Penetrating Packaging

The first instar larva is small enough to crawl through this period (.). It vigorously searches for the smell of food and searches packaged materials until it finds a small defect in the package and then penetrates. If it does not find food in about two days, it will die. It is amazing to most humans how this insect finds a way into a package. However, millions of years of evolution have taught it and its offspring to find a meal or die.

After finding food, the larva eats and starts to grow. It then spins a single silken thread from spinnerets under its mouth. This webbing has several purposes. It helps the larva crawl across surfaces. This could be the surface of grain or a burlap bag. The IMM webbing left by the larva acts as an oviposition site (egg laying) for females to cue in on an area that other moths have used to survive and grow. In the winter months the thick webbing acts as a blanket and can help the moths stay warm, continue growing, propagate; and it forms a
protective layer against its natural parasitic enemies.

During the sixth instar (molting stage) the IMM larvae needs to wander from this site. This inherent need to wonder causes it to chew its way out of the bag that it once penetrated as a small first instar larva. The IMM larvae will graze across a plastic bag, testing it occasionally for weakness. When it finds a weak spot, it will begin the laborious task of lashing at it with its rasping mouth parts (like a sickle). After hundreds of slashes it may break through or go on to another location. This is much like a man trying to dig a hole in the ground. Some locations are hard and rocky and some are soft and easy. The larva will then crawl through the round hole and may find a nice safe cardboard fluted box or a 90-degree angle to secure itself. The pupa stage is a defenseless quiescent stage that is vulnerable to attack by natural predators. The larva carefully chooses a safe perch to start pupation. This will be the location where the IMM adult will dry its wings when it emerges from its transformation to take the first flight of its life, perhaps into a sticky pheromone trap.

The first generation of IMM in much of North America emerges from the overwintering (large) larva in April-May. In the tropical regions of the United States it can stay active most
of the year. This moth doesn’t like to fly when the temperatures are below 62-65° F.  Pheromone traps should be placed when temperatures reach 60° degrees F/ 17° C or higher.

The IMM goes through a new generation every 4-6 weeks during the warm summer months and 5-8 weeks in the cooler months. In the insect rearing lab at Insects Limited, Inc. we can shorten a generation of IMM to 18 days when the temperatures are set for 29 C/ 85 F and 60% relative humidity on a special diet.

In the Midwest we normally have 3 generations per year (400 x 400 x 400 offspring). In warm summers like the ones we have experienced in the past five years, we are getting 4 generations per year (400 x 400 x 400 x 400 offspring). The reproductive potential then is 26 billion IMM from one pair. With the number of 90-degree weather days doubling last year in many parts of the country, one can see how this moth has been such a nuisance.

The IMM does not carry diseases known to man nor causes health problems like mosquitoes, bees, or flies. It is a nuisance pest that contaminates food in your home and your factory with its presence or its webbing. It can live outdoors naturally and feeds on grass seed and cereal protein.

In a survey conducted by Dr. M. Hirao of Japan, over 95% of the 200 households survey from around Japan had IMM indoors and also outdoors.

The IMM does not like hot weather. They are seldom found in the tropical areas like  southeast Asia or Hawaii. Found there are related cousins like the Rice moth or the Cocoa moth. The temperate region of the world is where the IMM survives best.

One characteristic that Alain VanRyckeghem of Insects Limited, Inc. recently discovered is that the IMM adults like to stay near the walls. The pheromone traps near the center of the room capture fewer adult males than the ones near walls. The adult moth seems to prefer resting on the walls in a vertical posture.

Pheromone traps are very effective in locating IMM. The traps should be placed in a convenient location away from children or fork truck operators. Write the date on the trap when they are first placed and again when the lures are changed. The lures should be replaced every 8-10 weeks indoor and 4 weeks outdoors. The traps should be changed then dust accumulates on the sticky surface or the numbers of moths make change necessary. Check the traps weekly if possible and remove all captured insects. Keep excellent records and maps of trap location. Predicting future population trends will be possible by closely evaluated and mapping the collected data.

Pest management begins with prevention and monitoring. The pheromone traps for stored product insects shouldn’t be considered a control tool but rather sensitive detection and monitoring tool. The accumulated data will help predict future populations for pest insects
and better determine the best time for directing a pesticide control program. After several years of collecting data a pest manager can fine-tune his/her pest management program to compensate for unusually warm weather or other circumstances that arise. The Indianmeal moth is predictable; programmed through 1000’s of years of evolution. It is a controllable nuisance pest of stored products. It all starts with knowing the pest…“Knowing the pest is half the battle in controlling it.”


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