Demography of the twospotted spider mite,Tetranychus urticae Koch

Summary A simple life table model was constructed for Tetranychus urticae in which daily survivorship of eggs and motil stages, fecundity, and development time was altered to assess the impact of each parameter on the intrinsic rate of increase. r. Interpretation of the trade-offs focused on management considerations.A second aspect of the study concerned age and stage structure in mite populations including the time path of convergence to a stable age distribution and the effect of changes in birth and death rates on the age profile. The stable stage distributions of 7 tetranychid mite species were computed using 25 separate life tables. In spite of the wide range of r-values induced by different experimental conditions, all of the stage distributions were quite similar averaging roughly 66% eggs, 26% immatures, and 8% adults. Several population studies were cited which reported stage distributions of growing mite populations. The empirical evidence suggested that natural mite populations are often quite near this stable distribution.A practical problem involving the extent to which hormoligosis (insecticide stimulation) affects mite population growth rate was addressed using the life table model and laboratory data from controlled studies. The findings suggested that mite populations treated with insecticide may attain a 1.4- to a 4.2-fold difference in population size relative to an untreated population after 2 generations and over a 1,300-fold potential difference after 10 generations.     

Behavioral aspects of dicofol resistance in the twospotted spider mite Tetranychus urticae

Behavioral analysis of near-isogenic dicofol-resistant and dicofol-susceptible spider mites did not uncover behavior patterns, present in resistant individuals yet absent in susceptible individuals, that would have reduced exposure to dicofol. On the contrary, homozygous resistant individuals were more likely than homozygous susceptible individuals to remain in contact with treated leaf areas. In the case of dicofol resistance in twospotted spider mites, resistance appears to have resulted in the loss, rather than the acquisition, of behavioral traits that lessen exposure to pesticide. Therefore, we conclude that behavioral resistance does not play a major role in twospotted spider mite resistance to dicofol.Deux génotypes de T. urticae Koch (un sensible et un résistant) ont servi à étudier les aspects comportementaux de la résistance aux pesticides: la durée et la fréquence des comportements de nutrition, de marche et d'attente ont été mesurés chez cet acarien. Dans toutes les expériences, des femelles de mêmes âges avaient été placées sur des feuilles jeunes de haricot (Phaseolus vulgaris) portant des résidus de dicofol.3 séries d'expériences ont été réalisées pour examiner:

Resistance status of the carmine spider mite,Tetranychus cinnabarinus and the twospotted spider mite,Tetranychus urticae to selected acaricides on strawberries

The carmine spider mite, Tetranychus cinnabarinus (Boisduval) and the twospotted spider mite, Tetranychus urticae Koch, are serious pests of strawberries and many other horticultural crops. Control of these pests has been heavily dependent upon chemical acaricides. Objectives of this study were to determine the resistance status of these two pest species to commonly used acaricides on strawberries in a year‐round intensive horticultural production region. LC₉₀ of abamectin for adult carmine spider mites was 4% whereas that for adult twospotted spider mites was 24% of the top label rate. LC_90s of spiromesifen, etoxazole, hexythiazox and bifenazate were 0.5%, 0.5%, 1.4% and 83% of their respective highest label rates for carmine spider mite eggs, 0.7%, 2.7%, 12.1% and 347% of their respective highest label rates for the nymphs. LC_90s of spiromesifen, etoxazole, hexythiazox and bifenazate were 4.6%, 11.1%, 310% and 62% of their respective highest label rates for twospotted spider mite eggs, 3%, 13%, 432,214% and 15% of their respective highest label rates for the nymphs. Our results suggest that T. cinnabarinus have developed resistance to bifenazate and that the T. urticae have developed resistance to hexythiazox. These results strongly emphasize the need to develop resistance management strategies in the region.     

Comparative toxicity of some acaricides to the predatory mite, Phytoseiulus persimilis and the twospotted spider mite, Tetranychus urticae

The relative toxicity of someacaricides to the predatory mite, Phytoseiulus persimilis and the twospottedspider mite, Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae) wasevaluated in laboratory. Five of theacaricides tested, including bifenazate,acequinocyl, chlorfenapyr, flufenoxuron andfenbutatin oxide, were much less toxic to adultfemales and immatures of P. persimilisthan to those of T. urticae, and adultfemale predators treated with these fiveacaricides produced 84±96% as many eggs as didcontrol females. Etoxazole did not seriouslyaffect the survival and reproduction of adultfemale predators but caused high mortalityrates in eggs and larvae of P.persimilis. Milbemectin and fenazaquin werevery toxic to adult females and immatures ofP. persimilis. Adult female predatorssurvived on a diet of spider mites treated withbifenazate, acequinocyl, chlorfenapyr,flufenoxuron and fenbutatin oxide, and theirfecundity, prey consumption and the sex ratioof the progeny were not substantially affected. Based on the results, bifenazate, acequinocyl,chlorfenapyr, flufenoxuron and fenbutatin oxideappeared to be the promising candidates for usein integrated mite management programs whereP. persimilis is the major naturalenemy.     

Chemical investigation of aggregation behaviour in the two-spotted spider mite Tetranychus urticae

The silk produced by the group-living mite Tetranychus urticae provides group protection and is used as an informative material during habitat settlement, egg laying, mating, and dispersal events. In this context, cues contained in the silk and other materials produced by mites [eggs, black faeces (BF) and white faeces + silk (WFS)] were investigated. Chemical compounds were extracted by hexane or methanol, and choice tests were used to determine the individual attractiveness of each extract. For both solvents, individuals did not respond to the extract from eggs and WFS. BF extracts were attractive for both solvents. After separating the BF methanol extract into four different chemical components using thin layer chromatography, no component was determined to be responsible for mite attraction. This work supports the evidence that the faeces of T. urticae do contain substances that promote behavioural changes. Not particular chemical compounds but combinations of them seem to induce the mites’ preference. Moreover, the response of mites to chemicals seemed to be context dependent as mites belonging to populations with different densities differed in their attraction to BF extracts.     

Effects of cultivar and irrigation management on population growth of the twospotted spider mite Tetranychus urticae on greenhouse ivy geranium

Greenhouse experiments were conducted to determine whether different ivy geranium cultivars and different irrigation frequencies influenced population growth of the twospotted spider mite (TSM), Tetranychus urticae. Results showed that mite numbers at harvest (about 4 weeks after plants were artificially infested) were very low on 'Sybil Holmes', but significantly higher on 'Amethyst 96'. Irrigation frequency of ivy geraniums had no measurable effect on TSM populations over a range in which water was applied when pot weight dropped 15, 30 or 45% from container capacity. However, the most frequently irrigated plants (15% treatment) produced as much or more growth than plants that received less water. These plants also had the lowest incidence of oedema. There was no significant interaction between water management and host plant resistance, implying the difference in host plant resistance to TSM between the two cultivars should remain constant, at least within the range of the irrigation frequencies studied. Our findings suggest that growers can take advantage of plant resistance to TSM on ivy geranium cultivars of current commercial importance, and that watering practices can be adjusted to optimize plant production without affecting pest populations.     

The entomopathogenic fungus Beauveria bassiana and its compatibility with triflumuron: effects on the twospotted spider mite Tetranychus urticae

Laboratory studies were conducted to determine the effects of the mycoinsecticide Naturalis-L (Beauveria bassiana conidial formulation) on the twospotted spider mite Tetranychus urticae. Compatibility of B. bassiana with triflumuron (benzoylphenyl urea typically used as an insecticide, but also with acaricide effects), was also investigated in order to incorporate both in the control of this pest. For each juvenile stage, 180–22,800 viable conidia/mL on deutonymphs, 380–12,160 viable conidia/mL on protonymphs, and 712–7480 viable conidia/mL on larvae were evaluated. For the adult stage, the concentrations ranged from 213 to 54,720 viable conidia/mL. The mortality data used in the analysis were those accumulated after 5 days of treatment for deutonymphs and protonymphs, 7 days for larvae and 9 days for adults. The lethal concentration to kill 50% (LC₅₀) for the juvenile stages was 3184 viable conidia/mL (their probit-log concentration regression lines were the same), and 1949 viable conidia/mL for adults. No significant differences in mortality were observed among egg age classes (24-, 48-, 72-, and 96-h-old eggs) at the tested concentrations (1400–22,800 viable conidia/mL). When B. bassiana was combined with 0.25 g Alsystin (25% triflumuron as a wettable powder)/L, mite egg mortality decreased significantly. Triflumuron reduced mycelial growth but not conidial germination of B. bassiana. This fungus is a possible candidate to be included in integrated pest management programs with triflumuron of T. urticae. In such programs, the possible antagonist effects of triflumuron should be considered.     

Distribution of the spider mite Tetranychus urticae Koch (Acarina,Tetranychidae) over the leaves of different cucumber cultivars

Distribution of spider mites over cucumber leaves is determined by the topical trophic specialization of the pest manifested in preference for the central leaf zone. After artificial infestation of leaves with female mites, the modified aggregated distribution of the pest depended on the number of mites on the leaf, the morpho-physiological state and stage of development of the leaf and the whole plant, and the cucumber cultivar.     

Role of the entomogenous fungus, Neozygites floridana, in population declines of the twospotted spider mite, Tetranychus urticae, on field corn

In field plots in which populations of predaceous species were suppressed using carbaryl, populations of the twospotted spider mite, Tetranychus urticae Koch, on field corn declined in association with aerial dispersal of the mites or with epizootics of the entomogenous fungus, Neozygites floridana Weiser & Muma. The relative importance of these two factors varied from year to year depending on environmental conditions. When moist weather conditions induced epizootics of N. floridana before corn plants became heavily infested with mites, the pathogen appeared to be the major factor causing mite population declines. When dry weather conditions allowed mite populations to expand unchecked until corn plants became entirely infested, mite aerial dispersal was the major factor associated with mite population declines. In every field in which there was an epizootic of N. floridana, routine applications of the fungicide maneb delayed epizootics and reduced or delayed the impact of the pathogen on mite populations. The total number of Neozygites-infected mites produced in maneb-treated plots throughout the test period was significantly greater than that in untreated plots when epizootics were initiated during periods of mite population growth. Fewer total infected mites were produced in maneb-treated plots compared to untreated plots when epizootics were initiated during periods of mite population decline.

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Résumé Dans des parcelles de maïs dont les populations d'espèces prédatrices avaient été éliminées par du carbaryl, des populations de T. urticae ont régressé en fonction de la dispersion aérienne des acariens ou d'épizooties provoquées par N. floridana. L'importance relative de ces deux causes varie d'année suivant les conditions écologiques. Le pathogène paraissait la principale cause de déclin des populations quand le temps humide a induit les épizooties par N. floridana avant que le maïs n'ait été largement contaminé par les acariens. Quand le temps sec a permis aux populations d'acariens de se développer sans frein jusqu'à contamination totale du maïs, la dispersion aérienne des acariens était la principale cause de déclin des populations d'acariens. Dans tous les champs où il y avait eu épizootie de N. floridana, des traitements de routine avec le fongicide meneb ont retardé les épizooties et réduit ou retardé l'impact du pathogène sur les populations d'acariens. Pendant toute la période d'étude, le nombre total d'acariens infestés par Neozygites était significativement plus élevé dans les parcelles traitées au maneb que dans les parcelles non traitées, lorsque les épizooties étaient provoquées pendant la période de croissance des populations d'acariens. Quand les épizooties ont été déclenchées pendant la période de déclin des populations d'acariens, un nombre plus faible d'acariens infestés était observé dans les parcelles traitées au maneb que dans les parcelles sans traitement.

     

Effects of mating status and age on dispersal behavior in the twospotted spider mite, Tetranychus urticae in response to fenvalerate-treated leaf surfaces

Effects of variation in age and mating status on dispersal of the twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), from fenvalerate-treated leaf surfaces were investigated. Unmated and mated female mites, 1 to 6 days in age, were scored for walkoff and spindown dispersal response on bean leaves treated with a sub-lethal, residual dose of fenvalerate. Variation in mite age did not have a pronounced effect on dispersal response. Significant differences in dispersal response due to mating type were observed, yet the mean differences in dispersal response between unmated and mated females was generally small. Our data suggest that the current practice of using mated female mites of unknown age when testing for among-population differences in dispersal response, in most cases, provides an adequate estimate of population response when differences among treatments in dispersal response are large. However, when testing for within-population differences in dispersal response, small treatment effects may be more easily measured using a single age class of mites, because this could decrease within-treatment variance.     

Identification of Wolbachia-responsive microRNAs in the two-spotted spider mite,Tetranychus urticae

Background

The two-spotted spider mite, Tetranychus urticae, is infected with Wolbachia, which have the ability to manipulate host reproduction and fitness. MicroRNAs (miRNAs) are small non-coding RNAs that are involved in many biological processes such as development, reproduction and host-pathogen interactions. Although miRNA was observed to involve in Wolbachia-host interactions in the other insect systems, its roles have not been fully deciphered in the two-spotted spider mite.

Results

Small RNA libraries of infected and uninfected T. urticae for both sexes (in total four libraries) were constructed. By integrating the mRNA data originated from the same samples, the target genes of the differentially expressed miRNAs were predicted. Then, GO and pathway analyses were performed for the target genes. Comparison of libraries showed that Wolbachia infection significantly regulated 91 miRNAs in females and 20 miRNAs in males, with an overall suppression of miRNAs in Wolbachia-infected libraries. A comparison of the miRNA and mRNA data predicted that the differentially expressed miRNAs negatively regulated 90 mRNAs in females and 9 mRNAs in males. An analysis of target genes showed that Wolbachia-responsive miRNAs regulated genes with function in sphingolipid metabolism, lysosome function, apoptosis and lipid transporting in both sexes, as well as reproduction in females.

Conclusion

Comparisons of the miRNA and mRNA data can help to identify miRNAs and miRNA target genes involving in Wolbachia-host interactions. The molecular targets identified in this study should be useful in further functional studies.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1122) contains supplementary material, which is available to authorized users.     

Ultrahistology of oogenesis and vitellogenesis in the spider mite Tetranychus urticae

Histology of the ovary of the spider mite Tetranychus urticae is described light and electron microscopically with special reference to oogenesis and vitellogenesis of this mite. Morphology of the ovary is comparable to the typical sac-like chelicerate ovary with oocytes protruding from the ovarian surface, thus resulting in a grape-like appearance. According to different oogenetic stages, a germ, pre-vitellogenic and vitellogenic region can be observed. Oogonia and primary oocytes characterized by extranuclear material or 'yolk nuclei' are situated in the germ region. Primary oocytes develop into three-nucleated nurse cells situated in the periphery of the pre-vitellogenic region, and into pre-vitellogenic oocytes protruding from the ovarian surface. Growth of oocytes is performed while they are in ovarian pouches by uptake of nurse cell cytoplasm and following extraovarian yolk precursors. Intraoocyte yolk synthesis interpreted from altered cytoplasmic organelles also occurs. Processes taking place during oogenesis and vitellogenesis in T. urticae are compared to published information on yolk synthesis of other animal species.     

Postharvest disinfestation of diapausing and non-diapausing twospotted spider mite (Tetranychus urticae) on persimmons: hot water immersion and coolstorage

The mortality response of diapausing and non-diapausing twospotted spider mite (Tetranychus urticae Koch) on persimmons to hot water immersion treatments between 44 and 54 °C was examined, for potential as a quarantine treatment. The mean immersion time for mean 99% mortality (LT₉₉) of diapausing mites at 44 °C was 211 min, and this time decreased with increasing temperature to 3.6 min at 54 °C. Non-diapausing mites were found to be less tolerant to temperatures below 48 °C, with an estimated LT₉₉ of 102 min at 44 °C, but had similar thermotolerance above 48 °C. In 47 °C water the immersion time required to kill 99% of diapausing mites was estimated at 67 min. This time was not reduced by subsequent coolstorage at 0 °C for up to eight weeks. Rather, coolstorage had the effect of keeping mites alive, relative to LT₉₉ estimates calculated for mites stored at 20 °C. Similarly the thermotolerance of mites did not change with increased time in diapause, even though mites in diapause for 12 weeks had high control mortality. Hot water immersion appears to be a potentially useful disinfestation method for persimmons.     

Geographic variation of diapause intensity in the spider mite Tetranychus urticae

Abstract. Eight strains of the spider mite Tetranychus urticae, originating from different localities in western and central Europe, with latitudes ranging from 40.5 to 60^oN, displayed marked differences in the period of chilling at 4^oC required for diapause termination under a diapause-maintaining short-day photoperiodic regime at 19^oC, to which the mites were transferred after the cold period. The higher the latitude from which the strains originated the longer was the period of chilling required for diapause termination, suggesting the presence of a gradient in diapause intensity, diapause being deeper the more northern the origin of the strains. Two strains originating from higher altitudes appeared to have a much deeper diapause than expected from their latitudinal origin. In addition, these two mountain strains showed mutual differences in diapause intensity, notwithstanding the fact that they originated from similar latitudes and altitudes; local climatic conditions probably act as strong selective forces with regard to diapause depth. All strains appeared to be sensitive to photoperiod during the period of diapause development. Diapause was quickly completed by a long-day photoperiod (LD 17:7 h), but was maintained by a short-day photoperiod (LD 10:14h). However, even under the latter regime sensitivity to photoperiod gradually diminished and eventually disappeared, thus leading to ‘spontaneous’ termination of diapause. The length of the period of diapause development, as measured by the sensitivity to photoperiod of diapausing mites, varied between strains; it was shorter in the southern strains and longer in the northern strains. The results indicate great variation in diapause intensity between strains, which is probably genetically determined and may have adaptive significance for this widespread species. When young females which had just entered diapause were kept for ever longer periods of time under the diapause inducing short-day regime at which they had been reared, before being transferred to the cold room, the duration of the period of chilling required for diapause termination was found to decrease proportionally in all three strains tested. These results suggest that intensification of diapause does not occur in T. urticae; diapause intensity seems to be highest at the beginning of diapause and to diminish gradually during diapause development.     

Predation risk affects diapause induction in the spider mite Tetranychus urticae

Whenever diapause induction triggers movement into another microhabitat or the development of protective morphological structures, this may also alter predation risk. If the risk of being eaten is lower in the diapause phase, then there may be selection favouring diapause induction in response to predators or their cues. In this article, we studied the effect of the predatory mite Typhlodromus pyri on diapause induction in the spider mite Tetranychus urticae. We used a Greek strain because under long-night photoperiods and low temperature only part of the population enters diapause, thereby leaving room for the impact of another factor. In spider mite groups under predation, the percentage diapause induction increased whenever night-lengths were such that diapause was induced (13–16 h of night). Given this diapause induction in response to predation risk, the question arises whether entering diapause helps spider mites to escape from predation and contribute more offspring to the spring generation next year.     

Demographic examination of sex ratio in the two-spotted spider mite, Tetranychus urticae

Primary sex ratio of arrhenotokous tetranychid mites depends on the age-specific schedule of ratios of progeny produced by individual females. Since primary sex ratio is conditional upon female age and since the proportion of females of a given age in a population is influenced by the rate of increase, both the agespecific ratio of males to females and the overall ratio of males to females depends on the rate of increase. We given an expression for this dependence and compare it to experimental results for the two-spotted spiter mite. These results imply that there is no standard sex ratio of spider mites because of interpopulation variation in rates of increase.

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Résumé Le taux sexuel des acariens tétranychidés arrhénotoques est défini comme le rapport de la somme des nombres de mâles sur la somme des nombres de femelles pour chaque âge de la distribution en âges. Comme le taux sexuel primaire dépend de l'âge de la femelle et comme la proportion de femelles d'un âge donné dans la population est influencée par le taux d'accroissement, alors le rapport mâle/femelle spécifique d'un âge déterminé et le rapport global mâle/femelle dépendent du taux d'accroissement. Nous avons cherché à exprimer cette dépendance et à la comparer aux résultats expérimentaux pour Tetranychus urticae. Ces résultats signifient qu'il n'y a pas de taux sexuel caractéristique de Tétranyques par suite des variations du taux d'accroissement suivant les populations.

     

Genetics of diapause supression in the two-spotted spider mite,Tetranychus urticae Koch

Starting from the Sambucus strain of the two-spotted spider miteTetranychus urticae Koch, the strains ND₁ and ND₂ were selected for lack of diapause under a short-day regimen (LD 1014, 18°C). The genetic basis of the suppression of diapause in ND₁ and ND₂ was analysed by means of mendelian crosses and backcrosses, using the photoperiodic cycle LD 1014 as diagnostic for the distinction of diapausing and non-diapausing phenotypes. Suppression of diapause is inherited as a recessive trait. From backcross analysis it was concluded that the suppression of diapause in ND₁ and ND₂ is under monogenic control. The major genes for suppression of diapause in ND₁ and ND₂ are alleles at a locus designated asd. A mutation for albinism of the locusa-p is pleiotropic for suppression of diapause. It was shown from crosses between ND₁ and the albino strain, thatd anda-p are distinct loci.     

Wolbachia-induced 'hybrid breakdown' in the two-spotted spider mite Tetranychus urticae Koch

The most common post-zygotic isolation mechanism between populations of the phytophagous mite Tetranychus urticae is 'hybrid breakdown', i.e. when individuals from two different populations are crossed, F1 hybrid females are produced, but F2 recombinant male offspring suffer increased mortality. Two-spotted spider mites collected from two populations, one on rose and the other on cucumber plants, were infected with Wolbachia bacteria. These bacteria may induce cytoplasmic incompatibility in their hosts: uninfected (U) females become reproductively incompatible with infected (W) males. We report on the effect of Wolbachia infections in intra- and interstrain crosses on (i) F1 mortality and sex ratios (a test for cytoplasmic incompatibility), and (ii) the number of haploid offspring and mortality in clutches of F1 virgins (a test for hybrid breakdown). U x W crosses within the rose strain exhibited partial cvtoplasmic incompatibility. More interestingly, F2 males suffered increased mortality, a result identical to the hybrid breakdown phenomenon. The experiments were repeated using females from the cucumber strain. In interstrain U x W and U x U crosses, hybrid breakdown was much stronger in the former (80 versus 26%). This is the first report of a Wolbachia infection causing a hybrid breakdown phenotype. Our results show that Wolbhachia infections can contribute to reproductive incompatibility between populations of T. urticae.