Bioassays to Investigate the Effects of Insect Oviposition on a Plant’s Resistance to Herbivores

Abstract

Plants respond to herbivory with diverse defence responses (Schoonhoven et al., 2005). Many herbivorous insects deposit their eggs on their host plants before their larvae start to feed. Thus, plants could use insect eggs as a signal to increase their resistance to herbivores. Here, we report experimental procedures to explore whether and how insect oviposition impacts on plant resistance against the feeding larvae. The described approach revealed that Nicotiana attenuata (N. attenuata) plants that were previously exposed to oviposition by lepidopteran moths respond to herbivory by generalist Spodoptera exigua (S. exigua) and specialist Manduca sexta (M. sexta) larvae with an increased induction of defence responses, which results in a decreased performance or immune state of the feeding larvae (Bandoly et al., 2015; Bandoly et al., 2016). Consequently, insect oviposition can prime feeding-induced plant defence (priming: an enhanced plant response to stress upon the experience of a prior stimulus; Hilker et al., 2015). Full-factorial experiments with standardised procedures for insect oviposition and larval herbivory allow to decipher the effect of the plant exposure to insect eggs on the larval performance, feeding damage and immune state as well as to discriminate egg-induced plant responses from egg-primed responses to larval feeding.