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.     

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.     

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     

The influence of fenbutatin-oxide use on organotin resistance in two-spotted mite Tetranychus urticae koch (Acari: Tetranychidae)

A strain of Tetranychus urticae from pears was evaluated for cyhexatin and fenbutatin-oxide resistance after field control failure to the latter occurred. High-level fenbutatin-oxide resistance was confirmed in the field strain. Fenbutatin-oxide resistance was >1,500 fold (based on flowable powder) and 127 fold (based on emulsifiable concentrate). However, the level of cyhexatin resistance was only 9.8 fold which was similar to levels previously found. This provides a stark warning against the overuse of fenbutatin-oxide.     

Host-plant acceptance and performance of Tetranychus urticae (Acari, Tetranychidae)

Abstract: Tetranychus urticae is a serious pest of several crops worldwide. It performs differentially on diverse host‐plant species. Because dispersion is mainly passive, the process of host‐plant selection should be viewed in terms of host‐plant acceptance and not in terms of host finding. The objectives of this study were to investigate: (1) the acceptance of strawberry (S) in comparison with onion (O), leek (L) and parsley (P) by T. urticae; and (2) the suitability of these host plants for the performance of T. urticae, in terms of fecundity and survival. Host‐plant acceptance was measured through females that settled on a test plant or females that left for another host plant. In another experiment, for a duration of 5 days, individual newly mated females were assigned to discs of each host plant and the fecundity, the maximum number of offspring obtained from one female that settled on the disc, the survival and the percentage of females that oviposited at least one egg were analysed. A choice test to measure the preference of females for different host plants was performed. Movements took place towards (S) from the three plants: (O), (L) and (P). Mites significantly moved to other places in the Petri dishes from leek‐origin discs. Dispersal of T. urticae from (S) to other host‐plant discs was similar for all plants. Mean fecundity was higher on (S) than on the other plants. The maximum number of offspring per female was highest on (S), lowest on (L) and (O), and intermediate on (P). Survival of females and percentage of females that laid at least one egg were independent of the host plant. The choice test showed that oviposition was higher on (S) and (P) and very poor on (L) and (O) and that more females settled on (S) and (P). Although mites migrated from parsley to strawberry, the first host plant has a higher acceptance of T. urticae in terms of maximum number of offspring per female than onion and leek, and a lower performance in terms of fecundity than strawberry. Parsley could be a good candidate for an associate plant in a strawberry crop; however, it needs more research under field conditions.     

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.

---

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.

     

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.     

Gene flow among Tetranychus urticae (Acari: Tetranychidae) populations in Greece

Polymorphism of four enzymatic loci has been examined in 27 populations of Tetranychus urticae in relation to their geographical distribution and to two ecological parameters: open field vs. greenhouse habitats, and species of the colonized host plant. Genetic differentiation was significantly correlated to geographical distance in both types of habitat. Mite density and distribution of infested plants appear to be important factors for the population structure of T. urticae . In open field, T. urticae specimens from citrus trees were genetically more similar to other 'citrus' samples collected in different localities than they were from mites collected in the same locality on other plant species.     

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.

     

Biological control of the two-spotted spider mite Tetranychus urticae on strawberries by the predatory phytoseiid mite Typhlodromus pyri (Acari, Tetranychidae, Phytoseiidae)

The ‘Mikulov’ strain of the predatory mite Typhlodromus pyri Scheuten from south Moravian vineyards was released on cultivated strawberries infested with the two-spotted spider mite, Tetranychus urticae Koch. The strawberries were grown in field plantations and under glass. Typhlodromus pyri on vine shoots were successfully introduced into the field strawberry plantation but they produced no demonstrable control of the spider mites and they eventually declined in density with their prey. In contrast, T. pyri gave good control of spider mites in the glasshouse despite the occurrence of low humidity and water stress of the plants.     

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)     

Isolation and characterization of microsatellite loci in the two‐spotted spider mite,Tetranychus urticae (Acari: Tetranychidae)

Sixteen microsatellite loci are described for the two‐spotted spider mite Tetranychus urticae, which is an agricultural pest. The microsatellite loci were obtained through the construction of an enriched library; these loci exhibited polymorphisms (2–5 alleles per locus) and high levels of observed (0.033–0.667, average 0.415) and expected (0.033–0.602, average 0.336) heterozygosities. The isolated microsatellite markers are expected to be useful for the construction of a linkage map of this species.     

Prey preference of predatory mite Amblyseius swirskii (Acari: Phytoseiidae) on Tetranychus urticae (Acari: Tetranychidae) and Bemisia tabaci (Hemiptera: Aleyrodidae)

Tetranychus urticae Koch (Acari: Tetranychidae) and Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) are major pests in greenhouse crops. Recently, Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) was shown to be an effective biological control agent of both pests. Therefore, the prey preference of A. swirskii was determined using immature stages of T. urticae and B. tabaci in three various treatments based on Manly's β preference index (β). These treatments consisted of immature stages of two prey species (egg, first and second instar nymphs) with densities 12:12, 6:6 and 3:3, respectively, and with 13 replicates. After 24?h starvation, same-aged females of A. swirskii were added to the leaf discs. All experiments were done on bean leaf discs in Petri dishes (8?cm in diameter) in laboratory conditions with 25?±?2°C, 70?±?5% relative humidity and the photoperiod of 16L:8D hours. Comparing the preference indices using t-tests indicates a significant preference of the predator on eggs (t?=?10.80, df?=?24, P?t?=?8.17, df?=?24, P?T. urticae than B. tabaci. Our findings suggest that developmental stages of prey have effect on the prey selection by A. swirskii.     

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.     

Oviposition model of overwintered adult Tetranychus urticae (Acari: Tetranychidae) and mite phenology on the ground cover in apple orchards

The phenology of overwintered Tetranychus urticae was studied on the ground cover in apple orchards in the early season, and an oviposition model of overwintered adults was developed. The movement of overwintered adults from trees to ground cover started from mid-March and continued until mid-April. One life cycle from eggs to new adults (the 1st generation adults) on the ground cover was from late March to early May. The longevity and fecundity of overwintered T. urticae were affected largely by temperature. The longevity ranged from 46.6 days at 10 degrees C to 6.5 days at 35 degrees C. The total fecundity was minimum (0.2 eggs) at 10 degrees C and maximum (45.5 eggs) at 25 degrees C. The relationship between total fecundity and temperature was described well by a nonlinear equation. The cumulative age-specific oviposition rate was described well by the two-parameter Weibull function. The overall adult survival exhibited a reverse logistic curve. Three temperature-dependent components, age-specific cumulative oviposition rate, temperature-dependent total fecundity and age-specific survival rate functions, were incorporated into an oviposition model. The oviposition model simulation described the occurrence pattern of eggs laid by overwintered T. urticae on the ground cover in apple orchards relatively well.     

Effects of pesticides on spin down and webbing production by the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae)

Spin down in response to pesticides is a known phenomenon. This study aimed at investigating the effects of varying acaricide concentrations and acaricidal combinations on the rate of spin down and thread length, the fate of mites after spinning down and, thus, the implications of spin down in the context of mite control and the relationship between webbing and the efficacy of ovicides. In response to cyhexatin at a concentration of up to 100 mg dm-3 the rate of spin down did not change, but in response to higher concentrations it occurred earlier and ceased before the end of the experiment. The mean thread length did not vary with the concentration of acaricide and, whilst the proportion of mites spinning down increased with a cyhexatin concentration of up to 10 mg dm-3, it did not increase further with higher concentrations thereafter. It is therefore postulated that at any given time only a certain proportion of mites have a propensity to spin down. In combination with cyhexatin, only amitraz (at low concentrations) increased the proportion of mites spinning down, but amitraz (at higher concentrations), flubenzimine and permethrin all inhibited spin down, which may be a useful attribute in pesticide formulations. With regard to the fate of mites after spinning down, they were able to climb back up threads, but the proportion doing so was too small to be of practical importance. Mites which spin down and remain at the end of a thread die, but those which reached another leaf were able to spin down again and were more likely to do so if the leaf bore a cyhexatin residue. Mites reaching another leaf are also able to lay eggs, the number being greater if the leaf which they reach is untreated. Spin down is therefore likely to be of significant advantage to Tetranychus urticae in avoidance of the effects of acaricides. Finally, some eggs were observed to be laid on webbing and not to come into direct contact with clofentezine residues. The use of a fine water spray to simulate dew increased the ovitoxicity of clofentezine, probably by resuspension of the pesticide, but not of amitraz, which inhibits webbing production. The avoidance of acaricides should be added to the several known advantages of webbing production for spider mites. It is concluded that, all other factors being equal, pesticide formulations which inhibit spin down and webbing production are likely to be more effective in control programmes than those which stimulate such behaviour.     

The effects of Pseudomonas putida biotype B on Tetranychus urticae (Acari: Tetranychidae)

This study investigated Pseudomonas putida biotype B as a potential biological control agent of Tetranychus urticae. The bacteria were isolated from greenhouse soil from Carsamba, Turkey. The experiment was carried out in a completely randomized plot design under laboratory conditions. For this purpose, spraying and dipping applications of a suspension of P. putida biotype B (10(8)-10(9) colony forming units/ml) were applied to newly emerged, copulated females. Dead mite and egg counts were started on the 3rd day after treatments, and observations were continued daily until all the mites had died and egg hatching had finished. Both types of bacterial application significantly reduced total egg numbers and egg hatching, compared to their respective controls. Bacterial spraying was significantly more effective than dipping-the spray application demonstrated 100% efficacy and resulted in the fewest viable eggs. The results of this study indicated that P. putida biotype B has a strong efficacy in causing mortality in T. urticae.