Spider Mite Densities Research Articles

Entomopathogenic fungi and their biological control of Tetranychus urticae: Two-spotted spider mites

The two-spotted spider mite (TSSM) Tetranychus urticae, is regarded as one of the most dangerous pests responsible for great losses in most of agricultural crops. It is a persistent pest in Saudi Arabia, especially in greenhouses where T. urticae is primarily controlled by chemical pesticides. The main problem for the two-spotted spider mites is its high resistance to pesticides and high fertility rate. In the long term, chemical pesticides cause health problems and economic losses, so it was necessary to search for a safe alternative method for human health and the environment. One of these alternative methods was the selection of plant varieties resistant to the TSSM, in addition to biological control that includes mites or predatory insects and entomopathogenic fungi. The growth, reproduction, and life-table parameters of T. urticae were examined in a laboratory setting with a 16L:8D photoperiod at 28 ± 1 °C and 65 ± 5% RH, in the presence of three major members of Family: Solanaceae tomato, eggplant, and pepper. Pepper was shown to be less conducive to T. urticae growth and reproduction compared to eggplant and tomato. Tetranychus urticae proceeded through all five stages of its life cycle (egg, larva, protonymph, deutonymph, and adult) on tested solanaceous plants, and these plants significantly influenced its growth, reproduction, and Life-table parameters. Additionally, entomopathogenic fungi have been used against insects that have proven highly effective in controlling and reducing the density of two-spotted spider mites. Eight fungi were isolated from 80 insect and mite samples collected from several Saudi Arabia regions. Analysis of the 18S rRNA sequences revealed that the fungal strains identified as Beauveria bassiana, Fusarium sp. F. equiseti, F. oxysporium, Scopulariopsis brevicaulis1, S. brevicaulis2, Aspergillus sclerotiorum, and Penicillium citrinum. The ability of isolated fungi to secrete enzymes degrading the two-spotted spider mite cuticle, namely lipase, protease, and chitinase, were studied.

Suppression of Powdery Mildew and Two-Spotted Spider Mite by UV-B Radiation and Mulching Type of Strawberry Cultivation in the Greenhouse

Powdery mildew and two-spotted spider mite are detrimental to strawberry plants and are controlled with traditional pesticides. To accommodate consumer demand, eco-friendly methods of pest control are required. Strawberries were cultivated (in soil and in a hydroponic system) for two years, and ultraviolet B (UV-B) irradiation was used as an alternative pest control during the harvesting season. Three varieties were grown (Seolhyang, Kingsberry, and Durihyang), and four UV-B lamp/mulch (black, green, and light reflection sheet [LRS]) combinations were used during harvesting: UV-B+black or green mulch, UV-B+black or green+LRS, no UV-B+black or green, and no UV-B+black or green+LRS. In all varieties, powdery mildew was 65% more controlled when UV-B irradiation was used. The adult two-spotted spider mite density was lowest in the UV-B lamp+black or green+LRS treatments. Therefore, UV-B irradiation during the strawberry harvesting season could effectively control powdery mildew and two-spotted spider mite with little side effect on the plants.

No influence on population dynamics of spider mites in cotton fields of intercropping with walnut, a poor-quality host

Intercropping is a common agricultural practice used to improve crop yields and profits; however, the intercrop species and its quality as a host for the main crop's key pests can affect the pests' population dynamics under intercropping conditions. Fruit trees - cotton intercropping systems are commonly applied in Xinjiang of China, and previous studies have confirmed that intercropping of cotton with species (e.g., jujube and apple) that are good spider mite hosts can increase the spider mite density in cotton. In this study, the effect of intercropping cotton with walnut, which is a poor host for the key spider mite pest Tetranychus truncatus, was examined. For this spider mite, feeding on walnut leads to significantly longer development time for larvae + nymphs and a short oviposition period which leads to a lower total fecundity, lower survival rate and lower intrinsic growth rate (rm) compared to cotton. Correspondingly, in the two-year, multiple-scale field study, we found that the population dynamics of spider mites in cotton did not significantly differ in the field plots between a walnut-cotton intercropping system and monocultural cotton. Similar trends of spider mite density were also observed in commercial fields. Based on previous work and the current study on fruit tree-cotton intercropping systems, we concluded that while intercropping cotton with intercrop species that are suitable spider mite hosts increase the spider mite population in intercropped cotton, the use of a poor host plant such as walnut has no significant effect on spider mites populations in cotton. Hence, our study results improved the understanding of pest management and monitoring in intercropped cotton systems.

Pests of Florida Hops: Preliminary Observations

Surveys of arthropods associated with hops at the University of Florida's Gulf Coast Research and Education Center, Wimauma, Florida, USA, from 2016 to 2020 reveal that spider mites are the primary pest of the crop. Lepidoptera and lace bugs also were observed causing occasional damage to the crop. Whiteflies and thrips have been observed on the crop in low numbers. The tall (5.5 m) canopy of the hops trellis creates a challenge to applying insecticides with adequate coverage. Sampling data indicate that spider mite densities tend to be higher in the upper canopy than at ground level. Efforts to control spider mites with releases of the commercially available predator Phytoseiulus persimilis showed promise. Naturally occurring spider mite predators observed on hops at Gulf Coast Research and Education Center include Stethorus sp., Neoseiulus sp., Orius sp., and trash bugs.

UV-induced citrus resistance to spider mites (Tetranychus urticae)

Under reduced solar UV radiation, such as in polycarbonate-covered nurseries, the two-spotted spider mite Tetranychus urticae is a major pest of all citrus cultivars, while under natural solar radiation, only sensitive cultivars are infested. We hypothesized that citrus resistance to T. urticae is induced by UV. We infested seedlings of Citrus volkameriana rootstock with T. urticae under natural and under UV-screened solar radiation, along with non-infested control seedlings. We then monitored the establishment of the spider mites and analyzed the volatile leaf profile using GC-MS. The density of spider mites was reduced dramatically on seedlings exposed to solar UV. Overall, ninety volatile compounds (47 monoterpenes, 35 sesquiterpenes, and 8 aldehydes) were detected in the leaves, many of them known to be herbivore-induced and/or UV enhanced. Their levels were affected not only by solar UV radiation or by mite infestation independently. Synergistic interaction of these two factors resulted in 90% of the volatiles suppressed by T. urticae infestation in the absence of UV radiation. This suggests that plant induced resistance is dependent on exposure to UV radiation.

Age-Dependent Functional and Numerical Responses of Neoseiulus cucumeris (Acari: Phytoseiidae) on Two-Spotted Spider Mite (Acari: Tetranychidae).

The age-specific functional and numerical responses of Neoseiulus cucumeris Oudemans (Mesostigmata: Phytoseiidae) on eggs of the two-spotted spider mite, Tetranychus urticae Koch (Prostigmata: Tetranychidae), were assessed in the laboratory using bean leaf discs. Densities of 2, 4, 8, 16, 32, 64, and 128 prey were provided to 4- (protonymph), 6- (deutonymph), 8-, 13-, 18-, 23-, 28-, 33-, and 40-d-old N. cucumeris individuals. The functional response of 28- and 40-d-old N. cucumeris fitted type II, whereas the other ages displayed a type III functional response. The longest handling time observed at the age of 4 d was 0.515 h, whereas the shortest handling time and highest value of maximum attack rate (T/Th) were associated with the age of the 28-d-old treatment (0.261 h and 91.95 prey/d, respectively). The numerical response of N. cucumeris showed a significant increase with increasing prey density, but its rate gradually decreased at higher densities. Therefore, the efficiency of conversion of ingested food was relatively higher at low two-spotted spider mite densities, whereas it was reduced at high two-spotted spider mite densities. The stronger functional response and predation capacity of N. cucumeris on two-spotted spider mite eggs indicated the high potential of this predatory mite as an effective biological control agent against two-spotted spider mite especially at its early and middle ages and also when higher prey densities are present.

Influence of a Neonicotinoid Seed Treatment on a Nontarget Herbivore of Soybean (Twospotted Spider Mite) and Diet Switching by a Co-occurring Omnivore (Western Flower Thrips).

Insecticidal neonicotinoid seed treatments are a common agricultural insect pest management strategy; however, effects on nontarget pests and omnivorous arthropods are understudied. We used a series of experiments to evaluate impacts of the neonicotinoid seed treatment thiamethoxam on densities of herbivorous twospotted spider mites (Tetranychus urticae Koch [Acari: Tetranychidae]) and feeding behavior of western flower thrips (Frankliniella occidentalis Pergande [Thysanoptera: Thripidae]), an omnivore that feeds on spider mite eggs but is also a significant plant pest. Spider mite densities were higher on neonicotinoid-treated soybeans, but only when mites were not spatially confined. We then examined how availability of thiamethoxam-treated food items (i.e., eggs from spider mites reared on treated soybeans, soybean leaf discs, or a combination of the two), and previous exposure to thiamethoxam-treated soybean impacted thrips feeding. Regardless of the presence of leaf tissue, thrips consumed fewer spider mite eggs laid by females reared on treated soybeans, suggesting spider mite eggs can serve as poisoned prey. Overall, thrips consumed less treated soybean leaf tissue, and thrips on treated leaf discs had a lower percentage of herbivorous feeding events and consumed more nontreated spider mite eggs, indicating a dietary shift from herbivory to predation. The neonicotinoid status of spider mite eggs and prior exposure of thrips also caused shifts in the number and size of leaf scars, likely as a result of altered foraging behavior and/or movement. Shifts between herbivory and predation have implications for thrips damage, virus transmission, and pest management, especially in systems with mixtures of nontreated and neonicotinoid-treated plants.

Mulching with coffee husk and pulp in strawberry affects edaphic predatory mite and spider mite densities.

Mulching of soil beds of strawberry fields is usually done with polyethylene film in southern Minas Gerais state, Brazil. This material is relatively expensive and difficult to discard after use. In some countries, mulching is done with the use of organic material that could have an advantage over the use of plastic for its easier degradation after use, and for favoring edaphic beneficial organisms. Predatory mites (especially Gamasina, Mesostigmata) may be abundant in the soil and could conceivably move to the soil surface and onto the short-growing strawberry plants at night, helping in the control or pest arthropods. The two-spotted spider mite, Tetranychus urticae Koch, is considered an important strawberry pest in that region, where the fungus Neozygites floridana (Weiser and Muma) has been found to infect it. Different mulching types could affect the incidence of this pathogen. Dehydrated coffee husk and pulp (DCHP) is a byproduct readily available in southern Minas Gerais, where could be used as organic mulching in strawberry beds. The temporary contact of that material with the soil of a patch of natural vegetation could facilitate its colonization by edaphic predatory mites helpful in the control of strawberry pests. The objective of this work was to study the effect of mulching type on the population dynamics of the two-spotted spider mite, associate mites and N. floridana, in a greenhouse and in the field. The use of DCHP increased the number of edaphic Gamasina on strawberry plants-Proctolaelaps pygmaeus (Müller) (Melicharidae) and Blattisocius dentriticus (Berlese) (Blattisociidae) were observed on strawberry leaflets, mainly in nocturnal samplings, indicating their possible daily migration from soil to plants. Lower levels of two-spotted spider mite occurred on plants from pots or soil beds mulched with DCHP instead of polyethylene film, possibly because of the slightly higher levels of mites of the family Phytoseiidae and infection by N. floridana. Adding DCHP onto the floor of natural vegetation did not result in higher diversity or levels of gamasine mites on DCHP. Complementary studies should be conducted to find ways to increase diversity and density of those organisms in strawberry beds, in an attempt to improve biological control of strawberry pests. The decision to use DCHP for mulching should also take into account other factors such as strawberry yield, costs and efficiency of weed management, to be evaluated in subsequent studies.

Influence of companion planting on damson hop aphid Phorodon humuli, two spotted spider mite Tetranychus urticae, and their antagonists in low trellis hops

The effects on population development of damson-hop aphid Phorodon humuli and two-spotted spider mite Tetranychus urticae from planting drive rows with grass (2002-3 only), Brassica juncea, Phacelia tanacetifolia (2004-6 only), a meadow-mix of grass and flowering plants were compared with a bare soil control on aphid-susceptible low trellis hop (Humulus lupulus L.) cultivars First Gold (FGO) and Herald (HER) in 2002-4 and on partially aphid-resistant cultivar Boadicea (BOA) in 2004-6. Aphid and mite natural enemies were monitored from beat and foliage samples. Irrespective of ground cover treatment, generalist predators prevented damaging aphid populations from developing on BOA each year, and a combination of aphid–specific and generalists on FGO/HER in two of the three years experiments. Fewest migrant aphids settled, and lower aphid populations ensued, on FGO/HER with meadow-mix than other treatments, but the difference was insufficient to prevent peak populations of ca 1000 per leaf in 2004. Numbers of aphidiid parasitoids reflected aphid population densities on leaves with the highest numbers on FGO/HER in 2004, and none on BOA in any year. Seven species of primary parasitoids were recorded, dominated by Aphidius matricariae and A. picipes (95%), and eight species of hyperparasitoids which became increasingly prevalent as the season progressed. Spider mite population densities remained below ten actives per leaf in all but one year. They were regulated by a combination of phytoseiid mites (six species dominated by Typhlodromus pyri) and insect predators. Hops with meadow-mix had the highest population densities of spider mites, but also the highest numbers of phytoseiids. Although companion plants depressed average cone weight by ca 18% compared with the bare soil control, that loss may be preventable by using additional fertilizers, in which case permanent meadow-mix would provide a suitable companion plant treatment for biological control of both P. humuli and T. urticae on aphid-resistant low trellis cultivars such as BOA, but used alone is unreliable on aphid-susceptible cultivars.

The influence of Tetranychus cinnabarinus-induced plant defense responses on Aphis gossypii development

Carmine spider mites (Tetranychus cinnabarinus) and cotton aphids (Aphis gossypii) are both serious pests of cotton, and cause reductions in yields of this key agricultural crop. In order to gain insights into how plant defense responses induced by one herbivore species affect the behavior and performance of another, we examined how infestation with T. cinnabarinus influences the development of A. gossypii using cotton as a model. In this study, we measured the activities of several important biochemical markers and secondary metabolites in the leaves of cotton seedlings responding to infestation by T. cinnabarinus. Furthermore, the influences of T. cinnabarinus infestation on the development of A. gossypii in cotton were also examined. Our data showed that the activities of several key defense enzymes, including phenylalanine ammonia-lyase (PAL), peroxidase (POD), lipoxygenase (LOX), and polyphenol oxidase (PPO), were substantially increased in cotton seedlings responding to spider mite infestation. Further, the contents of gossypol and condensed tannins, key defensive compounds, were significantly enhanced in leaves of cotton seedlings following T. cinnabarinus infestation. Moreover, the T. cinnabarinus-induced production of defense enzymes and secondary metabolites was correlated with infestation density. The developmental periods of A. gossypii on cotton seedling leaves infested with T. cinnabarinus at densities of 10 and 15 individuals cm−2 were 1.16 and 1.18 times that of control, respectively. Meanwhile, the mean relative growth rates of A. gossypii on cotton leaves infested with T. cinnabarinus at densities of 8, 10 and 15 individuals cm−2 were significantly reduced. Therefore, these data suggested that the developmental periods of A. gossypii were significantly lengthened and the mean relative growth rates were markedly reduced when cotton aphids were reared on plants infested with high densities of spider mites. This research sheds light on the role that inducible defense responses played in plant-mediated interspecific interactions between T. cinnabarinus and A. gossypii.

Generalist predators consume spider mites despite the presence of alternative prey

The broad feeding habits of generalist predators can lead to uncertainty about their impacts on particular pests. Due to prey switching, consumption of one pest species by generalist predators might decrease as densities of attractive alternative prey increase. To test this, we used molecular tools to examine presence/absence of two-spotted spider mites (Tetranychus urticae) in the guts of predatory Nabis and Geocoris bugs, in potato (Solanum tuberosum) crops grown using either organic or conventional farming methods. Previous work suggested that organic potato fields house relatively high densities of alternative prey, which might disrupt predators’ consumption of spider mites. While densities of spider mites and of the attractive alternative prey green peach aphids (Myzus persicae) did not consistently differ between farming systems, their densities varied widely between years and among fields within each year. The likelihood of detecting spider mite predation was not correlated with spider mite densities, such that we often recorded mite consumption in fields where these pests were rare. Spider mite consumption also was not significantly altered when we detected predation of green peach aphids. However, we found consistently higher numbers of both predator taxa in organic fields than in conventional fields. Altogether, we found that generalist predators continue to consume spider mites against a background of changing numbers of mites and aphids. This suggests that diverse alternative prey availability may not weaken the impact of robust populations of natural enemies found on organic farms.

Remote Sensing Evaluation of Two-spotted Spider Mite Damage on Greenhouse Cotton.

The objective of this study was to evaluate a ground-based multispectral optical sensor as a remote sensing tool to assess foliar damage caused by the two-spotted spider mite (TSSM), Tetranychus urticae Koch, on greenhouse grown cotton. TSSM is a polyphagous pest which occurs on a variety of field and horticultural crops. It often becomes an early season pest of cotton in damaging proportions as opposed to being a late season innocuous pest in the mid-southern United States. Evaluation of acaricides is important for maintaining the efficacy of and preventing resistance to the currently available arsenal of chemicals and newly developed control agents. Enumeration of spider mites for efficacy evaluations is laborious and time consuming. Therefore, subjective visual damage rating is commonly used to assess density of spider mites. The NDVI (Normalized Difference Vegetation Index) is the most widely used statistic to describe the spectral reflectance characteristics of vegetation canopy to assess plant stress and health consequent to spider mite infestations. Results demonstrated that a multispectral optical sensor is an effective tool in distinguishing varying levels of infestation caused by T. urticae on early season cotton. This remote sensing technique may be used in lieu of a visual rating to evaluate insecticide treatments.

Remote Sensing Evaluation of Two-spotted Spider Mite Damage on Greenhouse Cotton

The objective of this study was to evaluate a ground-based multispectral optical sensor as a remote sensing tool to assess foliar damage caused by the two-spotted spider mite (TSSM), Tetranychus urticae Koch, on greenhouse grown cotton. TSSM is a polyphagous pest which occurs on a variety of field and horticultural crops. It often becomes an early season pest of cotton in damaging proportions as opposed to being a late season innocuous pest in the mid-southern United States. Evaluation of acaricides is important for maintaining the efficacy of and preventing resistance to the currently available arsenal of chemicals and newly developed control agents. Enumeration of spider mites for efficacy evaluations is laborious and time consuming. Therefore, subjective visual damage rating is commonly used to assess density of spider mites. The NDVI (Normalized Difference Vegetation Index) is the most widely used statistic to describe the spectral reflectance characteristics of vegetation canopy to assess plant stress and health consequent to spider mite infestations. Results demonstrated that a multispectral optical sensor is an effective tool in distinguishing varying levels of infestation caused by T. urticae on early season cotton. This remote sensing technique may be used in lieu of a visual rating to evaluate insecticide treatments.

Beyond Focal Pests: Impact of a Neonicotinoid Seed Treatment and Resistant Soybean Lines on a Non-Target Arthropod.

Integrated pest management (IPM) tactics may effectively control focal pests, but it is also important to test the compatibility of different tactics, and consider non-target organisms. We investigated the effects of a neonicotinoid seed treatment and Rag resistance genes used for soybean aphid (Aphis glycines Matsumura) control on reproduction of a non-target herbivore (twospotted spider mite, Tetranychus urticae Koch) in short-term greenhouse experiments. We also examined interactions between spider mites and a specialist phytoseiid mite [Ambylseius fallacis (Garman)] and assessed the effects of a co-occurring opportunistic omnivore [Frankliniella occidentalis (Pergande)] by including thrips density as a covariate. There were no interactive or main effects of the presence of Rag genes on the densities of any of the arthropods. Overall, effects of the seed treatment on spider mite densities varied, with no difference when mites were confined in clip cages, and higher populations on seed-treated plants when on whole plants. Predatory mites had a consistent negative impact on spider mites, and densities of A. fallacis immatures were similar between seed treated and non-seed treated plants. However, the relationship between spider mite and thrips densities was different between these two plant types, but only in the clip cage experiment lacking predatory mites. This research highlights the importance of considering how IPM tactics might affect non-target organisms.

Effect of the postfeeding interval on olfactory responses of thrips to herbivore-induced cotton plants.

We investigated the responses of 3 thrips species, Frankliniella schultzei Trybom, F. occidentalis Pergrande, and Thrips tabaci Lindeman (Thysanoptera: Thripidae) to herbivore-damaged and undamaged cotton seedlings (Gossypium hirsutum L. [Malvales: Malvaceae]) at a range of time intervals following damage by adult Tetranychus urticae (Koch), adult T. ludeni (Zacher) (Acari: Tetranychidae) or Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) larvae in olfactometer assays. The intensity/frequency of the response of thrips to herbivore-induced plants decreased with time and ultimately disappeared in all cases; however, the rate at which the response declined was related to the herbivore species that inflicted the damage. All 3 species of thrips were attracted to plants damaged by T. urticae for longer than they were to plants damaged by T. ludeni. The duration for which damaged plants remained attractive was also affected by the degree of damage inflicted on cotton seedlings. For example, F. schultzei was attracted to plants damaged by a higher density of two-spotted spider mites (100/plant) for much longer than to plants damaged by a lower density of these mites (50/plant). The results reinforce previous studies that demonstrate that arrangement of variables influences the responses of thrips to their herbivore-induced cotton host plants. Results also show that these responses are variable in time following herbivore damage to cotton plants, which further demonstrates how difficult it is to generalize about the functional significance of these interactions.

Evaluation of a brushing machine for estimating density of spider mites on grape leaves.

Direct visual inspection and enumeration for estimating field population density of economically important arthropods, such as spider mites, provide more information than alternative methods, such as binomial sampling, but is laborious and time consuming. A brushing machine can reduce sampling time and perhaps improve accuracy. Although brushing technology has been investigated and recommended as a useful tool for researchers and integrated pest management practitioners, little work to demonstrate the validity of this technique has been performed since the 1950's. We investigated the brushing machine manufactured by Leedom Enterprises (Mi-Wuk Village, CA, USA) for studies on spider mites. We evaluated (1) the mite recovery efficiency relative to the number of passes of a leaf through the brushes, (2) mite counts as generated by the machine compared to visual counts under a microscope, (3) the lateral distribution of mites on the collection plate and (4) the accuracy and precision of a 10% sub-sample using a double-transect counting grid. We found that about 95% of mites on a leaf were recovered after five passes, and 99% after nine passes, and mite counts from brushing were consistently higher than those from visual inspection. Lateral distribution of mites was not uniform, being highest in concentration at the center and lowest at the periphery. The 10% double-transect pattern did not result in a significant correlation with the total plate count at low mite density, but accuracy and precision improved at medium and high density. We suggest that a more accurate and precise sample may be achieved using a modified pattern which concentrates on the center plus some of the adjacent area.

A reservoir weed for mites: Datura stramonium L. (Solanaceae) in the vicinity of cultivated solanaceous plants in Turkey

Twenty-six phytophagous, predacious and generalist mite species were found on the weed species Datura stramonium in the vicinity of solanaceous vegetables from two locations in Turkey during 2009–2010. Of seven species of phytophagous mites, Tetranychus urticae was the predominant species on the weed leaves. Additionally, 15 predacious mite species from seven families were identified: Phytoseiidae, Anystidae, Stigmaeidae, Bdellidae, Ascidae, Ameroseiidae and Iolinidae. Phytoseiidae (nine species) and Iolinidae (one species) were the most abundant predacious mites in the families. The dominant predacious species were Cydnodromus californicus and Pronematus ubiquitus. The Shannon index (H′), a biodiversity parameter of the predacious mites was very high compared to that of phytophagous mites that occurred at a high density. Among four generalist species from three families (Tydeidae, Acaridae and Oribatidae), one species, Zygoribatula microporosa, was found in the Turkish mite fauna. In Ankara, the population density of spider mites on the weed leaves began to increase in early July and peaked three times in late July, early September and mid-October in 2009–2010. In Bursa, the mites emerged in early June and peaked four times in early July, early August, early September and early October in 2010–2011. Cydnodromus californicus and Typhlodromus Anthoseius recki exhibited efficient numerical responses to spider mite populations from early August to early September. However, in Bursa, Sorenson’s coefficient confirmed that there were positive predator–prey associations among spider mites and these predacious mites. Although this weed is a source of predacious species when it is located in the vicinity of tomato fields, D. stramonium may play a role as a reservoir plant for phytophagous mites and permit increasing pest population in areas used for the cultivation of solanaceous vegetables due to predators’ delayed response to spider mite populations.

Density and growth rates of spider mites in relation to phenological stages of soybean cultivars in Brazil.

The population fluctuations of spider mites on different soybean cultivars were studied in two experiments performed in the municipalities of São Sepé (experiment 1) and Santa Maria (experiment 2) in the state of Rio Grande do Sul, Brazil. The number of cultivars was 20 in São Sepé and 25 in Santa Maria, and at each location leaves were sampled from 15 plants per cultivar every week throughout the entire plant developmental cycle, amounting to 11 and 10 samplings in experiment 1 and 2, respectively. The statistical analysis revealed that mite densities varied significantly with cultivar and time. Besides, the interaction between soybean cultivars and sampling times was significant at both locations. This indicates that the populations did not vary in the same way among cultivars over time, which is attributed to differences among the cultivars with respect to their phenology and response to spider mites. Equations for describing the mite population dynamics were estimated for each cultivar, mostly by fitting cubic equations to the weekly growth rates (per capita changes) in mite densities. We also found that the highest growth rates for mites on soybean cultivars in both locations occurred after the beginning of flowering, when the plants shifted from the vegetative to reproductive stages, about 3 weeks before reaching the peak densities.

Molecular verification of dispersal of phytoseiid mites from groundcover plants to tree leaves in Japanese peach orchards

A population survey of phytoseiid mites and of spider mites on randomly selected trees and their groundcover plant Paederia foetida L. (Rubiaceae) was conducted in Japanese peach orchards that used different pesticide practices. An organic orchard with wild groundcover and no synthetic chemicals used for pest control and a conventionally managed orchard with bare ground had no trees on which spider mite density was beyond the control threshold density (one mite per leaf). On the other hand, spider mite densities in some trees at conventionally managed orchards with wild groundcover were temporary beyond the control threshold level. The phytoseiid mite species composition on peach leaves estimated by previously established method using quantitative sequencing changed during the survey period and varied among orchards. PCR amplification of the internal transcribed spacer (ITS) region of ribosomal genes of Tetranychus kanzawai Kishida and Panonychus mori Yokoyama from three phytoseiid mite species, Neoseiulus californicus (McGregor), Amblyseius eharai Amitai and Swirski, and Euseius sojaensis (Ehara), collected on peach leaves was conducted. Results showed that the feeding preference for the three phytoseiid mite species was greater for T. kanzawai than for P. mori in the field. PCR amplification of the ITS sequences of Petrobia harti (Ewing) inhabiting Oxalis corniculata L. (Oxalidaceae) showed that phytoseiid mites move from groundcover plants to peach leaves, possibly through ambulatory and aerial dispersal.

施設栽培イチゴにおけるミヤコカブリダニと選択性化学農薬の併用によるハダニ密度抑制効果とハダニ低密度時の生息場所としての花の役割

施設栽培イチゴにおけるミヤコカブリダニと選択性化学農薬の併用によるハダニ密度抑制効果とハダニ低密度時の生息場所としての花の役割