Vertical dispersal of the two-spotted spider mite Tetranychus urticae, and the predatory mite Phytoseiulus persimilis on dwarf hops

1 The pattern of dispersion within plants of the two-spotted spider mite, Tetranychus urticae, and its predator, the phytoseiid Phytoseiulus persimilis, was studied on the dwarf hop variety First Gold from May to September in 1997 and 1998. 2 Spider mite populations developed on the lower leaves initially but, by late July, as the numbers of mites increased, most were found towards the top of plants. From early August, the numbers of spider mites decreased most rapidly on the upper parts of plants. 3 Where P. persimilis was released, the predator maintained the numbers of T. urticae below those found on non-release plots throughout the season. 4 By early August, the predator’s pattern of dispersion was similar to that of the pest. 5 Predators spread to non-release plots by 20 June in 1997 and 24 July in 1998 and eventually became more numerous than on the plots where they had been released.     

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.     

Integrated pest management of two-spotted mite Tetranychus urticae on greenhouse roses using petroleum spray oil and the predatory mite Phytoseiulus persimilis

From 1995 to 1999, four experiments were conducted on greenhouse roses to assess the effectiveness of the nC24 petroleum spray oil (PSO), D-C-Tron Plus, against two-spotted mite, Tetranychus urticae Koch (Acarina: Tetranychidae), and to determine how the oil could be most efficiently and effectively used in combination with the predatory mite Phytoseiulus persimilis Athias-Henriot (Acarina: Phytoseiidae) in an integrated pest management program. The results showed that 0.5% PSO applied fortnightly to roses gave excellent protection from T. urticae infestation when the mite population was not already established. However, PSO applied after roses were infested with T. urticae above the economic threshold only stabilised populations without reducing them below that threshold. Populations of P. persimilis in the upper and lower canopies were unchanged after two sprays of PSO at 7-day intervals, and application of PSO to the upper canopy was as effective in controlling T. urticae in the presence of P. persimilis as spraying the entire plant. Combining PSO with P. persimilis gave better control of T. urticae than using P. persimilis alone. The most cost-effective use of PSO in the presence of P. persimilis is, therefore, to apply spray only to the upper canopy. This will not affect control of powdery mildew with PSO. Comparison of a control program for T. urticae based on the monitored use of synthetic miticides with that based on calendar application of PSO revealed that both gave equally effective control. The benefits of combining PSO and P. persimilis in an integrated pest management program for T. urticae on roses over a program based on synthetic fungicides are discussed.     

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.     

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.     

Suitability of the spider mite Tetranychus evansi as prey for Phytoseiulus persimilis

Expeirments conducted to evaluate the suitability of T. evansi as a source of food for P. persimilis revealed that the primary factor responsible for the low oviposition rate and survivorship of the predator when fed T. evansi was the low amount of food ingested. P. persimilis detected and initiated feeding on T. evansi equally as well as on T. urticae. However, a feeding depressant was apparently responsible for a longer time spent by P. persimilis feeding on eggs of T. evansi than on eggs of T. urticae. Eggs of the former prey were totally consumed only occasionally. The depressant effect influenced subsequent feeding on T. urticae, increasing the time required for consumption and the number of partially consumed eggs for at least 3 days.

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Résumé Les expérience d'évaluation de l'adéquation de T. evansi comme proie pour P. persimilis ont montré que le principal facteur responsable des faibles taux de ponte et de survie du prédateur alimenté sur T. evansi est la faible quantité d'aliments ingérés. P. persimilis avait découvert et commencé à s'alimenter sur T. evansi aussi bien que sur T. urticae. Cependant, un facteur réduisant la prise de nourriture a été responsable du temps plus important consacré à s'alimenter sur oeufs de P. persimilis que sur oeufs de T. urticae. Les oeufs de la première proie n'ont été que rarement consommés intégralement. Cet effet dépressif a influencé l'alimentation ultérieure sur T. urticae, en augmentant le temps nécessaire pour la consommation et le nombre d'oeufs partiellement utilisés au moins pendant les trois jours suivants.

     

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.     

Fertilization in the two-spotted spider mite (Tetranychus urticae: Acari)

Different aspects of the fertilization of the two-spotted spider mite (Tetranychus urticae Koch) were studied. It appeared that after the mating act of virgin females, haploid eggs were produced first before the appearance of diploid eggs. From this and other facts, it was concluded that fertilization of the oocytes occurs in a very early stage of egg development. The fertilization is assumed to take place in the ovary and not in the oviduct.By using genetic markers, it could be proved that in most cases the first mating is effective. Later matings usually are ineffective. It is suggested that the sperm supply in the first mating determines the success of later matings.

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Zusammenfassung Die Befruchtung der Bohnenspinnmilbe wurde unter verschiedenen Gesichtspunkten untersucht. Nach der Begattung jungfräulicher Weibchen wurden zunächst haploide Eier abgelegt, bevor diploide Eier produziert wurden. Daraus und aus anderen Grüunden wird geschlossen, daß die Befruchtung der Oocyten in einem sehr frühen Stadium der Entwicklung erfolgt. Die Befruchtung findet vermutlicht im Ovar und nicht im Ovidukt statt.Unter Verwendung genetischer Markierung wurde nachgewiesen, daß in den meisten Fällen die erste Begattung ausschlaggebend ist. Spätere Kopulationen bleiben gewöhnlich wirkungslos. Es wird vermutet, daß die Spermafüllung bei der ersten Begattung den Erfolg späterer Begattungen bestimmt.

     

Digestive proteases in bodies and faeces of the two-spotted spider mite,Tetranychus urticae

Digestive proteases of the phytophagous mite Tetranychus urticae have been characterised by comparing their activity in body and faecal extracts. Aspartyl, cathepsin B- and L-like and legumain activities were detected in both mite bodies and faeces, with a specific activity of aspartyl and cathepsin L-like proteases about 5- and 2-fold higher, respectively, in mite faeces than in bodies. In general, all these activities were maintained independently of the host plant where the mites were reared (bean, tomato or maize). Remarkably, this is the first report in a phytophagous mite of legumain-like activity, which was characterised for its ability to hydrolyse the specific substrate Z-VAN-AMC, its activation by DTT and inhibition by IAA but not by E-64. Gel free nanoLC–nanoESI-QTOF MS/MS proteomic analysis of mite faeces resulted in the identification of four cathepsins L and one aspartyl protease (from a total of the 29 cathepsins L, 27 cathepsins B, 19 legumains and two aspartyl protease genes identified the genome of this species). Gene expression analysis reveals that four cathepsins L and the aspartyl protease identified in the mite faeces, but also two cathepsins B and two legumains that were not detected in the faeces, were expressed at high levels in the spider mite feeding stages (larvae, nymphs and adults) relative to embryos. Taken together, these results indicate a digestive role for cysteine and aspartyl proteases in T. urticae. The expression of the cathepsins B and L, legumains and aspartyl protease genes analysed in our study increased in female adults after feeding on Arabidopsis plants over-expressing the HvCPI-6 cystatin, that specifically targets cathepsins B and L, or the CMe trypsin inhibitor that targets serine proteases. This unspecific response suggests that in addition to compensation for inhibitor-targeted enzymes, the increase in the expression of digestive proteases in T. urticae may act as a first barrier against ingested plant defensive proteins.     

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.     

Discrimination through silk recognition: The case of the two-spotted spider mite Tetranychus urticae

Choosing a suitable habitat is a main step in the settlement process, particularly for species having weak movement abilities. Reliable cues are thus needed for habitat selection. In silk-spinning arthropods, silk can be used as a social cue to select an appropriate location. Silk can also provide information on the presence of related or non-related individuals. In this article, we compare the settlement behaviour of two strains of the two-spotted spider mite, Tetranychus urticae, in response to the presence of silk woven by an individual of its own or another strain. We then examined how individuals behaved when confronted with both types of silk (own/another strain) simultaneously. Both strains were sensitive to related silk. Settlement decision for both strains did not differ according to the origin of the silk. Mites used the silk as a communication cue for habitat selection and strain discrimination. Our results provide experimental evidence for the use of multiple social cues in the settlement decision by weaving mites.     

Aerial dispersal of the two-spotted spider mite (Tetranychus urticae) from field corn

Field data from 48 plots monitored during diverse weather conditions in two separate years were subjected to multiple regression analysis to determine which factors were related to spider-mite aerial dispersal. With the number of aerially dispersing mites as the dependent variable, partial regression coefficients (b) for mite population density and percent corn-leaf area infested with mites were positive, while those for percentNeozygites-infected mites and hours per week 90% r.h. were negative. When an aerial dispersal index (number of aerially dispersing mites/mites per plant) was used as the dependent variable, the partial regression coefficient for percent leaf area infested was positive, while coefficients for hours per week 90% r.h. and percentNeozygites-infected mites were negative. Mite aerial dispersal was greatest in predator-suppressed field plots under dry weather conditions. Mite aerial dispersal was substantially reduced in plots where moist weather conditions induced epizootics ofNeozygites floridana before corn plants became entirely infested with mites.     

Exudate from sporulating cultures of Hirsutella thompsonii inhibit oviposition by the two-spotted spider mite Tetranychus urticae

The acaricidal mycopathogen Hirsutella thompsonii has been found to secrete metabolites that are active against femaleTetranychus urticae. Specifically, the rose-colored exudate produced on sporulating cultures of Mexican HtM120I strain sterilized female spider mites in a dose-dependent fashion. Topical application of the exudate resulted in a 100% reduction in mite fecundity over the initial six days of experimentation. Depending upon the exudate dosage, mites partially recovered within 3 and 6 d post-treatment and produced a limited number of eggs. The spider mite active HtM120I exudate contained less detectable HtA toxin than the HtM120I broth filtrate, and it was innocuous when injected into the greater wax moth Galleria mellonella L. larvae. Broth filtrates of HtM120I cultures, although toxic to assayed G. mellonella larvae, did not inhibit mite oviposition to the degree or duration of the exudate preparations. These findings suggest that the factor responsible for suppressing oviposition in female spider mites is linked to the sporulation process and is distinct from the well-characterized HtA produced by vegetative cells. This revised version was published online in July 2006 with corrections to the Cover Date.     

UV radiation elevates arylalkylamine N-acetyltransferase activity and melatonin content in the two-spotted spider mite, Tetranychus urticae

Ultraviolet (UV) radiation produces reactive oxygen species (ROS) in mammals, where melatonin plays the role of a ROS scavenger. The melatonin synthetic enzyme arylalkylamine N-acetyltransferase (NAT) is a significant element in a possible ROS removal system. Changes in NAT activity and melatonin content were determined in the two-spotted spider mite Tetranychus urticae by irradiating it with monochromatic light using the Okazaki Large Spectrograph at the National Institute for Basic Biology, Okazaki, Japan. The NAT activity and melatonin content were suppressed by blue light (450nm). No effects of red light (650nm) on the NAT activity and melatonin content were observed. UV radiation had intensity-dependent dual effects on the NAT activity and melatonin content. In the UV-B (300nm) treatment, the NAT activity and melatonin content were suppressed at the intensity below 1mumolm(-2)s(-1) but elevated when the intensity was as high as 10mumolm(-2)s(-1). In the UV-A (350nm) treatment, the melatonin content was elevated when the intensity was as high as 10mumolm(-2)s(-1), though the NAT activity and melatonin content were suppressed at the intensity below 10 and 1mumolm(-2)s(-1), respectively. Elevation of the NAT activity and melatonin content by high intensity UV irradiation may indicate that the UV signals initiate melatonin synthesis for ROS removal in mites.     

Sequence of a cDNA encoding acetylcholinesterase from susceptible and resistant two-spotted spider mite,Tetranychus urticae

Acetylcholinesterase (AChE) from two-spotted spider mites, Tetranychus urticae was compared between an organophosphate susceptible (TKD) and a resistant (NCN) strain. The AChE of TKD had lower affinity to acetylthiocholine and propionylthiocholine than that of NCN, and the inhibition of AChE by DDVP, ambenonium, eserine and n-methyl-eserine showed that NCN was more insensitive than TKD. AChE cDNA sequence was determined, and the 687 amino acids of primary structure were deduced. There were six replacements of amino acid residues in TKD and two in NCN. #F331(439)C was the only substitution unique to NCN, however, this mutation existed homozygously in only two out of nine mites. This residue is one of the gorge lining components, and #F331(439)C might act an important role in the sensitivity of AChE to the inhibitors.     

联苯肼酯对智利小植绥螨的安全性及二者对二斑叶螨的联合控制作用

【目的】评价联苯肼酯对智利小植绥螨Phytoseiulus persimilis的安全性,以及该药剂与捕食性天敌智利小植绥螨联合使用的效果。【方法】采用室内生物测定与田间试验的方法测定了联苯肼酯对智利小植绥螨成螨和若螨致死率与繁殖能力的影响,以及二者联合使用对茄子上二斑叶螨的控制效果。【结果】结果表明143 mg/L联苯肼酯对智利小植绥螨成螨和若螨的存活和生殖能力均无显著影响,处理后96 h对若螨的最高致死率为2.30%,成螨为2.04%;处理组8 d的平均产卵量为15.08粒/雌,与对照平均产卵量15.45粒/雌无显著差异;处理组所产卵的平均孵化率为98.63%,与对照组平均孵化率98.13%无显著差异;联苯肼酯悬浮剂在143 mg/L浓度下对二斑叶螨的控制效果表现为速效性高于单独使用智利小植绥螨,但持效性低于智利小植绥螨,防效在第22天时开始下降。二者联合使用表现出较好的速效性与持效性,处理后第2天防效达97.35%,第18天时达100%。【结论】联苯肼酯对智利小植绥螨具有极高的安全性,该药剂与智利小植绥螨联合使用对二斑叶螨具有良好的控制效果。     

Effects of triflumuron on the two-spotted spider mite,Tetranychus urticae (Acari: Tetranichydae)

The effects of triflumuron on the mortality, fecundity, and fertility of the two-spotted spider mite, Tetranychus urticae, were evaluated in the laboratory. No differences in toxicity for larvae, protonymphs and deutonymphs were observed, but immature stages were 3.8-times more susceptible than adults at the LC₅₀. The compound exhibited a direct contact ovicidal activity influenced by eggs age. 48–72 hold eggs were significantly more sensitive than eggs of the other age classes. No hatch inhibition was observed in eggs laid by treated adult females using a sublethal dose at two physiological times (<12 and 48–72h old). However, fecundity decreased in younger treated females, but it increased in the older-ones. The toxicity for immatures and eggs, and the sublethal effects described suggest that triflumuron could be an interesting incorporation in integrated pest programs of T. urticae. This revised version was published online in July 2006 with corrections to the Cover Date.