Genetic demography of Ukrainian urban populations in the 1990s: the ethnic composition of the migration flow in the Kharkov population

Marriage records were used to study the dynamics of the migration flow into the population of Kharkov in 1960-1993. The decrease in the migration rate was accompanied by changes in the ethnic composition of the migrants. The entire migration flow from the republics of the Baltic region consisted of Russians and Ukrainians. The increase in the migration flow from Transcaucasia was mainly accounted for by the migration activity of indigenous populations. Most migrants from Moldova, Central Asia, Kazakhstan, and Kyrgyzstan were also representatives of the respective indigenous populations. Malecot's coefficient of isolation by distance (b) decreased from 0.00123 to 0.0081.     

Genetic Structure and Differentiation of Three Chinese Indigenous Cattle Populations

Levels of genetic differentiation, gene flow, and genetic structure of three indigenous cattle populations (Luxi, Bohai, and Minnan) and two reference cattle populations (Chinese Holstein and Qinhai yak) in China were estimated using the information from 12 microsatellites, and 141 microsatellite alleles were identified. The mean number of alleles per locus ranged from 2.9005 in yak to 4.9722 in Holstein. The observed heterozygosity ranged from 0.5325 (yak) to 0.7719 (Holstein); 29 private alleles were detected. The global heterozygote deficit across all populations amounted to 58.5% (p < 0.001). The overall significant (p < 0.001) deficit of heterozygotes because of inbreeding within breeds amounted to 43.2%. The five cattle populations were highly differentiated (F _st = 26.9%, p < 0.001) at all loci. The heterozygote deficit within the population was highest in Luxi cattle and lowest in yak. The average number of effective migrants exchanged per generation was highest (1.149) between Luxi and Holstein, and lowest (0.509) between Luxi and yak. With the application of prior population information, cluster analysis achieved posterior probabilities from 91% to 98% of correctly assigning individuals to populations. Combining the information of cluster analysis, gene flow, and Structure analysis, the five cattle populations belong to three genetic clusters, a taurine (Luxi and Chinese Holstein), a zebu (Bohai and Minnan), and a yak cluster. This indicates that Bohai black is closer to Bos indicus than Luxi cattle. The evolution and development of three indigenous cattle populations are discussed.     

Marriage structure of Yakut populations: Migrations

Rural and urban settlements of the Republic of Sakha (Yakutia) are characterized by intense marriage migrations: both indigenous residents of different uluses (districts) of the republic (7–30%) and migrants from outside Yakutia (7–29%) contract marriages in five administrative centers analyzed in this respect. All the populations studied are characterized by a wide geographic range of the birthplaces of persons contracted marriages there (from 14 to 24 uluses of Yakutia), without any predominant migration flow from one district to another. The proportion of homolocal marriages among indigenous ethnic groups (Evenks, Evens, and Yukagirs) is as high as 75–100%; this proportion among Yakuts varies from 26 to 68%; heterolocal marriages are more characteristic of Russian immigrants (41–95%). Positive assortative marriages among persons with the same birthplaces have been found in all populations except for Momsky ulus.     

THE EFFECT OF DELAYED POPULATION GROWTH ON THE GENETIC DIFFERENTIATION OF LOCAL POPULATIONS SUBJECT TO FREQUENT EXTINCTIONS AND RECOLONIZATIONS

I investigated the effects of delayed population growth on the genetic differentiation among populations subjected to local extinction and recolonization, for two different migration functions; (1) a constant migration rate, and (2) a constant number of migrants. A delayed period of population growth reduces the size of the newly founded populations for one or several generations. Whether this increases differentiation among local populations depends on the actual pattern of migration. With a constant migration rate, fewer migrants move into small populations than into large, thus providing ample opportunity for drift to act within a population. A prolonged period of population growth thus makes the conditions for enhanced differentiation between local populations less restrictive and also inflates the actual levels of differentiation. The effect depends on the relative magnitudes of k_e, the effective number of colonizers and k, the actual number of colonizers. When there is a constant number of migrants into a population per generation, migration into small populations is increased. This increase of migration in small populations counteracts the effects of genetic drift due to small population size. It increases the rate by which populations approach equilibrium, as small populations are swamped by migrants from larger populations closer to genetic equilibrium, and overall levels of differentiation are thus reduced. I also discuss situations for which the results of this paper are relevant.     

High genetic diversity in the blue-listed British Columbia population of the purple martin maintained by multiple sources of immigrants

To assess genetic diversity in the blue-listed purple martin (Progne subis) population in British Columbia, we analysed mitochondrial control region sequences of 93 individuals from British Columbia and 121 individuals collected from seven localities of the western and eastern North American subspecies P. s. arboricola and P. s. subis, respectively. Of the 47 haplotypes we detected, 34 were found exclusively in western populations, and 12 were found only in eastern populations. The most common eastern haplotype (25) was also found in three nestlings in British Columbia and one in Washington. Another British Columbia nestling had a haplotype (35) that differed by a C to T transition from haplotype 25. Coalescent analysis indicated that these five nestlings are probably descendents of recent immigrants dispersing from east to the west, because populations were estimated to have diverged about 200,000–400,000 ybp, making ancestral polymorphism a less likely explanation. Maximum likelihood estimates of gene flow among all populations detected asymmetrical gene flow into British Columbia not only of rare migrants from the eastern subspecies in Alberta but also a substantial number of migrants from the adjacent Washington population, and progressively lower numbers from Oregon in an isolation-by distance pattern. The influx of migrants from different populations is consistent with the migrant-pool model of recolonization which has maintained high genetic diversity in the small recovering population in British Columbia. Thus, the risk to this population is not from genetic erosion or inbreeding following a severe population crash, but from demographic stochasticity and extinction in small populations.     

The effect of biogeographic and phylogeographic barriers on gene flow in the brown smoothhound shark,Mustelus henlei,in the northeastern Pacific

We assessed the effects of the prominent biogeographic (Point Conception and the Peninsula of Baja California) and phylogeographic barriers (Los Angeles Region) of the northeastern Pacific on the population connectivity of the brown smoothhound shark, Mustelus henlei (Triakidae). Data from the mitochondrial control region and six nuclear microsatellite loci revealed significant population structure among three populations: northern (San Francisco), central (Santa Barbara, Santa Catalina, Punta Lobos, and San Felipe), and southern (Costa Rica). Patterns of long‐term and contemporary migration were incongruent, with long‐term migration being asymmetric and occurring in a north to south direction and a lack of significant contemporary migration observed between localities with the exception of Punta Lobos that contributed migrants to all localities within the central population. Our findings indicate that Point Conception may be restricting gene flow between the northern and central populations whereas barriers to gene flow within the central population would seem to be ineffective; additionally, a contemporary expansion of tropical M. henlei into subtropical and temperate waters may have been observed.     

Geographical variation of Plutella xylostella (Lepidoptera: Plutellidae) populations revealed by mitochondrial COI gene in China

The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is one of the most serious pests for cruciferous vegetable growers worldwide. To determine the relations of local and regional populations, we performed a mitochondrial COI gene analysis of eight P. xylostella populations from different locations in or around the Qinling Mountains and two other populations, one from Beijing and the other from Guangdong. The mtDNA divergences among the 10 populations were high, and 32 haplotypes were detected in 149 adults. The mean haplotype divergence was 1.7% (range 0.04–4.1%). Haplotype diversity in the 10 populations varied from 0.571 (AK) to 0.885 (HZ), and the nucleotide diversity varied from 0.00286 (AK) to 0.0117 (HZ). The results also did not show significant correlation between genetic and geographical distance. Also, the effective number of migrants between populations (Nm) ranged from 1.43 to infinite, suggesting that population exchange and gene flow among the P. xylostella populations occurred. However, principal component analysis (PCA) showed that the TB and TC populations were differentiated from other populations, indicating possible across‐mountain barrier to migration and gene flow.     

SIGNIFICANCE OF PASSIVE MIGRATION IN EVOLUTION OF INSECTICIDE RESISTANCE IN THE MOSQUITO CULEX PIPIENS (DIPTERA: CULICIDAE)

In order to determine the combined effects of migration and gene flow on evolution of insecticide resistance in the mosquito Culex pipiens, four samples were collected in China, among which two were collected along the railway from Beijing to Guangzhou. Bioassay data showed that the resistance levels of the four populations to dichlorvos were high and to parathion moderate as compared with the susceptible strain and there was no significant difference among the four populations to the same organophosphate (OP) insecticide. Starch electrophoresis was done to identify the frequency of known overproduced esterases and to analyze genetic diversity among various populations by electrophoretic polymorphism of five presumably neutral loci. The results indicated that the gene flow between populations existed and the number of effective migrants (Nm) was related to collection geography (Nm from 1.67 to 40.07). In contrast with lower genetic differentiation between two nearby populations (between GZ and ZS, ZZ and SQ) and higher genetic differentiation between two distant populations (between GZ and ZZ), there was a significant and inconsistent difference in the distribution of resistance alleles, A2‐B2 when explained only with active migration. This divergent situation could be straightened out when considering passive migration (such as railway transport) which increased the spread of A2‐B2 along the railway, i.e., in GZ and ZZ. The resistance alleles, A2‐B2, dispersing to around areas by active migration suffered from the limitation of gene flow and the speed of invasion.     

Adaptive migratory divergence among sympatric brook charr populations

Ecological processes clearly contribute to population divergence, yet how they interact over complex life cycles remains poorly understood. Notably, the evolutionary consequences of migration between breeding and non-breeding areas have received limited attention. We provide evidence for a negative association between interpopulation differences in migration (between breeding and feeding areas, as well as within each) and the amount of gene flow (m) among three brook charr (Salvelinus fontinalis) populations inhabiting Mistassini Lake, Quebec, Canada. Individuals (n = 1166) captured throughout lake feeding areas over two consecutive sampling years were genotyped (10 microsatellites) and assigned to one of the three populations. Interpopulation differences in migration were compared based on spatial distribution overlap, habitat selection, migration distance within feeding areas, and morphology. We observed a temporally stable, heterogeneous spatial distribution within feeding areas among populations, with the extent of spatial segregation related to differential habitat selection (represented by littoral zone substrate). Spatial segregation was lowest and gene flow highest (m = 0.015) between two populations breeding in separate lake inflows. Segregation was highest and gene flow was lowest (mean m = 0.007) between inflow populations and a third population breeding in the outflow. Compared to outflow migrants, inflow migrants showed longer migration distances within feeding areas (64-70 km vs. 22 km). After entering natal rivers to breed, inflow migrants also migrated longer distances (35-75 km) and at greater elevations (50-150 m) to breeding areas than outflow migrants (0-15 km; -10-0 m). Accordingly, inflow migrants were more streamlined with longer caudal regions, traits known to improve swimming efficiency. There was no association between the geographic distance separating population pairs and the amount of gene flow they exchanged. Collectively, our results are consistent with the hypothesis that reduced gene flow between these brook charr populations results from divergent natural selection leading to interpopulation differences in migration. They also illustrate how phenotypic and genetic differentiation may arise over complex migratory life cycles.     

MIGRATION ENHANCES ADAPTATION IN BACTERIOPHAGE POPULATIONS EVOLVING IN ECOLOGICAL SINKS

Migration between populations can be a major evolutionary force. However, some disagreement exists as to precisely how migration affects population adaptation. Some theories emphasize the inhibitory effects of gene flow between locally adapted populations, whereas others propose that migration can enhance adaptation. Migration has also been theorized to rescue sink populations from extinction. In our experiments, we serially passaged bacteriophage Φ6 host range mutants under sink conditions on a novel host while manipulating the source and number of migrants into these experimental populations. Migrants from two sources were used: mutant Φ6 phage able to infect a novel host (treatment) and wild‐type Φ6 phage unable to infect a novel host (control). We used quadratic regressions to determine the relationship between the number of migrants per passage and the absolute fitnesses of experimental populations following 30 passages. Our results showed that migration from a control population had no effect on absolute fitnesses of our serially passaged populations following 30 passages. By contrast, the relationship between migrants per passage and absolute fitnesses for populations receiving migrants able to infect the novel host was best described by an upwardly concave curve. These results suggest that intermediate levels of migration can have favorable impacts on evolutionary adaptation.     

Craniometric variation of the Ainu: an assessment of differential gene flow from northeast Asia into northern Japan, Hokkaido

In and after the latest Neolithic period in Japan (approximately B.P. 2,300 years), there were two distinct waves of migration from eastern Asia. One is well known as successive episodes in which indigenous inhabitants of main-island Japan were intruded on by new arrivals with advanced technology, and of a different genetic stock. Another migration of people and culture, identified as the Okhotsk culture, reached the northeastern part of Hokkaido. As opposed to main-island Japan, the morphological continuity from the Neolithic to recent inhabitants in Hokkaido (Ainu) is notable, so that the evidence of admixture easily could have escaped notice. In this study, the effects of gene flow from an outside source on the pattern of among-group variation of Hokkaido Ainu are examined by means of two models. One is the R-matrix model comparing observed and expected craniometric variation for estimating differential external gene flow into a region. The other is a simple simulation model that estimates admixture in a population with two parental populations. The two approaches give similar results. The results suggest the possibility of admixture between the migrants from Northeast Asia, the Okhotsk culture people, and the indigenous inhabitants in Hokkaido during the 5th to 12th centuries A.D., at least in northeastern Hokkaido. Such gene flow may have a certain degree of effect on the genetic structure of recent Ainu. The findings further suggest morphological heterogeneity in Northeast Asia during the Holocene that has relevance for understanding the morphological heterogeneity seen through time in the New World.     

Community composition, seasonal dynamics and interspecific correlation of waterbirds in the Qiantangjiang River estuary and Hangzhou Bay

Waterbird surveys were conducted regularly in the Qiantangjiang River estuary and Hangzhou Bay from July 2007 to November 2011. A total of 128 species (nine orders and 18 families) were recorded, including 119 migrants which accounted for 93% of the total species; eleven species were listed as National Protected Species. Inter-specific correlation analysis for 13 shorebird populations and nine duck populations recorded over time found that 21 pairs of shorebirds and 23 pairs of ducks were correlated. By looking at seasonal dynamics and migration patterns we were able to divide the migration process into six stages: (1) late July to late September was the migration peak of shorebirds, which were dominated by Limosa limosa, Calidris ruficollis and Charadrius mongolus. (2) Early October to mid-December was the migration peak of wintering migrants of shorebirds and ducks, which were the first two large groups in our study areas. (3) Late December to mid-February was the wintering period of migration waterbirds. (4) Late February to late March was the peak migration of ducks and the winter migrants of shorebirds dominated by Calidris alpina. (5) Early April to mid-May was the migration peak of passage migrants such as, Calidris ruficollis, Calidris acuminate and Limosa limosa but the population size of shorebird winter migrants dominated by Calidris alpine was still larger than the former. (6) Late May to mid-July was the breeding season of all egrets, summer migrants of gulls and several species of shorebirds. Our surveys show that interaction among species is possibly an important determinant of community composition of shorebirds and wintering ducks during the migration season. It may be the geographical position and community composition of migrant shorebirds across Hangzhou Bay that mean during the northward migration there are far more shorebirds than during the southward migration.     

Asymmetrical gene flow of the recently delisted passerine black‐capped vireo (Vireo atricapilla) indicates source‐sink dynamics in central Texas

Habitat fragmentation can produce metapopulations or source‐sink systems in which dispersal in crucial for population maintenance. Our objective was to investigate connectivity among black‐capped vireo (Vireo atricapilla) populations in tandem with a demographic study (Biological Conservation, 2016, 203, 108–118) to elucidate if central Texas populations act as a source‐sink system. We genotyped 343 individuals at 12 microsatellite loci to elucidate the movement ecology of the black‐capped vireo in central Texas surrounding Fort Hood; the largest and most stable breeding population of black‐capped vireos inhabit Fort Hood. To gain insight into gene flow among populations, we analyzed genetic differentiation, migration rates, number of migrants, and parentage. We found statistically significant, but low levels of genetic differentiation among several populations, suggesting some limited restriction to gene flow. Across approaches to estimate migration, we found consistent evidence for asymmetrical movement from Fort Hood to the other central Texas sites consistent with source‐sink dynamics. Our results are complementary to black‐capped vireo demographic studies done in tandem showing that portions of Fort Hood are acting as a source population to smaller central Texas populations.     

Patterns of gene flow and source‐sink dynamics in high altitude populations of the common toad Bufo bufo (Anura: Bufonidae)

Understanding patterns of genetic structure is fundamental for developing successful management programmes for deme‐structured organisms, such as amphibians. We used five microsatellite loci and DNA sequences of the mitochondrial control region to assess the relative influences of landscape (geographic distance, altitude and rivers as corridors for dispersal) and historical factors on patterns of gene flow in populations of the toad Bufo bufo in Central Spain. We sampled 175 individuals from eight populations distributed along two major river drainages and used maximum‐likelihood and Bayesian approaches to infer patterns of gene flow and population structure. The mitochondrial DNA data show closely‐related haplotypes distributed across the Iberian Peninsula with no geographic structuring, suggesting recent differentiation of haplotypes and extensive gene flow between populations. On the other hand, microsatellites provide finer resolution, showing that high altitude populations (> 2000 m) exchange lower numbers of migrants with other populations. The results of Bayesian estimates for recent migration rates in high altitude populations suggest source‐sink dynamics between ponds that are consistent with independent data from monitoring over the past 20 years. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 824–839.     

Biological affinities between migrant and parental populations of fishermen on the east coast of India.

We examined biological affinities between the migrant groups of fishermen in Puri and their parental counterparts using 3 sets of variables: genetic markers, anthropometric measurements, and quantitative dermatoglyphics. Results of both univariate and multivariate analyses suggest a significant migration effect, diversifying migrants from their parental populations, although the distance configurations based on each set of variables resemble each other. The migration effect is particularly remarkable for the anthropometric measurements. The plot of group centroids based on the discriminant analysis of the 7 populations depicts a clear segregation of migrants from the parental populations. Because of relatively large effective population sizes and short history of these populations in Puri, the role of genetic drift can be safely ruled out. However, a founder effect is a plausible reason for the observed differentiation of the migrants from their parental groups, especially given that certain rare variants that were not observed in the parental populations appear in the migrants. That the founders were a select group of fishermen with respect to body dimensions, not a random group, can be inferred from the occupational differences among the migrant groups, which in turn suggests phenotypic plasticity in the observed differentiation. Regression of mean phenotypic variance and heterozygosity on the distance from the centroid suggests a strong possibility of external gene flow into the migrant populations in Puri.     

Evidence for indigenous selection and distribution of the shea tree, Vitellaria paradoxa, and its potential significance to prevailing parkland savanna tree patterns in sub-Saharan Africa north of the equator

Aim Woody vegetation patterns in African savannas north of the equator are closely connected to human presence, but the distinctions between natural and anthropogenic landscapes have not been clear to many observers. Criteria for identifying savanna landscapes on a continuum of intensity of anthropic impact are explored. Methods A key savanna tree species, Vitellaria paradoxa (Sapotaceae), was used as model for evaluating anthropic impact. Fruits harvested from tree populations across the species range were analysed for variation in traits valued by indigenous peoples. A simple selection index was used to scale tree populations from a hypothetical wild state to a hypothetical domesticated state. Index values were compared with trait values along climate zone gradients and evaluated in the context of indigenous savanna management practices and historical species distribution reports. Results Trait values such as fruit size and shape, pulp sweetness, and kernel fat content show a significant influence of temperature and rainfall. At the same time, the mean values of groups of traits vary perpendicular to the general climatic zone gradient. Selection index values between Vitellaria populations vary up to sixfold, with highest values in central Burkina Faso. Comparison of present day Vitellaria distribution with historical range limits show range expansion by human migration. Main conclusions The prevalence of major economic tree species in the savannas of Africa north of the equator is a strong indicator of human involvement in tree dispersal. This conclusion is supported by paleobotanical evidence and by recent Vitellaria range expansion as a result of human migration. The presence of high mean values of several Vitellaria fruit traits in central Burkina Faso suggests that selection for desired characteristics has occurred. The impact of indigenous savanna peoples on woody species composition and spatial distribution is probably much greater than usually thought and is the result of a deliberate strategy of altering the landscape to provide needed human resources.     

Migration barriers protect indigenous brown trout (<Emphasis Type="Italic">Salmo trutta</Emphasis>) populations from introgression with stocked hatchery fish

Brown trout populations in the Belgian rivers Scheldt and Meuse have been intensively stocked in the past decades, often with material of uncertain origin. Moreover, the species habitat has become increasingly fragmented, preventing gene flow between neighboring populations. We assessed how this impacted genetic diversity and population structure by analyzing 12 wild populations (total n=309) and seven hatchery stocks (n=200) at the mitochondrial control region with SSCP and at 27 RAPD loci. Historical records indicate that brown trout from distant locations have been used to supplement hatchery stocks; nevertheless we detected non-Atlantic mitochondrial genomes in only one population of the Scheldt basin and in one hatchery. In general, the hatchery samples displayed a higher genetic diversity and differentiated less among each other (global F_ST(mtDNA)=0.311/F_ST(RAPD)=0.029) compared to the wild populations (global F_ST(mtDNA)=0.477/F_ST(RAPD)=0.204). This is due to frequent exchanges between hatcheries and regular supplementation from several indigenous populations. Gene pools present in most downstream sections from tributaries of the Meuse were similar to each other and to the hatchery samples, despite the presence of migration barriers. Assignment analyses indicated that the contribution of hatchery material to the upstream parts was limited or even completely absent in populations separated by a physical barrier. Intensive stocking and exchange between hatcheries has homogenized the downstream sections of the Meuse River, whereas the migration barriers preserved the indigenous upstream populations. As such, uncontrolled removal of barriers might result in an irreversible loss of the remnant indigenous gene pools.     

Across a migratory divide: divergent migration directions and non‐breeding grounds of Eurasian reed warblers revealed by geolocators and stable isotopes

Migratory divides represent narrow zones of overlap between parapatric populations with distinct migration directions and, consequently, expected divergent non‐breeding distributions. The composition of the mixed population at a migratory divide and the corresponding non‐breeding ranges remain, however, unknown for many Palaearctic‐African migrants. Here, we used light‐level geolocation to track migration direction and non‐breeding grounds of Eurasian reed warblers Acrocephalus scirpaceus from three breeding populations across the species’ migratory divide. Moreover, by using feathers grown at non‐breeding grounds, we quantified stable isotope composition for individuals with known southwestern (SW) and southeastern (SE) migration directions. On a larger sample per population, we then assessed the proportions of SW‐ and SE‐migrating phenotypes in each of the three populations. All tracked reed warblers from Germany and two thirds of the birds tagged from the Czech population headed initially SW. Nevertheless, about one third of the birds from the Czech site migrated towards SE. No tracking data have been obtained for the Bulgarian population. The initial migration direction determined by geolocators was a strong predictor of the non‐breeding region, with SW migrants staying in west Africa and SE migrants in central Africa. Feather δ³⁴S and δ¹⁵N values confirmed the predominance of SW migrants in the German population, the co‐occurrence of SW and SE migrants in the Czech population, and indicated a high (72%) proportion of SE migrants in the Bulgarian population. Thus, the combined approach of geolocator tracking and stable isotopic assignments provided clear evidence for the existence of a migratory divide in the southeast of central Europe and predicted non‐breeding range in central and central‐eastern Africa for the eastern population.     

Altitude, migration, and fertility in the Andes

In order to examine the relationship between hypoxia and reduced fertility of high Andean populations, a sample of 241 females living in the low-altitude Tambo Valley of Peru was studied. 63 of the subjects were born in the low-altitude valley, 121 were migrants from high altitudes, and 57 were migrants born in low altitudes. The rate of abortion was low among high-altitude subjects before they migrated, but became greater after migrating. It was found that the high-altitude populations had almost twice as long parity intervals than the low-altitude populations. Compared to migrants born at low altitudes, the high-altitude-born subjects who migrated to low altitudes had higher fertility rates. The results of the study are consistent with the hypothesis that high altitudes, through anoxia, have a lowering effect on fertility. Of the several possible explanations which might account for the increase in fertility of downward migrants on migration from high to low altitude (migration, socioeconomic factors, acculturation, seasonal male emigration from high altitude, and removal of hypoxia stress), altitude appears to be the most significant.     

Current status of insecticide resistance in the small brown planthopper, <Emphasis Type="Italic">Laodelphax striatellus</Emphasis>, in Japan,Taiwan, and Vietnam

The small brown planthopper, Laodelphax striatellus, is one of the most serious pest insects of rice plants. A large migration of the insects from overseas was reported in western parts of Japan in June 2008. Insecticide resistance to imidacloprid, fipronil and BPMC was compared among local populations in these western regions after migration. The insecticides were applied to the insects using a topical application method. In some populations, the resistance status coincided with that of the immigrant insects just after migration, i.e., resistance to imidacloprid but susceptibility to fipronil. In other populations, resistance was observed not only against imidacloprid but also fipronil. It is likely that the status of the latter populations resulted from intercrossing between domestic populations of the insects and migrants. Insecticide resistance was also assessed in other areas of northern and eastern parts of Japan. In general, these populations showed relatively low resistance, although resistance to fipronil was high in the eastern part of Japan where the density of domestic populations has recently increased. Insecticide susceptibilities were also assessed in several sites in Taiwan and the northern parts of Vietnam. Although susceptibilities differed among these sites or countries, they have recently seen a decline for all three insecticides.