Using haplotypes to monitor the migration of fall armyworm (Lepidoptera: Noctuidae) corn-strain populations from Texas and Florida

Fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), infestations in most of North America north of Mexico arise from annual migrations of populations that overwinter in southern Texas and Florida. A comparison of the cytochrome oxidase I haplotype profiles within the fall armyworm corn-strain, the subgroup that preferentially infests corn (Zea mays L.) and sorghum (Sorghum vulgare Pers.), identified significant differences in the proportions of certain haplotypes between the Texas and Florida populations. These proportional differences were preserved as the populations migrated, providing a molecular metric by which the source of a migrant population could be identified. The migratory pattern derived from this method for several southeastern states was shown to be consistent with predictions based on analysis of historical agricultural and fall armyworm infestation data. These results demonstrate the utility of haplotype proportions to monitor fall armyworm migration, and they also introduce a potential method to predict the severity of cotton crop infestations in the short term.     

Genetic characterization of fall armyworm (Lepidoptera: Noctuidae) host strains in Argentina

Fall armyworm is a major economic pest throughout the Western Hemisphere. Previous studies of populations in the southern United States, Brazil, and the Caribbean demonstrated the existence of two morphologically identical but genetically distinct host strains that can only be distinguished using genetic markers, including polymorphisms in the mitochondrial Cytochrome Oxidase I (COI) gene and in the Z-chromosome linked Triose phosphate isomerase (Tpi) gene. The strains differ in some physiological and behavioral characteristics, most notably their preference for different plant hosts, but are capable of hybridizing in the laboratory and in the field. These traits suggest that the strains are in the process of divergence, which may or may not be hemispheric in scope. The objective of this study was to determine whether the two strains are present in Argentina. It was found that the strain-diagnostic haplotypes of the COI and Tpi genes subdivided the Argentina population into two major groups. Each group displayed biases in their distribution among different host plants that were generally consistent with expected strain behavior. The overall results indicated that Argentina fall armyworm exhibit similar genetics and behavior to populations in the rest of the hemisphere. In addition, the Argentina populations had comparable haplotype frequencies to those from Brazil and Texas, consistent with possible interactions with these fall armyworm groups, but appeared to have had minimal exchanges with those from Puerto Rico or Florida.     

Noctuid migration in Texas within the nocturnal aeroecological boundary layer

Long-distance migration of adult corn earworm moths (Helicoverpazea), and several other noctuid moth species, facilitates seasonalexpansion of pest populations and consequent increased infestationsof agricultural crops on a continental scale in North America.Long-term field studies of population dynamics and migratoryflights of H. zea and fall armyworm (Spodoptera frugiperda)in the United States were evaluated using X-band radar observationsand profiles of atmospheric conditions. These studies identifiedcharacteristic patterns of migratory flight that are largelyassociated with vertical profiles of temperature and wind speed.Collective patterns of moth migrations were generally highlycorrelated with wind headings, but often at a significant angulardeviation. Preliminary analyses are presented between moth distributionsin the aerosphere estimated from discrete moth counts usingX-band radar and bulk reflectivity data from NEXRAD Dopplerradar. Identification of associations between atmospheric factorsand noctuid population dynamics and migratory flights will improvethe ability to predict infestations by pest species throughouttheir broad seasonal range expansion.     

Comparison of haplotype frequencies differentiate fall armyworm (Lepidoptera: Noctuidae) corn-strain populations from Florida and Brazil

Fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is a major economic pest throughout the Western Hemisphere. Populations can be subdivided into two morphologically identical but genetically distinct strains (corn-strain and rice-strain) that differ in their host plant preferences. These strains can be distinguished by using polymorphisms in the mitochondrial cytochrome oxidase 1 gene. Additional sequence analysis of this locus identified two sites that were highly polymorphic in the corn-strain population and that produced four different haplotype subgroups. Comparisons of the frequency distribution of these haplotypes found no seasonal or plant host specificities, but they did demonstrate that the Brazil corn-strain population is different from corn-strain fall armyworm found in Florida. The development of a rapid means of distinguishing fall armyworm populations originating from Brazil versus Florida provides an opportunity for investigating and comparing the genetic complexity and long-range movements of this important agricultural pest.     

Trajectory modeling revealed a southwest-northeast migration corridor for fall armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae) emerging from the North China Plain

The fall armyworm Spodoptera frugiperda, an invasive insect pest native to the Americas, has established populations throughout eastern China. The North China Plain—a key corn-producing area in East China with a unique topography—was invaded by fall armyworm in 2019 and is seriously threatened by this migratory pest. However, the spatiotemporal extent of the migratory movements of fall armyworm from the North China Plain remains poorly understood. Using an air transport-based trajectory modeling approach that incorporates flight behavior, we simulated the potential nocturnal migration trajectories of fall armyworm from the North China Plain based on historical meteorological data from June to October of 2015–2019, and examined the night-time atmospheric conditions associated with their possible flights. The emigration patterns showed monthly variation in the main landing area and common migration direction. The displacement of newly emerged moths from the North China Plain was concentrated in the Northeast China Plain (including Liaoning, Jilin and Heilongjiang provinces) before late summer, after which they were most likely to undertake return flights to the south (especially into Hubei, Anhui and Hunan provinces). This southwest-northeast aerial migration corridor follows the topography of East China and is affected by the East Asian monsoon. These topographic-atmospheric conditions have resulted in the North China Plain becoming a key stopover for fall armyworm populations engaging in multigenerational long-distance migration across East China. These findings contribute to our knowledge of fall armyworm migration and will aid in the implementation of management and control strategies against this highly migratory agricultural pest.     

Plant-incorporated Bacillus thuringiensis resistance for control of fall armyworm and corn earworm (Lepidoptera: Noctuidae) in corn

Fall armyworm, Spodoptera frugiperda (J.E. Smith), and corn earworm, Helicoverpa zea (Boddie), perennially cause leaf and ear damage to corn, Zea mays L., in the southeastern United States. Transgenic Bacillus thuringiensis (Bt) hybrids with the Bt11, MON810, or 176 events expressing the Cry1Ab insecticidal endotoxin from were evaluated for control fall armyworm and corn earworm at seven locations in Georgia during 1999 and 2000. Corn was planted at the recommended time for each location and 1 and 2 mo later in the southern locations. All Bt events consistently reduced whorl infestation and damage, although event 176 did not prevent whorl damage in the later plantings in the southern locations in both years. All events also reduced seedling damage by the lesser cornstalk borer, Elasmopalpus lignosellus (Zeller), in one trial and stalk infestations and tunnel length by southwestern corn borers, Diatraea grandiosella Dyar, in another trial. Hybrids containing Bt11 and MON810 events reduced ear infestations in all trials, although reductions were small in later plantings. Nevertheless, both events reduced grain damage from earworms and armyworms by an average +/- SE of 52.5 +/- 5.1% in all trials. The hybrid containing event 176 did not reduce ear infestations and damage. Total grain aflatoxin concentrations were not significantly affected by Bt resistance in any trial (N = 17). Yield responses were variable with the prevention of yield loss being proportional to the severity of insect damage. Although plantings made after the recommended time did not consistently benefit from Bt resistance, Bt11 and MON810 events were effective in reducing damage to field corn when large infestations occurred. The Bt11 and MON810 events mitigated the risk of severe lepidopteran damage to corn, thereby making later plantings of corn feasible in double-cropping systems.     

首次入侵广东的草地贪夜蛾迁入路径及天气背景分析

草地贪夜蛾 Spodoptera frugiperda (J. E. Smith)是联合国粮农组织全球预警的超级害虫,2019年1月入侵我国云南,并随季风远距离迁飞扩散,4月23日,广东省广州市增城区首次发现并确认该虫幼虫发生为害,对当地玉米等粮食作物构成严重威胁。本研究运用基于WRF模式的昆虫三维轨迹分析程序和GrADS气象图形软件,模拟了入侵广东的草地贪夜蛾的迁飞路径及天气背景场。结果表明:按照幼虫发育历期推算,首批草地贪夜蛾成虫迁入广东的时间可能为4月8日~13日;在此期间,越南北部及华南地区的西南低空急流可为草地贪夜蛾的迁飞提供运载气流,而风切变、降雨和下沉气流为草地贪夜蛾的迫降提供便利条件;4月9-10日存在草地贪夜蛾的有效迁飞路径,入侵广东省增城区草地贪夜蛾种群的有效虫源地分布在越南及老挝北部。本研究为华南地区草地贪夜蛾春季迁入种群的监测预警及防控提供了科学依据。     

First report of the fall armyworm,Spodoptera frugiperda (Lepidoptera: Noctuidae), natural enemies from Africa

The fall armyworm (FAW), Spodoptera frugiperda, is a major pest of maize in North and South America. It was first reported from Africa in 2016 and currently established as a major invasive pest of maize. A survey was conducted to explore for natural enemies of the fall armyworm in Ethiopia, Kenya and Tanzania in 2017. Smallholder maize farms were randomly selected and surveyed in the three countries. Five different species of parasitoids were recovered from fall armyworm eggs and larvae, including four within the Hymenoptera and one Dipteran. These species are new associations with FAW and were never reported before from Africa, North and South America. In Ethiopia, Cotesia icipe was the dominant larval parasitoid with parasitism ranging from 33.8% to 45.3%, while in Kenya, the tachinid fly, Palexorista zonata, was the primary parasitoid with 12.5% parasitism. Charops ater and Coccygidium luteum were the most common parasitoids in Kenya and Tanzania with parasitism ranging from 6 to 12%, and 4 to 8.3%, respectively. Although fall armyworm has rapidly spread throughout these three countries, we were encouraged to see a reasonable level of biological control in place. This study is of paramount importance in designing a biological control program for fall armyworm, either through conservation of native natural enemies or augmentative release.     

基于分子标记的入侵陕西草地贪夜蛾种群生物型分析

草地贪夜蛾Spodoptera frugiperda J. E. Smith是一种世界性入侵害虫,为了明确入侵陕西的草地贪夜蛾的种群生物型并了解其发生及扩散规律,本研究对采集自陕西省8个地市180个草地贪夜蛾样本分别进行了基于COI和Tpi分子标记的生物型鉴定。分析发现入侵陕西的草地贪夜蛾84%是水稻型母本与玉米型父本杂交形成的杂合玉米型草地贪夜蛾。COI分子标记的结果显示,样本中水稻型占比为84.44%,玉米型为15.56%;基于Tpi基因片段的结果表明除商洛样本SL-3外,其它样本均为玉米型。值得注意的是,SL-3与非洲特异型序列同源性达100%,此非洲特异单倍型为陕西省内首次、国内第2次出现。本研究为草地贪夜蛾的迁飞扩散规律及早期预警提供了新的理论基础。     

Effects of defoliation on the resistance and tolerance of rice,Oryza sativa,to root injury by the rice water weevil,Lissorhoptrus oryzophilus

Understanding plant‐mediated interactions in agricultural systems may facilitate the development of novel and improved management practices, which is important, as management of these insects is currently heavily reliant on insecticides. The fall armyworm, Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae, Prodeniini), is a sporadic pest of rice fields in the southern USA. In southwestern Louisiana, this defoliating insect typically attacks rice early in the growth season, before fields are flooded. Defoliation by fall armyworm larvae may trigger increased expression of plant defenses, which may result in increased resistance to subsequent herbivores. The rice water weevil (RWW), Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae, Stenopelmini), enters rice fields as an adult both before and after flooding, but oviposition and larval infestation occur only after fields are flooded. RWW may be affected by changes in plant resistance caused by fall armyworm defoliation before flooding. The objectives of this study were to investigate the plant‐mediated effects of natural and artificial defoliation on population densities of RWW larvae after flooding and on the ability of rice plants to compensate for root injury by RWW larvae. In the 2015 season, fall armyworm defoliation before flooding resulted in reduced RWW densities after flooding. However, in 2016 no significant effects of fall armyworm defoliation on densities of RWW larvae were detected. Similarly, mechanical defoliation of rice before flooding did not affect RWW densities after flooding. Although lowest yields were observed in plots subjected to both root injury and defoliation, there was little evidence of a greater than additive reduction in yields from simultaneous injury. These results suggest a lack of plant‐mediated interactions among these two pests in rice in the southern USA.     

Geographic Population Structure of the Sugarcane Borer,Diatraea saccharalis (F.) (Lepidoptera: Crambidae), in the Southern United States

The sugarcane borer moth, Diatraea saccharalis, is widespread throughout the Western Hemisphere, and is considered an introduced species in the southern United States. Although this moth has a wide distribution and is a pest of many crop plants including sugarcane, corn, sorghum and rice, it is considered one species. The objective was to investigate whether more than one introduction of D. saccharalis had occurred in the southern United States and whether any cryptic species were present. We field collected D. saccharalis in Texas, Louisiana and Florida in the southern United States. Two molecular markers, AFLPs and mitochondrial COI, were used to examine genetic variation among these regional populations and to compare the sequences with those available in GenBank and BOLD. We found geographic population structure in the southern United States which suggests two introductions and the presence of a previously unknown cryptic species. Management of D. saccharalis would likely benefit from further investigation of population genetics throughout the range of this species.     

Spatial distribution of Aphis glycines (Hemiptera: Aphididae): a summary of the suction trap network

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is an economically important pest of soybean, Glycine max (L.) Merrill, in the United States. Phenological information of A. glycines is limited; specifically, little is known about factors guiding migrating aphids and potential impacts of long distance flights on local population dynamics. Increasing our understanding of A. glycines population dynamics may improve predictions of A. glycines outbreaks and improve management efforts. In 2005 a suction trap network was established in seven Midwest states to monitor the occurrence of alates. By 2006, this network expanded to 10 states and consisted of 42 traps. The goal of the STN was to monitor movement of A. glycines from their overwintering host Rhamnus spp. to soybean in spring, movement among soybean fields during summer, and emigration from soybean to Rhamnus in fall. The objective of this study was to infer movement patterns of A. glycines on a regional scale based on trap captures, and determine the suitability of certain statistical methods for future analyses. Overall, alates were not commonly collected in suction traps until June. The most alates were collected during a 3-wk period in the summer (late July to mid-August), followed by the fall, with a peak capture period during the last 2 wk of September. Alate captures were positively correlated with latitude, a pattern consistent with the distribution of Rhamnus in the United States, suggesting that more southern regions are infested by immigrants from the north.     

Microsatellite analysis of medfly bioinfestations in California

The Mediterranean fruit fly, Ceratitis capitata, is a destructive agricultural pest with a long history of invasion success. This pest has been affecting different regions of the United States for the past 30 years, but a number of studies of medfly bioinfestations has focused on the situation in California. Although some progress has been made in terms of establishing the origin of infestations, the overall status of this pest in this area remains controversial. Specifically, do flies captured over the years represent independent infestations or the persistence of a resident population? We present an effort to answer this question based on the use of multilocus genotyping. Ten microsatellite loci were used to analyse 109 medflies captured in several infestations within California between 1992 and 1998. Using these same markers, 242 medflies from regions of the world having ‘established’ populations of this pest including Hawaii, Guatemala, El Salvador, Ecuador, Brazil, Argentina and Peru, were also analysed. Although phylogenetic analysis, amova analysis, the immanc assignment test and geneclass exclusion test analysis suggest that some of the medflies captured in California are derived from independent invasion events, analysis of specimens from the Los Angeles basin provides support for the hypothesis that an endemic population, probably derived from Guatemala, has been established.     

Combining ability in maize for fall armyworm and southwestern corn borer resistance based on a laboratory bioassay for larval growth

The fall armyworm, Spodoptera frugiperda (J. E. Smith), and southwestern corn borer, Diatraea grandiosella Dyar, are major insect pests of maize, Zea mays L., in the southern USA. Both insects feed extensively on leaves of plants in the whorl stage of growth. A diallel cross of seven inbred lines with different levels of susceptibility to leaf feeding damage in the field was evaluated in a laboratory bioassay for fall armyworm and southwestern corn borer larval growth. Diets were prepared from lyophilized leaf tissue of field-grown plants of the inbred lines and their 21 F₁ hybrids. One inbred line, Tx601, exhibited heavy leaf damage in field tests but showed moderate resistance in the laboratory bioassay. Both general and specific combining ability were highly significant sources of variation in the inheritance of fall armyworm and south-western corn borer larval growth in the laboratory bioassay. Tx601 showed excellent general combining ability for reduced larval growth of both species.This article is a contribution of the United States Department of Agriculture, Agricultural Research Service, in cooperation with the Mississippi Agricultural and Forestry Experiment Station. Journal No. J-8525     

Plant resistance and its effect on the peritrophic membrane of southwestern corn borer (Lepidoptera: Crambidae) larvae

The southwestern corn borer, Diatraea grandiosella Dyar (Lepidoptera: Crambidae), is a serious pest of corn, Zea mays L., in the southern United States. Corn germplasm lines with conventional genetic leaf-feeding resistance to this pest, the fall armyworm, Spodoptera frugiperda (J.E. Smith), and other lepidopterans have been released to the public by USDA-ARS scientists located in Mississippi. Recent studies suggest the insect resistant lines disrupt the integrity of the peritrophic membrane of the fall armyworm. The objectives of this study were to investigate any morphological differences in the structure of the peritrophic membrane of southwestern corn borer larvae feeding on resistant and susceptible corn hybrids and to quantify the damage. Larvae were reared under field and laboratory conditions on three corn hybrids (two resistant and one susceptible). Scanning electron microscopy was used to examine the peritrophic membrane for abnormalities such as holes or tears and to count the holes or tears in the membrane. Differences in the degree of damage to peritrophic membrane of larvae fed on resistant and susceptible plants were not detected. Up to five distinct layers of the membrane were observed in each larva. Variation in the amounts of damage to the peritrophic membrane observed from larvae feeding on all plant material was high. Plant resistance adversely affects growth and development of southwestern corn borer larvae, and further investigations are needed to explain the role of plant resistance and its relation to peritrophic membrane in southwestern corn borer larvae.     

Genetic divergence and evidence for sympatric host-races in the highly polyphagous brown tail moth,Euproctis chrysorrhoea (Lepidoptera: Erebidae)

The brown tail moth (BTM) Euproctis chrysorrhoea (Linnaeus 1758) (Lepidoptera: Erebidae) is a forest and ornamental pest in Europe and the United States. Its extreme polyphagy, and documented phenological shift associated with host use suggest the presence of distinct host-races. To test this hypothesis, we sampled BTM infesting different host species in several locations along its distribution, and used DNA sequence data (a total of 1,672 bp from cytochrome c oxidase subunit I, elongation factor 1-alpha, and wingless) to produce haplotype networks and reconstruct the phylogenetic relationships between individuals. Population genetic diversity indices pointed out a higher genetic diversity in Europe, particularly in the samples from southern Spain and southern England. Lower F _ST values were found between geographically closer populations when compared to more distant ones, but analyses of molecular variance and Mantel tests failed to reveal geographically associated genetic differentiation. However, haplotype networks and phylogenetic reconstructions revealed a previously unknown genetic differentiation within the BTM, with one lineage circumscribed to southern Europe. Although BTM haplotypes did not cluster according to their host plant, host-associated haplotypes were observed within certain geographic regions. Hence, our data support the existence of host-races of BTM within southern Spain and southern England, where populations from different hosts occur in sympatry.     

不同地区甜菜夜蛾种群的遗传多样性分析

甜菜夜蛾Spodoptera exigua (Hübner)是一种重要的农业害虫,曾给我国农牧业生产造成过重大的经济损失。为了阐明甜菜夜蛾的种群动态规律,改善和提高其预测、防治水平,我们应用扩增片段长度多态性(AFLP)技术对我国7个甜菜夜蛾种群的42头雄蛾的遗传多样性进行了研究分析。结果表明,不同种群个体间遗传相似性指数分布在0.143～0.824之间,同一种群内不同个体间的遗传相似性指数分布在0.250～0.786之间,同一种群内个体间的遗传相似性指数有许多小于不同种群个体间的。江西种群的多态性条带比例最低,为80.7%; 山东种群的多态性条带比例最高,达88.6%。总体而言,北方种群内的遗传多样性高于南方种群。聚类分析结果表明,同一种群的个体并不总能聚在一起,即种群间不存在明显的遗传分化。这些结果为明确我国甜菜夜蛾的迁飞规律及各发生危害区的虫源关系提供了进一步的实验依据。     

Diversity of Boll Weevil Populations in South America: A Phylogeographic Approach

A phylogeographic approach was conducted to assess the geographic structure and genetic variation in populations of the boll weevil Anthonomus grandis, which is the most harmful insect pest of cotton in the Americas. COI and COII mitochondrial gene sequences were analyzed to test a former hypothesis on the origin of the boll weevil in Argentina, Brazil and Paraguay, using samples from Mexico and USA as putative source populations. The analysis of variability suggests that populations from South American cotton fields and nearby disturbed areas form a phylogroup with a central haplotype herein called A, which is the most common and widespread in USA and South America. The population from Texas has the A haplotype as the most frequent and gathers in the same group as the South American populations associated with cotton. The sample from Tecomán (México) shows high values of within-nucleotide divergence, shares no haplotype in common with the South American samples, and forms a phylogroup separated by several mutational steps. The sample from Iguazú National Park (Misiones Province, Argentina) has similar characteristics, with highly divergent haplotypes forming a phylogroup closer to the samples from cotton fields, than to the Mexican group. We propose that in South America there are: populations with characteristics of recent invaders, which would be remnants of “bottlenecks” that occurred after single or multiple colonization events, probably from the United States, and ancient populations associated with native forests, partially isolated by events of historical fragmentation.     

Using stable isotope analysis to examine fall armyworm (Lepidoptera: Noctuidae) host strains in a cotton habitat

Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), or fall armyworm, is an important agricultural pest of several crops in the Western Hemisphere, including cotton (Gossypium L.). Two morphologically identical host strains of fall armyworm exist that differ in plant host use and habitat distribution. The corn-strain is a primary pest of corn, Zea mays L., whereas the rice-strain is the majority population infesting rice (Oryza spp.) and turfgrass (Cynodon spp.). With the increased use of Bacillus thuringiensis (Bt) toxin-expressing cotton varieties and the necessity of ensuring adequate refuge areas to prevent the spread of Bt toxin resistance, it is crucial to identify the alternative plant hosts available for the fall armyworm population infesting cotton. Stable isotope analysis combined with the molecular analysis of strain-specific markers was used to investigate whether one or both strains routinely develop on cotton grown in the Mississippi delta. We found that the majority of fall armyworm adults present during the early cotton growing season arose from C4 plants (e.g., corn and sorghum, Sorghum vulgare Pers.) and that the only strain likely to be developing on cotton (a C3 plant) in substantial numbers was the corn-strain. The population distribution patterns observed were consistent with corn providing an important refuge for the fall armyworm strain infesting cotton and suggested that late season populations in the Mississippi delta may be migrants from more northern corn areas.