it occurred following a single application. The predominant tetranychid mite species (either P. ulmi or T. urticae) varied from trial to trial; however, there was no apparent bias regarding stimulation of the two species. Horticultural mineral oil was used with acetamiprid in some trials in an attempt to mitigate mite outbreaks. However, the addition of oil did not counteract the tendency of acetamiprid to increase tetranychid mite populations, and in one trial, had a negative effect on predatory mite densities. Seasonal tetranychid mite density was positively related to the total grams AI (or number of applications) of acetamiprid, thus reducing the number of applications per season should lower the probability of mite outbreaks.AI active ingredient CMD cumulative mite days

Role of neonicotinyl insecticides in Washington apple integrated pest management. Part II. Nontarget effects on integrated mite control

The effect of neonicotinyl insecticides on integrated mite control in Washington apple was examined from 0 In a series of 20 field trials (54 treatments) designed primarily to look at efficacy against the codling moth, Cydia pomonella, nearly half of the treatments using four or more applications of acetamiprid had peak mite densities exceeding the economic threshold of 5 mites per leaf. Overall, acetamiprid treatments had 4.6-fold higher mite densities than the standard organophosphate insecticide treatment. Of the treatments with high mite populations, Panonychus ulmi, the European red mite, and Tetranychus urticae, the twospotted spider mite, were the dominant species in roughly equal numbers of cases. Only 11.1% of the thiacloprid treatments exceeded 5 mites per leaf; these experimental treatments included eight applications, whereas the current label restricts the number of applications at the rate for C. pomonella to two applications. One out of six clothianidin treatments caused a significantly higher mite density than the standard treatment; however, this material appeared to suppress predatory mites. Neonicotinyl insecticides did not eliminate predatory mites, but they inhibited their ability to respond normally to increasing prey populations. In field trials designed specifically to examine mite population densities where neonicotinyl insecticides were used, significantly higher levels of tetranychid mites occurred in one or more acetamiprid treatments (one, two or four applications) in five out of six trials. In the sixth trial (in a commercial orchard), only two acetamiprid applications were made, and mite populations were low in all treatments. While elevated mite densities were more likely to occur with four applications, in one case it occurred following a single application. The predominant tetranychid mite species (either P. ulmi or T. urticae) varied from trial to trial; however, there was no apparent bias regarding stimulation of the two species. Horticultural mineral oil was used with acetamiprid in some trials in an attempt to mitigate mite outbreaks. However, the addition of oil did not counteract the tendency of acetamiprid to increase tetranychid mite populations, and in one trial, had a negative effect on predatory mite densities. Seasonal tetranychid mite density was positively related to the total grams AI (or number of applications) of acetamiprid, thus reducing the number of applications per season should lower the probability of mite outbreaks.

Effects of NaCl-stressed citrus plants on life-history parameters of Tetranychus urticae (Acari: Tetranychidae).

Tetranychus urticae is an important pest of citrus, especially lemon and mandarin, under Mediterranean climate. Factors leading to this problem are poorly understood, but saline stress is suspected to contribute to spider mite outbreaks. In this study, the effect of NaCl concentration in nutritive solutions used to water potted young mandarin trees on population growth of T. urticae reared on leaf discs obtained from these plants was investigated. Although the differences observed between treated (5, 10, 30 and 60 mM NaCl) and control groups were in most cases not significant, when all biological parameters calculated were combined to obtain Ro, T and r(m), remarkable differences appeared, and a concentration-dependent effect was detected. Although high salt concentrations negatively affected T. urticae, at the lowest concentration tested the r(m) value was significantly higher than at the water control and this may contribute to the observed field explosions of T. urticae.

Diapause and implications for control of Penthaleus species and Halotydeus destructor (Acari: Penthaleidae) in southeastern Australia.

Blue oat mites, Penthaleus spp., and redlegged earth mites, Halotydeus destructor (Tucker) are major winter pests of a variety of crops and pastures. In southern Australia earth mites exhibit a facultative egg diapause to survive unfavorable summer conditions. The initiation of diapause egg production in earth mites was investigated using field and shade-house experiments. Species differed in their timing of diapause. H. destructor mainly produced diapausing eggs towards the end of the active mite season in spring, although small numbers were also produced in winter. In contrast, Penthaleus major (Dugés) produced diapause eggs almost immediately after emergence in autumn and continued producing these eggs throughout the season. Penthaleus falcatus (Qin and Halliday) also produced diapause eggs in early winter, although the first appearance of these eggs was slightly later in the season than for P. major. The diapause response of an undescribed species was also somewhat later than in P. major and P. falcatus, but earlier than in H. destructor. Electrophoresis of P. major samples indicated that clones of this parthenogenic species may differ in their timing of diapause egg production, providing another potential selective factor contributing to the maintenance of clonal diversity within this group. The results highlight the importance of determining species composition when devising control strategies for earth mite outbreaks.

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.

Association of powdery mildew and spider mite populations in apple and cherry orchards

Evidence is presented that shows densities, incidence, and reproduction of spider mites were greater on apple and cherry leaves infected with powdery mildew than on healthy leaves collected from orchards. In five apple and sour cherry orchards in 1996–1998, leaves infected with powdery mildew were more frequently infested with spider mites and mite densities were greater than on leaves without mildew. It appeared that spider mites colonized leaves after the mildew was present, but the mechanisms involved in this interaction are not known. In addition, laboratory experiments were conducted to evaluate the influence of cherry powdery mildew on reproduction of spider mites. Spider mite reproduction was enhanced by the presence of powdery mildew on detached sour cherry leaves in one laboratory trial, and the trend was similar in two other trials between 2 and 4 days after inoculation with mites. Mite reproduction did not differ between mildew treatments on later observation days (5 or 6 days after inoculation with mites) probably because of senescence and desiccation of the detached leaves. These findings may indicate that effective management of powdery mildew could reduce the need for acaricides and reduce the incidence of outbreaks of spider mites.

Tillage and Chlorpyrifos Treatment Effects on Peanut Arthropods—An Incidence of Severe Burrower Bug Injury

Abstract A 2-yr study was conducted on the effects of tillage and soil insecticide (chlorpyrifos) treatment on peanut arthropod pests. A 3 by 2 split-plot experiment with five replications was subjected to factorial ANOVA. Main plot treatments consisted of three tillage systems: conventional moldboard plow, strip tillage into a killed wheat cover crop, and strip tillage into corn stubble residue. Subplot insecticide treatments were granular chlorpyrifos applied at early pegging (growth stage R2) and untreated. Populations of corn earworn, Helicoverpa zea (Boddie), and velevetbean caterpillar, Anticarsia gemmatalis Hübner, were lower in strip tillage systems. Chlorpyrifos applications caused corn earworm outbreaks in all tillage systems, but these applications were more disruptive in strip tillage. Chlorpyrifos treatment also increased populations of fall armyworm, Spodoptera frugiperda (J.E. Smith), but had no measurable effect on velvetbean caterpillar populations. Pod damage from lesser cornstalk borer, Elasmopalpus lignosellus (Zeller), and wire-worms, Conoderus spp., was lower in strip tillage systems, and chlorpyrifos suppressed pod damage in all systems. Threecornered alfalfa hopper, Spissistilus festinus (Say), damage to peanut was greater in the wheat residue strip tillage system. Chlorpyrifos treatment reduced threecornered alfalfa hopper damage in all systems. Spider mite injury was not affected by tillage, but chlorpyrifos treatments resulted in mite outbreaks in all tillage systems. Burrower bug, Pangaeus bilineatus Say, injury to peanut kernels was greater in the strip tillage systems in 1999; and burrower bug injury was suppressed in the strip tillage systems by chlorpyrifos treatment. There was a significant interaction effect for burrower bug injury between tillage and insecticide treatment. Incidence of tomato spotted wilt virus also was reduced by strip tillage. Use of an effective fungicide program and a 3-yr crop rotation out of peanut production probably obscured any potential tillage effects on fungal diseases (southern stem rot, Rhizoctonia limb rot, and leaf spot). However, chlorpyrifos treatment increased Rhizoctonia limb rot incidence. Weed populations were generally greater in strip tillage systems, but postemergence herbicides effectively eliminated any potential confounding effect on yield and grade. Yield was not affected by tillage in either year, and chlorpyrifos had no effect on yield in 1998. In 1999, however, chlorpyrifos increased yield in both strip tillage systems. Neither tillage nor insecticide treatment affected grade (percentage total mature kernels) in 1998, but in 1999 grade was highest in conventional tillage and grade was improved by chlorpyrifos treatment in strip tillage systems. Crop value losses of $249 and $388/ha were attributed to burrower bug injury in untreated corn and wheat residue strip tillage systems, respectively. This injury may have been an anomaly of drought conditions but, given the potential economic impact, burrower bug merits further study in conservation tillage peanut production.

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.

Acaricidal and stimulatory effects of insecticides on Tetranychus urticae Koch (Acari: Tetranychidae) in cotton

Possible stimulatory or acaricidal effects of thiodicarb, dimethoate and endosulfan on the two‐spotted spider mite, Tetranychus urticae Koch, were tested in a glasshouse. Population development of T. urticae was monitored, with the expectation that any stimulatory or acaricidal effects would be reflected in different population growth relative to untreated plants. Acaricidal activity of the three insecticides was also investigated using a standard bioassay technique. Population growth on thiodicarb‐ or dimethoate‐treated plants was no different to that on untreated plants but was slower on plants treated with endosulfan. Bioassays showed that endosulfan was moderately acaricidal, that T. urticae was highly resistant to dimethoate and that thiodicarb was of very low acaricidal activity. No evidence of stimulatory effects of dimethoate or thiodicarb was found. The data suggest that stimulation is an unlikely explanation for outbreaks of T. urticae in cotton and that endosulfan sprayed for control of Helicoverpa spp. may delay the development of mite outbreaks.

Yield Reduction in ‘Tahiti‘ Lime from Panonychus Citri Feeding Injury Following Different Pesticide Treatment Regimes and Impact on the Associated Predacious Mites

A series of experiments was initiated on ‘Tahiti’ lime trees to assess possible involvement in yield reduction by one or more species of thrips, especially Frankliniella bispinosa (Morgan) and F. kelliae Sakimura (Thysanoptera: Thripidae). Different pesticides were applied to ensure adequate coverage on flowers and to maintain effective thrips control. Outbreaks of spider mites were anticipated because of the pesticides used and frequency of application. Therefore, population dynamics of the citrus red mite, Panonychus citri (McGregor) (Acari: Tetranychidae) and the predacious mites Typhlodromalus peregrinus (Muma) (Acari: Phytoseiidae) and Agistemus floridanus Gonzalez (Acari: Stigmaeidae) were monitored in four pesticide treatment regimes during flowering on ‘Tahiti’ lime, Citrus latifolia Tanaka in south Florida. Yield was significantly reduced in four pesticide treatment regimes by 41, 31, 28 and 17% relative to the untreated control. Elimination of predacious mites by the selected pesticides resulted in higher sustained populations of P. citri on treated trees compared to those untreated. The pesticide regimes resulted in differences in population densities of both citrus red mite and its key predators. Depending upon the treatment regime and application date(s), the duration and magnitude of disruption resulted in significant differences in yield. P. citri densities that averaged 5.2 or more per leaf during January–February, or 4.3 or more per leaf during January–March, or 3.9 or more per leaf during January– April contributed substantially to the feeding injury and resulted in reduced yield. Typhlodromalus peregrinus was the most common predacious mite collected during this study (80.4%) followed by A. floridanus with 15.7%.

Effect of early season insecticide use on predators and outbreaks of spider mites (Acari: Tetranychidae) in cotton

AbstractThe Australian cotton industry relies almost exclusively on synthetic insecticides for control of early season pests. These insecticides often disrupt predatory insect activity in the field. Potential predators of the twospotted spider mite, Tetranychus urticae Koch, in cotton, identified in field and confirmed in laboratory experiments, included a theridiid spider, a phytoseiid mite, a lacewing larva, predatory thrips, several Coccinellidae and several Hemiptera. These predators were mostly generalists, having previously been reported as predators of aphids or caterpillars of Helicoverpa spp. The effect of insecticides on T. urticae and its predators was evaluated in three field experiments. Cotton was artificially infested with T. urticae then sprayed five times at seven to ten day intervals with either dimethoate (140 g ai/ha), thiodicarb (750 g ai/ha and 187.5 g ai/ha), endosulfan (735 g ai/ha and 367.5 g ai/ha), methomyl (169 g ai/ha) or amitraz (400 g ai/ha). Tetranychus urticae populations reached higher densities in dimethoate, thiodicarb and methomyl treated cotton than in untreated cotton. Population densities of T. urticae in cotton treated with low rates of endosulfan or thiodicarb were similar to controls, while those in cotton treated with amitraz were lower. All insecticides caused significant reductions in at least one predator group. Significant negative relationships were found between early season abundance of predators and the mid-season abundance of T. urticae and positive relationships between predators and the lag-period for T. urticae outbreaks to develop. Predation is implicated as a key factor influencing the early season survival of T. urticae. The implications for developing integrated pest management strategies in cotton are discussed.

Influence of Selective Insecticides on Population Dynamics of European Red Mite (Acari: Tetranychidae), Apple Rust Mite (Acari: Eriophyidae), and Their Predator Amblyseius fallacies (Acari: Phytoseiidae) in Apple

The predaceous phytoseiid mite, Amblyseius falllacis (Garman), is important to the biological control of spider mites in deciduous fruit orchards. Insecticides applied for control of insect pests may be toxic to A. fallacis thereby causing spider mite outbreaks. Pyrethroids are highly toxic to A. fallacis and are not recommended for use after petal fall. Applications of pennethrin at pink and petal fall resulted in outbreaks of European red mites, Panonychus ulmi (Koch) because of the elimination of A. fallacis . Permethrin-treated trees had European red mite populations averaging 5 times higher than in untreated trees. Materials which conserved A. fallacis populations maintained European red mite below economic thresholds throughout the season. The apple rust mite, Aculus schlechtendali (Nalepa), served as an alternate food source for A. fallacis, particularly in trees which had low European red mite populations.

Population Dynamics of Amblyseius fallacies (Acari: Phytoseiidae) and European Red Mite (Acari: Tetranychidae) in Apple Trees Treated with Selected Acaricides

Experiments were conducted to evaluate the effects of early-scason ovicides, selective acaricides, horticultural oil, and potassium salts of fatty acids on the population dynamics of the phytoseiid predator Amblyseius fallacis (Garman) and its prey, the European red mite, Panonychus ulmi (Koch). Both ovicides prevented early-season European red mite outbreaks but only clofentezine-treated trees, with the help of A. fallacis, had low densities of European red mites throughout the entire season. However, treatment with clofentezine kcpt mites at subeconomic levels only if insecticide sprays did not disrupt predator mite populations. Two applications of permethrin drastically reduced natural enemies, and allowed European red mite outbreaks to occur. Selective acaricides varied in their effects on A. fallacies and European red mites. Although not significantly different from each other, all selective acaricides resulted in significantly fewer A. fallacis and European red mites than the untreated trees. Repeated applications of horticultural oils and M-Pede were required to reduce the European red mite populations and were no more effective in conserving predator mites than some of the selective acaricides.

Ovipositional Responses of Two Species of Spider Mites (Acari: Tetranychidae) to Sublethal Concentrations of Permethrin and Methyl Parathion on Corn

Reproductive stimulation of pests by sublethal dosages of insecticides fits into the general pharmacological hypothesis of hormoligosis. This phenomenon has been suggested as one of the factors causing insecticide-induced spider mite outbreaks. The ovipositional response of twospotted spider mite, Tetranychus urticae Koch, and Banks grass mite, Oligonychus pratensis (Banks), was examined using leaf discs and whole corn, Zea mays (L.) plants. Spider mites were exposed to various sublethal concentrations (LC05, LC10, LC25, and LC50) of permethrin and methyl parathion on corn. Studies using leaf discs were conducted by exposing the mites either directly to the insecticides or to their residues. The whole plant study dealt with only residual exposure. The cumulative number of eggs laid by Banks grass mites, when exposed to insecticide concentrations at LC05 and LC10 levels, was significantly lower than the untreated control under all treatment conditions. In contrast, twospotted spider mites did not show a reduction in oviposition at LC05 and LC10 levels. At higher concentrations (LC25 and LC50), both insecticides caused a significant reduction in the cumulative number of eggs laid by both species of spider mites. Spider mites directly exposed to insecticides laid significantly fewer eggs than mites that were exposed to the insecticide residues. The results of these studies indicate that hormoligosis is not a contributor to mite outbreaks that occur following applications of permethrin or methyl parathion at the rates tested.

'Thompson Seedless' grapevine vigour and abundance of Pacific spider mite (Tetranychus pacificusMcGregor) (Acari, Tetranychidae)

AbstractSpider mite outbreaks have been frequently related to factors that reduce plant vigour. We conducted a field study to determine the relationship between the abundance of Pacific spider mite,Tetranychus pacificusMcGregor, and abiotic factors related to the vigour of ‘Thompson Seedless’ grapevines,Vitis viniferaL. Our study supports previous observations on the relationship between Pacific mite abundance and vine vigour, and partially explains these differences in terms of the previously proposed hypotheses of differences in leaf N and leaf temperature on vines of different vigour. Pacific mite densities were 5.5‐fold higher on low‐vigour compared with high‐vigour vines. Total leaf N was weakly correlated with vine vigour and Pacific mite abundance. Average daily and afternoon leaf temperatures were higher on low‐vigour vines resulting in 45.3°D greater accumulation on low‐vigour vines compared with high‐vigour vines during the increasing phase of Pacific mite population growth. This difference represented 37.4% of the °D requirements for the development of 1 Pacific mite generation and could be partially responsible for the observed difference in Pacific mite abundance in relation to vine vigour. Other confounding factors are discussed and an additional hypothesis is proposed to further explain the relationship between vine vigour and Pacific mite abundance.