Population genetic structure of Bemisia tabaci MED (Hemiptera: Aleyrodidae) in Korea

Abstract

The sweet potato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a major agricultural pest that causes economic damages worldwide. In particular, B . tabaci MED (Mediterranean) has resulted in serious economic losses in tomato production of Korea. In this study, 1,145 B . tabaci MED females from 35 tomato greenhouses in different geographic regions were collected from 2016 to 2018 (17 populations in 2016, 13 in 2017, and five in 2018) and analyzed to investigate their population genetic structures using eight microsatellite markers. The average number of alleles per population ( N A ) ranged from 2.000 to 5.875, the expected heterozygosity ( H E ) ranged from 0.218 to 0.600, the observed heterozygosity ( H O ) ranged from 0.061 to 0.580, and the fixation index inbreeding coefficient ( F IS ) ranged from -0.391 to 0.872 over the three years of the study. Some significant correlation ( p < 0.05) was present between genetic differentiations ( F ST ) and geographical distance, and a comparatively high proportion of variation was found among the B . tabaci MED populations. The B . tabaci MED populations were divided into two well-differentiated genetic clusters within different geographic regions. Interestingly, its genetic structures converged into one genetic cluster during just one year. The reasons for this genetic change were speculated to arise from different fitness, insecticide resistance, and insect movement by human activities.

What Is the Spatial Extent of a Bemisia tabaci Population?

“…While some sampled populations appear to have undergone a population bottleneck, perhaps due to founder events typical of invasive populations or strong population suppression from insecticides [13,55,57], the majority of populations instead exhibit some degree of heterozygote deficit. [13,16,17,54,[56][57][58]60,61,65,66,70]. "MEAM 1" stands for Middle East-Asia Minor 1; "MED" stands for Mediterranean; "IO" stands for Indian Ocean; "SSA 1" stands for Sub-Saharan Africa 1.…”

“…This might follow from an absence of gene flow among divergent populations, suggesting that localized B. tabaci movements over the landscape may predominate, but could also arise if sampling schemes result in high rates of sibling sampling. Additional evidence of inbreeding in microsatellite datasets is strong linkage disequilibrium among loci, wherein allele frequencies among loci are correlated because they share a very recent common ancestor and are still being [13,16,17,54,[56][57][58]60,61,65,66,70]. "MEAM 1" stands for Middle East-Asia Minor 1; "MED" stands for Mediterranean; "IO" stands for Indian Ocean; "SSA 1" stands for Sub-Saharan Africa 1.…”

“…Unlike studies based on COI, microsatellite-based studies frequently report high levels of genetic diversity within invasive B. tabaci populations [ 43 , 46 , 55 , 56 , 64 ], though sometimes this is conflated with variation among cryptic species [ 46 ] or is indirectly inferred [ 43 ]. Some studies report increasing [ 65 ] or decreasing [ 13 , 45 , 58 ] genetic diversity over time, invoking extinction/recolonization dynamics or ongoing population expansion. Relevant to the question of what spatial scales best define B. tabaci populations, we examine four themes among B. tabaci microsatellite datasets that can shed light on the extent of gene flow among B. tabaci populations.…”

“…The fixation index (F ST ) [ 76 ], is a commonly used measure of genetic differentiation between populations, ranging from 0 (no differentiation) to 1 (complete differentiation). Of the 15 studies reporting values of F ST among populations within cryptic species, eight (53%) include ranges of F ST that bound zero [ 17 , 41 , 54 , 58 , 61 , 65 , 66 , 67 ], though upper estimates of F ST among studies sometimes exceed 0.5 [ 59 , 64 , 65 ] ( Figure 2 , Table S2 ). Differences in the geographic extent of sampling largely explain differences in the range of F ST among studies.…”

“…These studies are global in coverage, focus largely on populations of MEAM 1 and MED, and span collections from 1991−2018 ( Figure 1 , Table S1 ). Studies leverage a variety of genetic marker types [ 27 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 ], but, while the majority use microsatellites [ 13 , 16 , 17 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 ], use of single nucleotide polymorphisms is beginning to become more common [ 15 , 69 , 70 , 71 ] ( Figure 1 ). We organize our synthesis around insights gained from three common marker types (cytochrome oxidase I, microsatellites, single nucleotide polymorphisms) and associated measures of genetic diversity and differentiation, interpreting emergent patterns in light of potential underlying ecological and evolutionary processes.…”