Structural characterization of the silk of two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae)

The present investigation was undertaken to obtain information about the structural and morphological properties of the silk of two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) by means of the atomic force microscope (AFM), scanning electron microscope (SEM), energy dispersive X-ray spectrophotometer (EDX) and attenuated total reflection Fourier transmission infrared spectroscopy (ATR-FTIR) techniques. AFM images show that the shapes of silken threads produced by both female and male mites are similar and have non-uniform cylindrical structure. In general, the appearance of silks produced by female mites is smoother than those of the male mites. In addition, it is determined that the silk threads produced by both female and male individuals have single and double stranded structure. There were differences in the thread dimensions of female and male which could depend on the body size of the mites. However, there is no statistically significant correlation between the body size of the mites and their thread dimensions. The silk material was found to consist predominantly of C, N and O elements and minor fractions of Al, P, Cl and K. The ATR-FTIR spectrum of the silk of two-spotted spider mite exhibited characteristic vibrational modes originating from amid groups, which were attributed to random coil and β-sheet molecular conformation in the protein structure of the silk of two-spotted spider mite. Understanding the features of the two-spotted spider mite silks may be of practical importance for the future studies related to biomaterial and material science.