Tannic Acid as a Repellent and Toxicant to Alfalfa Weevil Larvae

A peculiarity in larval feeding of the alfalfa weevil, Hypera postica (Gyllenhal), was noted near Greeneville, Tenn., in 1964. The larvae had devoured all alfalfa in an untreated field except for an area at one end where some fallen oak tree tops lay. Around these tops the alfalfa was undamaged by the weevils; however, some leaves were mottled with what appeared to be exudate from the tree. This finding suggested that tannin, a well-known constituent of oak, possibly afforded the alfalfa protection against the weevil. Consequently, tests were initiated in the laboratory to determine if the larvae would feed on alfalfa sprayed with tannin.