Nuclear-mitochondrial barcoding exposes the global pest Western flower thrips (Thysanoptera: Thripidae) as two sympatric cryptic species in its native California

Molecular identification of Hymenopteran insects collected by using Malaise traps from Hazarganji Chiltan National Park Quetta, Pakistan

The order Hymenoptera holds great significance for humans, particularly in tropical and subtropical regions, due to its role as a pollinator of wild and cultivated flowering plants, parasites of destructive insects and honey producers. Despite this importance, limited attention has been given to the genetic diversity and molecular identification of Hymenopteran insects in most protected areas. This study provides insights into the first DNA barcode of Hymenopteran insects collected from Hazarganji Chiltan National Park (HCNP) and contributes to the global reference library of DNA barcodes. A total of 784 insect specimens were collected using Malaise traps, out of which 538 (68.62%) specimens were morphologically identified as Hymenopteran insects. The highest abundance of species of Hymenoptera (133/538, 24.72%) was observed during August and least in November (16/538, 2.97%). Genomic DNA extraction was performed individually from 90/538 (16.73%) morphologically identified specimens using the standard phenol-chloroform method, which were subjected separately to the PCR for their molecular confirmation via the amplification of cytochrome c oxidase subunit 1 (cox1) gene. The BLAST analyses of obtained sequences showed 91.64% to 100% identities with related sequences and clustered phylogenetically with their corresponding sequences that were reported from Australia, Bulgaria, Canada, Finland, Germany, India, Israel, and Pakistan. Additionally, total of 13 barcode index numbers (BINs) were assigned by Barcode of Life Data Systems (BOLD), out of which 12 were un-unique and one was unique (BOLD: AEU1239) which was assigned for Anthidium punctatum. This indicates the potential geographical variation of Hymenopteran population in HCNP. Further comprehensive studies are needed to molecularly confirm the existing insect species in HCNP and evaluate their impacts on the environment, both as beneficial (for example, pollination, honey producers and natural enemies) and detrimental (for example, venomous stings, crop damage, and pathogens transmission).

Tiny insects, big troubles: a review of BOLD's COI database for Thysanoptera (Insecta)

DNA Barcoding is an important tool for disciplines such as taxonomy, phylogenetics and phylogeography, with Barcode of Life Data System (BOLD) being the largest database of partial cytochrome c oxidase subunit I (COI) sequences. We provide the first extensive revision of the information available in this database for the insect order Thysanoptera, to assess: how many COI sequences are available; how representative these sequences are for the order; and the current potential of BOLD as a reference library for specimen identification and species delimitation. The COI database at BOLD currently represents only about 5% of the over 6400 valid thrips species, with a heavy bias towards a few species of economic importance. Clear Barcode gaps were observed for 24 out of 33 genera evaluated, but many outliers were also observed. We suggest that the COI sequences available in BOLD as a reference would not allow for accurate identifications in about 30% of Thysanoptera species in this database, which rises to 40% of taxa within Thripidae, the most sampled family within the order. Thus, we call for caution and a critical evaluation in using BOLD as a reference library for thrips Barcodes, and future efforts should focus on improving the data quality of this database.

Rapid and zero-cost DNA extraction from soft-bodied insects for routine PCR-based applications

Nucleic acid extraction is the first and foremost step in molecular biology studies. Extraction of DNA from small, soft-bodied insects is often time-consuming and costly. A fast, easy, and cost-effective DNA extraction method with greater yield and purity of DNA would aid in the rapid diagnostics, screening of large populations, and other routine PCR-based applications. The present study evaluated and standardized a rapid and zero-cost DNA extraction from soft-bodied small insects for routine molecular studies. Five rapid DNA extraction methods viz. extraction in sterile distilled water (SDW), 1X phosphate-buffered saline (PBS, pH 7.4), 1.4 M sodium chloride (NaCl), 20 mM ethylenediaminetetraacetic acid (EDTA, pH 8.0), and elution from blotted nitrocellulose membrane (NCM) were compared with standard CTAB extraction buffer and DNeasy^® Blood and Tissue Kit methods. The average yield, purity, storage stability, time, and cost of extraction were assessed for all the methods and compared. A method of DNA extraction by simply crushing the soft-bodied insects in SDW was ideal in terms of yield, purity, storability, and performing routine PCR-based applications including detection of pathogens from vector species. The extraction could be accomplished in 2.5 min only with zero-reagent cost. The method would be useful in rapid molecular diagnostics and screening large populations of soft-bodied insects.

Colour Response in Western Flower Thrips Varies Intraspecifically

Discrepancies in the published research as to the attraction of the economically important pest western flower thrips (WFT) to different colours confounds the optimisation of field traps for pest management purposes. We considered whether the different experimental conditions of independent studies could have contributed to this. Therefore, the behavioural response (i.e., landings) to different colour cues of two WFT laboratory populations from Germany (DE) and The Netherlands (NL), which had previously been independently shown to have different colour preferences, were tested in the same place, and under the same experimental conditions. Single-choice wind tunnel bioassays supported previous independent findings, with more of a NL population landing on the yellow LED lamp (588 nm) than the blue (470 nm) (p = 0.022), and a not-statistically significant trend observed in a DE population landing more on blue compared to yellow (p = 0.104). To account for potential original host rearing influences, both populations were subsequently established on bean for ~20 weeks, then yellow chrysanthemum for 4−8 and 12−14 weeks and tested in wind tunnel choice bioassays. Laboratory of origin, irrespective of the host plant rearing regime, remained a significant effect (p < 0.001), with 65% of the NL WFT landing on yellow compared to blue (35%), while 66% of the DE WFT landed on blue compared to yellow (34%). There was also a significant host plant effect (p < 0.001), with increased response to yellow independent of laboratory of origin after rearing on chrysanthemum for 12−14 weeks. Results suggest that differing responses of WFT populations to colour is, in this case, independent of the experimental situation. Long-term separate isolation from the wild cannot be excluded as a cause, and the implications of this for optimising the trap colour is discussed.

Reproductive Isolation in the Cryptic Species Complex of a Key Pest: Analysis of Mating and Rejection Behaviour of Onion Thrips (Thrips tabaci Lindeman)

Simple Summary

The onion thrips (Thrips tabaci), which is a key pest worldwide, includes three characteristic, distinct groups (i.e., lineages) under the same species name. In the current report, we addressed the question of whether individuals from these lineages recognize and assess each other as potential mating partners. We demonstrated that at least two of these lineages do not belong to the same species, since under our laboratory conditions no mating occurred between them. Moreover, specimens from these cross pairings often exhibited an escape response upon contact with the other thrips, while most of the pairs from the same lineages readily mated at their first interaction. The behaviour of males clearly indicated that they can assess the mating status of a female and usually only try to copulate with virgins. Our findings are important not only because in agriculture it is vital to know whether morphologically similar entities belong to the same species, but also because knowledge about the communication of insects and the possible role of the cues involved can help the development of new plant protection techniques.

Abstract

Thrips tabaci Lindeman is a serious pest of various cultivated plants, with three, distinct lineages within a cryptic species complex. Despite the well-known significance of this pest, many attributes of these lineages are not yet fully understood, including their reproductive behaviour. We performed no-choice-design cross-mating experiments under a controlled laboratory environment with virgin adult individuals from all three lineages. The behaviour of thrips was recorded with a camera mounted on a stereomicroscope, and the recordings were analysed in detail. We found that the so-called leek-associated lineages of this cryptic species complex are reproductively isolated from the tobacco-associated lineage; therefore, they represent different species. Divergence in the behaviour of conspecific and heterospecific pairs became evident only after contact. There were no marked differences between the lineages in their precopulatory and copulatory behaviour, except in the duration of the latter. We confirmed mating between thelytokous females and arrhenotokous males; however, we assume some form of loss of function in the sexual traits of asexual females. The post-mating behaviour of males indicated the presence and role of an anti-aphrodisiac pheromone. We also demonstrated differences between lineages regarding their activity and their propensity for exhibiting an escape response upon interaction with heterospecific thrips.

Problems with the Concept of "Pest" among the Diversity of Pestiferous Thrips

Almost all of the thrips species that are considered pests are members of a single subfamily of Thripidae, the Thripinae, a group that represents less than 30% of the species in the insect Order Thysanoptera. Three of the five major Families of Thysanoptera (Aeolothripidae, Heterothripidae, Melanthripidae) are not known to include any pest species. The Phlaeothripidae that includes more than 50% of the 6300 thrips species listed includes very few that are considered to be pests. Within the Thripidae, the members of the three smaller subfamilies, Panchaetothripinae, Dendrothripinae and Sericothripinae, include remarkably few species that result in serious crop losses. It is only in the subfamily Thripinae, and particularly among species of the Frankliniella genus-group and the Thrips genus-group that the major thrips species are found, including all but one of the vectors of Orthotospovirus infections. It is argued that the concept of pest is a socio-economic problem, with the pest status of any particular species being dependent on geographical area, cultivation practices, and market expectations as much as the intrinsic biology of any thrips species.

A comprehensive picture of foraging strategies of Neoseiulus cucumeris and Amblyseius swirskii on western flower thrips

BACKGROUND

This study evaluated the potential of Neoseiulus cucumeris Oudemans and Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) for controlling western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), by determining the functional response, numerical response, prey switching and mutual interference behaviors of the predators.

RESULTS

A type II functional response was detected for two predator species fed on WFT first instars. The attack rate was higher for A. swirskii than N. cucumeris, but the handling time of N. cucumeris was shorter. For two predator species, numerical response was affected by both prey density and oviposition time. The per capita searching efficiencies of the two predators decreased significantly with increasing predator densities. The interference coefficient for A. swirskii was less than that of N. cucumeris. Although N. cucumeris switched from feeding on WFT first instars to feeding on second instars, this behavior was not observed in A. swirskii.

CONCLUSIONS

Comparison of the two predator species foraging behaviors indicated optimal performance by A. swirskii at lower F. occidentalis densities. N. cucumeris was found to perform optimally at relatively higher prey densities. Moreover, N. cucumeris could be more effective in stabilizing the predator-prey system by switching behavior compared with A. swirskii. At higher predator densities, A. swirskii seemed to be an effective agent owing to its reduced intraspecific competition compared with N. cucumeris. Findings from this study will be useful in selecting appropriate agents and developing effective biocontrol programs to control WFT. © 2021 Society of Chemical Industry.

Frontiers Approaches to the Diagnosis of Thrips (Thysanoptera): How Effective Are the Molecular and Electronic Detection Platforms?

Simple Summary

Thrips are important agricultural and forest pests. They cause damage by sucking plant sap and transmitting several plant viruses. Correct identification is the key for epidemiological studies and formulating appropriate management strategies. The application of molecular and electronic detection platforms has improved the morphological character-based diagnosis of thrips species. This article reviews research on molecular and automated identification of thrips species and discusses future research strategies for rapid and high throughput thrips diagnosis.

Abstract

Thrips are insect pests of economically important agricultural, horticultural, and forest crops. They cause damage by sucking plant sap and by transmitting several tospoviruses, ilarviruses, carmoviruses, sobemoviruses, and machlomoviruses. Accurate and timely identification is the key to successful management of thrips species. However, their small size, cryptic nature, presence of color and reproductive morphs, and intraspecies genetic variability make the identification of thrips species challenging. The use of molecular and electronic detection platforms has made thrips identification rapid, precise, sensitive, high throughput, and independent of developmental stages. Multi-locus phylogeny based on mitochondrial, nuclear, and other markers has resolved ambiguities in morphologically indistinguishable thrips species. Microsatellite, RFLP, RAPD, AFLP, and CAPS markers have helped to explain population structure, gene flow, and intraspecies heterogeneity. Recent techniques such as LAMP and RPA have been employed for sensitive and on-site identification of thrips. Artificial neural networks and high throughput diagnostics facilitate automated identification. This review also discusses the potential of pyrosequencing, microarrays, high throughput sequencing, and electronic sensors in delimiting thrips species.

Differences in Gall Induction of Flower-like Galls on Haloxylon by Psyllids (Hemiptera: Aphalaridae), and the Emergence of Corresponding Parasitoids

Simple Summary

Haloxylon spp. have been infested by various gall inducers, and natural enemies that impact pest populations must be understood to build integrated pest control strategies affecting pest dynamics. However, limited studies report on the gall inducers and parasitoids of flower-like galls on Haloxylon, as well as the parasitic efficacy of the parasitoids. This study aimed to determine the main gall inducers that induced flower-like galls on Haloxylon ammodendron and H. persicum, and the parasitoid complex associated with them. In total, five species of gall inducers and three species of parasitoids were obtained from three types of flower-like galls on Haloxylon. Further, the parasitization indexes, emergence, and lifespan of parasitoids were also discussed. The present study may serve as a basis for understanding the importance of biological investigations of parasitoids in the gall inducers living in flower-like galls, which is important for pest control and the conservation of the ecological environment in the Haloxylon forest.

Abstract

Saxaul is a kind of dominant perennial psammophyte that widely distributes in arid and semi-arid desert areas, and it has multiple functions in preventing desertification, especially in windbreak and sand fixation. Various gall inducers induce galls on the saxaul, including the flower-like gall. Parasitoids have great potentiality in controlling gall inducers. However, studies about gall inducers and parasitoids of flower-like galls on Haloxylon, as well as the parasitic efficacy of the parasitoids, are rarely reported. In this study, the flower-like galls were observed on Haloxylon ammodendron and H. persicum in Fukang, Xinjiang, China. Two types of flower-like galls were found on H. ammodendron, while only one type was found on H. persicum. In total, five species of gall inducers and three species of parasitoids were obtained from the galls mentioned above. All the galls were induced by Caillardia (Hemiptera: Aphalaridae), which were mostly bivoltine in Fukang. Besides, their parasitoids Psyllaephaguscaillardiae and P. longiventris could be observed on all the types of galls. Additionally, correlative studies on the parasitization indexes demonstrated that all the dominant parasitoids of diverse flower-like galls were P. caillardiae, which were slightly more in number than the P. ogazae discovered in the flower bud-like galls. In addition, the relevance between the emergence or lifespan of parasitoids and temperature was also investigated. The results showed that the number of parasitoids emerging decreased rapidly after a period of enhancement with the increase of temperature, including an optimum temperature, while the lifespan of wasps gradually shortened with the temperature rising. Our results highlight the importance of the biological investigation of parasitoids in the gall inducers lived in closed galls, which may provide critical evidence for us to understand its potential application in biological control.

Morphological, Molecular Identification and Distribution of Trypanosome-Transmitting Dipterans from Cattle Settlements in Southwest Nigeria

INTRODUCTION

Glossina spp. (Glossinidae), Tabanus spp. (Tabanidae), Ancala spp. (Tabanidae), Atylotus spp. (Tabanidae) and Stomoxys spp. (Muscidae) are important transmitting vectors of African animal trypanosomosis in sub-Saharan Africa. There is paucity of information on the distribution and identification of these flies in cattle settlements in southwest Nigeria.

METHODS

The distribution patterns, genetic variations and diversities of dipteran flies in southwest Nigeria were described and identified using morphological and molecular analysis of the 28S rDNA gene.

RESULTS

Of the 13,895 flies examined morphologically between April 2016 and March 2017, tabanids were identified [Tabanus (0.34%), Ancala (0.03%), Atylotus (0.01%), Haematopota (0.014%) and Chrysops (0.11%)]. Two stomoxyine species were identified; Stomoxys niger niger Macquart (45.30%) and Stomoxys calcitrans Linnaeus (17.29%) and two Glossina spp. namely; Glossina p. gambiense Vanderplank, 1911 (0.46%) and Glossina tachinoides Westwood (0.51%) were identified. The identities were further confirmed in a BLAST search using their nucleotide sequences. The median-joining network of the 28S rDNA gene sequences indicated that fly species examined were genetically distinct. The apparent density of all the trapped flies was highest at a mean temperature of 26-28 ℃, humidity > 80% and rainfall of 150-220 mm/month. The distribution of flies was observed to increase as vegetation increased in density and decreased in areas with relatively high human population density (> 100/km²).

CONCLUSIONS

The population indices of the 28S rDNA gene of the flies suggest that analysis of nuclear DNA fragments may provide more information on the molecular ecology of these flies. Characterising fly species and assessing their impact are essential in distribution and monitoring AAT spread.

DNA Barcoding: A Reliable Method for the Identification of Thrips Species (Thysanoptera, Thripidae) Collected on Sticky Traps in Onion Fields

Simple Summary

Thrips species (Insecta, Thysanoptera) identification using traditional approach is not an easy. In the present study, DNA barcoding was used to support the thrips species characterization of a wide collection sampled in onion fields. Our findings confirmed the selected method as a simple and accurate approach identifying major thrips species, characterizing successfully nearly 86% of the samples collected in nine main species. The results here reported underlined the role of genetic markers as a valuable and useful method for species identification, especially when the morphological approach is unsure or even impossible.

Abstract

Several thrips species (Insecta, Thysanoptera) are globally known as important crop pests and vectors of viral diseases, but their identification is difficult because of their small body size and inconspicuous morphological differences. Sequencing variation in the mitochondrial cytochrome c oxidase I (COI) region has been proven to be useful for the identification of species of many groups of insect pests. Here, DNA barcoding has been used to identify thrips species collected with the use of sticky traps placed in an open onion field. A total of 238 thrips specimens were analyzed, 151 of which could be identified to species and 27 to genera belonging to the family Thripidae. Fifty-one specimens could not be assigned to any genus, with the closest BLAST match in the GenBank queries being below 98%, whilst six specimens were not recognized as Thysanoptera. The results indicate that, although there are a few pest thrips species not yet barcoded, most of the species that may cause damage to crops in Europe are represented in GenBank and other databases, enabling correct identification. Additionally, DNA barcoding can be considered a valuable alternative to the classic morphology method for identification of major thrips species.

Invasion Biology, Ecology, and Management of Western Flower Thrips

Western flower thrips, Frankliniella occidentalis, first arose as an important invasive pest of many crops during the 1970s-1980s. The tremendous growth in international agricultural trade that developed then fostered the invasiveness of western flower thrips. We examine current knowledge regarding the biology of western flower thrips, with an emphasis on characteristics that contribute to its invasiveness and pest status. Efforts to control this pest and the tospoviruses that it vectors with intensive insecticide applications have been unsuccessful and have created significant problems because of the development of resistance to numerous insecticides and associated outbreaks of secondary pests. We synthesize information on effective integrated management approaches for western flower thrips that have developed through research on its biology, behavior, and ecology. We further highlight emerging topics regarding the species status of western flower thrips, as well as its genetics, biology, and ecology that facilitate its use as a model study organism and will guide development of appropriate management practices.

Frankliniella species from China, with nomenclatural changes and illustrated key (Thysanoptera, Thripidae)

Species of the genus Frankliniella are almost all originally from the New World. Although eleven species in this genus have been listed from China before, only seven species here are recognised. The records of F. pallida and F. tritici from China are rejected as inadequately supported, F. hainanensis is a new synonym of F. schultzei, and F. zizaniophila is now considered a member of the genus Iridothrips. An identification key for the seven species is provided here, two of them are widespread across the Palearctic (F. intonsa and F. tenuicornis), one is presumably Oriental (F. lilivora), and four are introduced from the Americas (F. occidentalis, F. schultzei, F. cephalica and F. williamsi).

Agrilus mali Matsumara (Coleoptera: Buprestidae), a new invasive pest of wild apple in western China: DNA barcoding and life cycle

Agrilus mali Matsumara (Coleoptera: Buprestidae) is a wood-boring beetle distributed to eastern China that occasionally injures apple species. However, this wood-boring beetle is new to the wild apple forests (Malus sieversii) of the Tianshan Mountains (western China) and has caused extensive tree mortality. The development of a biological control program for these wild apple forests is a high priority that requires exploration of the life cycle, DNA barcoding and taxonomic status of A. mali. In this study, to determine the diversity of invasive beetles, a fragment of the mitochondrial cytochrome oxidase gene was analyzed. Based on the results, beetles from Gongliu and Xinyuan counties of Xinjiang were identical but differed from those in the apple nursery of Gongliu by a single-nucleotide substitution. We summarize the taxonomic status, relationships, and genetic distances of A. mali among other Agrilus species using the Tajima-Nei model in maximum likelihood phylogeny. Analysis revealed that A. mali was closely related to Agrilus mendax and both belong to the Sinuatiagrulus subgenus. The life cycle of A. mali was investigated based on a monthly regular inspection in the wild apple forests of Tianshan. Similar to congeneric species, hosts are injured by larvae of A. mali feeding on phloem tissue, resulting in serpentine galleries constructed between bark and xylem that prevent nutrient transport and leading to tree mortality. Future studies will focus on plant physiological responses to the invasive beetles and include surveys of natural enemies for a potential classical biological control program.

Molecular footprint of Frankliniella occidentalis from India: a vector of Tospoviruses

The western flower thrips, F. occidentalis is a vector of Tospoviruses and native to Western North America and Mexico. The present study is based on collected F. occidentalis specimens from Karnataka state in southern India and morphologically identified through available keys. The generated DNA barcode data show 99–100% similarity with the database sequences of F. occidentalis. The phylogenetic analysis (NJ, ML, and BA) shows three distinct clades of F. occidentalis in the present dataset with high bootstrap supports and posterior probabilities. The K2P genetic distances further depicted high similarity of the generated sequences from India and Netherlands. The Clade-1 (India + Netherlands) also shows a close relationship with Clade-2 (Kenya) rather than Clade-3 (Canada + USA). This study recorded the first genetic footprint of F. occidentalis in India and indicated the gene flow from the Netherlands to India. The similar molecular techniques may help to detect the invasion of many alien species in the near future and assists the quarantine regulations to protect the native ecosystem.

Host specificity of parasitoids (Encyrtidae) toward armored scale insects (Diaspididae): Untangling the effect of cryptic species on quantitative food webs

Host specificity of parasitoids may be measured by various specialization indices to assess the variation of interaction strength among species and the structure of the wider interaction network. However, the conclusions from analyses at the species and network levels may differ, which remains poorly explored. In addition, the recovery of cryptic species of hosts and parasitoids with molecular data may affect the structure of inferred interaction links. We quantified host specificity of hymenopteran parasitoids (family Encyrtidae) on armored scale insects (Hemiptera: Diaspididae) from a wide geographic sampling range across the Chinese Mainland based on both morphological and molecular species delimitation. Mitochondrial COI and nuclear 28S markers detected high cryptic species diversity in the encyrtids and to a lesser degree in the diaspidids, which divided generalist morphospecies into complexes of specialists and generalists. One-to-one reciprocal host-parasite links were increased in the molecular data set, but different quantitative species-level indices produced contrasting estimates of specificity from various one-to-multiple and multiple-to-multiple host-parasite links. Network indices calculated from DNA-based species, compared to morphology-based species definitions, showed lower connectance and generality, but greater specialization and compartmentalization of the interaction network. We conclude that a high degree of cryptic species in host-parasitoid systems refines the true network structure and may cause us overestimating the stability of these interaction webs.

Cryptic Plutella species show deep divergence despite the capacity to hybridize

Background

Understanding genomic and phenotypic diversity among cryptic pest taxa has important implications for the management of pests and diseases. The diamondback moth, Plutella xylostella L., has been intensively studied due to its ability to evolve insecticide resistance and status as the world’s most destructive pest of brassicaceous crops. The surprise discovery of a cryptic species endemic to Australia, Plutella australiana Landry & Hebert, raised questions regarding the distribution, ecological traits and pest status of the two species, the capacity for gene flow and whether specific management was required. Here, we collected Plutella from wild and cultivated brassicaceous plants from 75 locations throughout Australia and screened 1447 individuals to identify mtDNA lineages and Wolbachia infections. We genotyped genome-wide SNP markers using RADseq in coexisting populations of each species. In addition, we assessed reproductive compatibility in crossing experiments and insecticide susceptibility phenotypes using bioassays.

Results

The two Plutella species coexisted on wild brassicas and canola crops, but only 10% of Plutella individuals were P. australiana. This species was not found on commercial Brassica vegetable crops, which are routinely sprayed with insecticides. Bioassays found that P. australiana was 19-306 fold more susceptible to four commonly-used insecticides than P. xylostella. Laboratory crosses revealed that reproductive isolation was incomplete but directionally asymmetric between the species. However, genome-wide nuclear SNPs revealed striking differences in genetic diversity and strong population structure between coexisting wild populations of each species. Nuclear diversity was 1.5-fold higher in P. australiana, yet both species showed limited variation in mtDNA. Infection with a single Wolbachia subgroup B strain was fixed in P. australiana, suggesting that a selective sweep contributed to low mtDNA diversity, while a subgroup A strain infected just 1.5% of P. xylostella.

Conclusions

Despite sympatric distributions and the capacity to hybridize, strong genomic and phenotypic divergence exists between these Plutella species that is consistent with contrasting colonization histories and reproductive isolation after secondary contact. Although P. australiana is a potential pest of brassicaceous crops, it is of secondary importance to P. xylostella.

Electronic supplementary material

The online version of this article (10.1186/s12862-018-1183-4) contains supplementary material, which is available to authorized users.

Demographic analysis of arrhenotokous parthenogenesis and bisexual reproduction of Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae)

Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) is a serious pest that is capable of bisexual and arrhenotokous reproduction. In arrhenotokous reproduction, virgin females initially produce male offspring; later, when their sons are sexually mature, the mothers begin bisexual reproduction by carrying out oedipal mating with their sons. Because a virgin female produces many male offspring before oedipal mating occurs, multiple oedipal mating is common. In this study, we investigated the effect of multiple oedipal mating on the population growth of F. occidentalis by using the age-stage, two-sex life table theory. In the arrhenotokous cohorts, all unfertilized eggs developed into males. In the bisexual cohorts, the offspring sex ratio was significantly female biased with the mean number of female offspring and male offspring being 72.68 and 29.00, respectively. These were the same as the net reproductive rate of female offspring and male offspring. In arrhenotokous cohorts, the number of males available for oedipal mating significantly affected the production of female offspring. The number of female offspring increased as the number of sons available for oedipal mating increased. Correctly characterizing this unique type of reproduction will provide important information for predicting the timing of future outbreaks of F. occidentalis, as well as aiding in formulating successful management strategies against the species.

Unexpected High Intragenomic Variation in Two of Three Major Pest Thrips Species Does Not Affect Ribosomal Internal Transcribed Spacer 2 (ITS2) Utility for Thrips Identification

The mitochondrial cytochrome oxidase I gene (mtCO1) and the ribosomal internal transcribed spacer 2 region (ITS2) are among the most widely used molecular markers for insect taxonomic characterization. Three economically important species of thrips, Scirtothripsdorsalis, Thripspalmi, and Frankliniellaoccidentalis were selected to examine the extent of intragenomic variation within these two marker regions in the family Thripidae, and determine if this variation would affect the utility of markers in thrips molecular diagnostics. For each species, intragenomic (within individual) variation and intergenomic (among individuals) variation was assessed by cloning and sequencing PCR-amplified copies. Intergenomic variation was generally higher than intragenomic variation except in cases where intergenomic variation was very low, as in mtCO1 from S.dorsalis and F.occidentalis. Intragenomic variation was detected in both markers in all three of the thrips species, however, 2-3 times more intragenomic variation was observed for ITS2 than mtCO1 in both S.dorsalis and T.palmi. Furthermore, levels of intragenomic variation were low for both of the genes in F.occidentalis. In all of the three thrips species, no sex-based clustering of haplotypes was observed in either marker. Unexpected high intragenomic variation in ITS2 for two of three thrips species did not interfere with thrips diagnostics. However, caution should be taken in applying ITS2 to certain studies of S.dorsalis and T.palmi when high levels of intragenomic variation could be problematic or confounding. In such studies, mtCO1 may be a preferable marker. Possible reasons for discrepancies in intragenomic variation among genomic regions are discussed.

DNA Barcoding studies on Thrips in India: Cryptic species and Species complexes

Thrips are one of the major sucking pest and vector of plant viruses causing huge economic loss in agriculture. The accurate identification of thrips is crucial for effective pest management strategies. However, morphology based identification has limitations and warrants integration of molecular data. We attempted the largest DNA barcoding initiative on 370 sequences of 89 thrips morphospecies including 104 novel sequences from 39 morphospecies, including the type specimens of four species. The results of multiple species delimitation methods (BIN, ABGD, GMYC and bPTP) were consistent for 73 species (82%) with their morphological identifications. A total of 107 molecular operational taxonomic units (MOTUs) was recovered for 89 morphospecies by superimposing multiple methods and applying a three level nomenclature system. We detected more than one MOTU in 14 morphospecies indicating to have cryptic diversity including, two major vector species (Frankliniella schultzei and Thrips palmi). However, four morphospecies (Thrips moundi, Thrips carthami, Haplothrips andersi and Haplothrips gowdeyi) showed low genetic distances between them with overlapping in barcode gap that requires further analysis with multiple molecular markers and more specimens from wide geographical areas for better taxonomic judgment. We also presented the advantage of simultaneous use of multiple delimitation methods for detection and identification of cryptic species.

Low genetic diversity but strong population structure reflects multiple introductions of western flower thrips (Thysanoptera: Thripidae) into China followed by human-mediated spread

Historical invasion scenarios based on observational records are usually incomplete and biased, but these can be supplemented by population genetic data. The western flower thrips (WFT), Frankliniella occidentalis, invaded China in the last 13 years and has rapidly become one of the most serious pests in the country. To assess whether this invasion involved a single event or multiple events, we examined patterns of genetic diversity and population structure of WFT across 12 Chinese populations and a native US population based on mitochondrial DNA and/or 18 microsatellite loci. The average allelic richness and haplotype diversity in Chinese populations were significantly lower than in a population from its native range. The distribution of mitochondrial haplotypes suggested multiple independent invasions of WFT into China, including two invasions into the Beijing region. Based on microsatellite data, two distinct clusters were identified, with both of them splitting further into two clusters; in the Beijing region, the microsatellite data also provided evidence for two introductions. Both the absence of isolation by distance and the fact that distant populations were similar genetically suggest patterns of WFT movement linked to human activities. Our study therefore suggests multiple introductions of WFT into China and human-assisted spread.

Incomplete offspring sex bias in Australian populations of the butterfly Eurema hecabe

Theory predicts unified sex ratios for most organisms, yet biases may be engendered by selfish genetic elements such as endosymbionts that kill or feminize individuals with male genotypes. Although rare, feminization is established for Wolbachia-infected Eurema butterflies. This paradigm is presently confined to islands in the southern Japanese archipelago, where feminized phenotypes produce viable all-daughter broods. Here, we characterize sex bias for E. hecabe in continental Australia. Starting with 186 wild-caught females, we reared >6000 F1-F3 progeny in pedigree designs that incorporated selective antibiotic treatments. F1 generations expressed a consistent bias across 2 years and populations that was driven by an ~5% incidence of broods comprising ⩾80% daughters. Females from biased lineages continued to overproduce daughters over two generations of outcrossing to wild males. Treatment with antibiotics of differential strength influenced sex ratio only in biased lineages by inducing an equivalent incomplete degree of son overproduction. Brood sex ratios were nevertheless highly variable within lineages and across generations. Intriguingly, the cytogenetic signature of female karyotype was uniformly absent, even among phenotypic females in unbiased lineages. Molecular evidence supported the existence of a single Wolbachia strain at high prevalence, yet this was not clearly linked to brood sex bias. In sum, we establish an inherited, experimentally reversible tendency for incomplete offspring bias. Key features of our findings clearly depart from the Japanese feminization paradigm and highlight the potential for more subtle degrees of sex distortion in arthropods.

Armored Scales and Their Parasitoids on Commercial Avocados Grown in California or Imported from Mexico

Levels of armored scales (Hemiptera: Diaspididae) on Mexican Hass avocados imported into California over May 2008-June 2009 were monitored on 135 trucks entering the state via the Blythe border station, the entry point receiving the highest volume of fruit. Levels of live sessile scales were 3.9-fold higher than indicated in a previous survey (September 2007-April 2008) although levels of live eggs and crawlers were similar to previous levels. A survey of avocado fruit in California infested with armored scales detected four species known to be endemic but failed to find any of the seven exotic Diaspididae entering the state on Mexican fruit. Monitoring of Mexican armored scales on imported avocados from September 2007 to December 2010 recovered 10 species of parasitoids predominated by two species of Signiphora Ashmead (Hymenoptera: Signiphoridae). One of these species, Signiphora flavopalliata Ashmead, comprised 36% of all collected Mexican parasitoids and is a known hyperparasitoid. A survey of armored scale parasitoids present on commercial California avocados detected 17 genetic signatures, with only four of these in common with those detected on imported Mexican fruit. The implications of these findings are discussed.

DNA barcodes for bio-surveillance: regulated and economically important arthropod plant pests

Many of the arthropod species that are important pests of agriculture and forestry are impossible to discriminate morphologically throughout all of their life stages. Some cannot be differentiated at any life stage. Over the past decade, DNA barcoding has gained increasing adoption as a tool to both identify known species and to reveal cryptic taxa. Although there has not been a focused effort to develop a barcode library for them, reference sequences are now available for 77% of the 409 species of arthropods documented on major pest databases. Aside from developing the reference library needed to guide specimen identifications, past barcode studies have revealed that a significant fraction of arthropod pests are a complex of allied taxa. Because of their importance as pests and disease vectors impacting global agriculture and forestry, DNA barcode results on these arthropods have significant implications for quarantine detection, regulation, and management. The current review discusses these implications in light of the presence of cryptic species in plant pests exposed by DNA barcoding.

Morphological and Molecular Characterization of Reared Parasitoid Wasps of the Genus Glyptapanteles Ashmead 1904 (Insecta: Hymenoptera: Braconidae: Microgastrinae) Associated with Lepidoptera in India

Glyptapanteles Ashmead (Hymenoptera: Braconidae: Microgastrinae) is a cosmopolitan group of hyperdiverse parasitic wasps. The genus remains taxonomically challenging in India due to its highly speciose nature, morphological similarity amongst species and negligible host records. The Indian fauna is one of the most diverse and also the least studied. The present study is based on 60 populations reared from 35 host species, 100+ individual caterpillar rearings (1100 wasp specimens pinned and 2000 in alcohol) and from 12 different geographical locations of the country (11 states and one Union territory) that represent 26 provisional Glyptapanteles species within 8 species-groups. Out of 60 populations, phylogenetic analyses were performed on 38 based on mitochondrial cytochrome oxidase subunit I (COI) nucleotide sequences. Maximum likelihood and Bayesian inference methods displayed three and four major discrete Glyptapanteles clades, respectively. In clade A very few Indian species were grouped along with Neotropical and Thailand species. The other clades B and C grouped the majority of the Indian species and showed considerable host specificity in both the trees. All parasitic wasp species were gregarious in nature, except for two populations. Three different sets of data (morphology, host records, and COI) were integrated in order to generate accurate boundaries between species/species-groups. Illustrations of all parasitized caterpillars/cocoons and 42 habitus views of Glyptapanteles spp., distributional information, and GenBank accession numbers, are presented. The present study, perhaps the most comprehensive done to date in India, suggests the presence of several additional Glyptapanteles species, which were previously unrecognized.

Thysanoptera-Terebrantia of the Hawaiian Islands: an identification manual

An illustrated identification system is presented to 99 species and 49 genera in three families recorded from the Hawaiian Islands in the Thysanoptera suborder Terebrantia. Only seven (possibly eight) of these species are considered endemic, the remainder being adventive to these islands. The only previous study of Hawaiian Thysanoptera, by Zimmerman in 1948, included 47 Terebrantia species in 21 genera.

DNA Barcode Analysis of Thrips (Thysanoptera) Diversity in Pakistan Reveals Cryptic Species Complexes

Although thrips are globally important crop pests and vectors of viral disease, species identifications are difficult because of their small size and inconspicuous morphological differences. Sequence variation in the mitochondrial COI-5ʹ (DNA barcode) region has proven effective for the identification of species in many groups of insect pests. We analyzed barcode sequence variation among 471 thrips from various plant hosts in north-central Pakistan. The Barcode Index Number (BIN) system assigned these sequences to 55 BINs, while the Automatic Barcode Gap Discovery detected 56 partitions, a count that coincided with the number of monophyletic lineages recognized by Neighbor-Joining analysis and Bayesian inference. Congeneric species showed an average of 19% sequence divergence (range = 5.6% - 27%) at COI, while intraspecific distances averaged 0.6% (range = 0.0% - 7.6%). BIN analysis suggested that all intraspecific divergence >3.0% actually involved a species complex. In fact, sequences for three major pest species (Haplothrips reuteri, Thrips palmi, Thrips tabaci), and one predatory thrips (Aeolothrips intermedius) showed deep intraspecific divergences, providing evidence that each is a cryptic species complex. The study compiles the first barcode reference library for the thrips of Pakistan, and examines global haplotype diversity in four important pest thrips.

Identification through DNA barcoding of Tabanidae (Diptera) vectors of surra disease in India

Horse flies and deer flies are common names applied to members of the family Tabanidae (Diptera). Tabanid flies are pestiferous and of veterinary and medical importance, with about 244 species in India. They are major vectors of Trypanosoma evansi that causes trypanosomiasis (surra disease). Lack of stable morphological characters, and scarcity of taxonomic expertise, is major impediments for accurate species identification of these important pest and disease vectors. Molecular data, especially DNA barcode data, has been widely used in the identification of Diptera of economic importance. We evaluated the utility of DNA barcode data to discriminate the vectors of surra disease (trypanosomiasis) from India. We used barcode gap and reciprocal monophyly (neighbor-joining and Bayesian tree) criteria to analyze barcode data. A total of 46 specimens belonging to 7 species under four genera in two subfamilies were used for this study. DNA barcode data was not available previously for these species. Analysis revealed that all morphologically identifiable species can be discriminated using DNA barcoding data. Further, our study clearly demonstrated the presence of cryptic species in Chrysops dispar. Moreover, we revealed that closely related species without stable taxonomic distinguishing characters in the "Tabanus striatus species complex" can be discriminated using DNA barcode data.

Morphological and DNA Barcoding Evidence for Invasive Pest Thrips, Thrips parvispinus (Thripidae: Thysanoptera), Newly Recorded From India

South East Asia pest thrips species, Thrips parvispinus (Karny), is a serious pest on a number of agricultural and horticultural crops in a number of plant families. Based on an integrated approach of morphology and DNA barcoding, invasion of this serious pest is reported first time from India on papaya plantations. Molecular data have corroborated with the morphological identification. Haplotyping data suggested that the Indonesia may be a probable source of invasion of this pest to India.

Temporal Genetic Dynamics of an Invasive Species, Frankliniella occidentalis (Pergande), in an Early Phase of Establishment

Many species can successfully colonize new areas despite their propagules having low genetic variation. We assessed whether the decreased genetic diversity could result in temporal fluctuations of genetic parameters of the new populations of an invasive species, western flower thrips, Frankliniella occidentalis, using mitochondrial and microsatellite markers. This study was conducted in eight localities from four climate regions in China, where F. occidentalis was introduced in the year 2000 and had lower genetic diversity than its native populations. We also tested the level of genetic differentiation in these introduced populations. The genetic diversity of the samples at different years in the same locality was not significantly different from each other in most localities. F_ST and STRUCTURE analysis also showed that most temporal population comparisons from the same sites were not significantly differentiated. Our results showed that the invasive populations of F. occidentalis in China can maintain temporal stability in genetic composition at an early phase of establishment despite having lower genetic diversity than in their native range.

The Scirtothrips dorsalis Species Complex: Endemism and Invasion in a Global Pest

Invasive arthropods pose unique management challenges in various environments, the first of which is correct identification. This apparently mundane task is particularly difficult if multiple species are morphologically indistinguishable but accurate identification can be determined with DNA barcoding provided an adequate reference set is available. Scirtothrips dorsalis is a highly polyphagous plant pest with a rapidly expanding global distribution and this species, as currently recognized, may be comprised of cryptic species. Here we report the development of a comprehensive DNA barcode library for S. dorsalis and seven nuclear markers via next-generation sequencing for identification use within the complex. We also report the delimitation of nine cryptic species and two morphologically distinguishable species comprising the S. dorsalis species complex using histogram analysis of DNA barcodes, Bayesian phylogenetics, and the multi-species coalescent. One member of the complex, here designated the South Asia 1 cryptic species, is highly invasive, polyphagous, and likely the species implicated in tospovirus transmission. Two other species, South Asia 2, and East Asia 1 are also highly polyphagous and appear to be at an earlier stage of global invasion. The remaining members of the complex are regionally endemic, varying in their pest status and degree of polyphagy. In addition to patterns of invasion and endemism, our results provide a framework both for identifying members of the complex based on their DNA barcode, and for future species delimiting efforts.

Seasonal climatic variations influence the efficacy of predatory mites used for control of western flower thrips in greenhouse ornamental crops

The influence of seasonal greenhouse climate on the efficacy of predatory mites for thrips control was determined for potted chrysanthemum. Trials in controlled environment chambers, small-scale greenhouses and commercial greenhouses were conducted to determine which biological control agent-that is, Amblyseius swirskii Athias-Henriot or Neoseiulus cucumeris (Oudemans)-is more efficacious for control of western flower thrips, Frankliniella occidentalis (Pergande), in different seasons. Under simulated summer conditions, no differences were observed in the predation and oviposition rates of both predatory mites in the laboratory trials. However, small-scale greenhouse trials showed that A. swirskii performed better than N. cucumeris in summer (i.e., more efficacious thrips control, higher predator abundance and less overall damage to the crop). Under simulated winter conditions, laboratory trials demonstrated variable differences in predation rates of the two predatory mites. The small-scale greenhouse trials in winter showed no differences in thrips control and predatory mite abundance between the two predatory mites, but plants with A. swirskii had less damage overall. The results from the small-scale trials were validated and confirmed in commercial greenhouse trials. Overall, A. swirskii performed better in the summer and equally good or better (less damage overall) under winter conditions, whereas N. cucumeris is a more cost effective biological control agent for winter months.

Phylogeography of the walnut twig beetle, Pityophthorus juglandis, the vector of thousand cankers disease in North American walnut trees

Thousand cankers disease (TCD) of walnut trees (Juglans spp.) results from aggressive feeding in the phloem by the walnut twig beetle (WTB), Pityophthorus juglandis, accompanied by inoculation of its galleries with a pathogenic fungus, Geosmithia morbida. In 1960, WTB was only known from four U.S. counties (in Arizona, California, and New Mexico), but the species has now (2014) invaded over 115 counties, representing much of the western USA, and at least six states in the eastern USA. The eastern expansion places TCD in direct proximity to highly valuable (> $500 billion) native timber stands of eastern black walnut, Juglans nigra. Using mitochondrial DNA sequences, from nearly 1100 individuals, we examined variation among 77 samples of WTB populations across its extended range in the USA, revealing high levels of polymorphism and evidence of two divergent lineages. The highest level of genetic diversity for the different lineages was found in the neighboring Madrean Sky Island and Western New Mexico regions, respectively. Despite their proximity, there was little evidence of mixing between these regions, with only a single migrant detected among 179 beetles tested. Indeed, geographic overlap of the two lineages was only common in parts of Colorado and Utah. Just two haplotypes, from the same lineage, predominated over the vast majority of the recently expanded range. Tests for Wolbachia proved negative suggesting it plays no role in "driving" the spread of particular haplotypes, or in maintaining deep levels of intraspecific divergence in WTB. Genotyping of ribosomal RNA corroborated the mitochondrial lineages, but also revealed evidence of hybridization between them. Hybridization was particularly prevalent in the sympatric areas, also apparent in all invaded areas, but absent from the most haplotype-rich area of each mitochondrial lineage. Hypotheses about the specific status of WTB, its recent expansion, and potential evolutionary origins of TCD are discussed.

Agronomically important thrips: development of species-specific primers in multiplex PCR and microarray assay using internal transcribed spacer 1 (ITS1) sequences for identification

Thrips, the sole vector of plant Tospovirus, are major pests of many agricultural crops throughout the world. Molecular approaches have been applied in recent decades to identify these minute and morphologically difficult to distinguish insects. In this study, sequences of internal transcribed spacer 1 (ITS1) region of 15 agronomically important thrips, including several virus transmission species, have been analyzed in order to design species-specific primers for multiplex PCR and probes for microarray assay. That the ITS1 sequence distances within species were smaller than those among species suggests that the ITS1 fragment can be used for thrips species identification. The specificity and stability of these primers, combined with universal paired primers, were tested and verified in multiplex PCR. Using these specific primers as probes, microarray assay showed that PCR products of all thrips species hybridized consistently to their corresponding probes, though some signals were weak. We have demonstrated that multiplex PCR using specific primers based on ITS1 sequences is a simple, reliable, and cost-effective diagnostic tool for thrips species identification. Moreover, the DNA microarray assay is expected to extend into a reliable high-throughput screening tool for the vast numbers of thrips.

Diversity of Thrips Species and Vectors of Tomato Spotted Wilt Virus in Tomato Production Systems in Kenya

Thrips have been recognized as primary vectors of tomato spotted wilt virus (TSWV) with Frankliniella occidentalis (Pergande) reported as the most important and efficient vector, while other species such as Thrips tabaci Lindeman also include populations that can vector the virus. A study was undertaken to establish the diversity of thrips and presence of vectors for TSWV in four major tomato production areas in Kenya. The cytochrome oxidase 1 (CO1) gene was used to generate sequences from thrips samples collected from tomatoes and weeds, and phylogenetic analysis done to establish the variation within potential vector populations. Ceratothripoides brunneus Bagnall was the predominant species of thrips in all areas. F. occidentalis and T. tabaci were abundant in Nakuru, Kirinyaga, and Loitokitok but not detected at Bungoma. Other vectors of tospoviruses identified in low numbers were Frankliniella schultzei (Trybom) and Scirtothrips dorsalis Hood. Variation was observed in T. tabaci, F. occidentalis, and F. schultzei. Kenyan specimens of T. tabaci from tomato belonged to the arrhenotokous group, while those of F. occidentalis clustered with the Western flower thrips G group. The detection of RNA of TSWV in both of these species of thrips supported the role they play as vectors. The study has demonstrated the high diversity of thrips species in tomato production and the occurrence of important vectors of TSWV and other tospoviruses.

Classical Biological Control of Invasive Legacy Crop Pests: New Technologies Offer Opportunities to Revisit Old Pest Problems in Perennial Tree Crops

Advances in scientific disciplines that support classical biological control have provided "new tools" that could have important applications for biocontrol programs for some long-established invasive arthropod pests. We suggest that these previously unavailable tools should be used in biological control programs targeting "legacy pests", even if they have been targets of previously unsuccessful biocontrol projects. Examples of "new tools" include molecular analyses to verify species identities and likely geographic area of origin, climate matching and ecological niche modeling, preservation of natural enemy genetic diversity in quarantine, the use of theory from invasion biology to maximize establishment likelihoods for natural enemies, and improved understanding of the interactions between natural enemy and target pest microbiomes. This review suggests that opportunities exist for revisiting old pest problems and funding research programs using "new tools" for developing biological control programs for "legacy pests" could provide permanent suppression of some seemingly intractable pest problems. As a case study, we use citricola scale, Coccus pseudomagnoliarum, an invasive legacy pest of California citrus, to demonstrate the potential of new tools to support a new classical biological control program targeting this insect.

Characterization and Epidemiology of Outbreaks of Impatiens necrotic spot virus on Lettuce in Coastal California

California is the leading producer of lettuce (Lactuca sativa) for the United States and grows 77% of the country's supply. Prior to 2006, coastal California lettuce was only periodically and incidentally infected by a single tospoviruses species: Tomato spotted wilt virus (TSWV). However, beginning in 2006 and continuing through 2012, severe outbreaks of disease caused by Impatiens necrotic spot virus (INSV) have affected the coastal lettuce crop, though TSWV was also present. In contrast, TSWV was the only tospovirus associated with disease outbreaks in Central Valley lettuce during this period. Disease surveys conducted over two seasons (2008 and 2009) in 10 commercial fields (acreage of 6 to 20 ha) indicated that INSV was the only tospovirus associated with economically damaging disease outbreaks in lettuce in the coastal region, with incidences of 0.5 to 27% (mean = 5.7%). Molecular characterization of INSV isolates associated with these disease outbreaks revealed little genetic diversity and indicated that lettuce-infecting INSV isolates were nearly identical to those previously characterized from ornamental or other hosts from different locations in the United States and the world. Monitoring of thrips revealed moderate to large populations in all surveyed lettuce fields, and the majority of thrips identified from these fields were western flower thrips, Frankliniella occidentalis. There was significant positive correlation (r² = 0.91, P = 0.003) between thrips populations and INSV incidence in the most commonly encountered type of commercial lettuce (romaine, direct seeded, conventional) included in this study. A reverse-transcription polymerase chain reaction assay developed for detection of INSV in thrips showed promise as a monitoring tool in the field. Surveys for INSV reservoir hosts in the coastal production area revealed that the weeds little mallow (Malva parvifolia) and shepherd's purse (Capsella bursa-pastoris) were commonly infected. M. parvifolia plants infected in the field did not show obvious symptoms, whereas plants of this species inoculated in the laboratory with INSV by sap transmission developed necrotic spots and chlorosis. Eleven other weed species growing in the lettuce production areas were found to be hosts of INSV. Coastal crops found to be infected with INSV included basil (Ocimum basilicum), bell pepper (Capsicum annuum), calla lily (Zantedeschia aethiopica), faba bean (Vicia faba), radicchio (Cichorium intybus), and spinach (Spinacia oleracea). Thus, it is likely that INSV was introduced into coastal California lettuce fields via viruliferous thrips that initially acquired the virus from other local susceptible plant species. Results of this study provide a better understanding of INSV epidemiology in coastal California and may help growers devise appropriate disease management strategies.

Phylogenetic analysis of New Zealand tomato spotted wilt virus isolates suggests likely incursion history scenarios and mechanisms for population evolution

Tomato spotted wilt virus (TSWV) is an internationally significant pathogen with a wide host range, vectored by thrips. We have studied the sequence variation and evolutionary mechanisms at play in parts of the L, M and S subgenomes of 23 New Zealand TSWV isolates collected between 1992 and 2009, aiming to identify the possible geographic origins of isolates. Maximum-likelihood-based phylogenetic analyses of New Zealand and overseas TSWV isolates placed the L and M subgenome sequences of two isolates (MAF04 and PFR04) in distinct clades composed primarily of Korean, Japanese and Chinese isolates, in contrast to the remaining 21 isolates, which clustered with a cosmopolitan group of isolates. The nucleocapsid (N) gene sequences of MAF04 and PFR04 plus MAF02 clustered with Japanese isolates. Consequently, we postulate that these isolates may represent a distinct incursion into New Zealand, but we do not have enough evidence to indicate an incursion pathway. Alternately, these isolates may have arrived with an incursion that included a mixture of TSWV isolates of diverse international origins. The sequences of four of the TSWV isolates contained a number of sites with a mixture of nucleotides, suggesting that these isolates either consisted of several sequence variants or were from plants with mixed infections. One isolate (MAF02) was shown to be a either a reassortant or an S subgenome recombinant. Large amounts of low-level polymorphism were detected with low amino acid change fixation rates (purifying selection). Negative selection was indicated at four amino acid sites in the New Zealand TSWV N gene sequences.

The lesser of two weevils: molecular-genetics of pest palm weevil populations confirm Rhynchophorus vulneratus (Panzer 1798) as a valid species distinct from R. ferrugineus (Olivier 1790), and reveal the global extent of both

The red palm weevil (RPW) is a major pest of palms. It is native to southeast Asia and Melanesia, but in recent decades has vastly expanded its range as the result of multiple accidental anthropogenic introductions into the Middle East, Mediterranean Basin, Caribbean, and U.S.A. Currently regarded as a single species, Rhynchophorus ferrugineus (Olivier), RPW displays remarkable color variation across its range, and consequently has a taxonomic history littered with new species descriptions and synonymization. We compared DNA sequences of the mitochondrial cytochrome oxidase subunit I (COI) gene from RPW populations throughout the native and invaded ranges, to investigate the specific status and invasion history of this serious economic pest, and to identify possible common routes of entry. Analyses of COI haplotype data provide conclusive support, corroborated by sequences of additional nuclear gene regions, for the existence of at least two predominantly allopatric species. The true R. ferrugineus is native only to the northern and western parts of continental southeast Asia, Sri Lanka and the Philippines, and is responsible for almost all invasive populations worldwide. In contrast, the second species, which is currently synonymized under R. ferrugineus and should be resurrected under the name R. vulneratus (Panzer), has a more southern distribution across Indonesia, and is responsible for only one invasive population; that in California, U.S.A. The distribution of COI haplotypes is used to discuss the possible existence of further cryptic species, sources and routes of entry of different invasive populations, and the implications of our findings for current control methods.

Using population genetic methods to identify the origin of an invasive population and to diagnose cryptic subspecies of Telchin licus (Lepidoptera: Castniidae)

Telchin licus, the giant sugarcane borer, is an important pest species of sugarcane in northeast Brazil. Four subspecies of Telchin licus are recognized in Brazil based on their geographic distribution and subtle differences in wing colour pattern. Some taxa are morphologically indistinguishable, and their accurate identification is key to their efficient control. Mitochondrial genes sequences (cytochrome oxidase I and subunit 6 of the nicotinamide adenine dinucleotide dehydrogenase) were applied to delimit taxonomic entities of T. licus, and to infer the origin of a newly established population in the state of São Paulo. The molecular data indicated that specimens sampled at different regions in Brazil are morphologically cryptic but genetically isolated entities, and at least three subspecies were assigned to the sampled localities. These data also suggested that the population collected from the state of São Paulo must have a common origin with populations from northeast Brazil, which corroborate the hypothesis that ornamental plants infested with larvae of T. licus might have been transported from the northeast to the southeast regions.

Phylogeographic structure, outbreeding depression, and reluctant virgin oviposition in the bean thrips, Caliothrips fasciatus (Pergande) (Thysanoptera: Thripidae), in California

Bean thrips, Caliothrips fasciatus, is native to western North America. Once considered a pest of several crops in its native area, its pest status has waned over recent decades. However, due to its habit of aggregating in the navel of navel oranges, bean thrips remains economically important because some countries importing oranges from California have designated it a quarantine pest. Despite continued propagule pressure, bean thrips has never established outside North America. We examined genetic variation in mitochondrial DNA among Californian populations of C. fasciatus and found that potentially two cryptic species are present (supported by Kimura 2-P distances): a common widespread form B and a rarer form A with a very limited distribution. Form B showed strong phylogeographic structure, with many haplotypes having a limited geographic distribution. Inter-population crossing experiments between three geographically isolated populations of form B resulted in the production of some female offspring, indicating a degree of compatibility between these populations of this haplodiploid species. However, substantial outbreeding depression was also detected. A low frequency of offspring production by hetero-population pairs was evidence of pre-mating isolation, while post-mating isolation was also evident in the elevated mortality of fertilized eggs in successful hetero-population crosses. One surprising finding was the total lack of offspring production by virgin females when isolated individually. However, virgin females did produce sons in the presence of other virgin females. A test for the presence of Wolbachia showed that form B was not infected, but that some populations of the rarer form A were.

Variation in genetics and performance of Dutch western flower thrips populations

Invasion of pests may result in local adaptation and the development of biotypes specialized in different hosts. In this study, we investigated western flower thrips, Frankliniella occidentalis (Pergande), an invasive pest in Europe. Thrips from different commercial glasshouse crops within the Dutch Westland and a lab culture kept on chrysanthemum were compared. Genetic barcoding was applied for the identification of potential western flower thrips cryptic species in the Netherlands revealing that all western flower thrips populations studied belonged to the "glasshouse" strain reported in California as the only existing species in the Netherlands. Feeding and reproduction parameters in leaf disc and whole plant bioassays were scored. We detected significant differences in thrips feeding among host plants and thrips origin. Host plants differed in average thrips damage while thrips from different origins caused similar amounts of damage across host plants. In contrast, reproductive success of thrips on all plant species depended strongly on thrips origin. The thrips lab culture maintained on chrysanthemum obtained the highest levels of reproduction on chrysanthemum. Differences among the other thrips populations were relatively small. Amplified fragment length polymorphisms analyses were used to study genetic differences between western flower thrips populations and confirmed that the lab culture population was also genetically the most different of all studied populations. The results of the amplified fragment length polymorphisms analyses together with the better reproductive performance of thrips on the host plant on which they were maintained demonstrate the evolution of a lab biotype specialized in a particular host. This finding has potential relevance for future crop control and breeding programs.

Invasion genetics of the Western flower thrips in China: evidence for genetic bottleneck, hybridization and bridgehead effect

The western flower thrips, Frankliniella occidentalis (Pergande), is an invasive species and the most economically important pest within the insect order Thysanoptera. F. occidentalis, which is endemic to North America, was initially detected in Kunming in southwestern China in 2000 and since then it has rapidly invaded several other localities in China where it has greatly damaged greenhouse vegetables and ornamental crops. Controlling this invasive pest in China requires an understanding of its genetic makeup and migration patterns. Using the mitochondrial COI gene and 10 microsatellites, eight of which were newly isolated and are highly polymorphic, we investigated the genetic structure and the routes of range expansion of 14 F. occidentalis populations in China. Both the mitochondrial and microsatellite data revealed that the genetic diversity of F. occidentalis of the Chinese populations is lower than that in its native range. Two previously reported cryptic species (or ecotypes) were found in the study. The divergence in the mitochondrial COI of two Chinese cryptic species (or ecotypes) was about 3.3% but they cannot be distinguished by nuclear markers. Hybridization might produce such substantial mitochondrial-nuclear discordance. Furthermore, we found low genetic differentiation (global F(ST) = 0.043, P<0.001) among all the populations and strong evidence for gene flow, especially from the three southwestern populations (Baoshan, Dali and Kunming) to the other Chinese populations. The directional gene flow was further supported by the higher genetic diversity of these three southwestern populations. Thus, quarantine and management of F. occidentalis should focus on preventing it from spreading from the putative source populations to other parts of China.

Genetic structure of Graphocephala atropunctata (Hemiptera: Cicadellidae) populations across its natural range in California reveals isolation by distance

The genetic structure of 23 populations of Graphocephala atropunctata (Signoret) (Hemiptera: Cicadellidae: Cicadellinae), a vector of the plant pathogenic bacterium Xylellafastidiosa Wells et al., was investigated using ribosomal 28S and mitochondrial cytochrome C oxidase I gene sequences. The 28S sequences were identical across all G. atropunctata specimens and populations, but 16 mitochondrial haplotypes were detected and significant interpopulation differences were found in the distribution of these haplotypes. Pairwise estimates of Fst correlated positively with geographical distance between populations, a phenomenon known as genetic isolation by distance. Thus, despite potential for widespread movement of G. atropunctata through nursery and agricultural industries, isolated populations of G. atropunctata have remained genetically distinct, suggesting that negligible numbers of G. atropunctata are actually transported or population interbreeding rarely occurs. The phylogenetic relationship between G. atropunctata and two additional congeners, Graphocephala cythura Baker and Graphocephala flavovittata Metcalf, which have overlapping distributions with G. atropunctata, also was investigated. Although 28S sequences of G. flavovittata were strikingly similar to those of G. atropunctata, mitochondrial DNA (mtDNA) suggests that both species are genetically distinct from G. atropunctata.