CARDENOLIDES AS OVIPOSITION DETERRENTS TO 2 PIERIS SPECIES - STRUCTURE-ACTIVITY-RELATIONSHIPS

Oviposition responses of Pieris rapae and P. napi oleracea to 18 cardenolides were compared under the same conditions. Effects of different concentrations of selected cardenolides were also tested. Most of the compounds were deterrent to oviposition by both insects, but to significantly different degrees. P. rapae were strongly deterred by K-strophanthoside, K-strophanthin-beta, cymarin, convallatoxin, oleandrin, erysimoside, erychroside, and gitoxigenin. The most deterrent compounds for P. napi oleracea were erychroside, cymarin, erysimoside, convallatoxin, and K-strophanthoside. Strophanthidin-based glycosides were more deterrent than digitoxigenin-based ones, arid the number and type of sugar substitutions can have profound effects on activity. Both similarities and contrasts were found in responses of P. rapae and P. napi oleracea to these cardenolides. Cymarin was equally deterrent to both Pieris species at all concentrations tested. However, when compared with P. rapae, P. napi oleracea was less sensitive to most of the cardenolides. P. napi oleracea was insensitive to K-strophanthin-beta and oleandrin at 0.5 x 10(-4) M, which were highly deterrent to P. rapae.