The effect of phagostimulant mixtures on deterrent receptor(s) in two crucifer-feeding lepidopterous species

Abstract

Sinigrin was incorporated in varying concentrations into four background mixtures. One background mixture contained potassium chloride (KCl) and no stimulatory sugar or sugar alcohol, two backgrounds contained KCl and a single sugar or sugar alcohol (sucrose or inositol, respectively), and the fourth background contained KCl and both sugar and sugar alcohol (sucrose and inositol, respectively). The lateral sinigrin-sensitive cell of Mamestra configurata was suppressed by phagostimulants at a low sinigrin concentration range. Electrophysiological suppression of sinigrin-sensitive cells in both the lateral and medial sinigrin-sensitive cells of Trichoplusia ni was effective at a low to high sinigrin concentration range. Independent of sinigrin concentration, it appeared that inositol, sucrose, and their combination, equally suppressed the lateral sinigrin-sensitive cell of M.configurata and a combination of both inositol and sucrose suppressed the lateral and medial sinigrin-sensitive cells of T. ni . There was an interaction between inositol and sucrose; inositol did not suppress or enhance the response to sucrose of the sucrose-sensitive cells in either species, but sucrose suppressed the response of the medial M. configurata inositol-sensitive cell to inositol. Inositol and sucrose backgrounds were effective in suppressing responses to potassium chloride in M. configurata , but not in T. ni . These sensory-based mixture effects, all of which were suppressive, are used to propose mechanisms for the ameliorating effect of inositol and sucrose on the feeding deterrent action of sinigrin.