Genetics of hexythiazox resistance in two spotted spider mite,Tetranychus urticae Koch

Genetic analysis of the QRPH strain of two spotted spider mite Tetranychus urticae Koch indicates that hexythiazox resistance in that strain is not sex linked and has a dominance factor of 0.152 (incomplete dominance). Hexythiazox resistance appears to be controlled by a single gene.This work contributes in part for the fulfilment of the requirements of the degree of PhD at the University of Sydney.     

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.     

Phytochemical,acaricidal and biological activity of Dodonaea viscosa L. against the two spotted spider mite Tetranychus urticae Koch

Alcohol extract, saponins and flavones fractionated from Dodonaea viscosa leaves were tested for their acaricidal activity against the adult females of Tetranychus urticae Koch. It was found that crude alcohol extract was more potent than the isolates obtained. At LC₅₀ and LC₉₀ levels, the crude extract ranked the first. All the biotic factors are significantly affected. The fecundity was seriously reduced however, the hatchability of eggs was not affected. Two flavonoids were identified as Querectin 3–0-glucose 7-0-rhamnoside and the other as Querectin 3-0 arabinose 7-0 rhammoside from the ethyl acetate fraction of the alcohol extract.     

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.     

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.     

Evolutionary adaptation to host plants in a laboratory population of the phytophagous mite Tetranychus urticae Koch

Summary For evolutionary expansion of host range to occur in an herbivore population, genetic variation in ability to survive on and/or accept new hosts must be present. To determine whether a population of the phytophagous mite Tetranychus urticae contained such variation, I established lines from the population on two hosts on which mites initially showed both high juvenile mortality and low acceptance, tomato and broccoli. In less than ten generations, mites from the line kept on each host showed both lower mortality and greater acceptance on it than mites from a control line kept on lima bean, a favorable host for T. urticae. Host acceptance was measured by the proportion of mites attempting to disperse from leaves of the host. The line kept on tomato but not the one kept on broccoli also increased in development rate on its host. These results and those of a similar previous experiment on cucumber indicate that T. urticae populations can adapt to a diversity of initially unfavorable hosts. T. urticae populations therefore should be able to respond to temporal and spatial variation in host availability by adapting to the most abundant hosts.     

The formation of collective silk balls in the spider mite Tetranychus urticae Koch

Tetranychus urticae is a phytophagous mite that forms colonies of several thousand individuals. These mites construct a common web to protect the colony. When plants become overcrowded and food resources become scarce, individuals gather at the plant apex to form a ball composed of mites and their silk threads. This ball is a structure facilitating group dispersal by wind or animal transport. Until now, no quantitative study had been done on this collective form of migration. This is the first attempt to understand the mechanisms that underlie the emergence and growth of the ball. We studied this collective behaviour under laboratory conditions on standardized infested plants. Our results show that the collective displacement and the formation of balls result from a recruitment process: by depositing silk threads on their way up to the plant apex, mites favour and amplify the recruitment toward the balls. A critical threshold (quorum response) in the cumulative flow of mites must be reached to observe the emergence of a ball. At the beginning of the balls formation, mites form an aggregate. After 24 hours, the aggregated mites are trapped inside the silk balls by the complex network of silk threads and finally die, except for recently arrived individuals. The balls are mainly composed of immature stages. Our study reconstructs the key events that lead to the formation of silk balls. They suggest that the interplay between mites' density, plant morphology and plant density lead to different modes of dispersions (individual or collective) and under what conditions populations might adopt a collective strategy rather than one that is individually oriented. Moreover, our results lead to discuss two aspects of the cooperation and altruism: the importance of Allee effects during colonization of new plants and the importance of the size of a founding group.     

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.     

Differences among plant species in acceptance by the spider mite Tetranychus urticae Koch

Abstract:  The spider mite Tetranychus urticae Koch has a broad range of host plants. However, the spider mite does not accept all plants to the same degree because of differences in nutritive and toxic constituents. Other factors, such as the induction of secondary metabolites, the morphology of a leaf surface and the presence of natural enemies, also play an important role in plant acceptance. We compared plants from various families in their degree of acceptance by the spider mite, to get an indication of the plant's direct defence. Glycine max (soybean), Humulus lupulus (hop), Laburnum anagyroides (golden chain) and Nicotiana tabacum (tobacco) were highly accepted by the spider mites. Different glandular hair densities among tobacco cultivars did not affect their suitability towards spider mites significantly. Solanum melalonga (eggplant), Robinia pseudo-acacia (black locust), Vigna unguiculata (cowpea) and Datura stramonium (thorn apple) were accepted by the spider mites to a lesser degree. Vitis vinifera (grapevine) was poorly accepted by the spider mite. It might be that the food quality of the leaves was not high enough to arrest the spider mites. Also, Capsicum annuum (sweet pepper) and especially Ginkgo biloba (ginkgo) were poorly accepted by the spider mite, probably because of the presence and concentration of certain of the secondary metabolites in the leaves. The spider mites accepted all the plants belonging to the Fabaceae for feeding, but those belonging to the Solanaceae showed a larger variance in spider mite acceptance varying from well accepted (tobacco) to poorly accepted (sweet pepper).     

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.     

Life cycle of a non-diapausing population of the two-spotted spider mite,Tetranychus urticae Koch in a pear orchard

The life cycle of a non-diapausing T. urticae population was studied in a pear orchard in the southern part of Okayama Prefecture, western Honshû, Japan. The mites overwintered only on biennial weeds in the orchard without entering diapause, started to increase in number in early spring on them and then moved to other weeds as they emerged. The occurrence of the mites on pear began in early May several weeks after the unfolding of pear leaves and the population on pear was initiated by the migrants from the weeds around the base of pear trees. The population on pear showed two distinct peak occurrences, one in June and the other in mid-autumn. After pear leaves dropped in late autumn, the mites returned to biennial weeds for overwintering.     

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.

     

Inbreeding depression in an arrhenotokous mite (Tetranychus urticae Koch)

Five generations of inbreeding by sibmating in an arrhenotokous mite (Tetranychus urticae Koch) caused depression as measured in the hatchability of the eggs. It appeared that mainly the haploid eggs were affected.

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Zusammenfassung Inzucht über 5 Generationen verursachte bei einer arrhenotoken Spinnmilbe (Tetranychus urticae Koch) eine an der Schlüpffähigkeit der Eier gemessene Depression. Es schien, daß davon hauptsächlich die haploiden Eier betroffen waren.

     

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

Non-reciprocal hybrid infertility between the strains ZI and ZII of the spider mite Tetranychus urticae Koch, probably based on an interaction between a chromosomal gene N, and a non-chromosomal factor E, is studied. A hypothesis that N-E interaction causes egg mortality indirectly through the formation of recessive lethal genes, is tested and rejected.     

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.     

Integrated control of two spotted spider mite,Tetranychus urticae on cucumber grown under plastichouse conditions in egypt

Microclimatic conditions were monitored in cucumber grown under unheated plastichouses in three consecutive years, i.e. from 1990 to 1992 in Egypt. The relative humidity in the plastichouses constructed on either sandy or clay soil did not exceed 30% during mid-day time, while the average temperature did not drop below 30°C. Such conditions favoured population build up of the two spotted spider miteTetranychus urticae Koch. In 1993 and 1994, three plastichouses planted to cucumber, cultivar Rawa or Hana were selected. Relative humidity in two of them was maintained over 50% during the day using spraying nozzles, the third being kept as control. Mildew diseases induced by increased leaf wetness needed to be managed using fungicides.Phyioseiulus persimilis andP. longipes were released in the first two plastichouses, while acaricides were applied in the control. In early MayT. urticae population increase on the growing top of cucumber plants required two acaricidal applications as predatory mites did not migrate to the apical leaves which were too warm and dry. More than 80% of the maximum yield was obtained on average in plastichouses using increased relative humidity, but without any acaricidal applications.     

Influence of the spider mite, Tetranychus urticae Koch (Acarina, Tetranychidae) population density on its dynamics on different cucumber cultivars

The dependence of the population dynamics, dispersal behavior, and formation of the migration stage of the spider mite, Tetranychus urticae K. on the population density on cucumber plants differs between cultivars. The optimum spider mite density providing the maximum reproduction may be determined by the cucumber plants cultivar and the morphophysiological state of the plants.     

Factors affecting photoreactivation in UVB-irradiated herbivorous spider mite (Tetranychus urticae)

To investigate and identify the ticks prevalent in the North East part of India, scanning electron microscope (SEM) and DNA sequence of nuclear second internal transcribed spacer (ITS2) and mitochondrial 16S ribosomal DNA (rDNA) were used. Based on the morphological and molecular analysis, the ticks infesting cattle of North East India were found to be Rhipicephalus (Boophilus) microplus and Haemaphysalis bispinosa. ITS2 and 16S rDNA sequence from R. (B.) microplus and H. bispinosa were amplified using universal and gene specific primers, sequenced and analysed. The length of the amplified ITS2 sequence of R. (B.) microplus and H. bispinosa, were found to be approximately 1,500 and 1,700 bp, respectively. The length of the 16S rDNA sequences in both the ticks was found to be similar in size, but they differ in their base pair constitutions. This is the first report of the nucleotide sequences of ITS2 and 16S rDNA of H. bispinosa. Phylogenetic analysis revealed that H. bispinosa is a close relative of H. longicornis. A polymerase chain reaction–restriction fragment length polymorphism diagnostic tool was developed based on HindIII digestion of ITS2 in order to facilitate the identification of these two species which cannot be distinguished once it is fully-fed. Present study describes the use of SEM and 16S rDNA/ITS2 based molecular analysis in identification and differentiation of fully fed tick species.