Is sequestration structure-specific in the milkweed bug, Oncopeltus fasciatus?

Extracts of Oncopeltus fasciatus adults, fed from the first instar on sunflower seed diets impregnated with bufadienolides-cardenolide analogs, contained no detectable bufadienolides or polar steroid metabolites on TLC. O. fasciatus did sequester cardenolides from host and non-host sources, and bufadienolides were recovered from extracts of impregnated seeds. Possible reasons for the absence of detectable bufadienolides in these insects are suggested.