The present investigation was carried out on in vitro mass multiplication, larval feeding capacity, and pollination efficiency of two aphidophagous syrphids viz., Eupeodes frequens (Matsmura) and ...Episyrphus balteatus (De Geer) (Diptera: Syrphidae) on cabbage aphid (Brevicoryne brassicae L.) (Homoptera: Aphididae) on mustard crop under mid hill conditions. The results revealed that the incubation, larval, and pupal periods were 3.5, 12.4, and 11.9 days, respectively for E. frequens and 3.8, 13.7, and 8.8 days, for E. balteatus. Longevity of male and female was 15.2 and 17.6 days for E. frequens and 10.6 and 12.6 days for E. balteatus, respectively. When the adults were fed on different diets, adult longevity and fecundity recorded significantly maximum on 10% honey solution + fresh pollen grains. E. frequens consumed an average of 261.7 individuals of cabbage aphids per larva during total larval period, whereas the larva of E. balteatus consumed 393.6 cabbage aphids. The pollination efficiency of hoverflies on Indian mustard (Brassica juncea L.) was studied under caged conditions. It was observed that the plants pollinated by E. balteatus and E. frequens showed 55.12 and 52.97% seed set. Among the different diets, fresh pollen grains + 10% honey solutions recorded to be the best diet for mass rearing of syrphids.
Aphids are important agricultural pests and also biological models for studies of insect-plant interactions, symbiosis, virus vectoring, and the developmental causes of extreme phenotypic plasticity. ...Here we present the 464 Mb draft genome assembly of the pea aphid Acyrthosiphon pisum. This first published whole genome sequence of a basal hemimetabolous insect provides an outgroup to the multiple published genomes of holometabolous insects. Pea aphids are host-plant specialists, they can reproduce both sexually and asexually, and they have coevolved with an obligate bacterial symbiont. Here we highlight findings from whole genome analysis that may be related to these unusual biological features. These findings include discovery of extensive gene duplication in more than 2000 gene families as well as loss of evolutionarily conserved genes. Gene family expansions relative to other published genomes include genes involved in chromatin modification, miRNA synthesis, and sugar transport. Gene losses include genes central to the IMD immune pathway, selenoprotein utilization, purine salvage, and the entire urea cycle. The pea aphid genome reveals that only a limited number of genes have been acquired from bacteria; thus the reduced gene count of Buchnera does not reflect gene transfer to the host genome. The inventory of metabolic genes in the pea aphid genome suggests that there is extensive metabolite exchange between the aphid and Buchnera, including sharing of amino acid biosynthesis between the aphid and Buchnera. The pea aphid genome provides a foundation for post-genomic studies of fundamental biological questions and applied agricultural problems.
The sesquiterpene (E)-β-farnesene (EBF) is the alarm pheromone for many species of aphids 1. When released from aphids attacked by parasitoids or predators, it alerts nearby conspecifics to escape by ...walking away and dropping off the host plant 2, 3. The reception of alarm pheromone in aphids is accomplished through a highly sensitive chemosensory system. Although olfaction-related gene families including odorant receptors (ORs) and odorant-binding proteins (OBPs) have recently been identified from aphid genomes 4–6, the cellular and molecular mechanisms of EBF reception are still largely unknown. Here we demonstrate that ApisOR5, a member of the large superfamily of odorant receptors, is expressed in large placoid sensillum neurons on the sixth antennal segment and confers response to EBF when co-expressed with Orco, an obligate odorant receptor co-receptor, in parallel heterologous expression systems. In addition, the repellent behavior of Acyrthosiphon pisum to EBF disappears after knocking down ApisOR5 by RNAi as well as two A. pisum odorant-binding proteins known to bind EBF (ApisOBP3 and ApisOBP7). Furthermore, other odorants that can also activate ApisOR5, such as geranyl acetate, significantly repel A. pisum, as does EBF. Taken together, these data allow us to conclude that ApisOR5 is essential to EBF reception in A. pisum. The characterization of the EBF receptor allows high-throughput screening of aphid repellents, providing the necessary information to develop new strategies for aphid control.
Display omitted
•Alarm pheromone is detected by the LP sensilla on the sixth antennal segment•ApisOR5 is essential for both electrophysiological and behavioral responses to EBF•Characterizing the EBF receptor enables high-throughput screening of aphid repellents
Zhang et al. demonstrate that the alarm pheromone (E)-β-farnesene is detected in the pea aphid by odorant receptor ApisOR5 with the cooperation of odorant-binding proteins ApisOBP3 and ApisOBP7. This study also identifies geranyl acetate as a strong repellent, paving the way for high-throughput discovery of new aphid repellents.
Terrestrial insects deposit a layer of hydrocarbons (HCs) as waterproofing agents on their epicuticle. The insect-specific CYP4G genes, subfamily members of P450, have been found in all insects with ...sequenced genomes to date. They are critical for HC biosynthesis in Drosophila; however, their functional roles in other insects including the piercing-sucking hemipterous aphids remain unknown. In this study, we presented the molecular characterization and a functional study of the CYP4G51 gene in the pea aphid, Acyrthosiphon pisum (Harris). CYP4G51 transcript was detectable across the whole life cycle of A. pisum, and was prominently expressed in the aphid head and abdominal cuticle. Up-regulation of CYP4G51 under desiccation stress was more significant in the third instar nymphs compared with the adults. Also, up-regulation of CYP4G51 was observed when the aphids fed on an artificial diet compared with those fed on the broad bean plant, and was positively correlated with a high level of cuticular HCs (CHCs). RNAi knockdown of CYP4G51 significantly reduced its expression and caused reductions in both internal and external HCs. A deficiency in CHCs resulted in aphids being more susceptible to desiccation, with increased mortality under desiccation stress. The current results confirm that CYP4G51 modulates HC biosynthesis to protect aphids from desiccation. Moreover, our data also indicate that saturated and straight-chain HCs play a major role in cuticular waterproofing in the pea aphid. A. pisum CYP4G51 could be considered as a novel RNAi target in the field of insect pest management.
Display omitted
•Acyrthosiphon pisum CYP4G51 expression was up-regulated in response to desiccation stress.•Up-regulation of CYP4G51 by an artificial diet was positively correlated with an increase in CHCs.•RNAi knockdown of CYP4G51 resulted in a decrease in both the cuticular and internal HCs.•CYP4G51-suppressed aphids showed an increase in mortality due to desiccation.•Saturated and straight-chain CHCs are responsible for cuticular waterproofing in the pea aphid.
1. Eukaryotes commonly host communities of heritable symbiotic bacteria, many of which are not essential for their hosts' survival and reproduction. There is laboratory evidence that these ...facultative symbionts can provide useful adaptations, such as increased resistance to natural enemies. However, we do not know how symbionts affect host fitness when the latter are subject to attack by a natural suite of parasites and pathogens. 2. Here, we test whether two protective symbionts, Regiella insecticola and Hamiltonella defensa, increase the fitness of their host, the pea aphid (Acyrthosiphon pisum), under natural conditions. 3. We placed experimental populations of two pea aphid lines, each with and without symbionts, in five wet meadow sites to expose them to a natural assembly of enemy species. The aphids were then retrieved and mortality from parasitoids, fungal pathogens and other causes assessed. 4. We found that both Regiella and Hamiltonella reduce the proportion of aphids killed by the specific natural enemies against which they have been shown to protect in laboratory and cage experiments. However, this advantage was nullified (Hamiltonella) or reversed (Regiella) by an increase in mortality from other natural enemies and by the cost of carrying the symbiont. Symbionts therefore affect community structure by altering the relative success of different natural enemies. 5. Our results show that protective symbionts are not necessarily advantageous to their hosts, and may even behave more like parasites than mutualists. Nevertheless, bacterial symbionts may play an important role in determining food web structure and dynamics.
Recent genomic analyses of arthropod defense mechanisms suggest conservation of key elements underlying responses to pathogens, parasites and stresses. At the center of pathogen-induced immune ...responses are signaling pathways triggered by the recognition of fungal, bacterial and viral signatures. These pathways result in the production of response molecules, such as antimicrobial peptides and lysozymes, which degrade or destroy invaders. Using the recently sequenced genome of the pea aphid (Acyrthosiphon pisum), we conducted the first extensive annotation of the immune and stress gene repertoire of a hemipterous insect, which is phylogenetically distantly related to previously characterized insects models.
Strikingly, pea aphids appear to be missing genes present in insect genomes characterized to date and thought critical for recognition, signaling and killing of microbes. In line with results of gene annotation, experimental analyses designed to characterize immune response through the isolation of RNA transcripts and proteins from immune-challenged pea aphids uncovered few immune-related products. Gene expression studies, however, indicated some expression of immune and stress-related genes.
The absence of genes suspected to be essential for the insect immune response suggests that the traditional view of insect immunity may not be as broadly applicable as once thought. The limitations of the aphid immune system may be representative of a broad range of insects, or may be aphid specific. We suggest that several aspects of the aphid life style, such as their association with microbial symbionts, could facilitate survival without strong immune protection.
In an elaborate form of inter-species exploitation, many insects hijack plant development to induce novel plant organs called galls that provide the insect with a source of nutrition and a temporary ...home. Galls result from dramatic reprogramming of plant cell biology driven by insect molecules, but the roles of specific insect molecules in gall development have not yet been determined. Here, we study the aphid Hormaphis cornu, which makes distinctive “cone” galls on leaves of witch hazel Hamamelis virginiana. We found that derived genetic variants in the aphid gene determinant of gall color (dgc) are associated with strong downregulation of dgc transcription in aphid salivary glands, upregulation in galls of seven genes involved in anthocyanin synthesis, and deposition of two red anthocyanins in galls. We hypothesize that aphids inject DGC protein into galls and that this results in differential expression of a small number of plant genes. dgc is a member of a large, diverse family of novel predicted secreted proteins characterized by a pair of widely spaced cysteine-tyrosine-cysteine (CYC) residues, which we named BICYCLE proteins. bicycle genes are most strongly expressed in the salivary glands specifically of galling aphid generations, suggesting that they may regulate many aspects of gall development. bicycle genes have experienced unusually frequent diversifying selection, consistent with their potential role controlling gall development in a molecular arms race between aphids and their host plants.
•Novel aphid bicycle genes contribute to plant gall development•Variation in a bicycle gene alters plant gene expression and a gall phenotype•bicycle genes encode a large family of diverse, secreted, cysteine-rich proteins•Many bicycle genes have experienced repeated diversifying selection
Korgaonkar et al. report on novel secreted aphid proteins encoded by bicycle genes. Variation in the bicycle gene determinant of gall color alters expression of targeted plant genes, suggesting that BICYCLE proteins modulate gall development.
Forty three European population samples of mealy aphids from various winter and summer host plants were attributed to respective species of Hyalopterus by means of their partial sequences of ...mitochondrial COI gene. Used Hyalopterus samples emerged as monophyletic relative to outgroup and formed three major clades representing three host specific mealy aphid species in the Neighbor joining, Maximum parsimony, Maximum likelihood and Bayesian inference trees. Hyalopterus pruni and Hyalopterus persikonus emerged as a sister species, whilst Hyalopterus amygdali was located basally. Samples representing different clades in the molecular trees were used for canonical discrimination analysis based on twenty two morphological characters. Length of the median dorsal head hair enabled a 97.3 % separation of Hyalopterus amygdali from the remaining two species. No single character enabled satisfactory discrimination between apterous viviparous females of Hyalopterus pruni and Hyalopterus persikonus . A modified key for the morphological identification of Hyalopterus species is suggested and their taxonomic status discussed. Keywords: Europe, Hyalopterus amygdali , Hyalopterus pruni , Hyalopterus persikonus , molecular phylogeny, mitochondrial COI, morphological key to species
Some bacterial symbionts alter their hosts reproduction through various mechanisms that enhance their transmission in the host population. In addition to its obligatory symbiont Buchnera aphidicola, ...the pea aphid Acyrthosiphon pisum harbors several facultative symbionts influencing several aspects of host ecology. Aphids reproduce by cyclical parthenogenesis whereby clonal and sexual reproduction alternate within the annual life cycle. Many species, including the pea aphid, also show variation in their reproductive mode at the population level, with some lineages reproducing by cyclical parthenogenesis and others by permanent parthenogenesis. While the role of facultative symbionts has been well studied during the parthenogenetic phase of their aphid hosts, very little is known on their possible influence during the sexual phase. Here we investigated whether facultative symbionts modulate the capacity to produce sexual forms in various genetic backgrounds of the pea aphid with controlled symbiont composition and also in different aphid genotypes from natural populations with previously characterized infection status and reproductive mode. We found that most facultative symbionts exhibited detrimental effects on their hosts fitness under sex-inducing conditions in comparison with the reference lines. We also showed that the loss of sexual phase in permanently parthenogenetic lineages of A. pisum was not explained by facultative symbionts. Finally, we demonstrated that Spiroplasma infection annihilated the production of males in the host progeny by inducing a male-killing phenotype, an unexpected result for organisms such as aphids that reproduce primarily through clonal reproduction.
Aphids were the first animals reported as photoperiodic as their life cycles are strongly determined by the photoperiod. During the favourable seasons (characterised by long days) aphid populations ...consist exclusively of viviparous parthenogenetic females (known as virginoparae). Shortening of the photoperiod in autumn is perceived by aphids as the signal that anticipates the harsh season, leading to a switch in the reproductive mode giving place to the sexual morphs (oviparae females and males) that mate and lay winter-resistant (diapause-like) eggs. The molecular and cellular basis governing the switch between the two reproductive modes are far from being understood. Classical experiments identified a group of neurosecretory cells in the pars intercerebralis of the aphid brain (the so called group I of neurosecretory cells) that were essential for the development of embryos as parthenogenetic females and were thus proposed to synthesise a parthenogenesis promoting substance that was termed “virginoparin”. Since insulin-like peptides (ILPs) have been implicated in the control of diapause in other insects, we investigated their involvement in aphid photoperiodism. We compared the expression of two ILPs (ILP1 and ILP4) and an Insulin receptor coding genes in A. pisum aphids reared under long- and short-day conditions. The three genes showed higher expression in long-day reared aphids. In addition, we localised the site of expression of the two ILP genes in the aphid brain. Both genes were found to be expressed in the group I of neurosecretory cells. Altogether, our results suggest that ILP1 and ILP4 play an important role in the control of the aphid life-cycle by promoting the parthenogenetic development during long-day seasons while their repression by short days would activate the sexual development. Thus we propose these ILPs correspond to the so called “virginoparin” by early bibliography. A possible connection with the circadian system is also discussed.
Display omitted
•ILP1 and ILP4 expression is higher under parthenogenesis promoting conditions (long days) in holocyclic aphids.•No difference in levels of expression of ILPs in anholocyclic aphids reared under LD and SD photoperiods.•ILP1/4 transcripts are localised in the group I of neurosecretory cells in the pars intercerebralis of the protocerebrum.•Our results point to ILP1 and ILP4 being the parthenogenesis promoting factor called virginoparin in early bibliography.
PDF
