Tebufenpyrad (Pyranica®) resistance detected in two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) from apples in Western Australia

A strain (WA) of Tetranychus urticae Koch was collected from apples in Western Australia following a reported field-control failure of tebufenpyrad. The WA strain had been exposed to five tebufenpyrad applications over four seasons. The tebufenpyrad resistance in the WA strain was confirmed at 63.29× which is the first reported instance of tebufenpyrad resistance in T. urticae. The tebufenpyrad resistance in T. urticae conferred a >210× cross-resistance to pryidaben, a 24.60× cross-resistance to fenpyroximate and a 2.20× cross-resistance to chlorfenapyr.Exp Appl Acarol 22: 633–641 © 1998 Kluwer Academic Publishers     

Sublethal effects of Thymus vulgaris essential oil on life-table parameters of two-spotted spider mite,Tetranychus urticae Koch (Acari: Tetranychidae)

Sublethal effects of Thymus vulgaris were investigated on life-table parameters of Tetranychus urticae Koch (Acari: Tetranychidae) in the laboratory conditions at 25?±?1?°C, 70?±?10% RH and a 14:10?h (L:D) photoperiod. Bioassay was conducted to assess the effect of different concentrations of T. vulgaris essential oil on two-spotted spider mite. LC₅₀ and LC₂₀ of T. vulgaris on T. urticae were calculated as 18.86 and 6.24?μl/litre air for 24?h after treatment. In the sublethal effects, after 24?h exposure to LC₅₀ concentration, mortality, fecundity and longevity of the females that survived from treatment were determined. Results showed that T. vulgaris caused significant reductions in fecundity and longevity of adults. Life-table assay indicated that the intrinsic rate of increase (r _m), net reproductive rate (R ₀), finite rate of increase (λ), mean generation time (T), significantly reduced in treated females compared to control. These results suggest that T. vulgaris could be incorporated in integrated pest management programmes of T. urticae.     

Efficacy of Metarhizium anisopliae in controlling the two‐spotted spider mite Tetranychus urticae on common bean in screenhouse and field experiments

The efficacy of aqueous and emulsifiable formulations of the fungus Metarhizium anisopliae isolate ICIPE78 was evaluated on the population density of Tetranychus urticae infesting common bean plants under screenhouse and field conditions. Synthetic acaricide abamectin was included as a check. Bean plants were artificially infested with T. urticae and allowed to multiply. Three treatments were applied in the screenhouse and 1 treatment in field trials. Mite density was recorded 2 d before spraying and weekly postspraying. The number of pods per plant, number of seeds per pod, and the dry weight of seeds per plant were recorded only in the screenhouse trials. In both screenhouse and field trials, fungal formulations applied at the concentration of 10⁸ conidia/mL and the acaricide reduced the population density of mites as compared to the controls. There were significant differences in T. urticae population densities between the treatments at the various post‐spraying sampling dates. In the screenhouse, the mite densities were near zero from 3‐week postspraying in the treated leaves. At 4‐week postspraying, there were no more leaves in the untreated control (T1) and in the control water + Silwet‐L77 (T2). Fungal formulations were as effective as abamectin in reducing mite densities in both screenhouse and field experiments. There were significant differences in the production parameters during the 2 screenhouse trials, with fungal and abamectin treatments generally having the highest yield. Results of this study underline the potential of the M. anisopliae isolate ICIPE78 as an alternative to acaricides for T. urticae management.     

Mode of inheritance of resistance to three new acaricides in the Kanzawa spider mite Tetranychus kanzawai Kishida (Acari:Tetranychidae)

The genetics of resistance to three new types of acaricide tebufenpyrad, fenpyroximate and pyridaben was studied by crossing a resistant (R) with a susceptible (S) strain of Tetranychus kanzawai Kishida. The resistance ratios calculated from the LC50s of the R and S strains were 97, 1265 and 134 for tebufenpyrad, fenpyroximate and pyridaben, respectively. The responses to the three acaricides in F1 females from reciprocal crosses between the R and S strains showed that the modes of inheritance of resistance to tebufenpyrad, fenpyroximate and pyridaben were intermediate, incompletely dominant and completely recessive, respectively. Furthermore, the responses of F2 females from the reciprocal crosses indicated that the resistance to the three acaricides was under monogenic control.Exp Appl Acarol 22: 699708 © 1998 Kluwer Academic Publishers     

Diapause‐inducing signals prolong nymphal development in the two‐spotted spider mite Tetranychus urticae

Female two‐spotted spider mite Tetranychus urticae are grown under different photoperiods and the photoperiodic regulation of diapause is examined. The photoperiodic response curve for diapause induction was of the long day–short day type, with critical day lengths (CDLs) of 2 and 12.5 h; diapause was induced between these CDLs. The preimaginal period is significantly longer in diapausing females than in non‐diapausing females; moreover, a significant positive correlation is detected between diapause incidence and deutonymphal period. Diapause incidence is high when long‐night photoperiods are applied against a background of continuous darkness in the stages including the deutonymph; this stage appears to be the most sensitive to photoperiod. These observations suggest that diapause‐inducing conditions inhibit nymphal development, particularly in the deutonymphal stage when photoperiodic time measurement for determination of reproduction or diapause is carried out.     

Effects of host interaction with Wolbachia on cytoplasmic incompatibility in the two‐spotted spider mite Tetranychus urticae

The endosymbiotic bacterium Wolbachia pipientis infects a wide range of arthropods and induces a variety of reproductive anomalies, including cytoplasmic incompatibility (CI). Three populations of the two‐spotted spider mite, Tetranychus urticae, were investigated in the present study. Based on gene sequencing, they had different host genetic backgrounds but were infected with the same Wolbachia strain. We also examined the CI level relative to host background, male age, Wolbachia density, and Ankyrin (ANK) gene expression in T. urticae. The results of the present study suggest that: (1) CI differences between populations appear to be a result of host genetic background; (2) male age is not a factor determining intensity of CI; (3) Wolbachia density in males may serve as threshold factor necessary for the CI to occur in T. urticae, after which other factors become important in determining the strength of CI; and (4) hosts may modulate CI intensity through modulation of ANK gene expression in males. Our results describe a new type of interaction between Wolbachia and its hosts, and the effect of the interactions on CI. Further investigations on the functions of Wolbachia ankyrin gene products and their host targets, particularly with respect to host reproductive manipulation, are also imperative.     

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.

     

Nucleo-cytoplasmic interactions causing partial female sterility in the spider mite Tetranychus urticae Koch (Acari: Tetranychidae)

A case of non-reciprocal hybrid infertility between strains of the spider mite Tetranychus urticae Koch is described. Evidence is presented that the infertility results from an interaction between a chromosomal and a cytoplasmic factor. The presence or absence of the cytoplasmic factor seems to be controlled also by chromosomal genes.     

Potentiation of a propargite and fenpyroximate mixture against two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae)

Using susceptible and resistant reference strains and standard bioassay methods a new miticide product was screened for efficacy and cross-resistance against two-spotted spider mite, Tetranychus urticae Koch. Experimental product NN1 850.0 EW (fenpyroximate and propargite 3:10 ratio) was significantly (P<0.05) more toxic than either compound tested alone (co-toxicity index 1029). Non-overlapping 95% CIs at the LC₅₀ and LC₉₉ level suggest that there is no cross-resistance to NN1 850.0 EW from existing organophosphate and pyrethroid resistance. NN1 850.0 EW is worthy of further development for T. urticae control.     

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.     

Host plant associations in the spider mite Tetranychus urticae (Acari: Tetranychidae): insights from molecular phylogeography

This article integrates studies on the genetic variation of T. urticae populations and the interspecific variation of several tetranychid species. It aims at obtaining insights into the roles of the historical, geographical and ecological factors in the partitioning of variation of species. Two types of molecular markers were used to determine whether the patterns of genetic variation in mites inhabiting different host plants can shed light on the existence of host plant associations. The ribosomal sequences of the second internal transcribed spacer (ITS2), which evolves through concerted evolution, are good indicators of long-term isolation between populations and reveal exceptional homogeneity in a worldwide sampling of T. urticae. The mitochondrial cytochrome oxidase I (COI) sequences do not disclose old divergences related to host plant in this mite but rather suggest recent geographic colonization patterns of the species. Allozyme variation on a fine scale gives some evidence of host associations in the case of citrus trees. However, if any divergence of mites related to this host plant exists, it probably prevails in local populations only and it should not be old enough to be revealed by a phylogenetic analysis of mitochondrial COI sequences. The phyletic constraint in the evolution of feeding specificity in the family Tetra-nychidae is investigated based on a phylogenetic analysis of mitochondrial sequences. The results provide some support for the hypothesis that an evolutionary trend towards polyphagy has occurred in the family. Overall, it seems that the major characteristic of T. urticae is its high colonization potential. Polyphagy has enhanced its successful spread and may have led to connectivity between populations worldwide. © Rapid Science Ltd. 1998     

Partial hybrid sterility between strains of the arrhenotokous spider mite,Tetranychus urticae complex (Acari,Tetranychidae)

Crosses between strains belonging to the Tetranychus urticae complex often reveal some degree of mortality in the eggs laid by the F₄ females. Two such strains were studied. Non-Mendelian features characterize the F₁ infertility: F₁ females of the same cross differ considerably regarding mortality in their eggs, reciprocal crosses give different results and the degree of egg mortality changes when the F₁ female gets older. Moderate changes in physical circumstances and the quality of the host plant have little or no influence on egg mortality. Haploid eggs, laid by virgin F₁ females, suffer considerably more mortality than eggs fertilized by sperm from the paternal or the maternal strain. Nine generations of repeated backcrossing to males of the original paternal strain did not result in a notable reduction of egg mortality, although evidence from another study (De Boer, unpublished) makes it highly unlikely that agents with a strictly maternal inheritance are involved.     

Within-plant and within-leaf dispersion pattern of two-spotted spider mite,Tetranychus urticae Koch (Acari: Tetranychidae) on okra

Tetranychus urticae distribution on spatial scale both within leaf and within plant was assessed by the index of dispersion (Id), Lloyd's mean crowding index (Imc), Lloyd's patchiness index (Ip) and Morisita's index (I _δ). Id values in all leaves and leaf parts promised aggregated distribution regardless of leaf position and leaf areas. The values of Imc estimated were all larger than the mean. The value of Ip and I _δ  also indicated increased degree of aggregation and clumping in all leaves and leaf areas. While pattern of distribution is same in all the leaves and leaf parts, population estimated is high in young fully opened top leaves than the grown-up middle and bottom leaves. Within the young leaf, top area of upper side of the leaf housed relatively increased number of T. urticae than bottom area of upper side of the leaf. Because young fully opened leaves consistently contained major proportion of mites (48.33%), particularly the top leaf area (79.62%), these leaves and leaf areas can be used as sampling unit for population estimation to minimise the time spent on sampling. However, it warrants future research for predictive models to associate a number of mites of top leaf to other leaves and top area to other areas. Further, releasing predators in young fully opened leaves may increase predator efficiency if supplementary studies on predator–prey relationship on spatial scale are triggered.     

Fine structure and function of the prosomal glands of the two-spotted spider mite,Tetranychus urticae (Acari,Tetranychidae)

Summary The prosomal glands of Tetranychus urticae (Acari, Tetranychidae) were examined light and electron microscopically. Five paired and one unpaired gland are found both in females and males. The silk spinning apparatus consists of paired silk glands which extend laterally on both sides of the esophagus into the pedipalps. There, they enter the terminal silk gland bag which opens into a silk bristle at the apex of the pedipalps. The salivary secretions are formed in three paired glands which have an interconnecting duct, the podocephalic canal. The dorsal podocephalic glands may produce a serous secretion, the anterior podocephalic glands a mucous secretion, and the coxal organ may add a liquid, ion-rich secretion. These secretions pass the podocephalic canal and reach the mouth at the apex of the gnathosome. The function of the paired tracheal organs and the unpaired tracheal gland is still unclear. The tracheal gland may produce a secretion which facilitates the movement of the fused chelicerae and the stylets.This study was financed by a grant from the Deutsche Forschungsgemeinschaft (DFG Se 162/12)     

Effects of B-azolemiteacrylic on life-history traits and demographic parameters of two-spotted spider mite,Tetranychus urticae (Acari: Tetranychidae)

The present study was conducted to evaluate sublethal effects of B-azolemiteacrylic on the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). Female adults of T. urticae were exposed to LC₁₀ and LC₃₀ of the acaricide, and the effects on treated females and their offspring were evaluated. The results showed that the fecundity of F₀ female adults treated with LC₁₀ and LC₃₀ of B-azolemiteacrylic was reduced by 30.9 and 39.2%, respectively. Longevity and oviposition period of the females were significantly reduced as well. The developmental duration of egg and deutonymph stage of the F₁ generation were not significantly different from that of the control. The protonymph stage after LC₃₀ treatment lasted significantly longer, whereas the larva, deutonymph and female stage were significantly shorter than the control. The oviposition period of the F₁ generation was significantly shortened, the fecundity of each female decreased significantly, and the ratio of female-to-male was reduced too. Moreover, the average generation period of T. urticae after LC₁₀ and LC₃₀ treatments was shorter than that of the control, and the net production rate (R₀), intrinsic rate of increase (r_m) and finite rate of increase (λ) were all reduced by 33.3, 7.5 and 1.9% (LC₁₀ treatment) and by 51.3, 14.8 and 3.6% (LC₃₀ treatment), respectively. The population doubling time was prolonged by 7.5 and 14.8% after LC₁₀ and LC₃₀ treatments, respectively, compared with the control. These results indicate that B-azolemiteacrylic may effectively inhibit the development rate of the F₀ and F₁ populations of T. urticae, which will help design integrated strategies for the comprehensive control of T. urticae and rational use of pesticides in the field.

     

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, characterization, inheritance and linkage of microsatellite markers in Tetranychus kanzawai (Acari: Tetranychidae)

We isolated and characterized seven microsatellite markers in Tetranychus kanzawai (Acari: Tetranychidae). We also examined the conformity of the isolated markers to Mendelian laws and analyzed linkage among the microsatellite loci. All microsatellite markers fit expected 1:1 disomic segregation ratio and hence were inherited in a Mendelian manner. Significant pairwise linkage was detected in three pairs of microsatellite loci. These isolated microsatellite markers may become a powerful tool for the study of behavioral ecology, population genetics, and genome mapping of T. kanzawai.     

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.