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.
BACKGROUND: Previously, we reported that the majority of the Bemisia tabaci Mediterranean (MED) populations converged from two dominant genetic clusters (cluster 1 and 2) to one (cluster 2) during 1 year in greenhouse tomatoes in Korea. To find possible mechanisms for this phenomenon, we investigated the concurrent changes in resistance traits of the two clusters for three insecticide classes (organophosphate, pyrethroid, and neonicotinoid).RESULTS: Since the resistance mutation frequencies in regional samples were either high (i.e. the voltage-sensitive sodium channel L925I/T929V mutations and the F392 acetylcholinesterase 1 mutation) or zero (the nicotinic acetylcholine receptor R81T mutation), no meaningful correlation between the resistance allele frequency and genetic cluster was deduced. However, the actual resistance levels to all three insecticide classes were significantly higher in cluster 2 than in cluster 1, suggesting that cluster 2 has a higher resistance potential. Furthermore, thiamethoxam treatment to the mixed population of clusters 1 and 2 over three generations exhibited a strong tendency of population change from cluster 1 to cluster 2. CONCLUSION: Our results demonstrated that the insecticide resistance trait is one of the driving forces for rapid genetic cluster change in B. tabaci MED populations.
Aphis gossypii Glover (Hemiptera: Aphididae) is a serious polyphagous agricultural pest worldwide. In the present study, we used eight microsatellite markers to investigate the genetic structure and diversity of A. gossypii populations in Korea. Samples were collected from 37 locations in Korea (18 populations in 2016, 14 populations in 2017, and five populations in 2018) from pepper plants. A. gossypii had low to moderate genetic diversity, and expected heterozygosity (HE) ranged from 0.354 to 0.719. A Mantel test of isolation by distance indicated no relationship between genetic structure and geographic distance among all populations (r2 = 0.0004, p = 0.370), suggesting high gene flow among populations in Korea. Populations of A. gossypii in Korea were divided into two distinct genetic clusters (ΔK = 2). In 2016 and 2017, the genetic clusters changed into opposite genetic structures within one year mostly in northwest and southeast parts of Korea. Possible relevance of study results was discussed. Chemical control, cyclical parthenogenesis, and immigrants from the exterior might have resulted in this low genetic diversity and opposite genetic clusters.
Bemisia tabaci Mediterranean (Gennadius) (Hemiptera: Aleyrodidae) is an economically important insect pest worldwide. Previously, we have reported that most B. tabaci Mediterranean (MED) populations occurring in greenhouse tomatoes in Korea have been displaced from well-differentiated two genetic clusters (C1 and C2) to one (C2) during one-year period. To elucidate factors responsible for this phenomenon, we compared life history parameters of these two different genetic clusters through single and cross mating experiments on two different host plants, cucumber and tobacco, at 26°C. Intrinsic rate of increase (r), finite rate of increase (λ), and net reproductive rate (Ro) were significantly higher in the dominating cluster (C2) (0.247, 1.280, and 192.402, respectively on cucumber; 0.226, 1.253, and 133.792, respectively on tobacco) than in the other cluster (C1) (0.149, 1.161, and 50.539, respectively on cucumber; 0.145, 1.156, and 53.332, respectively on tobacco). Overall performances of cross mating groups, C2fC1m (C2 female × C1 male) and C1fC2m (C1 female × C2 male), were in-between those of C2 and C1, with C2fC1m performing better than C1fC2m. Thus, maternal inheritance appeared to be significantly associated with their life history parameters, with partial involvement of paternal inheritance. Our results demonstrated that the rapid displacement of genetic clusters of B. tabaci MED populations was clearly associated with differences in their life history parameters.
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