Population structure of the predatory mite Neoseiulus womersleyi in a tea field based on an analysis of microsatellite DNA markers

Abstract

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 F (ST) 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.

Fig. 1

Locations of the four sites in the tea field where we collected Neoseiulus womersleyi. Sampling dates were shown in Table 1

Fig. 2

Graphical inference to estimate the number of genetic clusters using the STRUCTURE software. (A) Mean log-likelihood values [L(K)] ± SD as a function of K, for K = 1 to K = 30, where K represents the number of clusters. (B) Rate of change in the log-likelihood of the data (∆K; Evanno et al. 2005) as a function of K

Fig. 3

The results of Bayesian clustering analysis and individual assignment analysis of Neoseiulus womersleyi using the STRUCTURE software for three clusters. The x-axis of the bar chars represents individual mites. The y-axis of the bar chars represents the individual assignment probabilities. Black, grey, and white components of each bar represent the proportion in each of the three clusters

Fig. 4

Neighbour–joining tree for seven subpopulations of Neoseiulus womersleyi collected in the tea field based on the Cavalli-Sforza and Edwards’ (1967) chord distance (Dc). Numbers are bootstrap support indices on loci (left) and on individuals (right), respectively

Fig. 5

The average and SD of the kinship coefficients (Loiselle et al. 1995) between individual Neoseiulus womersleyi grouped into each 50-m distance. Points labelled with different letters differ significantly (P < 0.05; pairwise comparisons using the Wilcoxon rank-sum test adjusted using Holm’s method)