Oviposition by lepidopteran herbivores on Nicotiana attenuata primes plant defence responses that are induced by the feeding larvae. While oviposition by both the generalist Spodoptera exigua and the specialist Manduca sexta primes the production of defensive phenylpropanoids, their larvae are differentially affected. We investigate here the impact of prior oviposition on the transcriptome and phytohormone levels of plants that were later attacked by larvae to find regulatory signals of this priming. In a full-factorial design, we evaluated the effects of oviposition and herbivory by both species. Oviposition alone had only subtle effects at the transcriptional level. Laval feeding alone induced species-specific plant responses. Larvae of the generalist regulated phytohormones and gene expression stronger than larvae of the specialist. A day after larvae started to feed, we detected no significant alterations of the plant's response to larval feeding due to prior oviposition by conspecific moths. Yet, oviposition by each of the species profoundly influenced the plant's transcriptional and phytohormonal response to feeding larvae of the other species. Remarkably, the species-specific plant responses to larval feeding shifted towards the response normally elicited by larvae of the ovipositing species. Thus, plants may already recognise an insect's identity upon its oviposition.
Overall design
The effect of feeding and oviposition by M. sexta and S.exigua was studied in a 3x3 full factorial design. Per treatments 11-12 plants were used, that were pooled into three samples for hybridization on the arrays. The feeding treatments followed insect oviposition at their natural developmental time (3 and 4 days after S. exiua and M. sexta oviposition, respectively) and were performed on a leaf systemic to the oviposited leaf. The leaves were harvested 1 day after feeding, respectively 5 and 6 days after oviposition.
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