Sinigrin as a feeding deterrent in two crucifer-feeding, polyphagous lepidopterous species and the effects of feeding stimulant mixtures on deterrency

The glucosinolate, sinigrin (allyl- or 2-propenyl glucosinolate), present in several Gruciferae, was incorporated in varying concentrations into four different diet background mixtures to study the behavioural reactions of Mamestra configurata and Trichoplusia ni. Sinigrin concentrations were chosen to mimic normal levels in naturally occurring cruciferous plants, or to represent a plant during a particular stage in its growth cycle. One diet background mixture contained potassium chloride (KC1) and no stimulatory sugar or sugar alcohol, two backgrounds contained KC1 and a single sugar or sugar alcohol (sucrose or inositol, respectively), and the fourth background contained KC1 and both sugar and sugar alcohol (sucrose and inositol, respectively). Sinigrin acted primarily to reduce (deter) feeding in all backgrounds, although the effect varied with sinigrin concentration, background and species. When inositol or sucrose was included in the mixture, the deterrent effect of sinigrin was decreased in both species. When inositol and sucrose were present, suppression of the deterrent effect of sinigrin was greatest for M. configurata . The effects of mixtures were not predictable from a knowledge of the action of individual components. Differences observed between species may reflect different sensory capabilities.