5.2. Light and insect herbivory
As insects feed, they damage the plants. Insect herbivores can be detected by the perception of damage-associated molecular patterns (DAMPs) or of herbivore-associated molecular patterns (HAMPs) which include fatty acid-amino conjugates (FACs; Heil, 2009). FACs are present in the oral secretion of most lepidopteran larvae (Yoshinaga et al., 2010). Although most of the molecular mechanisms connecting light with herbivore attack are not yet known, observations have been made indicating that especially UV-B light has a positive effect on the plant responses to insect herbivores (Escobar-Bravo, Klinkhamer, & Leiss, 2017). For example, Caputo, Rutitzky and Ballare (2006) showed that UV-B influences the attractiveness of Arabidopsis plants to diamondback moths (Plutella xylstella ). Moreover, they described that this beneficial effect of UV-B light on the reduction of egg number was compromised in the jar1 mutant suggesting that intact JA biosynthetic and signaling pathway are required for the defense response. A similar beneficial effect of UV was also observed in thedefenseless1 tomato mutant which is deficient in JA. Here, a strong activation of SA-associated defense responses by UV after thrips infestation was observed (Escobar-Bravo et al., 2019). UV-B treatment also enhanced the resistance of Arabidopsis to Spodopera litura herbivores through a JA-dependent mechanism (Qi et al., 2018). In addition Radhika et al. (2010) demonstrated that in lima bean (Phaseolus lunatus ) the JA-regulated secretion of extrafloral nectar (EFN) attracting ants which protect plants against herbivores is dependent on light (Kazan and Manners, 2011). These examples indicate that a close connection between herbivore resistance and UV-B signaling acting through JA biosynthesis and signaling pathways exists.