The predatory mite Neoseiulus womersleyi (Schicha) (Acari: Phytoseiidae) is an important natural enemy of the Kanzawa spider mite, Tetranychus kanzawaki Kishida (Acari: Tetranychidae), in tea fields. Attraction and preservation of natural enemies by habitat management to reduce the need for acaricide sprays is thought to enhance the activity of N. womersleyi. To better conserve N. womersleyi in the field, however, it is essential to elucidate the population genetic structure of this species. To this end, we developed ten microsatellite DNA markers for N. womersleyi. We then evaluated population structure of N. womersleyi collected from a tea field, where Mexican sunflower, Tithonia rotundifolia (Mill.), was planted to preserve N. womersleyi. Seventy-seven adult females were collected from four sites within 200 m. The fixation indexes FST among subpopulations were not significantly different. The kinship coefficients between individuals did not differ significantly within a site as a function of the sampling dates, but the coefficients gradually decreased with increasing distance. Bayesian clustering analysis revealed that the population consisted of three genetic clusters, and that subpopulations within 100 m, including those collected on T. rotundifolia, were genetically similar to each other. Given the previously observed population dynamics of N. womersleyi, it appears that the area inhabited by a given cluster of the mite did not exceed 100 m. The estimation of population structure using microsatellite markers will provide valuable information in conservation biological control.
Abstract:We investigated the control of Kanzawa spider mite, Tetranychus kanzawai Kishida on tea by utilizing "natural enemy preservation plants". The plants were used as hosts for the growth of the predatory mite Neoseiulus womersleyi (Schicha). First, we screened for plants on which N. womersleyi would proliferate, using Tetranychus urticae Koch as the non-pest prey, and identified Tithonia rotundifolia as a candidate natural enemy preservation plant. Next, we tested the effectiveness of T. rotundifolia for supporting a population of N. womersleyi and thus suppressing the population density of T. kanzawai on tea. When T. urticae were released onto T. rotundifolia growing at the edge of a tea field, the population density of N. womersleyi increased and the dispersal of N. womersleyi towards the middle of the tea field was observed. In addition, the density of T. kanzawai in the test plot was lower than in the control plot. These results suggest that N. womersleyi proliferated on natural enemy preservation plants suppressed the population density of T. kanzawai and that T. rotundifolia is effective as a natural enemy preservation plant.
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