Plant response to feeding aphids promotes aphid dispersal

Plant responses against biotic stress agents are affected by a number of environmental conditions, including the presence of other pests and pathogens. Moreover, the impact of infestation on subsequent plant colonization by conspecifics can vary, reflecting the high diversity in the co-evolutionary processes shaping host-plant interactions. Here, we address this issue by studying how aphid-plant interplay can influence the subsequent colonization of zucchini plants (Cucurbita pepo L., Cucurbitaceae) by conspecific Aphis gossypii Glover (Hemiptera: Aphididae, Aphidini). Previous infestation does not impact development time, longevity, and fertility of aphids. However, a previous infestation affects the distribution of the newly produced nymphs on the plant - they actively disperse on the plant, rather than starting their feeding activity where they were originally deposited, as observed in controls. Interestingly, this altered dispersal behaviour is reproduced by saliva application, suggesting the occurrence of an elicitor triggering a plant response affecting the strategy of host-plant colonization by A.gossypii. The hypothesis that salicylic acid (SA) induction can trigger the observed behavioural response in a secondary infestation, was confirmed by exposure to methyl salicylate, a volatile product of the SA pathway. This evidence was further corroborated by analysis of gene expression profiles. Aphid infestation showed a transcriptional up-regulation of genes underlying the biosynthesis of SA and of genes modulating the SA-mediated defence response. Collectively, the experimental data consistently indicate regulation of aphid behaviour, mediated by plant metabolic changes following aphid infestation.