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Insects possess a fairly sophisticated olfactory system in their antennae to detect odorants essential for their survival and reproduction. Among them, insect first perceives odour sources by odorant-binding proteins (OBPs) to locate host-plants. Methyl salicylate, (Z)-3-hexenyl acetate and dibutyl phthalate are major volatile components of Ulmus pumila and Ricinus communis and elicit strong responses of the scarab beetle Holotrichia oblita adults. However, olfactory perception of the scarab beetle to these odorant compounds is unclear. In the current study, we cloned the OBP6 and OBP7 of H. oblita. The expression pattern shows that the two genes were highly expressed in the antennae of female beetles. Binding assays verified that the HoblOBP6 had a better binding affinity to methyl salicylate, and so did HoblOBP7 to (Z)-3-hexenyl acetate and dibutyl phthalate. The effect on the responses of female beetles to the three compounds was decreased significantly after these two genes were silenced by RNA interference. These results indicate that HoblOBP6 and HoblOBP7 are essential for female H. oblita perception of methyl salicylate, (Z)-3-hexenyl acetate and dibutyl phthalate. Our study provides important insights into the olfactory mechanism of female H. oblita to ester plant volatiles and could facilitate the development of potential pest control strategies in the field.

Combining the entomopathogenic nematodes (EPNs), Heterorhabditis beicherriana LF strain and Bacillus thuringiensis (Bt) HBF-18 strain is a practical strategy to manage the larvae of Holotrichia parallela Motschulsky. However, the intrinsic resistance mechanism between H. parallela larvae and the EPN-Bt combination is unknown. Herein, antioxidant enzymes [superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)] and detoxifying enzymes [carboxylesterase (CarE), glutathione S-transferase (GST), and acetylcholinesterase (AChE)] of H. parallela larvae showed an activation-inhibition trend throughout the EPN-Bt exposure time course. Eight potentially key antioxidant and detoxifying enzyme genes in response to EPN-Bt infection were identified from the midgut of H. parallela larvae through RNA-seq. Spatiotemporal analysis showed they were ubiquitously expressed in all development stages and tissues. After silencing CAT, CarE, and GST1, the enzyme activities were significantly decreased by 30.29%, 68.80%, and 34.63%, respectively. Meanwhile, the mortality of grubs was increased by 18.40%, 46.30%, and 42.59% after exposure to EPN-Bt for 1 day. The expression level change trends of phosphatidylinositol 3-kinase (PI3K), protein kinase B (Akt), cap ‘n’ collar isoform-C (CncC), kelch-like ECH-associated protein 1 (Keap1), and CarE were consistent when exposed to EPN-Bt. Furtherly, RNAi-mediated PI3K silencing showed a similar downregulated trend between PI3K/Akt/CncC and CarE. Furthermore, silencing PI3K rendered grubs more susceptible to EPN-Bt and accelerated symbiotic bacteria multiplication in grubs. Overall, these results suggest that PI3K/Akt/CncC pathway mediates the expression of CarE and participates in the resistance of H. parallela larvae to EPN-Bt infection.

The neuro-mechanisms that regulate insect reproduction are not fully understood. Biogenic amines, including octopamine, are neuromodulators that have been shown to modulate insect reproduction in various ways, e.g., promote or inhibit insect mating or oviposition. In this study, we examined the role of octopamine in regulating the reproduction behaviors of a devastating underground insect pest, the dark black chafer (Holotrichia parallela). We first measured the abundance of octopamine in different neural tissues of the adult chafer pre- and post-mating, demonstrating that octopamine decreased in the abdominal ganglia of females but increased in males post-mating. We then fed the adult H. parallela with a concentration gradient of octopamine to test the effects on insect reproductive behaviors. Compared with its antagonist mianserin, octopamine at the concentration of 2 µg/mL resulted in the highest increase in males' preference for sex pheromone and females' oviposition, whereas the mianserin-treatment increased the survival rate and prolonged the lifespan of H. parallela. In addition, we did not observe significant differences in egg hatchability between octopamine and mianserin-treated H. parallela. Our results demonstrated that octopamine promotes H. parallela mating and oviposition with a clear low dosage effect, illustrated how neural substrates modulate insect behaviors, and provided insights for applying octopamine in pest management.

Pheromone binding proteins (PBPs), a subfamily of the odorant binding proteins (OBPs), capture and transfer sex pheromones across the sensillum lymph to pheromone receptors and initiate insect courtship and mating. In this study, we functionally characterized ten OBPs from the black chafer, Holotrichia oblita (HoblOBPs), among which six HoblOBPs (HoblOBP2, 4, 5, 8, 9 and 24) were shown to recognize sex pheromones using electroantennography assays (EAG) and in vitro fluorescence competitive binding assays. Insect tropism to sex pheromones was significantly reduced after those genes were knocked down in vivo, e.g. HoblOBP24 RNAi reduced the tropism of H. oblita to methyl glycinate by 34%. Furthermore, molecular docking revealed key residues for the binding of the six HoblOBPs with sex pheromones. And hydrogen bonds and hydrophobic forces were shown to be the main forces in the binding of the six HoblOBPs and their sex pheromone ligands. Our study characterized six H. oblita PBPs and their binding abilities to sex pheromone ligands. The results will improve our understanding on the olfactory mechanisms that H. oblita utilizes to recognize sex pheromones, and will promote the development of novel strategies for controlling H. oblita and other insect pests.

With the advent of next-generation sequencing, it is now possible to rapidly identify the entire repertoire of olfactory genes likely to be involved in chemical communication of an insect species. It remains, however, a challenge to identify olfactory proteins, such as odorant receptors and odorant-binding proteins (OBPs), vis-a-vis the odorants they detect. It has been reported that exposing the olfactory system to a physiologically relevant odorant alters the transcript levels of odorant receptor(s) involved in the detection of the tested odorant. We applied this paradigm in an attempt to identify putative OBPs from the scarab beetle Holotrichia oblita involved in the reception of plant-derived kairomones. Twenty-nine OBP genes were identified in the H. oblita transcriptome, 20 of which were enriched in antennae compared with nonolfactory tissues. Of these, 2 OBP genes, HoblOBP13 and HoblOBP9, were upregulated upon exposure to one of the female attractants (E)-2-hexenol and phenethyl alcohol; none of the OBP transcripts changed upon exposure to methyl anthranilate, which does not attract H. oblita females. Binding assays showed that HoblOBP13 and HoblOBP9 have high affinity for (E)-2-hexenol and phenethyl alcohol, respectively. RNAi treatment showed that transcripts of both HoblOBP13 and HoblOBP9 declined in a time-course manner 24–72 h postinjection. OBP-dsRNA-treated female beetles showed significantly lower attraction to (E)-2-hexenol and phenethyl alcohol than did water-injected beetles and those treated with GFP-dsRNA. We, therefore, concluded that HoblOBP13 and HoblOBP9 are essential for H. oblita reception of the plant-derived kairomones (E)-2-hexenol and phenethyl alcohol.

Holotrichia parallela is one of the agriculturally important scarab beetle pests in China. In this study, HparOBP14 was cloned, which is the most abundantly expressed among the OBP genes in the legs of female H. parallela adults. Sequence comparison and phylogenetic analysis showed that HparOBP14 has a Plus-C structure motif. The expression profile analysis revealed that HparOBP14 expression was the highest in the female antennae and then in the legs. The fluorescence competitive binding experiment of the recombinant HparOBP14 protein showed that HparOBP14 had an affinity with 6-methyl-5-heptene-2-one (plant volatile), 3-methylindole, p-cymene, methanol, formaldehyde, α-pinene, and geraniol (organic fertilizer volatile). Knockdown HparOBP14 expression decreased significantly the EAG response of the injected female adults to p-cymene, methanol, formaldehyde, α-pinene, and geraniol. Similarly, the injected female adults were significantly less attracted to geraniol and methanol. Therefore, HparOBP14 might bind organic matter volatiles during oviposition. These results are not only helpful to analyze the olfactory recognition mechanism of female adult H. parallela when choosing suitable oviposition sites, but also to provide target genes for green prevention and control of H. parallela in the future.

Background Entomopathogenic nematodes (EPNs) emerge as compatible alternatives to conventional insecticides in controlling Holotrichia parallela larvae (Coleoptera: Scarabaeidae). However, the immune responses of H. parallela against EPNs infection remain unclear. Results In present research, RNA-Seq was firstly performed. A total of 89,427 and 85,741 unigenes were achieved from the midgut of H. parallela larvae treated with Heterorhabditis beicherriana LF for 24 and 72 h, respectively; 2545 and 3156 unigenes were differentially regulated, respectively. Among those differentially expressed genes (DEGs), 74 were identified potentially related to the immune response. Notably, some immune-related genes, such as peptidoglycan recognition protein SC1 (PGRP-SC1), pro-phenoloxidase activating enzyme-I (PPAE-I) and glutathione s-transferase (GST), were induced at both treatment points. Bioinformatics analysis showed that PGRP-SC1, PPAE-I and GST were all involved in anti-parasitic immune process. Quantitative real-time PCR (qRT-PCR) results showed that the three immune-related genes were expressed in all developmental stages; PGRP-SC1 and PPAE-I had higher expressions in midgut and fat body, respectively, while GST exhibited high expression in both of them. Moreover, in vivo silencing of them resulted in increased susceptibility of H. parallela larvae to H. beicherriana LF. Conclusion These results suggest that H. parallela PGRP-SC1, PPAE-I and GST are involved in the immune responses to resist H. beicherriana LF infection. This study provides the first comprehensive transcriptome resource of H. parallela exposure to nematode challenge that will help to support further comparative studies on host-EPN interactions.

Additional file 1: Table S1. The annotations of PGRP-SC1, PPAE-I and GST. Table S2:. The annotations of symbiotic bacteria in the transcriptomes of the Holotrichia parallela larvae postexposure to H. beicherriana LF for 72 h. Table S3. Summary of all species name, gene name, abbreviation and GenBank accession involved in phylogenetic analysis. Table S4. Oligonucleotides used for qRT-PCR and RNAi. The T7 promoter sequence is bolded in RNAi. Fig. S1. Rationality evaluation results of PGRP-SC1 (a), PPAE-I (b) and GST (c) 3D model. The red regions (A, B, L) represents the residues in most favoured regions; Bright yellow regions (a, b, l, p) represents the residues in additional allowed regions; Dark yellow regions (~a, ~b, ~l, ~p) represents the residues in generously allowed regions.

A sophisticated olfactory system is part of the explanation for the prominence of insects among animals because of the essential roles of the olfactory system in foraging, host seeking, mating, ovipositing and avoiding toxic substances. In this study, we sequenced and analysed the transcriptomes of olfactory tissue (antennae) and non-olfactory tissue (legs) of the scarab beetle, Holotrichia oblita Faldermann, which is a serious underground pest in China. We obtained approximately 80.2 million 150bp reads that were assembled into 61,038 unigenes with an average length of 890bp. Among the transcripts, 70% of the unigenes were annotated. A total of 44 odorant receptors (ORs) and 9 ionotropic receptors (IRs) were identified based on homology searches. Then, quantitative real-time PCR experiments were performed to investigate the expression patterns of 32 putative chemosensory genes. The results showed that these genes were highly expressed in olfactory organs (antennae) and might play a key role in the olfaction-related behaviours in H. oblita. Based on the results of our phylogenetic analysis and the detailed tissue and sex-biased expression characteristics, the different roles of the receptor proteins in the olfactory system were also indicated. The results of this study will provide the foundation for further understanding of the olfactory odorant receptors of H. oblita at the molecular level and ultimately help to develop novel targets for manipulating this pest.

ObjectivePrevious studies showed that flight muscles degenerate after migration in some aphid species; however, the underlying molecular mechanism remains virtually unknown. In this study, using the wheat aphid,Sitobion avenae, we aim to investigate aphid flight muscle degeneration and the underlying molecular mechanism.ResultsSitobion avenaestarted to differentiate winged or wingless morphs at the second instar, the winged aphids were fully determined at the third instar, and their wings were fully developed at the fourth instar. After migration, the aphid flight muscles degenerated via programmed cell death, which is evidenced by a Terminal deoxynucleotidyl transferase dUTP-biotin nick-end labeling assay. Then, we identified a list of differentially expressed genes before and after tethered flights using differential-display reverse transcription-PCR. One of the differentially expressed genes, ubiquitin-ribosomal S27a, was confirmed using qPCR. Ubiquitin-ribosomal S27a is drastically up regulated following the aphids’ migration and before the flight muscle degeneration. Our data suggested that aphid flight muscles degenerate after migration. During flight muscle degeneration, endogenous proteins may be degraded to reallocate energy for reproduction.

Additional file 5: Figure S3. Alignment (left) and phylogenetic analysis (right) of amino acids sequences of ubiquitin-ribosomal S27a from18 insects. The tree shown is an observed divergency tree inferred from alignment. Statistical support for each individual node on the tree is shown above the nodes. GreenBox stands for Coleoptera, BlueBox stands for Lepidoptera, YellowBox stands for Diptera and RedBox stands for Hemiptera. Al Agriotes lineatus (CAJ01876), Cg Carabus granulates (CAH04347), Md Micromalthus delibis (CAJ01880), Tc Tribolium castaneum (XP_969023), Tb Timarcha balearica (CAJ01881), Bm Byoxsm mori (ABM55591), Px Plutella xylostella (P68202), Pd Papilio dardanus (CAH04128), Sf Spodoptera frugiperda (P68203), Se Spodoptera exigua (Deduced), Dm Drosophila melanogaster (NP_476778), Aa Aedes aegypti(AAS79344), Dc Diaphorina citri (ABG81958) Ga Graphocephala atropunctata (DQ445503), Mh Maconellicoccus hirsutus(ABM55591), Of Oncopeltus fasciatus (ABN54483), AP Acyrthosiphon pisum (NP_001155610), Sa Sitobion avenae (Deduced).

Odorant-binding proteins (OBPs) play an important role in insect olfactory processes and are thought to be responsible for the transport of pheromones and other semiochemicals across the sensillum lymph to the olfactory receptors within the antennal sensilla. As an important general odorant binding protein in the process of olfactory recognition, LstiGOBP1 of Loxostege sticticalis L. has been shown to have good affinity to various plant volatiles. However, the binding specificity of LstiGOBP1 should be further explored in order to better understand the olfactory recognition mechanism of L. sticticalis. In this study, real-time PCR experiments indicated that LstiGOBP1 was expressed primarily in adult antennae. Homology modelling and molecular docking were then conducted on the interactions between LstiGOBP1 and 1-heptanol to understand the interactions between LstiGOBP1 and their ligands. Hydrogen bonds formed by amino acid residues might be crucial for the ligand-binding specificity on molecular docking, a hypothesis that was tested by site-directed mutagenesis. As predicted binding sites for LstiGOBP1, Thr15, Trp43 and Val14 were replaced by alanine to determine the changes in binding affinity. Finally, fluorescence assays revealed that the mutants Thr15 and Trp43 had significantly decreased binding affinity to most odours; in mutants that had two-site mutations, the binding to the six odours that were tested was completely abolished. This result indicates that Thr15 and Trp43 were involved in binding these compounds, possibly by forming multiple hydrogen bonds with the functional groups of the ligands. These results provide new insights into the detailed chemistry of odours' interactions with proteins.

Loxostege sticticalis Linnaeus is an economically important agricultural pest, and the larvae cause great damage to crops, especially in Northern China. However, effective and environmentally friendly chemical methods for controlling this pest have not been discovered to date. In the present study, we performed HiSeq2500 sequencing of transcriptomes of the male and female adult antennae, adult legs and third instar larvae, and we identified 54 candidate odorant receptors (ORs), including 1 odorant receptor coreceptor (Orco) and 5 pheromone receptors (PRs), 18 ionotropic receptors (IRs), 13 gustatory receptors (GRs), 34 odorant binding proteins (OBPs), including 1 general odorant binding protein (GOBP1) and 3 pheromone binding proteins (PBPs), 10 chemosensory proteins (CSPs) and 2 sensory neuron membrane proteins (SNMPs). The results of RNA-Seq and RT-qPCR analyses showed the expression levels of most genes in the antennae were higher than that in the legs and larvae. Furthermore, PR4, OR1-4, 7-11, 13-15, 23, 29-32, 34, 41, 43, 47/IR7d.2/GR5b, 45, 7/PBP2-3, GOBP1, OBP3, 8 showed female antennae-biased expression, while PR1/OBP2, 7/IR75d/CSP2 showed male antennae-biased expression. However, IR1, 7d.3, 68a/OBP11, 20-22, 28/CSP9 had larvae enriched expression, and OBP15, 17, 25, 29/CSP5 were mainly expressed in the legs. The results shown above indicated that these genes might play a key role in foraging, seeking mates and host recognition in the L. sticticalis. Our findings will provide the basic knowledge for further studies on the molecular mechanisms of the olfactory system of L. sticticalis and potential novel targets for pest control strategies.

Odorant-binding proteins (OBPs) are important parts of insect olfactory systems, and sensitive olfaction is vital for phytophagous insects in host foraging. Electrophysiological studies are helpful in understanding olfactory sensing in Sitobion avenae (Hemiptera: Aphididae), but the functions of odorant-binding proteins in this insect are poorly understood. In this study, we used fluorescence competition assays to measure the binding specificities of SaveOBPs. The results showed that both SaveOBP2 and SaveOBP3 were superior to SaveOBP7 in binding green leaf volatiles. It was unexpected that SaveOBP7 bound trans-β-farnesene strongly, which was known as alarm pheromone of this species. Host volatiles were recognized much more easily by SaveOBP2, and the observed binding activity of SaveOBP2 equaled for tested green leaf volatiles. Our results imply that SaveOBP7 might play a more important role in aphid alarm pheromone discrimination.

Odorant-binding proteins (OBPs) are found in both insects and vertebrates, and it is believed that they are involved in chemical communication. In this study, we identify and express 2 OBPs from the scarab beetle, Holotrichia oblita Faldermann (Coleoptera: Scarabaeidae). HoblOBP1 shows more similarities with other scarab beetle OBPs, whereas HoblOBP2 is more diverse. N-phenyl-1-naphthylamine (1-NPN) is used as a fluorescent probe in ligand-binding experiment, and results indicate that both HoblOBPs prefer plant volatiles to putative H. oblita sex pheromones. HoblOBP1 shows binding affinity to a wider range of test compounds, but HoblOBP2 displays more specific binding affinity. Cinnamaldehyde and 2,4-di-tert-butylphenol bind to HoblOBP1 can elicit strong electrophysiological responses of the antennae from female H. oblita adults, respectively. Methyl salicylate also shows good affinity to HoblOBP2 and it can elicit moderate electrophysiological responses. Although, β-ionone is one of the ligands of the strongest binding, it elicits a weak electrophysiological response. In the immunocytochemical analysis, we observe that HoblOBP1 and HoblOBP2 are coexpressed in sensilla basiconica and placodea in both sexes.

The peritrophic membrane (PM) plays an important role in protecting insects. The PM proteins are important to determinate the formation and function of the PM. A new PM protein, named Lsti99, was identified from the PM of Loxostege sticticalis larvae by cDNA library screening. The full cDNA of Lsti99 is 1392 bp in length, contains an open reading frame (ORF) of 1245 bp that encodes a preprotein of 415 amino acid residues with a 17-amino acid signal peptide. The sequence of Lsti99 showed no homology to other known PM proteins. The recombinant Lsti99 was successfully expressed in insect cells (Sf9) using recombinant baculoviruses and was used to isolate the antibodies to Lsti99 from the polyclonal antiserum. Lsti99 was expressed mainly in the PM, but weaker bands could be detected in the head and integument as well. The Lsti99 protein could be separated from the PM complex by chitinase in vitro, but M2R did not show effect in vitro confirming the chitin-binding activity of Lsti99. The biochemical and physiological functions of Lsti99 in L. sticticalis require further investigation.

The scarab beetle Holotrichia oblita Faldermann (Coleoptera: Scarabaeidae) is a predominant underground pest in the northern parts of China, and its larvae (grubs) cause great economic losses because of its wide range of host plants and covert habitats. Environmentally friendly strategies for controlling adults would have novel and broad potential applications. One potential pest management measure is the regulation of olfactory chemoreception to control target insect pests. In the process of olfactory recognition, odorant-binding proteins (OBPs) are believed to carry hydrophobic odorants from the environment to the surface of olfactory receptor neurons. To obtain a better understanding of the relationship between OBP structures and their ligands, homology modelling and molecular docking have been conducted on the interaction between HoblOBP1 and hexyl benzoate in the present study. Based on the results, site-directed mutagenesis and binding experiments were combined to describe the binding sites of HoblOBP1 and to explore its ligand-binding mechanism. After homology modelling of HoblOBP1, it was found that the three-dimensional structure of HoblOBP1 consists of six α-helices and three disulphide bridges that connect the helices, and the hydrophobic pockets are both composed of five helices. Based on the docking study, we found that van der Waals interactions and hydrophobic interactions are both important in the bonding between HoblOBP1 and hexyl benzoate. Intramolecular residues formed the hydrogen bonds in the C terminus of the protein and the bonds are crucial for the ligand-binding specificity. Finally, MET48, ILE80 and TYR111 are binding sites predicted for HoblOBP1. Using site-directed mutagenesis and fluorescence assays, it was found that ligands could not be recognized by mutant of Tyr111. A possible explanation is that the compound could not be recognized by the mutant, and remains in the binding cavity because of the loss of the intramolecular hydrogen bonding that acts as a holder. So we believe that Tyr111 of HoblOBP1 is a key binding site. We also believe that Ile80A is a very important binding site, especially to some ligands.

It was previously thought that the odorant binding proteins (OBPs) in the sensillum lymph might serve as carriers, which could carry lipophilic odorant molecules to olfactory receptors. In this study, two novel OBP genes of the scarab beetle Holotrichia oblita were screened using an antennal cDNA library. The full cDNA of HoblOBP3 and HoblOBP4 was cloned using reverse transcription PCR and rapid amplification of the cDNA ends. Homology modeling of both OBPs was performed using SWISS-MODEL on-line tools. Next, the two OBPs were expressed in Escherichia coli and purified using Ni ion affinity chromatography. The ligand-binding properties of HoblOBP3 and HoblOBP4 in 42 ligands respectively were measured using the fluorescence probe N-phenyl-naphthylamine (1-NPN). The results obtained from competitive binding assays demonstrated that HoblOBP4 showed a broader range of binding affinities to the test compounds, while HoblOBP3 displays more specific binding affinity. Furthermore, other OBPs and CSPs were expressed in Escherichia coli and purified using Ni ion affinity chromatography. Binding curves were measured for binary mixtures of OBPs and CSPs using 1-NPN, and the Scatchard plots exhibited “J”-like nonlinear correlation trends in some samples. In addition, competitive binding assays of the HoblOBP1 and HoblOBP2 mixtures and of the HoblOBP2 and HoblOBP4 mixtures with representative compounds unexpectedly demonstrated good affinity, which revealed extreme differences that were only obtained using the individual proteins. In the immunocytochemical analysis, colocalization of HoblOBP1 and HoblOBP2, and of HoblOBP2 and HoblOBP4, was detected in the sensilla basiconica and sensilla placodea, respectively. All of these results suggested that HoblOBP1 and HoblOBP2, as well as HoblOBP2 and HoblOBP4, may serve as heterodimers in the sensillum lymph.

Odorant binding proteins play a crucial role in transporting semiochemicals across the sensillum lymph to olfactory receptors within the insect antennal sensilla. In this study, the general odorant binding protein 2 gene was cloned from the antennae of Loxostege sticticalis, using reverse transcription PCR and rapid amplification of cDNA ends. Recombinant LstiGOBP2 was expressed in Escherichia coli and purified by Ni ion affinity chromatography. Real-time PCR assays indicated that LstiGOBP2 mRNA is expressed mainly in adult antennae, with expression levels differing with developmental age. Ligand-binding experiments using N-phenyl-naphthylamine (1-NPN) as a fluorescent probe demonstrated that the LstiGOBP2 protein has binding affinity to a broad range of odorants. Most importantly, trans-11-tetradecen-1-yl acetate, the pheromone component of Loxostege sticticalis, and trans-2-hexenal and cis-3-hexen-1-ol, the most abundant plant volatiles in essential oils extracted from host plants, had high binding affinities to LstiGOBP2 and elicited strong electrophysiological responses from the antennae of adults.

We present the complete sequence of the mitochondrial genome (mitogenome) of the cotton bollworm Helicoverpa armigera. The 15,347-bp mitogenome of H. armigera was arranged in the same order described for all other sequenced lepidopterans, which differs from the most common type found in insects, due to the movement of trnM to a position 5'-upstream of trnI. The gene overlap in the H. armigera mitogenome is totally 23 bp in six locations. The H. armigera mitogenome has a total of 175 bp of intergenic spacer sequences spread over 14 regions ranging in size from 1 to 45 bp. The nucleotide composition of the whole mitogenome of H. armigera is highly A+T biased, accounting for 80.97%, with a slightly positive AT skewness and negative GC skewness, indicating the occurrence of more A than T, C more than G. The protein-encoding genes have typical mitochondrial start codons, except for cox1, which contains the unusual CGA. The cox1, cox2, and nad4 genes have incomplete stop codons (T). The lrRNA and srRNA genes are 1395 and 794-bp long, respectively. All tRNAs have a typical cloverleaf structure of mitochondrial tRNAs, except for trnS1(AGN), the dihydrouridine arm of which could not form a stable stem-loop structure. The H. armigera A+T-rich region contains a conserved structure combining the motif ATAGA and a 19-bp poly-T stretch, but absence of the 9-bp poly-A element upstream of trnM.

BACKGROUND: IPP-10 is a novel neonicotinoid insecticide recently developed in China and has good activity against sucking insects. Studies were carried out to investigate the activity of IPP-10 against Rhopalosiphum padi L. RESULTS: The results demonstrated that IPP-10 had both contact and systemic activity, including acropetal and basipetal translocation in wheat vascular bundles. Starved R. padi were allowed to stay on wheat treated with a sublethal dose of IPP-10. The results of studying their feeding behaviour from an electrical penetration graph (EPG) revealed a decrease in total time and bout duration of xylem and phloem ingestion, but the total time and bout duration of phloem salivation were significantly prolonged. The frequency (7.03 ± 0.49 Hz) of the xylem ingestion waveform produced by aphids on wheat treated with IPP-10 was significantly lower than that of blank control aphids (8.20 ± 0.30 Hz). Consequently, aphids born on wheat treated with IPP-10 were obviously lighter and less fecund than the control aphids. CONCLUSION: These tests indicated that IPP-10 had both contact and systemic activity, with sublethal effects resulting in reduction in R. padi feeding behaviour, growth rate and fecundity. Copyright © 2010 Society of Chemical Industry