Wingless Morphs Research Articles

Cell death and wing reduction during the metamorphosis of sex-specific flightless morphs in winter geometrid moths.

Winter geometrid moths show striking sexual dimorphism by having female-specific flightless morphs. The evolutionary grades of wing reduction in winter geometrid moths vary and range from having short wings, vestigial wings, to being wingless. Although the ontogenetic processes underlying the development of the wingless or short-wing morphs in Lepidoptera has been well studied, the mechanisms underlying the development of vestigial wing morphs in winter geometrid moths during metamorphosis are poorly understood. In the winter geometrid moth Sebastosema bubonaria Warren, 1896, the males have functional wings, but the females have vestigial wings. Here, we studied the ontogenetic processes affecting wing reduction in the winter geometrid moth S. bubonaria using light microscopy and transmission electron microscopy, and compared the ontogenetic process of wing reduction in this species with that in another species of the wingless-female winter moth that we investigated previously. Our results showed that, in the vestigial-wing morphs, the loss of pupal wing epithelium was terminated in the middle of the wing degeneration process, whereas in the wingless morph, the pupal wing epithelium disappeared almost completely and the final appearance of the wings differed slightly among flightless morphs. We propose that the extent and location of cell death in the pupal wing play an important role in the various patterns of reduced wings that are observed in flightless moths.

Functional Characterization of the Nuclear Receptor Gene SaE75 in the Grain Aphid, Sitobion avenae

Ecdysteroid hormones are key regulators of insect development and metamorphosis. Ecdysone-inducible E75, a major component of insect ecdysone signaling pathway, has been well characterized in holometabolous insects, however, barely in hemimetabolous species. In this study, a total of four full-length E75 cDNAs from the English grain aphid, Sitobion avenae, were identified, cloned, and characterized. The four SaE75 cDNAs contained 3048, 2625, 2505, and 2179 bp open reading frames (ORF), encoding 1015, 874, 856, and 835 amino acids, respectively. Temporal expression profiles showed that SaE75 expression was low in adult stages, while high in pseudo embryo and nymphal stages. SaE75 was differentially expressed between winged and wingless morphs. RNAi-mediated suppression of SaE75 led to substantial biological impacts, including mortality and molting defects. As for the pleiotropic effects on downstream ecdysone pathway genes, SaHr3 (hormone receptor like in 46) was significantly up-regulated, while Sabr-c (broad-complex core protein gene) and Saftz-f1 (transcription factor 1) were significantly down-regulated. These combined results not only shed light on the regulatory role of E75 in the ecdysone signaling pathway, but also provide a potential novel target for the long-term sustainable management of S. avenae, a devastating global grain pest.

Salivary carbonic anhydrase II in winged aphid morph facilitates plant infection by viruses

Aphids are the most common insect vector transmitting hundreds of plant viruses. Aphid wing dimorphism (winged vs. wingless) not only showcases the phenotypic plasticity but also impacts virus transmission; however, the superiority of winged aphids in virus transmission over the wingless morph is not well understood. Here, we show that plant viruses were efficiently transmitted and highly infectious when associated with the winged morph of Myzus persicae and that a salivary protein contributed to this difference. The carbonic anhydrase II (CA-II) gene was identified by RNA-seq of salivary glands to have higher expression in the winged morph. Aphids secreted CA-II into the apoplastic region of plant cells, leading to elevated accumulation of H+. Apoplastic acidification further increased the activities of polygalacturonases, the cell wall homogalacturonan (HG)-modifying enzymes, promoting degradation of demethylesterified HGs. In response to apoplastic acidification, plants accelerated vesicle trafficking to enhance pectin transport and strengthen the cell wall, which also facilitated virus translocation from the endomembrane system to the apoplast. Secretion of a higher quantity of salivary CA-II by winged aphids promoted intercellular vesicle transport in the plant. The higher vesicle trafficking induced by winged aphids enhanced dispersal of virus particles from infected cells to neighboring cells, thus resulting in higher virus infection in plants relative to the wingless morph. These findings imply that the difference in the expression of salivary CA-II between winged and wingless morphs is correlated with the vector role of aphids during the posttransmission infection process, which influences the outcome of plant endurance of virus infection.

Estragole, a potential attractant of the winged melon aphid Aphis gossypii.

Aphids are sap-sucking insect pests of economic importance. They exhibit polyphenism, producing two kinds of morphotypes; winged (alate) and wingless (aptera) morphs. While wingless morphs can be controlled by insecticides, winged morphs are a challenge for targeted control measures as they can fly. Although colored sticky traps are used to control and monitor winged aphids, only a small population is trapped, making sticky traps less effective in controlling aphids. Studies have shown that fragrant oils applied to sticky traps increased attraction of sap-sucking insects like whiteflies and thrips. Here, we tested selected essential oils for their attractiveness to winged Aphis gossypii in potato fields. In field assays, selected essential oils with yellow or colorless sticky traps attracted more winged A. gossypii than controls. The combination of yellow traps baited with essential oils attracted ~2-3-fold more winged A. gossypii than did colorless traps baited with essential oils. In a multi-cycle 2 year study, yellow sticky traps baited with basil oil consistently attracted more winged A. gossypii than yellow sticky traps baited with lavender, geranium or tea tree oils. In electrophysiological studies, winged A. gossypii's antennae responded consistently to estragole in basil oil. In olfactometer assays with estragole, winged A. gossypii spent significantly more time in the treatment arm of the olfactometer than in the control arm, validating estragole's attractiveness. Furthermore, yellow sticky traps baited with pure estragole, in potato fields, attracted similar number of winged A. gossypii as yellow sticky traps baited with basil oil. Our findings demonstrate the potential of using basil oil as a potential attractant to improve the efficacy of sticky traps in the monitoring and control of winged aphids. © 2023 Society of Chemical Industry.

MiR-92a-1-p5 Modulated Expression of the flightin Gene Regulates Flight Muscle Formation and Wing Extension in the Pea Aphid, Acyrthosiphon pisum (Hemiptera: Aphidoidea).

Aphids exhibit wing polyphenism. Winged and wingless aphid morphs are produced by parthenogenesis depending on population density and host plant quality. Recent studies showed that microRNAs in alate and apterous individuals have differential expression and are involved in wing dimorphism of Acyrthosiphon pisum. From which miR-92a-1-p5 can target the mRNA of flight muscle gene flightin in vitro, but what effect they have on wing development of aphid is unclear. Here with the nanocarrier-delivered RNA interference (RNAi) method, flightin gene was knocked down in winged nymphs of A. pisum. Results showed that the majority (63.33%) of adults had malformed wings, the shape of dorsal longitudinal muscle (DLM) was deformed severely, the dorsoventral flight muscle (DVM) became wider and looser in aphids with flightin reduction compared with the negative control. Overexpression of miR-92a-1-p5 caused decreased expression of flightin and malformed wings of aphids, with a mutant ratio of 62.50%. Morphological analysis of flight musculature showed the consistent result as that with flightin knockdown. These results suggest that flightin is essential for flight musculature formation and wing extension in A. pisum, which can be modulated by miR-92a-1-p5.

Selection of Reference Genes for RT-qPCR Analysis of Wing Dimorphism in English Grain Aphid, Sitobion avenae (Hemiptera: Aphididae).

The English grain aphid, Sitobion avenae (Fabricius), exhibits classic and dramatic phenotypic plasticity in wing development. Both genetic and environmental inputs contribute to the wing polyphenism in aphids, an extreme form of phenotypic plasticity in which a single genotype produces discrete winged and wingless morphs. Validated reference genes are needed to accurately normalize temporal and spatial variation in gene expression estimates by RT-qPCR. In this research, the stability of 11 candidate reference genes selected from S. avenae transcriptomes was evaluated under an array of abiotic and biotic conditions relevant to wing development. RefFinder, a comprehensive software integrating rankings from delta Ct, BestKeeper, NormFinder, and geNorm, offered a series of reference genes for every experimental condition. Overall, helicase (HEL) and ubiquitin ribosomal protein S27A fusion protein (RpS27) are suited for most of the conditions examined in this study, although exceptions do exist. Specifically, NADH dehydrogenase (Ap-NADH) and 28S ribosomal RNA (28S) are recommended for insecticide and antibiotic treatments, while ribosomal RNA L14 (RPL14) and 18S ribosomal RNA (18S) are selected for density treatment, respectively. This study provides a suite of reference genes to investigate the wing polyphenism in S. avenae, and is important for application of RT-qPCR in future experiments of novel tactics to control aphids.

Sexual selection on population-level mating opportunities drives morph ratios in a fig wasp with extreme male dimorphism

BackgroundAlternative mating tactics are widespread in animals and associated with extreme morphological polymorphism in some insects. Some fig wasps have both highly modified wingless males and dispersing winged males. Wingless males mate inside figs before females disperse, while winged males mate elsewhere after dispersal. Hamilton proposed a model for this system with morphs determined by alternative alleles. This has an equilibrium where the proportion of winged males equals the proportion of females dispersing unmated; i.e. the proportion of matings that they obtain. Previously, we have shown qualitative support for this prediction across nine wing-dimorphic fig wasp species. Here I test the quantitative prediction in the fig wasp Pseudidarnes minerva. In addition, some fig wasp species that lack winged males, but have two wingless morphs, show a conditional strategy with morph determination influenced by the number of wasps developing in a patch. I also test for this alternative pattern in the wing-dimorphic P. minerva.ResultsI sampled 114 figs that contained a mean of 2.1 P. minerva wasps from 44 trees across four sites in Sydney, Australia. At the whole population level, the proportion of winged males (0.84 or 0.79 corrected for sampling bias) did not differ significantly from the proportion of unmated females (0.84), providing strong quantitative support for the prediction of Hamilton’s model. In addition, there was no evidence for other factors, such as local mate competition or fighting between wingless males, that could violate simplifying assumptions of the model. Meanwhile, the proportion of winged males was not correlated with the number of wasps per fig, providing no evidence for a conditional strategy.ConclusionThe morph ratio in P. minerva is consistent with Hamilton’s simple Mendelian strategy model, where morph ratios are set by average mating opportunities at the population level. This contrasts with some fig wasps from another subfamily that show conditional morph determination, allowing finer scale adaptation to fig-level mating opportunities. However, these conditional cases do not involve wing polymorphism. Male polymorphism is common and variable in fig wasps and has evolved independently in multiple lineages with apparently different underlying mechanisms.

Transcriptome analysis of the male polymorphisms of fig wasp species Philotrypesis tridentata

Intraspecific male polymorphism exhibiting extreme differences in morphology, behavior and life history presents good opportunities to explore adaptation mechanisms to different environments. In this study, we examined the transcriptomic differences between wingless and winged morphs of a fig wasp species Philotrypesis tridentata to investigate molecular basis to maintain polymorphisms. The winged male adults fly outside fig syconia to mate, while the wingless only stay and mate inside fig syconia where they have developed. We identified 2,391 differentially expressed genes (DEGs) with 1,396 highly expressed in winged morphs and 995 in wingless morphs. We performed Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses on the DEGs and differential alternative splicing genes and analyzed the top ten DEGs with the highest differential expression in each morph. The results showed that genes related to biosynthesis processes, lipid metabolism, energy production, flight and defense of the complex environments outside fig syconia were up-regulated in winged morphs. Genes involved in substance and energy metabolism and chemical reception were up-regulated in wingless morphs which might relate to their living inside fig syconia. The differences in highly expressed genes between two morphs prove adaptation of P. tridentata male polymorphism to different living environments.

MiR-147b-modulated expression of vestigial regulates wing development in the bird cherry-oat aphid Rhopalosiphum padi

BackgroundMost aphids exhibit wing polyphenism in which wingless and winged morphs produce depending on the population density and host plant quality. Although the influence of environmental factors on wing polyphenism of aphids have been extensively investigated, molecular mechanisms underlining morph differentiation (i.e. wing development /degeneration), one downstream aspect of the wing polyphenism, has been poorly understood.ResultsWe examined the expression levels of the twenty genes involved in wing development network, and only vestigial (vg) showed significantly different expression levels in both whole-body and wall-body of third instar nymphs, with 5.4- and 16.14- fold higher expression in winged lines compared to wingless lines, respectively in Rhopalosiphum padi. vg expression was higher in winged lines compared to wingless lines in third, fourth instar nymphs and adults. Larger difference expression was observed in third (21.38-fold) and fourth (20.91-fold) instar nymphs relative to adults (3.12-fold). Suppression of vg using RNAi repressed the wing development of third winged morphs. Furthermore, dual luciferase reporter assay revealed that the miR-147 can target the vg mRNA. Modulation of miR-147b levels by microinjection of its agomir (mimic) decreased vg expression levels and repressed wing development.ConclusionsOur findings suggest that vg is essential for wing development in R. padi and that miR-147b modulates its expression.

Mechanisms and consequences of flight polyphenisms in an outbreaking bark beetle species.

Flight polyphenisms naturally occur as discrete or continuous traits in insects. Discrete flight polyphenisms include winged and wingless morphs, whereas continuous flight polyphenisms can take the form of short- or long-distance fliers. The mountain pine beetle (Dendroctonus ponderosae) exhibits polyphenic variation in flight distance but the consequences of this flight variation on life history strategies of beetles is unknown. This study assessed the effect of flight on two particular aspects of beetle biology: (1) an energetic trade-off between flight distance and host colonisation capacity; and (2) the relationship between flight distance and pheromone production. A 23h flight treatment was applied to a subset of beetles using computer-linked flight mills. After flight treatment, both flown and unflown (control) beetles were given the opportunity to colonise bolts of host trees, and beetles that entered hosts were aerated to collect pheromone. A trade-off occurred between initiation of host colonisation and percentage body mass lost during flight, which indicates energy use during flight affects host acceptance in female mountain pine beetles. Furthermore, production of the aggregation pheromone trans-verbenol by female beetles was influenced by both percentage body mass lost during flight and flight distance. Male production of exo-brevicomin was affected by beetle condition following flight but not by the energy used during flight. These novel results give new insight into the polyphenic flight behaviour of mountain pine beetles. Flight variation is adaptive by acting to maintain population levels through safe and risky host colonisation strategies. These findings suggest mechanisms that facilitate the extremities of the continuous flight polyphenism spectrum. These opposing mechanisms appear to maintain the high variation in flight exhibited by this species.

Comparative transcriptional analysis provides insights of possible molecular mechanisms of wing polyphenism induced by postnatal crowding in Aphis gossypii

BackgroundAphis gossypii is a worldwide sap-sucking pest with a variety of hosts and a vector of more than 50 plant viruses. The strategy of wing polyphenism, mostly resulting from population density increasing, contributes to the evolutionary success of this pest. However, the related molecular basis remains unclear. Here, we identified the effects of postnatal crowding on wing morph determination in cotton aphid, and examined the transcriptomic differences between wingless and wing morphs.ResultsEffect of postnatal crowding on wing determination in A. gossypii was evaluated firstly. Under the density of 5 nymphs·cm− 2, no wing aphids appeared. Proportion of wing morphs rised with the increase of density in a certain extent, and peaked to 56.1% at the density of 20 nymphs·cm− 2, and reduced afterwards. Then, transcriptomes of wingless and wing morphs were assembled and annotated separately to identify potentially exclusively or differentially expressed transcripts between these two morphs, in which 3 126 and 3 392 unigenes annotated in Nr (Non-redundant protein sequence) database were found in wingless or wing morphs exclusively. Moreover, 3 187 up- and 1 880 down-regulated genes were identified in wing versus wingless aphid. Pathways analysis suggested the involvement of differentially expressed genes in multiple cellular signaling pathways involved in wing morphs determination, including lipid catabolic and metabolism, insulin, ecdysone and juvenile hormone biosynthesis. The expression levels of related genes were validated by the reverse transcription quantitative real time polymerase chain reaction (RT-qPCR) soon afterwards.ConclusionsThe present study identified the effects of postnatal crowding on wing morphs induction and demonstrated that the critical population density for wing morphs formation in A. gossypii was 20 nymphs·cm− 2. Comparative transcriptome analysis provides transcripts potentially expressed exclusively in wingless or wing morph, respectively. Differentially expressed genes between wingless and wing morphs were identified and several signaling pathways potentially involved in cotton aphid wing differentiation were obtained.

Morph-specific differences in life history traits between the winged and wingless morphs of the aphid, <i>Sitobion avenae</i> (Fabricius) (Hemiptera: Aphididae)

Life history traits were evaluated in the wing polyphenic aphid, Sitobion avenae (Fabricius), by rearing the winged and wingless morphs under the laboratory conditions. Winged morph with large thoraces exhibited a significantly greater morphological investment in flight apparatus than wingless morph with small thoraces. Compared to the winged morph, the wingless morph produced significantlymore nymphs and exhibited significantly faster nymph development rates. In addition, the age at which reproduction first occurred for the winged morph was significantly delayed, and higher mortality was recorded.The results suggest that the fitness differences associated with wingsmay be related to nymph development, adult fecundity, and mortality. Based on these results, the trends and exceptions of life history traits for the wing polyphenic insects are discussed.

The genes expression difference between winged and wingless bird cherry-oat aphid Rhopalosiphum padi based on transcriptomic data

Aphids produce wing and wingless morphs, depending on the environmental conditions during their complex life cycles. Wing and wingless variations play an important role in migration and host alternation, affecting the migration and host alternation processes. Several transcriptional studies have concentrated on aphids and sought to determine how an organism perceives environmental cues and responds in a plastic manner, but the underlying mechanisms have remained unclear. Therefore, to better understand the molecular mechanisms underlying the wing polyphenism of this fascinating phenomenon, we provide the first report concerning the wing development of aphids in bird cherry-oat aphid Rhopalosiphum padi with comparative transcriptional analysis of all the developmental stages by RNA-Seq. We identified several candidate genes related to biogenic amines and hormones that may be specifically involved in wing development. Moreover, we found that the third instar stage might be a critical stage for visibility of alternative morphs as well as changes in the expression of thirty-three genes associated with wing development. Several genes, i.e., Wnt2, Fng, Uba1, Hh, Foxo, Dpp, Brk, Ap, Dll, Hth, Tsh, Nub, Scr, Antp, Ubx, Asc, Srf and Fl, had different expression levels in different developmental stages and may play important roles in regulating wing polyphenism.

Effects of photoperiod and light intensity on wing dimorphism and development in the parasitoid Sclerodermus pupariae (Hymenoptera: Bethylidae)

Sclerodermus pupariae Yang et Yao (Hymenoptera: Bethylidae), a newly described ectoparasitoid, has been used as a biocontrol agent against several buprestid and cerambycid pests in China. Both winged and wingless female morphs of S. pupariae can find and parasitize hosts; however, winged parasitoids can disperse faster and further to new habitats and thus are more adapted to spatial and temporal changes in host densities than wingless morphs. In the present study, we determined the effects of photoperiod and associated light intensity on the parasitoid development time from egg to adult, the proportion of winged females, fecundity, and progeny sex ratio. Significantly more winged female parasitoid progeny were produced with long-day photoperiods and high light intensity compared to short day-photoperiods and low light intensity treatments. Photoperiod alone (regardless of light intensity) has significant impact on developmental time of parasitoid progeny. Light intensity, interacted with photoperiod, significantly affected the degree of phenotypic partitioning and development time, but light intensity and photoperiod did not significantly influence the parasitoid fecundity and sex ratio. These results are relevant to laboratory rearing of S. pupariae when the optimal light conditions are needed to produce winged female parasitoids.

Molecular Mechanisms of Wing Polymorphism in Insects.

Many insects are capable of developing into either long-winged or short-winged (or wingless) morphs, which enables them to rapidly match heterogeneous environments. Thus, the wing polymorphism is an adaptation at the root of their ecological success. Wing polymorphism is orchestrated at various levels, starting with the insect's perception of environmental cues, then signal transduction and signal execution, and ultimately the transmitting of signals into physiological adaption in accordance with the particular morph produced. Juvenile hormone and ecdysteroid pathways have long been proposed to regulate wing polymorphism in insects, but rigorous experimental evidence is lacking. The breakthrough findings of ecdysone receptor regulation on transgenerational wing dimorphism in the aphid Acyrthosiphon pisum and of insulin signaling in the planthopper Nilaparvata lugens greatly broaden our understanding of wing polymorphism at the molecular level. Recently, the advent of high-throughput sequencing coupled with functional genomics provides powerful genetic tools for future insights into the molecular bases underlying wing polymorphism in insects.

ITRAQ-Based Comparative Proteomic Analysis Reveals Molecular Mechanisms Underlying Wing Dimorphism of the Pea Aphid, Acyrthosiphon pisum.

Wing dimorphism is a widespread phenomenon in insects with an associated trade-off between flight capability and fecundity. Despite the molecular underpinnings of phenotypic plasticity that has already been elucidated, it is still not fully understood. In this study, we focused on the differential proteomics profiles between alate and apterous morphs of the pea aphid, Acyrthosiphon pisum at the fourth instar nymph and adult stages, using isobaric tags for relative and absolute quantitation (iTRAQ) in a proteomic-based approach. A total of 5,116 protein groups were identified and quantified in the three biological replicates, of which 836 were differentially expressed between alate and apterous morphs. A bioinformatics analysis of differentially expressed protein groups (DEPGs) was performed based on gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG). KEGG enrichment analysis showed that DEPGs mainly participated in energy metabolism, amino acid biosynthesis and metabolism, and signal sensing and transduction. To verify the reliability of proteomics data, the transcriptional expression of 29 candidates of differentially expressed proteins were analyzed by quantitative real-time PCR (qRT-PCR), showing that 26 genes were consistent with those at proteomic levels. In addition, differentially expressed proteins between winged and wingless morphs that were linked to olfactory sense were investigated. Quantitative real-time PCR revealed the tissue- and morph-biased expression profiles. These results suggested that olfactory sense plays a key role in wing dimorphism of aphids. The comparative proteomic analysis between alate and apterous morphs of the pea aphid provides a novel insight into wing development and dimorphism in aphids and will help facilitate our understanding of these concepts at molecular levels.

Solid-phase microextraction-based cuticular hydrocarbon profiling for intraspecific delimitation in Acyrthosiphon pisum.

Insect cuticular hydrocarbons (CHCs) play critical roles in reducing water loss and chemical communication. Species-specific CHC profiles have been used increasingly as an excellent character for species classification. However, considerably less is known about their potential for population delimitation within species. The aims of this study were to develop a solid-phase microextraction (SPME)-based CHC collection method and to investigate whether CHC profiles could serve as potential chemotaxonomic tools for intraspecific delimitation in Acyrthosiphon pisum. Optimization of fibers for SPME sampling revealed that 7 μm polydimethylsiloxane (PDMS) demonstrated the most efficient adsorption of CHCs among five different tested fibers. SPME sampling showed good reproducibility with repeated collections of CHCs from a single aphid. Validation of SPME was performed by comparing CHC profiles with those from conventional hexane extractions. The two methods showed no qualitative differences in CHCs, although SPME appeared to extract relatively fewer short-chained CHCs. While CHC profiles of a given population differed among developmental stages, wing dimorphism types, and host plants, wingless adult aphids showed very low variance in relative proportions of individual CHC components. Reproducibility of CHC profiles was explored further to classify wingless adult morphs of A. pisum from five different geographic regions that showed no variation in mitochondrial COI gene sequences. Our results demonstrate that CHC profiles are useful in intraspecific delimitation in the field of insect chemotaxonomy.

Winged Pea Aphids Can Modify Phototaxis in Different Development Stages to Assist Their Host Distribution.

The pea aphid, Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae), shows wing polyphenism (winged and wingless morphs) in its life cycle. The winged morph is adapted for dispersal; its two developmental adult stages (for dispersal and reproduction) are based on its breeding periods. The two morphs show different phototactic behavior and the winged can change its preference to light according to the developmental stages. To determine the mechanism and ecological functions of phototaxis for A. pisum, we first investigated the phototaxis of the two aphid morphs at different stages and analyzed the phototactic response to lights of different wavelengths; the correlation between alate fecundity and their phototactic behaviors were then studied. Finally, we focused on the possible functions of phototaxis in aphid host location and distribution in combination with gravitaxis behaviors. Negative phototaxis was found for breeding winged adults but all the other stages of both winged and wingless morphs showed positive phototaxis. The reactions of the aphids to different wavelengths were also different. Nymph production in winged adults showed negative correlation to phototaxis. The dopamine pathway was possibly involved in these behavior modifications. We speculated that winged adults can use light for dispersal in the early dispersal stage and for position holding in the breeding stage. Based on our results, we assume that light signals are important for aphid dispersal and distribution, and are also essential for the pea aphids to cope with environmental changes.

Long Chain Alcohols Produced by Trichoderma citrinoviride Have Phagodeterrent Activity against the Bird Cherry-Oat Aphid Rhopalosiphum padi.

In this study we report the effects of fungal metabolites isolated from cultures of the fungus Trichoderma citrinoviride ITEM 4484 on the feeding preference of the aphid Rhopalosiphum padi, a major pest of cereal crops. Different phagodeterrent metabolites were purified by a combination of direct and reverse phase column chromatography and thin-layer chromatography. Chemical investigations, by spectroscopic and chemical methods, led to the identification of different long chain primary alcohols (LCOHs) of the general formula R-OH, wherein R is a long, unbranched, unsubstituted, linear aliphatic group. LCOHs have been reported as components of lepidopteran pheromone blends, but their phagodeterrent effect to aphids is herein reported for the first time. The effects of LCOHs on R. padi were studied by behavioral and electrophysiological bioassays. Feeding preference tests that were carried out with winged and wingless morphs of R. padi showed that LCOHs had high phagodeterrent activity and restrained aphids from settling on treated leaves at a concentration as low as 0.15 mM (0.036 g/l). The results of different electrophysiological analyses indicated that taste receptor neurons located on the aphid tarsomeres were involved in the LCOHs perception. Behavioral assays carried out with some commercial agrochemicals, including azadirachtin A, pyrethrum and a mineral oil-based product, in combination with 1-hexadecanol, the LCOH most abundantly produced by T. citrinoviride ITEM 4484, showed that these different active principles could be applied together, resulting in a useful increase of the phagodeterrent effect. The data shown indicate that these compounds can be profitably utilized for novel applications in biotechnical control of aphid pests. Furthermore, the tested LCOHs have no chiral centers and therefore can be obtained with good yield and at low cost through chemical synthesis, as well as from natural sources.

Insulin-Related Peptide 5 is Involved in Regulating Embryo Development and Biochemical Composition in Pea Aphid with Wing Polyphenism.

In aphids there is a fecundity-dispersal trade-off between wingless and winged morphs. Recent research on the molecular mechanism of wing morphs associated with dispersal reveals that insulin receptors in the insulin signaling (IS) pathway regulate alternation of wing morphs in planthoppers. However, little is known about whether genes in the IS pathway are involved in developmental regulation in aphid nymphs with different wing morphs. In this study, we show that expression of the insulin-related peptide 5 gene (Apirp5) affects biochemical composition and embryo development of wingless pea aphids, Acyrthosiphon pisum. After comparing expression levels of major genes in the IS pathway between third instar winged and wingless nymphs, we found that Apirp5 showed higher expression in head and thorax in the wingless nymphs than in the winged nymphs. Although microinjection treatment affects physical performance in aphids, nymphs with RNA interference of Apirp5 had less weight, smaller embryos, and higher carbohydrate and protein contents compared to the control group. Comparison between winged and wingless nymphs showed a similar trend. These results indicate that Apirp5 is involved in embryo development and metabolic regulation in wing dimorphic pea aphid.