Toxicity of imidacloprid to Galendromus occidentalis, Neoseiulus fallacis and Amblyseius andersoni (Acari: Phytoseiidae) from hops in Washington State, USA

The toxicity of systemic and spray formulations of imidacloprid to Galendromus occidentalis Nesbitt, Neoseiulus fallacis Garman and Amblyseius andersoni (Chant) from hop yards in Washington State was evaluated in laboratory bioassays. The field rate of imidacloprid for hop aphids (0.13 g a.i. l) was highly toxic (100% mortality) to G. occidentalis and N. fallacis but less so (35.6% mortality) to A. andersoni. Half and quarter rates were also highly toxic to G. occidentalis and N. fallacis (79.5-100% mortality) but again had lower toxicity to A. andersoni (8.2-31.3% mortality). Systemic toxicity (via consumption of spider mite motiles feeding on leaf discs cut from imidacloprid-treated (0.13 g a.i. l) dwarf bean plants) was also high for G. occidentalis (98.3% mortality), as was toxicity from dried residues (93-98% mortality). Residual toxicity to N. fallacis was also high (89% mortality). The significance of these results for biological control of spider mites in hops and other crops is discussed.     

Evaluation of extracts and oils of tick-repellent plants from Sweden

Abstract. Leaves of Myrica gale Linnaeus (Myricaceae), Rhododendron tomentosum (Stokes) H. Harmaja (formerly Ledum palustre Linnaeus: Ericaceae) and Artemisia absinthium Linnaeus (Asteraceae) were extracted with organic solvents of different polarities and the essential oils of leaves were obtained by steam distillation. The extracts or oils were tested in the laboratory for repellency against host-seeking nymphs of Ixodes ricinus Linnaeus (Acari: Ixodidae). Rhododendron tomentosum oil, 10%, diluted in acetone, exhibited 95% repellency; R. tomentosum and A. absinthium extracts in ethyl acetate, > 70% repellency; A. absinthium extract in hexane, approximately 62% repellency; and M. gale oil, 10%, approximately 50% repellency on I. ricinus nymphs. Compounds in the leaf extracts or in the oils were collected by solid phase microextraction (SPME) and identified by gas chromatography-mass spectrometry (GC-MS) and/or MS. Characteristic volatiles detected from oil or extract of M. gale were the monoterpenes 1,8-cineole, alpha-terpineol, 4-terpineol and thujenol; and of R. tomentosum myrcene and palustrol. Characteristic volatiles from leaf extracts of A. absinthium were sabinene, oxygenated monoterpenes, e.g. thujenol and linalool, and geranyl acetate. Each plant species synthesized numerous volatiles known to exhibit acaricidal, insecticidal, 'pesticidal' and/or arthropod repellent properties. These plants may be useful sources of chemicals for the control of arthropods of medical, veterinary or agricultural importance.     

Efficacy and persistence of rosemary oil as an acaricide against twospotted spider mite (Acari: Tetranychidae) on greenhouse tomato

Efficacy of rosemary, Rosmarinus officinalis L., essential oil was assessed against twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), as well as effects on the tomato, Lycopersicum esculatum Mill., host plant and biocontrol agents. Laboratory bioassay results indicated that pure rosemary oil and EcoTrol (a rosemary oil-based pesticide) caused complete mortality of spider mites at concentrations that are not phytotoxic to the host plant. The predatory mite Phytoseiulus persimilis Athias-Henriot is less susceptible to rosemary oil and EcoTrol than twospotted spider mite both in the laboratory and the greenhouse. Rosemary oil repels spider mites and can affect oviposition behavior. Moreover, rosemary oil and rosemary oil-based pesticides are nonpersistent in the environment, and their lethal and sublethal effects fade within 1 or 2 d. EcoTrol is safe to tomato foliage, flowers, and fruit even at double the recommended label rate. A greenhouse trial indicated that a single application of EcoTrol at its recommended label rate could reduce a twospotted spider mite population by 52%. At that rate, EcoTrol did not cause any mortality in P. persimilis nor did it affect their eggs. In general, EcoTrol was found to be a suitable option for small-scale integrated pest management programs for controlling twospotted spider mites on greenhouse tomato plants.     

Toxicity and ovicidal activity of different plant extracts on two-spotted spider mite,Tetranychus urticae Koch (Acari: Tetranychidae)

The acaricidial, persistent and ovicidal activities of four methanolic extracts of Anisosciadium orientale DC., Scaligeria meifolia Boiss., Trigonella elliptica Boiss. and Ptelea viscosa L. were assessed against the two-spotted spider mite, Tetranychus urticae Koch, in a bioassay under laboratory conditions. All the extracts exhibited significant adult female mite mortality as compared to control and S. meifolia extract showed highest toxicity based on the LC₅₀ when compared with the other extracts tested. In the persistence test, the mites were exposed to 1, 24, 48 and 72 h old residues of 50% lethal concentration of methanolic extracts. The results showed that the lethal concentration effects of plant extracts fade within two or three days. S. meifolia caused high ovicidal activity (45.84%) followed by A. orientale (41.40%), T. elliptica (40.11%) and P. viscosa (37.66%). The results suggest that the methanolic extracts of A. orientale, S. meifolia, T. elliptica and P. viscosa have the potential to be used in mite pest management.     

Isolation and identification of acaricidal compounds in Inula japonica (Asteraceae)

We identified acaricidal compounds in Inula japonica Thunberg (Asteraceae) that were effective against carmine spider mite, Tetranychus cinnabarinus (Boisduval). Petroleum-ether extracts from I. japonica were toxic to T. cinnabarinus, with a 50% lethal concentration (LC50) value of 1.18 mg/ml. Silica gel column chromatography was used to separate the acaricidal components. Seventeen of 38 fraction groups had mite mortality rates >50%, nine fraction groups had rates >60%, and three fraction groups had rates >80% at 2 mg/ml. The major volatile compounds in the bioactive fraction groups were identified by gas chromatography-mass spectroscopy, and beta-sitosterol (1), stigmasterol (2), lupeol (3), and alpha-amyrin (4) were identified and determined to have acaricidal activity against T. cinnabarinus in vitro.     

Toxicity of plant essential oils to Tetranychus urticae (Acari: Tetranychidae) and Phytoseiulus persimilis (Acari: Phytoseiidae)

Fifty-three plant essential oils were tested for their toxicity against eggs and adults of Tetranychus urticae Koch as well as adults of Phytoseiulus persimilis Athias-Henriot, by using a filter paper diffusion bioassay without allowing direct contact. Responses varied according to oil type and dose, and mite species. In a plastic container (4.5 by 9.5 cm) bioassay at 14 x 10(-3) microl/ml air, caraway seed, citronella java, lemon eucalyptus, pennyroyal, and peppermint oils gave > 90% mortality against adult T. urticae, whereas 82 and 81% mortality was observed with sage and spearmint oils, respectively. With the exception of sage oil, the other six essential oils were highly effective against T. urticae eggs at 9.3 x 10(-3) microl/ml air. Against adult P. persimilis, these six test oils caused > 90% mortality at 7.1 x 10(-3) microl/ml air. Particularly peppermint oil at 4.7 x 10(-3) microl/ml air was highly toxic. In an acrylic cage (30 by 30 by 40 cm ) test, lemon eucalyptus, pennyroyal, peppermint, and spearmint oils were highly effective against adult T. urticae at 1.4 x 10(-3) microl/ml air. These results indicate that the mode of delivery of these essential oils was largely a result of action in the vapor phase via the respiratory system. The essential oils described herein merit further study as potential fumigants for T. urticae control.     

Toxicity of three acaricides to Tetranychus urticae (Tetranychidae: Acari) and Orius insidiosus (Anthocoridae: Hemiptera)

Management for twospotted spider mite, Tetranychus urticae Koch, populations in peanut, Arachis hypogaea L., relies on acaricides. The outcomes of acaricide applications are most predictable when complete information on their toxicity and specificity is available. Specifically, the degrees to which acaricides impact different stages of T. urticae and natural enemies combined determine the overall efficacy of an acaricide application. The objectives of this study were to determine stage-specific direct and residual efficacies of three acaricides (fenpropathrin, etoxazole, and propargite) against T. urticae, and the direct and residual toxicity of the acaricides to Orius insidiosus (Say) adults. Direct toxicity of acaricides to T. urticae was measured on peanut cuttings. All acaricide treatments caused significant mortality to a mixed stage population of T. urticae, and mortality did not differ among the acaricides 7 d after treatment. When toxicity to eggs was tested, the proportion of eggs that hatched for all acaricide treatments was significantly lower than the control, with etoxazole and propargite causing 100% mortality. Exposure to acaricide residues caused < 30% mortality of T. urticae adults 1 and 2 d after treatment and was not significantly different from the control. Fenpropathrin and propargite caused 100% mortality and etoxazole caused > 50% mortality of O. insidious adults after direct exposure to the acaricides. Residual toxicity of acaricides to O. insidiosus adults varied but remained toxic to O. insidiosus longer than to T. urticae. Fenpropathrin had the longest residual effect on O. insidiosus adults, causing > 95% mortality after 14 d; etoxazole and propargite caused < 30% mortality after 14 d.     

Chemical composition and acaricidal properties of Deverra scoparia essential oil (Araliales: Apiaceae) and blends of its major constituents against Tetranychus urticae (Acari: Tetranychidae)

The essential oil of Deverra scoparia Coss. & Durieu was investigated for its acaricidal activity against the worldwide pest twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). The essential oil was analyzed by fast gas chromatography (GC) and GC-mass spectrometry. The activities of its individual and blended constituents were determined. Our study showed that female mortality increased with increasing D. scoparia oil concentrations, with LD50 and LD90 values at 1.79 and 3.2 mg liter(-1), respectively. A reduction in fecundity had already been observed for concentrations of 0.064, 0.08, and 0.26 mg liter(-1) D. scoparia essential oil. Ten major components, comprising 98.52% of the total weight, were identified; a-pinene was the most abundant constituent (31.95%) followed by sabinene (17.24%) and delta3-carene (16.85%). The 10 major constituents of D. scoparia oil were individually tested against T. urticae females. The most potent toxicity was found with alpha-pinene, delta3-carene, and terpinen-4-ol. The presence of all constituents together in the artificial mixture caused a significant decrease in the number of eggs laid by females, at 0.26 mg liter(-1) (11 eggs), compared with the control (50 eggs). The toxicity of blends of selected constituents indicated that the presence of all constituents was necessary to reproduce the toxicity level of the natural oil.     

Laboratory evaluation of avermectin as a selective acaricide for use withMetaseiulus occidentalis (Nesbitt) (acarina: Phytoseiidae)

The suggestion that adding a light oil to avermectin B₁ would increase the toxicity of avermectin to spider mites and reduce its effect on predaceous mites was tested in laboratory trials withTetranychus urticae Koch andMetaseiulus occidentalis (Nesbitt) on almond and bean foliage. No differences were found in the toxicity of avermectin + oil vs. avermectin alone at the doses tested forT. urticae; all (0.025, 0.5, 1, and 5 ppm) were highly toxic. Mortality ofM. occidentalis females and larvae was not different on avermectin + oil vs. avermectin alone, but females produced more progeny on the avermectin + oil-treated foliage. At doses of 0.5 to 5 ppm, avermectin was sufficiently toxic to deplete predator populations in the field. Development of predator larvae on avermectin + oil and on avermectin alone was not different. Avermectin + oil on almond foliage aged outdoors was highly toxic after 96 h toT. urticae adults butM. occidentalis larvae survived well on residues by 96 h.M. occidentalis female survival and productivity were not different from the controls by 48 h. Hence a predator mite population might recover through larvae hatching onto residues. Avermectin + oil (3 ppm) residue on bean foliage held outdoors was still highly toxic toT. urticae after 33 days. In contrast,M. occidentalis females and larvae survived well on 48-to 96-hour-old residues. Neither predators nor spider mites placed on treated foliage (3 ppm) were able to reach untreated foliage in tests using bean plant seedlings with one leaf sprayed and one left unsprayed. Furthermore, whenM. occidentalis females were exposed to 3 ppm avermectin for 300 s or longer, mortality was significant and the fecundity of females that had been exposed for as few as 30 s was reduced significantly. Thus, while avermectin is significantly more toxic toT. urticae than toM. occidentalis, its value as a selective acaricide will depend upon learning to use it at rates that will allow the retention of sufficient prey so that surviving predators can persist. Based on these laboratory tests, such selective doses are likely to lie below 1 ppm and can best be determined in field trials.     

Comparative toxic and sublethal effects of fluvalinate on two-spotted spider mite and European red mite

Four fluvalinate formulations differed in their residual toxicity to female two-spotted spider mite (TSM), Tetranychus urticae adults; the emulsifiable concentrate (EC) was the most toxic. In contrast, there was little difference in toxicity between the formulations with the European red mite (ERM) Panonychus ulmi with the exception of the EC formulation which was the least toxic. Fluvalinate 2F caused minimal (<10%) TSM and ERM egg mortality. Fluvalinate 2F was more toxic and caused greater larval dispersal for the TSM compared to the ERM at the field concentration and below. The toxicity of fluvalinate 2F to TSM and ERM protonymphs, deutonymphs and adults was low, approximately <20% at field concentration. Dispersal was the main response to fluvalinate and this was positively correlated with increasing concentration. The combined mortality and dispersal LC₅₀ was five times lower for ERM protonymphs and adults, but 11 times higher for ERM deutonymphs compared to equivalent TSM life stages. Fluvalinate 2F reduced TSM development from the protonymph and deutonymph stages to a greater extent compared to the ERM. The mortality response to fluvalinate 2F was unaffected by host type (peach or apple) for the TSM whereas ERM mortality was higher on apple compared to peach. TSM dispersal was higher from apple compared to peach whereas ERM dispersal was similar on both host types. Oviposition by both mite species was lower on apple than peach leaves. A 1 h exposure to fluvalinate 2F reduced ERM oviposition for 12 days.     

Acaricidal activity of Juglans regia leaf extracts on Tetranychus viennensis and Tetranychus cinnabarinus (Acari: Tetranychidae)

Leaf extracts of the walnut, Juglans regia L., were evaluated under laboratory conditions to determine their acaricidal activity on the mites Tetranychus cinnabarinus (Boisduval) and Tetranychus viennensis Zacher (Acari: Tetranychidae). Extracts had both contact and systemic toxicity to these mites. The four solvents tested for preparing crude extracts were petroleum ether, chloroform, ethyl acetate, and methanol. Methanol was the most efficient solvent, with an extraction rate from 17.06 + 0.80 to 20.27 +/- 0.28%. Petroleum ether was the least effective solvent, with extraction rates from 2.30 +/- 0.13 to 2.71 +/- 0.13%. However, the crude extracts with petroleum ether resulted in the highest mite mortality (79.04 +/- 0.52%) in a slide dip bioassay. Mites mortalities from the concentrated extracts prepared by chloroform, ethyl acetate, methanol, or distilled water were significantly lower than petroleum ether. The mean lethal concentrations (LC50) of the extracts from petroleum ether, chloroform, ethyl acetate, methanol, and distilled water to the two mite species were 0.73 +/- 0.04, 1.66 +/- 0.28, 4.96 +/- 0.35, 7.45 +/- 0.67, and 9.91 +/- 0.32 mg/ml, respectively. After liquid chromatography and thin-layer chromatography, the concentrated extracts of petroleum ether were separated into eight fractions and tested for acaricidal activity. Fraction 6 produced significantly higher mite mortality rates than the other groups, killing approximately 90% of both species.     

Acaricidal properties of a Chenopodium-based botanical

The emulsifiable concentrate UDA-245 [25% EC (vol:vol)], based on an essential oil extract from Chenopodium ambrosioides variety ambrosioides, a North American herbaceous plant, was compared with commercially available pesticides for their effectiveness to control the adult stage and egg hatch of the twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) and the European red mite, Panonychus ulmi (Koch) (Acari: Tetranychidae). After a laboratory bioassay with adult twospotted spider mites, a 0.5% concentration of UDA-245 was more effective than 0.7% (AI) of neem oil (Neem Rose Defense). After a similar bioassay with the European red mite, a 0.5% concentration UDA-245 was as effective as 0.006% (AI) of abamectin (Avid). UDA-245 at 0.5% significantly reduced egg hatch of the twospotted spider mite, 5 and 9 d after treatment and of the European red mite 6 d after treatment. Egg hatch was significantly lower using 0.006% (AI) of abamectin, 0.7% of neem oil, and 1.0% insecticidal soap than UDA-245. Residual tests indicated that UDA-245 may be persistent in the environment only for a few hours. Only 23% mortality was noted when mites were introduced on bean leaves 1 h after treatment with a 2% concentration of UDA-245. At the recommended dose of 0.5%, UDA-245 was not considered phytotoxic for most plants tested, i.e., lettuce, roses, and tomatoes. Results suggest that a greenhouse integrated pest management program using UDA-245 could effectively and selectively control mite infestations by treating "hot spots" with negligible effect on biological control agents when treating before introduction or when natural enemies are absent.     

Efficacy of Curcuma aeruginosa rhizome and Adhatoda vasica plant extracts, on red spider mite, Tetranychus urticae in Livistona rotundifolia

Queen palm, Livistona rotundifolia foliage contributes greatly in export industry. Red spider mite (RSM) (Tetranychus urticae) infests on the foliage and reduces its affordable market quality. T. urticae is found in dry environment and is one of the phytophagous mite belongs to family Tetranychidae. Different chemicals such as 80% sulphur + Diazinon @ (50g+12ml/10L) are recommended against red spider mite, but these have lesser effect on this tiny mite. Since these chemicals are not environment friendly, Green Farms Ltd., in Sri Lanka prefers to use biological agents for mite management. Extracts of Curcuma aeruginosa rhizome and Adhatoda vasica plant parts were studied separately causing mortality on T. urticae. Field experiments were conducted to study the efficacy of C. aruginosa extract for controlling RSM on L. rotundifolia leaves. Curcuma aruginosa was tested at concentrations of 2, 5, 10, 15, 20 and 25 g/L and a control with equal amount of water. C aruginosa extracts of different concentrations were treated six times at five days interval on the palms separately. Living spider mites and eggs were pre-counted in marked leaves before applying C. aruginosa extracts. Next count was taken a day prior to next spraying. The result revealed that all the concentrations except 2 g/L were found to be effective compared to control. However there was no difference between the concentrations from 5 to 25 g/L. Hence C. aruginosa rhizome extract at its lowest concentration of 5 g/L is equally effective for the control of RSM on L. rotundifolia leaves. In another experiment extracts of Adhatoda vasica bark, leaves, and flower and water as control were applied thrice with three days interval. Pre treatment counting of living spider mites and eggs were taken in marked leaves. Post count was taken a day prior to next spraying. Third and forth counting were done after three days and four weeks from final spraying respectively. The results revealed that bark, flowers were found to be more effective compared to control. Flowers and bark were the best and hence there is no need of third sprayings as almost all the spider mites population were eradicated after second spraying. Flower extraction showed best performance until three months since final spraying. Flower and bark extracts showed higher acaricidal property and leaf showed moderate acaricidal property.     

Potential use of essential oils from Cameroon applied as fumigant or contact insecticides against Sitophilus zeamais Motsch. (Coleoptera: Curculionidae)

Essential oils from seven plants species currently found in Cameroon were extracted by steam distillation and tested for their insecticidal activities against Sitophilus zeamats Motsch. Responses varied with the test applied and the plant species. For the contact toxicity, the acetone was used in order to dilute the pure essential oil. Formulations of 1% of essential oils of Xylopia aethiopica and Ocimum gratissimum were the most toxic and led to 96 and 98% of mortality respectively after 24 h. There was no death in control (0% of mortality). Fumigation test were done by applying 300 microl of pure essential oils in the bottom of closed 800 ml glass containers. In that case, the essential oil of Hyptis spicigera was the most toxic (fumigant) after 48 hours of fumigation followed by Annona seregalensis and Xylopia aethiopica 96 and 95% of mortality respectively. Some of the essential oils of plant species tested are promising for pest control in farmer granaries. However, further investigations are to be done on formulation and side effects.     

Temperature-dependent fumigant activity of essential oils against twospotted spider mite (Acari: Tetranychidae)

Fumigant activity of 34 commercial essential oils was assessed on female adults and eggs of twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) at three temperatures (5, 15, and 25 degrees C). Common thyme, cinnamon, and lemongrass oils were equally effective on twospotted spider mite adults showing 85.8-100% mortality at 5 and 10 microl/liter air at 25 degrees C. At a lower temperature of 15 degrees C, lemongrass and peppermint resulted in > or =90% mortality of adults at 10 microl/liter air. Only lemongrass was relatively active at 5 microl/liter air, at 15 degrees C. At 5 degrees C, lemongrass and peppermint caused significantly higher adult mortality than controls but only at 10 microl/liter air. Common thyme oil showed the highest ovicidal activity at 5 microl/liter air at 25 degrees C. Among the main components of common thyme and lemongrass oils, citral was lethal to twospotted spider mite adults at all tested temperatures. Carvacrol, thymol, and citral caused the same inhibitory effects on the hatch of twospotted spider mite eggs at 25 degrees C. However, citral was more active than other compounds to twospotted spider mite eggs at 15 degrees C. Therefore, we conclude that citral has the best potential for development as a fumigant against twospotted spider mite on agricultural products harvested late in the growing season.     

A comparison of the toxic and sub-lethal effects of fluvalinate and esfenvalerate on the twospotted spider mite (Acari: Tetranychidae)

There was no difference in the direct toxicity of fluvalinate and esfenvalerate to twospotted spider mite (TSSM), Tetranychus urticae Koch. adults. The residual toxicity LC₅₀ of esfenvalerate was lower. Neither pyrethroid was toxic (<10% mortality) to TSSM eggs or adults at their recommended field concentrations. Fluvalinate was twice as toxic (45% mortality) than esfenvalerate to TSSM larvae at 0.01 g.a.i L^-1. The toxicity of the pyrethroids to TSSM protonymphs and deutonymphs was similar (16–28% mortality at 0.1 g a.i. L^-1). Dispersal from the treated surface was the main response to both pyrethroids by TSSM protonymphs, deutonymphs and adults. Maximum run-off by TSSM adults from fluvalinate and esfenvalerate treated surfaces was found with 0.01 and 0.005 g a.i. L^-1 respectively. Spin-down from pyrethroid treated surfaces was positively correlated with concentration. Oviposition was negatively correlated with concentration. Fluvalinate caused greater reductions in oviposition than esfenvalerate. Both pyrethroids reduced TSSM development rate from larval, protonymph and deutonymph stages, but fluvalinate caused larger reductions. Both pyrethroids prevented mating: for ten days oviposition 93% and 98% of offspring were male for esfenvalerate and fluvalinate respectively at 0.1 g a.i. L^-1. These findings are discussed with respect to the incidence of pyrethroid induced mite outbreaks.     

The invasive spider mite Tetranychus evansi (Acari: Tetranychidae) alters community composition and host-plant use of native relatives

The tomato spider mite Tetranychus evansi Baker and Pritchard (Acari: Tetranychidae), is a worldwide pest of solanaceous crops that has recently invaded many parts of the world. In the present study we examined the ecological impact of its arrival in the Mediterranean region. The spider mite and phytoseiid mite assemblages in various crop and non-crop plants in three areas of Valencia (Spain) were studied a few months before and 10 years after the invasion of T. evansi. According to rarefaction analyses, the invasion of T. evansi did not affect neither the total number of species in the mite community examined (spider mite and phytoseiid species) nor the number of species when the two communities were examined separately. However, after the invasion, the absolute and relative abundance of the native Tetranychus species was significantly reduced. Before the invasion, T. urticae and T. turkestani were the most abundant spider mites, accounting for 62.9 and 22.8 % of the specimens. After the invasion, T. evansi became the most abundant species, representing 60 % of the total spider mites recorded, whereas the abundance of T. urticae was significantly reduced (23 %). This reduction took place principally on non-crop plants, where native species were replaced by the invader. Null model analyses provided evidence for competition structuring the spider mite community on non-crop plants after the invasion of T. evansi. Resistance to acaricides, the absence of efficient native natural enemies, manipulation of the plant defenses and the web type produced by T. evansi are discussed as possible causes for the competitive displacement.     

Gene Pyramiding of Peptidase Inhibitors Enhances Plant Resistance to the Spider Mite Tetranychus urticae

The two-spotted spider mite Tetranychus urticae is a damaging pest worldwide with a wide range of host plants and an extreme record of pesticide resistance. Recently, the complete T. urticae genome has been published and showed a proliferation of gene families associated with digestion and detoxification of plant secondary compounds which supports its polyphagous behaviour. To overcome spider mite adaptability a gene pyramiding approach has been developed by co-expressing two barley proteases inhibitors, the cystatin Icy6 and the trypsin inhibitor Itr1 genes in Arabidopsis plants by Agrobacterium-mediated transformation. The presence and expression of both transgenes was studied by conventional and quantitative real time RT-PCR assays and by indirect ELISA assays. The inhibitory activity of cystatin and trypsin inhibitor was in vitro analysed using specific substrates. Single and double transformants were used to assess the effects of spider mite infestation. Double transformed lines showed the lowest damaged leaf area in comparison to single transformants and non-transformed controls and different accumulation of H(2)O(2) as defence response in the leaf feeding site, detected by diaminobenzidine staining. Additionally, an impact on endogenous mite cathepsin B- and L-like activities was observed after feeding on Arabidopsis lines, which correlates with a significant increase in the mortality of mites fed on transformed plants. These effects were analysed in view of the expression levels of the target mite protease genes, C1A cysteine peptidase and S1 serine peptidase, identified in the four developmental mite stages (embryo, larvae, nymphs and adults) performed using the RNA-seq information available at the BOGAS T. urticae database. The potential of pyramiding different classes of plant protease inhibitors to prevent plant damage caused by mites as a new tool to prevent pest resistance and to improve pest control is discussed.     

Efficacy of Elettaria cardamomum L. (Zingiberaceae) essential oil on the two spotted spider mite,Tetranychus urticae Koch (Acari: Tetranychidae)

Two-spotted spider mite, Tetranychus urticae Koch is the major pest of various plants worldwide. Now the control is dependent on the use of chemical pesticides. Plant compounds are recently known as biopesticides. Essential oil of Elettaria cardamomum was researched on repellent and oviposition inhibition of T. urticae. The LC₅₀ values of fumigant toxicity of this oil on adults and eggs of the two spotted spider mite were 7.26 and 8.82?μL/L air, respectively. Also LT₅₀ value of essential oil at 45?μL/L air was 23.86?h and LT₅₀ value of essential oil at 60?μL/L air was 9.01?h. In addition, different concentrations of the essential oil of E. cardamomum significantly affected oviposition deterrence and repellency of adults. The results of this study indicated that essential oil of E. cardamomum may be considered as a biopesticide to control two spotted spider mites.     

Differences among plant species in acceptance by the spider mite Tetranychus urticae Koch

Abstract:  The spider mite Tetranychus urticae Koch has a broad range of host plants. However, the spider mite does not accept all plants to the same degree because of differences in nutritive and toxic constituents. Other factors, such as the induction of secondary metabolites, the morphology of a leaf surface and the presence of natural enemies, also play an important role in plant acceptance. We compared plants from various families in their degree of acceptance by the spider mite, to get an indication of the plant's direct defence. Glycine max (soybean), Humulus lupulus (hop), Laburnum anagyroides (golden chain) and Nicotiana tabacum (tobacco) were highly accepted by the spider mites. Different glandular hair densities among tobacco cultivars did not affect their suitability towards spider mites significantly. Solanum melalonga (eggplant), Robinia pseudo-acacia (black locust), Vigna unguiculata (cowpea) and Datura stramonium (thorn apple) were accepted by the spider mites to a lesser degree. Vitis vinifera (grapevine) was poorly accepted by the spider mite. It might be that the food quality of the leaves was not high enough to arrest the spider mites. Also, Capsicum annuum (sweet pepper) and especially Ginkgo biloba (ginkgo) were poorly accepted by the spider mite, probably because of the presence and concentration of certain of the secondary metabolites in the leaves. The spider mites accepted all the plants belonging to the Fabaceae for feeding, but those belonging to the Solanaceae showed a larger variance in spider mite acceptance varying from well accepted (tobacco) to poorly accepted (sweet pepper).