Plant Glucosinolate Content and Host-Plant Preference and Suitability in the Small White Butterfly (Lepidoptera: Pieridae) and Comparison with Another Specialist Lepidopteran.

Glucosinolates are used in host-plant recognition by insects specialized on Brassicaceae, such as Pieris rapae L. (Lepidoptera: Pieridae). This research investigated the association between P. rapae oviposition and larval survival and host-plant glucosinolate content using 17 plant species in which glucosinolate content had previously been determined. Two-choice oviposition tests (comparing each plant species to Arabidopsis thaliana L.) and larval survival experiments showed that indolic glucosinolate content had a positive effect on oviposition preference and larval survival in P. rapae. In the host plants tested, the effects of indolic glucosinolates on oviposition preference and of glucosinolate complexity index and aliphatic glucosinolates without sulfur-containing side chains on total oviposition were smaller on P. rapae than on Plutella xylostella L. (Lepidoptera: Plutellidae), another lepidopteran specialized on glucosinolate-containing plants. This study suggests that high indolic glucosinolate content could make crop plants more susceptible to both P. rapae and P. xylostella, but this effect seems to be greater for P. xylostella. Additionally, as some differences in oviposition and larval survival between P. rapae and P. xylostella occurred in some individual plants, it cannot be concluded that bottom-up factors are always similar in these two specialist insects.

Plant-Insect Interactions.

The central part of the study of plant-insect interactions comes from our quest for knowledge on why and how these interactions occur [...].

Glucosinolate Induction and Resistance to the Cabbage Moth, Mamestra brassicae, Differs among Kale Genotypes with High and Low Content of Sinigrin and Glucobrassicin.

The cabbage moth, Mamestra brassicae L. (Lepidoptera: Noctuidae), is a generalist insect pest of cruciferous crops. We tested glucosinolate induction by jasmonic acid (JA) and salicylic acid (SA), and by these phytohormones combined with feeding by M. brassicae larvae in four genotypes of kale, Brassica oleracea L. var. acephala (Brassicaceae). The genotypes tested had high glucobrassicin (genotype HGBS), low glucobrassicin (genotype LGBS), high sinigrin (genotype HSIN), and low sinigrin content (genotype LSIN). Application of JA increased indolic and total glucosinolate content in all kale genotypes 1, 3, and 9 days after treatment. For SA-treated plants, glucosinolate induction varied depending on the number of days after treatment and the genotype. Overall, herbivory by M. brassicae accentuated and attenuated the effects of JA and SA, respectively, on plant glucosinolate content. Larvae of M. brassicae gained less weight on leaves from plants treated with JA compared to leaves from control plants and plants treated with SA. In bioassays with leaf discs, a significant reduction of defoliation only occurred in JA-treated plants of the HSIN genotype. This research shows that previous herbivory alters the susceptibility of kale to M. brassicae and that induction of glucosinolates varies among kale genotypes differing in their glucosinolate content.

Phylloplane location of glucosinolates in Barbarea spp. (Brassicaceae) and misleading assessment of host suitability by a specialist herbivore.

Glucosinolates are plant secondary metabolites used in host plant recognition by insects specialized on Brassicaceae, such as the diamondback moth (DBM), Plutella xylostella. Their perception as oviposition cues by females would seem to require their occurrence on the leaf surface, yet previous studies have reached opposite conclusions about whether glucosinolates are actually present on the surface of crucifer leaves. DBM oviposits extensively on Barbarea vulgaris, despite its larvae not being able to survive on this plant because of its content of feeding-deterrent saponins. Glucosinolates and saponins in plant tissue and mechanically removed surface waxes from leaves of Barbarea spp. were analyzed with high-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS). Surface waxes from leaves of Barbarea spp. contained glucosinolates, but not feeding-deterrent saponins. Our research is the first to show that glucosinolates are present on the leaf surface of Barbarea spp., but not in other crucifers investigated, resolving some conflicting results from previous studies. Our research is also the first to quantify glucosinolates on the leaf surface of a crucifer, and to show that the concentrations of glucosinolates found on the leaf surface of Barbarea spp. are sufficient to be perceived by ovipositing DBM.