Many spider mites belonging to the genus Tetranychus are of agronomical importance. With limited morphological characters, Tetranychus mites are usually identified by a combination of morphological characteristics and molecular diagnostics. To clarify their molecular evolution and phylogeny, the mitochondrial genomes of the green and red forms of Tetranychus urticae as well as T. kanzawai, T. ludeni, T. malaysiensis, T. phaselus, T. pueraricola were sequenced and compared. The seven mitochondrial genomes are typical circular molecules of about 13,000 bp encoding and they are composed of the complete set of 37 genes that are usually found in metazoans. The order of the mitochondrial (mt) genes is the same as that in the mt genomes of Panonychus citri and P. ulmi, but very different from that in other Acari. The J-strands of the mitochondrial genomes have high (∼84%) A+T contents, negative GC-skews and positive AT-skews. The nucleotide sequence of the cox1 gene, which is commonly used as a taxon barcode and molecular marker, is more highly conserved than the nucleotide sequences of other mitochondrial genes in these seven species. Most tRNA genes in the seven genomes lose the D-arm and/or the T-arm. The functions of these tRNAs need to be evaluated. The mitochondrial genome of T. malaysiensis differs from the other six genomes in having a slightly smaller genome size, a slight difference in codon usage, and a variable loop in place of the T-arm of some tRNAs by a variable loop. A phylogenic analysis shows that T. malaysiensis first split from other Tetranychus species and that the clade of the family Tetranychoidea occupies a basal position in the Trombidiformes. The mt genomes of the green and red forms of T. urticae have limited divergence and short evolutionary distance.

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Although a variety of factors underlying diapause have been identified in arthropods and other organisms, the molecular mechanisms regulating diapause are still largely unknown. Here, to better understand this process, we examined diapause-associated genes in the two-spotted spider mite, Tetranychus urticae, by comparing the transcriptomes and proteomes of early diapausing and reproductive adult females. Amongst genes underlying diapause revealed by the transcriptomic and proteomic data sets, we described the noticeable change in Ca -associated genes, including 65 Ca -binding protein genes and 23 Ca transporter genes, indicating that Ca signalling has a substantial role in diapause regulation. Other interesting changes in diapause included up-regulation of (1) glutamate receptors that may be involved in synaptic plasticity changes, (2) genes involved in cytoskeletal reorganization including genes encoding each of the components of thick and thin filaments, tubulin and members of integrin signalling and (3) genes involved in anaerobic energy metabolism, which reflects a shift to anaerobic energy metabolism in early diapausing mites.

The geomagnetic field (GMF) is well documented for its essential role as a cue used in animal orientation or navigation. Recent evidence indicates that the absence of GMF (mimicked by the near-zero magnetic field, NZMF) can trigger stress-like responses such as reduced body weight, as we have previously shown in the brown planthopper, Nilaparvata lugens. In this study, we found that consistent with the significantly decreased body weight of newly emerged female (−14.67%) and male (−13.17%) adult N. lugens, the duration of the phloem ingestion feeding waveform was significantly reduced by 32.02% in 5th instar nymphs reared under the NZMF versus GMF. Interestingly, 5th instar nymphs that exhibited reduced feeding had significantly higher glucose levels (+16.98% and +20.05%; 24 h and 48 h after molting), which are associated with food aversion, and expression patterns of their appetite-related neuropeptide genes (neuropeptide F, downregulated overall; short neuropeptide F, down-regulated overall; adipokinetic hormone, up-regulated overall; and adipokinetic hormone receptor, down-regulated overall) were also altered under the absence of GMF in a manner consistent with diminishing appetite. Moreover, the expressions of the potential magnetosensor cryptochromes (Crys) were found significantly altered under the absence of GMF, indicating the likely upstream signaling of the Cry-mediated magnetoreception mechanisms. These findings support the hypothesis that strong changes in GMF intensity can reduce adult body weight through affecting insect feeding behavior and underlying regulatory processes including appetite regulation. Our results highlight that GMF could be necessary for the maintenance of energy homeostasis in insects.

The geomagnetic field (GMF) is well documented for its essential role as a cue used in animal orientation or navigation. Recent evidence indicates that the absence of GMF can trigger stress-like responses such as reduced body weight, as we have previously shown in newly emerged adults of the brown planthopper, Nilaparvata lugens. To test the hypothesis that reduced feeding in the absence of the GMF leads to a decrease of N. lugens body weight, we compared magnetic responses in feeding behavior, glucose levels, and expression of magnetoreception-and appetite-related genes in brown planthopper nymphs exposed to either a near-zero magnetic field (NZMF, i.e., GMF absence) or typical GMF conditions. In addition to observing the expected responses in the expression of the potential magnetosensor cryptochromes, the food intake of 5 th instar nymphs was significantly reduced in insects reared in the absence of GMF. Insects that exhibited reduced feeding reared in the absence of the GMF also had higher glucose levels which is associated with food aversion.Expression patterns of appetite-related neuropeptide genes were also altered in the absence of GMF in a manner consistent with diminishing appetite. These findings support the hypothesis that strong changes in GMF intensity can affect insect feeding behavior and underlying regulatory processes.Our results provide further evidence that magnetoreception and regulatory responses to GMF changes can affect a wide variety of biological processes.