Dipnet (DN) sampling is routinely employed for macroinvertebrate bioassessments in wetlands, but it has been demonstrated that some taxa are more effectively collected with activity traps (AT). The ...Minnesota Pollution Control Agency (MPCA) used both DN and AT methods to evaluate the biological condition of depressional wetlands in the Mixed Wood Plains (MWP) and Temperate Prairies (TP) ecoregions. Two indices of biotic integrity (IBIs) were developed for each ecoregion using: 1) DN data alone and 2) composite samples consisting of both DN and AT data. ATs collected more active taxa such as diving beetles and swimming Hemiptera. DNs collected more taxa and collected more skating taxa and those associated with sediment or vegetation. A comparison of the effectiveness of the IBIs to evaluate biological condition indicated that the composite data had a slightly better relationship with anthropogenic disturbance and was marginally more precise. A comparison of sampling and processing costs revealed that sampling using composite samples was 130 % greater and processing was 50 % greater compared to DN-only samples. Based on the cost and limited benefit of adding AT samples, a DN-only sampling protocol is recommended to assess biological condition in depressional wetlands.
Spatial distribution of boll injury caused by stink bugs to developing cotton (Gossypiumhirsutum L.) bolls was studied in five commercial fields ( approximately 22 ha each) in 2011 and 2012 to ...understand variability in boll injury dynamics within fields. Cotton bolls and stink bugs were sampled weekly from a georeferenced grid of sampling points (one sample per 0.40 ha) in each field, but no samples were taken within 30 m of field edges. The inverse distance weighted interpolation, variogram analysis, and Moran's 7 were used to describe spatial variability of boll damage within the fields. Boll injury was found to be spatially associated at distances ranging from =75 to 275 m with an average distance approximately 150 m. An exponential variogram model was selected as the best fitting model to describe the spatial association in four of the five fields. Moran's 7 indicated that spatial association was significant in three of the five fields. The spread of boll injury from stink bugs was gradual in most fields and always exceeded the treatment threshold during the fourth or fifth week of bloom. Capture of stink bugs using a sweep net was inefficient, strongly suggesting that quantifying boll injury is a better sampling method and predictor of stink bug activity when sampling all but the edges of the field. These data suggest that scouts need to sample boll injury from sample locations separated by at least 150 m to assure independence in the central part of large fields. Second, future researchers who plan to use parametric statistical methods could use a 150-m grid, as opposed to a denser grid that would require greater time and effort.
Wing polyphenism is an evolutionarily successful feature found in a wide range of insects. Long-winged morphs can fly, which allows them to escape adverse habitats and track changing resources, ...whereas short-winged morphs are flightless, but usually possess higher fecundity than the winged morphs. Studies on aphids, crickets and planthoppers have revealed that alternative wing morphs develop in response to various environmental cues, and that the response to these cues may be mediated by developmental hormones, although research in this area has yielded equivocal and conflicting results about exactly which hormones are involved. As it stands, the molecular mechanism underlying wing morph determination in insects has remained elusive. Here we show that two insulin receptors in the migratory brown planthopper Nilaparvata lugens, InR1 and InR2, have opposing roles in controlling long wing versus short wing development by regulating the activity of the forkhead transcription factor Foxo. InR1, acting via the phosphatidylinositol-3-OH kinase (PI(3)K)-protein kinase B (Akt) signalling cascade, leads to the long-winged morph if active and the short-winged morph if inactive. InR2, by contrast, functions as a negative regulator of the InR1-PI(3)K-Akt pathway: suppression of InR2 results in development of the long-winged morph. The brain-secreted ligand Ilp3 triggers development of long-winged morphs. Our findings provide the first evidence of a molecular basis for the regulation of wing polyphenism in insects, and they are also the first demonstration--to our knowledge--of binary control over alternative developmental outcomes, and thus deepen our understanding of the development and evolution of phenotypic plasticity.
Highly reduced genomes of 144–416 kilobases have been described from nutrient-provisioning bacterial symbionts of several insect lineages 1–5. Some host insects have formed stable associations with ...pairs of bacterial symbionts that live in specialized cells and provide them with essential nutrients; genomic data from these systems have revealed remarkable levels of metabolic complementarity between the symbiont pairs 3, 4, 6, 7. The mealybug Planococcus citri (Hemiptera: Pseudococcidae) contains dual bacterial symbionts existing with an unprecedented organization: an unnamed gammaproteobacteria, for which we propose the name Candidatus Moranella endobia, lives inside the betaproteobacteria Candidatus Tremblaya princeps 8. Here we describe the complete genomes and metabolic contributions of these unusual nested symbionts. We show that whereas there is little overlap in retained genes involved in nutrient production between symbionts, several essential amino acid pathways in the mealybug assemblage require a patchwork of interspersed gene products from Tremblaya, Moranella, and possibly P. citri. Furthermore, although Tremblaya has the smallest cellular genome yet described, it contains a genomic inversion present in both orientations in individual insects, starkly contrasting with the extreme structural stability typical of highly reduced bacterial genomes 4, 9, 10.
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► At 139 kilobases, Tremblaya princeps has the smallest reported cellular genome ► Tremblaya is gene sparse and encodes no functional aminoacyl-tRNA synthetases ► Despite its extremely small size, the Tremblaya genome has a genomic inversion ► Moranella lives inside Tremblaya and complements missing metabolic genes
The brown planthopper, Nilaparvata lugens, the most destructive pest of rice, is a typical monophagous herbivore that feeds exclusively on rice sap, which migrates over long distances. Outbreaks of ...it have re-occurred approximately every three years in Asia. It has also been used as a model system for ecological studies and for developing effective pest management. To better understand how a monophagous sap-sucking arthropod herbivore has adapted to its exclusive host selection and to provide insights to improve pest control, we analyzed the genomes of the brown planthopper and its two endosymbionts.
We describe the 1.14 gigabase planthopper draft genome and the genomes of two microbial endosymbionts that permit the planthopper to forage exclusively on rice fields. Only 40.8% of the 27,571 identified Nilaparvata protein coding genes have detectable shared homology with the proteomes of the other 14 arthropods included in this study, reflecting large-scale gene losses including in evolutionarily conserved gene families and biochemical pathways. These unique genomic features are functionally associated with the animal's exclusive plant host selection. Genes missing from the insect in conserved biochemical pathways that are essential for its survival on the nutritionally imbalanced sap diet are present in the genomes of its microbial endosymbionts, which have evolved to complement the mutualistic nutritional needs of the host.
Our study reveals a series of complex adaptations of the brown planthopper involving a variety of biological processes, that result in its highly destructive impact on the exclusive host rice. All these findings highlight potential directions for effective pest control of the planthopper.
Nutritional symbionts play a major role in the ecology and evolution of insects. The recent accumulation of knowledge on the identity, function, genomics, and phylogenetic relationships of ...insect–bacteria symbioses provides the opportunity to assess the effects of symbiont acquisitions and replacements on the shift into novel ecological niches and subsequent lineage diversification. The megadiverse insect order Hemiptera presents a particularly large diversity of symbiotic associations that has frequently undergone shifts in symbiont localization and identity, which have contributed to the exploitation of nutritionally imbalanced diets such as plant saps or vertebrate blood. Here we review the known ecological and evolutionary implications of symbiont gains, switches, and replacements, and identify future research directions that can contribute to a more comprehensive understanding of symbiosis as a major driving force of ecological adaptation.
The cotton mealybug Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae) is a polyphagous insect that attacks tens of plant and causes substantial economic loss. Insect chitinases are required ...to remove the old cuticle to allow for continued growth and development. Though insect chitinases have been well studied in tens of insects, their functions in mealybug are still not addressed. Here, we sequenced the transcriptomes of adult males and females, from which eight chitinase genes were identified. We then used the method of rapid amplification of cDNA ends to amplify their full length. Phylogenetic analysis indicated that these genes clustered into five subgroups. Among which, group II PsCht2 had the longest transcript and was highly expressed at second instar nymph. PsCht10, PsCht3‐3 and PsIDGF were highly expressed in the adult females, whereas PsCht4 and PsCht4‐1 were significantly expressed at the male pupa and adult male. Next, we knocked down all eight chitinase genes by feeding the double‐stranded RNA. Knockdown of PsCht4 or PsCht4‐1 led to the failure of moult and, silencing PsCht5 resulted in pupation defect, while silencing PsCht10 led to small body size, suggesting these genes have essential roles in development and can be used as a potential target for pest control.
Target insensitivity contributing to imidacloprid resistance in Nilaparvata lugens has been reported to occur either through point mutations or quantitative change in nicotinic acetylcholine ...receptors (nAChRs). However, the metabolic resistance, especially the enhanced detoxification by P450 enzymes, is the major mechanism in fields. From one field-originated N. lugens population, an imidacloprid resistant strain G25 and a susceptible counterpart S25 were obtained to analyze putative roles of P450s in imidacloprid resistance. Compared to S25, over-expression of twelve P450 genes was observed in G25, with ratios above 5.0-fold for CYP6AY1, CYP6ER1, CYP6CS1, CYP6CW1, CYP4CE1 and CYP425B1. RNAi against these genes in vivo and recombinant tests on the corresponding proteins in vitro revealed that four P450s, CYP6AY1, CYP6ER1, CYP4CE1 and CYP6CW1, played important roles in imidacloprid resistance. The importance of the four P450s was not equal at different stages of resistance development based on their over-expression levels, among which CYP6ER1 was important at all stages, and that the others might only contribute at certain stages. The results indicated that, to completely reflect roles of P450s in insecticide resistances, their over-expression in resistant individuals, expression changes at the stages of resistance development, and catalytic activities against insecticides should be considered. In this study, multiple P450s, CYP6AY1, CYP6ER1, CYP4CE1 and CYP6CW1, have proven to be important in imidacloprid resistance.
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•Four P450 genes (CYP6AY1, CYP6ER1, CYP6CS1 and CYP6CW1) proved to confer imidacloprid resistance in N. lugens.•The importance of the four P450s varied during different stages of development of the resistance.•CYP6ER1 was important at all stages of resistance development while others might only play roles at some stages.
The Hemiptera (aphids, cicadas, and true bugs) are a key insect order, with high diversity for feeding ecology and excellent experimental tractability for molecular genetics. Building upon recent ...sequencing of hemipteran pests such as phloem-feeding aphids and blood-feeding bed bugs, we present the genome sequence and comparative analyses centered on the milkweed bug Oncopeltus fasciatus, a seed feeder of the family Lygaeidae.
The 926-Mb Oncopeltus genome is well represented by the current assembly and official gene set. We use our genomic and RNA-seq data not only to characterize the protein-coding gene repertoire and perform isoform-specific RNAi, but also to elucidate patterns of molecular evolution and physiology. We find ongoing, lineage-specific expansion and diversification of repressive C2H2 zinc finger proteins. The discovery of intron gain and turnover specific to the Hemiptera also prompted the evaluation of lineage and genome size as predictors of gene structure evolution. Furthermore, we identify enzymatic gains and losses that correlate with feeding biology, particularly for reductions associated with derived, fluid nutrition feeding.
With the milkweed bug, we now have a critical mass of sequenced species for a hemimetabolous insect order and close outgroup to the Holometabola, substantially improving the diversity of insect genomics. We thereby define commonalities among the Hemiptera and delve into how hemipteran genomes reflect distinct feeding ecologies. Given Oncopeltus's strength as an experimental model, these new sequence resources bolster the foundation for molecular research and highlight technical considerations for the analysis of medium-sized invertebrate genomes.
Chemosensory proteins (CSPs) are believed to play a key role in the chemosensory process in insects. Sequencing genomic DNA and RNA encoding CSP1, CSP2 and CSP3 in the sweet potato whitefly Bemisia ...tabaci showed strong variation between B and Q biotypes. Analyzing CSP-RNA levels showed not only biotype, but also age and developmental stage-specific expression. Interestingly, applying neonicotinoid thiamethoxam insecticide using twenty-five different dose/time treatments in B and Q young adults showed that Bemisia CSP1, CSP2 and CSP3 were also differentially regulated over insecticide exposure. In our study one of the adult-specific gene (CSP1) was shown to be significantly up-regulated by the insecticide in Q, the most highly resistant form of B. tabaci. Correlatively, competitive binding assays using tryptophan fluorescence spectroscopy and molecular docking demonstrated that CSP1 protein preferentially bound to linoleic acid, while CSP2 and CSP3 proteins rather associated to another completely different type of chemical, i.e. α-pentyl-cinnamaldehyde (jasminaldehyde). This might indicate that some CSPs in whiteflies are crucial to facilitate the transport of fatty acids thus regulating some metabolic pathways of the insect immune response, while some others are tuned to much more volatile chemicals known not only for their pleasant odor scent, but also for their potent toxic insecticide activity.
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