Research Overview on Occurrence and Control of Tetranychus urticae Koch in China

Tetranychus urticae Koch;Insecticide resistance;Chemical control This paper elaborates the occurrence factors and damage characteristics of Tetranychus urticae Koch in China,and emphatically summarizes three main control strategies of T.urticae,namely agricultural control,chemical control and biological control,as well as research progress in its resistance mechanisms.The problems existing in controlling T.urticae and its resistance management strategies are put forward,to provide a theoretical basis for the resistance management and comprehensive control of T.urticae.

Temperature-dependent development of Neoseiulus barked （Acari： Phytoseiidae） on Tetranychus urticae （Acari： Tetranychidae） at seven constant temperatures

The effect of seven constant temperatures of 15, 20, 25, 27, 30, 35 and 37℃ on developmental time ofNeoseiulus barkeri Hughes were determined in laboratory conditions under 65% - 5% RH and a photoperiod of 12 ： 12 （L ： D） h on nymphal stages of Tetranychus urticae Koch. Total developmental time of females （from egg to adult emergence） at the above-mentioned temperatures was 26.59, 14.43, 6.32, 5.64, 4.59, 3.98 and 4.67 days, respectively. Developmental rate of the N. barkeri increased as temperature increased from 15 to 35℃, but declined at 37℃. A linear and two nonlinear models were fitted to developmental rate of immature stages ofN. barkeri to predict the developmental rate as a function of temperature, as well as to estimate the thermal constant （K） and critical temperatures （i.e., Tmin, Topt and Tmax）. The estimated values of the Tmin and K for total developmental time using the linear model were 12.07℃ and 86.20 degree-days （DD）, respectively. The Trnin and Tmax estimated by the Sharpe-Schoolfield-Ikemoto （SSI） model were 11.90℃ and 37.41℃, respectively. The estimated Topt for overall immature stage development ofN. barkeri by the Lactin and SSI models were 33.89℃ and 24.51℃, respectively. Based on the biological criteria of model evaluation, the linear and SSI models were found to be the best models for describing the developmental rate of overall immature stages of N. barkeri and estimating the temperature thresholds.

Toxicity, inheritance and biochemistry of clofentezine resistance in Tetranychus urticae

This study evaluates the toxicological and biochemical response of two-spotted spider mites to clofentezine selection pressure. The mortality rate of Tetranychus urticae in adult females depends on increased clofentezine concentration and clofentezine was found to be effective against females. The resistance rate of the CUM strain selected 12 times once per generation with clofentezine was increased from 1.28- to 105.27-fold. The interaction of some synergists with clofentezine was analyzed in the clofentezine-resistant CLOF 12 strain. Synergists had no effect on clofentezine toxicity. The clofentezine-resistant CLOF 12 strain showed resistance against chlorpyrifos, abamectin, propargite, fenpyroximate and amitraz. The modes of inheritance of resistance to clofentezine were found to be incompletely dominant and not sex-linked. Esterase enzyme activity was detected both by gel electrophoresis and microplate reader methods, while glutathione S-transferase （GST） and monooxygenase （P450） activity were detected only by the microplate reader method. During the selection period the esterase, the GST and the P450 enzymes activities were raised from 7.69, 7.09 and 0.003 3 to 18.40, 13.11 and 0.003 7 milli-optical density/rain/rag proteins, respectively. An increase was observed in the band intensity of esterases and esterase enzymes may play a role in clofentezine resistance in T. urticae.

Frequencies and mechanisms of pesticide resistance in Tetranychus urticae field populations in China

The two-spotted spider mite Tetranychus urticate is an important agricultural pest worldwide.It is extremely polyphagous and has developed resistance to many pesticides.Here,we assessed the pesticide resistance of seven field populations of T.urticae in China,their target site mutations and the activities of their detoxification enzymes.The results showed that abamectin and the traditional pesticides pyridaben,profenofos and bifenthrin had higher resistance or lower toxicity than more recently developed pesticides including chlorfenapyr,spinetoram,cyflumetofen,cyenopyrafen,bifenazate and B-azolemiteacrylic.The frequency of point mutations related to abamectin resistance,G314D in the glutamate-gated chloride channel 1(GluCl1)and G326E in GluC13,ranged 47%-70%and 0%-97%,respectively.The frequency of point mutations in A1215D and F1538I of the voltage-gated sodium channel gene(VGSC),which may increase resistance to pyrethroids,ranged 88%-100%and 10%-100%,respectively.For target sites related to organophosphate resistance,mutation frequencies ranged 25%-92%for G119S and 0%-23%for A201S in the acetycholinesterase gene(Ace).Mutation G126S in the bifenazate resistance-related cytochrome b gene(Cytb)was observed in three of the seven T.urticae populations.Higher activities of detoxification enzymes(P450,GST,CarEs and UGTs)were observed in two T.urticae populations,with significant difference in the XY-SX population.These results provide useful information on the status of pesticide resistance of T.urticae in China and suggest that T.urticae field populations may have multiple resistance mechanisms.

Divergent methylation pattern in adult stage between two forms of Tetranychus urticae （Acari： Tetranychidae）

The two-spotted spider mite, Tetranychus urticae Koch has two forms： green form and red form. Understanding the molecular basis of how these two forms established without divergent genetic background is an intriguing area. As a well-known epigenetic process, DNA methylation has particularly important roles in gene regulation and developmental variation across diverse organisms that do not alter genetic background. Here, to investigate whether DNA methylation could be associated with different phenotypic conse- quences in the two forms of T. urticae, we surveyed the genome-wide cytosine methylation status and expression level of DNA methyltransferase 3 （Tudnmt3） throughout their entire life cycle. Methylation-sensitive amplification polymorphism （MSAP） analyses of 585 loci revealed variable methylation patterns in the different developmental stages. In particular, principal coordinates analysis （PCoA） indicates a significant epigenetic differentiation be- tween female adults of the two forms. The gene expression of Tudnmt3 was detected in all examined developmental stages, which was significantly different in the adult stage of the two forms. Together, our results reveal the epigenetic distance between the two forms of T. urticae, suggesting that DNA methylation might be implicated in different developmental demands, and contribute to different phenotypes in the adult stage of these two forms.

智利小植绥螨防治设施西瓜二斑叶螨的研究与应用

为探明智利小植绥螨(Phytoseiulus persimilis Athias-Henriot)防治设施西瓜二斑叶螨的关键技术和持续控害效果,研究了不同释放时期和释放量条件下智利小植绥螨对西瓜二斑叶螨的防治效果,并持续调查了连续4年释放智利小植绥螨的防治效果。结果表明,释放时期显著影响智利小植绥螨对二斑叶螨的防治效果,二斑叶螨平均数量≤2头/片叶时,释放智利小植绥螨对二斑叶螨的控制效果最好,最大防治效果为82.3%,当二斑叶螨平均数量>50头/片叶时,防治效果较差,不宜释放;释放量也显著影响智利小植绥螨对二斑叶螨的防治效果,按照25头/m^(2)和30头/m^(2)释放智利小植绥螨7、14 d的防治效果均能超过80%,14 d的防治效果显著高于43%联苯肼酯悬浮剂;连续4年定点定棚使用智利小植绥螨防治二斑叶螨,天敌释放量逐年降低,10头/m^(2)释放量即可有效控制二斑叶螨为害,防治效果为89.7%。

GARP: A family of glycine and alanine-rich proteins that helps spider mites feed on plants

Spider mites(Tetranychidae)are destructive agricultural pests which have evolved strategies to overcome plant defenses,such as the ability to puncture the leaves of their hosts to feed.The expression of many genes with unknown functions is altered during feeding,but little is known about the role of these genes in plant–mite interactions.Here,we identified 3 novel gene families through analysis of genomic and transcriptomic data from 3 spider mite species.These GARP family genes encode glycine and alanine-rich proteins;they are present in mites(Acariformes)but absent in ticks(Parasitiformes)in the subclass Acari,indicating that these genes have undergone a significant expansion in spider mites and thus play important adaptive roles.Transcriptomic analysis revealed that the expression of GARP genes is strongly correlated with feeding and the transfer to new hosts.We used RNA interference to silence GARP1d in the two-spotted spider mite Tetranychus urticae,which inhibited feeding and egg laying and significantly increased mortality when the mites were transferred to soybean shoots;a similar effect was observed after TuVATPase was silenced.However,no changes in mite mortality were observed after TuGARP1d-silenced mites were placed on an artificial diet,which was different from the effect of TuVATPase silencing.Our results indicate that GARP family members play important roles in mite–plant interactions.Additional studies are needed to clarify the mechanisms underlying these interactions.

Comparative transcriptomics reveals hidden issues in the plant response to arthropod herbivores

Plants experience different abiotic/biotic stresses,which trigger their molecular machinery to cope with them. Besides general mechanisms prompted by many stresses, specific mechanisms have been introduced to optimize the response to individual threats. However, these key mechanisms are difficult to identify. Here, we introduce an in-depth species-specific transcriptomic analysis and conduct an extensive meta-analysis of the responses to related species to gain more knowledge about plant responses. The spider mite Tetranychus urticae was used as the individual species, several arthropod herbivores as the related species for meta-analysis, and Arabidopsis thaliana plants as the common host. The analysis of the transcriptomic data showed typical common responses to herbivory, such as jasmonate signaling or glucosinolate biosynthesis. Also, a specific set of genes likely involved in the particularities of the Arabidopsis-spider mite interaction was discovered. The new findings have determined a prominent role in this interaction of the jasmonateinduced pathways leading to the biosynthesis of anthocyanins and tocopherols. Therefore, tandem individual/general transcriptomic profiling has been revealed as an effective method to identify novel relevant processes and specificities in the plant response to environmental stresses.

Intraguild predation among Scolothrips Iongicornis （Thysanoptera： Thripidae）, Neoseiulus californicus and Typhlodromus bagdasarjani （Acari： Phytoseiidae） under laboratory conditions

This study was carried out on the ability of predatory thrips Scolothrips longi- cornis Priesner to feed on 2 phytoseiid species and vice versa. Also the effect of predation of Neoseiulus californicus （McGregor） on Typhlodromus bagdasarjani Wainstein and Aru- tunjan and vice versa was evaluated. The larvae, prepupae, and pupae of thrips and the eggs, larvae, and protonymphs of phytoseiids were selected as intraguild prey. The in- traguild predation （IGP） among S. longicornis and 2 phytoseiid species was unidirectional and in favor of phytoseiids, i.e., S. longicornis was not able to feed on larval stages of 2 phytoseiids. However, N. californicus and T. bagdasarjani fed on the 1st instar larvae （1.39 and 0.80 per day）, 2nd instar larvae （0.87 and 0.55 per day）, prepupae （0.51 and 0.48 per day）, and pupae of thrips （0.51 and 0.49 per day, respectively）. Both phytoseiids fed on eggs, larvae, and protonymphal stages of each other. Females of N. californicus con- sumed more phytoseiid larvae （2.49 per day） than T. bagdasarjani, which consumed 1.08 N. californicus larvae per day. When Tetranychus urticae was presented as an extraguild prey, intensity oflGP between 2 species ofphytoseiids and on larval stages ofS. longicornis reduced significantly. Therefore, it is concluded that （i） IGP existed among the 3 examined species and lack of feeding of S. longicornis on 2 phytoseiid species can be justified by its feeding type （monophagy）, （ii） N. californicus was much more prone to IGP than was T. bagdasarjani.