Mark Dreiling, Bugwood.org
The Mediterranean flour moth was first reported in North America in 1889. Authorities differ as to the origins of this now cosmopolitan insect of stored goods. Some believe it came from Europe, by way of the Mediterranean region, while others believe it originated in Central America.
The adult moth is a pale-gray color and from one-forth to one-half inch long, with a wingspread of slightly less than one inch. The wings are marked with two indistinct, black zigzag lines. The hindwings are a dirty white. When at rest, the moth extends the forelegs which raises the head and gives the body a sloping appearance. This posture is very distinctive and is a more reliable character for identification than the wing markings which may be rubbed off.
The female moth lays from 116 to 678 small white eggs in accumulations of flour, meal, waste grain, and other food sources. Commonly, the eggs are attached to the food. Within a few days (three days at eighty to ninety degrees F) the eggs hatch into small whitish or pinkish larvae, with a very hard and dark colored head and small black spots on the body, that immediately begin to spin silken tubes. The larvae remain within the tubes until fully mature, which takes approximately forty days. When fully grown, the larvae will leave the immediate area where they were feeding and wander about in search of a location to spin silken cocoons. Within the cocoons, they transform into reddish-brown pupae. After eight to twelve days the adult moths emerge. During very warm weather, the Mediterranean flour moth may complete its life cycle (egg to adult) in five to seven weeks. In Pennsylvania, there may be three to four generations per year under favorable conditions.
The Mediterranean flour moth can be found on a great variety of foodstuffs in addition to flour, grain residues (insect-infected grain, broken kernels, and dust), and various whole grains. Although this insect is not as serious a pest as the Indian meal moth and some of the grain infesting beetles, it still causes clogging of machinery with its webbing, and at times causes grain mill shut-downs. In recent times, the use of fumigants has greatly reduced the incidence of the Mediterranean flour moth.
Prevention is the best strategy to avoid insect problems in stored grains. Proper bin sanitation before introduction of new grain minimizes the need for pesticides. Good sanitation involves the removal of old grain and dust in and around the grain bin. This includes removal of old grain from corners, floors, and walls and grain that may have spilled on the exterior of the bin. Any grain remaining when a bin is emptied can harbor insect infestations which will move into the new grain. After the bin is cleaned, and all needed repairs have been made, the floor and wall surfaces both inside and outside the bin should be treated, if the grain will be stored for more than six months. Take special care to treat all cracks, crevices, and areas around doorways and other places where insects could hide or enter. Spray the bins about four to six weeks prior to storing grain.
Before grain is placed in a bin it should be screened to eliminate fine materials and broken kernels. Grain placed in a clean bin should be checked at two week intervals during warm months and at one month intervals during cooler months for the presence of hot spots, moldy areas, and live insects. If any of these conditions exist, the grain should be aerated to lower the moisture level and temperature.
Grain that is to be stored for longer than six months may need a protective application of an approved insecticide. Treatments can be applied as the grain is loaded into the bin through the use of a metering device calibrated to apply the proper amounts. After the grain is binned and leveled, a surface dressing can be applied to prevent insects from entering the grain on the surface.
If infestation occurs in spite of these precautions, fumigation of the grain will be necessary. Because of the high toxicity of registered fumigants and technical knowledge needed for their proper use, a qualified pesticide applicator should be contacted to perform the fumigation.
Pesticides are poisonous. Read and follow directions and safety precautions on labels. handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.
Authored by: Steve Jacobs, Sr. Extension Associate and Dennis Calvin, Assistant Professor
Last updated October 1988