Phylogenetic-Related Divergence in Perceiving Suitable Host Plants among Five Spider Mites Species (Acari: Tetranychidae)

Abstract

Spider mites belonging to the genus Tetranychus infest many important agricultural crops in both fields and greenhouses worldwide and are diversified in their host plant range. How spider mites perceive their suitable host plants remains not completely clear. Here, through two-host-choice designs (bean vs. tomato, and bean vs. eggplant), we tested the efficacies of the olfactory and gustatory systems of five spider mite species (T. urticae, T. truncatus, T. pueraricola, T. piercei, and T. evansi), which differ in host plant range in sensing their suitable host plant, by Y-tube olfactometer and two-choice disc experiments. We found that spider mites cannot locate their suitable host plants by volatile odours from a long distance, but they can use olfactory sensation in combination with gustatory sensation to select suitable host plants at a short distance. Highly polyphagous species displayed strong sensitivity in sensing suitable host plants rather than the lowered sensitivity we expected. Intriguingly, our principal component analyses (PCAs) showed that the similarity among five spider mite species in the performance of perceiving suitable host plants was highly correlated with their relative phylogenetic relationships, suggesting a close relationship between the chemosensing system and the speciation of spider mites. Our results highlight the necessity of further work on the chemosensing system in relation to host plant range and speciation of spider mites.

Keywords: Y-tube olfactometer; chemosensing system; feeding preference; two-choice disc.

Figure 1

Schematic of the Y type olfactory device.

Figure 2

Olfactory selection of five species of spider mites (A) between bean and tomato and (B) between bean and eggplant plants. TuG, Tpu, Ttr, Tpi and Te represent T. urticae (green form), T. pueraricola, T. truncatus, T. piercei and T. evansi, respectively. The numbers of individuals selected for each plant are labelled in the brackets near the bars. NC, number of individuals that made no selection.

Figure 3

Selectivity of five species of spider mites to bean and tomato within 72 h. **, *** represent p < 0.01 and p < 0.001, respectively; NS, no significant difference; NC, number of individuals that made no selection. (A,B) for T. urticae; (C,D) for T. pueraricola; (E,F) for T. truncates; (G,H) for T. piercei; (I,J) for T. evansi.

Figure 4

PCA results of host selection of spider mites. (A) PCA of leaf disc selection of bean and tomato by spider mites. (B) PCA of leaf disc selection of bean and eggplant by spider mites. (C) PCA of leaf disc selection and Y-tube olfactory selection. (D) Relative positions of five species of spider mites in phylogenetic trees inferred by DNA sequences. The tree was depicted according to the previous phylogenetic studies using 18S and 28S rRNA genes, mitochondrial cytochrome c oxidase subunit 1 gene [17], RNA-Seq data [18] and mitochondrial genome [19] with a maximum likelihood method.