Characterization of the swede midge, Contarinia nasturtii, first instar larval salivary gland transcriptome

Proteins in saliva of gall-forming insect larvae govern insect-host plant interactions. Contarinia nasturtii, the swede midge, is a pest of brassicaceous vegetables (cabbage, cauliflower, broccoli) and canola. We examined the salivary gland (SG) transcriptome of first instar larvae reared on Brassica napus and catalogued genes encoding secreted proteins that may contribute to the initial stages of larval establishment, the synthesis of plant growth hormones, extra-oral digestion and evasion of host defenses. A significant portion of the secreted proteins with unknown functions were unique to C. nasturtii and were often members of larger gene families organized in genomic clusters with conservation patterns suggesting that they are undergoing selection.

Horizontally transmitted parasitoid killing factor shapes insect defense to parasitoids

Interkingdom competition occurs between hymenopteran parasitoids and insect viruses sharing the same insect hosts. It has been assumed that parasitoid larvae die with the death of the infected host or as result of competition for host resources. Here we describe a gene family, parasitoid killing factor (pkf), that encodes proteins toxic to parasitoids of the Microgastrinae group and determines parasitism success. Pkfs are found in several entomopathogenic DNA virus families and in some lepidopteran genomes. We provide evidence of equivalent and specific toxicity against endoparasites for PKFs found in entomopoxvirus, ascovirus, baculovirus, and Lepidoptera through a mechanism that elicits apoptosis in the cells of susceptible parasitoids. This highlights the evolutionary arms race between parasitoids, viruses, and their insect hosts.

De Novo Whole-Genome Assembly of the Swede Midge (Contarinia nasturtii), a Specialist of Brassicaceae, Using Linked-Read Sequencing

The swede midge, Contarinia nasturtii, is a cecidomyiid fly that feeds specifically on plants within the Brassicaceae. Plants in this family employ a glucosinolate-myrosinase defense system, which can be highly toxic to nonspecialist feeders. Feeding by C. nasturtii larvae induces gall formation, which can cause substantial yield losses thus making it a significant agricultural pest. A lack of genomic resources, in particular a reference genome, has limited deciphering the mechanisms underlying glucosinolate tolerance in C. nasturtii, which is of particular importance for managing this species. Here, we present an annotated, scaffolded reference genome of C. nasturtii using linked-read sequencing from a single individual and explore systems involved in glucosinolate detoxification. The C. nasturtii genome is similar in size and annotation completeness to that of the Hessian fly, Mayetiola destructor, but has greater contiguity. Several genes encoding enzymes involved in glucosinolate detoxification in other insect pests, including myrosinases, sulfatases, and glutathione S-transferases, were found, suggesting that C. nasturtii has developed similar strategies for feeding on Brassicaceae. The C. nasturtii genome will, therefore, be integral to continued research on plant-insect interactions in this system and contribute to effective pest management strategies.

Role of the peritrophic matrix in insect-pathogen interactions

The peritrophic matrix (PM) is an acellular chitin and glycoprotein layer that lines the invertebrate midgut. The PM has long been considered a physical as well as a biochemical barrier, protecting the midgut epithelium from abrasive food particles, digestive enzymes and pathogens infectious per os. This short review will focus on the latter function, as a barrier to pathogens infectious per os. We focus on the evidence confirming the role of the PM as protective barrier against pathogenic microorganisms of insects, mainly bacteria and viruses, as well as the evolution of a variety of mechanisms used by pathogens to overcome the PM barrier.

Examining population structure of a bertha armyworm, Mamestra configurata (Lepidoptera: Noctuidae), outbreak in western North America: Implications for gene flow and dispersal

The bertha armyworm (BAW), Mamestra configurata, is a significant pest of canola (Brassica napus L. and B. rapa L.) in western North America that undergoes cyclical outbreaks every 6–8 years. During peak outbreaks millions of dollars are spent on insecticidal control and, even with control efforts, subsequent damage can result in losses worth millions of dollars. Despite the importance of this pest insect, information is lacking on the dispersal ability of BAW and the genetic variation of populations from across its geographic range which may underlie potential differences in their susceptibility to insecticides or pathogens. Here, we examined the genetic diversity of BAW populations during an outbreak across its geographic range in western North America. First, mitochondrial cytochrome oxidase 1 (CO1) barcode sequences were used to confirm species identification of insects captured in a network of pheromone traps across the range, followed by haplotype analyses. We then sequenced the BAW genome and used double-digest restriction site associated DNA sequencing, mapped to the genome, to identify 1000s of single nucleotide polymorphisms (SNP) markers. CO1 haplotype analysis identified 9 haplotypes distributed across 28 sample locations and three laboratory-reared colonies. Analysis of genotypic data from both the CO1 and SNP markers revealed little population structure across BAW’s vast range. The CO1 haplotype pattern showed a star-like phylogeny which is often associated with species whose population abundance and range has recently expanded and combined with pheromone trap data, indicates the outbreak may have originated from a single focal point in central Saskatchewan. The relatively recent introduction of canola and rapid expansion of the canola growing region across western North America, combined with the cyclical outbreaks of BAW caused by precipitous population crashes, has likely selected for a genetically homogenous BAW population adapted to this crop.

Proteomics analysis of Trichoplusia ni midgut epithelial cell brush border membrane vesicles

The insect midgut epithelium is composed of columnar, goblet, and regenerative cells. Columnar epithelial cells are the most abundant and have membrane protrusions that form the brush border membrane (BBM) on their apical side. These increase surface area available for the transport of nutrients, but also provide opportunities for interaction with xenobiotics such as pathogens, toxins and host plant allelochemicals. Recent improvements in proteomic and bioinformatics tools provided an opportunity to determine the proteome of the T. ni BBM in unprecedented detail. This study reports the identification of proteins from BBM vesicles (BBMVs) using single dimension polyacrylamide gel electrophoresis coupled with multi-dimensional protein identification technology. More than 3000 proteins were associated with the BBMV, of which 697 were predicted to possess either a signal peptide, at least one transmembrane domain or a GPI-anchor signal. Of these, bioinformatics analysis and manual curation predicted that 185 may be associated with the BBMV or epithelial cell plasma membrane. These are discussed with respect to their predicted functions, namely digestion, nutrient uptake, cell signaling, development, cell-cell interactions, and other functions. We believe this to be the most detailed proteomic analysis of the lepidopteran midgut epithelium membrane to date, which will provide information to better understand the biochemical, physiological and pathological processes taking place in the larval midgut.

The complete genome sequence of a second alphabaculovirus from the true armyworm, Mythimna unipuncta: implications for baculovirus phylogeny and host specificity

The Mythimna unipuncta nucleopolyhedrovirus isolate KY310 (MyunNPV-KY310) is an alphabaculovirus isolated from a true armyworm (Mythimna unipuncta) population in Kentucky, USA. Occlusion bodies of this virus were examined by electron microscopy and the genome sequence was determined by 454 pyrosequencing. MyunNPV-KY310 occlusion bodies consisted of irregular polyhedra measuring 0.8-1.8 µm in diameter and containing multiple virions, with one to six nucleocapsids per virion. The genome sequence was determined to be 156,647 bp with a nucleotide distribution of 43.9% G+C. 152 ORFs and six homologous repeat (hr) regions were annotated for the sequence, including the 38 core genes of family Baculoviridae and an additional group of 26 conserved alphabaculovirus genes. BLAST queries and phylogenetic inference confirmed that MyunNPV-KY310 is most closely related to the alphabaculovirus Leucania separata nucleopolyhedrovirus isolate AH1, which infects Mythimna separata. In contrast, MyunNPV-KY310 did not exhibit a close relationship with Mythimna unipuncta nucleopolyhedrovirus isolate #7, an alphabaculovirus from the same host species. MyunNPV-KY310 lacks the gp64 envelope glycoprotein, which is a characteristic of group II alphabaculoviruses. However, this virus and five other alphabaculoviruses lacking gp64 are placed outside the group I and group II clades in core gene phylogenies, further demonstrating that viruses of genus Alphabaculovirus do not occur in two monophyletic clades. Potential instances of MyunNPV-KY310 ORFs arising by horizontal transfer were detected. Although there are now genome sequences of four different baculoviruses from M. unipuncta, comparison of their genome sequences provides little insight into the genetic basis for their host specificity.

The Effect of Diet on Midgut and Resulting Changes in Infectiousness of AcMNPV Baculovirus in the Cabbage Looper, Trichoplusia ni

Insecticide resistance has been reported in many important agricultural pests, and alternative management methods are required. Baculoviruses qualify as an effective, yet environmentally benign, biocontrol agent but their efficacy against generalist herbivores may be influenced by diet. However, few studies have investigated the tritrophic interactions of plant, pest, and pathogen from both a gene expression and physiological perspective. Here we use microscopy and transcriptomics to examine how diet affects the structure of peritrophic matrix (PM) in Trichoplusia ni larvae and consequently their susceptibility to the baculovirus, AcMNPV. Larvae raised on potato leaves had lower transcript levels for chitinase and chitin deacetylase genes, and possessed a thicker and more multi-layered PM than those raised on cabbage or artificial diet, which could contribute to their significantly lower susceptibility to the baculovirus. The consequences of these changes underline the importance of considering dietary influences on pathogen susceptibility in pest management strategies.

Infection of the chalcid parasitoid Pteromalus venustus Walker (Hymenoptera: Pteromalidae) with the male-killing symbiont Arsenophonus nasoniae (Gamma-Proteobacteria: Enterobacteriaceae)

The male-killing symbiont Arsenophonus nasoniae is a gamma-proteobacterium that infects parasitic wasps; the male progeny of infected females exhibit increased embryonic death. In this study, we examined methods to horizontally infect Pteromalus venustus (a parasitoid infesting populations of the alfalfa leafcutting bee Megachile rotundata) with A. nasoniae. We then tested the success of these methods via semi-quantitative PCR and quantitative digital PCR, using a molecular marker specific to A. nasoniae. Controlled parasitoid mating experiments were then undertaken to determine whether infections of A. nasoniae in P. venustus induce the male-killing phenotype as has been reported for other host species; evidence of this male-killing phenotype was observed in the current study. Over the course of the eight parasitoid generations following introduction of A. nasoniae infection in P. venustus, the male component of the parasitoid sex ratio was substantially reduced in the infected population (1.05 ♂: 1.00 ♀) compared to the control population (2.46 ♂: 1.00 ♀). Establishment of stable A. nasoniae infections in P. venustus populations could lower the proportion of male progeny, thus negatively impacting the mating success of females, and reducing overall populations of the parasitoid in alfalfa leafcutting bee populations.

The complete genome sequence of a third distinct baculovirus isolated from the true armyworm, Mythimna unipuncta, contains two copies of the lef-7 gene

A baculovirus isolate from a USDA Forest Service collection was characterized by electron microscopy and analysis of its genome sequence. The isolate, formerly referred to as Pseudoletia (Mythimna) sp. nucleopolyhedrovirus #7 (MyspNPV#7), was determined by barcoding PCR to derive from the host species Mythimna unipuncta (true armyworm) and was renamed Mythimna unipuncta nucleopolyhedrovirus #7 (MyunNPV#7). The occlusion bodies (OBs) and virions exhibited a size and morphology typical for OBs produced by the species of genus Alphabaculovirus, with occlusion-derived virions consisting of 2-5 nucleocapsids within a single envelope. The MyunNPV#7 genome was determined to be 148,482 bp with a 48.58% G+C nucleotide distribution. A total of 159 ORFs of 150 bp or larger were annotated in the genome sequence, including the 38 core genes of family Baculoviridae. The genome contained six homologous repeat regions (hrs) consisting of multiple copies of a 34-bp imperfect palindrome. Phylogenetic inference from concatenated baculovirus core gene amino acid sequence alignments placed MyunNPV#7 with group II alphabaculoviruses isolated from other armyworm and cutworm host species of lepidopteran family Noctuidae. MyunNPV#7 could be distinguished from other viruses in this group on the basis of differences in gene content and order. Pairwise nucleotide distances suggested that MyunNPV#7 represents a distinct species in Alphabaculovirus. The MyunNPV#7 genome was found to contain two copies of the late expression factor-7 (lef-7) gene, a feature not reported for any other baculovirus genome to date. Both copies of lef-7 encoded an F-box domain, which is required for the function of LEF-7 in baculovirus DNA replication.

Baculoviruses require an intact ODV entry-complex to resist proteolytic degradation of per os infectivity factors by co-occluded proteases from the larval host

Baculoviruses orally infect caterpillars in the form of occlusion-derived viruses (ODVs). The ODV-envelope contains a number of proteins which are essential for oral infectivity, called per os infectivity factors (PIFs). Most of these PIFs are involved in the formation of an ODV-entry complex that consists of a stable core, formed by PIF1, PIF2, PIF3 and PIF4, and the more loosely associated PIFs P74 (PIF0) and P95 (PIF8). PIF1, PIF2 and PIF3 are essential for formation of the stable core, whereas deletion of the pif4 gene results in the formation of a smaller complex. P74 is not needed for formation of the stable core. We show here in larva-derived ODVs of the Autographa californica multicapsid nucleopolyhedrovirus that PIF-proteins are degraded by host-derived proteases after deletion of a single pif-gene. Constituents of the stable core-complex appeared to be more resistant to proteases as part of the complex than as monomer, as in ODVs of a p74 deletion mutant only the stable core was found but no PIF monomers. When the stable core lacks PIF4, it lost its proteolytic resistance as the resulting smaller core complex was degraded in a pif4 deletion mutant. We also identified PIF6 as a loosely associated component of the entry complex that appeared nevertheless important for the proteolytic resistance of the stable core, which was degraded after deletion of pif6. We conclude from these results that an intact entry-complex in the ODV-envelope is prerequisite for proteolytic resistance of PIF-proteins under the alkaline conditions of the larval midgut.

The Complete Genome Sequence of a Second Distinct Betabaculovirus from the True Armyworm, Mythimna unipuncta

The betabaculovirus originally called Pseudaletia (Mythimna) sp. granulovirus #8 (MyspGV#8) was examined by electron microscopy, host barcoding PCR, and determination of the nucleotide sequence of its genome. Scanning and transmission electron microscopy revealed that the occlusion bodies of MyspGV#8 possessed the characteristic size range and morphology of betabaculovirus granules. Barcoding PCR using cytochrome oxidase I primers with DNA from the MyspGV#8 collection sample confirmed that it had been isolated from the true armyworm, Mythimna unipuncta (Lepidoptera: Noctuidae) and therefore was renamed MyunGV#8. The MyunGV#8 genome was found to be 144,673 bp in size with a nucleotide distribution of 49.9% G+C, which was significantly smaller and more GC-rich than the genome of Pseudaletia unipuncta granulovirus H (PsunGV-H), another M. unipuncta betabaculovirus. A phylogeny based on concatenated baculovirus core gene amino acid sequence alignments placed MyunGV#8 in clade a of genus Betabaculovirus. Kimura-2-parameter nucleotide distances suggested that MyunGV#8 represents a virus species different and distinct from other species of Betabaculovirus. Among the 153 ORFs annotated in the MyunGV#8 genome, four ORFs appeared to have been obtained from or donated to the alphabaculovirus lineage represented by Leucania separata nucleopolyhedrovirus AH1 (LeseNPV-AH1) during co-infection of Mythimna sp. larvae. A set of 33 ORFs was identified that appears only in other clade a betabaculovirus isolates. This clade a-specific set includes an ORF that encodes a polypeptide sequence containing a CIDE_N domain, which is found in caspase-activated DNAse/DNA fragmentation factor (CAD/DFF) proteins. CAD/DFF proteins are involved in digesting DNA during apoptosis.

MacoNPV baculovirus midgut-specific gene expression during infection of the bertha armyworm, Mamestra configurata

Baculoviruses have two forms, occlusion derived virus (ODV) which is responsible for primary infection in host midgut tissue and budded virus (BV), which infects all other host tissues during secondary infection. This study examined the primary infection by ODV of midgut cells of bertha armyworm Mamestra configurata fourth instar larvae and measured the expression of viral genes over a time course of infection. Both digital PCR and RNA sequencing methods showed the profile of transcription to be different from those produced by AcMNPV BV infection of in vitro cell cultures. This included having unique collections of genes expressed early, as well as much greater late gene expression of p6.9 and much reduced expression of polh and p10. These differences likely reflect characteristics unique to the critical step of in vivo midgut cell infection, and provide insights into the processes that regulate viral gene expression in different host tissues.

Characterization of Melanoplus sanguinipes oviposition stimulating protein expression and re-examination of its potential role in stimulating oviposition

Melanoplussanguinipes oviposition stimulating protein (MsOSP) was characterized and its role in stimulating oviposition in virgin females was examined. A 967nt MsOSP mRNA sequence with homology to previously characterized N-terminal amino acid sequence data for MsOSP was identified in a RNAseq library generated from an mRNA pool from the long hyaline tubule (LHT) of the male accessory gland complex. This transcript contained a predicted 729nt open reading frame encoding the 242aa putative MsOSP protein and had the second highest read abundance in the library. The MsOSP transcript was detected exclusively in the LHT tissue of adult males and its abundance increased with time until 7 days post-eclosion. Western blot analysis using an anti-MsOSP antibody showed high levels of MsOSP protein in the LHT luminal secretions of virgin males and to a lesser degree was associated with the aedeagus and ejaculatory duct. MsOSP was shown to be a major protein component of the spermatophore packet transferred from the male to female during copulation. However, only minor amounts of MsOSP could be detected in the female bursa, spermatheca and oviduct. Intrahemocoelic injection of LHT luminal protein into mature virgin females stimulated oviposition in ∼ 65% of females. A similar but non-significant trend was observed upon injection of purified recombinant MsOSP protein, and immunoprecipitation of LHT protein with anti-MsOSP antibody led to abrogation of oviposition stimulation upon injection of mature virgin females. Despite the demonstration of stimulation of oviposition upon intrahemocoelic injection of LHT-derived-MsOSP into mature virgin females, the potential mode of action of MsOSP in this process remains to be determined. MsOSP cannot be detected in the tissues other than the bursa, spermatheca and oviduct of female grasshoppers and relatively large quantities of MsOSP are required to stimulate oviposition upon injection.

The genome of a baculovirus isolated from Hemileuca sp. encodes a serpin ortholog

The genome sequence of a baculovirus from Hemileuca sp. was determined. The genome is 140,633 kb, has a G+C content of 38.1 %, and encodes 137 putative open-reading frames over 50 amino acids. 126 of these ORFs showed similarity to other baculovirus genes in the database including all 37 core genes. Of the remaining 11 predicted genes, one is related to a lepidopteran serpin gene. This is the first report of a baculovirus encoding a member of this family of serine protease inhibitors, and to our knowledge the first report of a viral serpin outside the Poxviridae. The genome also contained three homologous repeat sequences. Phylogenetic analysis indicated that the virus is a group II Alphabaculovirus and belongs to a lineage that includes Orgyia leucostigma, Ectropis obliqua, Apocheima cinerarium, and Euproctis pseudoconspersa nucleopolyhedroviruses.

Characterization of novel components of the baculovirus per os infectivity factor complex

Baculovirus occlusion-derived virus (ODV) infects insect midgut cells under alkaline conditions, a process mediated by highly conserved per os infectivity factors (PIFs), P74 (PIF0), PIF1, PIF2, PIF3, PIF4, and PIF5 (ODV-E56). Previously, a multimolecular complex composed of PIF1, PIF2, PIF3, and P74 was identified which was proposed to play an essential role during ODV entry. Recently, more proteins have been identified that play important roles in ODV oral infectivity, including PIF4, PIF5, and SF58, which might work in concert with previously known PIFs to facilitate ODV infection. In order to understand the ODV entry mechanism, the identification of all components of the PIF complex is crucial. Hence, the aim of this study was to identify additional components of the PIF complex. Coimmunoprecipitation (CoIP) combined with proteomic analysis was used to identify the components of the Autographa californica multiple nucleopolyhedrovirus (AcMNPV) PIF complex. PIF4 and P95 (AC83) were identified as components of the PIF complex while PIF5 was not, and this was confirmed with blue native PAGE and a second CoIP. Deletion of the pif4 gene impaired complex formation, but deletion of pif5 did not. Differentially denaturing SDS-PAGE further revealed that PIF4 forms a stable complex with PIF1, PIF2, and PIF3. P95 and P74 are more loosely associated with this complex. Three other proteins, AC5, AC68, and AC108 (homologue of SF58), were also found by the proteomic analysis to be associated with the PIF complex. Finally the functional significance of the PIF protein interactions is discussed.

Role of enhancin in Mamestra configurata nucleopolyhedrovirus virulence: selective degradation of host peritrophic matrix proteins

To infect per os, baculovirus virions cross the peritrophic matrix (PM) to reach the midgut epithelium. Insect intestinal mucins (IIMs) are PM proteins that protect the PM and aid passage of the food bolus through the gut. Some baculoviruses, including Mamestra configurata nucleopolyhedrovirus (MacoNPV-A), encode metalloproteases, known as enhancins, that facilitate infection by degrading IIMs. We examined the interaction between MacoNPV-A enhancin and M. configurata IIMs both in vivo and in vitro. Per os inoculation of M. configurata larvae with MacoNPV-A occlusion bodies (OBs) resulted in the degradation of McIIM4 within 4 h of OB ingestion, while McIIM2 was unaffected. The PM recovered by 8 h post-inoculation. To investigate whether enhancin was responsible for the degradation of IIM, a recombinant Autographa californica multiple nucleopolyhedrovirus expressing MacoNPV enhancin (AcMNPV-enMP2) was constructed. Enhancin was found to be a component of occlusion-derived virions in AcMNPV-enMP2 and MacoNPV-A. In in vitro assays, McIIM4 was degraded after MacoNPV-A and AcMNPV-enMP2 treatments. Degradation of McIIM4 was inhibited by EDTA, a metalloprotease inhibitor, indicating that the degradation was due to enhancin activity. Thus, MacoNPV-A enhancin is able to degrade major structural PM proteins, but exhibits target substrate specificity.

Characterization of the Mamestra configurata (Lepidoptera: Noctuidae) larval midgut protease complement and adaptation to feeding on artificial diet, Brassica species, and protease inhibitor

The midgut protease profiles from 5th instar Mamestra configurata larvae fed various diets (standard artificial diet, low protein diet, low protein diet with soybean trypsin inhibitor [SBTI], or Brassica napus) were characterized by one-dimensional enzymography in gelatin gels. The gut protease profile of larvae fed B. napus possessed protease activities of molecular masses of approximately 33 and 55 kDa, which were not present in the guts of larvae fed artificial diet. Similarly, larvae fed artificial diet had protease activities of molecular masses of approximately 21, 30, and 100 kDa that were absent in larvae fed B. napus. Protease profiles changed within 12 to 24 h after switching larvae from artificial diet to plant diet and vice versa. The gut protease profiles from larvae fed various other brassicaceous species and lines having different secondary metabolite profiles did not differ despite significant differences in larval growth rates on the different host plants. Genes encoding putative digestive proteolytic enzymes, including four carboxypeptidases, five aminopeptidases, and 48 serine proteases, were identified in cDNA libraries from 4th instar M. configurata midgut tissue. Many of the protease-encoding genes were expressed at similar levels on all diets; however, three chymoptrypsin-like genes (McSP23, McSP27, and McSP37) were expressed at much higher levels on standard artificial diet and diet containing SBTI as was the trypsin-like gene McSP34. The expression of the trypsin-like gene McSP50 was highest on B. napus. The adaptation of M. configurata digestive biochemistry to different diets is discussed in the context of the flexibility of polyphagous insects to changing diet sources.

Analysis of the temporal expression of Trichoplusia ni single nucleopolyhedrovirus genes following transfection of BT1-Tn-5B1-4 cells

Trichoplusia ni single nucleopolyhedrovirus (TnSNPV), a 134,394-bp double-stranded DNA group II Nucleopolyhedrovirus, is pathogenic to the lepidopteran T. ni. TnSNPV transcription is temporally regulated and divided into three promoter sequence-dependent classes (early, late and very late genes). A viral oligonucleotide DNA microarray containing all potential (144) viral genes of TnSNPV was designed to investigate global viral gene expression during cell infection. Total BT1-Tn-5B1-4 cellular mRNAs extracted between 0 and 72 h posttransfection with TnSNPV genomic DNA were hybridized to the microarray. Initial average expression of early genes was detected between 12 and 24 h posttransfection while late genes were mainly detected between 24 and 72 h posttransfection. The microarray expression profiling data verified many computer predicted promoter assignments. K-means clustering was used to sort the 144 genes based on their temporal expression pattern similarities. This clustering resulted in the confirmation and temporal class assignment of previously unidentified genes and promoters.

Isolation and characterization of plaque-purified strains of Malacosoma disstria Nucleopolyhedrovirus

Seven plaque-purified genotypic variants or strains, derived from a previously described field isolate of the Malacosoma disstria Nucleopolyhedrovirus (MadiNPV) from Alberta populations of forest tent caterpillar, were characterized based on distinctive restriction endonuclease fragment patterns. Two strains, MadiNPV-pp3 and MadiNPV-pp11, were selected for further characterization, as they represented strains producing high and low budded virus (BV) titres, respectively, in the M. disstria cell line UA-Md203. Analysis of restriction endonuclease fragment profiles indicated the genomes differed significantly in size, 133.8 +/- 2.4 kb for MadiNPV-pp3 and 118.1 +/- 3.5 kb for MadiNPV-pp11. These strains were characterized based on their BV production in three different cell lines derived from M. disstria haemocytes. Compared with MadiNPV-pp11, MadiNPV-pp3 produced two- to three-fold more BVs in UA-Md203 and 210 other cell lines; however, BV production was only marginally higher for MadiNPV-pp3 in the UA-Md221 cell line. Similarly, the yield of polyhedral inclusion bodies was significantly higher for MadiNPV-pp3 in UA-Md203 and 210 cell lines than for MadiNPV-pp11 but not in the UA-Md221 cell line. This data, although derived from a limited number of cell lines, suggested MadiNPV-pp3 may have a broader tissue tropism than MadiNPV-pp11.

Sequence analysis of the complete genome of Trichoplusia ni single nucleopolyhedrovirus and the identification of a baculoviral photolyase gene

The genome of the Trichoplusia ni single nucleopolyhedrovirus (TnSNPV), a group II NPV which infects the cabbage looper (T. ni), has been completely sequenced and analyzed. The TnSNPV DNA genome consists of 134,394 bp and has an overall G + C content of 39%. Gene analysis predicted 144 open reading frames (ORFs) of 150 nucleotides or greater that showed minimal overlap. Comparisons with previously sequenced baculoviruses indicate that 119 TnSNPV ORFs were homologues of previously reported viral gene sequences. Ninety-four TnSNPV ORFs returned an Autographa californica multiple NPV (AcMNPV) homologue while 25 ORFs returned poor or no sequence matches with the current databases. A putative photolyase gene was also identified that had highest amino acid identity to the photolyase genes of Chrysodeixis chalcites NPV (ChchNPV) (47%) and Danio rerio (zebrafish) (40%). In addition unlike all other baculoviruses no obvious homologous repeat (hr) sequences were identified. Comparison of the TnSNPV and AcMNPV genomes provides a unique opportunity to examine two baculoviruses that are highly virulent for a common insect host (T. ni) yet belong to diverse baculovirus taxonomic groups and possess distinct biological features. In vitro fusion assays demonstrated that the TnSNPV F protein induces membrane fusion and syncytia formation and were compared to syncytia formed by AcMNPV GP64.

Effect of Flavonoids on Feeding Preference and Development of the Crucifer Pest Mamestra configurata Walker

Thirty-seven flavonoid compounds (9 flavones, 18 flavonols, 8 flavanones, and 2 flavanonols) were investigated for their effect on feeding choice with bertha armyworm (Mamestra configurata Walker; BAW). Feeding choice was dependent upon subtle differences in biochemical structure. Unsubstituted flavone and flavanone were the strongest feeding deterrents in the choice bioassay, while 7.4'-dihydroxyflavone and dihydroquercetin stimulated BAW to feed. The constitutive flavonoids of Brassica napus, isorhamnetin-3-sophoroside-7-glucoside and kaempferol-3,7-diglucoside, were effective deterrents when supplemented at concentrations higher than endogenous levels. In a no-choice bioassay, flavone reduced both larval weight as well as larval and pupal development time.

Identification and genomic analysis of a second species of nucleopolyhedrovirus isolated from Mamestra configurata

MacoNPV-96B is a nucleopolyhedrovirus isolated from naturally infected Mamestra configurata (Lepidoptera: Noctuidae) larvae. It was initially identified due to its completely different restriction endonuclease profile relative to the previously sequenced Mamestra configurata virus MacoNPV-90/2 (Q. Li, C. Donly, L. Li, L. G. Willis, D. A. Theilmann, and M. Erlandson, 2002, Virology 294, 106-121). The MacoNPV-96B host range and virulence were also found to differ significantly from those of the previous isolate. To further understand the complex of viruses infecting M. configurata, the genome of MacoNPV-96B was completely sequenced and analyzed in comparison with the genome of MacoNPV-90/2 and other sequenced baculoviruses. MacoNPV-96B consists of 158,482 bp, and 168 open reading frames (ORFs) of 150 nucleotides or longer with minimal overlap have been identified. The genome of MacoNPV-96B is 3422 bp larger than MacoNPV-90/2 and although gene arrangement is virtually identical, there are 9 ORFs unique to MacoNPV-96B and 10 unique to MacoNPV-90/2. bro genes were found to be associated with nonhomologous regions, suggesting that bro genes may facilitate recombination between genomes. A major difference in the gene content between the two viruses is a 5.4-kb insert in MacoNPV-96B, which is highly homologous to a cluster of Xestia c-nigrum granulovirus (XecnGV) ORFs, suggesting recent recombination events between these two viruses. Nucleotide sequence and amino acid sequence identity between the common ORFs of MacoNPV-96B and MacoNPV-90/2 average 87 and 90%, respectively. The sequence data suggest that MacoNPV-96B and MacoNPV-90/2 are closely related but have diverged and evolved into two separate species. This is the first study to identify highly related but separately evolving viruses in the same insect host and geographic location. A new Identity-GeneParityPlot analysis was developed to perform a comparison of two viral genomes in gene content and arrangement as well as homology level of individual ORFs.

Size and map locations of early transcription products on the Autographa californica nuclear polyhedrosis virus genome

The size classes and map locations of early transcripts of Autographa californica nuclear polyhedrosis virus were identified by probing Northern blots with cloned viral DNA fragments. Twelve abundant and 30 minor transcripts were detected by 4 hr postinfection. There was an increase in the abundancy and number of virus-specific transcripts between 6 and 8 hr postinfection, coincident with the onset of DNA replication. The change in transcription pattern did not occur in cells infected at the nonpermissive temperature with a DNA-negative mutant indicating that these early transcripts were synthesized prior to the initiation of viral DNA replication. Two early transcripts, 4.6 and 1.1 kb, mapped to the genomic region of the temperature-sensitive lesion, between 60.1 and 62.0%.