Biological control of twospotted spider mite, <Emphasis Type="Italic">Tetranychus urticae</Emphasis>, with predatory mite, <Emphasis Type="Italic">Neoseiulus californicus</Emphasis>, in strawberries

Greenhouse and field experiments were conducted from 2005 to 2007 to determine the effectiveness of different release times with the predatory mite, Neoseiulus californicus (McGregor), for control of the twospotted spider mite (TSSM), Tetranychus urticae Koch, in strawberries (Fragaria x ananassa Duchesne). The effect of N. californicus releases over time and on development of TSSM populations during a growing season were evaluated. Our hypothesis was that repeated applications of N. californicus, which is currently recommended by biological control companies, might be unnecessary to attain season-long control of TSSM. In greenhouse trials, three treatments consisting of releases of N. californicus at five-day intervals: day 0, day 5, and day 10, and an untreated control were evaluated. The treatment releases significantly reduced TSSM below the control within five days of each release. Neoseiulus californicus significantly reduced TSSM in treatments with high densities (leaflets with ≥ 40 TSSM) below that of treatments with lower densities (leaflets with ≤ 10 TSSM) demonstrating that if released at a predator: prey ratio of 1:10, timing of release does not alter the effectiveness of N. californicus in controlling TSSM. However, we found that if the ratio of predator: prey remains adequate, N. californicus is a more efficient predator at high TSSM densities. Field studies included three treatments consisting of releases of N. californicus at one-month intervals. All treatments significantly reduced TSSM compared with the control plots (no releases). Releases applied early in the season sustained TSSM significantly below those in the control plots for the whole season. Our results indicate that one release of N. californicus is able to sustained control of TSSM in strawberry throughout a growing season if released when TSSM populations are low early in the season in the southeastern United States.     

Toxicity of some insecticides to <Emphasis Type="Italic">Tetranychus urticae</Emphasis>, <Emphasis Type="Italic">Neoseiulus californicus</Emphasis> and <Emphasis Type="Italic">Tydeus californicus</Emphasis>

Three mite species are frequently found on vegetable crops in Italy: the pest Tetranychus urticae Koch (Acari: Tetranychidae), the predator Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) and the unspecialised feeder Tydeus californicus (Banks) (Acari: Tydeidae). In laboratory trials, the direct and residual effects of six insecticides recommended for the control of aphids, whiteflies and thrips in vegetable crops, (Biopiren® plus (pyrethrins), Confidor® (imidacloprid), Oikos® (azadirachtin), Plenum® (pymetrozine), Naturalis® (Beauveria bassiana) and Rotena® (rotenone)), were evaluated for the three mite species. All the products affected the mites and their effect was often favourable towards T. urticae and unfavourable towards N. californicus and T. californicus. Rotenone was more toxic to eggs than females of T. urticae. It was highly toxic to N. californicus and caused the death of all treated females of T. californicus. Pyrethrins and imidacloprid increased T. urticae fecundity, but decreased fecundity of N. californicus. Imidacloprid decreased T. californicus fecundity more than pyrethrins. Beauveria bassiana was not toxic to T. urticae and T. californicus, but induced high mortality in the progeny of treated females of N. californicus. Azadirachtin and pymetrozine were the least toxic to T. urticae and N. californicus, but decreased production of larvae in T. californicus. Implications for integrated pest management on vegetables are discussed.     

The predatory mite <Emphasis Type="Italic">Neoseiulus womersleyi</Emphasis> (Acari: Phytoseiidae) follows extracts of trails left by the two-spotted spider mite <Emphasis Type="Italic">Tetranychus urticae</Emphasis> (Acari: Tetranychidae)

As it walks, the two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) spins a trail of silk threads, that is followed by the predatory mite, Neoseiulus womersleyi Schicha (Acari: Phytoseiidae). Starved adult female N. womersleyi followed T. urticae trails laid down by five T. urticae females but did not follow a trail of one T. urticae female, suggesting that the amount of spun threads and their chemical components should correlate positively with the number of T. urticae individuals. To examine whether chemical components of T. urticae trails are responsible for the predatory mite’s trail following, we collected separate T. urticae threads from the exuviae and eggs, and then washed the threads with methanol to separate chemical components from physical attributes of the threads. Female N. womersleyi did not follow T. urticae trails that had been washed with methanol but contained physical residues, but they did follow the direction to which the methanol extracts of the T. urticae trails was applied. These results suggest that the predatory mite follows chemical, not physical, attributes of T. urticae trails.     

Potential long-term storage of the predatory mite <Emphasis Type=Italic>Phytoseiulus</Emphasis><Emphasis Type=Italic>persimilis</Emphasis>

Increasing the ability to store mass-reared natural enemies during periods or seasons of low demand is a critical need of the biocontrol industry. We tested the hypothesis that chemicals can enhance long-term cold storage of a predatory mite Phytoseiulus persimilis Athias-Henriot. The research objective was to determine the effect of cryoprotectant and carbohydrate chemicals on in-storage survival of predators. In-storage survival at 8°C was greater for predators sprayed with glycerol (5%, v/v) or glucose (10% and 20%, v/v) than with water spray controls. After 74 days in the cryoprotectant experiment, predator survival declined to 11.5% in the 5% glycerol treatment and 7.8% in the water spray control. After 88 days in the carbohydrate experiment, predator survival declined to 22% in the 20% glucose treatment and 2% in the water spray control. Although many individuals expired within 50 days in both experiments, a few females survived more than 200 days. This research suggests that select cryoprotectants and carbohydrates have a limited capacity to facilitate long-term storage of P. persimilis.     

Effects of adjuvant and conidial concentration on the efficacy of <Emphasis Type=Italic>Beauveria bassiana</Emphasis> for the control of the two spotted spider mite, <Emphasis Type=Italic>Tetranychus urticae</Emphasis>

Greenhouse experiments were conducted on various crops (cucumber, tomato, eggplant, green bean) to ascertain the effects of Break-thru^® (polyether-polymethylsiloxane-copolymer, a silicone surfactant) and an oil emulsion, on Beauveria bassiana (Balsamo) Vuillemin (Bb) applications for the control of the two spotted spider mite, Tetranychus urticae Koch. The objectives were to compare a) the efficacy of Bb control when applied in aqueous Break-thru^® or an oil emulsion; b) the effects of various concentrations of Bb conidia, as affected by each surfactant; and c) the effects of Break-thru^® on the activity of the fungus. Conidia were suspended either in an aqueous Break-thru^® or an emulsifiable formulation at different conidial concentrations (1.05 × 10⁶, 2.1 × 10⁶ and 4.2 × 10⁶ conidia ml^?1) and sprayed onto leaves 2 weeks after artificial pest inoculation. Two sprays were performed, with an interval of one week from one spray to another, and T. urticae population counts (both motile and egg stages) were made on plant leaves 7 days after each spray. Bb conidia in Break-thru^® were more efficacious than conidia in emulsifiable formulation. With the highest rate of conidia (4.2 × 10⁶ conidia ml^?1), mortality of adult mites ranged from 60 ± 4.2 (mean ± SE) to 85.7 ± 4.3% in the Break-thru^® suspension and 39.4 ± 7 to 61.3 ± 6% in the oil emulsion. Leaf damage index was also substantially reduced from 70% in the unsprayed control to 40% by the application of Bb conidia at the highest rate with Break-thru^®. Break-thru^® can be combined with Bb in the integrated management of T. urticae and Isolate R444 is a promising candidate for the control of the pest.     

UV-B susceptibility and photoreactivation in embryonic development of the two-spotted spider mite, <Emphasis Type="Italic">Tetranychus urticae</Emphasis>

Developmental errors are often induced in the embryos of many organisms by environmental stress. Ultraviolet-B radiation (UV-B) is one of the most serious environmental stressors in embryonic development. Here, we investigated susceptibility to UV-B (0.5 kJ m^?2) in embryos of the two-spotted spider mite, Tetranychus urticae, to examine the potential use of UV-B in control of this important agricultural pest worldwide. Peak susceptibility to UV-B (0% hatchability) was found in T. urticae eggs 36–48 h after oviposition at 25 °C, which coincides with the stages of morphogenesis forming the germ band and initial limb primordia. However, hatchability recovered to?~?80% when eggs irradiated with UV-B were subsequently exposed to visible radiation (VIS) at 10.2 kJ m^?2, driving photoreactivation (the photoenzymatic repair of DNA damage). The recovery effect decreased to 40–70% hatchability, depending on the embryonic developmental stage, when VIS irradiation was delayed for 4 h after the end of exposure to UV-B. Thus UV-B damage to T. urticae embryos is critical, particularly in the early stages of morphogenesis, and photoreactivation functions to mitigate UV-B damage, even in the susceptible stages, but immediate VIS irradiation is needed after exposure to UV-B. These findings suggest that nighttime irradiation with UV-B can effectively kill T. urticae eggs without subsequent photoreactivation and may be useful in the physical control of this species.     

Effects of azadirachtin on the two-spotted spider mite, <Emphasis Type="Italic">Tetranychus urticae</Emphasis> (Acari: Tetranychidae)

Effects of sublethal azadirachtin exposure to the biological performance of Tetranychus urticae Koch was studied under laboratory conditions. Bioassay was used to asses the effect of different concentrations of azadirachtin on longevity, fecundity, fertility, and offspring development. Azadirachtin (64 and 128 ppm) affected fecundity and mortality but had no effect on fertility and offspring development. A subsequent life-table study with 80 ppm of azadirachtin found that the compound caused a reduction of 50% in survival to adult stage. The peak of reproduction was reached at 5 days causing a decrease in the mean fecundity to almost eight times than of untreated females. The net reproductive rate (R ₀), the intrinsic rate of increase (r _m), and the finite rate of increase () of treated females were lower. Treatment showed a negative value of r _m, resulting in a declining population. These results suggest that azadirachtin could be incorporated in Integrated Pest Management (IPM) programmes of T. urticae.This revised version was published online in May 2005 with a corrected cover date.     

Vasa expression and germ-cell specification in the spider mite <Emphasis Type="Italic">Tetranychus urticae</Emphasis>

The specification of germ cells is an important process during the development of all animals. Expression of an evolutionarily conserved gene such as vasa can be used as a marker for germ cell fate. We have isolated a vasa-related gene from the two-spotted spider mite (Tetranychus urticae) and used it to examine the segregation of germ cells in this animal. In spider mites, vasa expression first appears in a group of cells that do not join the initial blastoderm surface. Instead, these cells remain in the interior of the blastoderm and then migrate to posterior regions of the embryo, where they form a cluster that appears in regions of the embryo consistent with the gonads. The expression pattern of this spider mite vasa homologue implies a novel process acts to specify germ cells in this species and that the specification of germ cells is an evolutionarily labile process.     

Effects of anoxia and hypoxia on the two-spotted spider mite, <Emphasis Type="Italic">Tetranychus urticae</Emphasis> (Acari: Tetranychidae)

We investigated the potential use of anoxic (0% O₂) and hypoxic (lower O₂ concentration than in the atmosphere) conditions for controlling the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). Adult T. urticae females were exposed to O₂ concentrations of 0, 0.5, 1, 2, or 21% (control) with a constant CO₂ concentration of 0.05% at 1 atm and 25 °C under continuous darkness for 24 h. The survival and fecundity at 8 days after treatment significantly decreased when the O₂ concentration was lower than 0.5% and 1%, respectively; the lethal concentration at 50% survival (LC₅₀) was 0.55%. The miticidal hypoxic condition (0.5% O₂) led to physiological disorders in host plants. The degree of physiological disorders differed among the plant species tested. Although tomato seedlings died after the hypoxia treatment, in kidney bean and cucumber seedlings the primary leaves remained and lateral buds developed instead of the apical buds that ceased. Hypoxia treatment could be useful as a physical measure for controlling spider mites depending on plant species or cultivars.     

Arbuscular mycorrhizal symbiosis increases host plant acceptance and population growth rates of the two-spotted spider mite <Emphasis Type="Italic">Tetranychus urticae</Emphasis>

Most terrestrial plants live in symbiosis with arbuscular mycorrhizal (AM) fungi. Studies on the direct interaction between plants and mycorrhizal fungi are numerous whereas studies on the indirect interaction between such fungi and herbivores feeding on aboveground plant parts are scarce. We studied the impact of AM symbiosis on host plant choice and life history of an acarine surface piercing-sucking herbivore, the polyphagous two-spotted spider mite Tetranychus urticae. Experiments were performed on detached leaflets taken from common bean plants (Phaseolus vulgaris) colonized or not colonized by the AM fungus Glomus mosseae. T. urticae females were subjected to choice tests between leaves from mycorrhizal and non-mycorrhizal plants. Juvenile survival and development, adult female survival, oviposition rate and offspring sex ratio were measured in order to estimate the population growth parameters of T. urticae on either substrate. Moreover, we analyzed the macro- and micronutrient concentration of the aboveground plant parts. Adult T. urticae females preferentially resided and oviposited on mycorrhizal versus non-mycorrhizal leaflets. AM symbiosis significantly decreased embryonic development time and increased the overall oviposition rate as well as the proportion of female offspring produced during peak oviposition. Altogether, the improved life history parameters resulted in significant changes in net reproductive rate, intrinsic rate of increase, doubling time and finite rate of increase. Aboveground parts of colonized plants showed higher concentrations of P and K whereas Mn and Zn were both found at lower levels. This is the first study documenting the effect of AM symbiosis on the population growth rates of a herbivore, tracking the changes in life history characteristics throughout the life cycle. We discuss the AM-plant-herbivore interaction in relation to plant quality, herbivore feeding type and site and the evolutionary implications in a multi-trophic context.     

Preference and performance of the two-spotted spider mite <Emphasis Type="Italic">Tetranychus urticae</Emphasis> (Acari: Tetranychidae) on strawberry cultivars

The first record of human infestation and feeding by the native tick species Ixodes australiensis is reported in Australia based on a specimen collected from an adult male. Human infestation by ticks in Australia is reviewed and a concise list of anthropophagic ticks occurring in Australia is presented.     

Sublethal effects of spirodiclofen on life history and life-table parameters of two-spotted spider mite (<Emphasis Type="Italic">Tetranychus urticae</Emphasis>)

Laboratory bioassays were conducted to evaluate the effects of spirodiclofen on life history and life-table parameters of two-spotted spider mite (Tetranychus urticae Koch) females treated at pre-ovipositional period with a series of acaricide concentrations starting with the concentration discriminative for eggs and immatures i.e. the lowest concentration that causes 100% mortality of those stages. After a 24 h exposure, the proportion of females that survived treatments was 0.71 (6 mg/l), 0.51 (12 mg/l), 0.41 (24 mg/l), 0.30 (48 mg/l) and 0.25 (96 mg/l). At the end of the trial, the survival rate of females treated with the lowest concentration was significantly lower than the survival rate of untreated females but it remained above that of females treated with higher concentrations. Total fecundity/fertility significantly decreased as concentrations of spirodiclofen increased. Viable eggs were laid by females treated with 6, 12 and 24 mg/l, and total fertility was reduced by 42, 84 and 97%, respectively. Compared with control, the gross fecundity/fertility of the treated females was significantly reduced throughout the trial, except in females treated with 6 mg/l. All concentrations caused a significant reduction in the net fecundity/fertility throughout the trial. The females treated with 12 mg/l had significantly reduced net reproductive rate (R ₀ = 6.45), compared to females treated with 6 mg/l (R ₀ = 23.35) and to untreated females (R ₀ = 28.92); there was no significant difference between the last two treatments. The intrinsic rate of increase (r _m ) and finite rate of increase (λ) were significantly reduced in treated females (r _m = 0.141, λ = 1.156 and r _m = 0.214, λ = 1.232; 12 and 6 mg/l, respectively), compared to control (r _m = 0.251, λ = 1.276). The reduction was significantly greater in females treated with the highest concentration. As a result of the lowered r _m , the doubling time in treated females was significantly extended. Sublethal effects of spirodiclofen and its impact on T. urticae management are discussed.     

Antixenosis and antibiosis response of common bean (<Emphasis Type="Italic">Phaseolus vulgaris</Emphasis>) to two-spotted spider mite (<Emphasis Type="Italic">Tetranychus urticae</Emphasis>)

The two-spotted spider mite, Tetranychus uticae Koch (Acari: Tetranychidae), is globally one of the most devastating pests that feed on numerous crops, including common bean (Phaseolus vulgaris L.). This study was aimed to evaluate the effects of genotype and morphological attributes of common bean on T. uticae. Forty common bean accessions were used to investigate antixenosis and antibiosis through assessing mite feeding preference and reproduction under laboratory conditions. Three resistant (i.e., 56, 63, 238) and two susceptible (i.e., 182, 236) accessions, along with cultivars Naz (resistant) and Akhtar (susceptible), were used in a life-table study. Both antixenosis and antibiosis mechanism were observed in all of the accessions, albeit a negative correlation occurred. Significant differences were observed for all traits of T. urticae: developmental time of immature stages, reproduction, adult longevity and life-table parameters. Based on the intrinsic rate of increase, the accessions 56, 63, 182, 238, and cv. Naz impose high antibiotic effects on T. urticae. Although significant variation existed among accessions for morphological factors, only glandular trichomes correlated with mite fecundity and feeding preference.     

Acaricidal property of the essential oil from <Emphasis Type="Italic">Lippia gracilis</Emphasis> against <Emphasis Type="Italic">Tetranychus urticae</Emphasis> and a natural enemy, <Emphasis Type="Italic">Neoseiulus californicus</Emphasis>, under greenhouse conditions

The essential oil from the leaves of Lippia gracilis was investigated for fumigant and residual activity against Tetranychus urticae (Acari: Tetranychidae) and Neoseiulus californicus (Acari: Phytoseiidae). The results were compared to eugenol, Ortus^® and Azamax^®, as positive controls. Gas chromatography (GC) and GC/mass spectrometry analysis enabled the identification of 28 compounds, accounting for 99.1?±?0.6% of the essential oil. The major constituents were carvacrol (61%), p-cymene (11%) and thymol (11%). Mites were more susceptible to the oil in fumigant tests than in residual tests. Among the components, thymol and β-caryophyllene had the greatest fumigant and residual toxicity against T. urticae, respectively. The role of selected constituents (carvacrol, p-cymene, thymol, limonene, β-pinene, 1,8-cineole, terpinolene and β-caryophyllene) in the acaricidal properties of the L. gracilis essential oil is also discussed. Fumigant and residual effects of Lippia oil were more selective than eugenol with regard to a natural enemy of T. urticae, Neoseiulus californicus. Experiments under greenhouse conditions demonstrated greater toxicity of the Lippia oil in comparison to the positive control at 24, 48 and 72 h after treatment. The results suggest that Lippia oil is a good candidate for the formulation of a botanical acaricide for the integrated management of T. urticae.     

Hexadecanoid pathway in plants: Lipoxygenase dioxygenation of (7<Emphasis Type=Italic>Z</Emphasis>,10<Emphasis Type=Italic>Z</Emphasis>,13<Emphasis Type=Italic>Z</Emphasis>)-hexadecatrienoic acid

7,10,13-Hexadecatrienoic acid (16:3) is abundant in many plant species. However, its metabolism through the lipoxygenase pathway is not sufficiently understood. The goal of present work was to investigate the oxygenation of 16:3 by different plant lipoxygenases and to study the occurrence of oxygenated derivatives of 16:3 in plant seedlings. The recombinant maize 9-lipoxygenase specifically converted 16:3 into (7S)-hydroperoxide. Identification of this novel oxylipin was substantiated by data of GC-MS, LC-MS/MS, ¹H-NMR, and 2D-COSY as well as by deuterium labeling from [²H₆]16:3. Soybean lipoxygenase 1 produced 91% (11S)-hydroperoxide and 6% racemic 14-hydroperoxide. Recombinant soybean lipoxygenase 2 (specifically oxidizing linoleate into 13-hydroperoxide) lacked any specificity towards 16:3. Lipoxygenase 2 produced 7-, 8-, 10-, 11-, 13-, and 14-hydroperoxides of 16:3, as well as a significant amount of bis-allylic 9-hydroperoxide. Seedlings of several examined plant species possessed free hydroxy derivatives of 16:3 (HHTs), as well as their ethyl esters. Interestingly, HHTs occur not only in “16:3 plants”, but also in typical “18:3 plants” like pea and soybean seedlings.     

<Emphasis Type=Italic>Boletus kermesinus</Emphasis>, a new species of <Emphasis Type=Italic>Boletus</Emphasis> section <Emphasis Type=Italic>Luridi</Emphasis> from central Honshu,Japan

Boletus kermesinus, a new species of Boletus section Luridi, is fully described and illustrated based on the materials collected in subalpine coniferous forests of central Honshu, Japan. It has distinctive features of dark-red basidiomata having distinct viscidity in the pileus surface, usually unchanging flesh, discolorous red pores, and an entirely reticulate stipe becoming coarsely lacerate-rimose with age.     

Consumption rate and functional response of the predaceous mite<Emphasis Type="Italic"> Kampimodromus aberrans</Emphasis> to two-spotted spider mite <Emphasis Type="Italic">Tetranychus urticae</Emphasis> in the laboratory

Prey stage preference of female Kampimodromus aberrans (Oudemans) (Phytoseiidae) at constant densities of different stages of Tetranychus urticae Koch (Tetranychidae), functional response types and parameters of the predator females to the varying densities of eggs, larvae, protonymphs and deutonymps of T. urticae were determined in order to establish its potential for the mite biological control. Experiments were conducted at 25 ± 1°C, 65 ± 10% RH and 16:8 (L:D) photoperiod. Our results indicated that the predator consumed significantly more prey larvae than other prey stages. Functional response type of predator was determined by a logistic regression model. The predator exhibited a Type II response on all prey stages. The attack rate (α) and handling time (T _h ) coefficients of a Type II response were estimated by fitting a “random-predator” equation to the data. The lowest estimated value α and the highest value of T _h (including digestion) were obtanined for the predator feeding on deutonmph. The lowest value of T _h were obtained for the predator feeding on prey larvae, but the attack rate value obtained on larva wasn’t different than that obtained on egg and protonymph. According to our results, K. aberrans could be an efficient biological control agent of T. urticae at least at low prey densities. However, further field based studies are needed to draw firm conclusions.