Insect Detoxification Research Articles

Impact of the insect gut microbiota on ecology, evolution, and industry.

Insects harbor diverse microorganisms in the gut, providing their host with physiological and ecological advantages. For example, gut symbionts contribute to detoxification in phytophagous insects, degradation of lignocellulose in xylophagous insects, and in many insects, protection from pathogens by producing antimicrobial compounds. Furthermore, an unexpected function of the insect gut microbiota has been discovered-plastic degradation. Based on these diverse abilities of the insect gut microbiota that have been sophisticated under the natural environment, recent studies have aimed at applying the potential of gut microbes in the medical, engineering, and industrial fields.

Transcriptome analysis reveals gene expression changes of the fat body of silkworm (Bombyx mori L.) in response to selenium treatment.

A comparative transcriptome analysis was conducted to investigate the gene expression changes in the fat body of silkworm after treatment with different concentrations (50μM and 200μM) of selenium (Se). 912 differential expression genes (DEGs) (371 up-regulated and 541 down-regulated) and 1420 DEGs (1078 up-regulated and 342 down-regulated) were identified in silkworm fat body treated with 50μM and 200μM of Se, respectively. In case of 50μM group, DEGs were mainly enriched in the peroxisome pathway and fatty acid metabolism pathway, and later were associated with antioxidant defense and nutrition regulation. After 200μM Se-treatment, DEGs were mainly located in the glycerolipid metabolism and arachidonic acid metabolism pathways, which further encoded detoxification related genes. Furthermore, 32 candidate DEGs from these pathways had been selected to confirm the RNA-seq data. Among these DEGs, 14 genes were up-regulated in the 50μM Se-treated group (only three genes in the 200μM Se-treated group) which were involved in lipid metabolism and antioxidant defense, and 13 up-regulated genes (only two genes were up-regulated in the 50μM Se-treated group) were involved in detoxification of the 200μM Se-treated group. These changes showed that lower concentration of Se could regulate the nutrition and promote antioxidation pathways; whereas, high levels of Se promoted the detoxification of silkworm. These findings can be helpful to understand the possible mechanisms of Se action and detoxification in silkworm and other insects.

Transcriptomics of monarch butterflies (Danaus plexippus) reveals that toxic host plants alter expression of detoxification genes and down-regulate a small number of immune genes.

Herbivorous insects have evolved many mechanisms to overcome plant chemical defences, including detoxification and sequestration. Herbivores may also use toxic plants to reduce parasite infection. Plant toxins could directly interfere with parasites or could enhance endogenous immunity. Alternatively, plant toxins could favour down-regulation of endogenous immunity by providing an alternative (exogenous) defence against parasitism. However, studies on genomewide transcriptomic responses to plant defences and the interplay between plant toxicity and parasite infection remain rare. Monarch butterflies (Danaus plexippus) are specialist herbivores of milkweeds (Asclepias spp.), which contain toxic cardenolides. Monarchs have adapted to cardenolides through multiple resistance mechanisms and can sequester cardenolides to defend against bird predators. In addition, high-cardenolide milkweeds confer monarch resistance to a specialist protozoan parasite (Ophryocystis elektroscirrha). We used this system to study the interplay between the effects of plant toxicity and parasite infection on global gene expression. We compared transcriptional profiles between parasite-infected and uninfected monarch larvae reared on two milkweed species. Our results demonstrate that monarch differentially express several hundred genes when feeding on A.curassavica and A.incarnata, two species that differ substantially in cardenolide concentrations. These differentially expressed genes include genes within multiple families of canonical insect detoxification genes, suggesting that they play a role in monarch toxin resistance and sequestration. Interestingly, we found little transcriptional response to infection. However, parasite growth was reduced in monarchs reared on A.curassavica, and in these monarchs, several immune genes were down-regulated, consistent with the hypothesis that medicinal plants can reduce reliance on endogenous immunity.

Insect genomes: progress and challenges.

In the wake of constant improvements in sequencing technologies, numerous insect genomes have been sequenced. Currently, 1219 insect genome-sequencing projects have been registered with the National Center for Biotechnology Information, including 401 that have genome assemblies and 155 with an official gene set of annotated protein-coding genes. Comparative genomics analysis showed that the expansion or contraction of gene families was associated with well-studied physiological traits such as immune system, metabolic detoxification, parasitism and polyphagy in insects. Here, we summarize the progress of insect genome sequencing, with an emphasis on how this impacts research on pest control. We begin with a brief introduction to the basic concepts of genome assembly, annotation and metrics for evaluating the quality of draft assemblies. We then provide an overview of genome information for numerous insect species, highlighting examples from prominent model organisms, agricultural pests and disease vectors. We also introduce the major insect genome databases. The increasing availability of insect genomic resources is beneficial for developing alternative pest control methods. However, many opportunities remain for developing data-mining tools that make maximal use of the available insect genome resources. Although rapid progress has been achieved, many challenges remain in the field of insect genomics.

Expression and functional analysis of P450 gene induced tolerance/resistance to lambda-cyhalothrin in quercetin fed larvae of beet armyworm Spodoptera exigua (Hübner).

Beet armyworm, Spodoptera exigua (Hübner) is an agronomical important and most devastating polyphagous pest that damages a variety of crops around the globe including China. Quercetin is one of the abundant dietary flavonoids and the important defense allelochemicals in plants. Therefore, the changes in insect detoxification enzymes activities in response to plants allelochemicals may result increased the sensitivity to insecticides. In this study, we examined the induced effect of quercetin on larval tolerance to lambda-cyhalothrin in S. exigua. Application of cytochrome P450 inhibitor piperonyl butoxide (PBO) significantly synergized the lambda-cyhalothrin toxicity in quercetin-fed S. exigua larvae. Moreover, larval weight significantly reduced in quercetin, lambda-cyhalothrin, and quercetin + lambda-cyhalothrin treatment. Furthermore, our results showed that the P450 detoxification enzyme effectively increased in all treatments as compared to the control. Quantitative Real-time PCR analysis revealed that expression level of CYP6AE10 significantly upregulated in larvae treated with quercetin, lambda-cyhalothrin and quercetin + lambda-cyhalothrin in the midgut and fat body respectively. In addition, RNAi mediated knockdown of CYP6AE10 in S. exigua larvae significantly decreased the transcription level of target cytochrome P450 gene followed by the exposure with quercetin, lambda-cyhalothrin, and quercetin + lambda-cyhalothrin. Similarly, the knockdown of CYP6AE10 by the injection of dsRNA led to increased mortality after the treatment with respective chemicals. Overall, these data showed that P450s might possibly play an important role in the metabolic adaptation of S. exigua larvae to its host plant defense allelochemicals as well as insecticides. In conclusion, S. exigua can take benefit from its host plant’s secondary metabolites to elaborate its defense against synthetic insecticides.

Assessment of bioaccumulation and detoxification of cadmium in soil-plant-insect food chain

The present study investigated the accumulation of Cd (II) and its transfer through the soil-plant (Ricinus communis L.) - insect (Samia ricini Donovan) terrestrial food web and detoxification mechanisms involved. Cd accumulation in R. communis L. followed the order: roots ˃ stems ˃ leaves. With the increase in Cd concentration in plant, increase in Cd accumulation in larvae was observed. Transfer of Cd (II) was highest from soil to root followed by larvae to excreta, root to leaf and leaf to larvae. Sub-cellular partitioning of Cd was performed in the larval bodies to determine possible detoxification strategies by the insect larvae. Heat stable protein was found to be the dominant metal-binding compartment of Cd. The results revealed a dose dependent increase in Cd (II) concentration along food chain. The excretion pattern of Cd by the silkworm larvae and sub-cellular distribution showed sequestration of Cd feeding on Cd treated R. communis leaves.

Dietary Stress From Plant Secondary Metabolites Contributes to Grasshopper (Oedaleus asiaticus) Migration or Plague by Regulating Insect Insulin-Like Signaling Pathway.

Diets essentially affect the ecological distribution of insects, and may contribute to or even accelerate pest plague outbreaks. The grasshopper, Oedaleus asiaticus B-Bienko (OA), is a persistent pest occurring in northern Asian grasslands. Migration and plague of this grasshopper is tightly related to two specific food plants, Stipa krylovii Roshev and Leymus chinensis (Trin.) Tzvel. However, how these diets regulate and contribute to plague is not clearly understood. Ecological studies have shown that L. chinensis is detrimental to OA growth due to the presence of high secondary metabolites, and that S. krylovii is beneficial because of the low levels of secondary metabolites. Moreover, in field habitats consisting mainly of these two grasses, OA density has negative correlation to high secondary metabolites and a positive correlation to nutrition content for high energy demand. These two grasses act as a ‘push-pull,’ thus enabling the grasshopper plague. Molecular analysis showed that gene expression and protein phosphorylation level of the IGF → FOXO cascade in the insulin-like signaling pathway (ILP) of OA negatively correlated to dietary secondary metabolites. High secondary metabolites in L. chinensis down-regulates the ILP pathway that generally is detrimental to insect survival and growth, and benefits insect detoxification with high energy cost. The changed ILP could explain the poor growth of grasshoppers and fewer distributions in the presence of L. chinensis. Plants can substantially affect grasshopper gene expression, protein function, growth, and ecological distribution. Down-regulation of grasshopper ILP due to diet stress caused by high secondary metabolites containing plants, such as L. chinensis, results in poor grasshopper growth and consequently drives grasshopper migration to preferable diet, such as S. krylovii, thus contributing to grasshopper plague outbreaks.

Two delta class glutathione S-transferases involved in the detoxification of malathion in Bactrocera dorsalis (Hendel).

The oriental fruit fly Bactrocera dorsalis (Hendel), a widespread agricultural pest, has evolved resistance to many insecticides, including organophosphorus compounds. Glutathione S-transferases (GSTs) are involved in xenobiotic detoxification and insecticide resistance in many insects. However, the role of delta class GSTs in detoxifying malathion in B. dorsalis is unknown. Here, we evaluated the roles of two delta class GSTs in malathion detoxification in this species. Two delta class GSTs genes, BdGSTd1 and BdGSTd10, were characterized in B. dorsalis. They were highly expressed in 5-day-old adults, as well as in midgut and Malpighian tubules. Upon malathion exposure, the two genes were upregulated by 2.63- and 2.85-fold, respectively. Injection of double-stranded RNA targeting BdGSTd1 or BdGSTd10 significantly reduced their mRNA levels in adults and also significantly increased adult susceptibility to malathion. The expression of these two GSTs in Escherichia coli helped the host to endure malathion stress at a concentration of 10µg mL-1 according to a Cell Counting Kit-8 assay. High-performance liquid chromatography analyses indicated that malathion could be significantly depleted by the two delta GSTs. The role of BdGSTd10 in malathion sequestration was also discussed. BdGSTd1 and BdGSTd10 play important roles in the detoxification of malathion in B. dorsalis. © 2019 Society of Chemical Industry.

Role of PTP/PTK trans activated insulin-like signalling pathway in regulation of grasshopper (Oedaleus asiaticus) development.

Protein tyrosine phosphatase (PTPs) and protein tyrosine kinase (PTKs) genes are responsible for the regulation of insect insulin-like pathway (ILP), cells growth, metabolism initiation, gene transcription and observing immune response. Signal transduction in insect cell is also associated with PTPs and PTKs. The grasshopper (Oedaleus asiaticus) 'Bey-Bienko' were treated withdsRNA of protein tyrosine non-receptor type 4 (PTPN4) and protein tyrosine kinase 5 (PTK5) along with control (water). Applying dsPTK5 treatments in 5th instar of Oedaleus asiaticus, significant reduction was recorded in body dry mass, growth rate and overall performance except survival rate. Whereas with PTPN4, no such significant impact on all of these growth parameters was recorded. Expression of genes in ILP 5th instar of Oedaleus asiaticus by the application of dsPTPN4 and dsPTK5 revealed that PTK, INSR (insulin receptor), IRS (insulin receptor substrate), PI3K (phosphoinositide 3-kinase), PDK (3-phosphoinositide-dependent protein kinase), Akt (protein kinase B) and FOXO (forkhead transcription factor) significantly expressed with downregulation except PTPN4, which remained non-significant. On the other hand, the phosphorylation level of ILP four proteins in O. asiaticus with the treatment of dsPTPN4 and dsPTK5 significantly affected P-IRS and P-FOXO, while P-INSR and P-AKT remained stable at the probability level of 5%. This indicated that the stress response in the O. asiaticus insulin-like signalling pathway (ILP) reduced. Regarding association of protective enzymatic activities, ROS (relative oxygen species), CAT (catalase) and PO (phenol oxidase) increased significantly with exposure to dsPTK5 as compared to dsPTPN4 and control, while exposure of 5th instar of O. asiaticus to dsPTPN4 treatment slightly raised CAT and PO activities with but significant contribution. No such significant effect on MFO and POD was seen using dsPTPN4 and dsPTK5. This showed that in the ILP of O. asiaticus, PTK5 was detrimental to growth, body mass and overall performance, which ultimately benefited insect detoxification with high-energy cost.

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.

The molecular genetic basis of herbivory between butterflies and their host plants

Interactions between herbivorous insects and their host plants are a central component of terrestrial food webs and a critical topic in agriculture, where a substantial fraction of potential crop yield is lost annually to pests. Important insights into plant–insect interactions have come from research on specific plant defences and insect detoxification mechanisms. Yet, much remains unknown about the molecular mechanisms that mediate plant–insect interactions. Here we use multiple genome-wide approaches to map the molecular basis of herbivory from both plant and insect perspectives, focusing on butterflies and their larval host plants. Parallel genome-wide association studies in the cabbage white butterfly, Pieris rapae, and its host plant, Arabidopsis thaliana, pinpointed a small number of butterfly and plant genes that influenced herbivory. These genes, along with much of the genome, were regulated in a dynamic way over the time course of the feeding interaction. Comparative analyses, including diverse butterfly/plant systems, showed a variety of genome-wide responses to herbivory, as well as a core set of highly conserved genes in butterflies as well as their host plants. These results greatly expand our understanding of the genomic causes and evolutionary consequences of ecological interactions across two of nature’s most diverse taxa, butterflies and flowering plants.

Cloning and Functional Analysis of CncC and Keap1 Genes in Silkworm.

CncC/keap1-ARE is an important signaling pathway for detoxification and antioxidation in Diptera and Coleoptera insects. However, such a signaling pathway has not been studied in Bombyx mori. In this study, BmCncC and Bmkeap1 genes were cloned, their amino acid sequences were analyzed, and each functional domain was mapped. Through phylogenetic analysis and sequence comparison among multiple species, we found that the Neh1 motif of CncC was highly conserved and the DLG motif was replaced by the DMG motif in Neh2. Conformational analysis showed that Neh1 of BmCncC forms a hairpin structure to bind DNA. The DGR region of Bmkeap1 contained abundant β sheets, which was involved in the recognition of Neh2. The transcription and expression analyses showed that both BmCncC and Bmkeap1 were highly expressed in the first instar larvae, and these two genes were expressed at a high level in the reproductive gland, fat body, and head. The transcriptional and expression levels of Akt and BmCncC in the fat body were significantly upregulated, and the expression of Bmkeap1 was downregulated after the phoxim treatment in silkworm. The transcriptional levels of CncC-regulated detoxification enzymes GST, cyp4M5, cyp6AE2, and cyp9G3 were increased by 4.026-, 5.246-, 3.821-, and 9.787-fold, respectively, while the activities of GST and CYP450 were increased by 1.521- and 1.231-fold, respectively, after phoxim treatment. These results indicated that the BmCncC/Bmkeap1 signaling pathway was activated by phoxim, leading to the expression of downstream detoxifying enzymes and detoxification of phoxim in silkworm.

Cytochrome P450 diversification and hostplant utilization patterns in specialist and generalist moths: Birth, death and adaptation.

Across insect genomes, the size of the cytochrome P450 monooxygenase (CYP) gene superfamily varies widely. CYPome size variation has been attributed to reciprocal adaptive radiations in insect detoxification genes in response to plant biosynthetic gene radiations driven by co-evolution between herbivores and their chemically defended hostplants. Alternatively, variation in CYPome size may be due to random "birth-and-death" processes, whereby exponential increase via gene duplications is limited by random decay via gene death or transition via divergence. We examined CYPome diversification in the genomes of seven Lepidoptera species varying in host breadth from monophagous (Bombyx mori) to highly polyphagous (Amyelois transitella). CYPome size largely reflects the size of Clan 3, the clan associated with xenobiotic detoxification, and to some extent phylogenetic age. Consistently across genomes, families CYP6, CYP9 and CYP321 are most diverse and CYP6AB, CYP6AE, CYP6B, CYP9A and CYP9G are most diverse among subfamilies. Higher gene number in subfamilies is due to duplications occurring primarily after speciation and specialization ("P450 blooms"), and the genes are arranged in clusters, indicative of active duplicating loci. In the parsnip webworm, Depressaria pastinacella, gene expression levels in large subfamilies are high relative to smaller subfamilies. Functional and phylogenetic data suggest a correlation between highly dynamic loci (reflective of extensive gene duplication, functionalization and in some cases loss) and the ability of enzymes encoded by these genes to metabolize hostplant defences, consistent with an adaptive, nonrandom process driven by ecological interactions.

Determination of the protein expression profiles of Propsilocerus akamusi (Tokunaga) Malpighian tubules response to cadmium stress by iTRAQ coupled LC–MS/MS

Propsilocerus akamusi (Tokunaga) is an important prey species for fish and aquatic birds, which represent an important link in the aquatic food chain as other species of Chironomidae. Malpighian tubules (MT) play an important role in metabolism and detoxification of harmful compounds and metal accumulation. Our previous studies have reported that P. akamusi have an extraordinary resistance to Cd. In this paper, iTRAQ-based proteomics technology was first used to study the differential proteomics of MT of Propsilocerus akamusi under sublethal Cd stress for different time courses. 118 differential expressed proteins (DEPs) were identified through LC–MS/MS and further classified into 26 GO functional groups. Our results showed that metabolic process was the main biological functional categories. Cluster of orthologous groups of proteins (COG) analysis was also performed based on the number of unique proteins identified in each functional category, 21 metabolism-related DEPs were identified. P. akamusi adapted to Cd stress mainly by inducing the processes of lipid metabolism of MT and lipid may play a possible protection role in cadmium resistance in MT. The results provide important information for research on molecular mechanisms of Cd-stress adaption in Malpighian tubules of P. akamusi. Biological significancePropsilocerus akamusi (old species name: Tokunagayusurika akamusi) is an important prey species for fish and aquatic birds, which represent an important link in the aquatic food web as other species of Chironomidae. Malpighian tubules constitute a versatile organ which is able to exert excretory of chemical compounds, acting in the insect metabolism and detoxification of harmful compounds and metal accumulation. Our previous studies have reported that P. akamusi have an extraordinary resistance to Cd. However, up to now, there has been a lack of research on the molecular mechanisms of adaption to Cd stress in the Malpighian tubules of this species. Study on the adaptive mechanisms to Cd stress in Malpighian tubules of Propsilocerus akamusi through comparative proteome analysis is one important way to solve this problem. The aim of the present study was to understand the molecular mechanisms of adaption of the Malpighian tubules of P. akamusi exposed to Cd stress and assess the high expression of proteins involved in cellular adaptation to Cd stress. This will provide information about how this organ is responding to disturbances of contaminated ecosystems.

Laboratory evaluation of insecticidal activity of plant essential oils against the vine mealybug, "Planococcus ficus"

Planococcus ficus is a principal mealybug pest of vineyards worldwide. Minthostachys verticillata and Eucalyptus globulus essential oils (EO) were evaluated as insecticidal products on P. ficus , and the main components of M. verticillata and E. globulus EO were also tested as insecticidal compounds against vine mealybug females under laboratory conditions. The results revealed that M. verticillata EO was more toxic than E. globulus EO, while pulegone (LC50 39.60 µL/L) was more toxic than the other constituents of the EO studied. Menthofuran, an oxidation product of pulegone by cytochrome P450 enzymes, showed an LC50 value of 63.97 µL/L. Thus, the mechanism of insect detoxification did not reduce the toxic potential of the pulegone. In addition, 1,8-cineole had a higher insecticidal property than its isomer 1,4-cineole. Our studies suggest that the pulegone can be a useful fumigant botanical insecticide to protect crops against vine mealybug attacks.

P450-mediated detoxification of botanicals in insects

In recent years, botanical insecticides have gradually replaced the traditional synthetic insecticides, with the properties of strong pertinence and environment friendly. Many new botanical insecticides are developed and used, meanwhile insect develop its resistance to these insecticides. Previous studies have proved that Cytochrome P450 monooxygenases (CYPs) play a critical role in insect detoxification. Genomic and proteomic approaches focused on P450 expression and regulation at the transcript and protein levels have made substantial progress. The review covers the recent years’ research of typical botanicals metabolism mediated by CYPs, the relationship between function and structural characters of P450 enzymes, as well as the expression and regulation of related P450 genes in botanicals metabolism.

Gossypol toxicity and detoxification in Helicoverpa armigera and Heliothis virescens

Gossypol is a polyphenolic secondary metabolite produced by cotton plants, which is toxic to many organisms. Gossypol's aldehyde groups are especially reactive, forming Schiff bases with amino acids of proteins and cross-linking them, inhibiting enzyme activities and contributing to toxicity. Very little is known about gossypol's mode of action and its detoxification in cotton-feeding insects that can tolerate certain concentrations of this compound. Here, we tested the toxicity of gossypol and a gossypol derivative lacking free aldehyde groups (SB-gossypol) toward Helicoverpa armigera and Heliothis virescens, two important pests on cotton plants. Larval feeding studies with these two species on artificial diet supplemented with gossypol or SB-gossypol revealed no detectable toxicity of gossypol, when the aldehyde groups were absent. A cytochrome P450 enzyme, CYP6AE14, is upregulated in H. armigera feeding on gossypol, and has been claimed to directly detoxify gossypol. However, using in vitro assays with heterologously expressed CYP6AE14, no metabolites of gossypol were detected, and further studies suggest that gossypol is not a direct substrate of CYP6AE14. Furthermore, larvae feeding on many other plant toxins also upregulate CYP6AE14. Our data demonstrate that the aldehyde groups are critical for the toxicity of gossypol when ingested by H. armigera and H. virescens larvae, and suggest that CYP6AE14 is not directly involved in gossypol metabolism, but may play a role in the general stress response of H. armigera larvae toward plant toxins.

Molecular identification and expression patterns of carboxylesterase genes based on transcriptome analysis of the common cutworm, Spodoptera litura (Lepidoptera: Noctuidae)

Carboxylesterases (CXEs) belong to a family of metabolic enzymes that are widely distributed in insects and other organisms and can rapidly degrade the components of sex pheromones and plant volatiles with an acetate functional group. The common cutworm, Spodoptera litura, is an important agricultural pest around the world, causing vast economic losses every year. The female sex pheromones of S. litura comprise four acetates, Z9, E11-14:OAc; Z9, E12-14:OAc; Z9-14:OAc; and E11-14:OAc, but the degradation mechanisms of these components are not well understood. By analysing previously obtained transcriptomic data of the sex pheromone glands, we identified a total of 24 putative CXE genes in S. litura. Gene expression patterns and phylogenetic analysis revealed 5 genes with antennae-specific or biased expression, and clustered with genes showed involvement in the degradation of sex pheromones or other detoxification in other insects. SlitCXE10 was expressed specifically in the antennae of both sexes, and SlitCXE14, 17, 19, and 21 had high antenna biased expression. Interestingly, RT-PCR and qPCR tests indicated that SlitCXE24 had significantly higher expression in PG than in other tissue, and that it could be a potential candidate gene for sex pheromone degradation in PG. This study is the first to provide solid background information for the further elucidation of sex pheromone degradation, and ultimately provides potential targets for the disruption of sexual communication in S. litura for new pest management.

Gene expression analysis of overwintering mountain pine beetle larvae suggests multiple systems involved in overwintering stress, cold hardiness, and preparation for spring development.

Cold-induced mortality has historically been a key aspect of mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), population control, but little is known about the molecular basis for cold tolerance in this insect. We used RNA-seq analysis to monitor gene expression patterns of mountain pine beetle larvae at four time points during their overwintering period—early-autumn, late-autumn, early-spring, and late-spring. Changing transcript profiles over the winter indicates a multipronged physiological response from larvae that is broadly characterized by gene transcripts involved in insect immune responses and detoxification during the autumn. In the spring, although transcripts associated with developmental process are present, there was no particular biological process dominating the transcriptome.

Biochemical basis of synergism between pathogenic fungus Metarhizium anisopliae and insecticide chlorantraniliprole in Locusta migratoria (Meyen).

We challenged Locusta migratoria (Meyen) grasshoppers with simultaneous doses of both the insecticide chlorantraniliprole and the fungal pathogen, Metarhizium anisopliae. Our results showed synergistic and antagonistic effects on host mortality and enzyme activities. To elucidate the biochemical mechanisms that underlie detoxification and pathogen-immune responses in insects, we monitored the activities of 10 enzymes. After administration of insecticide and fungus, activities of glutathione-S-transferase (GST), general esterases (ESTs) and phenol oxidase (PO) decreased in the insect during the initial time period, whereas those of aryl acylamidase (AA) and chitinase (CHI) increased during the initial period and that of acetylcholinesterase (AChE) increased during a later time period. Activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) decreased at a later time period post treatment. Interestingly, treatment with chlorantraniliprole and M. anisopliae relieved the convulsions that normally accompany M. anisopliae infection. We speculate that locust mortality increased as a result of synergism via a mechanism related to Ca2+ disruption in the host. Our study illuminates the biochemical mechanisms involved in insect immunity to xenobiotics and pathogens as well as the mechanisms by which these factors disrupt host homeostasis and induce death. We expect this knowledge to lead to more effective pest control.