Possible Source Populations of the White-backed Planthopper in the Greater Mekong Subregion Revealed by Mitochondrial DNA Analysis

The genomic history and global migration of a windborne pest

Many insect pests, including the brown planthopper (BPH), undergo windborne migration that is challenging to observe and track. It remains controversial about their migration patterns and largely unknown regarding the underlying genetic basis. By analyzing 360 whole genomes from around the globe, we clarify the genetic sources of worldwide BPHs and illuminate a landscape of BPH migration showing that East Asian populations perform closed-circuit journeys between Indochina and the Far East, while populations of Malay Archipelago and South Asia undergo one-way migration to Indochina. We further find round-trip migration accelerates population differentiation, with highly diverged regions enriching in a gene desert chromosome that is simultaneously the speciation hotspot between BPH and related species. This study not only shows the power of applying genomic approaches to demystify the migration in windborne migrants but also enhances our understanding of how seasonal movements affect speciation and evolution in insects.

The Genetic Diversity of White-Backed Planthoppers (Sogatella furcifera) between Myanmar and Yunnan Province of China

In order to clarify the migration route and the source of white-backed planthopper (WBPH) (Sogatella furcifera) between Myanmar and Yunnan Province, China, we collected six populations throughout Myanmar and five populations around the border areas in Yunnan Province, China. A total of 790 base pairs in the mtDNA COI genes from 416 individuals were obtained. A total of 43 haplotypes were identified, among which 37 were unique haplotypes, and the remaining 6 were shared among different populations. Two common shared haplotypes (H_1 and H_2) had a widespread distribution in all populations and accounted for 88.8% of the total haplotype frequency, suggesting a high-level gene flow among the Myanmar and Yunnan populations. Bayesian skyline plot (BSP) analysis results indicated that the effective population size of WBPH expanded between about 10,000 and 7000 years ago, and S. furcifera might follow the post-LGM (Last Glacial Maximum) expansion pattern. Based on the total migrant (Nem) value, it can be deduced that north and northeast Myanmar were the primary migration sources for WBPH populations in the southwest and south Yunnan regions. This study aims to contribute to the sustainable regional management of this important rice pest and provide new insights into the genetic diversity of WBPH in Southeast Asia.

Species-specific markers for Nilaparvata lugens and Sogatella furcifera (Hemiptera: Delphacidae) based on mitochondrial cytochrome oxidase I

Brown planthopper (BPH), Nilaparvata lugens (Stål) and white-backed planthopper (WBPH), Sogatella furcifera (Horváth) are the most destructive sucking insect pests of rice in all rice growing parts of the world. For their accurate identification at early stages, we have developed two species-specific markers (SNL4F and SNL4R for BPH; SNF2F and SNF2R for WBPH) based on mitochondrial cytochrome oxidase I (COI) for their easy detection using Polymerase Chain Reaction (PCR). The markers were developed based on nucleotide differences in COI gene and were subjected to various tests based on PCR-based gel images. The designed primers were cross-checked with five other species, which confirmed their specificity. The primers were also found to be efficient in identification of their respective species (BPH and WBPH) in all the individuals sampled from different regions of India. The lowest detection sensitivity of both the primers was up to 1 ng/µl DNA after testing them through a series of varied DNA concentrations. The species-specific primers developed in this study will help in easy and rapid identification of BPH and WBPH in all the stages of their development and in turn facilitate their timely management.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03693-x.

A New Mitochondrial Genome of Sogatella furcifera (Horváth) (Hemiptera: Delphacidae) and Mitogenome-Wide Investigation on Polymorphisms

Simple Summary

We completed one mitogenome of white-backed planthopper (WBPH), Sogatella furcifera (Horváth), with finding heteroplasmy phenomenon confirmed by PCR reaction and Sanger sequencing method. This heteroplasmy was not observed in WBPHs (n = 24) collected from the fields, suggesting that it may be uncommon in fields. We also analyzed single nucleotide polymorphisms, insertion and deletions, and simple sequence repeats among three currently available WBPH mitogenomes of Korea and China, suggesting that identified intraspecific variations could be potential candidates for developing markers to distinguish geographical populations of WBPH including Korean and Chinese. Phylogenetic analysis of 32 mitogenomes of Delphacidae including the three WBPH mitogenomes suggested that Delphacinae seems to be monophyletic and Sogatella species including WBPH are clearly formed as one clade.

Abstract

White-backed planthopper (WBPH), Sogatella furcifera (Horváth), is one of the major sap-sucking rice pests in East Asia. We have determined a new complete mitochondrial genome of WBPH collected in the Korean peninsula using NGS technology. Its length and GC percentages are 16,613 bp and 23.8%, respectively. We observed one polymorphic site, a non-synonymous change, in the COX3 gene with confirmation heteroplasmy phenomenon within individuals of WBPH by PCR amplification and Sanger sequencing, the first report in this species. In addition, this heteroplasmy was not observed in wild WBPH populations, suggesting that it may be uncommon in fields. We analyzed single nucleotide polymorphisms, insertion, and deletions, and simple sequence repeats among the three WBPH mitogenomes from Korea and China and found diverse intraspecific variations, which could be potential candidates for developing markers to distinguish geographical populations. Phylogenetic analysis of 32 mitogenomes of Delphacidae including the three WBPH mitogenomes suggested that Delphacinae seems to be monophyletic and Sogatella species including WBPH are clearly formed as one clade. In the future, it is expected that complete mitogenomes of individuals of geographically dispersed WBPH populations will be used for further population genetic studies to understand the migration pathway of WBPH.

Migration of Sogatella furcifera between the Greater Mekong Subregion and northern China revealed by mtDNA and SNP

Background

The white-backed planthopper (WBPH), Sogatella furcifera (Horváth) (Hemiptera, Delphacidae), is a migratory pest of rice in Asia. Shandong Province, in northern China, is located on the migration pathway of WBPH between southern and northeast China. The potential sources of WBPH in northern China are poorly understood. We studied the sources of WBPH in Shandong Province by determining the population genetic structure of WBPH in 18 sites distributed in Shandong and in six regions of the Greater Mekong Subregion (GMS). We used mitochondrial gene and single-nucleotide polymorphism (SNP) markers for analysis.

Results

All of the WBPH populations studied in the seven regions had low genetic diversity. Pairwise F_ST values based on mtDNA ranged from − 0.061 to 0.285, while F_ST based on SNP data ranged from − 0.007 to 0.009. These two molecular markers revealed that 4.40% (mtDNA) and 0.19% (SNP) genetic variation could be explained by the interpopulation variation, while the rest came from intrapopulation variation. The populations in the seven geographic regions comprised four hypothetical genetic clusters (K = 4) not associated with geographic location. Eighty-four of 129 individuals distributed across the given area were designated as recent migrants or of admixed ancestry. Although the substantial migration presented, a weak but significant correlation between genetic and geographic distances was found (r = 0.083, P = 0.004).

Conclusion

The Greater Mekong Subregion was the main genetic source of WBPH in Shandong, while other source populations may also exist. The genetic structure of WBPH is shaped by both migration and geographic barriers. These results help clarify the migration route and the source of WBPH in northern China.

Migration sources and pathways of the pest species Sogatella furcifera in Yunnan, China, and across the border inferred from DNA and wind analyses

The migration sources and pathways of Sogatella furcifera (Horváth) in topologically complex regions like Yunnan, China, and adjacent montane areas have long been a challenging task and a bottleneck in effective pest forecast and control. The present research reinvestigated this issue using a combination of mtDNA and long-term historical wind field data in an attempt to provide new insights. Genetic analyses showed that the 60 populations of S. furcufera collected across Myanmar, Thailand, Laos, Vietnam, Yunnan, Guizhou, and Sichuan lack genetic structure and geographic isolation, while spatial analysis of haplotype and diversity indices discovered geographic relevance between populations. Migration rate analysis combined with high-resolution 10-year wind field analysis detected the following migration sources, pathways, and impacted areas which could explain the outbreak pattern in Yunnan. (a) Dominating stepwise northward migrations originated from northern Indochina, southern Yunnan, and central-eastern Yunnan, impacting their northern areas. (b) Concurring summer-autumn southward (return) migration originated from nearly all latitude belts of Sichuan and Yunnan mainly impacting central and southern Yunnan. (c) Regular eastward and summer-autumn westward migrations across Yunnan. The northward migration reflects the temporal rhythm of gradual outbreaks from the south to the north in a year, while the return migration may explain the repeated or very severe outbreaks in the impacted areas. To form a better pest forecast and control network, attention must also be paid to the northern part of Yunnan to suppress the impact of return migration in summers and autumns.

Minimum sample sizes for invasion genomics: Empirical investigation in an invasive whitefly

Analysis of population genetics provides insights into the evolutionary processes, among which the sample size choice is per se a crucial issue in the analysis. Genome-wide high-throughput techniques based on RADseq have been increasingly used in studies on the population genomics of invasive species. However, there is little information available regarding optimal sample sizes for analyzing population genomics of invasive species. In this study, we first use type IIB endonucleases restriction site-associated DNA (2b-RAD) to mine thousands of single nucleotide polymorphisms (SNPs) for native and introduced populations in Q1 clade (SPB and 17JN) and Q2 clade (ISQ and UAS0601) of the whitefly, Bemisia tabaci (Gennadius) MED (also known as B. tabaci biotype Q). Then, we used resampling techniques to create simulated populations with a random subset of individuals and 3,000 SNPs to determine how many individuals should be sampled for accurate estimates of intra- and interpopulation genetic diversity. We calculated the intrapopulation genetic diversity parameters (unbiased expected heterozygosity, observed heterozygosity, and the number of effect alleles) and pairwise genetic differentiation F ST; finally, an ad hoc statistic, ΔK, was used to determine the optimal value. Our results showed that a sample size greater than four individuals (n ≥ 4) has little impact on estimates of genetic diversity within whitefly populations; moreover, precise estimate of F ST can be easily achieved at a very small simple size (n = 3 or 4). Our results will provide in-depth understanding of the optimization of sampling schemes in population genomics of invasive species.

Extensive gene flow of white-backed planthopper in the Greater Mekong Subregion as revealed by microsatellite markers

The white-backed planthopper (WBPH), Sogatella furcifera (Horváth), is a destructive pest of rice in the Greater Mekong Subregion (GMS) countries including Cambodia, Laos, Myanmar, Thailand, Vietnam, and China’s Yunnan Province. Our previous study not only confirmed the immigration sources of the WBPH in China’s Yunnan Province were from Myanmar, Vietnam, and Laos, but also indicated that Cambodia was likely an additional migration source. To further clarify the migration sources and patterns of the WBPH in the GMS, we investigated the genetic structure of 42 WBPH populations using microsatellite loci markers. The analysis of genetic diversity, heterozygosity deficit, and heterozygosity excess based on the nuclear markers suggest that there is extensive gene flow between the 42 sampled populations from the GMS. The genetic structure confirmed the immigration sources of WBPH as revealed by mitochondrial markers and trajectory analyses methods in previous studies. These findings will aid in the sustainable regional management of this insect pest in the GMS.