Diatomaceous earth is an inert substance--mostly silica in a very spiny arrangement. It is active as long as it remains in place, but because it is a dust, it easily wears off. It affects insects as a repellent and drying agent, which causes susceptible insects when they become coated with it, to lose their waxy cover and dry out. In the case of flea beetles and grasshoppers, effectiveness is primarily due to repellency, which to be effective needs to be maintained with a fair amount of application. Reapplication at fairly frequent intervals (say two times a week) is often necessary, particularly if it is washed off by rain or irrigation. Plants can be washed after the flea beetles (or other insects) are gone, or they can be left with the dust. Diatomaceous earth is not a pesticide in the normal sense, i.e., acting on nervous systems or other physiological processes in the pests, and it has no observed effects if ingested. It is sometimes used as a feed-trough additive for livestock to assist with control of some parasites. Carbaryl (Sevin) is the most effective consumer insecticide for flea beetles and permethrin is also good.