RICE WEEVIL Sitophilus oryza

This insect is a member of the order Coleoptera. It is in the family Curculionidae, the weevils or "snout beetles". The alfalfa weevil is another member of this family that we will study.

This insect is one of the most important pests of stored grain in the world. Its original home may have been India and it was spread throught the world in grain shipments. The rice weevil is primarily found in the southern US - North Carolina and south. The granary weevil (Sitophilus granarius) occurs in the northern US - north of NC.

Biology

Rice and granary weevils are primary pests, they attack whole kernels. The female uses the mandibles at the end of her "snout" to chew a cavity in the seed. She turns around and lays an egg in the cavity. The hole is sealed over with just the tip of the egg sticking out. Only about 50% of the 400 or so eggs that she lays will hatch. Eggs hatch in about 3 days.

The legless larva is creamy white with a dark brown head. There are 3 larval instars. The entire larval period lasts about 18 days, followed by a 6 day pupal period. The adult emerges about 3 days later, after it has hardened. They live about 6 months. Rice weevils can fly, granary weevils cannot.

Most weevils draw up their legs and "play possum" if disturbed. The rice weevil is attracted to light, the granary weevil is not.

Ideal conditions are - temperature in the low 80's (F) and high humidity. Grain moisture needs to be 13% to 17%.