UV exposure induces resistance against herbivorous insects in broccoli

Abstract

UV-radiation (UV-A and UV-B) can affect the behaviour of herbivorous insects either directly or indirectly through plantinsect interactions. Short-wavelength radiation is perceived by plants through specific receptors which results particularly in the biosynthesis of secondary plant metabolites. Known induced substances are mainly flavonoids which primarily act as sunscreens, but also have the potential to influence the development of herbivorous insects. This study investigated the development of the cabbage aphid (Brevicoryne brassicae, Hemiptera: Aphididae) and the diamondback moth (Plutella xylostella, Lepidoptera: Plutellidae) on UV-exposed broccoli plants (Brassica oleracea, Brassicales: Brassicaceae). Constant low-intensity UV-radiation emitted by UV-lamps in the greenhouse increased the developmental time of both insect species. On UV-exposed plants P. xylostella reached lower pupa weights, while B. brassicae showed higher adult weights, but significantly reduced fecundity compared to aphids on plants isolated from UV-radiation. In outdoor experiments the global UV-radiation was manipulated in small greenhouses equipped with plastic-films of different UV-absorbing properties. The reduction of ambient UV-radiation by UV-absorbing plastic-films resulted in increased pupa weight of P. xylostella and fecundity of B. brassicae.