Common Name: Granary Weevil
Scientific Name: Sitophilus granarius (Linnaeus)
This weevil has been a major pest for centuries. It occurs worldwide in the cooler climates. In the United States, it is usually found breeding from, and including, North Carolina northward.
Adults about 1/8-1/4″ (3-4.8 mm) long. Color usually shining reddish brown but sometimes nearly black, elytra (wing covers) lack any pale marks. Punctures or pits on thorax elongated. Wings vestigal (greatly reduced), cannot fly.
Male’s snout/beak shorter, wider, with more distinct punctures than that of female’s. Larva legless. Color white with a dark head. Thickened in middle (humpbacked), relatively smooth. Labial palp with less than 7 (usually 5) apical sensory palpillae (tiny fingerlike projections).
(1) Rice weevil (Sitophilus oryzae) and maize weevil (S. zeamais) have 4 faint pale spots on elytra (wing covers), punctures (pits) on thorax round or irregular in shape. (2) Broadnosed grain weevil (Caulophilus oryzae) with a short broad snout, snout length about twice width or less.
The granary weevil female bores a hole into a kernel of grain and lays an egg, sealing the opening with a gelatinous material. The egg hatches in a few days and the larva feeds on the internal portion of the kernel. A female can lay more than 200 eggs under favorable conditions (range 36-254). There are 4 larval instars which require 19-34 days for development. Pupation occurs within the kernel and requires 5-16 days.
The entire life cycle (egg to egg) may be as short as 1 month during the summer or as long as 5 months during the winter, being very dependent upon the temperature. There are usually 4 generations per year. The adults can live for 7-8 months.
Because its wings are vestigal, the granary weevil is confined to stored grain and is primarily transported by man. The larva typically requires a whole kernel for development but can develop in caked grain material. It attacks all kinds of grains and grain products. When disturbed, it draws its legs up to its body and plays “possum. “Adults are not attracted to light.
Follow the standard control procedures for stored product pest. All stages can be killed by exposure to temperatures of 120F (49C) for 1 hour or 130F (54C) for 30 minutes.