Only the larval stages of the moths consume grain. Therefore, adult moths may be present in treated grain, which is protected from larval damage by the insecticide. Further, the life cycle of the insect is interrupted and multiplication does not occur, as all larvae are killed by the protectant.
In order to be effective, grain protectants are developed and formulated to maintain their toxic properties for an extended period.
By contrast, a major stored grain insect of field peas, the pea weevil (Bruchus pisorum) is not controlled by seed treatments. Pea weevils infest the seed before harvest and do not ingest the seed during storage. Thus, multiplication can occur, uninhibited.