How to visualize the spider mite silk?

Tetranychus urticae (Acari: Tetranychidae) is a phytophagous mite that forms colonies of several thousand individuals. Like spiders, every individual produces abundant silk strands and is able to construct a common web for the entire colony. Despite the importance of this silk for the biology of this worldwide species, only one previous study suggested how to visualize it. To analyze the web structuration, we developed a simple technique to dye T. urticae'silk on both inert and living substrates. Fluorescent brightener 28 (FB) (Sigma F3543) diluted in different solvents at different concentrations regarding the substrate was used to observe single strands of silk. On glass lenses, a 0.5% dimethyl sulfoxide solution was used and on bean leaves, a 0.1% aqueous solution. A difference of silk deposit was observed depending the substrate: rectilinear threads on glass lenses and more sinuous ones on bean leaves. This visualizing technique will help to carry out future studies about the web architecture and silk used by T. urticae. It might also be useful for the study of other silk-spinning arthropods. Microsc. Res. Tech. 2009. © 2009 Wiley-Liss, Inc.     

Quantitative and temporal analysis of effects of twospotted spider mite (acari: Tetranychidae) female sex pheromone on male guarding behavior

Responses of male twospotted spider mite,Tetranychus urticae (Koch), to female sex pheromone were described by a glass slide bioassay and computerized pathway digitizer. Pheromone was extracted from quiescent deutonymphs and fractionated by HPLC, and responses of guarding males to each fraction, all fractions combined, unfractionated extract, and a hexane control were bioassayed for 6 min. Mean angular velocities, linear velocities, percent time stationary, and distance from the 3-mm-diameter treatment circle were calculated for each mite at 20-sec intervals and these behavioral parameters regressed on time. Analysis of variance of regression-equation intercepts showed that no differences in initial male angular velocities were observed among treatments, but initial linear velocities were greater in response to all fractions combined and to extract than to individual fractions, and greater in response to individual fractions than to the control. Angular velocities decreased and linear velocities increased more rapidly in response to individual fractions than to all fractions combined and extract, while males turned preferentially in one direction and were stationary (no displacement) more often in response to all-fraction combinations than to individual fractions and the control. Significant differences were observed among the parameter values elicited by individual fractions, suggesting that active fractions differed qualitatively. The described changes in movement parameters show that maleT. urticae response to presence of pheromone occurs almost immediately, and that multiple pheromonal components are necessary to elicit maximum male response. The overall effect of pheromonal components was to decrease the rate at which males moved away from the treatment cycle, thereby causing male arrestment.     

Prior exposure to carbaryl alters behavior ofTetranychus urticae Koch on acaricide-treated leaf surfaces

Preadult exposure to carbaryl affected the subsequent behavior of two-spotted spider mites (Tetranychus urticae Koch) on leaf surfaces with discontinuous acaricide residues. In dicofol bioassays, preexposure to carbaryl caused a loss of avoidance behavior (eliminating the tendency of mites to feed and stand longer off treated areas). In amitraz bioassays, preexposure to carbaryl had the opposite effect. It increased the propensity of mites to feed and stand off amitraz-treated areas, resulting in increased avoidance of amitraz. Carbaryl preexposure therefore resulted in diametrically opposed behavioral changes in subsequent encounters with two acaricides. These effects provide additional evidence of the unpredictable nature of interactions between pesticides and show how a chemical, irrespective of degree of toxicity, can alter the behavior of arthropods in response to subsequent chemical encounters.     

Arrestment of male twospotted spider mite caused by female sex pheromone

A glass slide bioassay was used to evaluate male twospotted spider mite,Tetranychus urticae Koch, arrestment caused by quiescent deutonymph extract. Males that were guarding quiescent deutonymphs prior to being tested were arrested by a 3-mm-diameter circle of quiescent deutonymph extract; nonguarding males and adult females were not arrested. Extracts of allT. urticae instars tested caused male arrestment, but mean arrestment duration was longest with quiescent deutonymph extract. Arrestment by volatile perception of pheromone and upwind orientation to point sources of extract were not observed. The mono- and sesquiterpene alcohols previously identified as components of the pheromone did not arrest males. HPLC separation of extract resulted in four active fractions; a subtractive bioassay showed that three were essential to elicit maximum male response.     

Vitamin a deficiency modifies response of predatory miteAmblyseius potentillae to volatile kairomone of two-spotted spider mite,Tetranychus urticae

A volatile kairomone of the two-spotted spider mite,Tetranychus urticae, elicits a searching response of the phytoseiid predatorAmblyseius potentillae, only when the predator is reared on a carotenoid-free diet. However, after addition of crystalline -carotene or vitamin A acetate to the predator's rearing diet this searching response was absent. Because vitamin A and -carotene are indispensable nutrients for diapause induction, the carotenoid-deficient predators increase their fitness by searching for two-spotted spider mites, when other spider mites are unavailable. Two-spotted spider mites, among others, contain the carotenoids required for diapause induction, but are an inferior prey due to the dense webbing they produce. When the predators have carotenoids at their disposal, they do better by searching for other spider mites that are more profitable in terms of reproductive success. Such a prey is the European red spide mite,Panonychus ulmi. The volatile kairomone of this prey elicits a searching response of the predator whether it has a carotenoid deficiency or not.     

Absence of farnesol in strawberry and hop foliage

The farnesol content of foliage has been proposed as an indicator of susceptibility to the two-spotted spider mite in various crops. The use of this chemical marker was investigated for strawberry and hop varieties. No farnesol was detectable in any of the varieties tested. The techniques necessary for analysis and identification of farnesol from foliage are discussed.     

Influence of monoterpene vapors on spruce spider mite,Oligonychus ununguis,adult females

Adult female spruce spider mite,Oligonychus ununguis (Jacobi), were exposed to various concentrations of four host conifer monoterpene vapors (limonene,-pinene,-pinene, and ³-carene) for 24 hr to determine the lethal and sublethal effects. All four compounds were toxic to the mites. Further, at concentrations below the calculated LC₅₀s, all four compounds decreased oviposition by the mites and three of the compounds (limonene,-pinene, and-pinene) influenced movement. WhereasO. ununguis populations may not normally be exposed to high concentrations of host monoterpenes, trees continuously emit some monoterpene vapors, and when trees are damaged or under stress, oleoresin may accumulate at points on the external surface of tree tissues thereby exposing mites to the influence of monoterpene vapors.     

Strawberry resistance toTetranychus urticae Koch: Effects of flower,fruit, and foliage removal—comparisons of air- vs. nitrogen-entrained volatile compounds

An increase in resistance to the two-spotted spider mite (TSSM),Tetranychus urticae Koch, is observed in field-grown strawberry plants during the period from flowering to postharvest. This seasonal phenomenon was investigated to determine the influence of the metabolic sink, that is, fruiting in the plant. Removal of flowers and fruit and partial removal of foliage did not alter the pattern of resistance of the strawberry plant to TSSM. Bioassays were conducted in concert with chemical analyses. Headspace chemicals emitted from foliage samples were entrained in air and trapped on Tenax, identified, and compared with those entrained in nitrogen and trapped. Terpenes were among the major compounds entrained in air, whereas alcohols were obtained with nitrogen. The air-entrained headspace compounds did not appear to correlate quantitatively with the development of mite resistance in the control plants or those subjected to metabolic sink (flower and fruit) removal. Evidence was obtained for the presence of heretofore unreported strawberry foliage headspace components, namely, (Z)-3-hexenyl 2-meth-ylbutyrate, (Z)-3-hexenyl tiglate, (E)--ocimene, (Z)--ocimene, -farnesene, and germacrene D.     

Volatile herbivore-induced terpenoids in plant-mite interactions: Variation caused by biotic and abiotic factors

Plants may defend themselves against herbivores by enhancing the effectiveness of natural enemies of herbivores. This is termed indirect defense, which may be induced by herbivore damage. An important aspect of induced indirect defense is the attraction of the herbivore's natural enemies to infested plants by the plant emitting so-called herbivore-induced synomone (HIS) in response to herbivore damage. In this paper, we review the role of terpenoids in the induced indirect defense of plants against herbivorous mites. HIS are emitted from both damaged and undamaged areas of infested plants, and the composition of HIS varies among different plant species. The emission of HIS may also vary within a plant species, depending upon: (1) plant cultivar, (2) leaf growth stage, (3) the herbivore species that is attacking, and (4) abiotic conditions (light intensity, time of year, and water stress). Predatory mites cope with this variation of HIS by innate recognition as well as temporary specialization to a certain HIS via learning.     

Comparison of cultivars of ornamental crop Gerbera jamesonii on production of spider mite-induced volatiles, and their attractiveness to the predator Phytoseiulus persimilis

We investigated whether volatiles produced by spider mite-damaged plants of four gerbera cultivars differ in attractiveness to Phytoseiulus persimilis, a specialist predator of spider mites, and how the mite-induced odor blends differ in chemical composition. The gerbera cultivars differed in resistance, as expressed in terms of spider mite intrinsic rate of population increase (r _m). In order of increasing resistance these were Sirtaki, Rondena, Fame, and Bianca. To correct for differences in damage inflicted on the cultivars, we developed a method to compare the attractiveness of the blends, based on the assumption that a larger amount of spider mite damage leads to higher attraction of P. persimilis. Spider mite-induced volatiles of cultivars Rondena and Bianca were preferred over those of cultivar Sirtaki. Spider mite-induced volatiles of cultivars Sirtaki and Fame did not differ in attractiveness to P. persimilis. Sirtaki plants had a lower relative production of terpenes than the other three cultivars. This was attributed to a low production of cis--bergamotene, trans--bergamotene, trans--bergamotene, and (E)--farnesene. The emission of (E)--ocimene and linalool was lower in Sirtaki and Fame leaves than in Bianca and Rondena. The importance of these chemical differences in the differential attraction of predatory mites is discussed.