Spider Mite Densities Research Articles

Economic threshold for Tetranychus urticae (Acari: Tetranychidae) in clementine mandarins Citrus clementina

Tetranychus urticae is a key pest of citrus in Spain, especially of clementine mandarin trees. The effects of this mite on fruit production were assessed in 24 clementine trees for three consecutive years. Trees were visited weekly and spider mite and phytoseiid mite populations and leaf flush patterns were estimated. At the end of the season, mandarins were harvested, weighed, and mite damage (scarring on the fruit) characterized. Negative relationships between spider mite density and yield (kg/tree) and fruit damage (% scarred fruit rind) were found. The multivariate regressions highlighted the key role of phytoseiid mites and leaf flush patterns, which were negatively related to fruit damage. The shortest sampling period that satisfactorily predicted fruit damage at harvest, extended from August to mid-October. For IPM purposes, an action threshold of 31.1 mites m⁻² of symptomatic leaf was estimated. Taking into account spider mite dynamics, the economic threshold ranged from 10 to 15 mites m⁻² of symptomatic leaf. When this threshold is exceeded growers would have a 1-week window to apply the control technologies against T. urticae of their choice.

Effects of Aldicarb and Neonicotinoid Seed Treatments on Twospotted Spider Mite on Cotton

Twelve field experiments and one laboratory experiment were conducted to determine the effects of furrow applied aldicarb and seed treatments of thiamethoxam, imidacloprid, Avicta (thiamethoxam + abamectin), Aeris (imidacloprid + thiodicarb), and acephate on twospotted spider mite, Tetranychus urticae Koch, on cotton, Cossypium hirsutum L. For the field experiments, data were pooled across all experiments for analysis. Aeris, thiamethoxam, and imidacloprid treatments resulted in twospotted spider mite densities greater than those in the untreated check, aldicarb, and acephate treatments. However, cotton treated with Avicta (thiamethoxam + abamectin) had 34% fewer mites than other neonicotinoid seed treatments when infestations occurred near cotyledon stage. Untreated check and aldicarb treatments had the lowest mite densities. Only aldicarb reduced mite densities below that in the untreated check. In a laboratory trial, the fecundity of twospotted spider mite was measured. While neonicotinoid seed treatments increased mite densities in the field, they did not increase fecundity in the laboratory experiment. Foliar applied thiamethoxam slightly elevated average fecundity in the laboratory experiment. Increased use of neonicotinoid seed treatments instead of furrow applied aldicarb is likely at least partly responsible for recent increased twospotted spider mite infestations in seedling cotton across the mid-south.

Impact of Twospotted Spider Mite (Acari: Tetranychidae) Duration of Infestation on Cotton Seedlings

The yield response of cotton, Gossypium hirsutum L., to twospotted spider mite, Tetranychus urticae Koch, duration of infestation during the seedling stage was measured at Starkville and Stoneville, MS, during 2010 and 2011. The treatments included a noninfested control, infestations lasting for 7, 14, 21, or 28 d, and a season long infested control. Twospotted spider mites from a greenhouse colony were inoculated on all of the infested cotton plots during the three-leaf stage. Applications of miticides were made to terminate infestations at the desired timings for each treatment. Twospotted spider mite densities and injury ratings were determined for each treatment at the end of the infestation period and yield was measured at the end of the season. Twospotted spider mite densities and injury rating significantly increased as duration of infestation increased. Significant differences in yield were observed between treatments. These data suggest infestations initiated at the three-leaf cotton growth stage with population densities at a minimum of 0.39 mites/cm2 existing > 14 d could result in reduction of cotton yields.

福岡県における促成栽培イチゴの育苗期に発生するハダニ類の土着天敵

To validate the possibility of integrated pest management (IPM) utilizing natural enemies against spider mites (Acari: Tetranychidae) during the seedling-rearing period of strawberry, we investigated the dominant species of their natural enemies both on kidney bean traps infested with Tetranychus urticae Koch and on strawberry seedlings in four seedling-rearing fields per year in 2010 and 2011. While the predatory thrips, Scolothrips takahashii Priesner and phytoseiid mites were predominantly captured on the traps, predatory thrips was the only natural enemy observed on strawberry seedlings in all fields. Even when the densities of spider mites on strawberry seedlings were relatively low, predatory thrips were frequently observed. These results suggest that S. takahashii could be an effective agent to control spider mites in IPM for a seedling-rearing period of strawberry.

<p><strong>Assessment of an integrated pest mite and disease management program on Florida citrus utilizing 224°C or 235°C horticultural mineral oils (HMO)*</strong></p>

The objective of this work was to compare HMO-only foliar spray programs with grower´s usual practices for the control of the fungal pathogen greasy spot, Mycosphaerella citri Whiteside, and for suppression of arthropod pests, primarily the citrus rust mite, Phyllocoptruta oleivora (Ashmead), the pink citrus rust mite, Aculops pelekassi (Keifer), and the spider mites, Eutetranychus banksi (McGregor) and Panonychus citri (McGregor). Four cooperators with 2.38 to 5.22 hectare blocks of either ‘Hamlin’ or ‘Valencia’ oranges were switched to 224°C or 235°C horticultural mineral oil (HMO)-only foliar spray programs applied at 46.8 liters/hectare for four years. HMO applications varied from one to three applications in the test blocks per location at each year. Cooperating grower spray programs included various fungicides, acaricides, insecticides, and HMOs. First year transition from the standard fungicide-insecticide-acaricide programs resulted in active citrus rust mite development, and multiple HMO treatments were required in three of the four sites for their control. Subsequent rust mite populations in years two, three, and four did not develop in three of four sites using the HMO-only foliar spray programs. Spider mite densities in the four HMO blocks never reached levels of economic injury during any year of the study. One of the cooperators was dropped after the third (2002) season, as the test block in his property was sprayed sometime early in 2003 with a pesticide that eliminated beneficial mite populations. No secondary arthropod or disease problems developed in any of the remaining three HMO-only blocks through March 2004. The percentage of greasy spot infected leaves was significantly greater in each HMO block most years compared to the grower spray programs. However, there were no differences in leaf retention, tree canopy vigor, or yields between the HMO-only foliar spray program and the control pesticide programs. The severity of greasy spot on leaves averaged in the lowest rating category (e.g., 0 to 5%) in all treatment blocks in all years and ranged from 0.1 to 2.0% in the HMO blocks versus 0.2 to 1.5% in the control blocks. Greasy spot was effectively controlled with HMO-only treatments through the four years of this study in all orchard sites. Comparative effects between the HMO and grower spray programs on beneficial mites in the families Phytoseiidae, Stigmaeidae and Tydeidae are reported through 2002. All three mite families failed to re-establish in the four HMO-only foliar spray program blocks by the end of the third year.

<p><strong>Seasonal population development of spider mites (Acari: Tetranychidae) and their predators in sprayed and unsprayed apple orchards in Van, Turkey*</strong></p>

The aim of this study was to determine the seasonal population dynamics of spider mites [Panonychus ulmi (Koch), Amphitetranychus viennensis (Zacher), Bryobia rubrioculus (Scheuten)] and their natural enemies [Kampimodromus aberrans (Oudemans),Acari, Phytoseiidae; Zetzellia mali (Ewing),Acari, Stigmaeidae; and Stethorus punctillumWeise, Coleoptera, Coccinellidae] on Golden Delicious and Starking Delicious apple cultivars in three apple orchards of Van, Turkey, during 2002–2003. Surveys were carried out weekly from May to November in sprayed and unsprayed apple orchards. The results of study indicated that the population densities of spider mites began to increase generally in early May, reached the maximum level from mid June to lateAugust and persisted until late September in both years. During 2002 the dominant species on both apple cultivars was P. ulmi, whereas in 2003 it was A. viennensis. In this two-year period, the population densities of P. ulmi and A. viennensis reached the maximum level of 318.1 and 427.2 mites per leaf, respectively, in sprayed orchards. In unsprayed orchard, spider mites remained at very low levels because of the presence of K. aberrans which was the only predator of spider mites. On the other hand, in sprayed orchards, although S. punctillum and Z. mali were the most abundant predatory species on spider mites, they could not control them in either apple cultivar and years.

The potential of four mite species (Acari: Phytoseiidae) as predators of sucking pests on protected cucumber (Cucumis sativus L.) crop

Protected crop experiments were conducted to study the suitability and efficacy of Phytoseiid mite species as predators of western flower thrips Frankliniella occidentalis (Pergande), carmine spider mite Tetranychus cinnabarinus (Boisduval) and greenhouse whitefly Trialeurodes vaporariorum(Westwood) in cucumber (Cucumis sativus L.) under greenhouse conditions. In this study, predatory mites Neoseiulus pseudolongispinosus Euseius castaneae Euseius utilis and Euseius finlandicus (Oudemans) (Phytosiidae) were investigated for their potential as biological control agents in treated along with untreated check. The current findings to judge the biocontrol potential of predators showed that laboratory bred adults and nymph instars of all predators efficiently preyed upon sucking arthropods and pests populations were drastically reduced in treated plants than in untreated control where their intensities were numerous. Among all predators, N. pseudolongispinosus was the most proficient and steadfast predator in controlling thrips and whitefly populations, contrary to E. finlandicus that proved better in reducing spider mite density in treated crop. The current findings indicated the potential of Phytoseiid predators for their augmentative releases to give best control of sucking pests in protected cucumber plants. Keywords: Biological control, predaceous mite, greenhouse, cucumber, phytoseiidae.

Varying abundance and dispersal of the two-spotted spider mite (Tetranychus urticae Koch, 1836, Acari: Prostigmata: Tetranychidae) on Mi-tomato plants differing in allelic combination

Varying abundance and dispersal of the two-spotted spider mite (Tetranychus urticae Koch, 1836, Acari: Prostigmata: Tetranychidae) on Mi-tomato plants differing in allelic combination It is well known that the presence of the Mi-1.2 gene determines the resistance of tomato plants (Solanum lycopersicum L.) to 3 root-knot nematode species and some insect herbivores of the order Hemiptera. In this study, the density and dispersal of two-spotted spider mites (Tetranychus urticae) on tomato plants of 4 cultivars were evaluated under greenhouse conditions, to find out whether tomatoes differing in allelic combination of the Mi-1.2 gene exhibit similar or different resistance to the mite pest. The results show, for the first time, that the same initial number of mites develops into populations that vary in abundance and distribution depending on tomato allelic composition of the Mi-1.2 gene. The results indicate that the mite-pest develops more slowly on tomato plants of cultivar ‘Motelle’, carrying 2 dominant alleles for the Mi-1.2 gene, than on heterozygous ‘Altess F1’ tomatoes and both cultivars carrying only recessive alleles of this gene: ‘Moneymaker’ and ‘Plaisence F1’. This suggests that the Mi-1.2 gene may be involved in tomato resistance against spider mites when this dominant gene is expressed homozygously, but this needs to be verified by further research.

Variogram Analysis of Hyperspectral Data to Characterize the Impact of Biotic and Abiotic Stress of Maize Plants and to Estimate Biofuel Potential

A considerable challenge in applied agricultural use of reflection-based spectroscopy is that most analytical approaches are quite sensitive to radiometric noise and/or low radiometric repeatability. In this study, hyperspectral imaging data were acquired from individual maize leaves and the main objective was to evaluate a classification system for detection of drought stress levels and spider mite infestation levels across maize hybrids and vertical position of maize leaves. A second objective was to estimate biomass and biofuel potential (heating value) of growing maize plants. Stepwise discriminant analysis was used to identify the five spectral bands (440, 462, 652, 706, and 784 nm) that contributed most to the classification of three levels of drought stress (moderate, subtle, and none) across hybrids, leaf position, and spider mite infestation. Regarding the five selected spectral bands, average reflectance values and standard variogram parameters ("nugget", "sill", and "range" derived from variogram analysis) were examined as indicators of spider mite and/or drought stress. There was consistent significant effect of drought stress on average reflectance values, while only one spectral band responded significantly to spider mite infestations. Different variogram parameters provided reliable indications of spider mite infestation and drought stress. Based on independent validation, variogram parameters could be used to accurately predict spider mite density but were less effective as indicators of drought stress. In addition, variogram parameters were used as explanatory variables to predict biomass and biofuel potential of individual maize plants. The potential of using variogram analysis as part of hyperspectral imaging analysis is discussed.

Agroforestry management affects coffee pests contingent on season and developmental stage

Abstract1 Management of vegetational diversity in agroecosystems is a potentially regulating factor of pest population dynamics and may affect developmental stages in different ways.2 We investigated the population dynamics of red spider mites, coffee leaf miners, and coffee berry borers in three management types of coffee agroforests: increasing plant diversity from a few shade tree species (simple‐shade agroforests), intermediate‐shade tree species (complex‐shade agroforests) to high‐shade tree species (abandoned coffee agroforests) in Ecuador. Furthermore, we studied how changes in agroforestry management affect population stage structure of each coffee pest.3 Our results show that agroforestry management affected seasonal patterns of coffee pests in that higher densities of red spider mites were observed from August to December, coffee leaf miners from December to February, and coffee berry borers from May to July. Moreover, specific developmental stages of red spider mites, coffee leaf miners, and coffee berry borers differed in their responses to agroforestry management. During all stages, red spider mite reached higher densities in simple‐shade agroforests compared with complex‐shade and abandoned agroforests. Meanwhile, coffee leaf miner densities decreased from simple‐shade to complex‐shade and abandoned agroforests, but only for larvae, not pupae. Similarly, only coffee berry borer adults (but not eggs, larvae and pupae) demonstrated a response to agroforestry management. Environmental variables characterizing each agroforestry type proved to be important drivers of pest population densities in the field.4 We emphasize the importance of considering seasonal differences and population structure while investigating arthropod responses to different habitat types because responses change with time and developmental stages.

Prey preference of Orius sauteri between Western Flower Thrips and spider mites

AbstractPrey preference of polyphagous predators plays an important role in the suppression of various species of pest insects. In this study, the prey preference of Orius sauteri (Poppius) (Heteroptera: Anthocoridae) between deutonymphs of Tetranychus urticae Koch (Acari: Tetranychidae) and second instars of Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), and the influence of spider mite density on the preference were examined in the laboratory in three‐dimensional set‐ups at 25 ± 1 °C and 70 ± 5% r.h. The results showed that the predatory bug in the presence of equal densities of the two prey species had a clear preference for thrips (preference index β: 0.86 ± 0.02), consuming 7.2 thrips larvae and 1.5 spider mite deutonymphs during the experimental periods of 6 h. The number of thrips consumed by O. sauteri did not change when the density ratio of thrips to spider mites was decreased from 1:1 to 1:5. Predation on spider mites increased when their ratio to thrips increased, but the disproportionate predation (i.e., the functional response) of O. sauteri towards spider mites resulted in a linear increase in the preference for F. occidentalis. The possible implications of these findings for the suppression of spider mites by O. sauteri in relation to the recent invasion of F. occidentalis into China are discussed.

From the laboratory to the field: contrasting effects of multi‐trophic interactions and agroforestry management on coffee pest densities

AbstractOnly few factors influencing pest populations can be studied in the laboratory, but many population‐driving factors interact in the field. Therefore, complementary laboratory and field approaches are required for reliable predictions of real‐world patterns and processes. Laboratory and field experiments with the red spider mite, Oligonychus ilicis McGregor (Acari: Tetranychidae), and the coffee leaf miner, Leucoptera coffeella Guérin‐Méneville (Lepidoptera: Lyonetiidae), on coffee plants, Coffea arabica L. (Rubiaceae), were combined to study the relative importance of biotic interactions, including resource preferences and natural‐enemy impact, and habitat factors, such as agroforestry type and management intensity, on coffee pest densities. In the laboratory, leaf discs cut from undamaged coffee plants were significantly preferred by red spider mites over those from plants infested with conspecific mites, leaf rust pathogens [Hemileia vastatrix Berkeley & Broome (Uredinales)], or coffee leaf miners, resulting in higher reproductive success. Similarly, undamaged plants were preferred by coffee leaf miners over red spider mite‐infested plants. However, in the field, red spider mite densities were positively correlated with coffee leaf miner and leaf rust densities, thereby contrasting with laboratory predictions. Hence, our study suggests that the importance of resource preferences and fitness expected based on laboratory experiments was suppressed by environmental conditions in the field, though other unassessed biotic interactions could also have played a role. Furthermore, intensified agroforestry was characterized by higher red spider mite densities, whereas densities of its major natural enemy, the predatory mite Amblyseius herbicolus Chant (Acari: Phytoseiidae), were not related to agroforestry management. Densities of coffee leaf miner and its main natural enemy, a eulophid parasitoid (Hymenoptera), were not affected by management practices. In conclusion, patterns found in the laboratory did not hold for the field, emphasizing the difficulties of extrapolating small‐scale experiments to larger spatial scales and the need to combine both approaches.

Visible/Near Infrared Reflectance (VNIR) Spectroscopy for Detecting Twospotted Spider Mite (Acari: Tetranychidae) Damage in Strawberries

The twospotted spider mite, Tetranychus urticae Koch, is among the most economically important pests in strawberries (Fragaria spp.). As T. urticae feeds, it ingests mesophyll cells that contain pigments essential for physiologic function and alters radiant energy use of the leaf tissue, severely compromising plant health and productivity. In our study, diffuse reflectance spectroscopy in the visible and near infrared (VNIR) portions of the spectrum was used to identify specific spectral regions altered by T. urticae feeding and to quantitatively assess T. urticae density. During the 2006-2007 growing season, 80 strawberry leaflets with varying levels of T. urticae infestation were collected. Spectral classification of both mite density (continuous) and mite density class (categorical) were developed. Spider mite density classes were low infestation (0-20 mites/leaflet), moderate infestation (20-50 mites/leaflet), and high infestation (> or = 50 mites/leaflet). Continuous spectral prediction for leaf infestation was developed using partial least squares (PLS) regression. Classification trees were used to train spectra to categorical levels of infestation. Both models were calibrated with 67% of the samples, and accuracy was evaluated using the remaining 33%. Categorical validation accuracy was 81%, with odds ratios for correctly predicting extreme categories (low and high) of 33 and 47.7, respectively. Continuous validation efficiency was also high, with an r2 between predicted and observed of 0.85 and a root-mean-squared error (RMSE) of 12.2 mites per leaf. Developing a spectral pest monitoring system would provide a diagnostic tool allowing early and effective intervention for precision management of T. urticae in strawberry.

Environmentally mediated coffee pest densities in relation to agroforestry management, using hierarchical partitioning analyses

Understanding pest density patterns in the field is important to account for distinct environmental variables potentially influencing populations across different habitat types. Here, we assessed the relative importance of single environmental abiotic and biotic variables on densities of three major coffee pests, i.e., spider mites, leaf miners and berry borers, in simple, complex and abandoned agroforests of coastal Ecuador, using hierarchical partitioning methods. Most of the variation in spider mite and leaf miner densities was accounted for by the abiotic variables temperature and relative humidity, while agroforestry type, relative humidity and tree diversity were more important in explaining densities of berry borers. Furthermore, densities of spider mites and berry borers, but not leaf miners, were affected by agroforestry type, with lower densities in structurally complex agroforests. In conclusion, very different environmental variables influence coffee pest population density. Understanding such species density–environmental relationships provide insights on how to predict and manage populations in the field.

ダイズにおけるハダニおよび天敵類の発生消長と殺虫剤散布の影響

The seasonal fluctuation and species composition of spider mites and their predators on soybean were investigated in an agrochemical sprayed plot and an unsprayed control plot from 1999 to 2001 in Ibaraki, central Japan. Sprayed plots were treated with cypermethrin and fenitrothion (1999), acephate and imidacloprid (2000), and permethrin (2001). In both plots, spider mite populations showed three peaks in 1999 (June, August and October–November), and two in 2001 (August and September–November). In 2000, the populations peaked only once (August), because soybean flowered and fruited more than one month earlier than in other years and as a result, all leaves had dropped by late September. Of the spider mite species sampled, Tetranychus kanzawai Kishida, T. parakanzawai Ehara, T. pueraricola Ehara et Gotoh and T. urticae Koch (green form) dominated in both plots and at almost all times. Predators were phytoseiid mites, such as Gynaeseius liturivorus (Ehara), Amblyseius tsugawai Ehara, Neoseiulus californicus (McGregor), and N. womersleyi (Schicha), and insects like Scolothrips takahashii Priesner and Feltiella sp. The population density of G. liturivorus was positively related to the occurrence of phytophagous thrips until August when the thrips became scarce. Synchronized with spider mite density were phytoseiid mites other than G. liturivorus after August, and Scolothrips takahashii throughout the observation periods. Agrochemical spraying had an initial detrimental effect on phytoseiid mites and S. takahashii, but they had recovered by two–four weeks after spraying, suggesting that the effect of chemical spraying on predators was weak.

Aesthetic Damage Thresholds for Twospotted Spider Mites (Acari: Tetranychidae) on Impatiens: Effect of Plant Age and Level of Infestation

The effects of plant age and infestation level of twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), on visible plant damage, and the effect of plant age on spider mite population growth on impatiens, Impatiens wallerana Hook.f. (Ericales: Balsaminaceae), were determined by inoculating impatiens plants of three different ages with two densities of spider mites. Each plant was inoculated with either one adult female mite per three leaves or six leaves based on the average number of leaves on plants of each of the three age classes. Subsequently, leaf damage was correlated with mite-days (cumulative spider mite density) per leaf. The results showed that older aged plants exhibited greater damage than younger plants. Regression models of damage thresholds for each plant age suggest that monitoring for spider mites must be done periodically throughout the entire plant production cycle, but that more attention should be given toward the end of the cycle. Measurements of visible leaf damage were correlated with plant marketability. Specifically, the level of damage (proportion of damaged leaves per plant) at which plant marketability changes from a “premium” to a “discounted” category was 0.04–0.06. Thus, regression equations of the damage threshold could be used to estimate a cumulative spider mite density or mite-days equivalent to the economic threshold. Based on these equations, 5% leaf damage corresponds to 2.1, 1.51, and 1.25 mite-days for youngest, intermediate, and oldest plants, respectively. Because the damage threshold on impatiens was shown to be very low, the action threshold for biological control is essentially zero, and predators would need to be released as soon as damage is observed.

Aesthetic Damage Thresholds for Twospotted Spider Mites (Acari: Tetranychidae) on Impatiens: Effect of Plant Age and Level of Infestation

The effects of plant age and infestation level of twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), on visible plant damage, and the effect of plant age on spider mite population growth on impatiens, Impatiens wallerana Hook.f. (Ericales: Balsaminaceae), were determined by inoculating impatiens plants of three different ages with two densities of spider mites. Each plant was inoculated with either one adult female mite per three leaves or six leaves based on the average number of leaves on plants of each of the three age classes. Subsequently, leaf damage was correlated with mite-days (cumulative spider mite density) per leaf. The results showed that older aged plants exhibited greater damage than younger plants. Regression models of damage thresholds for each plant age suggest that monitoring for spider mites must be done periodically throughout the entire plant production cycle, but that more attention should be given toward the end of the cycle. Measurements of visible leaf damage were correlated with plant marketability. Specifically, the level of damage (proportion of damaged leaves per plant) at which plant marketability changes from a "premium" to a "discounted" category was 0.04-0.06. Thus, regression equations of the damage threshold could be used to estimate a cumulative spider mite density or mite-days equivalent to the economic threshold. Based on these equations, 5% leaf damage corresponds to 2.1, 1.51, and 1.25 mite-days for youngest, intermediate, and oldest plants, respectively. Because the damage threshold on impatiens was shown to be very low, the action threshold for biological control is essentially zero, and predators would need to be released as soon as damage is observed.

Impact of sulfur on density of Tetranychus pacificus (Acari: Tetranychidae) and Galendromus occidentalis (Acari: Phytoseiidae) in a central California vineyard

Sulfur is the oldest and most widely used fungicide in the vineyards of California, where it is used for control of powdery mildew (Uncinula necator [Schw.] Burr). For decades, sulfur use has been associated with outbreaks of Tetranychus pacificus McGregor (Acari: Tetranychidae) on cultivated grapes in the San Joaquin Valley. I undertook large-scale field studies to test this association, to evaluate the impact of sulfur on Galendromus occidentalis (Nesbit) (Acari: Phytoseiidae), a major predator of T. pacificus, and to determine if timing of sulfur applications with respect to grape bloom has an impact on T. pacificus density. The studies took place in a 32 ha vineyard in Fresno County, and all fungicide applications were made with commercial-scale equipment. In 1998 a 'high sulfur' treatment, a combination of wettable sulfur and sulfur dust, was compared to 'low sulfur,' in which demethylation inhibitor (DMI) fungicides partially substituted for sulfur. In 1999 treatments were 'sulfur,' 'DMI,' 'sulfur pre-bloom' (here sulfur was applied prior to grape bloom, in late May, and then DMIs were applied until mid-season) and 'sulfur post-bloom' (the reverse of 'sulfur pre-bloom'). In each year, the T. pacificus population increase came after the end of fungicide applications, and results clearly show a relationship between sulfur use and T. pacificus density. In 1998, mean T. pacificus density was 2.7 times higher and mean G. occidentalis density 2.5 times higher in 'high sulfur' compared to 'low sulfur.' In 1999, the highest T. pacificus counts were in the 'sulfur' and 'sulfur pre-bloom' treatments, 4.8 times higher than 'sulfur post-bloom' and 2 times higher than 'DMIs.' Density of G. occidentalis was 2.3 times as high in 'sulfur' or 'sulfur pre-bloom' than 'DMIs.' The predator/prey ratio was not significantly different among treatments in 1998, but in 1999 it was highest in the 'sulfur pre-bloom' treatment. In 1999, density of Homeopronematus anconai (Baker) (Acari: Tydeidae) was 2.7 times higher in 'sulfur pre-bloom' compared to 'sulfur,' and higher by 2.7 times in 'DMI' compared to 'sulfur post-bloom,' suggesting a negative effect of sulfur on this tydeid. These results do not support the hypotheses that the cause of the increase in T. pacificus density is due to negative effects of sulfur on phytoseiids or tydeids. Rather, it appears that a plant-based explanation is likely, first, because of the differences in pre-bloom versus post-bloom sulfuring, and second, because of the long lag time between the end of the sulfur applications and the corresponding increase in spider mite density.

Species composition and seasonal changes of spider mite density on a leguminous plant Pueraria lobata

Populations of spider mites were sampled from kudzu vine Pueraria lobata (Willd.) from 1997 to 1999 at two study sites in Ibaraki, central Japan. Of the five spider mite species sampled, Tetranychus pueraricola Ehara and Gotoh was the most abundant (accounting for 75.6–96.9% of mites) in each of the three years. The next most abundant species were T. ludeni Zacher (0.8–19.0%), T. parakanzawai Ehara (1.1–9.7%) and T. piercei McGregor (3.1%), but their density and species richness varied from year to year and from site to site. The populations peaked in June and/or September–October. Predators associated with spider mite populations were phytoseiid mites such as Amblyseius tsugawai Ehara, Phytoseius nipponicus Ehara and Neoseiulus womersleyi (Schicha), Scolothrips takahashii Priesner, Oligota spp., Feltiella spp. and stigmaeid mites such as Agistemus exsertus Gonzalez and A. terminalis (Quayle), which were well synchronized with spider mite density. Overwintered females began to appear and oviposit on some herbaceous weeds growing at the study sites in early April. Spider mites appeared on kudzu vine leaves in early May just after flushing. Most colonies (defined as areas surrounded with silky spider mite threads) had only one species but a small percentage had two or three species.

Impact of transgenic Bacillus thuringiensis cotton on a non‐target pest Tetranychus spp. in northern China

AbstractField studies were carried out to evaluate the effect of two transgenic cotton varieties (SGK321 carrying Cry1A+CpTI and DP99B carrying Cry1Ac) and the conventional variety (shiyuan321‐parental line of SGK321) on spider mites, Tetranychus spp. from 2002 to 2004. In 2002, this experiment included three treatments: Bt cotton field (SGK321) treated with acaricides against spider mites, untreated non‐Bt cotton field (Shiyuan321), and untreated Bt cotton field (SGK321). In 2003–2004, there are four types of treatments after a new transgenic Bt cotton variety, DP99B (non‐chemical control), was added into the experiments. The results showed that there were no significant difference in densities of spider mites among Bt without acaricides and non‐Bt without acaricides cotton fields, nor was there a significant difference in damage of spider mites to cotton among these treatments (P > 0.1). However, there are significant differences (P < 0.05) in densities of spider mites and damage caused by spider mites between cotton fields with and without acaricides. Acaricide significantly reduced the densities of spider mites in Bt cotton (P < 0.05). These results suggest that Bt cotton has no effect on spider mites populations. However, spider mites have the potential for severe damage in Bt cotton fields. Acaricides are essential tools in controlling cotton spider mites in northern China.