Rapid and specific detection of Pentastiridius leporinus by recombinase polymerase amplification assay

Pentastiridius leporinus (Hemiptera: Cixiidae) is the main vector of an emerging and fast spreading sugar beet disease, the syndrome 'basses richesses' (SBR), in different European countries. The disease is caused by the γ-3-proteobacterium 'Candidatus Arsenophonus phytopathogenicus' and the phytoplasma 'Candidatus Phytoplasma solani' which are exclusively transmitted by planthoppers and can lead to a significant loss of sugar content and yield. Monitoring of this insect vector is important for disease management. However, the morphological identification is time consuming and challenging as two additional cixiid species Reptalus quinquecostatus and Hyalesthes obsoletus with a very close morphology have been reported in sugar beet fields. Further, identification of females and nymphs of P. leporinus at species level based on taxonomic key is not possible. In this study, an isothermal nucleic acid amplification based on recombinase polymerase amplification (RPA) was developed to specifically detect P. leporinus. In addition, real-time RPA was developed to detect both adults (male and female) and nymph stages using pure or crude nucleic acid extracts. The sensitivity of the real-time RPA for detection of P. leporinus was comparable to real-time PCR, but a shorter time (< 7 min) was required. This is a first report for real-time RPA application for P. leporinus detection using crude nucleic acid templates which can be applied for fast and specific detection of this vector in the field.

Musashi orchestrates melanism in Laodelphax striatellus

In insects, melanism, a fundamental pigmentation process, is of significant importance in evolutionary biology due to its complex genetic foundation. We investigated the role of the RNA-binding gene Musashi (msi) in melanism in Laodelphax striatellus, a Hemiptera species. We identified a single L. striatellus msi homolog, Lsmsi, encoding a 357 amino acid protein with 2 RNA recognition motifs. RNA interference-mediated knockdown of LsMsi resulted in complete body melanism and increased cuticular permeability. Additionally, we found the involvement of G protein-coupled receptor A42 and tyrosine hydroxylase (Th) in L. striatellus melanism. Knockdown of LsTh lightened the epidermis, showing dehydration signs, while LsA42 knockdown enhanced LsTh expression, leading to melanism. Surprisingly, Lsmsi knockdown decreased both LsA42 and LsTh expression, which was expected to cause whitening but resulted in melanism. Further, we found that Lsmsi influenced downstream genes like phenoloxidase homolog LsPo and dopa decarboxylase (Ddc) homolog LsDdc in the tyrosine-mediated melanism pathway. Extending to Nilaparvata lugens and Sogatella furcifera, we demonstrated the conserved role of msi in melanism among Delphacidae. Given MSI proteins' roles in cancer and tumors in vertebrates, our study is the first to link msi in insects to Delphacidae body color melanization via the tyrosine-mediated pathway, offering fresh perspectives on the genetic basis of insect melanism and msi functions.

New Cretaceous Fossil Achilidae Taxa (Insecta, Hemiptera, Fulgoromorpha) from Burmese Ambers with Description of Niryasaburniini Trib. Nov

A new species Niryasaburnia nigrutomia sp. nov. of the planthopper family Achilidae from Burmese amber collected from Hukawng Valley (Tanai) of northern Myanmar, is described, notably based on forewing pattern coloration and metatibiotarsal teeth conformation. A new fossil genus with its type species Sinuovenaxius kachinensis gen. et sp. nov. is also described. The tribe Niryasaburniini trib. nov. is established to include Niryasaburnia Szwedo, 2004, and Sinuovenaxius gen. nov., based on a unique combination of characters, of which the following states are particularly notable: head with compound eyes around half the length of pronotum, late forking of ScP+R and CuA after the fusion of Pcu+A1 on the forewing, apical teeth of metatarsomeres I and II both with subapical platellar sensilla, and a unique hindwing pattern with simple RP and biforked MP, CuA with two terminals only, and with A2 simple, reaching the posterior wing margin. The hindwing venation of this new tribe with RP with only one terminal and both MP and CuA with two terminals is unique in Achilidae.

A plant virus manipulates the long-winged morph of insect vectors

Wing dimorphism of insect vectors is a determining factor for viral long-distance dispersal and large-area epidemics. Although plant viruses affect the wing plasticity of insect vectors, the potential underlying molecular mechanisms have seldom been investigated. Here, we found that a planthopper-vectored rice virus, rice stripe virus (RSV), specifically induces a long-winged morph in male insects. The analysis of field populations demonstrated that the long-winged ratios of male insects are closely associated with RSV infection regardless of viral titers. A planthopper-specific and testis-highly expressed gene, Encounter, was fortuitously found to play a key role in the RSV-induced long-winged morph. Encounter resembles malate dehydrogenase in the sequence, but it does not have corresponding enzymatic activity. Encounter is upregulated to affect male wing dimorphism at early larval stages. Encounter is closely connected with the insulin/insulin-like growth factor signaling pathway as a downstream factor of Akt, of which the transcriptional level is activated in response to RSV infection, resulting in the elevated expression of Encounter. In addition, an RSV-derived small interfering RNA directly targets Encounter to enhance its expression. Our study reveals an unreported mechanism underlying the direct regulation by a plant virus of wing dimorphism in its insect vectors, providing the potential way for interrupting viral dispersal.

New morphological and biological contributions to adults and immature forms of Pissonotusparaguayensis (Fulgoromorpha, Delphacidae) in wetlands of Argentina

In the search for insects as biological control agents for the water primrose, the delphacid Pissonotusparaguayensis (Delphacidae) was found on Ludwigiagrandiflorasubsp.hexapetala (Onagraceae) in a wetland of Central East Argentina. The morphology of the unknown females (brachypterous and macropterous) and immature stages are described and illustrated. Adults and nymphs were collected in wetlands of Del Plata River Basin, from Buenos Aires to the northeastern part of Argentina. A rearing methodology was developed to perform biological studies. Both winged forms and structural features of the female genitalia are described for the first time at the genus level. Eggs and immature stages are described and keyed; fifth nymphal instars may be easily recognised by the yellowish colouration, blackish on dorsal of head, thorax and abdomen with conspicuous yellowish pits, ventrally only darkened on base of frons extended to lower level of eyes and dorsal surface of antennomeres I and II, and legs with distinctive black marks at femoro-tibial joint and apex. The geographical distribution is updated, expanding its range into Argentina, making Buenos Aires the southernmost limit of the genus in America. Biological information of the species is also reported here: life cycle, fecundity, oviposition behaviour, and host plant. Field observations showed that P.paraguayensis breeds, feeds, and causes damage to L.g.subsp.hexapetala. This delphacid presents a certain degree of specificity to the Ludwigia species in the Jussiaea section in host specificity tests. More studies are required to test this species as a potential biological control agent.

Revision of the Neotropical genus Trigava O'Brien, 1999 (Hemiptera, Fulgoromorpha, Dictyopharidae, Nersiini), with descriptions of two new species from Peru and Brazil

The Neotropical planthopper genus Trigava O'Brien, 1999 (Hemiptera, Fulgoromorpha, Dictyopharidae, Nersiini) is revised. Four species are included: T.brachycephala (Melichar, 1912) (the type species, from Peru), T.obrieni Song, Malenovský & Deckert, sp. nov. (from Brazil), T.peruensis Song, O'Brien & Bartlett, sp. nov. (from Peru), and T.recurva (Melichar, 1912) (from Bolivia and Peru). Lectotypes are designated for Igavabrachycephala Melichar, 1912 and Igavarecurva Melichar, 1912. All species are described, including habitus photographs and detailed illustrations of the male genitalia. Male and female genitalia are described for this genus for the first time. A key for identification of the species of Trigava and a distribution map are provided.

Accumulation of Fungal Pathogens Infecting the Invasive Spotted Lanternfly, Lycorma delicatula

In the eastern United States, populations of the invasive spotted lanternfly, Lycorma delicatula, are abundant and spreading. Four species of naturally occurring entomopathogenic fungi have previously been reported as infecting these planthoppers, with two of these causing epizootics. Nymphal- and adult-stage lanternflies in Pennsylvania and New York were surveyed for entomopathogenic fungal infections from October 2021 to November 2023, and assays were conducted to confirm the pathogenicity of species that were potentially pathogenic. Beauveria bassiana was the most abundant pathogen, but we report an additional 15 previously unreported species of entomopathogenic fungi infecting spotted lanternflies, all in the order Hypocreales (Ascomycota). The next most common pathogens were Fusarium fujikuroi and Sarocladium strictum. While infection prevalence by species was often low, probably impacted to some extent by the summer drought in 2022, together these pathogens caused a total of 6.7% mortality. A significant trend was evident over time within a season, with low levels of infection among nymphs and higher infection levels in mid- and late-stage adults, the stages when mating and oviposition occur.

FoxO is required for optimal fitness of the migratory brown planthopper, Nilaparvata lugens (Hemiptera: Delphacidae)

The forkhead box O (FoxO) protein is the main transcriptional effector downstream of the insulin/insulin-like signaling pathway and regulates many developmental and physiological processes. Holometabolous insects with loss-of-function mutations in FoxO exhibit phenotypes distinct from those of hemimetabolous insects in which RNA interference was used. Despite the functional importance of FoxO, whether hemimetabolous insects share an evolutionally conserved function of FoxO with holometabolous insects remains to be clarified. We used the clustered regularly interspaced short palindromic repeats/CRISPR-associated 9 (CRISPR/Cas9) genome editing-system to establish a homozygous FoxO-null mutant (NlFoxO4E ) of the wing-dimorphic brown planthopper (BPH) Nilaparvata lugens, an economically important insect pest of rice fields. The phenotypes of NlFoxO4E mutants included extended nymphal duration, shortened lifespan, reduced reproduction, and decreased stress resistance. In addition, depletion of NlFoxO promoted cell proliferation in wing buds and led to 100% long-winged morphs, in stark contrast to short-winged wild-type BPHs. These findings indicate that NlFoxO is highly functionally conserved with its counterpart in holometabolous insects, and is required for optimal fitness of N. lugens. The insights from FoxO studies may facilitate the identification of potential target genes for BPH control applications.

A new species of the genus Dentatissus Chen, Zhang & Chang (Hemiptera, Fulgoroidea, Issidae) from the Korean Peninsula, with a key to the genus

A new species of the family Issidae (Hemiptera, Auchenorrhyncha, Fulgoroidea), Dentatissuslongispinosussp. nov., is described from the Korean Peninsula. Morphological information is presented with photographs based on male and female specimens. A key to species of the genus Dentatissus is also provided.

Rescue of the first alphanucleorhabdovirus entirely from cloned complementary DNA: An efficient vector for systemic expression of foreign genes in maize and insect vectors

Recent reverse genetics technologies have enabled genetic manipulation of plant negative-strand RNA virus (NSR) genomes. Here, we report construction of an infectious clone for the maize-infecting Alphanucleorhabdovirus maydis, the first efficient NSR vector for maize. The full-length infectious clone was established using agrobacterium-mediated delivery of full-length maize mosaic virus (MMV) antigenomic RNA and the viral core proteins (nucleoprotein N, phosphoprotein P, and RNA-directed RNA polymerase L) required for viral transcription and replication into Nicotiana benthamiana. Insertion of intron 2 ST-LS1 into the viral L gene increased stability of the infectious clone in Escherichia coli and Agrobacterium tumefaciens. To monitor virus infection in vivo, a green fluorescent protein (GFP) gene was inserted in between the N and P gene junctions to generate recombinant MMV-GFP. Complementary DNA (cDNA) clones of MMV-wild type (WT) and MMV-GFP replicated in single cells of agroinfiltrated N. benthamiana. Uniform systemic infection and high GFP expression were observed in maize inoculated with extracts of the infiltrated N. benthamiana leaves. Insect vectors supported virus infection when inoculated via feeding on infected maize or microinjection. Both MMV-WT and MMV-GFP were efficiently transmitted to maize by planthopper vectors. The GFP reporter gene was stable in the virus genome and expression remained high over three cycles of transmission in plants and insects. The MMV infectious clone will be a versatile tool for expression of proteins of interest in maize and cross-kingdom studies of virus replication in plant and insect hosts.

Genome comparison reveals inversions and alternative evolutionary history of nutritional endosymbionts in planthoppers (Hemiptera: Fulgoromorpha)

The evolutionary success of sap-feeding hemipteran insects in the suborder Auchenorrhyncha was enabled by nutritional contributions from their heritable endosymbiotic bacteria. However, the symbiont diversity, functions, and evolutionary origins in this large insect group have not been broadly characterized using genomic tools. In particular, the origins and relationships among ancient betaproteobacterial symbionts Vidania (in Fulgoromorpha) and Nasuia/Zinderia (in Cicadomorpha) are uncertain. Here, we characterized the genomes of Vidania and Sulcia from three Pyrops planthoppers (family Fulgoridae) to understand their metabolic functions and evolutionary histories. We find that, like in previously characterized planthoppers, these symbionts share nutritional responsibilities, with Vidania providing seven out of ten essential amino acids. Sulcia lineages across the Auchenorrhyncha have a highly conserved genome but with multiple independent rearrangements occurring in an early ancestor of Cicadomorpha or Fulgoromorpha and in a few succeeding lineages. Genomic synteny was also observed within each of the betaproteobacterial symbiont genera Nasuia, Zinderia, and Vidania, but not across them, which challenges the expectation of a shared ancestry for these symbionts. The further comparison of other biological traits strongly suggests an independent origin of Vidania early in the planthopper evolution and possibly of Nasuia and Zinderia in their respective host lineages. This hypothesis further links the potential acquisition of novel nutritional endosymbiont lineages with the emergence of auchenorrhynchan superfamilies.

Cryptic diversity and virulence of Beauveria bassiana recovered from Lycorma delicatula (spotted lanternfly) in eastern Pennsylvania

The entomopathogenic fungus Beauveria bassiana is cosmopolitan and known to infect a variety of sap-sucking pests like aphids, mealybugs, and scales in the order of Hemiptera. In Fall 2017, spotted lanternfly (SLF) adults killed by the fungal entomopathogen B. bassiana were found in Berks County, Pennsylvania. In 2018-2020 we collected SLF and nearby non-target insects killed by Beauveria spp. from 18 field sites in southeastern Pennsylvania. We identified 159 Beauveria isolates from SLF and six isolates from non-targets. Five isolates of B. bassiana and one isolate of B. brongniartii were identified from the non-targets. Based on sequence data from the nuclear B locus (Bloc) intergenic region, all the isolates from SLF were identified as B. bassiana, but there were 20 different strains within this species, grouped into two clades. Three B. bassiana strains (A, B, and L) were found in most field sites and were the most prevalent. Representative isolates for these three strains were used in laboratory bioassays and were compared to a commercial B. bassiana strain (GHA). Strain B was inferior to A, L, and GHA against nymphs; strains A and L had greater efficacy than B and GHA against adults. We also quantified conidial production on SLF cadavers. This paper discusses the diversity of these B. bassiana strains in SLF populations and implications for biological control of this abundant invasive.

Development of Molecular-Based Species Identification and Optimization of Reaction Conditions for Molecular Diagnosis of Three Major Asian Planthoppers (Hemiptera: Delphacidae)

Asian planthoppers (Hemiptera: Delphacidae) that include brown planthoppers (BPH, Nilaparvata lugens, Stål), white-backed planthoppers (WBPH, Sogatella furcifera, Horváth), and small brown planthoppers (SBPH, Laodelphax striatellus, Fallén) are the primary sucking-type pests of rice. These three insects share morphological and sequence similarities. As insecticide resistance patterns and control strategies vary according to species, the accurate discrimination of these species is important. Here, we developed six species-specific primers based on partial mitochondrial genome sequences. The primers were successfully used in multiplex PCR, loop-mediated isothermal amplification (LAMP) assays, and conventional PCR. Here, we used genomic DNA obtained using the DNA-releasing technique (tissue samples were incubated at 95 °C for 5 min with 30 μL nuclease-free water, and the supernatant was used). We showed that multiplex PCR could analyze the density of each species following a mass collection in the field; the LAMP assay can diagnose the species within 40 min; conventional PCR can be widely applied to a large number of field samples, as well as individuals or mass collections. In conclusion, these results demonstrate the potential of the species-specific primers and DNA-releasing technique for accurate multiplex PCR and LAMP assays, which may assist the intensive field monitoring of integrated management of these species.

Biology and Management of the Spotted Lanternfly, Lycorma delicatula (Hemiptera: Fulgoridae), in the United States

Spotted lanternfly, Lycorma delicatula (White), invaded the eastern United States in 2014 and has since caused economic and ecological disruption. In particular, spotted lanternfly has shown itself to be a significant pest of vineyards and ornamental plants and is likely to continue to spread to new areas. Factors that have contributed to its success as an invader include its wide host range and high mobility, which allow it to infest a wide range of habitats, including agricultural, urban, suburban, and managed and natural forested areas. Management is dependent on chemical use, although no single currently available control measure alone will be sufficient.

Versatile Roles of Microbes and Small RNAs in Rice and Planthopper Interactions

Planthopper infestation in rice causes direct and indirect damage through feeding and viral transmission. Host microbes and small RNAs (sRNAs) play essential roles in regulating biological processes, such as metabolism, development, immunity, and stress responses in eukaryotic organisms, including plants and insects. Recently, advanced metagenomic approaches have facilitated investigations on microbial diversity and its function in insects and plants, highlighting the significance of microbiota in sustaining host life and regulating their interactions with the environment. Recent research has also suggested significant roles for sRNA-regulated genes during rice-planthopper interactions. The response and behavior of the rice plant to planthopper feeding are determined by changes in the host transcriptome, which might be regulated by sRNAs. In addition, the roles of microbial symbionts and sRNAs in the host response to viral infection are complex and involve defense-related changes in the host transcriptomic profile. This review reviews the structure and potential functions of microbes and sRNAs in rice and the associated planthopper species. In addition, the involvement of the microbiota and sRNAs in the rice-planthopper-virus interactions during planthopper infestation and viral infection are discussed.

Batkoa major infecting the invasive planthopper Lycorma delicatula

The entomopathogenic fungi Batkoa major and Beauveria bassiana caused co-epizootics in populations of invasive spotted lanternflies, Lycorma delicatula, in 2018 in northeastern North America. Although first described from North America in 1888, the biology and ecology of Batkoa major had not been studied since that time. This entomophthoralean fungus found infecting L. delicatula in 2018 produces conidia and rhizoids similar in appearance to the original description. We conducted laboratory bioassays to investigate infection of different ages and sexes of these planthoppers, inoculating via showered conidia. All nymphs, and male and female adults were susceptible to infection. Adult males died more quickly than adult females or fourth instars. Batkoa major grew out of cadavers of adult males more frequently than adult females or fourth instar nymphs. Rhizoids that provide attachment of cadavers to substrates were produced from adult cadavers more frequently than conidia. Resting spores were not observed in vivo or in vitro in the lab, or in the field.

Abdominal-B contributes to abdominal identity in the brown planthopper, Nilaparvata lugens (Hemiptera: Delphacidae)

The homeotic complex gene Abdominal-B (Abd-B) is involved in regulating the development of posterior abdomens and has been extensively studied in holometabolous insects. However, the function of Abd-B in hemimetabolous insects is not fully understood. Here, we functionally characterize an Abd-B homologue in the brown planthopper (BPH), Nilaparvata lugens. The full-length cDNA of the N. lugens Abd-B homologue (NlAbd-B) is 2334 nt, with an open reading frame of 1113 bp. NlAbd-B has the highest expression level at the egg stage relative to the nymphal and adult stages and is mainly expressed in the fourth to the ninth abdominal segment of embryos. RNA interference (RNAi)-mediated knockdown of NlAbd-B in nymphs disrupted the development of genitalia both in females and males and caused a genitalia-to-leg transformation. Parental RNAi of NlAbd-B in both female and male adults caused an extra abdominal segment in offspring nymphs, while parental RNAi of the N. lugens abdominal-A homologue in both female and males adults led to embryos with leg-like appendages on the second to the eighth abdominal segment. These findings suggest that NlAbd-B plays a pivotal role in genital development and posterior abdominal patterning and thus highlight the conservational role of Abd-B in holometabolous and hemimetabolous insects.

Silencing of Decapentaplegic (Dpp) gene inhibited the wing expansion in the white-backed planthopper, Sogatella furcifera (Horváth) (Hemiptera: Delphacidae)

The Decapentaplegic gene controls wing patterning and spreading by regulating downstream genes in many insect species. However, the molecular characteristics, expression, and biological function of Dpp in Sogatella furcifera remain poorly understood. In this study, we cloned the Dpp gene from S. furcifera and examined its expression levels in different development stages, wing typed adults, and tissues. Then, the function of SfDpp gene was analyzed using an RNA interference (RNAi)-based approach. The results showed that the full-length complementary DNA  of the SfDpp gene consists of 1034 bp and contains a 954-bp open reading frame encoding 317 amino acids. SfDpp has a transforming growth factor-β (TGF-β) propeptide superfamily domain and a TGF-β superfamily domain, typical of members of the TGF-β superfamily. Quantitative real-time polymerase chain reaction showed that the expression of SfDpp reached its highest expression level 40 min after eclosion. RNAi-based gene silencing inhibited transcript levels of the corresponding messenger RNA in S. furcifera nymphs injected with double-stranded RNA of SfDpp and resulted in death of 29.17% and 26.67% of 4th and 5th instar nymphs, respectively. The wing deformity rate of the adults was 74.12% and 3.41% after SfDpp gene silencing in 4th and 5th instar nymphs, respectively. Examining wing development-associated genes showed that two target genes of Dpp (Vestigial and Spalt) were both dramatically downregulated after SfDpp was silenced. Our results demonstrate that downregulated SfDpp in early development causes wing expansion failure in S. furcifera. Thus, Dpp may be a target gene for restricting the migration of rice-damaging planthoppers.

Planthopper-Secreted Salivary Calmodulin Acts as an Effector for Defense Responses in Rice

The brown planthopper (Nilaparvata lugens, BPH) and small brown planthopper (Laodelphax striatellus, SBPH) are major pests of rice (Oryza sativa) in Asia. These piercing-sucking insects secrete saliva into the host during feeding. Nevertheless, it is largely unknown how planthoppers use salivary effectors to enable continuous feeding on rice. Here, we screened their salivary proteomes and selected eight salivary proteins conserved between SBPH and BPH as candidate effectors. Silencing calmodulin (CaM) impeded BPH and SBPH from penetrating the phloem. Hence, their food intake, survival, and fecundity on rice plants were reduced. By contrast, CaM silencing had a small effect on the survival rate of BPH and SBPH raised on artificial diet. The CaM amino acid sequences were the same for both BPH and SBPH. CaM was highly expressed in their salivary glands and secreted into the rice plants during feeding. Bacterially expressed recombinant CaM protein exhibited calcium-binding activity. In planta expression disclosed that CaM was localized to the plant cytoplasms and nuclei and suppressed plant defenses such as hydrogen peroxide (H₂O₂) accumulation and callose deposition. CaM-silenced BPH and SBPH nymphs elicited relatively high levels of H₂O₂ and callose accumulation in rice plants. The foregoing results reveal that CaM is an effector as it enables the planthopper to reach the phloem by suppressing callose deposition and H₂O₂ accumulation in rice.

Vitellogenin from planthopper oral secretion acts as a novel effector to impair plant defenses

Vitellogenin (Vg) is a well-known nutritious protein involved in reproduction in nearly all oviparous animals, including insects. Recently, Vg has been detected in saliva proteomes of several piercing-sucking herbivorous arthropods, including the small brown planthopper (Laodelphax striatellus, SBPH). Its function, however, remains unexplored. We investigated the molecular mechanism underlying SBPH orally secreted Vg-mediated manipulation of plant-insect interaction by RNA interference, phytohormone and H₂ O₂ profiling, protein-protein interaction studies and herbivore bioassays. A C-terminal polypeptide of Vg (VgC) in SBPH, when secreted into rice plants, acted as a novel effector to attenuate host rice defenses, which in turn improved insect feeding performance. Silencing Vg reduced insect feeding and survival on rice. Vg-silenced SBPH nymphs consistently elicited higher H₂ O₂ production, a well-established defense mechanism in rice, whereas expression of VgC in planta significantly hindered hydrogen peroxide (H₂ O₂ ) accumulation and promoted insect performance. VgC interacted directly with the rice transcription factor OsWRKY71, a protein which is involved in induction of H₂ O₂ accumulation and plant resistance to SBPH. These findings indicate a novel effector function of Vg: when secreted into host rice plants, this protein effectively weakened H₂ O₂ -mediated plant defense through its association with a plant immunity regulator.

New mimarachnids (Hemiptera, Fulgoromorpha, Fulgoroidea) in mid-Cretaceous Burmese amber

A new genus and species, Multistriaorthotropagen. et sp. nov., and a new species, Dachibangushuisp. nov., of Mimarachnidae are described from the mid-Cretaceous Burmese amber. These new taxa display unique wing color patterns and extend the Mesozoic diversity of Mimarachnidae. The evolution of wing venation, phylogenetic placement of Mimarachnidae, and anti-predation defenses of this family in Burmese amber forest are briefly discussed.

A genome-wide identification and analysis of the homeobox genes in the brown planthopper, Nilaparvata lugens (Hemiptera: Delphacidae)

The homeobox family is a large and diverse superclass of genes, many of which act as transcription factors that play important roles in tissue differentiation and embryogenesis in animals. The brown planthopper (BPH), Nilaparvata lugens, is the most destructive pest of rice in Asia, and high fecundity contributes significantly to its ecological success in natural and agricultural habits. Here, we identified 94 homeobox genes in BPH, which could be divided into 75 gene families and 9 classes. This number is comparable to the number of homeobox genes found in the honeybee Apis mellifera, but is slightly less than in Drosophila or the red flour beetle Tribolium castaneum. A spatio-temporal analysis indicated that most BPH homeobox genes were expressed in a development and tissue-specific manner, of which 21 genes were highly expressed in ovaries. RNA interference (RNAi)-mediated functional assay showed that 22 homeobox genes were important for nymph development and the nymph to adult transition, whereas 67 genes were dispensable during this process. Fecundity assay showed that knockdown of 13 ovary-biased genes (zfh1, schlank, abd-A, Lim3_2, Lmxb, Prop, ap_1, Not, lab, Hmx, vis, Pknox, and C15) led to the reproductive defect. This is the first comprehensive investigation into homeobox genes in a hemipteran insect and thus helps us to understand the functional significance of homeobox genes in insect reproduction.

Regulation of RNA Interference Pathways in the Insect Vector Laodelphax striatellus by Viral Proteins of Rice Stripe Virus

RNA interference (RNAi), especially the small interfering RNA (siRNA) and microRNA (miRNA) pathways, plays an important role in defending against viruses in plants and insects. However, how insect-transmitted phytoviruses regulate the RNAi-mediated antiviral response in vector insects has barely been uncovered. In this study, we explored the interaction between rice stripe virus (RSV) and the miRNA and siRNA pathways of the small brown planthopper, which is a vector insect. The transcript and protein levels of key genes in the two RNAi pathways did not change during the RSV infection process. When the expression of insect Ago1, Ago2, or Translin was silenced by the injection of double-stranded RNAs targeting these genes, viral replication was promoted with Ago2 silencing but inhibited with Translin silencing. Protein-protein binding assays showed that viral NS2 and RNA-dependent RNA polymerase interacted with insect Ago2 and Translin, respectively. When NS2 was knocked down, the transcript level of Ago2 increased and viral replication was inhibited. Therefore, viral NS2 behaved like an siRNA suppressor in vector insects. This protein-binding regulation of insect RNAi systems reflects a complicated and diverse coevolution of viruses with their vector insects.

Two new species of the genus Saigona Matsumura (Hemiptera, Fulgoromorpha, Dictyopharidae) from China

Two new species of the genus Saigona Matsumura, 1910, S.baiseensis Zheng & Chen sp. nov. and S.maculata Zheng & Chen sp. nov., from China (Guanxi) are described and illustrated. A revised identification key to the 16 species of Saigona is provided. 15 species of the genus are known from China only.

Characterization of protein-protein interactions between rice viruses and vector insects

Planthoppers are the most notorious rice pests, because they transmit various rice viruses in a persistent-propagative manner. Protein-protein interactions (PPIs) between virus and vector are crucial for virus transmission by vector insects. However, the number of known PPIs for pairs of rice viruses and planthoppers is restricted by low throughput research methods. In this study, we applied DeNovo, a virus-host sequence-based PPI predictor, to predict potential PPIs at a genome-wide scale between three planthoppers and five rice viruses. PPIs were identified at two different confidence thresholds, referred to as low and high modes. The number of PPIs for the five planthopper-virus pairs ranged from 506 to 1985 in the low mode and from 1254 to 4286 in the high mode. After eliminating the "one-too-many" redundant interacting information, the PPIs with unique planthopper proteins were reduced to 343-724 in the low mode and 758-1671 in the high mode. Homologous analysis showed that 11 sets and 31 sets of homologous planthopper proteins were shared by all planthopper-virus interactions in the two modes, indicating that they are potential conserved vector factors essential for transmission of rice viruses. Ten PPIs between small brown planthopper and rice stripe virus (RSV) were verified using glutathione-S-transferase (GST)/His-pull down or co-immunoprecipitation assay. Five of the ten PPIs were proven positive, and three of the five SBPH proteins were confirmed to interact with RSV. The predicted PPIs provide new clues for further studies of the complicated relationship between rice viruses and their vector insects.

Two new bamboo-feeding species of the genus Kirbyana Distant, 1906 from China (Hemiptera, Fulgoromorpha, Cixiidae)

Two new bamboo-feeding species of the cixiid planthopper genus Kirbyana Distant, 1906 (Hemiptera: Fulgoromorpha: Cixiidae: Eucarpiini), K.aspina Zhi & Chen, sp. nov. and K.furcata Zhi & Chen, sp. nov., are described and illustrated from southern China. A key to all known species and a map of their geographic distributions are provided.

Transcriptome Analysis of the Regulatory Mechanism of FoxO on Wing Dimorphism in the Brown Planthopper, Nilaparvata lugens (Hemiptera: Delphacidae)

Simple Summary

The brown planthopper (BPH) Nilaparvata lugens can develop into either long-winged or short-winged adults depending on environmental stimuli received during larval stages. The transcription factor NlFoxO serves as a key regulator determining alternative wing morphs in BPH, but the underlying molecular mechanism is largely unknown. Here, we investigated the transcriptomic profile of forewing and hindwing buds across the 5th-instar stage, the wing-morph decision stage. Our results indicated that NlFoxO modulated the developmental plasticity of wing buds mainly by regulating the expression of cell proliferation-associated genes.

Abstract

The brown planthopper (BPH), Nilaparvata lugens, can develop into either short-winged (SW) or long-winged (LW) adults according to environmental conditions, and has long served as a model organism for exploring the mechanisms of wing polyphenism in insects. The transcription factor NlFoxO acts as a master regulator that directs the development of either SW or LW morphs, but the underlying molecular mechanism is largely unknown. Here, we microinjected SW-destined morphs with double stranded-RNA (dsRNA) targeting NlFoxO (dsNlFoxO) to change them into LW-winged morphs. In parallel, SW-destined morphs microinjected with dsRNA targeting the gene encoding green fluorescence protein (dsGfp) served as a negative control. The forewing and hindwing buds of 5th-instar nymphs collected at 24, 36, and 48 h after eclosion (hAE) were used for RNA sequencing. We obtained a minimum of 43.4 million clean reads from forewing and hindwing buds at a single developmental time. Differentially expressed genes (DEGs) were significantly enriched in various Gene Ontology (GO) terms, including cellular process, binding, and cell part. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment pathway analysis showed that up-regulated genes in dsNlFoxO-treated forewing and hindwing buds were largely associated with the cell cycle and DNA replication. Furthermore, most up-regulated genes displayed higher expression at 24-, and 36-hAE relative to 48 hAE, indicating that wing cells in LW-destined wings might actively proliferate during the first 36 h in 5th-instar nymphs. Our findings indicated that LW development in BPH was likely dependent on the duration of cell proliferation in the 5th-instar stage, which sheds light on the molecular basis of wing polymorphism in insects.

A new species of the genus Euxaldar Fennah, 1978 (Hemiptera, Fulgoromorpha, Issidae) from China and revision on the molecular phylogeny of the family

A new species Euxaldar daweishanensis Yang, Chang & Chen, sp. nov. is described and illustrated from southwestern China. The female genitalia of the genus Euxaldar is described and presented for the first time. A checklist and key to the known species of the genus are provided. A revised molecular phylogenetic analysis of the family Issidae based on combined partial sequences of 18S, 28S, COI, and Cytb is provided using both Maximum likelihood and Bayesian inference analyses.

Mind the gap: the delayed recovery of a population of the biological control agent Megamelus scutellaris Berg. (Hemiptera: Delphacidae) on water hyacinth after winter

Cold winter temperatures significantly affect the biological control effort against water hyacinth, Pontederia ( = Eichhornia) crassipes Mart. (Pontederiaceae), in more temperate regions around the world. The population dynamics of the planthopper Megamelus scutellaris Berg. (Hemiptera: Delphacidae), a newly released biological control agent of water hyacinth, were recorded on the Kubusi River in the Eastern Cape Province (South Africa) over 15 months to determine the population recovery post-winter. Megamelus scutellaris incurred a severe population decline at the onset of winter when the water hyacinth plants became frost damaged. The combined effect of a population bottleneck and low minimum winter temperatures (6.12°C) below the agent's lower developmental threshold (11.46°C) caused a post-winter lag in agent density increase. Subsequently, the maximum agent population density was only reached at the end of the following summer growing season which allowed the water hyacinth population to recover in the absence of any significant biological control immediately post-winter. Supplementary releases of agents from mass-reared cultures at the beginning of the growing season (spring) is suggested as a potential method of reducing the lag-period in field populations in colder areas where natural population recovery of agents is slower.

Structural Features and Phylogenetic Implications of Four New Mitogenomes of Caliscelidae (Hemiptera: Fulgoromorpha)

To explore the differences in mitogenome variation and phylogenetics among lineages of the Hemiptera superfamily Fulgoroidea, we sequenced four new mitogenomes of Caliscelidae: two species of the genus Bambusicaliscelis (Caliscelinae: Caliscelini), namely Bambusicaliscelis flavus and B. fanjingensis, and two species of the genus Youtuus (Ommatidiotinae: Augilini), namely Youtuus strigatus and Y. erythrus. The four mitogenomes were 15,922-16,640 bp (base pair) in length, with 37 mitochondrial genes and an AT-rich region. Gene content and arrangement were similar to those of most other sequenced hexapod mitogenomes. All protein-coding genes (PCGs) started with a canonical ATN or GTG and ended with TAA or an incomplete stop codon single T. Except for two transfer RNAs (tRNAs; trnS1 and trnV) lacking a dihydrouridine arm in the four species and trnC lacking a dihydrouridine stem in the Youtuus species, the remaining tRNAs could fold into canonical cloverleaf secondary structures. Phylogenetic analyses based on sequence data of 13 PCGs in the 28 Fulgoroidea species and two outgroups revealed that Delphacidae was monophyletic with strong support. Our data suggest that Fulgoridae is more ancient than Achilidae. Furthermore, Flatidae, Issidae, and Ricaniidae always cluster to form a sister group to Caliscelidae.

Skipping the Insect Vector: Plant Stolon Transmission of the Phytopathogen 'Ca. Phlomobacter fragariae' from the Arsenophonus Clade of Insect Endosymbionts

Simple Summary

Numerous plant sap-feeding insects are vectors of plant-pathogenic bacteria that cause devastating crop diseases. Some of these bacteria had initially been insect endosymbionts that eventually evolved the capacity to survive in plants after being frequently transmitted to plants by their insect hosts during feeding. An example for this evolutionary transition is the bacterial symbiont ‘Candidatus Phlomobacter fragariae’ (hereafter Phlomobacter) of the planthopper Cixius wagneri. Upon transmission to strawberry plants by its insect vector, the bacterium accumulates in the plant phloem and causes Strawberry Marginal Chlorosis disease. Using quantitative PCR and transmission electron microscopy, we demonstrate an additional plant-to-plant transmission route: Phlomobacter can be transmitted from an infected plant to daughter plants through stolons, a specific type of stem from which daughter plants can develop. Our results show that Phlomobacter was abundant in stolons and was efficiently transmitted to daughter plants, which developed disease symptoms. Hence, Phlomobacter is not only able to survive in plants, but can even be transmitted to new plant generations, independently from its ancestral insect host.

Abstract

The genus Arsenophonus represents one of the most widespread clades of insect endosymbionts, including reproductive manipulators and bacteriocyte-associated primary endosymbionts. Two strains belonging to the Arsenophonus clade have been identified as insect-vectored plant pathogens of strawberry and sugar beet. The bacteria accumulate in the phloem of infected plants, ultimately causing leaf yellows and necrosis. These symbionts therefore represent excellent model systems to investigate the evolutionary transition from a purely insect-associated endosymbiont towards an insect-vectored phytopathogen. Using quantitative PCR and transmission electron microscopy, we demonstrate that ‘Candidatus Phlomobacter fragariae’, bacterial symbiont of the planthopper Cixius wagneri and the causative agent of Strawberry Marginal Chlorosis disease, can be transmitted from an infected strawberry plant to multiple daughter plants through stolons. Stolons are horizontally growing stems enabling the nutrient provisioning of daughter plants during their early growth phase. Our results show that Phlomobacter was abundant in the phloem sieve elements of stolons and was efficiently transmitted to daughter plants, which rapidly developed disease symptoms. From an evolutionary perspective, Phlomobacter is, therefore, not only able to survive within the plant after transmission by the insect vector, but can even be transmitted to new plant generations, independently from its ancestral insect host.

The complete mitochondrial genome of Ricania shantungensis (Hemiptera: Ricaniidae) in Korea

In this study, we have sequenced and annotated the complete mitochondrial genome of Ricania shantungensis (Hemiptera: Ricaniidae) for the first time. The circular mitogenome of R. shantungensis was 15,789 bp, including 13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNAs, and a single control region of 1,363 bp. Its AT ratio was 74.6%. According to the phylogenetic tree, R. shantungensis was clustered with the genus Ricania.

Parahiraciini (Hemiptera, Fulgoromorpha, Issidae): one new genus, two new species and three new subtribes

A new genus Pusulissusgen. nov. with two new species P.phiaoacensissp. nov. and P.coronomensissp. nov. are described respectively from Vietnam and China in the tribe Parahiraciini of the family Issidae. A molecular phylogeny using combined genes (18S, 28S, COX1 and Cytb) confirms its placement in the tribe Parahiraciini. The tribe is divided into three subtribes: Scantiniinasubtribe nov. with the type genus Scantinius Stål, 1866, and Vindilisinasubtribe nov. with type genus Vindilis Stål, 1870 plus Nisoprincessa Gnezdilov, 2017, and the nominal subtribe Parahiraciina Cheng & Yang, 1991 subtribe nov. The characteristics of these subtribes are provided, with a key to identification. Genus Folifemurum Che, Zhang & Wang, 2013 is transferred to HemisphaeriiniMongolianina, and genus Gelastyrella Yang, 1994 is maintained as a valid name.

Transcriptome Analysis Reveals Functional Diversity in Salivary Glands of Plant Virus Vector, Graminella nigrifrons

Insect salivary glands play an important role for host feeding, specifically by secreting salivary proteins for digestion and potentially modulating host defenses. Compared to other hemipterans, the significance of salivary glands is less studied in the black-faced leafhopper, Graminella nigrifrons, a crop pest that vectors several agronomically important plant viruses. To identify functionally important genes in the salivary glands of the black-faced leafhopper, we compared transcriptomes between adult salivary glands (SG) and the remaining carcasses. We identified 14,297 salivary gland-enriched transcripts and 195 predicted secretory peptides (i.e., with a signal peptide and extracellular localization characteristics). Overall, the SG transcriptome included functions such as 'oxidoreduction', 'membrane transport', and 'ATP-binding', which might be important for the fundamental physiology of this tissue. We further evaluated transcripts with potential contributions in host feeding using RT-qPCR. Two SG-enriched transcripts (log2 fold change > 5), GnP19 and GnE63 (a putative calcium binding protein), were significantly upregulated in maize-fed adults relative to starved adults, validating their importance in feeding. The SG-enriched transcripts of the black-faced leafhopper could play a potential role for interacting with maize and could be targets of interest for further functional studies and improve pest control and disease transmission.

Two new species of the genus Indolipa Emeljanov (Hemiptera, Fulgoromorpha, Cixiidae) from Yunnan Province, China, with a key to species

Two new species of Indolipa Emeljanov, 2001 (Fulgoromorpha, Cixiidae) from Yunnan Province, China, I.fugongensis Zhi & Chen, sp. nov. and I.longlingensis Zhi & Chen, sp. nov. are described. Color images for the adults of the two new species and line drawings for the genitalia are provided. In addition, a key to all known species of Indolipa Emeljanov is included.

Applications of Beauveria bassiana (Hypocreales: Cordycipitaceae) to Control Populations of Spotted Lanternfly (Hemiptera: Fulgoridae), in Semi-Natural Landscapes and on Grapevines

Spotted lanternfly, Lycorma delicatula (White), is an invasive Asian insect that was initially found in Berks County, Pennsylvania, in 2014. As of early 2020, this pest had been found in five more eastern states and it is expected to continue to expand its geographical range. Lycorma delicatula is highly polyphagous but seems to prefer tree-of-heaven, Ailanthus altissima. However, grape growers in Pennsylvania have reported significant damage and loss of vines caused by L. delicatula adults. In fall 2018, two fungal entomopathogens (Beauveria bassiana and Batkoa major) drove localized collapses in L. delicatula populations in Berks County, Pennsylvania. In 2019, we tested applications of a commercialized mycoinsecticide based on B. bassiana strain GHA on L. delicatula populations in a public park in southeastern Pennsylvania. A single application of B. bassiana reduced fourth instar nymphs by 48% after 14 d. Applications of B. bassiana to L. delicatula adults in the same park resulted in 43% mortality after 14 d. Beauveria bassiana spores remained viable on foliage for 5-7 d after spraying. We also conducted semi-field bioassays with B. bassiana GHA (formulated as BoteGHA and Aprehend) and another mycoinsecticide containing Isaria fumosorosea Apopka Strain 97 against L. delicatula adults feeding on potted grapes. All the mycoinsecticides killed ≥90% of adults after 9 d using direct applications. Aprehend killed 99% of adults after 9 d with exposure to residues on sprayed grapes. These data show that fungal entomopathogens can help to suppress populations of L. delicatula in agroecosystems and natural areas.

Two new genera with species of the tribe Sarimini (Hemiptera, Fulgoromorpha, Issidae) from China

Tempsarima Chang & Chen, gen. nov. (Hemiptera: Issidae: Sarimini), with type species Tempsarima bipunctata Chang & Chen, sp. nov. and Tetrichina Chang & Chen, gen. nov. (Hemiptera: Issidae: Sarimini), with type species Tetrichina trihamulata Chang & Chen, sp. nov. are described and illustrated from Hainan Province of China. The female genitalia characters of Issidae are discussed.

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

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

Molecular characterization of insulin-like peptides in the brown planthopper, Nilaparvata lugens (Hemiptera: Delphacidae)

Insulin-like peptides (ILPs) including insulin, insulin-like growth factor (IGF) and relaxin are evolutionarily conserved hormones in metazoans, and they are involved in diverse physiological processes. The migratory brown planthopper (BPH), Nilaparvata lugens, encodes four ILP genes (Nlilp1, Nlilp2, Nlilp3 and Nlilp4) but their physiological roles are largely unknown. Sequence analysis showed that NlILP1 contained a relaxin-specific G protein-coupled receptor-binding motif and a variant motif of cysteine residues, and NlILP2 and NlILP4 resembled vertebrate IGFs. RNA interference (RNAi)-mediated gene silencing showed that depletion of each of Nlilp1, 2 and 3 significantly delayed the developmental duration of nymphs, and this effect could be exacerbated by double or triple gene depletion. Depletion of Nlilp1, Nlilp2 or Nlilp3 induces the accumulation of glucose, trehalose and glycogen, which is contradictory to depletion of the insulin receptor (NlInR1) in the BPH. Depletion of Nlilp1 significantly enhanced starvation resistance in both females and males although its extent was smaller than NlInR1 depletion. A parental RNAi assay showed that depletion of each of Nlilp1-4 dramatically impaired female fecundity. These findings indicate that NlILP1-4 have redundant and distinct roles in physiological processes in the BPH, thereby enhancing our understanding of the contribution of each NlILP to the ecological success of this species in natural habitats.

First records of the genera Sivaloka Distant, 1906, with two new species from China, and description of a new species of genus Kodaianella Fennah, 1956 (Hemiptera, Fulgoromorpha, Issidae)

The genus Sivaloka Distant, 1906 (Hemisphaeriinae, Kodaianellini) is recorded from China for the first time, with two new species Sivalokaarcuata Chang & Chen, sp. nov. (China: Guizhou) and Sivalokatrigona Chang & Chen, sp. nov. (China: Guangxi). One new species of Kodaianella Fennah, 1956, Kodaianellafurcata Chang & Chen, sp. nov. (China: Guangxi) is also described and illustrated; female genitalia of two known species in Kodaianella are described. A checklist of species of the tribe Kodaianellini with their distribution and a key to genera are provided.

A new genus of the tribe Sarimini (Fulgoromorpha, Issidae) from the Guangxi Province of China

A new genus with a new species Eusarimissus hezhouensis gen. nov. et sp. nov. from Guangxi Province of China are described in the tribe Sarimini of the family Issidae. Molecular sequences of 18S, 28S and COXI genes are provided for the new taxon. Phylogenetic analysis places this taxon sister to a previously sequenced but not yet described Sarimini genus 'Eusarima sp. 4'. Taxonomic notes are provided for the genus Eusarima Yang, 1994. The species Eusarima (Nepalius) iranica Gnezdilov & Mozaffarian, 2011 is transferred to the genus Sarima Melichar 1903.

The MTase15 regulates reproduction in the wing-dimorphic planthopper, Nilaparvata lugens (Hemiptera: Delphacidae)

S-Adenosyl-l-methionine-dependent methyltransferases (SAMMTases) modulate important cellular and metabolic activities in both prokaryotes and eukaryotes. Here, we functionally characterized an SAMMTase gene (MTase15) in the migratory brown planthopper (BPH), Nilaparvata lugens, which is the most notorious rice pest in Asia. The cDNA sequence of MTase15 is 2764 nt in length with an open reading frame of 1218 nt encoding 405 amino acid residues. Quantitative real-time PCR analysis showed that MTase15 was readily detected from egg to adult stages and extensively distributed in various body parts of adult females and males, with slightly high levels in ovary and testis, respectively. In addition, MTase15 was transcriptionally regulated by the insulin signalling pathway in BPH. RNA-interference-mediated knockdown of MTase15 (dsMtase15) resulted in deficiencies in vitellogenin synthesis and oogenesis, and female infertility. Males with Mtase15 knockdown retained the capability of producing sperms with normal viability, but less sperm was transferred to wild-type (wt) females during copulation, and eggs laid by these wt females arrested embryogenesis. These findings not only assign a functional role to MTase15, but also provide a link between the insulin signalling pathway and epigenetic regulation in BPH reproduction.

Challenging battles of plants with phloem-feeding insects and prokaryotic pathogens

For the past 4 decades, intensive molecular studies of mostly leaf mesophyll cell-infecting pathogens and chewing insects have led to compelling models of plant-pathogen and plant-insect interactions. Yet, some of the most devastating pathogens and insect pests live in or feed on the phloem, a systemic tissue belonging to the plant vascular system. Phloem tissues are difficult to study, and phloem-inhabiting pathogens are often impossible to culture, thus limiting our understanding of phloem-insect/pathogen interactions at a molecular level. In this Perspective, we highlight recent literature that reports significant advances in the understanding of phloem interactions with insects and prokaryotic pathogens and attempt to identify critical questions that need attention for future research. It is clear that study of phloem-insect/pathogen interactions represents an exciting frontier of plant science, and influx of new scientific expertise and funding is crucial to achieve faster progress in this important area of research that is integral to global food security.

Evidence suggesting interactions between immunodominant membrane protein Imp of Flavescence dorée phytoplasma and protein extracts from distantly related insect species

AIMS

In this study, binding between the immunodominant membrane protein Imp of the 16SrV-D phytoplasma associated with Flavescence dorée disease (FD-Dp) and insect proteins of vectors and non-vectors of FD-Dp was tested.

METHODS AND RESULTS

Six Auchenorrhyncha species, from distantly related groups were selected: Scaphoideus titanus, Euscelidius variegatus, Macrosteles quadripunctulatus, Zyginidia pullula (Cicadomorpha), Ricania speculum and Metcalfa pruinosa (Fulgoromorpha). The vector status of each species was retrieved from the literature or determined by transmission trials in this study. A His-tagged partial Imp protein and a rabbit polyclonal antibody were synthesized and used for Western and Far-Western dot Blot (FWdB) experiments. Total native and membrane proteins (MP) were extracted from entire bodies and organs (gut and salivary glands) of each insect species. FWdB showed decreasing interaction intensities of Imp fusion protein with total proteins from entire bodies of S. titanus, E. variegatus (competent vectors) and M. quadripunctulatus (non-vector), while no interaction signal was detected with the other three species (non-vectors). A strong signal detected upon interaction of FD-D Imp and MP from guts of closely related insects supports the role of this organ as the first barrier to ensure successful transmission.

CONCLUSIONS

Our results showed that specific Imp binding, correlated with vector status, is involved in interactions between FD-Dp and insect proteins.

SIGNIFICANCE AND IMPACT OF THE STUDY

Integrating knowledge on host-pathogen protein-protein interactions and on insect phylogeny would help to identify the actual range of vectors of phytoplasma strains of economic importance.

Salivary DNase II from Laodelphax striatellus acts as an effector that suppresses plant defence

Extracellular DNA, released by damaged plant cells, acts as a damage-associated molecular pattern (DAMP). We demonstrated previously that the small brown planthopper (Laodelphax striatellus, SBPH) secreted DNase II when feeding on artificial diets. However, the function of DNase II in insect feeding remained elusive. The influences of DNase II on SBPHs and rice plants were investigated by suppressing expression of DNase II or by application of heterogeneously expressed DNase II. We demonstrated that DNase II is mainly expressed in the salivary gland and is responsible for DNA-degrading activity of saliva. Knocking down the expression of DNase II resulted in decreased performance of SBPH reared on rice plants. The dsDNase II-treated SBPH did not influenced jasmonic acid (JA), salicylic acid (SA), ethylene (ET) pathways, but elicited a higher level of H2 O2 and callose accumulation. Application of heterogeneously expressed DNase II in DNase II-deficient saliva slightly reduced the wound-induced defence response. We propose a DNase II-based invading model for SBPH feeding on host plants, and provide a potential target for pest management.

Current understanding of the molecular players involved in resistance to rice planthoppers

Rice planthoppers are the most widespread and destructive pest of rice. Planthopper control depends greatly on the understanding of molecular players involved in resistance to planthoppers. This paper summarizes the recent progress in the understanding of some molecular players involved in resistance to planthoppers and the mechanisms involved. Recent researches showed that host-plant resistance is the most promising sustainable approach for controlling planthoppers. Planthopper-resistant varieties with a host-plant resistance gene have been released for rice products. Integrated planthopper management is a proposed strategy to prolong the durability of host-plant resistance. Bacillus spp. and their gene products or insect pathogenic fungi have great potential for application in the biological control of planthoppers. Enhancement of the activity of the natural enemies of planthoppers would be more cost-effective and environmentally friendly. Various molecular processes regulate rice-planthopper interactions. Rice encounters planthopper attacks via transcription factors, secondary metabolites, and signaling networks in which phytohormones have central roles. Maintenance of cell wall integrity and lignification act as physical barriers. Indirect defenses of rice are regulated via chemical elicitors, honeydew-associated elicitor, amendment with silicon and biochar, and salivary protein of BPH as elicitor or effector. Further research directions on planthopper control and rice defense against planthoppers are also put forward. © 2019 Society of Chemical Industry.

Volatiles mediate host-selection in the corn hoppers Dalbulus maidis (Hemiptera: Cicadellidae) and Peregrinus maidis (Hemiptera: Delphacidae)

Volatile organic compounds (VOCs) released by plants are generally involved in host recognition and host selection for many phytophagous insects. However, for leafhoppers and planthoppers, host recognition is mainly thought to involve a phototactic response, but it is not clear if a host plant could be selected based on the volatile cues it emits. In this study we evaluated olfactory responses in dual choice tests of two Hemiptera species, Dalbulus maidis (De Long) (Cicadellidae) and Peregrinus maidis (Ashmead) (Delphacidae), vectors of maize-stunting diseases, to three maize (Zea mays L.) germplasms, a temperate and a tropical hybrid and a landrace. VOCs emitted by the germplasms were collected and identified using gas chromatography-mass spectrometry. The temperate hybrid released significantly more VOCs than the tropical hybrid and the landrace, and its volatile profile was dominated by (±)-linalool. D. maidis preferred odours emitted from the temperate hybrid, whereas P. maidis preferred odours from the tropical hybrid and the landrace over the temperate one. In order to test if linalool plays a role in the behavioural responses, we assayed this compound in combination with the tropical hybrid, to provide other contextual olfactory cues. D. maidis was attracted to the tropical hybrid plus a 0.0001% linalool solution, indicating that this compound could be part of a blend of attractants. Whereas addition of linalool resulted in a slight, though not significant, reduction in host VOC attractiveness for P. maidis. Both hopper species responded to olfactory cues in the absence of supplementary visual cues.

The histone deacetylase NlHDAC1 regulates both female and male fertility in the brown planthopper, Nilaparvata lugens

Histone acetylation is a specific type of chromatin modification that serves as a key regulatory mechanism for many cellular processes in mammals. However, little is known about its biological function in invertebrates. Here, we identified 12 members of histone deacetylases (NlHDACs) in the brown planthopper (BPH), Nilaparvata lugens. RNAi-mediated silencing assay showed that NlHdac1, NlHdac3 and NlHdac4 played critical roles in female fertility via regulating ovary maturation or ovipositor development. Silencing of NlHdac1 substantially increased acetylation level of histones H3 and H4 in ovaries, indicating NlHDAC1 is the main histone deacetylase in ovaries of BPH. RNA sequencing (RNA-seq) analysis showed that knockdown of NlHdac1 impaired ovary development via multiple signalling pathways including the TOR pathway. Acoustic recording showed that males with NlHdac1 knockdown failed to make courtship songs, and thus were unacceptable to wild-type females, resulting in unfertilized eggs. Competition mating assay showed that wild-type females overwhelmingly preferred to mate with control males over NlHdac1-knockdown males. These findings improve our understanding of reproductive strategies controlled by HDACs in insects and provide a potential target for pest control.

Host and geography together drive early adaptive radiation of Hawaiian planthoppers

The interactions between insects and their plant host have been implicated in driving diversification of both players. Early arguments highlighted the role of ecological opportunity, with the idea that insects "escape and radiate" on new hosts, with subsequent hypotheses focusing on the interplay between host shifting and host tracking, coupled with isolation and fusion, in generating diversity. Because it is rarely possible to capture the initial stages of diversification, it is particularly difficult to ascertain the relative roles of geographic isolation versus host shifts in initiating the process. The current study examines genetic diversity between populations and hosts within a single species of endemic Hawaiian planthopper, Nesosydne umbratica (Hemiptera, Delphacidae). Given that the species was known as a host generalist occupying unrelated hosts, Clermontia (Campanulaceae) and Pipturus (Urticaceae), we set out to determine the relative importance of geography and host in structuring populations in the early stages of differentiation on the youngest islands of the Hawaiian chain. Results from extensive exon capture data showed that N. umbratica is highly structured, both by geography, with discrete populations on each volcano, and by host plant, with parallel radiations on Clermontia and Pipturus leading to extensive co-occurrence. The marked genetic structure suggests that populations can readily become established on novel hosts provided opportunity; subsequent adaptation allows monopolization of the new host. The results support the role of geographic isolation in structuring populations and with host shifts occurring as discrete events that facilitate subsequent parallel geographic range expansion.

Rescue of a plant cytorhabdovirus as versatile expression platforms for planthopper and cereal genomic studies

Plant viruses have been used as rapid and cost-effective expression vectors for heterologous protein expression in genomic studies. However, delivering large or multiple foreign proteins in monocots and insect pests is challenging. Here, we recovered a recombinant plant cytorhabdovirus, Barley yellow striate mosaic virus (BYSMV), for use as a versatile expression platform in cereals and the small brown planthopper (SBPH, Laodelphax striatellus) insect vector. We engineered BYSMV vectors to provide versatile expression platforms for simultaneous expression of three foreign proteins in barley plants and SBPHs. Moreover, BYSMV vectors could express the c. 600-amino-acid β-glucuronidase (GUS) protein and a red fluorescent protein stably in systemically infected leaves and roots of cereals, including wheat, barley, foxtail millet, and maize plants. Moreover, we have demonstrated that BYSMV vectors can be used in barley to analyze biological functions of gibberellic acid (GA) biosynthesis genes. In a major technical advance, BYSMV vectors were developed for simultaneous delivery of CRISPR/Cas9 nuclease and single guide RNAs for genomic editing in Nicotiana benthamiana leaves. Taken together, our results provide considerable potential for rapid screening of functional proteins in cereals and planthoppers, and an efficient approach for developing other insect-transmitted negative-strand RNA viruses.