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Abstract Background Aphis 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. Results Effect 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. Conclusions The 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.

Abstract: Polyphenism constitutes a key example of the adaptability of a genotype to a shifting environment. In aphids, the relative production of apterous and alate individuals is influenced by cues resulting from increases in population density, changes in plant quality, and natural enemies. The ability to respond to multiple environmental cues offers aphids an effective way to optimize their fitness. Understanding the mechanisms behind alate morph production is particularly important in aphid species that are agricultural pests. We tested the effects of crowding and host plant quality cues on morph determination in Aphis glycines Matsumura (Hemiptera: Aphididae). We exposed A. glycines to pre‐natal and post‐natal crowding under laboratory conditions. In the field, we reared nymphs of A. glycines at high‐density vs. low‐density conditions in clip cages set on the top vs. bottom nodes of infested and uninfested soybean plants, Glycine max (L.) Merrill (Fabaceae). Apterous adult body size was used as an estimate of aphid performance, and the proportion of morphs developing under each condition was determined. Both pre‐ and post‐natal crowding induced the production of asexual alate individuals by A. glycines. In the field, we observed additive negative effects of lower overall plant quality (infested vs. uninfested plants), within‐plant differences in nutritional quality (bottom vs. top nodes), and high vs. low levels of crowding on aphid size. These three factors also interacted to increase the proportion A. glycines nymphs that developed wings. Our results suggest two levels in the production of asexual alate individuals by A. glycines: (1) a moderate level in response to aggregation, triggered by crowding cues, and (2) a high level in response to plant quality deterioration, triggered by both plant quality and crowding cues. These two processes ensure a flexible production of asexual alate individuals, allowing aphids to adapt to changing environmental conditions. [ABSTRACT FROM AUTHOR]

1. Winged dispersal is vital for aphids as predation pressure and host plant conditions fluctuate. 2. Ant-tended aphids also need to disperse, but this may represent a cost for the ants, resulting in an evolutionary conflict of interest over aphid dispersal. 3. The combined effects of aphid alarm pheromone, indicating predation risk, and ant attendance on the production of winged aphids were examined in an experiment with Aphis fabae ( Homoptera: Aphididae) ( Scopoli 1763) aphids and Lasius niger ( Formicidae: Formicinae) ( Linné, 1758) ants. 4. This study is the first to investigate the joint effects of alarm pheromone and ant attendance, and also the first to detect an influence of alarm pheromone on the production of winged morphs in A. fabae. 5. After a period of 2 weeks, it was found that aphid colonies exposed to intermittent doses of alarm pheromone produced more winged individuals, whereas ant tending had the opposite effect. The effects were additive on a log scale, and ant attendance had a greater proportional influence than exposure to alarm pheromone. A tentative conclusion is that ants have gained the upper hand in an evolutionary conflict about aphid dispersal. [ABSTRACT FROM AUTHOR]