The Indian meal moth, Pyralis farinalis (Lepidoptera: Pyralidae), is the most common insect pest of grain products stored in the home pantry in Rhode Island. Larvae seen on ceilings and counters are often the first indication of a problem, and adults may be seen flying throughout the house, particularly in the evening. Larvae feed on grain, dried fruit and nuts, cereal products, and even undried floral arrangements and wreaths with seeds.

Description:

The Indian meal moth has a wing span of about 18-20 mm (3/4 inch). The outer two-thirds of the wings are bronze to reddish-brown, while the inner third is a grayish white. The larvae (caterpillars) are about 12 mm (1/2 inch) long when mature. They are a dirty white color, sometimes exhibiting pink or green hues, depending on the food they have been feeding on. The head and prothoracic shield are brown. The cocoon is a loose, oval-shaped capsule that mature larvae spin around themselves prior to transforming into the pupal stage. The pupa is a capsule-shaped intermediate stage between the larva and the adult. The final formation of the adult occurs during the pupal stage. The eggs are white, flattened sideways and too small to be easily seen with the naked eye.

Life Cycle:

Adult moths usually emerge, mate and lay eggs at night. Females lay from 40 to 400 eggs in 18 days, on or adjacent to food material, either singly or in groups. Eggs may also be placed directly on the exterior of packaging material. Eggs start hatching within four to eight days. The 2 mm (1/16 inch) larva soon begins searching for food. Those emerging on the outside of a container are often able to penetrate containers that appear well sealed. Larvae mature in 21 to 70 days, depending on food, temperature and length of the days. Mature larvae usually leave their food supply and wander about looking for a place to pupate. In heavy infestations, pupation may occur far from the original food source. The life cycle (egg to adult) can take as few as 27 days or as long as 305 days. There are generally four to six generations a year. During the fall and winter months, larvae will often enter diapause (a form of hibernation) only to emerge as adults in the spring.

Damage:

As the larva feeds, it spins a web leaving behind a silken thread wherever it crawls. Small particles of food often adhere loosely to the thread, making it conspicuous. The extensive webbing can spoil more food than the larvae can consume. Although there is no harm in consuming an occasional larva (most of us have), homeowners generally want to discard infested food products.

Other Insect Pests of Stored Food:

Sawtoothed Grain Beetles [Oryzaephilus surinamensis (Coleoptera: Cucjidae)]:

Sawtoothed grain beetles are another commonly found pantry pest. These beetles feed on numerous food products, including cereals, bread, dried fruits, nuts, sugar, macaroni and seeds. They do not feed on undamaged, whole grains. Adults are 6 mm (1/4 inch) long, slender, flattened and brownish-red. They have six saw-like teeth on either side of the thorax behind the head. The female lays 45-287 white, shiny eggs into foodstuff. The eggs hatch in three to five days. The larvae are yellowish-white and less than 6 mm (1/4 inch) long when mature. Larvae pupate within the food material; the complete life cycle may occur in 40 to 60 days, and there may be as many as six generations each year.

Dermestid Beetles (Coleoptera: Dermestidae):

Several species of dermestids feed on dried meats, cheeses, dead insects, hides and woolens. However, in some cases they can also feed on stored foods including grains, seeds and dried fruit. These insects are often called carpet beetles because some species are damaging to wool carpeting. Adult dermestid beetles may be oval or round and are mottled gray to black. Both the adults and the larvae are 4-10 mm (1/8-3/8 inch) long. The larvae are banded with long, dark hairs. Up to six generations can occur each year.

Dermestid beetle adult (Clemson University Extension)	Dermestid beetle larva (Clemson University Extension)

Control Methods:

The following suggestions may be useful in bringing an infestation quickly under control. Prompt action can be important in preventing losses of quantities of foods stored on kitchen or pantry shelves.

l. Carefully examine all susceptible foods that may have been exposed to the moths. Do not forget bird seed, dog, cat and fish foods, as these are often the source of an infestation. Insects may even be found in wrapped products which have not yet been opened in the home. All infested packages should be discarded. There is no satisfactory way of separating the insects from the food products, flour or meal, although freezing for several days in a chest freezer is probably effective in killing them (microwaving gives mixed results).

2. The contents from opened packages which appear to be uninfested should be transferred to glass jars or quality plastic containers with tightly fitting tops. It is possible, however, that eggs were laid in these products and they may hatch later and lead to a new infestation. These containers should also prevent new invasions.

3. Remove all food containers and utensils from the infested area (shelf paper may also need to be removed) and clean thoroughly, first with a vacuum cleaner and then with soap and water. Special attention should be paid to cracks, corners and drawers where bits of flour, meal or other products may have accumulated. Remove and destroy cocoons that may be found on ceilings of cupboards, behind shelves, in corners, and particularly in the holes for shelf support brackets.

4. In most cases, a single thorough clean-up will control these insects. Continue to observe the area for several months after cleaning. If moths reappear, the clean-up may have been inadequate or newly infested packages may have been brought into the kitchen. Repeat the clean-up process with greater care. We do not recommend the use of insecticides in food pantries.

Long-term storage of flour and meal products often leads to infestation; such products should be purchased in quantities suitable for early use unless adequate containers are employed.

Text adapted from the University of Nebraska-Lincoln, the Cornell Cooperative Extension and
the Connecticut Agricultural Experiment Station, 1999.