Lesser grain borer beetle
The lesser grain borer beetle, scientifically known as Rhyzopertha dominica, is a small insect commonly found in stored grains around the world. Measuring about 1/10 of an inch (2-3 mm) long, this reddish-brown beetle is recognized for its downward-curving snout, or proboscis, which it uses to bore into food, particularly grains, wood, and even paper products. It is a significant pest for crops like peanuts and wheat.
The beetle has a unique life cycle, during which the female lays between 200 to 500 eggs in the dry materials where she resides. The larvae hatch within a few days and undergo several molts before reaching the pupal stage, ultimately emerging as adults after approximately 30 to 58 days. While the lifespan of the lesser grain borer beetle ranges from 24 to 133 days, some individuals can live up to 18 months.
In terms of survival, these beetles have natural predators such as mites and other beetles, and they are also vulnerable to parasitic threats. Farmers often combat lesser grain borer infestations using various methods including insecticides and traps. Despite its status as a pest, the lesser grain borer beetle is not considered a threatened species.
On this Page
Subject Terms
Lesser grain borer beetle
The lesser grain borer beetle is found throughout the world wherever grains are stored. This beetle and its larvae, or young, are known for feeding on grains, wood, and paper products. They are a major pest of peanuts. They are close relatives of other borer beetles, such as the Bamboo borer that feeds mostly on bamboo products but can any plant material. The lesser grain borer beetle is also known as the American wheat weevil, Australian wheat weevil, and stored grain borer.
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Family: Bostrichidae
Genus: Rhyzopertha
Species: Dominica
The lesser grain borer beetle typically grows to be about 1/10 of an inch (two to three millimeters) long. Its reddish-brown body has a tiny head, a round thorax, or mid-body section, and a square-shaped abdomen, or lower-body section. Its six legs extend from beneath its thorax and abdomen. On its head, the lesser grain borer beetle has two tiny antennae which help it sense its surroundings. The lesser grain borer beetle is also known as the lesser grain borer weevil. A weevil is a kind of beetle which has a downward-curving snout which it uses to bore into its food. This snout is also called a proboscis. A proboscis is a tube-like sensory organ which may be used to collect food. The trunk of an elephant is one kind of proboscis.
Over its abdomen, the lesser grain borer beetle has elytra which cover its delicate rear wings. Each elytrum, or wing covering, is formed from one the lesser grain borer beetle's front wings. These elytra are square and come together to form what appears to be a solid piece of exoskeleton, or external skeleton. In truth, these two pieces are able to lift away from the lesser grain borer beetle's rear wings when the insect flies.
As its name suggests, the lesser grain borer beetle spends most of its life boring into small grains. It is often found living in and feeding on stored wheat grains, cork, wooden boxes, and paper products.
Like other beetles, the lesser grain borer beetle chews its food with its strong, biting mandibles, or jaws. It moves its food from its mandibles to its throat with its maxillae and its lips. These two mouthparts are also used for tasting the food. Unlike some foods, the diet of the lesser grain borer beetle is considered very difficult to digest. To solve this problem the lesser grain borer beetle houses intestinal bacteria inside its body. Unlike a parasite, or an animal which lives on or in another animal and causes harm to its host, the bacteria inside the lesser grain borer beetle do not harm the beetle. Instead they help the beetle to break down the substances of wood and other dry products. This kind of relationship in which two animals of different species work together is called a symbiotic relationship.
Generally, the lesser grain borer beetle mates during the spring and summer. After mating, the female deposits her fertilized eggs in the wood or other dry substance in which she lives. Females may lay between 200 and 500 eggs over an average four-to-six-month life span.
In about three days, young beetles hatch from the eggs. At this stage the lesser grain borer beetle is in its larval form. It molts, or sheds, its skin many times before developing into its pupal stage. After 30 to 58 days, depending on temperature, it reaches the pupal stage. The pupal stage is the last developmental stage before the lesser grain borer beetle reaches maturity. After molting its pupal skin, the young lesser grain borer beetle emerges as a full-grown lesser grain borer beetle.
The life span of the lesser grain borer beetle is between 24 and 133 days, although some may live up to 18 months. Males live longer than females. Mites and other species of beetles may prey on the lesser grain borer beetle. They are also susceptible to harmful parasites. Farmers may use insecticides, traps, and fumigation to kill the lesser grain borer beetle. Lesser grain borer beetles are not a threatened species.
Bibliography
Johnson, Doug. “Insect Pests of Stored Grain: Lesser Grain Borer - Entomology.” UK Entomology, 2024, entomology.ca.uky.edu/ef137. Accessed 19 Apr. 2024.
“Lesser Grain Borer Rhyzopertha Dominica.” Extension Entomology, 2016, extension.entm.purdue.edu/publications/E-238/E-238.html. Accessed 19 Apr. 2024.