Insects In General Research Articles

Protease inhibitors: recent advancement in its usage as a potential biocontrol agent for insect pest management.

Plant-derived protease inhibitors (PIs) are a promising defensin for crop improvement and insect pest management. Although agronomist made significant efforts in utilizing PIs for managing insect pests, the potentials of PIs are still obscured. Insect ability to compensate nutrient starvation induced by dietary PI feeding using different strategies, that is, overexpression of PI-sensitive protease, expression of PI-insensitive proteases, degradation of PI, has made this innumerable collection of PIs worthless. A practical challenge for agronomist is to identify potent PI candidates, to limit insect compensatory responses and to elucidate insect compensatory and resistance mechanisms activated upon herbivory. This knowledge could be further efficiently utilized to identify potential targets for RNAi-mediated pest control. These vital genes of insects could be functionally annotated using the advanced gene-editing technique, CRISPR/Cas9. Contemporary research is exploiting different in silico and modern molecular biology techniques to utilize PIs in controlling insect pests efficiently. This review is structured to update recent advancements in this field, along with its chronological background.

Pest categorisation of Aleurocanthus spp.

The Panel on Plant Health performed a pest categorisation of Aleurocanthus spp., a well‐defined insect genus of the whitefly family Aleyrodidae (Arthropoda: Hemiptera). Difficulties within the taxonomy of the genus give doubt about the ability to accurately identify some members to species level. Nevertheless, the genus is thought to currently include about ninety species mainly reported from tropical and subtropical areas. The genus is listed in Council Directive 2000/29/EC and is regulated on Citrus, Fortunella and Poncirus. Several Aleurocanthus species are highly polyphagous; Aleurocanthus spiniferus has hosts in 38 plant families; Aleurocanthus woglumi has more than 300 hosts including Pyrus, Rosa and Vitis vinifera as well as Citrus. A. spiniferus is present in the EU in restricted areas of Italy and Greece, where it is under official control. No other Aleurocanthus spp. are known to occur in the EU. Host plants for planting, excluding seeds, and cut flowers or branches are the main pathways for entry. Outside of the EU, the genus can be found in regions that have climate types which also occur within the EU, suggesting establishment is possible. Aleurocanthus spp. can be significant pests of crops that are also grown in the EU. Phytosanitary measures are available to reduce the likelihood of entry into the EU, e.g. sourcing host plants for planting from pest free areas. As a genus Aleurocanthus does satisfy all the criteria that are within the remit of EFSA to assess and required by risk managers to give it consideration as a Union quarantine pest. Aleurocanthus does not meet all of the criteria to allow it consideration by risk managers as a Union regulated non‐quarantine pest (RNQP). Specifically, Aleurocanthus is not widespread in the EU.

Description of the female and egg of Phantasca phantasma (Westwood, 1859) (Phasmatodea: Diapheromeridae: Diapheromerinae).

The neotropical genus of stick insects, Phantasca Redtenbacher, 1906, was recently revised by Hennemann et al. (2018). However, the females and eggs of several species remain unknown, including all five species recorded from Brazil. The female and egg of Phantasca phantasma (Westwood, 1859) are here described for the first time, based on material available at the Museu de Zoologia da Universidade de São Paulo, Brazil (MZSP). A set of measurements of males is also given, in addition to the measurements of the holotype presented in Hennemann et al. (2018). This complement to the description of P. phantasma is particularly important because it is the type species of the genus (designated by Zompro, 2001), therefore providing additional grounds for future taxonomic decisions involving Phantasca.

Origanum vulgare Terpenoids Induce Oxidative Stress and Reduce the Feeding Activity of Spodoptera littoralis.

Terpenoids are toxic compounds produced by plants as a defense strategy against insect herbivores. We tested the effect of Origanum vulgare terpenoids on the generalist herbivore Spodoptera littoralis and the response of the plant to herbivory. Terpenoids were analyzed by GC-FID and GC-MS and quantitative gene expression (qPCR) was evaluated on selected plant genes involved in both terpene biosynthesis. The insect detoxification response to terpenes was evaluated by monitoring antioxidant enzymes activity and expression of insect genes involved in terpene detoxification. O. vulgare terpenoid biosynthesis and gene expression was modulated by S. littoralis feeding. The herbivore-induced increased level of terpenoids (particularly carvacrol and p-cymene) interacted with the herbivore by decreasing larval survival and growth rate. The assimilation by S. littoralis of more than 50% of ingested terpenes correlated with the possible toxic effects of O. vulgare terpenoids. In choice test experiments, carvacrol and γ-terpinene mediated the larval feeding preferences, wherease the prolonged feeding on O. vulgare terpenoids (particularly on γ-terpinene) exerted relevant antinutritional effects on larvae. S. littoralis was found to react to O. vulgare terpenoids by increasing its antioxidant enzymes activities and gene expression, although this was not sufficient to sustain the toxicity of O. vulgare terpenoids.

Establishment of a high-sensitivity reporter system in mammalian cells for detecting juvenoids using juvenile hormone receptors of Daphnia pulex.

Environmental waters are polluted by various chemicals originating from human activities. Recently, the environmental risk of juvenile hormones (JHs) to aquatic microcrustaceans has been recognized by risk assessors and researchers. JH is a major arthropod hormone that regulates molting and reproduction and has analogs that have been used as insect growth regulators. JHs are known to disturb the sex determination system of Daphnia, which is a keystone animal in limnetic ecosystems and is not the target of extermination. To assess the risk of contaminant chemicals and to protect biodiversity, reliable methods for detecting such chemicals are essential. In this study, we attempted to establish a practical in vitro reporter assay system for detecting chemicals with JH activity. Using a newly constructed reporter vector (modified from the JH response element of Tribolium castaneum Krüppel homolog 1, which is a major JH responsive gene in insects), strong JH-dependent transcriptional activity (>40-fold activation) was found in Chinese hamster ovary cells that express JH receptors of Daphnia pulex. Dose-response analysis conducted on several JH and non-JH chemicals revealed that the established reporter assay system has strict specificity to JH chemicals, and the half maximum effective concentration (EC50 ) was between 10-7 and 10-9 m. These results suggest that the new system is a rapid and economical method for assessing the environmental risk of JH-active chemicals.

The regulation of three new members of the cytochrome P450 CYP6 family and their promoters in the cotton aphid Aphis gossypii by plant allelochemicals.

The expression of P450 genes in insects can be induced by plant allelochemicals. To understand the induction mechanisms, we measured the expression profiles of three P450 genes and their promoter activities under the induction of plant allelochemicals. The inducible expression of CYP6CY19 was the highest among three genes, followed by those of CYP6CY22 and CYP6DA1. The regions from -687 to +586 bp of CYP6DA1, from -666 to +140 bp of CYP6CY19 and from -530 to +218 bp of CYP6CY22 were essential for basal transcriptional activity. The cis-elements for plant allelochemicals induction were identified between -193 and +56 bp of CYP6DA1, between -157 and +140 bp of CYP6CY19 and between -108 and +218 bp of CYP6CY22. These promoter regions were found to contain a potential aryl hydrocarbon receptor element binding site with a conservative sequence motif 5'-C/TAC/ANCA/CA-3'. All these four plant allelochemicals were able to induce the expression of these P450 genes. Tannic acid had a better inductive effect than other three plant allelochemicals. Our study identified the plant allelochemical responsive cis-elements. This provides further research targets aimed at understanding the regulatory mechanisms of P450 genes expression and their interactions with plant allelochemicals in insect pests. © 2018 Society of Chemical Industry.

Molecular mechanisms influencing efficiency of RNA interference in insects.

RNA interference (RNAi) is an endogenous, sequence-specific gene-silencing mechanism elicited by small RNA molecules. RNAi is a powerful reverse genetic tool, and is currently being utilized for managing insects and viruses. Widespread implementation of RNAi-based pest management strategies is currently hindered by inefficient and highly variable results when different insect species, strains, developmental stages, tissues, and genes are targeted. Mechanistic studies have shown that double-stranded ribonucleases (dsRNases), endosomal entrapment, deficient function of the core machinery, and inadequate immune stimulation contribute to limited RNAi efficiency. However, a comprehensive understanding of the molecular mechanisms limiting RNAi efficiency remains elusive. Recent advances in dsRNA stability in physiological tissues, dsRNA internalization into cells, the composition and function of the core RNAi machinery, as well as small-interfering RNA/double-stranded RNA amplification and spreading mechanisms are reviewed to establish a global understanding of the obstacles impeding wider understanding of RNAi mechanisms in insects. © 2018 Society of Chemical Industry.

BmHpo mutation induces smaller body size and late stage larval lethality in the silkworm, Bombyx mori.

As a core member of the Hippo signaling pathway, Hpo plays a critical role in regulating growth and development. Previous studies reported that loss of function of Hpo results in increased proliferation, reduced apoptosis and induction of tissue overgrowth in Drosophila. In this study, we used CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats/Cas9) to study Hpo gene (BmHpo) function in the lepidopteran insect Bombyx mori, known commonly as the silkworm. Sequence analysis of BmHpo revealed an array of deletions in mutants. We found that BmHpo knockout resulted in defects in body size regulation, in developmental defects and pigment accumulation and early death. Our data show that BmHpo is essential for regulation of insect growth and development and that CRISPR/Cas9 technology can serve as a basis for functional analysis of target genes in lepidopteran insects.

Revision of the soft scale genus Paralecanium (Hemiptera: Coccomorpha: Coccidae) with the introduction of three new genera and twenty new species

The soft scale insect genus Paralecanium Cockerell (Hemiptera: Coccomorpha: Coccidae), mainly characterised by the possession of fan-shaped marginal setae, has never been revised and most of the species currently recognised were described in the early part of the twentieth century. The present revision is based on the morphology of the adult females and redescribes and illustrates all 34 species or subspecies previously included in the genus. These three subspecies have been raised to full specific rank, namely P. expansum javanicum (Green) to P. javanicum (Green) stat. n.; P. expansum rotundum (Green) to P. rotundum (Green) stat. n. and P. frenchii macrozamiae (Fuller) to P. macrozamiae (Fuller) stat. n. Of the remaining previously recognised species, three have been made junior synonyms: P. album Takahashi is here considered to be a junior synonym of P. metallicum (Green), syn. n.; P. angkorense Takahashi is considered to be a junior synonym ofP. cocophyllae Banks, syn. n.; and P. limbatum Green is considered to be a junior synonym of P. geometricum (Green), syn. n. Paralecanium marianum Cockerell from Brazil is clearly not closely related to Paralecanium and so a new genus, Mariacoccus Hodgson Williams gen. n., has been introduced to take it and the adult female is redescribed and illustrated; comparison of the adult female of M. marianus with that of Coccus lizeri (Fonseca) showed that the latter species is a junior synonym of M. marianus (Cockerell), syn. n. Based on the morphology of the above species and on the new species mentioned below, two new genera have been introduced: Insularicoccus Hodgson Williams gen. n. (type species P. carolinensis Beardsley), and Discochiton Hodgson Williams gen. n. (type species D. martini Hodgson, spec. n.). This brings the number of soft scale genera with fan-shaped marginal setae to three. Diagnoses of each of these 3 genera are presented, along with a key to the genera based on adult female morphology. The species that have been left in Paralecanium Cockerell are: P. calophylli (Green), P. frenchii (Maskell), P. geometricum (Green), P. hainanense Takahashi, P. machili Takahashi, P. macrozamiae (Fuller), P. maculatum Takahashi, P. marginatum (Green), P. maritimum (Green), P. minutum Takahashi, P. neomaritimum Takahashi, P. ovatum Morrison, P. pahanense Takahashi, P. peradeniyense (Green), P. planum (Green) and P. zonatum (Green). The species transferred to Discochiton as comb. n. are: P. album Takahashi, P. cocophyllae Banks, P. expansum (Green), P. javanicum (Green), P. luzonicum Cockerell, P. malainum Takahashi, P. mancum (Green), P. metallicum (Green), P. milleri Takahashi, P. pseudexpansum (Green), P. quadratum (Green), P. rotundum (Green),P. trifasciatum (Green) and P. vacuum Morrison. The only species transferred to Insularicoccus is the type species, namelyP. carolinense (Beardsley), comb. n. In addition, adult females of the following 11 new species are described and illustrated in the genus Paralecanium (as defined here) spec. n.: P. acinaces Hodgson, P. busoense Hodgson, P. claviseta Hodgson, P. comperei Hodgson, P. cypripedium Hodgson, P. elongatum Hodgson, P. leei Hodgson, P. morobeense Hodgson, P. neoguineense Hodgson, P. palawanense Hodgson and P. vacerra Hodgson. In addition, the following 8 species are described and illustrated as Discochiton spec. n.: D. browni Hodgson, D. crenulatum Hodgson, D. diplodiscus Hodgson, D. martini Hodgson, D. papillatum Hodgson, D. paucipedis Hodgson, D. sarawakense Hodgson and D. seychellarum Williams Hodgson, and 1 species of Insularicoccus is described as new and illustrated, namely I. syzygium Hodgson spec. n. Keys, based on adult female morphology, are provided for separation of all the species in each genus. As part of this revision, the morphological characters used to diagnose species in this group of genera are re-evaluated and a number of new characters found; greater emphasis has been placed on some character-states, so the basic morphology of this group of genera is also described. Lectotypes have been designated for 22 species, namely: Lecanium calophylli Green; L. expansum Green; L. expansum javanicum Green; L. expansum metallicum Green; L. expansum rotundum Green; rotundum Green; L. geometricum Green; L. limbatum Green; L. mancum Green; L. marginatum Green; L. maritimum Green; L. peradeniyense Green; L. planum Green; L. pseudexpansum Green; L. quadratum Green; L. trifasciatum Green and L. zonatum Green. Also: Paralecanium album Takahashi; P. hainanense Takahashi; P. malianum Takahashi; P. marianum Cockerell; P. neomaritimum Takahashi and P. vacuum Morrison. Finally, an example of the first-instar nymphs, second-instar males and second/third instar females of both Paralecanium and Discochiton are described and illustrated and compared with those already known in the tribe Paralecaniini.

Progress in innate immunity-related genes in insects

Insects have evolved a strong innate immune system to defense pathogens and adverse conditions. Insect innate immune system comprises of humoral immunity and cellular immunity. Humoral immunity mainly includes three signaling pathways, i.e., Toll, IMD and JAK/STAT, by which signal transduction and immune pathways regulate expression of immune-related genes and activate antimicrobial peptides and other effectors. Cellular immunity contains phagocytosis, encapsulation and nodulation of pathogens, which is mediated by hemolymph cells. In recent years, with the rapid development of insect genomics, a large number of immune-related genes have been characterized from insect genome data using bioinformatic methods. Studies on these genes have significantly deepened the understanding of molecular mechanisms of insect innate immune system. Insect immune-related genes can be divided into seven categories by gene functions: recognition, signaling transduction, modulator, effectors, melanization, RNA interference and other genes. The humoral immunity and cellular immunity are regulated by the interactions among these immune-related genes. In this review, we summarize the classification, function and evolution of insect immune-related genes, and propose future research directions of insect innate immunity, which will be helpful for understanding molecular mechanisms of insect innate immune system and developing new strategies for controlling pest insects.

Host-mediated RNA interference targeting acuticular protein gene impaired fecundity inthe green peach aphid Myzus persicae.

The green peach aphid (Myzus persicae) is a devastating sap-sucking insect pest that damages many host plants worldwide and causes billions of dollars of crop losses. Induction of RNA interference (RNAi) through oral feeding of small interfering RNA (siRNA) has been demonstrated in aphids. Therefore, host-mediated delivery of double-stranded RNA (dsRNA) specific to vital structural genes of aphids has been envisaged as a tool for the development of resistance against this aphid species. Cuticular protein (CP) senses seasonal photoperiodism and drives a shift from clonal to sexual generation in aphids. Thus, attenuation of CP gene expression is likely to result in a different reproductive orientation in aphids and thereby affect their fecundity. A gene encoding CP in M. persicae has been targeted for RNAi-mediated knockdown. Transgenic Arabidopsis expressing dsRNA homologous to the MyCP gene was developed. The dsRNA-transgenics produced gene-specific siRNAs fed by aphids infesting the transgenics. A reverse transcription-quantitative polymerase chain reaction (RT-qPCR) study revealed an attenuated level of transcripts of the CP gene in aphid nymphs reared on the transgenic plants. Decreased expression of the CP gene resulted in a noticeable decline in aphid fecundity on the transgenic Arabidopsis plants. Increasing genetic resistance is the only sustainable way of minimizing the use of toxic agrochemicals to protect plants. Host-mediated RNAi of important insect genes has been proposed as a potential avenue for developing crop resistance against insect pests. This study demonstrated the potential of MyCP dsRNA in developing RNAi-based resistance to M. persicae. RNAi-mediated resistance is expected to be more durable compared with other transgenic strategies. © 2018 Society of Chemical Industry.

Identification of four heat shock protein genes and their expression in response to thermal stress in two strains of Neoseiulus barkeri (Acari: Phytoseiidae)

To explore the effects of heat shock proteins in the conventional strain (CS) and high temperature-adapted strain (HTAS) of Neoseiulus barkeri, we cloned and characterized the cDNA of the NbHsp40, NbHsp60, NbHsp70, and NbHsp90 genes and examined changes in expression levels with short-term exposure to heat or cold stress. All four of the genes showed highly conserved amino acid sequences and high homology to Galendromus occidentalis and N. cucumeris. Phylogenetic analysis of NbHsps indicated a high consistency with the known genes of model insects. These results demonstrate variations in the sensitivity of NbHsps to heat or cold stress; i.e., the expression of NbHsp60 did not change with the application of heat and cold stress, NbHsp90 and NbHsp40 were upregulated at high temperature compared to that at low temperature responses, and the expression of NbHsp70 increased with both heat and cold stress. Hsp expression also differed between the two strains: The application of a 40°C heat shock resulted in a decrease in the expression of NbHsp40/70/90 in the CS within 1–2 h, but increased in the HTAS strain in 2 h. However, exposure to cold stress (0 °C and 5 °C) did not result in distinct changes in the expression of NbHsps in the CS, but a significant decrease in the HTAS. The expression of NbHsps further demonstrates that the HTAS has been acclimated to high temperatures. The results also determine that heat acclimation decreases cold tolerance in HTAS mites. This study reveals differences in the characteristics of heat and cold tolerance between the two strains of N. barkeri and provides useful information for future commercialization of N. barkeri for pest biological control, particularly the HTAS. Furthermore, it also describes high heat tolerance in HTAS at the molecular level.

Phylogeny and evolution of the cholesterol transporter NPC1 in insects

Sterols are essential nutrients for eukaryotes. Insects are obligate sterol auxotrophs and must acquire this key nutrient from their diets. The digestive tract is the organ for absorbing nutrients as well as sterols from food. In mice, the Niemann-Pick type C1 Like 1 (NPC1L1) gene is highly expressed in the intestine and is critical for cholesterol absorption. In contrast, the molecular mechanisms for the absorption of dietary sterols in insects have not been well studied. We annotated NPC1 genes in 39 insects from 10 orders using available genomic and transcriptomic information and inferred phylogenetic relationships. Insect NPC1 genes were grouped into two sister-clades, NPC1a and NPC1b, suggesting a likely duplication in the ancestor of insects. The former exhibited weaker gut-biased expression or a complete lack of tissue-biased expression, depending on the species, while the latter was highly enriched in the gut of three lepidopteran species. This result is similar to previous findings in Drosophila melanogaster. In insects, NPC1a accumulated non-synonymous substitutions at a lower rate than NPC1b. This pattern was consistent across orders, indicating that NPC1a evolved under stronger molecular constraint than NPC1b.

Mode of action of nanoparticles against insects.

The employment of nanoparticles obtained through various synthesis routes as novel pesticides recently attracted high research attention. An impressive number of studies have been conducted to test their toxic potential against a wide number of arthropod pests and vectors, with major emphasis on mosquitoes and ticks. However, precise information on the mechanisms of action of nanoparticles against insects and mites are limited, with the noteworthy exception of silica, alumina, silver, and graphene oxide nanoparticles on insects, while no information is available for mites. Here, I summarize current knowledge about the mechanisms of action of nanoparticles against insects. Both silver and graphene oxide nanoparticles have a significant impact on insect antioxidant and detoxifying enzymes, leading to oxidative stress and cell death. Ag nanoparticles also reduced acetylcholinesterase activity, while polystyrene nanoparticles inhibited CYP450 isoenzymes. Au nanoparticles can act as trypsin inhibitors and disrupt development and reproduction. Metal nanoparticles can bind to S and P in proteins and nucleic acids, respectively, leading to a decrease in membrane permeability, therefore to organelle and enzyme denaturation, followed by cell death. Besides, Ag nanoparticles up- and downregulate key insect genes, reducing protein synthesis and gonadotrophin release, leading to developmental damages and reproductive failure. The toxicity of SiO2 and Al2O3 nanoparticles is due to their binding to the insect cuticle, followed by physico-sorption of waxes and lipids, leading to insect dehydration. In the final section, insect nanotoxicology research trends are critically discussed, outlining major challenges to predict the ecotoxicological consequences arising from the real-world use of nanoparticles as pesticides.

DNA barcodes successfully delimit morphospecies in a superdiverse insect genus

Polypedilum Kieffer (Diptera: Chironomidae), with 520 currently known species worldwide, can be extremely difficult to identify species level based on the morphology. We used 3,670 cytochrome c oxidase subunit I (COI) barcodes to explore the efficiency of the COI barcodes to differentiate between species in a superdiverse aquatic insect genus. The Barcode of Life Data System (BOLD) presented 286 BIN clusters in Polypedilum, representing 163 morphospecies, of which 93 were contributed from our laboratory. Molecular operational taxonomic units (OTUs) ranged from 158 to 345, based on Automatic Barcode Gap Discovery (ABGD), the Barcode Index Number (BIN), Bayesian Poisson tree processes (bPTP), generalized mixed Yule coalescent (GMYC), jMOTU, multi‐rate Poisson tree processes (mPTP), neighbor‐joining (NJ) tree and prethreshold clustering. In comparison, GMYC, bPTP, mPTP and BIN suggested more species than warranted by morphology, while ABGD, jMOTU, NJ, prethreshold clustering and ABGD yielded a conservative number of species when setting higher thresholds. Nine species complexes with deep intraspecific divergences indicated 18 potentially cryptic species, which require further taxonomic research including complete life histories and nuclear genetic data to be resolved. The discrimination of Polypedilum species by DNA barcodes proved to be successful in 94.4% of all studied morphological species.

Transgenic soybean plants expressing Spb18S dsRNA exhibit enhanced resistance to the soybean pod borer Leguminivora glycinivorella (Lepidoptera: Olethreutidae).

The soybean pod borer [SPB; Leguminivora glycinivorella (Mats.) Obraztsov] is a major soybean pest in northeastern Asia. A useful method for addressing this problem is the generation of transgenic plants producing double-stranded RNA (dsRNA) that target essential insect genes. In this study, we confirmed that 18S ribosomal RNA is critical for SPB development. Downregulated Spb18S expression induced by dsRNA injection increased larval mortality rates and resulted in early pupation. We also assessed whether Spb18S is silenced in SPB larvae fed on transgenic soybean expressing Spb18S dsRNA. Transgenic plants downregulated Spb18S expression levels and second-instar larval survival rates. Moreover, such plants were less damaged by SPB larvae than control plants under field conditions.

Signatures of DNA Methylation across Insects Suggest Reduced DNA Methylation Levels in Holometabola.

It has been experimentally shown that DNA methylation is involved in the regulation of gene expression and the silencing of transposable element activity in eukaryotes. The variable levels of DNA methylation among different insect species indicate an evolutionarily flexible role of DNA methylation in insects, which due to a lack of comparative data is not yet well-substantiated. Here, we use computational methods to trace signatures of DNA methylation across insects by analyzing transcriptomic and genomic sequence data from all currently recognized insect orders. We conclude that: 1) a functional methylation system relying exclusively on DNA methyltransferase 1 is widespread across insects. 2) DNA methylation has potentially been lost or extremely reduced in species belonging to springtails (Collembola), flies and relatives (Diptera), and twisted-winged parasites (Strepsiptera). 3) Holometabolous insects display signs of reduced DNA methylation levels in protein-coding sequences compared with hemimetabolous insects. 4) Evolutionarily conserved insect genes associated with housekeeping functions tend to display signs of heavier DNA methylation in comparison to the genomic/transcriptomic background. With this comparative study, we provide the much needed basis for experimental and detailed comparative analyses required to gain a deeper understanding on the evolution and function of DNA methylation in insects.

Targeting symbiosis-related insect genes by RNAi in the pea aphid-Buchnera symbiosis

The growth and reproduction of phloem sap-feeding insects requires the sustained function of intracellular bacteria localized in specialized cells known as bacteriocytes, giving the potential to target the bacterial symbiosis as a novel strategy for controlling sap-feeding insect pests. We focused on two genes in the pea aphid Acyrthosiphon pisum, amiD and ldcA1, which were acquired horizontally from bacteria and have the annotated function to degrade immunogenic bacterial peptidoglycan. We hypothesized that AmiD and LdcA1 function to eliminate peptidoglycan fragments released by the bacterial symbiont Buchnera inhabiting the bacteriocytes, thereby protecting the Buchnera from host attack. Consistent with this hypothesis, expression of amiD and ldcA1 was enriched in bacteriocytes and varied significantly with aphid age, conforming to an inverse curvilinear relationship for amiD and negative linear relationship for ldcA1. RNAi against amiD and ldcA1 administered orally to larval pea aphids caused a significant reduction in Buchnera abundance and activity, accompanied by depressed aphid growth rates. For RNAi experiments, the aphids were co-administered with dsRNA against an aphid nuclease nuc1, protecting the dsRNA against non-specific degradation. These experiments demonstrate that selective suppression of insect symbiosis-related gene function can reduce the performance of an insect pest. Phylogenetic analysis identified amiD and ldcA1 in sequenced genomes of other aphid species, and amiD in related groups of phloem-feeding insects, offering the opportunity for specific controls against a range of insect pests.

Improved insect-proofing: expressing double-stranded RNA in chloroplasts.

RNA interference (RNAi) was discovered almost 20 years ago and has been exploited worldwide to silence genes in plants and animals. A decade later, it was found that transforming plants with an RNAi construct targeting an insect gene could protect the plant against feeding by that insect. Production of double‐stranded RNA (dsRNA) in a plant to affect the viability of a herbivorous animal is termed trans‐kingdom RNAi (TK‐RNAi). Since this pioneering work, there have been many further examples of successful TK‐RNAi, but also reports of failed attempts and unrepeatable experiments. Recently, three laboratories have shown that producing dsRNA in a plant's chloroplast, rather than in its cellular cytoplasm, is a very effective way of delivering TK‐RNAi. Our review examines this potentially game‐changing approach and compares it with other transgenic insect‐proofing schemes. © 2018 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Factors Affecting Synonymous Codon Usage of Housekeeping Genes in drosophila Melanogaster

Housekeeping genes (HK genes) are required for cell survival and the maintenance of basic cellular functions. The investigation of factors affecting codon usage patterns in HK genes of insects can help in understanding the molecular evolution of insects and aid the development of insect pest management strategies. In this study, we employed bioinformatics approaches to analyze the codon usage bias (CUB) of HK genes in the insect model organism, Drosophila melanogaster. A comparison of CUB between 1107 HK genes and 1084 high tissue specifcity genes suggested that HK genes have higher CUB in D. melanogaster. In addition, we found that CUB inversely correlates with the non-synonymous substitution rate of HK genes. Therefore, we attempted to identify the factors that potentially infuence the codon usage pattern of HK genes. Our results suggest that mutation pressure and natural selection highly correlate with CUB in the HK genes of D. melanogaster and that two topological properties of HK proteins (proportion of protein interacting length and protein connectivity) also correlate with CUB in the HK genes of D. melanogaster. This study provides insight into CUB in the HK genes of D. melanogaster, and the results can support future investigations of potential applications in agricultural and biomedical feld.