Extremely low fecundity and highly female-biased sex ratio in nest-living spider mite Schizotetranychus brevisetosus (Acari: Tetranychidae)
2017
Tamura, Kaori | Ito, Katsura
Spider mites show various life types characterized by spinning behavior, web structure, and sociality. Individuals of the woven-nest (WN) species construct silken nests on the undersurface of host leaves, inside which they develop and reproduce. This nesting behavior may be related with the defense mechanism and life history traits of mites in the stable habitat (e.g., evergreen trees). If the WN life type affects the life-history traits, these traits may be similar within WN species. The WN species are known to be fragmentarily distributed in diverse genera, Stigmaeopsis, Schizotetranychus, Eotetranychus, and Oligonychus, and their life types are suspected to have secondarily converged. However, their life histories have not been elucidated except for several species in specific genera. To supply the information in Schizotetranychus, we investigated the demographic traits and the sex ratio of Schizotetranychus brevisetosus, which shows the WN life type and lives on the evergreen Japanese blue oak Quercus glauca. We estimated the development time of females as 22.6 ± 3.1 days (mean ± SD, n = 22) and the fecundity of fertilized females as 13.7 ± 5.9 (n = 37) at 25°C. The sex ratio of males to the total number of adults at emergence was low (0.072). The intrinsic rate of natural increase (rₘ) was estimated as 0.060 day⁻¹, one of the lowest ever reported for spider mites at the same temperature. The present results were similar to other WN species in that fecundity and male ratio were low.
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