Minsheng You

A heterozygous moth genome provides insights into herbivory and detoxification

How an insect evolves to become a successful herbivore is of profound biological and practical importance. Herbivores are often adapted to feed on a specific group of evolutionarily and biochemically related host plants, but the genetic and molecular bases for adaptation to plant defense compounds remain poorly understood. We report the first whole-genome sequence of a basal lepidopteran species, Plutella xylostella, which contains 18,071 protein-coding and 1,412 unique genes with an expansion of gene families associated with perception and the detoxification of plant defense compounds. A recent expansion of retrotransposons near detoxification-related genes and a wider system used in the metabolism of plant defense compounds are shown to also be involved in the development of insecticide resistance. This work shows the genetic and molecular bases for the evolutionary success of this worldwide herbivore and offers wider insights into insect adaptation to plant feeding, as well as opening avenues for more sustainable pest management.

Developmental and insecticide-resistant insights from the de novo assembled transcriptome of the diamondback moth, Plutella xylostella.

We present here the de novo assembly and annotation of the transcriptome of Plutella xylostella (diamondback moth (DBM)), a widespread destructive pest of cruciferous plants, using short reads generated by Illumina sequencing from different developmental stages and insecticide-resistant strains. A total of 171,262 non-redundant sequences, denoted as unigenes, were obtained. They represented approximately 100-fold of all DBM mRNA and EST sequences in GenBank thus far. We identified 38,255 unigenes highly similar to the known functional protein-coding genes, most of which were annotated using gene ontology (GO) and orthologous groups of proteins (COG). Global profiling of differentially expressed unigenes revealed enriched GOs and biological pathways that were related to specific developmental stages and insecticide resistance. We also evaluated the resistance-related single nucleotide polymorphism (SNP) using this high-throughput genotyping method. The newly developed transcriptome will facilitate researches on the DBM developmental biology and insecticide resistance evolution, and ultimately provide better pest management systems.

Habitat Management to Suppress Pest Populations: Progress and Prospects

Habitat management involving manipulation of farmland vegetation can exert direct suppressive effects on pests and promote natural enemies. Advances in theory and practical techniques have allowed habitat management to become an important subdiscipline of pest management. Improved understanding of biodiversity-ecosystem function relationships means that researchers now have a firmer theoretical foundation on which to design habitat management strategies for pest suppression in agricultural systems, including landscape-scale effects. Supporting natural enemies with shelter, nectar, alternative prey/hosts, and pollen (SNAP) has emerged as a major research topic and applied tactic with field tests and adoption often preceded by rigorous laboratory experimentation. As a result, the promise of habitat management is increasingly being realized in the form of practical worldwide implementation. Uptake is facilitated by farmer participation in research and is made more likely by the simultaneous delivery of ecosystem services other than pest suppression.

PsOr1, a potential target for RNA interference-based pest management

Insect pests cause billions of dollars in agricultural losses, and attempts to kill them have resulted in growing threats from insecticide resistance, dietary pesticide pollution and environmental destruction. New approaches to control refractory insect pests are therefore needed. The host‐plant preferences of insect pests rely on olfaction and are mediated via a seven transmembrane‐domain odorant receptor (Or) family. The present study reports the cloning and characterization of PsOr1, the first candidate member of the Or gene family from Phyllotreta striolata, a devastating beetle pest that causes damage worldwide. PsOr1 is remarkably well conserved with respect to other insect orthologues, including DmOr83b from Drosophila melanogaster. These insect orthologues form an essential non‐conventional Or sub‐family and may play an important and generalized role in insect olfaction. We designed double‐stranded (ds) RNA directly against the PsOr1 gene and exploited RNA interference (RNAi) to control P. striolata. The chemotactic behavioural measurements showed that adult beetles were unable to sense the attractant or repellent odour stimulus after microinjection of dsRNA against PsOr1. Reverse Transcription (RT)‐PCR analysis showed specific down‐regulation of mRNA transcript levels for this gene. Furthermore, host‐plant preference experiments confirmed that silencing PsOr1 by RNAi treatment impaired the host‐plant preferences of P. striolata for cruciferous vegetables. These results demonstrate that this insect control approach of using RNAi to target PsOr1 and its orthologues might be effective in blocking host‐plant‐seeking behaviours in diverse insect pests. The results also support the theory that this unique receptor type plays an essential general role in insect olfaction.

DNA sequencing reveals the midgut microbiota of diamondback moth, Plutella xylostella (L.) and a possible relationship with insecticide resistance.

Background Insect midgut microbiota is important in host nutrition, development and immune response. Recent studies indicate possible links between insect gut microbiota and resistance to biological and chemical toxins. Studies of this phenomenon and symbionts in general have been hampered by difficulties in culture-based approach. In the present study, DNA sequencing was used to examine the midgut microbiota of diamondback moth (DBM), Plutella xylostella (L.), a destructive pest that attacks cruciferous crops worldwide. Its ability to develop resistance to many types of synthetic insecticide and even Bacillus thuringiensis toxins makes it an important species to study. Methodology/Principal Findings Bacteria of the DBM larval midgut in a susceptible and two insecticide (chlorpyrifos and fipronil) resistant lines were examined by Illumina sequencing sampled from an insect generation that was not exposed to insecticide. This revealed that more than 97% of the bacteria were from three orders: Enterobacteriales, Vibrionales and Lactobacillales. Both insecticide-resistant lines had more Lactobacillales and the much scarcer taxa Pseudomonadales and Xanthomonadales with fewer Enterobacteriales compared with the susceptible strain. Consistent with this, a second study observed an increase in the proportion of Lactobacillales in the midgut of DBM individuals from a generation treated with insecticides. Conclusions/Significance This is the first report of high-throughput DNA sequencing of the entire microbiota of DBM. It reveals differences related to inter- and intra-generational exposure to insecticides. Differences in the midgut microbiota among susceptible and insecticide-resistant lines are independent of insecticide exposure in the sampled generations. While this is consistent with the hypothesis that Lactobacillales or other scarcer taxa play a role in conferring DBM insecticide resistance, further studies are necessary to rule out other possibilities. Findings constitute the basis for future molecular work on the functions of insect midgut microbiota taxa and their possible role in conferring host resistance to toxins.

DBM-DB: the diamondback moth genome database

The diamondback moth Genome Database (DBM-DB) is a central online repository for storing and integrating genomic data of diamondback moth (DBM), Plutella xylostella (L.). It provides comprehensive search tools and downloadable datasets for scientists to study comparative genomics, biological interpretation and gene annotation of this insect pest. DBM-DB contains assembled transcriptome datasets from multiple DBM strains and developmental stages, and the annotated genome of P. xylostella (version 2). We have also integrated publically available ESTs from NCBI and a putative gene set from a second DBM genome (KONAGbase) to enable users to compare different gene models. DBM-DB was developed with the capacity to incorporate future data resources, and will serve as a long-term and open-access database that can be conveniently used for research on the biology, distribution and evolution of DBM. This resource aims to help reduce the impact DBM has on agriculture using genomic and molecular tools. Database URL: http://iae.fafu.edu.cn/DBM/

Characterization and expression of the cytochrome P450 gene family in diamondback moth, Plutella xylostella (L.)

Cytochrome P450 monooxygenases are present in almost all organisms and can play vital roles in hormone regulation, metabolism of xenobiotics and in biosynthesis or inactivation of endogenous compounds. In the present study, a genome-wide approach was used to identify and analyze the P450 gene family of diamondback moth, Plutella xylostella, a destructive worldwide pest of cruciferous crops. We identified 85 putative cytochrome P450 genes from the P. xylostella genome, including 84 functional genes and 1 pseudogene. These genes were classified into 26 families and 52 subfamilies. A phylogenetic tree constructed with three additional insect species shows extensive gene expansions of P. xylostella P450 genes from clans 3 and 4. Gene expression of cytochrome P450s was quantified across multiple developmental stages (egg, larva, pupa and adult) and tissues (head and midgut) using P. xylostella strains susceptible or resistant to insecticides chlorpyrifos and fiprinol. Expression of the lepidopteran specific CYP367s predominantly occurred in head tissue suggesting a role in either olfaction or detoxification. CYP340s with abundant transposable elements and relatively high expression in the midgut probably contribute to the detoxification of insecticides or plant toxins in P. xylostella. This study will facilitate future functional studies of the P. xylostella P450s in detoxification.

A simulation model of spruce budworm (Lepidoptera: Tortricidae) feeding on balsam fir and white spruce

Abstract A process-oriented model of feeding by the spruce budworm, Choristoneura fumiferana (Clem.), was developed to simulate the seasonal patterns of defoliation on growing shoots of balsam fir, Abies balsamea (L.) Mill., and white spruce, Picea glauca (Moench.) Voss. The model simulates larval and shoot growth, seasonal dynamics and feeding by a spruce budworm population based on the density of overwintering spruce budworm and shoots, budworm stage-specific survival rates and input daily minimum and maximum air temperature. The model, which was validated with extensive field data, can be used to determine the effect on defoliation of specific mortality rates inflicted on spruce budworm at any point during larval development. Analysis of model behaviour revealed that weather had little influence on the final degree of defoliation. The model also provides a simple explanation for the observation that white spruce is generally less defoliated than balsam fir. It emphasizes the need to consider foliage abundance in terms of number and potential size of shoots, as well as larval rates and the timing of mortality to predict defoliation more accurately from estimates of spruce budworm population density.

Metagenomic Sequencing of Diamondback Moth Gut Microbiome Unveils Key Holobiont Adaptations for Herbivory

Herbivore specialists adapt to feed on a specific group of host plants by evolving various mechanisms to respond to plant defenses. Insects also possess complex gut microbiotas but their potential role in adaptation is poorly understood. Our previous study of the genome of diamondback moth, Plutella xylostella, revealed an intrinsic capacity to detoxify plant defense compounds, which is an important factor in its success as a pest. Here we expand on that work with a complete taxonomic and functional profile of the P. xylostella gut microbiota obtained by metagenomic sequencing. Gene enrichment in the metagenome, accompanied by functional identification, revealed an important role of specific gut bacteria in the breakdown of plant cell walls, detoxification of plant phenolics, and synthesis of amino acids. Microbes participating in these pathways mainly belonged to three highly abundant bacteria: Enterobacter cloacae, Enterobacter asburiae, and Carnobacterium maltaromaticum. Results show that while the gut microbial community may be complex, a small number of functionally active species can be disproportionally important. The presence of specific enzymes in the microbiota community, such as supporting amino acid synthesis, digestion and detoxification functions, demonstrates the beneficial interactions between P. xylostella and its gut microbiota. These interactions can be potential targets for manipulation to provide novel pest management approaches.

Biology, ecology, and management of the diamondback moth in China

The diamondback moth (DBM), Plutella xylostella (L.), costs the Chinese economy US