Indian Meal Moths

Scientific Name:Plodia interpunctella (Hubner)
CLASS/ORDER/FAMILY: Insecta
METAMORPHOSIS: Complete

Introduction:

The Indianmeal moth was given its common name by an early entomologist (Asa Fitch) who found it feeding on cornmeal (Indian meal). It is probably the most encountered pest of stored products found in the home and in grocery stores in the United States. Of Old World origin, it is now found worldwide.All stages of the Indian meal moth may be found in homes. The adult is a small moth, about 3/8 inch long with a wing span of about 5/8 inch. The overall body color is generally dirty gray but the tip half of the wing is rusty brown or nearly bronze. This wing marking pattern allows Indian meal moth to be easily distinguished from other household moths.

The caterpillar stage is usually cream colored, sometimes with yellowish-green or pinkish shades, and has a dark brown head. Normally they stay associated with foods, but the full grown caterpillars, about 2/3 inch long, may be seen as they wander in search of a place to pupate.

Recognition

Adults with wingspread (wing tip to wing tip) about 5/8-3/4" (16-20 mm). Wings pale gray but front wing with outer 2/3's reddish brown with a coppery luster. Mature larva usually about 1/2" (range 9-19 mm) long. Usually dirty white but color may vary to a greenish or pinkish or brownish hue depending on its food, with head and prothratic plate/shield yellowish bron to reddish brown. With 5 pairs of well-developed prolegs on abdomen and each bearing crochets (hooks).

Prespiracular tubercule (wartlike area between spiracle and front edge of segment) of prothorax with 2 setae (hairs). Tubercule VI on mesothorax (wartlike area near and above leg) with one seta (hair). Body without pinnicula (dark or pale wartlike area at base of hairs or setae) on mesothorax, and 1st 9 abdominal segments.Rim around spiracles of about even thickness.

Similar Groups

Carpet/tapestry moth (Trichophaga tapetzella) with basal 1/3 of front wing dark brown to black,, remainder of wing white mottled with gray and black. Other small moths lack front wing with basal 1/3 pale and reainder dark, wing span of about 5/8-3/4" (16-19 mm), and/or hind wing broader than front wing and fringed with long hairlike scales.

Biology

Chiefly at night, the female lays 100-400 eggs, singly or in small groups, on the larval food material during a period of 1-18 days. Upon hatching, the larva establishes itself in a crevice of the food material. It feeds in or near a tunnellike case it has webbed together of frass or silk. The larval period lasts 13-288 days, depending primarily on temperature and food availability. When the last instar larva is ready to pupate, it leaves the food and wanders about until a suitable pupation site is found. There are usually 4-6 generations per year (range 4-8), with the life cycle (egg to egg) typically requiring 25-135 days (range 25-305).

Indian meal moths develop in many kinds of stored foods. Coarsely ground grains and cereal products are commonly infested. Dried herbs, dried fruits, and nuts are also highly favored. Pet foods such as dried dog food, flaked fish food, and bird seed can also become infested. Indian meal moth may also breed in ornamental items made of dried flowers or seeds.

The moths usually fly at dusk and through the night. Females lay tiny eggs (ca. 0.5 mm) on or near potential food items. The newly hatched caterpillars (larvae) seek out foods and begin to develop. As they feed they often produce silk that loosely binds to food fragments. In large, undisturbed containers feeding is concentrated on the surface as the larvae do little burrowing. However, caterpillars may occur throughout the product within small, loose packages typically found in household pantries. The caterpillars are capable of chewing through plastic bags and thin cardboard.

Habits

The adults cause no damage. The larvae are surface feeders and generally produce a lot of webbing throughout the infested part of the materials. They are general feeders and attack grain and grain products, a wide vriety of dried fruits, seeds, nuts, graham crackers, powdered milk, biscuits, chocolate, candies, dried red peppers, dried dog food, and bird seed. They are very destructive wherever dried fruits are stored. Preferred are the coarser grades of flour such as whole wheat, graham flour, and cornmeal, but they can breed in shelled or ear corn.

Control

Infested material should be immediately discarded, used up, or somehow treated to disinfest. Treatments involve using heat or cold to kill any larvae and eggs that may be in the food. Cold treatment requires putting infested items in deep freeze for at least two or three days. Effectiveness of cold treatment may be improved by alternating freezing treatments with rewarming to room temperatures for a few days. High temperature treatments involve oven heating at around 120 to 140 degrees F for 20 minutes. (Somewhat longer intervals are needed if treated items are bulky, requiring longer periods to raise internal temperatures.) Injury to the food is possible with excessively high temperature treatments.

Since insects also can develop on spilled food, thoroughly clean areas where food was stored by vacuuming or sweeping upall spilled food. The thoroughness of the cleaning is important primarily to eliminate food for surviving insects to feed on. The nature of the cleaning agent (soapy water, bleach, etc.) is less important than the permanent elimination of the food.

Heat or cold treated objects are capable of being immediately reinfested as long as Indian meal moths remain in the home so extra care should be taken during this stage. Although adult moths may only live for a week or so, larvae that have recently pupated in hidden areas of the home may also be a potential source of reinfestation. Therefore Indian meal moths must be denied access to all food sources for the length of time that is required to complete the pupal stage plus how long the adult life span can be. A month should be adequate to cover this period.Follow the standard control procedures for stored product pests but remember that pupation takes place away from the infested food material.