Insect Quiz December, 2006

December 2006 Quiz

You are enjoying a cup of coffee in the dining room which is adjacent to the kitchen when you notice a whitish worm, about 1/2 inch long, crawling up the wall.  You look around the room for more of these insects and you notice what looks like a cocoon near the ceiling.  You don’t see any obvious source of these insects.

1.  What is this insect?

This is an Indianmeal moth larva, Plodia interpunctella.  It has a dark colored head and a smooth body with few hairs on it.  Although it is usually white, sometimes the body can look pink, yellow, green, or brown.  Adult moths are about 1/4 - 3/8 inch long.  They are distinctly colored as the first 1/3 of their wings are light brownish or grayish and the latter 2/3 of their wings are coppery brown (if the scales are rubbed off their wings, it may appear to be one color).  Adult moths commonly fly at night and are attracted to lights

2.  What kind of damage, if any, does this insect cause?

Indianmeal moth larvae eat a wide variety of dried food products including flour, pasta, cereal, and other grain products, spices, chocolate, dried fruit, such as raisins and dates, dry beans, nuts, bird seed, dry pet food.  They can even feed in non-food items such as rodent baits (those made from grain), dried plant displays, and grass seed.  They contaminate the food they eat, especially from silken webbing they construct.  Adult moths do not feed.

3.  Why are they on the walls?

When larvae are done feeding and are ready to pupate, the typically move from the food source and disperse.  It is common to see Indianmeal moth larvae moving on walls and ceilings as they look for protected corners, cracks and crevices, to make their cocoons.  The caterpillars don’t usually go too far; the food source is normally in the same room where the larvae are found or in an adjacent one.

4.  What is the best control of this insect?

The first step is to find the source of the infestation.  Check stored food products in cupboards and pantry, especially boxes and bags that are already open.  Don’t forget areas where you may keep dry pet food or bird seed.  Think broadly as there are many types of products they can infest. 

When you discover the problem, wrap it in plastic and throw it away.  You can save bird seed, pet food, or lightly infested food products, by freezing them at 0o F. for at least four days.  You should automatically freeze unopened food packages older than 60 days, even if insects haven't been seen.  Store susceptible food in insect-proof containers with tight lids or in a refrigerator. 

If you see a few Indianmeal moth adults after you have thrown away infested foods that could just be the result of adults emerging from pupae outside infested containers (like the larva you saw crawling up the wall).  They will eventually go away on their own as long as they are can’t find any food products to lay their eggs.  However, if persistent numbers of Indianmeal moths are seen, look for additional food sources.

Insecticides are not practical or necessary.  Spraying moths or larvae found out in the open does not eliminate the pests if a food source is present.  Plus you risk accidently contaminating dishes, glasses, and utensils.  Sanitation is the best method to eliminate stored product insects.