Lesser Grain Borers
Order:
Coleoptera
Family: Bostrichidae
Species: Rhyzopertha dominica (Fabricius)
The
lesser grain borer, Rhyzopertha dominica, is a serious pest of
stored grains including whole kernels and cereal products.
Both the larvae and adult beetles will bore into healthy kernels,
reducing the grains to empty shells.
Cosmopolitan in distribution, infestations are commonly spread
through commerce.
The adult borers are strong fliers and therefore without being
directly introduced from a contaminated source.
Biology and Habits
Stored-product pests are separated into categories based on their feeding behavior. This beetle is best characterized as both an internal and external feeder. Larvae can enter slightly damaged grains and feed until maturation, or they may feed on the food particles left by other larvae and adults. Larvae are white in color, and their C-shaped bodies are slightly covered with short setae (hairs). The head is almost completely hidden underneath the prothorax. Only the powerful mandibles can be seen from above.
Pupation usually occurs within the protective shell of the hollowed-out grain, but pupae may be also found in dust accumulation outside the inhabited foods. The dark brown adults (2 to 3 mm in length) emerge from the grains and begin feeding.
The
tuberculate (knobby) prothorax and the distinctive rows of punctures on
the elytra (wing covers) are two important identifying features of the
adult beetle.
Antennae have 10 segments terminating with a large three-loosely
segmented club.
Eggs are laid singly or in clusters of 2 to 30.
Fertile females may deposit 200 to 500 white eggs on the outer
surface of grains or in the accumulated dust debris.
The developmental time from egg to adult average about 58 days.
The adults are capable of living for several months.
Control
Careful
inspections, along with pheromone trap lures, can assist in determining
the presence or absence of infestations.
The lesser grain borer may inhabit dried meat and many different
types of whole grains including corn, wheat, peanuts, beans, spices (e.g.,
celery seed, poppy seed, and fennel), and birdseed.
This beetle has also been found in pelleted rodenticides and boring
into cardboard and wooden boxes.
Inspection of incoming products and areas suspected of supporting
populations can lead to the location of infested goods.
Small
quantities of infested materials should be discarded and not consumed
due to an odor associated with infestation.
Product destruction, sanitation, and limited residual applications
or space sprays may be effective in controlling small isolated infestations.
Fumigation is usually required to control larger infestations since
all life stages are associated with whole grains.
Grain protectants are also employed to discourage establishment
of infestations.
Remember, always consult labeling of registered insecticides prior
to usage.
Microencapsulated
and wettable powder insecticide formulations used as perimeter sprays
can reduce outdoor populations and often prevent entry into structures. Residual insecticides applied to cracks and crevices frequented
by springtails can reduce indoor populations rapidly. Aerosol formulations of pyrethrum or pyrethroid insecticides
are effective as contact sprays.
(Courtesy of the National Pest Control Association.)