Defense of pyrethrum flowers: repelling herbivore and recruiting carnivore by producing aphid alarm pheromone

Jinjin Li, Hao Hu, Jing Mao, Lu Yu, Geert Stoopen, Manqun Wang, Roland Mumm, Norbert C.A. de Ruijter, Marcel Dicke, Maarten A. Jongsma*, Caiyun Wang

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

E)‐β‐farnesene (EβF) is the predominant constituent of the alarm pheromone of most aphid pest species. Moreover, natural enemies of aphids use EβF to locate their aphid prey. Some plant species emit EβF, potentially as a defense against aphids, but field demonstrations are lacking.Here, we present field and laboratory studies of flower defense showing that ladybird beetles are predominantly attracted to young stage‐2 pyrethrum flowers that emitted the highest and purest levels of EβF. By contrast, aphids were repelled by EβF emitted by S2 pyrethrum flowers. Although peach aphids can adapt to pyrethrum plants in the laboratory, aphids were not recorded in the field. Pyrethrum's (E)‐β‐farnesene synthase (EbFS) gene is strongly expressed in inner cortex tissue surrounding the vascular system of the aphid‐preferred flower receptacle and peduncle, leading to elongated cells filled with EβF. Aphids that probe these tissues during settlement encounter and ingest plant EβF as evidenced by the release in honeydew. These EβF concentrations in honeydew induce aphid alarm responses, suggesting an extra layer of this defense.Collectively, our data elucidate a defensive mimicry in pyrethrum flowers: the developmentally regulated and tissue‐specific EβF accumulation and emission both prevents attack by aphids and recruits aphid predators as bodyguards.
Original languageEnglish
Pages (from-to)1607-1620
JournalNew Phytologist
Volume223
Issue number3
Early online date14 May 2019
DOIs
Publication statusPublished - Aug 2019

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