Feeding choice and performance of the generalist Spodoptera exigua and the specialist Pieris rapae are modified by glucosinolate profile variation in genetically modified lines of Arabidopsis thaliana

Glucosinolates and their hydrolysis products in plants of the order Brassicales are known for their defensive properties against insect herbivores. Arabidopsis thaliana genetic lines with mutations that modify glucosinolate profiles allow testing specific effects of these chemicals on insect herbivores. The wild type Col-0 and five genetically modified (GM) lines were used in this study: (i) myb28myb29 lacks aliphatic glucosinolates; (ii) cyp79B2cyp79B3 lacks indolyl glucosinolates; (iii) pad3 does not produce camalexin; (iv) the nitrile-producing line 35S:ESP; and (v) the double knockout tgg1tgg2 does not produce isothiocyanates naturally present in wild type Col-0. These genetic lines were used to evaluate performance and feeding choice of the generalist Spodoptera exigua and the specialist Pieris rapae. In no-choice experiments, differences in glucosinolate hydrolysis products did not affect performance of the specialist Pieris rapae, but the lack of indolyl glucosinolates significantly influenced pupae weight and days to pupation. When given a choice, P. rapae larvae did not show any statistically significant preferences for genetic lines with different hydrolysis products either. In contrast, performance of the generalist Spodoptera exigua was significantly affected by both type of glucosinolate and hydrolysis products (increased in the absence of aliphatic and indolyl glucosinolates. Results from feeding choice trials showed that S. exigua had a significant feeding preference for the double mutant tgg1tgg2, which virtually lacks hydrolysis products. Overall, this study provides evidence that variation in glucosinolate profiles and hydrolysis products can influence insect performance and feeding choices, and that insect responses are species-specific.