Grain Storage Inspections Should Begin Close to Thanksgiving
Inspecting grain bins for pests on or before Thanksgiving is a great rule of thumb for Chouteau County producers. The Lesser grain borer Rhyzopertha dominica is one of the most injurious beetles known to attack stored grain. The Lesser grain borer belongs to the Bostrichidae family of beetles, which are mostly wood boring insects. R. dominica causes major physical and off-odor damage to grain in storage.
Identifying Characteristics: Adults are dark reddish-brown to black in color, and 2-3 mm in length. The head is hidden under the prothorax. The hard shell like forewings (elytra) have distinct rows of pits. Antennae have ten segments with the last three enlarged forming a distinctive 3-segmented club.
Larvae are white, stout bodied, C-shaped and immobile.
Description of Damage: Adults and larvae feed on the germ and endosperm, which reduces wheat kernels to hollow husks. The Lesser grain borer also burrows through the kernel and causes distinctive and heavy damage. R. dominica will survive and develop in the accumulated “flour” produced as the seeds are chewed up. Signs of infestation include large amounts of flour, tunnels and irregularly shaped holes in cereals.
Summary of Lifecycle: The female lays her eggs loosely among the grain so that larva and adults can cause multiple injury. Females lay up to 500 eggs over 3 months in optimal conditions of 91°F and a relative humidity between 50% to 60%. A lesser grain borer can develop from egg to adult in 25-58 days. The larva pupates inside a tunnel in the grain kernel. When the adult emerges, it chews its way out of the grain kernel. The adult may live up to 240 days.
Procedures for assessing populations/economic thresholds: Inspect grain to prevent cross contamination. No economic thresholds exist for R. dominica. The unpleasant odor associated with infestations of lesser grain borer makes infested material unpalatable. If an infestation is found, the grain should be removed from the facility, fumigated, mixed or utilized for livestock feed.
Discussion of feasible management methods/control measures: Stored grain should be spread uniformly and the surface should be leveled. Top-dress grain with residual insecticide. Additional precautions should be taken if grain moisture is above 12-13 %. Aerate the grain using dry ambient air, which maintains uniform temperatures throughout the bin. Maintain grain temperature within 10 degrees of the average daily outside temperature. Clean spilled grain and, inspect grain every two weeks for signs of insects, and moisture problems. If an infestation is discovered, feed the grain, sell at a reduced price, or fumigate. Fumigants are extremely hazardous and have a short life span. A licensed professional should apply fumigants.
For additional information on grain storage management please contact the MSU Extension Chouteau County office at 622-3751 or stop in at the green building located behind the Chouteau County Courthouse.
Montana State University U.S. Department of Agriculture and Montana Counties Cooperating. MSU Extension is an equal opportunity/affirmative action provider of educational outreach.
