Differential accumulation of leucine and methionine in red and green pea aphids leads to different fecundity in response to nitrogen fertilization

A color morph-specific salivary carotenoid desaturase enhances plant photosynthesis and facilitates phloem feeding of Myzus persicae (Sulzer)

BACKGROUND

Body-color polymorphisms in insects are often explained by environmental selective advantages. Differential fitness related to body coloration has been demonstrated in Myzus persicae (Sulzer): performance of the red morph is in general better than that of the green morph on tobacco plants. However, the molecular mechanism involved is largely unclear.

RESULTS

Here we showed that the red morph of M. persicae had higher expression of a carotenoid desaturase CarD763 in the whole body, salivary gland and saliva relative to the green morph. Also, 18% individuals displayed faded red body color 5 days post dsCarD763 treatment. Furthermore, knockdown of CarD763 in the red morph significantly prolonged the time needed to locate phloem and shortened the duration of phloem feeding. Honeydew production and survival rate decreased as well. In contrast, overexpression of CarD763 in tobacco leaves facilitated aphid feeding, enhanced honeydew production and improved the survival rate of aphids. Compared with those fed by dsGFP aphids, plants infested by dsCarD763-treated aphids had higher ROS accumulation, lower lycopene content and photosynthetic rate, and maximum photon quantum yield. The reverse was true when plants overexpressed CarD763.

CONCLUSION

These findings demonstrated that CarD763, a red morph-specific salivary protein, could enhance aphid feeding and early colonization by promoting plant photosynthesis. © 2024 Society of Chemical Industry.

Markers of resistance to pea aphid, Acyrthosiphon pisum Harris in Pisum sativum L. accessions

One of the major insect pests in Pisum sativum L. (is Acyrthosiphon pisum Harris (Hemiptera: pests in Pisum sativum L. (Hemiptera: Aphididae) is Acyrthosiphon pisum Harris (Hemiptera: Aphididae). An effective strategy for aphid control is the resistant host plant use. The current study aimed to identify resistance mechanisms and assess biochemical and morphological markers of pea aphid resistance in pea accessions. Meteorological variables affected the pea aphid density, which positively correlated with temperature, while precipitation amount and humidity negatively impacted. The aphid number was significantly and positively associated with the leaf area and the nitrogen content but negatively correlated with calcium and phosphorus levels. The pea aphid-resistant cultivars L 123-7-11, L 128-1and L 125-5 had small leaf areas, and high phosphorus and calcium content but a low nitrogen level. In the mutual influence of the plant indicators, phosphorus concentration had the highest negative impact on pea aphid density, followed by calcium. The plant marker inclusion in the pea breeding process is an efficient tool for a substantial selection program improvement for aphid resistance. Therefore, resistant host plants are essential tools promoting considerable selection program improvement for aphid resistance in the P. sativum breeding process and helping develop sustainable and environmentally friendly agriculture.

The Plasmid pEX18Gm Indirectly Increases Caenorhabditis elegans Fecundity by Accelerating Bacterial Methionine Synthesis

Plasmids are mostly found in bacteria as extrachromosomal genetic elements and are widely used in genetic engineering. Exploring the mechanisms of plasmid-host interaction can provide crucial information for the application of plasmids in genetic engineering. However, many studies have generally focused on the influence of plasmids on their bacterial hosts, and the effects of plasmids on bacteria-feeding animals have not been explored in detail. Here, we use a "plasmid-bacteria-Caenorhabditis elegans" model to explore the impact of plasmids on their host bacteria and bacterivorous nematodes. First, the phenotypic responses of C. elegans were observed by feeding Escherichia coli OP50 harboring different types of plasmids. We found that E. coli OP50 harboring plasmid pEX18Gm unexpectedly increases the fecundity of C. elegans. Subsequently, we found that the plasmid pEX18Gm indirectly affects C. elegans fecundity via bacterial metabolism. To explore the underlying regulatory mechanism, we performed bacterial RNA sequencing and performed in-depth analysis. We demonstrated that the plasmid pEX18Gm upregulates the transcription of methionine synthase gene metH in the bacteria, which results in an increase in methionine that supports C. elegans fecundity. Additionally, we found that a pEX18Gm-induced increase in C. elegans can occur in different bacterial species. Our findings highlight the plasmid-bacteria-C. elegans model to reveal the mechanism of plasmids' effects on their host and provide a new pattern for systematically studying the interaction between plasmids and multi-species.

Moderately decreasing fertilizer in fields does not reduce populations of cereal aphids but maximizes fitness of parasitoids

Examination of the tradeoff between the extent of decreasing nitrogen input and pest suppression is crucial for maintaining the balance between essential yield and an efficient, sustainable pest control strategy. In this study, an experiment with four manipulated nitrogen fertilizer levels (70, 140, 210, and 280 kg N ha⁻¹ = conventional level) was conducted to explore the effects of decreasing nitrogen on cereal aphids (Sitobion avenae and Rhopalosiphum padi) (Hemiptera: Aphididae), Aphidiinae parasitoids (Hymenoptera: Braconidae: Aphidiinae), and body sizes of parasitoids. The results indicated that nitrogen application, in the range of 70–280 kg N ha⁻¹, has the potential to impact the populations of cereal aphids and their parasitoids. However, both differences between densities of cereal aphids and their parasitoids in moderate (140–210 kg N ha⁻¹) and those in high nitrogen input (280 kg N ha⁻¹) were not significant, and the parasitism rate was also unaffected. A higher parasitism rate reduced population growth of the cereal aphid (S. avenae). Additionally, a moderate decrease of nitrogen fertilizer from 280 to 140–210 kg N ha⁻¹ maximized the body sizes of Aphidiinae parasitoids, indicating that a moderate decrease of nitrogen fertilizer could facilitate biocontrol of cereal aphid by parasitoids in the near future. We conclude that a moderate decrease in nitrogen application, from 280 to 140–210 kg N ha⁻¹, does not quantitatively impact the densities of cereal aphids or the parasitism rate but can qualitatively maximize the fitness of the parasitoids.

Plant nutrient quality impacts survival and reproductive fitness of the dengue vector Aedes aegypti

BACKGROUND

In a recent study using DNA barcoding, we identified the plants fed upon by four Afro-tropical mosquito species that vector dengue, malaria, and Rift Valley fever. Herein, we have expanded on this study by investigating the role of three of the plants, Pithecellobium dulce (Fabaceae), Leonotis nepetifolia (Lamiaceae), and Opuntia ficus-indica (Cactaceae), on the survival, fecundity, and egg viability of the dengue vector Aedes aegypti.

METHODS

We tested these effects using females that received (i) an initial three rations of blood meals and (ii) no blood meal at all. Two controls were included: age-matched females fed on glucose solution with or without an initial blood meal and those fed exclusively on blood meals. Data were collected daily over a 30-day period. The amino acid contents of Ae. aegypti guts and their respective diets were detected by coupled liquid chromatography-mass spectrometry.

RESULTS

Females fed on P. dulce and an exclusively blood meal diet had a shorter survival than those fed on glucose. On the other hand, females fed on L. nepetifolia survived longer than those fed exclusively on blood meals, whereas those fed on O. ficus-indica had the shortest survival time. With an initial blood meal, females fed on L. nepetifolia laid 1.6-fold more eggs while those fed on the other diets laid fewer eggs compared to those fed exclusively on blood meals. Hatching rates of the eggs laid varied with the diet. Mass spectroscopic analysis of gut contents of mosquitoes exposed to the different diets showed qualitative and quantitative differences in their amino acid levels.

CONCLUSION

Our findings highlight the central role of plant nutrients in the reproductive fitness of dengue vectors, which may impact their disease transmission potential.

Asymmetric Interaction between Aphis spiraecola and Toxoptera citricida on Sweet Orange Induced by Pre-Infestation

Indirect interactions between herbivorous insects that share the same host have been focused on insects feeding on herbaceous plants, while few studies investigate similar interactions on woody plants. We investigated performance and feeding behavior of two citrus aphids, Aphis spiraecola Patch and Toxoptera citricida Kirkaldy, on sweet orange as affected by prior infestation of conspecifics and heterospecifics. Results showed that pre-infestation-induced interactions between A. spiraecola and T. citricida were asymmetric, with A. spiraecola gaining more fitness. In detail, pre-infestation by A. spiraecola decreased adult weight, enhanced survival rate and accelerated phloem sap acceptance of conspecifics. However, A. spiraecola pre-infestation did not affect performance or feeding behavior of T. citricida. In another infestation sequence, the pre-infestation of T. citricida did not affect conspecifics, but positively affected heterospecifics, indicated as a decreased pre-reproductive period, enhanced survival rate, adult weight, fecundity, and feeding efficiency, i.e., faster access and acceptance of phloem sap, and longer phloem sap ingestion duration. Furthermore, we found A. spiraecola pre-infestation enhanced amino acid concentration, amino acid to sugar ratio, activated salicylic acid and jasmonic acid marker gene expression, while T. citricida pre-infestation only depressed jasmonic acid marker gene expression. Changes in nutrient and phytohormone-dependent defense probably underlie the asymmetric effect.

Development of fly tolerance to consuming a high-protein diet requires physiological, metabolic and transcriptional changes

Mortality in insects consuming high-protein-and-low-carbohydrate diets resembles a type III lifespan curve with increased mortality at an early age and few survivors that live a relatively long lifespan. We selected for a Drosophila line able to live for a long time on an imbalanced high-protein-low-carbohydrate diet by carrying out five rounds of breeding to select for the most long-lived survivors. Adaptation to this diet in the selected line was studied at the biochemical, physiological and transcriptomic levels. The selected line of flies consumed less of the imbalanced food but also accumulated more storage metabolites: glycogen, triacylglycerides, and trehalose. Selected flies also had a higher activity of alanine transaminase and a higher urea content. Adaptation of the selected line on the transcriptomic level was characterized by down-regulation of genes encoding serine endopeptidases (Jon25i, Jon25ii, betaTry, and others) but up-regulation of genes encoding proteins related to the immune system, such as antimicrobial peptides, Turandot-family humoral factors, hexamerin isoforms, and vitellogenin. These sets of down- and up-regulated genes were similar to those observed in fruit flies with suppressed juvenile hormone signaling. Our data show that the physiological adaptation of fruit flies to a high-protein-low-carbohydrate diet occurs via intuitive pathways, namely a decrease in food consumption, conversion of amino acids into ketoacids to compensate for the lack of carbohydrate, and accumulation of storage metabolites to eliminate the negative effects of excess amino acids. Nevertheless, transcriptomic adaptation occurs in a counter-intuitive way likely via an influence of gut microbiota on food digestion.

Diversity of arthropods on Acacia mangium (Fabaceae) and production of this plant with dehydrated sewage sludge in degraded area

Sewage sludge is an organic matter-rich material with abundant fractions of nitrogen and other macro and micronutrients, essential for plant growth and development such as Acacia mangium Willd. (Fabales: Fabaceae) used in recovering actions of degraded areas. The objective of this study was to evaluate over 24 months the abundance and diversity of chewing and pollinator insects and arthropod predators on A. mangium plants and the mass production and soil coverage by this plant, fertilized with dehydrated sewage sludge, in a degraded area. The experimental design was in randomized blocks with two treatments (with and without dehydrated sewage sludge) and 24 replications. The number of leaves per branch and branches per plant, defoliation percentage by chewing insects, soil cover and abundance of chewing and pollinator insects and arthropod predators were higher on A. mangium plants fertilized with dehydrated sewage sludge. Nasutitermes sp. (Blattodea: Termitidae) and Trigona spinipes F. (Hymenoptera: Apidae) were the most observed insects on trunks and leaves, respectively, of A. mangium plants fertilized with dehydrated sewage sludge. The A. mangium fertilization increases the populations of different insect and spider groups on this plant.

Juvenile hormone mediates the positive effects of nitrogen fertilization on weight and reproduction in pea aphid

BACKGROUND

The positive effects of nitrogen fertilization on the performance of phytophagous insects have been reported extensively; the physiological and molecular basis involved, however, is largely unclear. Here, we test experimentally whether enhancement of juvenile hormone (JH) is responsible for the increased weight and fecundity of pea aphid (Acyrthosiphon pisum) under nitrogen fertilization.

RESULTS

Aphids fed on Medicago truncatula with nitrogen fertilization have a greater amino acid content, higher weight at the fourth instar and adult stage, and produce more offspring than those without nitrogen fertilization. Furthermore, nitrogen fertilization upregulates the transcripts of JH biosynthesis-related genes and increases JH titre at the fourth instar and adult stage, suggesting that JH is involved in the positive responses of aphids to nitrogen fertilization. Application of 100 ng JH increases adult weight and fecundity in aphids fed on M. truncatula without nitrogen fertilization. Conversely, impairing JH signalling by pharmacologically inhibiting the target of rapamycin pathway or by knocking down JH biosynthetic gene decreases adult weight and fecundity in aphids fed on M. truncatula with nitrogen fertilization, whereas application of JH rescued the phenotype.

CONCLUSION

The increased JH titre at the fourth instar and adult stage is required for the increases of weight and fecundity of A. pisum under nitrogen fertilization. © 2018 Society of Chemical Industry.

mTOR Complex 1 Implicated in Aphid/Buchnera Host/Symbiont Integration

Obligate nutritional endosymbioses are arguably the most intimate of all interspecific associations. While many insect nutritional endosymbioses are well studied, a full picture of how two disparate organisms, a bacterial endosymbiont and a eukaryotic host, are integrated is still lacking. The mTOR pathway is known to integrate nutritional conditions with cell growth and survival in eukaryotes. Characterization and localization of amino acid transporters in aphids suggest the mTOR pathway as a point of integration between an aphid host and its amino acid-provisioning endosymbiont Buchnera aphidicola. The mTOR pathway is unannotated in aphids and unstudied in any nutritional endosymbiosis. We annotated mTOR pathway genes in two aphid species, Acyrthosiphon pisum and Myzus persicae, using both BLASTp searches and Hidden Markov Models. Using previously collected RNAseq data we constructed new reference transcriptomes for bacteriocyte, gut, and whole insect tissue for three lines of M. persicae. Annotation of the mTOR pathway identified homologs of all known invertebrate mTOR genes in both aphid species with some duplications. Differential expression analysis showed that genes specific to the amino acid-sensitive mTOR Complex 1 were more highly expressed in bacteriocytes than genes specific to the amino acid-insensitive mTOR Complex 2. Almost all mTOR genes involved in sensing amino acids showed higher expression in bacteriocytes than in whole insect tissue. When compared to gut, the putative glutamine/arginine sensing transporter ACYPI000333, an ortholog of SLC38A9, showed 6.5 times higher expression in bacteriocytes. Our results suggest that the mTOR pathway may be functionally important in mediating integration of Buchnera into aphid growth and reproduction.